.c 


LIBRARY   OF   THE 


University  of  California. 


C 1RCCL  A  TI KG    B K A NC //, 


Return  in  JRS  weekfTj  or  a  week  before  the  end  of  the  term, 


\ 


•• 


* 


ELEMENTS 


OF 


CHEMISTRY, 


INCLUDING 


THE  RECENT  DISCOVERIES  AND  DOCTRINES 
OF  THE  SCIENCE. 


BY  THE  LATE 

EDWARD  TURNER,  M.D. 


SEofttonJ 


WITH  NOTES  AND  EMENDATIONS, 
BY  FRANKLIN  BACHE,  M.  D. 

PROFESSOR  OF  CHEMISTRY  IN  THE  PHILADELPHIA  COLLEGE  OF  PHARMACY- 


PHILADELPHIA: 

THOMAS,  COWPERTHWAIT  &  CO.  247  MARKET  STREET. 
1840. 


ENTERED,  according  to  the  Act  of  Congress,  in  the  year  1839,  by  THOMAS, 
COWPERTHVVAIT  &  Co.,  in  the  Clerk's  Office  of  the  District  Court  for  the  Eastern 
District  of  Peunsylvania. 


PREFACE  TO  THE  FIFTH  LONDON  EDITION. 


IN  preparing  a  fifth  edition  of  these  Elements,  I  have  not  lost  sight  of  the 
plan  on  which  the  work  was  originally  framed.  Its  object  is  still,  without 
entering-  minutely  into  the  details  of  processes  and  experiments,  to  present  a 
concise  and  connected  view  of  the  facts  and  theories  of  Chemistry.  It  has 
been  found  impossible,  so  numerous  are  the  cultivators  of  this  science,  and 
so  rapid  its  progress,  to  avoid  numerous  changes  and  additions.  These  have 
necessarily  been  interwoven  with  the  texture  of  the  volume,  and  it  would  be 
useless,  were  it  practicable,  to  enter  into  an  exact  enumeration  of  them  ;  but 
it  may  be  convenient  to  some  readers  that  the  more  important  variations 
from  former  editions  should  be  specified. 

In  the  first  section  there  are  but  few  changes,  and  those  relate  chiefly  to 
Radiant  Heat.  In  that  on  Light,  a  summary  of  the  laws  of  reflection  and 
refraction,  agreeably  to  the  wishes  of  some  of  my  pupils,  has  been  supplied. 
The  article  on  Electricity  has  been  almost  entirely  recomposed  ;  and,  owing 
to  the  kindness  of  Mr.  Snow  Harris,  I  have  been  enabled  to  embody  many 
results  of  his  late  researches,  prior  to  their  appearance  in  a  printed  form 
before  the  public.  I  have  to  acknowledge  a  similar  kindness  in  Mr.  Faraday, 
whose  discoveries  in  Galvanism  have  compelled  me  to  remodel  the  whole  of 
the  fourth  section.  To  procure  all  the  facts  required  for  that  purpose,  I  have 
been  obliged  to  delay  writing  the  section  on  Galvanism  until  the  other  parts 
of  the  volume  were  completed.  This  will  account  for  the  labours  of  Mr. 
Faraday  not  being  referred  to  in  other  portions  of  the  volume,  which,  though 
placed  after  the  fourth  section,  were,  in  fact,  printed  some  weeks  earlier. 

A  few  changes  have  been  made  in  the  section  on  the  Laws  of  Combina- 
tion, where  will  also  be  found  a  description  of  the  mode  of  employing  sym- 
bols in  Chemistry.  I  ventured  in  the  last  edition  to  introduce  chemical 
symbols  as  an  organ  of  instruction,  and  subsequent  experience  has  afforded 
such  convincing  evidence  of  their  value  in  this  point  of  view,  that  I  cannot 
too  earnestly  urge  the  chemical  student  to  employ  them  at  an  early  period 
of  his  studies.  The  present  state  of  Chemistry  renders  the  use  of  abbreviated 
or  symbolic  language  almost  unavoidable ;  and  the  question  now  is,  not  so 
much  whether  they  shall  be  used,  as  whether  they  shall  be  generally  under- 
stood.  To  ensure  this,  it  is  essential  that  a  uniform  system  be  adopted;  and 
I  have  hence  felt  the  necessity  of  strictly  conforming  to  the  method  intro- 
duced by  Berzelius  and  adopted  on  the  Continent.  The  tables  which  have 
been  given  in  the  sections  of  the  second  and  third  parts,  with  the  primary 


view  of  showing  analogies  of  chemical  constitution,  will  serve  the  useful 
secondary  purpose  of  supplying  a  guide  to  the  employment  of  symbols.  By 
reference  to  them,  the  student  will  see  the  meaning  of  any  symbols  he  may 
meet  with  in  the  text. 

The  large  number  of  compounds  which  have  gradually  accumulated,  pos- 
sessing the  aspect  and  general  characters  of  salts,  and  yet  not  composed  of 
acids  and  alkalies  in  the  general  acceptation  of  these  terms,  have  been  ar- 
ranged as  separate  orders  of  a  large  class  of  saline  substances,  which  are 
inseparably  allied  by  analogy  of  composition.  But  in  associating  substances 
naturally  connected,  I  have  abstained  from  violating  any  established  usages 
in  terminology.  Changes  in  chemical  nomenclature  should  be  attempted 
rather  by  a  community  of  chemists  than  by  an  individual;  and  if  the  labours 
of  the  Committee  which  the  British  Association  has  appointed  for  promoting 
uniformity  in  the  use  of  symbols,  shall  be  attended  with  that  success  which 
its  proposer  anticipates,  a  like  task  in  reference  to  chemical  nomenclature 
may  well  be  imposed  on  the  same  Committee.  For  the  greater  part  of  our 
knowledge  of  the  compounds  here  referred  to,  we  are  indebted  to  Berzelius, 
and  the  principal  facts  concerning  them  are  drawn  from  his  writings. 

Owing  to  the  activity  displayed  in  organic  analysis  by  several  Continental 
chemists,  especially  by  Liebig  and  Dumas,  the  necessary  additions  and 
changes  in  the  Third  Part  have  been  very  considerable.  I  am  conscious 
that  the  arrangement  of  organic  substances  stands  in  need  of  revision ;  but 
it  is  easy  to  trace  defects  in  any  given  arrangement  on  such  a  subject,  and 
very  difficult  to  fix  on  one  which  shall  not  be  liable  to  equal  objection.  Con- 
sidering facility  of  consultation  of  far  more  importance  to  the  reader  than 
critical  propriety  of  classification,  I  have  thought  it  right  for  the  present  to 
describe  organic  compounds  nearly  in  the  same  order  as  in  former  editions. 

In  the  Appendix  will  be  found  an  interesting  communication,  kindly  sent 
me  by  Mr.  Graham,  on  the  nature  of  certain  hydrated  salts  and  peroxides, 
and  on  phosphuretted  hydrogen.  It  likewise  contains  other  notices  which 
either  reached  me  too  late  for  insertion  in  the  body  of  the  work,  or  were 
accidentally  omitted. 

I  have  again  to  express  my  thanks  to  Dr.  Franklin  Bache,  Editor  of  the 
American  edition,  for  several  valuable  suggestions. 

London,  November  1, 1834. 


ADVERTISEMENT  OP  THE  AMERICAN  EDITOR. 


SOME  time  after  the  death  of  the  author  of  these  Elements,  a  new  Ameri- 
can edition  was  called  for;  and,  the  appearance  of  a  new  London  edition  not 
being- anticipated,  it  was  deemed  expedient  to  reprint  the  former  edition,  with 
such  notes  and  additions  as  the  progress  of  the  science  might  render  neces- 
sary. After  the  printing  had  advanced  as  far  as  "  Sulphur,'*  it  was  ascer- 
tained that  a  new  edition  was  in  course  of  publication  in  London,  under  the 
editorial  management  of  Professor  Liebig  and  Mr.  Wilton  G.  Turner  ;  and, 
upon  the  reception  of  the  First  and  Second  Parts,  reaching  to  the  end  of  Inor- 
ganic Chemistry,  the  printing  was  continued  from  the  new  work,  under  the 
expectation  that  the  Third  Part,  embracing  Organic  Chemistry,  would  reach 
this  country  in  time  to  allow  the  printing  to  be  completed,  without  interrup- 
tion, from  the  new  London  edition.  This  expectation  has  been  disappointed ; 
and  the  publishers,  after  waiting  eighteen  months  for  the  appearance  of  the 
Third  Part,  have  been  reluctantly  compelled  to  finish  the  work  by  reprintfng 
the  Organic  Chemistry  from  the  former  edition. 

Philadelphia,  December,  1839. 


CONTENTS, 


INTRODUCTION 


PART  I. 

IMPONDERABLE  SUBSTANCES. 

SECT.  I.     Heat,  or  Caloric  -                         -          ^r.  -    '        5 

Communication  of  Heat  by  Contact  -      6 

Conduction  of  Heat     -             -             -            .'..-  6 

Radiation               -  -    '  8 

Cooling1  of  Bodies         -  14 

Effects  of  Heat     -  -    15 

Expansion  15 

Liquefaction                -  -    36 

Vaporization         -             -             -  41 

Constitution  of  Gases  with  respect  to  Heat  -    53 

Sources  of  Heat            -                     £ '  «.'  "  -          54 

II.  Light  -    54 

Reflection  of  Light       -             -            *  55 

Refraction  of  Light  -    58 

Decomposition  of  Light            -  V>        65 

Terrestrial  Light    -            -        H  ,,*          «  -    68 

III.  Electricity              -            -             -  71 

Theories  of  Electricity  -  -  73 
Causes  of  Electric  Excitement  -  -  75 
Electroscopes  and  Electrometers  -  ?**;.'"  i  .  80 

Laws  of  Electrical  Accumulation  --^  -  83 
Historical  Notice  -  .  ^  :-  ^'-vH  -  86 

IV.  Galvanism                            -  .        87 

Voltaic  Arrangements  or  Circles     -            -  -  88 

Theories  of  Galvanism  -         94 

Laws  of  the  Action  of  VoHaic  Cjtrcles  -  97 

Effects  of  Galvanism     -  -  i  .r        99 

Chemical  Action  of  Galvanism  101 

Theory  of  Electro-chemical  Decomposition       106 

Magnetic  Effects  of  Galvanism           **  109 

Volta-electric  Induction     -        *;-  -      117 


PART  II. 

INORGANIC  CHEMISTRY. 
PRELIMINARY  REMARKS     -  T  ,  T  .  _.  121 

SECT.  I.    Affinity      .  .  .  .  .  -124 

Changes  that  accompany  Chemical  Action  127 


Circumstances  that  modify  and  influence  the  Ope- 
ration of  Affinity       -          ^*  "  •'-  "'         128 
Measure  of  Affinity       -  133 
SECT,  II.     Proportions  in  which  Bodies  unite,  and  the  Laws  of 

Combination              -             -  -             134 
Chemical  Equivalents  of  Elementary  Substances      14] 

Atomic  Theory            ".>        V       £  i        :  *    -  142 

Theory  of  Volumes           -    -           V  144 

Chemical  Symbols       •  *  „•->•'-     150 

Isomeric  Bodies     '.-•*      ij?  .  -          .  •.             152 

III.  Oxygen      -  -    .       153 

Theory  of  Combustion          •             -  -             156 

IV.  Hydrogen               -            -           V        —  -  -       158 

Water                       „.  161 

Peroxide  of  Hydrogen   -             '.  .        '' '  1'      163 

V.    Nitrogen           -            .           •-           '-  -            166 
The  Atmosphere 

Protoxide  of  Nitrogen  174 

Binoxide  of  Nitrogen  r  » f~  -             -       176 

Hyponitrous  Acid    -  178 

Nitrous  Acid     -         -^-   g£*    '  '-:         ,/-       179 

Nitric  Acid            V       ggS         -  -            181 

VI.    Carbon        -          ^  -       184 

Carbonic  Acid  187 

Carbonic  Oxide  Gas    «>,-*» :          -  -             -       189 

VII.     Sulphur  191 

Sulphurous  Acid  Gas     -  -       192 

Sulphuric  Acid         .  193 

Hyposulphurous  Acid    -  -       196 

Hyposulphuric  Acid         •    •-  -.',          -  -             197 

VIII.     Phosphorus              .         ,--     £S|'  -            -       197 

Oxide  of  Phosphorus  200 

Hypophosphorous  Acid  -      200 

Phosphorous  Acid    -  201 

Phosphoric  Acid  -       201 

Pyrophosphoric  Acid  203 

Metaphosphoric  Acid    -          .  •  ,.    •  .-..'        -      203 

IX.    Boron    ....        1j£$    '"  ..  204 

BoracicAcid     -         ;"-        "V-  .            .      205 

X.    Silicon   -            -            -        ^^  *        -  -            205 

Silicic  Acid  (Silica)        »            .  -            -      207 

XI.     Selenium  -  .  -        |:;-*  J    -    ^         208 

Oxide  of  Selenium  -       209 

Selenious  Acid         -            -'        *:  V  209 

SelenicAcid      -         " -:"  ,        -V    -  .            .      209 

XII.    Chlorine             -  211 

Hydrochloric  Acid        ..  -      214 

Hypochlorous  Acid           '  ',.'  '  217 

Chlorous  Acid   -            -            -  .219 

Chloric  Acid                        ^  220 

Perchloric  Acid  -      221 

Quadrochloride  of  Nitrogen  221 

Chlorides  of  Carbon        -             .  •*     222 
Bichloride  of  Sulphur 
Chlorides  of  Phosphorus 

Chlorocarbonic  Acid  Gas   -*.  224 
Terchloride  of  Boron     - 

Terchloride  of  Silicon  225 

Chloro-nitrous  Gas        •-..  •       225 

Nature  of  Chlorine  -        ,    -  -            226 


I 


SECT.  XIII.     Iodine 227 

Hydriodic  Acid        ....  229 

Oxide  of  Iodine  and  lodous  Acid           *             -  231 

lodic  Acid  231 

Periodic  Acid    -             -            *             -            -  232 

Chlorides  of  Iodine  233 

Teriodide  of  Nitrogen                 -                          -  233 

Iodides  of  Phosphorus                       -  234 

Iodide  of  Sulphur                        -             -             -  234 

Periodide  of  Carbon             -            -            %'",  234 

XIV.    Bromine       -                         -            -           *>  -^        -  234 

Hydrobromic  Acid               -        V£,»    *        -  237 

Bromic  Acid     -             -             -             .",-        -  238 

Chloride  of  Bromine                     ^.;       *:£..£  238 

Bromide  of  Iodine         -             -         >Y~          -  239 

Bromide  of  Sulphur              -  239 

Bromides  of  Phosphorus            -                         -  239 

Bromide  of  Carbon  -             -        ^»V  239 

Terbromide  of  Silicon   -             -            ~-        -..;-*  .240 

XV.     Fluorine  240 

Hydrofluoric  Acid         . .^                                  .  240 

Fluoboric  Acid         -                      f  .  242 

Fluosilicic  Acid             -            -            *            -  244 

COMPOUNDS  OF  THE  SIMPLE  NON-METALLIC  ACIDJFIABLE  COMBUSTIBLES 

WITH  EACH  OTHER           .      *                 TV*                        \  ':;»"•  245 

SECT.  I.    Hydrogen  and  Nitrogen. — Ammoniacal  Gas           -  245 

II.    Compounds  of  Hydrogen  and  Carbon    "-    '"    .v ••& ''  <  247 

Light  Carburetted  Hydrogen     -          ^."         .  248 

Olefiant  Gas         "  i ;'  250 

III.  Compounds  of  Hydrogen  and  Sulphur         -            -  252 

Hydrosulphuric  Acid  252 

Persulphuret  of  Hydrogen         -  254 

IV.  Hydrogen  arid  Selenium. — Hydroselenic  Acid  -  255 
V.     Compounds  of  Hydrogen  and  Phosphorus   -             -  256 

Solid  Phosphurelted  Hydrogen         .  256 

Phosphuretted  Hydrogen           ...  257 

VI.     Compounds  of  Nitrogen  and  Carbon      -             .  259 

Bicarburet  of  Nitrogen,  or  Cyanogen  Gas          .  259 

Paracyanogen           ...          •••'•/'•  260 

Mellon  -            -            -                                 -    .  260 

VII.    Compound  of  Phosphorus  and  Nitrogen              «.  260 

Phosphuret  of  Nitrogen             -        \--1f           .  260 

VIII.    Compounds  of  Sulphur  with  Carbon,  &c.          r  »  -:  261 

Bisulphuret  of  Carbon   *             .        "  *^         •  261 

Sulphuret  of  Phosphorus      -        |*  i«  •+-    ".*•;..  262 

Bisulphuret  of  Selenium             .         \V            .-  262 

Seleniuret  of  Phosphorus      •        '    .         '   .  /  262 

Sulphuret  of  Nitrogen                             .            .  262 

GENERAL  PROPERTIES  OF  METALS   -          -            -        t:.*     *   *    -  263 

SECT.  I.    Potassium    -                                      -            .-            .  276 

Protoxide  (Potassa)               -             -             -  278 

Teroxide                          ....  ggQ 

Chloride  and  Iodide                           -           "  ./j.  280 

Bromide  and  Fluoride   ....  281 

Hydrogen  and  Potassium     •             -             .  281 

Carburet            -            -             -             .  281 

Sulphurets                -            -            -  281 


Phosphurets  and  Seleniurcts      -            .  -       283 

SECT.    II.    Sodium              ....  283 

Protoxide  (Soda)             -                     . ,  V   ;  .       284 
Sesquioxide               ...             .  ^1        284 

Chloride             .            .            .        g  ,-    .  .      284 

Iodide           ....        Sp,  \        284 

Bromide  and  Fluoride   -            -        / ',  -       285 

Sulphurets    ....        V->  285 

III.  Lithium      -            ...            -             .  .285 

Protoxide  (Lithia)     -             .             .  286 

Chloride  and  Fluoride     -             .            *•'•  *  ':  .    286 

IV.  Barium             .            .            .          -.            .  287 

Protoxide  (Baryta)           -             -             -•"  -     287 

Peroxide        -             -                     ^V  288 

Chloride  and  Iodide         •        VV  -     288 

Bromide  and  Fluoride           .        •   ...  289 

Protosulphuret    -            -            -         >  *,  •  -  ".;"   289 

V.     Strontium         -            -             .            *-  ~  289 

Protoxide  (Strontia)         -         *ri        /  -  .  ;  -     290 

Peroxide        -                          .        >W        <  290 

Chloride.  -  *        *£§  .    .':;•'•    290 

\           Iodide  and  Fluoride  -             -            -  291 

Protosulphuret    -            -         <  V       8  *-  .  fe|    291 

VI.     Calcium             .        -    *          ^             .'  291 

Protoxide  (Lime)             -            -        '   v   "  r'  .     291 

Peroxide        .  292 

Chloride,  Iodide,  Bromide,  and  Fluoride  •->>'•    293 

Protosulphuret           -            -        ^  293 

Phosphuret  294 

VII.    Magnesium      ...           _.  294 

Protoxide  (Magnesia)       -  294 

Chloride,  Iodide,  Bromide,  £nd  Fluoride        -  295 

VIII.    Aluminium                                       -  296 

Sesquioxide  (Alumina)           -             -         f   -  297 

Sesquichloride     .  -    299 

Sesquisulphuret,   Sesquiphosphuret,  and    Sesqui- 

seleniuret         -  299 

IX.     Glucinium,  Yttrium,  Thorium,  arid  Zirconium  300 

Glucinium           .             .                     .'"I  -     300 

Yttrium        .            .             .  301 

Thorium  301 

Zirconium     ....  302 

X.     Manganese              •             .            -             -  304 

Protoxide      ....  305 

Sesquioxide          -             -             -         V."  -     306 

Peroxide       ...            -            *  '%        *  307 

Red  Oxide          -            -            -            V  -    307 
Varvicite       -                       '   - 
Manganic  Acid  - 

Permanganic  Acid     -  309 

Protochloride       -  -     309 
Perchloride  and  Perfluoride  - 

Protosulphuret    -            -            -            -  •     310 

XI.  Iron      -                         .  311 

Protoxide  and  Sesquioxide 

Black  or  Magnetic  Oxide,     -             -  315 

Chlorides,  Iodides,  Bromides,  and  Fluorides         -     316 

Sulphurets     - 

Phosphurets  and  Carburets 

XII.  Zinc  and  Cadmium       -            -            >V  -  r-       319 


CONTENTS,  XI 

Zinc        -            -            -            -            -  -     319 

Cadmium       .....  321 

SECT.    XIII.    Tin              ...  -    322 

Protoxide  and  Sesquioxidc     -             -             -  323 
Binoxide               .....     324 

Chlorides       -            -            .  324 

Iodides   -             -             -             -             .  -     325 

Sulphurets     -  325 

Terphosphuret    -  326 

XIV.     Cobalt  and  Nickel         ....  326 

Cobalt     .            -            -            -           v^  -     326 

Nickel           -        :'   /           .            .            ,  329 

XV.     Arsenic      -                     /  >  ^        .  .     331 

Arsenious  Acjd         -            -        *',  •  i1-        »  332 
Arsenic  Acid       .....    336 

Chlorides       -             .            -            .          '-  336 

Periodide         ^>             -  .337 

Sesquibromide          -            -                       I  • .  337 

Protohyduret  and  Arseniuretted  Hydrogen  -     337 
Sulphurets     - 

XVI.    Chromium  and  Vanadium               -  -     339 

Chromium     -                                                     -  339 
Vanadium            .....     343 

XVII.     Molybdenum,  Tungsten,  and  Columbiurn          -  349 
Molybdenum        -                          ...     349 

Tungsten       •».-.-•>                                       ,  351 
Columbium                       ....     353 

XVIII.     Antimony         .                          .  355 

Sesquioxide          -                          ..  356 

Antimonious  Acid    ....  357 

Antimonic  Acid  -             -             -         '••»-  -     358 

Chlorides      -           ^            •        > '.-/        -,  358 

Bromide  -          %    .        -            -        x  .  :v  .    358 
Sulphurets    -                                               \  V->:       358 
Oxychloride         .             .             .            '„    .     ,  „     359 

Oxysulphuret  359 

XIX.     Uranium  and  Cerium          -  360 

Uranium       .....  360 

Cerium                -  -     362 

XX.     Bismuth,  Titanium,  and  Tellurium       -             -  363 

Bismuth              »          -i  -        -            -  -     363 

Titanium      •    -    ;   -            .        /  .            .  364 

Tellurium          -i        V  . -•         .            .  -     367 

XXI.    Copper              .  369 

Red  or  Dioxide    -            -            -            -  -     370 

Black  or  Protoxide    -  370 

Superoxide           .            .                     •-    i-  .     371 

Chlorides       -            -            -        g*£    ,        .  371 
Iodides    -            .            .             ..,«/.    372 

Sulphurets  and  Phosphurets  -        •  ^V           .  372 

XXII.    Lead  -    372 

Dinoxide  and  Protoxide         ...  374 

Red  Oxide  and  Peroxide              -           .-  -     375 

Chloride        -                         -  375 

Iodide,  Bromide,  and  Fluoride     -  -     376 

Sulphuret,  Phosphuret,  and  Carburet              -  376 

XXIII.     Mercury  or  Quicksilver      -             -             .  -     377 

Protoxide  and  Peroxide          •             -  378 
Protochloride       .....     379 

Bichloride     .....  379 


Iodides    -             .                          .             .  -     381 

Bromides       -             -             .        "'    .  ^        -  381 

Sulpharets            -             -             .             -  -     382 

SECT.    XXIV.    Silver    ....        •>,  '        M        382 

Oxide      -            -             .            .  .384 

Chloride,  Iodide,  and  Sulphuret         -             -  384 

XXV.    Gold           ....        ' '-,~;  .    385 

Oxides  .  -.  .        :-.   „'    '        .  \       386 

Chlorides            s.  -'    J^'      :"  -;V.        v  -     387 

Tersulphuret         N •. •-*    •->>         "'. .V* '•-**  v  388 

Iodides    -         %           v  ^   ig®";1         -  -    388 

XXVI.    Platinum          -           ,,j.-   (    ^         -            T  389 

Oxides    -             -             .             .             .  .390 

Chlorides,  Iodides,  and  Sulphurets     -  391 

XXVII.     Palladium,  Rhodium,  Osmium,  and  Iridium  -     392 

Palladium     -             .             -        r  .           >»  392 

Rhodium             v,     •  .V  "    P|p        .,  •     393 

Osmium        -            .%-     K    -          "*_:.'   ^    -  396 

Iridium  -             -        %#V    ^  ^            -  -     397 

XXVIII.     Metallic  Combinations  - 

Amalgams           -        '•*  -r  *    T  *•         -^  /  -     399 

Alloys          •%    r  400 

GENERAL  REMARKS  ON  SALTS    -            -            »  f     '  .         -U\V  •    402 

Crystallization         ;   ^            -1     "r  ?     .-"  ;          -            -  409 

SECT.  I.    Oxy-salts    .        .  >. ..-;        .        ;;;;..^      , '.  .    419 

Sulphates    .1            ..  "          .        $&,    '•'-.    !V./  421 

Double  Sulphates            :v        -, ;            .  -     428 

Sulphites        -         fe^Si'     :-,-'            -             -  431 

Nitrates               v,  !        *  ^    j®^         -  -     431 

Nitrites      -4,    •    '   *•  •'    •  :;^:          ,.•           -  435 

Chlorates            >:        ^  •>;        «^        .  .     435 

Chlorite*     ^|    }.-   -      --            -            -  436 

lodales                .             .             .        .    *,  -    437 

Bromates      ,             .             .        >    .1.  '•     ^    *  438 
Phosphates                                                           •'/.    438 

Pyrophosphates         *             -            ,<•  442 

Metaphosphates  -          •'•-«<    ;    '»-       " :    -.    -  -     443 

Arseniates    -           ,  i.  .     ,' .«  y  444 

Arsenites            /  ;                  ?>+*                     ,  '•    446 

Chromates    -                          .  447 

Borates               V^           •  »    448 

Carbonates    .        ".    *             .yv     '"% ":J    ^V  449 

II.    Hydro-salts  .    455 

Ammoniacal  Salts     -             -         A:  »  456 

Phosphuretted  Hydrogen  Salts    -                        ,  -  "  458 

III.  Sulphur-salts     -  458 

Hydro-sulphurets             .            .  -    459 

Carbo-sulphurets       -  460 

Arsenio-sulphurets                        -  -    461 

Molybdo-sulphurets  463 

Antimonio-sulphurets       .        ^-'T-  .     464 

Tungsto-sulphurets  -             .            -            -:v  464 

IV.  Haloid  Salts             -                     &&"       '  .,-:t  -    464 

Double  Chlorides       -             -         :    . v  465 
Hydrargo-bichlorides    -                                   f  •'•*  .  465 

Auro-chlorides       -  465 

Platino-chlorides                                   —  -     466 

Palladio-chlorides  -            -        ;    .            -  467 


CONTEXTS,  X11L 

Rhodio-chloricles          ....     467 

Iridio-chlorides      -  468 

Osmio-chlorides                         -  468 

Qxychlorides             ....  468 

Chlorides  with  Ammonia             -             -  469 

Chlorides  with  Phosphuretted  Hydrogen        -  470 

Double  Iodides                 -             -             -  -    470 

Platino-biniodides               ...  470 

Oxy iodides                                                    .  I  -     471 

Double  Bromides      -                       =  *«  ••*'      •   »  .       471 

Double  Fluorides             -      •. .  ;'•  •  /•.    ^ .  •  •     471 

Hydro-fluorides     -             -                       .  ;»  471 

Boro-fluorides               -             -             -  -     472 

Silico-fluorides       -             -             -  472 

Titano-fluorides                                      -  -     473 

Oxy  fluorides  473 


PART  III. 

ORGANIC  CHEMISTRY. 

VEGETABLE  CHEMISTRY             ......  476 

SECT.  I.     Vegetable  Acids           ....  473 

Oxalic  Acid         -                                                     -  479 

Acetic  Acid                            -          -  •'•           -  483 

Lactic  Acid         -                         -            -            -  486 

Kinic  Acid                                          ,    '  487 

Malic  Acid          .....  488 

Citric  Acid                             .            .            -  489 

Tartaric  Acid     -             -                          -             -  490 

Racemic  Acid  -  -  \  -  .':.-""  492 

Benzoic  Acid  -  -  '-'V  .  493 

Meconic  Acid  -  -  ..'•  .  494 

Metameconic  Acid  -  •  .•<* -.'*-  «  -  -  495 

Tannic  Acid  (Tannin)  -  ~- -  -,..'  495 

Gallic  Acid  -  -  497 

Pyrogallic  Acid  -  -  -  498 

Metagallic,  Ellagic,  Succinic,  and  Mucic  Acid  499 
Camphoric,  Valerianic,  Rocellic,  and  Moroxylic 

Acid  -  -  -  -500 

Chloroxalic,  Boletic,  Igasuric,  Suberic,  Zumic, 

and  Pectic  Acid  .  -  501 

Lactucic,  Crameric,  Caincic,  and  Indigotic  Acid  502 

Carbazotic  Acid  -  -  -  .  503 

SECT  II.  Vegetable  Alkalies  -  "*  ^  -  504 

Morphia  ?  -  -  -  -  505 

Narcotina  r  .  .  .  .  507 

Codeia  -  -  -  -  .  508 

Narceia  -  -  509 

Cinchonia  and  Quinia  -  '  '?*  -  509 

Aricina  T  .  .  .  .  511 

Strychnia  and  Brucia  -  -  -  511 

Veratria  and  Emetia  ...  512 
Picrotoxia,  Coryddia,  Solania,  Cynopia,  ancl  Del- 

phia     -  .  ,513 

Sanguinaria  and  Nicotina     -             -  514 

III.    Neutral  Substances              -                                      -  514 

Sugar            -            -            -            -  „  515 

Starch  or  Fecula. — Amidine        -  r  .517 

B 


Gum  518 

Lignin    -                                       -                          -  520 

SECT.  IV.    Oleaginous,  Resinous,  and  Bituminous  Substances  520 

Oleaginous  Substances                    f''v ,         •    -  521 

Fixed  Oils   -                          -        ;^.            .  521 

Volatile  or  Essential  Oils  522 

Essence  of  Turpentine                            -  523 

Camphor     -                                    ..  .*  524 

Oil  of  Cloves  and  Oil  of  Mustard      .i*  524 

Oil  of  Bitter  Alrnonds         -  524 

Benzule     -        f.^i-' '       ;  .  ,V        -  524 

Bcnzamide       -                          -  526 

Benzoine  -                          -     /       -  526 

Coumarin  526 

Resinous  Substances        -                                       -  527 

Resins    -                          -                          -  527 

Amber,  Balsams,  Gum-resins,  and  Caoutchouc  528 

Wax             -             r           '-             ;             -  529 

Bituminous  Substances         -  530 

Bitumen      -                                                 ...  530 

Petroleum,   Mineral   Tar,   Asphaltum, 

Mineral  Pitch,  and  Retinasphaltum  530 

Inflammable  principles  of  Tar       **•  530 

Creosote     -                                       -  530 

Picarnar  and  Capnomor       .-    ••  531 

Pittacal     -        :.;•>>,•'    •-:  \t<:        -  532 

Pit-coal                            -  532 

Brown  Coal  and  Common  or  Black  Coal  532 

Glance  Coal      -                      ,A  V  ,'        -  533 

V.    Spirituous  and  Ethereal  Substances      -  533 

Alcohol               -'  f    ;;w;;-    1^,-v        -            -  533 

Ether                                 ^^|  «,  •_ ,      , -N  535 

Sulpho-vinic  Acid    -                                       -  538 

Ethero-sulphuric  and  Ethero-phosphoric  Acid  539 

Oil  of  Wine              -            -            -            -  540 

Hydrochloric  Ether        -  540 

Hydriodic,  Hydrobromic,  Nitrous,  and  Oxalic 

Ether       -                                                     -  541 
Acetic,  Tartaric,  Citric,  Malic,  Cyanuric,  Sul- 

phocyanic,  and  Chloric  Ether        -             -  542 

Pyroacetic  and  Pyroxylic  Spirit  543 

VI.     Colouring  Matters  -             -             -        ;  '  •    .         -  544 

Blue  Dyes     -                          -             . "          -  545 

Red  Dyes            -            -            -            -            -  547 

Yellow  Dyes             -  ^        -         -    *        'V  548 

Black  Dyes         -                                                   -  548 

VII.     Substances  which,  so  far  as  is  known,  do  not  belong 

to  either  of  the  preceding  Sections       -             -  549 

Vegetable  Albumen  and  Gluten         -  549 

Yeast  and  Asparagin       -                                       -  550 

Bassorin  and  Caffein                                          -  551 

Cathartin,  Fungin,  Suberin,  Ulmin,  Lupulin,  &c.  552 
Olivile,  Sarcocoli,  Rhubarbarin,  Rhein,  Rhapoii- 

ticin,  &c.                                                              -  553 
Scillitin,  Senegin,  Saponin,  Arthanatin,  Extractive 

Matter,  &c.                         -             -  554 

Salicin,  Populin,  and  Meconin     -                          -  555 

Columbin,  Elatin,  and  Sinapisin        -             -  556 

VIII.    Spontaneous  Changes  of  Vegetable  Matter              -  557 

Saccharine  Fermentation      -            -            -  557 


CONTEXTS.  XV 

Vinous  Fermentation       ....  558 

Acetous  Fermentation                         -             -  560 

Putrefactive  Fermentation            -  561 

SECT.  IX.    Chemical  Phenomena  of  Germination  and  Vegetation  562 

Germination        ...                          -  562 

Growth  of  Plants      ....  564 

Food  of  Plants     -                                                    -  566 

ANIMAL  CHEMISTRY    -                                                                -  568 

PROXIMATE  ANIMAL  SUBSTANCES        -                                       -  568 

SECT.  I.    Substances  which  are  neither  Acid  nor  Oleaginous  568 

Fibrin     -             -                                       -  568 

Albumen       -             -  569 

Gelatin   -             -             -             -             -             -  571 

Urea                                                      -             -  572 

Sugar  of  Milk  and  Sugar  of  Diabetes      -             -  573 

II.     Animal  Acids   ....  574 

Uric  or  Lithic  Acid         -                                       -  574 

Purpuric  and  Rosacic  Acid   -  575 

Hippuric  and  Formic  Acid                                     -  576 

Allantoic  Acid                         -                           -  577 

III.  Animal  Oils  and  Fats  .  -  577 
Train  Oil,  Spermaceti  Oil,  Animal  Oil  of  Dippel, 

&,c.            .             .             ,             -             -  578 

Margarine,  Oleine,  and  Margaric  and  Oleic  Acid  579 
Stearic   and  Sebacic  Acid,  Butyrme,  Phocenine, 

Hircine,  and  Glycerine                          -             -  580 

Spermaceti,  Ethal,  Adipocire,  and  Cholesterine  581 

Ambergris,  Ambreine,  and  Ambreic  Acid           -  582 

MOKE  COMPLEX  ANIMAL  SUBSTANCES,  AND  SOME  FUNCTIONS  OF  ANIMAL 

BODIES       .'                                                -  ,  582 

SECT.  I.  Blood,  Respiration,  and  Animal  Heat  -  582 

Blood  -  -  -  -  -  582 

Respiration  -  -  -  -  -  590 

Animal  Heat  -  ...  596 

II.     Secreted  Fluids  subservient  to  Digestion            -  598 

Saliva     -                                                                  -  598 

Pancreatic  and  Gastric  Juice             -             -  599 

Bile         -                         -           ;-  '          -            -  600 

Biliary  Concretions            ...  601 

III.  Chyle,  Milk,  and  Eggs  -  -  -  -  602 
Chyle  .  -  -  .  -602 

Milk  -  -  -  -  -  603 

Eggs  " -\  605 

IV.  Liquids  of  Serous  and  Mucous  Surfaces,  &c.  -  606 

Humours  of  the  Eye  606 

Mucus  ......  606 

Pus 607 

Sweat     -                                                                -  608 

V.     Urine  and  Urinary  Concretions             -             -  608 

Urine      -                                                                  -  608 

Urinary  Concretions  612 

VI.     Solid  Parts  of  Animals        -                                       -  614 

Bones                                                  •  614 

Teeth,  Horn,  Tendons,  Muscle,  £c.         -            -  615 

VII.    Putrefaction 616 


CONTENTS. 

PART  IV. 

ANALYTICAL  CHEMISTRY. 

SECT.  I.     Analysis  of  Mixed  Gases                                       -  618 

II.     Analysis  of  Minerals             -             -  620 

III,     Analysis  of  Mineral  Waters       -                          -  625 

Composition  of  Mineral  Waters  629 

APPENDIX. 

Constitution  of  certain  Hydrated  Salts  and  Peroxides,  and 

of  Phosphuretted  Hydrogen      -             -             -  633 

Table  of  the  Force  of  Aqueous  Vapour  -                          -  636 
Table  of  the  Force  of  the  Vapours  of  Alcohol,  Ether, 

&c. 638 

Table  of  the  Strength  of  Sulphuric  Acid      -             ;  .  639 

Table  of  the  Strength  of  Nitric  Acid      -         V   .'   '        .  640 

Table  of  the  Strength  of  Alcohol  641 
Table  of  Specific  Gravities  corresponding  to  the  Degrees 

of  Baume's  Hydrometer                          -             -  642 

Mercaptan  and  Mercaptum         -             -             -             -  642 

Mellon,  Melam,  Melamine,  Ammeline,  and  Ammelide  643 

Carburetted  Hydrogen  in  the  Atmosphere           -             -  644 

Benziri  and  Benzone              -                       ;  -             •  644 

Origin  of  Naphtha                                                               -  644 

Xanthic  and  Hydroxanthic  Acid      -             -  644 

Transmission  of  Heat  through  Solids  and  Liquids  645 

Polarization  and  Double  Refraction  of  Heat  646 

Velocity  of  Electricity    -                                                    -  646 

Daniell's  Constant  Battery  -  647 

Nitrosulphuric  Acid       -                                       -  647 

Liquid  and  Solid  Carbonic  Acid.     •            -            -  648 

INDEX    -            .            .            .            -            .            -  649 


INTRODUCTION. 


MATERIAL  substances  are  endowed  with  two  kinds  of  properties,  physical 
and  chemical ;  and  the  study  of  the  phenomena  occasioned  by  them  has  given 
rise  to  two  corresponding  branches  of  knowledge,  Natural  Philosophy  and 
Chemistry. 

The  physical  properties  are  either  general  or  secondary.  The  general 
are  so  called  because  they  are  common  to  all  bodies ;  the  secondary,  from 
being  observable  in  some  substances  only.  Among  the  general  may  be  enu- 
merated extension,  impenetrability,  mobility,  extreme  divisibility,  gravitation, 
porosity,  and  indestructibility. 

Extension  is  the  property  of  occupying  a  certain  portion  of  space :  a  sub- 
stance is  said  to  be  extended  when  it  possesses  length,  breadth,  and  thick- 
ness. By  impenetrability  is  meant  that  no  two  portions  of  matter  can  occupy 
the  same  space  at  the  same  moment.  Every  thing  that  possesses  extension 
and  impenetrability  is  matter. 

Matter,  though  susceptible  of  rest  and  motion,  has  no  inherent  power 
either  of  beginning  to  move  when  at  rest,  or  of  arresting  its  progress  when 
in  motion.  Its  indifference  to  either  state  has  been  expressed  by  the  term 
vis  inertia,  as  if  it  depended  on  some  peculiar  force  resident  in  matter;  but 
it  arises,  rather,  from  matter  being  absolutely  passive,  and  thereby  subject  to 
the  influence  of  every  force  which  is  capable  of  acting  upon  it. 

Matter  is  divisible  to  an  extreme  degree  of  minuteness.  A  grain  of  gold  may 
be  so  extended  by  hammering  that  it  will  cover  50  square  inches  of  surface, 
and  contain  two  millions  of  visible  points ;  and  the  gold  which  covers  the 
silver  wire,  used  in  making  gold  lace,  is  spread  over  a  surface  twelve  times  as 
great.  (Nicholson's  Introduction  to  Natural  Philosophy,  vol.  i.)  A  grain  of 
iron,  dissolved  in  nitro-muriatic  acid,  and  mixed  with  3137  pints  of  water, 
will  be  diffused  through  the  whole  mass :  by  means  of  the  ferro-cyanuret  of 
potassium,  which  strikes  a  uniform  blue  tint,  some  portion  of  iron  may  be 
detected  in  every  part  of  the  liquid.  This  experiment  proves  the  grain  of 
iron  to  have  been  divided  into  rather  more  than  24  millions  of  parts ;  and  if 
the  same  quantity  of  iron  were  still  further  diluted,  its  diffusion  through  the 
whole  liquid  might  be  proved  by  concentrating  any  portion  of  it  by  evapora- 
tion, and  detecting  the  metal  by  its  appropriate  tests. 

A  keen  controversy  existed  at  one  time  concerning  the  divisibility  of 
matter;  some  philosophers  affirming  it  to  be  infinitely  divisible, while  others 
maintained  an  opposite  opinion.  Owing  to  the  imperfection  of  our  senses, 
the  question  cannot  be  determined  by  direct  experiment;  because  matter  cer- 
tainly continues  to  be  divisible  long  after  it  has  ceased  to  be  an  object  of 
sense.  The  decision,  if  effected  at  all,  can  only  be  accomplished  indirectly, 
as  an  inference  from  other  phenomena.  In  favour  of  the  former  view  it  was 
urged,  on  mathematical  grounds,  that  a  surface  admits  of  division  without 
limit;  and  that  to  whatever  degree  matter  is  divided,  it  may  still  be  con- 
ceived, in  possessing  extension  and  surface,  to  be  susceptible  of  still  furlher 
division.  Plausible,  however,  as  this  mode  of  reasoning  may  appear  the 
opposite  opinion  is  daily  becoming  more  general.  It  is  now  commonly  be- 
lieved that  matter  consists  of  ultimate  particles  or  molecules,  which  may  in- 
deed be  conceived  to  be  divisible,  but  which  by  hypothesis  are  assumed  to 
be  infinitely  hard  and  impenetrable,  and  on  that  account  to  be  incapable  of 


2  INTRODUCTION. 

division.  These  ultimate  particles  have  received  the  appellation  of  atoms, 
(from  the  privative  A  and  rejuveiv  to  cut,)  as  expressive  of  their  nature.  The 
arguments  adduced  in  support  of  this  opinion  are  principally  drawn  from 
the  phenomena  of  chemistry,  and  from  the  relations  which  have  been  ob- 
served to  exist  between  the  composition  and  form  of  crystallized  bodies. 
These  subjects  will  be  considered  in  their  proper  place ;  but  I  may  observe, 
in  order  to  show  the  nature  of  the  argument,  that  the  supposed  existence  of 
atoms  accounts  for  numerous  facts,  which  cannot  be  satisfactorily  explained 
on  any  other  principle. 

All  bodies  descend  in  straight  lines  towards  the  centre  of  the  earth,  when 
left  at  liberty  at  a  distance  from  its  surface.  The  power  which  produces 
this  effect  is  termed  gravity,  attraction  of  gravitation,  or  terrestrial  attrac- 
tion ;  and  the  force  required  to  separate  a  body  from  the  surface  of  the  earth, 
or  prevent  it  from  descending  towards  it,  is  called  its  weight.  Every  particle 
of  matter  is  equally  affected  by  gravity ;  and,  therefore,  the  weight  of  any 
body  will  be  proportionate  to  the  number  of  ponderable  particles  which  it 
contains. 

The  minute  particles  of  which  bodies  consist,  are  disposed  in  such  a  man- 
ner as  to  leave  certain  intervals  or  spaces  between  them,  and  this  arrange- 
ment is  called  porosity.  These  interstices  may  sometimes  be  seen  by  the 
naked  eye,  and  frequently  by  the  aid  of  glasses ;  but  were  they  wholly  in. 
visible,  it  would  still  be  certain  that  they  exist.  All  substances,  even  the 
most  compact,  may  be  diminished  in  bulk  either  by  mechanical  force  or  a 
reduction  of  temperature.  It  hence  follows  that  their  particles  must  touch 
each  other  at  a  very  few  points  only,  if  at  all;  for  if  their  contact  were  so 
perfect  as  to  leave  no  interstitial  spaces,  then  would  it  be  impossible  to 
diminish  the  dimensions  of  a  body,  because  matter  is  incompressible  and 
cannot  yield.  When,  therefore,  a  body  expands,  the  distance  between  its  par- 
ticles is  increased  ;  and,  conversely,  when  it  contracts  or  diminishes  in  size, 
its  particles  approach  each  other. 

By  indestructibility  is  meant,  that,  according  to  the  present  laws  of  na- 
ture, matter  never  ceases  to  exist.  This  statement  seems  at  first  view  con- 
trary to  fact.  Water  and  volatile  substances  are  dissipated  by  heat,  and  lost ; 
coals  and  wood  are  consumed  in  the  fire,  and  disappear.  But  m  these  and 
all  similar  phenomena  not  a  particle  of  matter  is  annihilated.  Tne  apparent 
destruction  is  owing  merely  to  a  change  of  form  or  composition  ;  for  the 
same  material  particles,  after  having  undergone  any  number  of  such  changes, 
may  still  be  proved  to  possess  the  characteristic  properties  of  matter. 

The  secondary  properties  of  matter  are  opacity,  transparency,  softness, 
hardness,  elasticity,  colour,  density,  solidity,  fluidity,  and  others  of  a  like 
nature.  Several  of  these  properties,  especially  those  last  specified,  depend  on 
the  relative  intensity  of  two  opposite  forces — cohesion  and  repulsion.  It  is 
inferred,  from  the  divisibility  of  matter,  that  the  substance  of  solids  and 
liquids  is  made  up  of  an  infinity  of  minute  particles  adhering  together  so  as 
to  constitute  larger  masses;  and  that  the  mutual  adhesion  of  these  particles 
is  owing  to  a  power  of  reciprocal  attraction.  This  force  is  called  cohesion, 
cohesive  attraction,  or  the  attraction  of  aggregation,  in  order  to  distinguish 
it  from  terrestrial  attraction.  Gravity  is  exerted  between  different  masses  of 
matter,  and  acts  at  sensible  and  frequently  at  very  great  distances;  while  co- 
hesion exerts  its  influence  only  at  insensible  and  infinitely  small  distances. 
It  enables  similar  molecules  to  cohere,  and  tends  to  keep  them  in  that  con- 
dition. It  is  best  exemplified  by  the  force  required  to  separate  a  hard  body, 
such  as  iron,  or  marble,  into  smaller  fragments ;  or  by  the  weight  which 
twine  or  metallic  wire  will  support  without  breaking. 

The  tendency  of  cohesion  is  manifestly  to  bring  the  ultimate  particles  of 
bodies  into  immediate  contact;  and  such  would  be  the  result  of  its  influence, 
were  it  not  counteracted  by  an  opposing  force,  a  principle  of  repulsion,  which 
prevents  their  approximation.  It  is  a  general  opinion  among  philosophers, 
supported  by  very  strong  facts,  that  this  repulsion  is  owing  to  the  agency  of 
heat,  which  is  somehow  attached  to  the  elementary  molecules  of  matter, 


INTRODUCTION.  6 

causing  them  to  repel  one  another.  Material  substances  are,  therefore,  subject 
lo  the  action  of  two  contrary  and  antagonizing  forces,  one  tending  to  sepa- 
rate their  particles,  the  other  to  bring  them  into  closer  proximity.*  The 
form  of  bodies,  as  to  solidity  and  fluidity,  is  determined  by  the  relative  in- 
tensity  of  these  powers.  Cohesion  predominates  in  solids,  in  consequence 
of  which  their  particles  are  prevented  from  moving  freely  on  one  another. 
The  particles  of  a  fluid,  on  the  contrary,  are  far  less  influenced  by  cohesion, 
being  free  to  move  on  each  other  with  very  slight  friction.  Fluids  are  of 
two  kinds;  elastic  fluids  or  aeriform  substances,  and  inelastic  fluids  or 
liquids.  Cohesion  seems  wholly  wanting  in  the  former.  They  yield  readily 
to  compression,  and  expand  when  the  pressure  is  removed  :  indeed,  the  space 
they  occupy  is  chiefly  determined  by  the  force  which  compresses  them.  The 
latter,  on  the  contrary,  do  not  yield  perceptibly  to  ordinary  degrees  of  com- 
pression, nor  does  an  appreciable  dilatation  ensue  from  the  removal  of  pres- 
sure; the  tendency  of  repulsion  being  in  them  counterbalanced  by  cohesion. 
Matter  is  subject  to  another  kind  of  attraction  different  from  those  yet 
mentioned,  termed  chemical  attraction,  or  affinity.  Like  cohesion,  it  acts 
only  at  insensible  distances,  and  thus  differs  entirely  from  gravity.  It  is  dis- 
tinguished from  cohesion  by  being  exerted  between  dissimilar  particles  only, 
while  the  attraction  of  cohesion  unites  similar  particles.  Thus,  a  piece  of 
marble  is  an  aggregate  of  smaller  portions  attached  to  each  other  by  cohe- 
sion, and  the  parts  so  attached  are  called  integrant  particles;  each  of  which, 
however  minute,  being  as  perfect  marble  as  the  mass  itself.  But  the  inte- 
grant particles  consist  of  two  substances,  lime  and  carbonic  acid,  which  are 
different  from  one  another  as  well  as  from  marble,  and  are  united  by  chemi- 
cal attraction.  They  are  the  component  or  constituent  parts  of  marble.  The 
integrant  particles  of  a  body  are,  therefore,  aggregated  together  by  cohesion; 
the  component  parts  are  united  by  affinity. 

The  chemical  properties  of  bodies  are  owing  to  affinity,  and  every  chemi- 
••  cal  phenomenon  is  produced  by  the  operation  of  this  principle.  Though  it 
extends  its  influence  over  all  substances,  yet  it  affects  them  in  very  dif- 
ferent degrees,  and  is  subject  to  peculiar  modifications.  Of  three  bodies,  A, 
B,  and  C,  it  is  often  found  that  B  and  C  evince  no  affinity  for  one  another, 
and,  therefore,  do  not  combine;  that  A,  on  the  contrary,  has  an  affinity  for 
B  and  C,  and  can  enter  into  separate  combination  with  each  of  them ;  but 
that  A  has  a  greater  attraction  for  C  than  for  B,  so  that  if  we  bring  C  in 
contact  with  a  compound  of  A  and  B,  A  will  quit  B  and  unite  by  preference 
with  C.  The  union  of  two  substances  is  called  combination  ;  and  its  result 
is  the  formation  of  a  new  body  endowed  with  properties  peculiar  to  itself, 
and  different  from  those  of  its  constituents.  The  change  is  frequently  at- 
tended by  the  destruction  of  a  previously  existing  compound,  and  in  that 
case  decomposition  is  said  to  be  effected. 

The  operation  of  chemical  attraction,  as  thus  explained,  lays  open  a  wide 
and  interesting  field  of  inquiry.  One  may  study,  for  example,  the  affinity 
existing  between  different  substances ;  an  attempt  may  be  made  to  discover 
the  proportion  in  which  they  unite ;  and  finally,  after  collecting  and  arrang- 
ing an  extensive  series  of  insulated  facts,  general  conclusions  may  be  deduced 
from  them.  Hence  chemistry  may  be  defined  the  science,  the  object  of 
which  is  to  examine  the  relations  that  affinity  establishes  between  bodies, 
ascertain  with  precision  the  nature  and  constitution  of  the  compounds  it  pro- 
duces, and  determine  the  laws  by  which  its  action  is  regulated. 

*  It  should  be  borne  in  mind,  however,  that  the  force  which  tends  to  bring 
the  elementary  molecules  into  closer  proximity,  is  derived  from  an  innate 
property  of  ponderable  matter ;  while  the  force  which  tends  to  separate  them 
is  dependent  on  the  operation  of  a  distinct  principle,  caloric,  the  particles  of 
which,  being  self-repellent,  force  the  ponderable  particles  asunder.  In  order 
to  explain  why  the  caloric  remains  attached  to  the  ponderable  molecules, 
it  is  necessary  to  suppose  that  its  particles,  though  self-repellent,  have  an 
attraction  for  ponderable  matter,  Ed. 


4  INTRODUCTION. 

Material  substances  are  divided  by  the  chemist  into  simple  and  compound. 
He  regards  those  bodies  as  compound,  which  may  be  resolved  into  two  or 
more  parts ;  and  those  as  simple  or  elementary,  which  contain  but  one  kind 
of  ponderable  matter.  The  number  of  the  latter  amounts  only  to  fifty-four; 
and  of  these  all  the  bodies  Jn  the  earth,  as  far  as  our  knowledge  extends,  are 
composed.  The  list,  a  few  yea*s  ago,  was  somewhat  different  from  what  it 
is  at  present;  for  the  acquisition  of  improved  methods  of  analysis  has  ena- 
bled chemists  to  demonstrate  that  substances,  which  were  once  supposed  to 
be  simple,  are  in  reality  compound ;  and  it  is  probable  that  a  similar  fate 
awaits  some  of  those  which  are  at  present  regarded  as  simple. 

The  composition  of  a  body  may  be  determined  in  two  ways,  analytically 
or  synthetically.  By  the  former  method  the  elements  of  a  compound  are  se- 
parated from  one  another,  as  when  water  is  resolved  by  the  agency  of  gal- 
vanism into  oxygen  and  hydrogen  ;  by  synthesis  they  are  made  to  combine, 
as  when  oxygen  and  hydrogen  unite  by  the  electric  spark,  and  generate  a 
portion  of  water.  Each  of  these  kinds  of  proof  is  satisfactory  ;  but  when 
they  are  conjoined — when  we  first  resolve  a  particle  of  water  into  its  ele- 
ments, and  then  reproduce  it  by  causing  them  to  unite — the  evidence  is  in 
the  highest  degree  conclusive. 

I  have  followed,  in  the  composition  of  this  treatise,  the  same  general  ar- 
rangement which  I  adopt  in  my  lectures.  It  is  divided  into  four  principal 
parts.  The  first  comprehends  an  account  of  the  nature  and  properties  of 
Heat,  Light,  and  Electricity, — agents  so  diffusive  and  subtile,  that  the  com- 
mon attributes  of  matter  cannot  be  perceived  in  them.  They  are  altogether 
destitute  of  weight :  at  least,  if  they  possess  any,  it  cannot  be  discovered  by 
our  most  delicate  balances,  and  hence  they  have  received  the  appellation  of 
Imponderables.  They  cannot  be  confined  and  exhibited  in  a  mass  like  ordi- 
nary bodies ;  they  can  be  collected  only  through  the  intervention  of  other 
substances.  Their  title  to  be  considered  material  is,  therefore,  questionable, 
and  the  effects  produced  by  them  have  accordingly  been  attributed  by  some 
to  certain  motions  or  affections  of  common  matter.  It  must  be  admitted, 
however,  that  they  appear  to  be  subject  to  the  same  powers  that  act  on  mat- 
ter in  general,  and  that  some  of  the  laws  which  have  been  determined  con- 
cerning them,  are  exactly  such  as  might  have  been  anticipated  on  the  sup- 
position of  their  materiality.  It  hence  follows,  that  we  need  only  regard 
them  as  subtile  species  of  matter,  in  order  that  the  phenomena  to  which 
they  give  rise  may  be  explained  in  the  language,  and  according  to  the  prin- 
ciples, which  are  applied  to  material  substances  in  general;  and  I  shall, 
therefore,  consider  them  as  such  in  my  subsequent  remarks. 

The  second  part  comprises  Inorganic  Chemistry.  It  includes  the  doctrine 
of  affinity,  and  the  laws  of  combination,  together  with  the  chemical  history 
of  all  the  elementary  principles  hitherto  discovered,  and  of  those  compound 
bodies  which  are  not  the  product  of  organization.  Elementary  bodies  are 
divided  into  the  non-metallic  and  metallic  ;  and  the  substances  contained  in 
each  division  are  treated  in  the  order  which,  it  is  conceived,  will  be  most 
convenient  for  the  purposes  of  teaching.  From  the  important  part  which 
oxygen  plays  in  the  economy  of  nature,  it  is  necessary  to  begin  with  the  de- 
scription of  that  principle;  and  from  the  tendency  it  has  to  unite  with  other 
bodies,  as  well  as  the  importance  of  the  compounds  it  forms  with  them,  it 
will  be  useful,  in  studying  the  history  of  each  elementary  body,  to  describe 
the  combinations  into  which  it  enters  with  oxygen  gas.  The  remaining 
compounds  which  the  non-metallic  substances  form  with  each  other,  will 
next  be  considered.  The  description  of  the  individual  metals  w.ill  be  accom- 
panied by  a  history  of  their  combinations,  first  with  the  simple  non-metallic 
bodies,  and  afterwards  with  each  other.  The  last  division  of  this  part  will 
comprise  a  history  of  the  salts. 

The  third  general  division  of  the  work  is  Organic  Chemistry,  a  subject 
which  will  be  conveniently  discussed  under  two  heads,  the  one  comprehend- 
ing- the  products  of  vegetable,  the  other  of  animal  life. 

The  fourth  part  contains  brief  directions  for  the  performance  of  Analysis. 


CHEMISTRY. 

PART  I. 

IMPONDERABLE  SUBSTANCES. 

SECTION  I. 
HEAT,  OR  CALORIC. 

THE  term  Heat,  in  common  language,  has  two  meanings :  in  the  one  case, 
it  implies  the  sensation  experienced  on  touching  a  hot  body ;  in  the  other,  it 
expresses  the  cause  of  that  sensation.  When  used  in  the  latter  sense,  it  is 
synonymous  with  the  word  Caloric,  (from  Calor,  heat,)  which  is  employed 
exclusively  to  signify  the  cause  or  agent  by  which  all  the  effects  of  heat  are 
produced. 

Heat,  on  the  supposition  of  its  being  material,  is  a  subtile  fluid,  the  parti- 
cles of  which  repel  each  other,  and  are  attracted  by  all  other  substances.  It 
is  imponderable :  that  is,  it  is  so  exceedingly  light,  that  a  body  undergoes  no 
appreciable  change  of  weight,  either  by  the  addition  or  abstraction  of  heat. 
It  is  present  in  all  bodies,  and  cannot  be  wholly  separated  from  them.  For 
if  a  substance,  however  cold,  be  transferred  into  an  atmosphere  which  is 
still  colder,  a  thermometer  placed  in  the  body  will  indicate  the  escape  of 
heat.  That  its  particles  repel  one  another,  is  proved  by  observing  that  it 
flies  off  from  a  heated  body ;  and  that  it  is  attracted  by  other  substances,  is 
inferred  from  the  tendency  it  has  to  penetrate  their  particles,  and  to  be  re- 
tained by  them. 

Heat  may  be  transferred  from  one  body  to  another.  Thus,  if  a  cup  of 
mercury  at  60°  be  plunged  into  hot  water,  heat  passes  rapidly  from  one  into 
the  other,  until  the  temperature  in  both  is  the  same ;  that  is,  till  a  thermo- 
meter placed  in  each  stands  at  the  same  height.  All  bodies  on  the  earth  are 
constantly  tending  to  attain  an  equality,  or  what  is  technically  called  an 
equilibrium,  of  temperature.  If,  for  example,  a  number  of  substances  of 
different  temperatures  be  enclosed  in  an  apartment,  in  which  there  is  no 
actual  source  of  heat,  they  will  very  soon  acquire  an  equilibrium ;  so  that 
a  thermometer  will  stand  at  the  same  point  in  all  of  them.  The  varying 
sensations  of  heat  and  cold,  which  we  experience,  are  owing  to  a  like  cause. 
On  touching  a  hot  body,  heat  passes  from  it  into  the  hand,  and  excites  the 
feeling  of  warmth  ;  when  we  touch  a  cold  body,  heat  is  communicated  to  it 
from  the  hand,  and  thus  arises  the  sensation  of  cold. 

As  this  transfer  of  heat  is  constantly  going  forward,  it  is  important  to 
determine  by  what  means,  and  according  to  what  laws,  the  equilibrium  is 


established.  Now,  it  is  found  that  heat  is  communicated  from  a  hot  body 
to  others  which  are  colder  in  two  ways;  by  direct  contact,  and  by  what  is 
called  radiation.  By  direct  contact,  when  the  hot  body  touches  a  cold  one, 
so  that  the  heat  may  pass  directly  from  one  into  the  other ;  as  when  a  bar 
of  iron  is  put  into  a  fire,  or  the  hand  plunged  into  hot  water.  By  radiation, 
when  the  heat  leaps  as  it  were  from  a  hot  to  a  cold  body,  through  an  appre- 
ciable interval ;  as  when  a  red-hot  ball,  suspended  in  the  vacuum  of  an  air- 
pump,  distributes  its  heat  to  surrounding  objects,  or  as  when  we  are  warmed 
by  standing  at  some  distance  before  a  fire.  In  studying  these  phenomena 
we  must  regard  both  the  loss  of  heat  in  the  hot  body,  and  the  gain  of  heat 
in  the  cold  one.  The  mode  in  which  a  hot  body  cools  is,  firstly,  by  giving 
off  heat  from  its  surface  either  by  contact  or  radiation,  or  both  conjointly  ; 
and,  secondly,  by  the  heat  in  its  interior  passing  from  particle  to  particle 
through  its  substance  to  its  surface.  The  heating  of  a  cold  body  is  effected, 
firstly,  by  heat  passing  into  its  surface  either  by  contact  or  radiation,  or  by 
both  conjointly ;  and,  secondly,  by  the  heat  at  its  surface  passing  from  par- 
ticle to  particle  through  its  interior  portions.  Hence,  in  tracing  the  laws 
which  regulate  the  distribution  of  heat,  we  shall  successively  consider  the 
communication  of  heat  from  one  body  to  another  by  contact,  its  passage 
from  particle  to  particle  of  the  same  substance,  or  the  conduction  of  heat, 
and  its  transfer  from  a  sensible  distance,  or  radiation. 

COMMUNICATION  OF  HEAT  BY  CONTACT. 

The  principal  conditions  which  influence  the  communication  of  heat  from 
one  body  to  another  by  contact,  are  the  degree  of  contiguity  and  the  con- 
ducting power  of  the  substances.  The  more  perfect  the  approximation,  the 
more  rapid,  c&teris  paribus,  is  the  transfer.  The  contact  of  two  solids,  or  of 
a  solid  with  a  gas,  is  in  general  of  a  less  perfect  kind,  and  at  fewer  points, 
than  that  between  a  solid  and  a  liquid ;  and  hence,  so  far  as  contact  alone  is 
concerned,  the  transfer  is  more  rapid  in  the  latter  case  than  in  the  former. 
It  is  still  more  rapid  when  liquids  are  mixed  with  each  other,  or  gases  with 
gases,  owing  to  the  intermixture  of  their  particles.  When  bodies  touch 
each  other  at  their  surfaces  only,  the  question  becomes  one  of  conduction, 
the  rapidity  of  transfer  depending  on  the  velocity  with  which  heat  passes 
through  the  substances  in  contact.  Thus,  if  a  hot  mass  of  iron  and  another 
of  marble,  of  equal  size,  form,  and  temperature,  be  plunged  into  equal  quan- 
tities of  cold  water,  the  iron  will  cool  faster  than  the  marble ;  because  heat 
passes  more  rapidly  through  the  substance  of  the  former  than  through  that 
of  the  latter.  Were  two  pieces  of  hot  iron  similarly  plunged,  one  into  mer- 
cury and  the  other  into  water,  the  piece  in  contact  with  mercury  would  cool 
most  rapidly ;  because  that  metal  is  a  better  conductor  than  water.  Were 
the  experiment  made  by  immersing  the  iron  in  mercury  and  the  marble  in 
water,  the  rapidity  of  cooling  in  the  former  would  very  much  exceed  that  in 
the  latter,  from  two  causes; — both  from  heat  passing  more  rapidly  through 
iron  than  through  marble,  and  from  its  being  conveyed  away  more  rapidly 
by  mercury  than  by  water.  The  same  principle  explains  the  unequal  sen- 
sation caused  by  bodies  of  equal  temperature.  Thus  the  hand  receives  a 
more  vivid  impression  of  warmth  by  touching  hot  iron  than  from  glass  of 
the  same  temperature  ;  because  the  quantity  of  heat  which  in  a  given  time 
can  be  brought  from  the  interior  to  the  surface  of  the  hot  body,  so  as  to  pass 
into  the  skin,  is  much  greater  in  iron  than  in  glass.  In  like  manner,  cold 
iron  feels  colder  than  glass  of  the  same  temperature ;  because  the  former 
conveys  away  from  the  skin  more  heat  in  a  given  time  than  the  glass. 

CONDUCTION  OF  HEAT. 

By  this  term  is  expressed  the  passage  of  heat  from  particle  tc  particle 
through  the  substance  of  bodies.  Heat  is  said  to  be  conducted  by  them,  or 
to  pass  by  conduction,  and  the  property  on  which  its  transmission  depends 
is  termed  conducting  power. 


HEAT.  7 

Heat  obviously  passes  through  bodies  with  different  degrees  of  velocity. 
Some  substances  oppose  very  little  impediment  to  its  passage,  while  it  is 
transmitted  slowly  by  others.  Daily  experience  teaches  that  though  we 
cannot  leave  one  end  of  a  rod  of  iron  for  some  time  in  the  fire,  and  then 
touch  its  other  extremity,  without  danger  of  being  burned ;  yet  this  may  be 
done  with  perfect  safety  with  a  rod  of  glass  or  of  wood.  The  heat  will 
speedily  traverse  the  iron  bar,  so  that,  at  the  distance  of  a  foot  from  the  fire, 
it  is  impossible  to  support  its  heat;  while  we  may  hold  a  piece  of  red-hot 
glass  two  or  three  inches  from  its  extremity,  or  keep  a  piece  of  burning 
charcoal  in  the  hand,  though  the  part  in  combustion  be  only  a  few  lines  re- 
moved from  the  skin.  The  observation  of  these  and  similar  facts  has  led 
to  the  division  of  bodies  into  conductors  and  non-conductors  of  heat.  The 
former  division,  of  course,  includes  those  bodies,  such  as  the  metals,  which 
allow  heat  to  pass  freely  through  their  substance ;  and  the  latter  comprises 
those  which  do  not  give  an  easy  passage  to  it,  such  as  stones,  glass,  wood, 
and  charcoal. 

Various  methods  have  been  adopted  for  determining  the  relative  conduct- 
ing power  of  different  substances.  The  mode  devised  by  Ingenhauz*  was 
to  cover  small  rods  of  the  same  form,  size,  and  length,  but  of  different  mate- 
rials, with  a  layer  of  wax,  to  plunge  their  extremities  into  heated  oil,  and 
note  to  what  distance  the  wax  was  melted  on  each  during  the  same  interval. 
The  metals  were  found,  by  this  method,  to  conduct  heat  better  than  any 
other  substances;  and  of  the  metals,  silver  is  the  best  conductor;  gold  comes 
next ;  then  tin  and  copper,  which  are  nearly  equal ;  then  platinum,  iron,  and 
lead. 

Some  experiments  have  been  made  by  M.  Despretz,  apparently  with  great 
care,  on  the  relative  conducting  power  of  the  metals  and  some  other  sub- 
stances,  and  the  results  are  contained  in  the  following  table.  (An.  de  Ch.  et 
de  Ph.  xxxvi.  422.) 

Gold        -  -         1000  Tin         .  ,        303.9 

Silver       -  -  973  Lead       -  .         179.6 

Copper    -  .  898.2          Marble   -  -  23.6 

Platinum  -  381  Porcelain  -  12.2 

Iron        -  -          374.3         Fine  clay  -          11.4 

Zinc        -  -  363 

The  substances  employed  for  these  experiments  were  made  into  prisms  of 
the  same  form  and  size.  To  one  extremity  a  constant  source  of  heat  was 
applied,  and  the  passage  of  heat  along  the  bar  was  estimated  by  small  ther- 
mometers placed  at  regular  distances,  with  their  bulbs  fixed  in  the  substance 
of  the  prism. 

An  ingenious  plan  was  adopted  by  Count  Rumford  (Phil.  Trans.  1792,) 
for  ascertaining  the  relative  conducting  power  of  the  different  materials  em- 
ployed for  clothing.  He  enveloped  a  thermometer  in  a  glass  cylinder  blown 
into  a  ball  at  its  extremity,  and  filled  the  interstices  with  the  substance  to 
be  examined.  Having  heated  the  apparatus  to  the  same  temperature  in 
every  instance  by  immersion  in  boiling  water,  he  transferred  it  into  melting 
ice,  and  observed  carefully  the  number  of  seconds  which  elapsed  during  the 
passage  of  the  thermometer  through  135  degrees.  When  there  was  air  be- 
tween the  thermometer  and  cylinder,  the  cooling  took  place  in  576  seconds ; 
when  the  interstices  were  filled  with  fine  lint,  it  took  place  in  1032" ;  with 
cotton  wool  in  1046" ;  with  sheep's  wool  in  1118";  with  raw  silk  in  1284"; 
with  beaver's  fur  in  1296" ;  with  eider  down  in  1305" ;  and  with  hare's  fur 
in  1315".  The  general  practice  of  mankind  is,  therefore,  fully  justified  by 
experiment.  In  winter  we  retain  the  animal  heat  as  much  as  possible 
by  covering  the  body  with  bad  conductors,  such  as  silk  or  woollen 
stuffs  ;  and  in  summer  cotton  or  linen  articles  are  employed  with  an  oppo- 
site intention. 


*  Ingenhauz,  Journal  de  Phys.  1789,  p.  68. 


The  conducting  power  of  solid  bodies  does  not  seem  to  be  related  to  any 
of  the  other  properties  of  matter ;  but  it  approaches  nearer  to  the  ratio  of 
their  densities  than  to  that  of  any  other  property.  Count  Rumford  found  a 
considerable  difference  in  the  conducting  power  even  of  the  same  material, 
according  to  the  state  in  which  it  was  employed.  His  observations  seem  to 
Warrant  the  conclusion,  that,  in  the  same  substance,  the  conducting  power 
increases  with  the  compactness  of  structure.. 

Liquids  may  be  said,  in  one  sense  of  the  word,  to  have  the  power  of  con- 
veying heat  with  great  rapidity,  though  in  reality  they  are  very  imperfect 
Conductors.  This  peculiarity  is  owing  to  the  joint  influence  of  two  circum- 
stances,— the  mobility  which  subsists  among  the  particles  o.f  all  fluids,  and 
the  change  of  size  or  volume  invariably  produced  by  a  change  of  temperature. 
When  any  particles  of  a  liquid  are  heated,  they  expand,  thereby  becoming 
specifically  lighter  than  those  which  have  not  received  an  increase  of  tem- 
perature ;  and  if  the  former  happen  to  be  covered  by  a  stratum  of  the  latter, 
these  from  their  greater  density  will  descend,  while  the  warmer  and  lighter 
particles  will  be  pressed  upwards.  It,  therefore,  follows  that  if  heat  enter  at 
the  bottom  of  a  vessel  containing  a  liquid,  a  double  set  of  currents  must  be 
immediately  established,  the  one  of  hot  particles  rising  towards  the  surface, 
and  the  other  of  colder  particles  descending  to  the  bottom.  Now  these  cur- 
rents take  place  with  such  rapidity,  that  if  a  thermometer  be  placed  at  the 
bottom,  and  another  at  the  top  of  a  long  jar,  the  fire  being  applied  below,  the 
upper  one  will  begin  to  rise  almost  as  soon  as  the  lower.  Hence,  under  cer- 
tain circumstances,  heat  is  communicated  or  rather  carried  through  liquids 
with  rapidity. 

But  if,  instead  of  heating  the  bottom  of  the  jar,  the  heat  enter  by  the  upper 
surface,  very  different  phenomena  will  be  observed.  The  intestine  move- 
ments cannot  then  be  formed,  because  the  heated  particles,  from  being  lighter 
than  those  below  them,  remain  constantly  at  the  top;  the  heat  can  descend 
through  the  fluid,  only  by  transmission  from  particle  to  particle,  a  process 
which  takes  place  so  very  tardily,  as  to  have  induced  Count  Rumford  to  deny 
that  water  can  conduct  at  all.  In  this,  however,  he  was  mistaken ;  for  the 
opposite  opinion  has  been  successfully  supported  by  Dr.  Hope,  Dr.  Thomson, 
and  the  late  Dr.  Murray,  though  they  all  admit  that  water,  and  liquids  in 
general,  mercury  excepted,  possess  the  power  of  conducting  heat  in  a  very 
slight  degree. 

It  is  extremely  difficult  to  estimate  the  conducting  power  of  aeriform  fluids. 
Their  particles  move  so  freely  on  each  other,  that  the  moment  a  particle  is 
dilated  by  heat,  it  is  pressed  upwards  with  great  velocity  by  the  descent  of 
colder  and  heavier  particles ;  so  that  an  ascending  and  descending  current  is 
instantly  established.  Besides,  these  bodies  allow  a  passage  through  them 
by  radiation.  Now  the  quantity  of  heat  which  passes  by  these  two  channels 
is  so  much  greater  than  that  which  is  conducted  from  particle  to  particle, 
that  we  possess  no  means  of  determining  their  proportion.  It  is  certain, 
however,  that  the  conducting  power  of  gaseous  fluids  is  exceedingly  imper- 
fect, probably  even  more  so  than  that  of  liquids, 

RADIATION. 

When  the  hand  is  placed  beneath  a  hot  body  suspended  in  the  air,  a  dis- 
tinct sensation  of  warmth  is  perceived,  though  from  a  considerable  distance. 
This  effect  does  not  arise  from  the  heat  being  conveyed  by  means  of  a  hot 
current;  since  all  the  heated  particles  have  a  uniform  tendency  to  rise. 
Neither,  for  reasons  above  assigned,  can  it  depend  upon  the  conducting 
power  of  the  air;  because  aerial  substances  possess  that  power  in  a  very  low 
degree,  while  the  sensation  in  the  present  case  is  excited  almost  on  the  in- 
stant. There  is  yet  another  mode  by  which  heat  passes  from  one  body  to 
another;  and  as  it  takes  place  in  all  gases,  and  even  in  vacua,  it  is  inferred 
that  the  presence  of  a  medium  is  not  necessary  to  its  passage.  This  mode 
of  distribution  is  called  radiation  of  heat,  and  the  heat  so  distributed  is 


called  radiant,  or  radiated  heat.  It  appears,  therefore,  that  a  heated  body 
suspended  in  the  air  cools,  or  is  reduced  to  an  equilibrium  with  surrounding- 
bodies,  in  three  ways  ;  first,  by  the  conducting  power  of  the  air,  the  influence 
of  which  is  very  trifling- ;  secondly,  by  the  mobility  of  the  air  in  contact 
with  it;  and  thirdly,  by  radiation. 

Laws  of  Distribution.  Heat  is  emitted  from  the  surface  of  a  hot  body 
equally  in  all  directions,  and  in  right  lines,  like  radii  drawn  from  the  centre 
to  the  circumference  of  a  circle  ;  so  that  a  thermometer  placed  at  the  same 
distance  on  any  side  would  stand  at  the  same  point,  if  the  effect  of  the  as- 
cending current  of  hot  air  could  be  averted.  The  calorific  rays,  thus  dis- 
tributed, pass  freely  through  a  vacuum  and  the  air,  without  being  arrested 
by  the  latter  or  in  any  way  affecting  its  temperature.  When  they  fall  upon 
the  surface  of  a  solid  or  liquid  substance,  they  may  be  disposed  of  in  three 
different  ways : — 1,  they  may  rebound  from  its  surface,  or  be  reflected ; 
2,  they  may  be  received  into  its  substance,  or  be  absorbed ;  and,  3,  they  may 
pass  directly  through  it,  or  be  transmitted.  In  the  first  and  third  cases,  the 
temperature  of  the  body  on  which  the  rays  fall  is  altogether  unaffected; 
whereas,  in  the  second,  it  is  increased.  The  heating  influence  varies  with 
the  distance  from  the  radiating  body.  Common  observation  teaches  that  the 
heat  of  a  fire  is  less,  the  further  we  are  removed  from  it;  just  as  the  light 
grows  faint  in  proportion  as  we  recede  from  a  lamp.  The  rate  or  law  of 
decrease,  as  ascertained  by  careful  experiment,  and  as  may  be  inferred  from 
mathematical  considerations,  is,  that  the  intensity  of  heat  diminishes  in  the 
same  ratio  as  the  squares  of  the  distances  from  the  radiating  point  increase. 
Thus  the  thermometer  will  indicate  four  times  less  heat  at  two  inches,  nine 
times  less  at  three  inches,  and  sixteen  times  less  at  four  inches,  than  it  did 
when  it  was  only  one  inch  from  the  heated  substance. 

The  radiation  of  heat  by  hot  bodies  is  singularly  influenced  by  the  nature 
and  condition  of  their  surfaces,  a  circumstance  which  was  first  examined  by 
the  late  Sir  John  Leslie,  to  whose  Essay  on  Heat,  published  in  1804,  we 
must  still  refer  for  most  of  our  knowledge  on  this  subject,  Leslie  employed 
in  his  experiments  a  hollow  tin  cube  filled  with  hot  water  as  the  radiating 
substance.  The  rays  proceeding  from  it  were  brought,  by  means  of  a  con- 
cave mirror,  into  a  focus,  in  which  the  bulb  of  a  differential  thermometer 
was  placed.  By  adapting  thin  plates  of  different  metals  to  the  sides  of  the 
tin  cube,  and  turning  them  successively  towards  the  mirror,  he  found  a  very 
variable  effect  produced  upon  the  thermometer.  A  bright  smooth  polished 
plate  of  metal  radiated  very  imperfectly  ;  but  if  its  surface  were  in  the  least 
degree  dull  or  rough,  the  radiating  power  was  immediately  augmented.  Or 
if  the  metallic  surface  were  covered  with  a  thin  layer  of  isinglass,  paper, 
wax,  or  resin,  its  power  of  radiation  increased  surprisingly.  It  follows  from 
these  researches  that  velocity  of  radiation  depends  more  on  the  surface  than 
the  substance  of  a  radiating  body  : — that  the  most  imperfect  radiators  are  to 
be  sought  among  those  bodies  which  are  highly  smooth  and  bright,  such  as 
polished  gold,  silver,  tin,  and  brass;  but  that  these  same  metals  radiate  freely 
when  their  smoothness  and  polish  are  destroyed,  as  by  scratching  their  sur- 
faces with  a  file,  or  covering  them  with  whiting  or  lampblack.  A  metallic 
surface  seems  adverse  to  radiation  independently  of  its  smoothness,  since  a 
highly  polished  piece  of  glass  radiates  far  better  than  an  equally  polished 
metallic  surface.  Scratching  a  surface  probably  favours  radiation  by  mul- 
tiplying the  number  of  radiating  points. 

Some  interesting  experiments  by  Dr.  Stark  of  Edinburgh  have  appeared 
(Phil.  Trans.  1833,  Part  II.)  illustrative  of  the  connexion  between  radia- 
tion and  the  colour  of  surfaces.  The  bulb  of  a  delicate  thermometer  was 
successively  surrounded  by  equal  weights  of  differently  coloured  wool,  was 
placed  in  a  glass  tube,  heated  by  immersion  in  hot  water  to  180°,  and  then 
cooled  to  50°  in  cold  water.  The  times  of  cooling  were  21  minutes  with 
black  wool,  26  with  red  wool,  and  27  with  white  wool.  Concurring  results 
were  obtained  with  flour  of  different  colours.  Likewise,  black  wool  was 
found  to  collect  more  dew  than  an  equal  weight  of  white  wool,  other 


10  HEAT. 

circumstances  being  alike.  This  is  the  first  time  that  direct  experiments, 
seemingly  unexceptionable,  have  been  made  in  proof  of  the  influence  of 
colour  over  radiation. 

Reflection  of  Heat. — The  existence  of  a  reflecting  power  may  be  shown  by 
standing  at  the  side  of  a  fire  in  such  a  position  that  the  heat  cannot  reach 
the  face  directly,  and  then  placing  a  plate  of  tinned  iron  opposite  the  grate, 
and  at  such  an  inclination  as  permits  the  observer  to  see  in  it  the  reflection 
of  the  fire :  as  soon  as  it  is  brought  to  this  inclination,  a  distinct  impression 
of  heat  will  be  perceived  upon  the  face.  If  a  line  be  drawn  from  a  radiating 
substance  to  the  point  of  a  plane  surface  by  which  its  rays  are  reflected,  and 
a  second  line  from  that  point  to  the  spot  where  its  heating  power  is  exerted, 
the  angles  which  these  lines  form  with  a  line  perpendicular  to  the  reflecting 
plane  are  called  the  angles  of  incidence  and  reflection,  and  are  invariably 
equal  to  each  other.  It  follows  from  this  law,  that  when  a  heated  body  is 
placed  in  the  focus  of  a  concave  parabolic  reflector,  the  diverging  rays  which 
strike  upon  it  assume  a  parallel  direction  with  respect  to  each  other ;  and 
that  when  these  parallel  rays  impinge  upon  a  second  concave  reflector  stand- 
ing opposite  to  the  former,  they  are  made  to  converge,  so  as  to  meet  together 
in  its  focus.  Their  united  influence  is  thus  brought  to  bear  upon  a  single 
point. 

It  has  been  known  for  ages  that  the  heat  contained  in  the  solar  rays  admits 
of  being  reflected  by  mirrors,  and  a  like  property  has  long  since  been  re- 
cognized in  the  rays  emitted  by  red-hot  bodies ;  but  that  heat  emanates  in 
invisible  rays,  which  are  subject  to  the  same  laws  of  reflection  as  those  that 
are  accompanied  by  light,  is  a  modern  discovery,  noticed  indeed  by  Lambert, 
but  first  decisively  established  by  Saussure  and  Pictet  of  Geneva.  They  first 
proved  it  of  an  iron  ball  heated  so  as  not  to  be  luminous  even  in  the  dark, 
and  then  of  a  vessel  of  boiling  water,  (Pictet's  Essai  sur  le  Feu,  p.  65, 1790); 
but  for  most  of  our  knowledge  of  this  subject  we  must  again  refer  to  the 
labours  of  Leslie.  He  demonstrated  that  the  reflecting  power  depends  on  the 
nature  and  condition  of  surfaces,  and  that  those  qualities  which  are  adverse 
to  radiation,  are  precisely  such  as  promote  reflection.  Bright  smooth 
metallic  surfaces,  as  polished  silver,  brass,  or  tin,  which  are  retentive  of  their 
own  heat,  are  little  prone  to  receive  heat  from  other  sources,  but  cause  such 
rays  to  fly  off  from  them  ;  while  those  qualities  of  a  surface  which  facilitate 
radiation  from  a  hot  body,  likewise  unfit  it  for  reflecting  the  rays  which  fall 
upon  it  from  surrounding  objects.  His  experiments,  indeed,  justify  the  con- 
clusion that  the  faculty  of  radiation  is  inversely  as  that  of  reflection. 

Absorption  of  Heat. — Every  increase  of  temperature  arising  from  radiant 
heat  is  due  to  its  absorption  or  reception  into  the  body  on  which  it  falls.  It 
is  admitted  that  heat  cannot  be  transmitted  directly  through  opaque  bodies, 
and,  therefore,  that  all  the  rays  impinging  on  such  objects  must  either  be 
reflected  or  absorbed :  those  which  are  reflected,  cannot  be  absorbed;  and 
those  which  are  not  reflected,  must  be  absorbed.  The  number  of  absorbed 
rays  is  supplemental  to  that  of  the  reflected  rays.  It  hence  follows  that  as 
the  reflecting  power  is  materially  influenced  by  the  nature  of  surfaces,  the 
absorptive  power  must  be  so  likewise.  Those  qualities  of  a  surface  which 
increase  reflection  are  to  the  same  extent  adverse  to  absorption  ;  and  those 
which  favour  absorption  are  proportionally  injurious  to  reflection.  Since, 
moreover,  as  was  shown  in  the  last  article,  trie  property  of  radiation  is  in- 
versely as  that  of  reflection,  the  power  of  radiating  is  directly  proportional, 
to  that  of  absorbing  heat*  These  inferences  are  fully  justified  by  the  re- 

*  The  remarks  of  the  author  on  the  passage  of  caloric  through  surfaces, 
may,  perhaps,  be  extended  with  advantage.  Surfaces,  as  to  the  transmission 
of  caloric,  may  be  divided  into  two  sets;  1st,  those  which  offer  an  easy 
passage  to  caloric,  either  inwards  or  outwards;  and  2d,  those  through  which 
caloric  passes  with  difficulty.  The  first  set  of  surfaces  are  at  the  same  time 
good  absorbers  and  radiators ;  the  second  set  combine  the  qualities  of  good 


HEAT.  11 

searches  of  Leslie,  and  have  received  additional  confirmation  by  a  decisive  ex- 
periment made  by  my  colleague,  Dr.  Ritchie.     (Royal  Inst.  Journal,  v.  305.) 

The  colour  of  surfaces  influences  the  absorption  of  radiant  heat.  This 
has  been  observed  by  several  persons  of  the  sun's  rays,  and  of  terrestrial 
heat  associated  with  light,  as  will  be  stated  in  the  next  section ;  but  the  de- 
pendence of  the  absorptive  power  for  simple  heat  on  colour  has  not  till  lately 
been  noticed.  From  researches  by  Dr.  Stark  already  referred  to  (page  9), 
it  seems  that  differently  coloured  wools  wound  upon  the  bulb  of  a  thermome- 
ter, and  exposed  within  a  glass  tube  to  hot  water,  rose  from  50°  to  170°  in 
the  following  times, — black  wool  in  4'  30",  dark  green  in  5',  scarlet  in  5' 
30",  white  in  8'. 

An  interesting  connexion  has  been  traced  by  MM.  Nobili  and  Melloni  be- 
tween the  absorbing  and  conducting  power  of  surfaces.  (An.  de  Ch.  et  de 
Ph.  xlviii.  198.)  In  their  experiments,  variations  of  temperature  were  esti- 
mated by  a  new  instrument  called  thermo-multiplier,  consisting  of  a  thermo- 
electric combination  on  the  principle  of  those  to  be  hereafter  described  in 
the  article  on  Thermo- Electricity :  it  is  attached  to  a  delicate  galvanometer, 
which  acts  as  a  thermometer  by  measuring  the  degree  of  galvanic  excite- 
ment, which  excitement  is  thought  to  vary  directly  as  the  temperature. 
These  researches,  if  free  from  fallacy,  justify  the  inference  that  the  radiating 
and  absorbing  powers  of  surfaces  for  simple  heat  are  in  the  inverse  order  of 
their  conducting  power. 

Transmission  of  .Heat  — Radiant  heat  passes  with  perfect  freedom  through 
a  vacuum.  The  air  and  gaseous  substances  present  but  a  feeble  barrier  to 
its  progress;  so  feeble,  indeed,  that  the  degree  of  impediment  which  they 
occasion  has  not  yet  been  appreciated.  Transparent  media  of  a  denser  kind, 
on  the  contrary,  such  as  the  diamond,  rock-crystal,  glass,  arid  water,  even  in 
thin  strata,  greatly  interfere  with  its  passage,  and  when  in  moderately  thick 
masses,  intercept  it  altogether.  This  last  remark,  however,  is  only  applica- 
ble to  simple  heat,  that  is,  to  heat  unassociated  with  light.  The  solar  rays 
pass  readily  through  the  substance  of  glass,  both  heat  and  light  being  re- 
fracted in  their  passage,  as  is  shown  by  the  operation  of  a  burning-glass  or 
lens  ;  and  though  much  of  the  heat  emitted  by  the  flame  of  a  lamp,  or  a  red- 
hot  ball  of  iron,  is  arrested  by  glass,  many  calorific  rays  are  directly  trans- 
mitted along  with  the  light.  But  the  result  is  different  when  the  heated  body 
is  not  luminous.  A  thin  screen  of  glass,  interposed  between  such  an  object 
and  a  thermometer,  certainly  intercepts  most  of  the  rays  that  fall  upon  it; 
and  the  sole  question  which  can  be  raised  is,  whether  the  small  effect  on  the 
thermometer  is  caused  by  direct  transmission,  or  by  the  screen  first  becom- 
ing warm  by  the  absorption  of  the  rays,  and  then  acting  on  the  thermometer 
by  radiation.  Leslie  adopted  the  latter  view,  denying  that  any  rays  of  simple 
heat  can  pass  by  direct  transmission  through  glass;  and  Sir  D.  Brewster 
has  supported  this  opinion  by  an  argument  suggested  by  his  optical  re- 
searches. (Phil.  Trans.  1816,  p.  106.)  He  discovered  that  when  heat  passes 
by  conduction  through  the  substance  of  glass,  a  crystalline  arrangement  of 
its  particles  is  occasioned,  the  progress  of  which  from  particle  to  particle 
may  be  distinctly  traced  by  the  polarizing  property  which  the  crystalline 
points  of  the  glass  immediately  assume.  The  same  phenomena  appear  when 
radiant  heat  falls  upon  a  plate  of  glass,  and,  therefore,  it  was  inferred  that  the 
heat  passes  through  by  conduction  and  not  by  transmission.  This  argu- 
ment, however,  is  scarcely  conclusive;  and  I  cannot  help  thinking  that  Mr. 
B.  Powell,  in  his  late  very  full  digest  of  the  whole  subject  of  radiant  heat 
(Reports  of  the  British  Association,  p.  269)  attaches  to  it  more  importance 
than  it  deserves.  The  observations  of  Sir  D.  Brewster  afford  undeniable  evi- 

reflectors  and  retainers.  The  absorbing  and  radiating  power  on  the  one 
hand,  and  the  reflecting  and  retaining  power  on  the  other,  would,  therefore, 
seem  to  be  common  properties,  belonging  to  two  distinct  sets  of  surfaces. 
Ed. 


12  HEAT. 

dence  of  radiant  heat  being-  arrested  by  glass,  a  point  which  no  one  disputes ; 
but  it  does  not  follow  that  no  rays  are  transmitted.  His  method  of  inquiry 
was  not  calculated  to  detect  transmitted  rays,  since  they  could  not  affect  the 
temperature  of  the  medium. 

The  most  elaborate  experiments  in  favour  of  the  permeability  of  transpa- 
rent media  were  condacted  by  De  la  Roche,  who  estimated  the  transmitted 
rays  by  the  difference  of  effect  occasioned  by  two  glass  screens,  one  of  which 
was  transparent  and  the  other  blackened.  (Biot's  Traite  de  Physique,  iv. 
638.)  Prevost  conducted  a  similar  inquiry  by  employing  moveable  screens, 
which  constantly  presented  a  cool  surface  to  the  thermometer,  thereby  ex- 
pecting to  exclude  all  interference  from  conduction  and  secondary  radiation  ; 
and  some  experiments  on  the  same  principle  were  performed  some  years  ago 
by  Dr.  Christison  and  myself.  Several  ingenious  experiments  have  been 
made  on  this  subject  by  Dr.  Ritchie ;  and  it  has  lately  been  examined  by 
MM.  Nobili  and  Melloni  with  the  aid  of  their  thermo-multiplier.  All  these 
experimenters  concur  in  the  belief  of  direct  transmission.  The  total  effect 
from  this  cause  is,  however,  very  small ;  and  with  screens  of  moderate  thick- 
ness it  is  wholly  imperceptible.  De  la  Roche  found  that  the  ratio  of  the 
transmitted  to  the  intercepted  rays  continually  augments,  the  nearer  the  tem- 
perature of  the  radiating  body  approaches  to  incandescence. 

Theory  of  Radiation. — The  tendency  which  all  bodies  evince  to  attain  an 
equality  of  temperature  by  means  of  radiation,  has  given  rise  to  two  inge- 
nious theories,  suggested  respectively  by  Pictet  and  Prevost.  According  to 
the  former,  bodies  of  equal  temperature  do  not  radiate  at  all ;  and  when  the 
temperature  is  unequal,  the  hotter  give  calorific  rays  to  the  colder  bodies  till 
an  equilibrium  is  established,  at  which  moment  the  radiation  ceases.  Pre- 
vost, on  the  contrary,  conceived  radiation  to  go  on  at  all  times,  and  from  all 
substances,  whether  their  temperature  were  the  same  or  different  from  that 
of  surrounding  objects.  (Recherches  sur  la  Chaleur.)  Consistently  with  this 
view,  the  temperature  of  a  body  falls  whenever  it  radiates  more  heat  than  it 
absorbs;  its  temperature  is  stationary  when  the  quantities  emitted  and  re- 
ceived are  equal ;  and  it  grows  warm  when  the  absorption  exceeds  the  radia- 
tion. A  hot  body  surrounded  by  others  colder  than  itself,  affords  an  instance 
of  the  first  case ;  the  second  happens  when  all  the  substances  within  the 
sphere  of  each  other's  radiation  have  the  same  temperature ;  and  the  third 
occurs  when  a  body  is  introduced  into  a  room  which  is  warmer  than  itself. 
Of  these  theories  the  preference  is  very  generally  accorded  to  the  latter. 
Most  of  the  phenomena  of  radiation,  indeed,  admit  of  a  satisfactory  expla- 
nation by  both ;  but  on  the  whole,  the  theory  of  Prevost  is  more  generally 
applicable.  A  favourable  example  for  tracing  this  preference  is  afforded  by 
the  law  of  cooling  in  vacuo,  established  by  Dulong  and  Petit.  Another  argu- 
ment in  its  favour  is  deducible  from  the  close  analogy  which  exists  between 
the  laws  of  heat  and  light.  Luminous  bodies  certainly  exchange  rays  with 
one  another.  A  feeble  light  sends  rays  to  one  of  greater  intensity;  and  the 
quantity  of  light  emitted  by  each,  does  not  seem  to  be  at  all  influenced  by 
the  vicinity  of  the  other.  Since,  therefore,  the  radiation  of  light  is  not  pre- 
vented by  the  presence  of  other  luminous  bodies,  it  is  probable  that  the  ra- 
diation of  heat  is  equally  uninfluenced  by  the  proximity  of  other  radiating 
substances. 

Adopting,  for  the  reasons  just  stated,  the  theory  of  Prevost,  it  will  be  use- 
ful to  examine  a  few  instances  of  its  application ; — and,  first,  in  regard  to 
the  experiments  with  conjugate  mirrors.  If  a  metallic  ball  in  the  focus  of 
one  mirror,  and  a  thermometer  in  that  of  the  other,  be  of  the  same  tempera- 
ture as  the  surrounding  objects  (say  at  60°),  the  thermometer  will  remain 
stationary.  It  will  indeed  receive  rays  from  the  ball ;  but  as  it  emits  an 
equal  number  in  return,  its  temperature  will  be  unchanged.  If  the  ball  is 
above  60°  the  thermometer  will  rise,  because  it  then  receives  a  greater  num- 
ber of  rays  than  it  gives  out.  If,  on  the  contrary,  the  ball  is  below  60°,  the 
thermometer,  being  the  warmer  of  the  two  bodies,  emits  more  rays  than  it 
receives,  and  its  temperature  will  fall. 


HEAT.  13 

The  same  mode  of  reasoning  explains  an  interesting  experiment  original- 
ly performed  by  the  Florentine  Academicians,  and  since  carefully  repeated 
by  Pictet.  He  placed  a  piece  of  ice  instead  of  the  metallic  ball  in  the  focus 
of  his  mirror,  and  observed  that  the  thermometer  in  the  opposite  focus  im- 
mediately descended,  but  rose  again  as  soon  as  the  ice  was  removed.  On 
replacing  the  ice  in  the  focus,  the  thermometer  again  fell,  and  reascended 
when  it  was  withdrawn.  It  was  supposed  by  some  philosophers  that  this 
experiment  proved  the  existence  of  frigorific  rays,  endowed  with  the  proper- 
ty of  communicating  coldness ;  whereas,  all  the  preceding  remarks  were 
made  on  the  supposition  that  cold  is  merely  a  negative  quality  arising  from 
the  diminution  of  heat.  Nor  is  the  foregoing  experiment  in  the  least  degree 
inconsistent  with  such  an  opinion :  on  the  contrary,  it  is  readily  accounted 
for  by  the  theory  of  Prevost,  and  might  have  been  anticipated  by  its  applica- 
tion. The  thermometer,  in  fact,  has  its  temperature  lowered,  because  it 
emits  more  rays  than  it  receives;  and  it  rises  when  the  ice  is  removed,  be- 
cause it  then  receives  a  number  of  calorific  rays  radiated  by  the  warmer 
surrounding  objects,  which  were  intercepted  by  the  ice  while  it  was  in  the 
focus.* 

An  elegant  application  of  this  theory  was  made  by  Dr.  Wells  to  account 
for  the  formation  of  dew.  The  most  copious  deposite  of  dew  takes  place 
when  the  weather  is  clear  and  serene ;  and  the  substances  that  are  covered 
with  it  are  always  colder  than  the  contiguous  strata  of  air,  or  than  those 
bodies  on  which  dew  is  not  deposited.  In  fact,  dew  is  a  deposition  of  water 

*  In  explaining  the  experiment  of  the  apparent  radiation  of  cold,  it  is 
necessary  to  distinguish  two  cases  in  which  the  equilibrium  of  temperature 
is  disturbed :  1st,  where  a  body  is  raised  above  the  temperature  of  the  sur- 
rounding medium ;  and  2d,  where  it  is  below  the  temperature  of  such  me- 
dium. If  a  thermometer,  after  being  heated  to  the  boiling  point,  be  held  in 
the  air,  it  immediately  commences  to  project  its  caloric  into  the  surrounding 
colder  medium.  If,  however,  we  hold  a  ball  of  snow  near  the  bulb  of  a 
thermometer  which  has  been  standing  in  a  temperate  apartment,  the  mer- 
cury falls ;  not  because  the  caloric  is  projected  from  the  instrument,  but 
rather  because  the  caloric  is  drawn  into  the  snow.  The  calorific  tension  of 
the  space  occupied  by  the  snow  is  diminished,  arid  the  caloric  of  the  sur- 
rounding medium  is  drawn  in  by  what  might  be  conveniently  called  calori- 
fic induction.  The  effect,  at  first,  is  felt  in  the  immediate  vicinity  of  the 
cold  body,  and  is  thence  propagated  in  right  lines  successively  to  greater 
and  greater  distances.  If  these  views  be  admitted  as  correct,  it  will  not  be 
difficult  to  conceive  how  the  direction  of  this  motion  of  caloric  by  induction 
may  be  changed  by  the  interposition  of  mirrors.  There  can  be  little  doubt, 
that  caloric  constitutes  a  medium  which  pervades  all  space,  and  thsf  rows 
of  calorific  particles  in  right  lines  must  exist  in  every  conceivable  direction. 
In  the  experiment  cited  in  the  text,  the  ice  in  the  focus  of  one  mirror  pro- 
duces, by  induction,  a  deficiency  of  caloric  in  its  surface ;  a  number  of  pre- 
existing rays  which  are  continuous  with  an  equal  number  parallel  with  the 
axis  of  the  mirror,  are  drawn  into  the  ice.  Let  it  be  supposed  that  a  par- 
ticular row  of  particles  is  put  in  motion  by  induction,  it  is  clear  that  a  de- 
ficiency of  caloric  will  be  the  consequence  at  some  point  on  the  surface  of 
the  mirror.  This  cannot  be  supplied  by  the  mirror  itself,  and  hence  it  will 
be  made  up  by  the  first  particle  in  the  continuous  parallel  row.  This  pro- 
duces an  induction  in  the  parallel  row,  which  results  in  creating  a  deficiency 
of  caloric  in  some  point  of  the  surface  of  the  second  mirror.  Finally,  a 
similar  induction  of  caloric  is  created  in  the  corresponding  row  of  particles, 
leading  to  the  focus  of  the  second  mirror  where  the  thermometer  is  placed, 
which  necessarily  indicates  a  reduction  of  temperature.  In  this  way  we 
think  the  experiment  of  the  radiation  of  cold  may  be  explained,  without  the 
aid  of  M.  Prevost's  theory,  which  we  conceive,  on  the  whole,  to  be  less  sim- 
ple than  that  of  M.  Pictet.—^. 


14  HEAT. 

previously  existing  in  the  air  as  vapour,  and  which  loses  its  gaseous  form, 
only  in  consequence  of  being-  chilled  hy  contact  with  colder  bodies.  In 
speculating,  therefore,  about  the  cause  of  this  phenomenon,  the  chief  object 
is 'to  discover  the  cause  of  the  reduction  of  temperature.  The  explanation 
proposed  by  Dr.  Wells,  in  his  excellent  Treatise  on  Dew,  and  now  almost 
universally  adopted,  is  founded  on  the  theory  of  Prevost.  If  it  be  admitted 
that  bodies  radiate  at  all  times,  their  temperature  can  remain  stationary,  only 
by  their  receiving  from  surrounding  objects  as  many  rays  as  they  emit; 
and  should  a  substance  be  so  situated  that  its  own  radiation  may  continue 
uninterruptedly  without  an  equivalent  being  returned  to  it,  its  temperature 
must  necessarily  fall.  Such  is  believed  to  be  the  condition  of  the  ground  in 
a  calm  starlight  evening.  The  calorific  rays  which  are  then  emitted  by 
substances  on  the  surface  of  the  earth,  are  dispersed  through  free  space  and 
lost:  nothing  is  present  in  the  atmosphere  to  exchange  rays  with  them,  and 
their  temperature  consequently  diminishes.  If,  on  the  contrary,  the  weather 
be  cloudy,  the  radiant  heat  proceeding  from  the  earth  is  intercepted  by  the 
clouds,  an  interchange  is  established,  and  the  ground  retains  nearly,  if  not 
quite,  the  same  temperature  as  the  adjacent  portions  of  air. 

All  the  facts  hitherto  observed  concerning  the  formation  of  dew,  tend  to 
confirm  this  explanation.  It  is  found  that  dew  is  deposited  sparingly  or  not 
at  all  in  cloudy  weather ;  that  all  circumstances  which  promote  free  radia- 
tion are  favourable  to  its  deposition ;  that  good  radiators  of  heat,  such  as 
grass,  wood,  the  leaves  of  plants,  the  filamentous  substances  in  general,  re- 
duce their  temperature,  in  favourable  states  of  the  weather,  to  an  extent  of 
ten,  twelve,  or  even  fifteen  degrees  below  that  of  the  circumambient  air; 
and  that  while  these  are  drenched  with  dew,  pieces  of  polished  metal,  smooth 
stones,  and  other  imperfect  radiators,  are  barely  moistened,  and  are  nearly 
as  warm  as  the  air  in  their  vicinity. 

COOLING  OF  BODIES. 

It  appears  from  the  preceding  remarks  on  the  transmission  of  heat,  that 
the  cooling  of  bodies  takes  place  by  twro  very  different  methods.  When  a 
hot  body  is  enveloped  in  solid  substances,  its  heat  is  withdrawn  solely  by 
means  of  communication,  and  the  velocity  of  cooling  is  dependent  on  the 
conducting  power.  The  refrigeration  is  effected  in  a  similar  manner  when 
the  heated  body  is  immersed  in  a  liquid  ;  but  the  velocity  of  cooling  depends 
partly  on  the  conducting  power  of  the  liquid,  and  partly  on  the  mobility  of 
its  particles.  In  elastic  fluids  the  cooling  takes  place  both  by  communication 
and  radiation ;  and  in  a  vacuum  it  is  produced  solely  by  radiation. 

The  term  velocity  of  cooling  above  employed,  signifies  the  number  of  de- 
grees lost  by  a  hot  body  during  equal  intervals  of  time,  as  one  minute  or 
one  second ;  and  by  the  law  of  cooling  is  meant  the  relation  which  the  velo- 
cities of  cooling  bear  to  each  other.  The  first  attempt  to  fix  the  law  of 
cooling  was  by  Newton.  Observing  that  the  velocity  of  cooling  in  a  hot 
body  diminishes  continually  as  the  excess  of  its  temperature  declines,  he 
conceived  that  the  heat  lost  during  each  interval  of  time  was  a  constant 
fraction  of  its  excess  of  heat  at  the  beginning  of  that  interval.  Thus,  if  a 
body,  heated  to  1000  degrees  above  the  temperature  of  the  surrounding  air, 
were  to  lose  l-10th  of  that  excess,  or  100  degrees,  during  the  first  second, 
he  thought  it  would  lose  l-10th  of  the  remaining  900,  or  90  degrees,  during 
the  next  second,  and  1-lOth  of  the  residual  810,  or  81  degrees,  during  the 
third  second  ;  so  that  the  number  of  degrees  lost  during  the  first  five  seconds 
would  be  100,  90,  81,  72-9,  and  65-6.  These  numbers  would,  therefore,  de- 
note the  velocity  of  cooling  during  each  succeeding  second ;  and  on  exam- 
ing  their  mutual  relation,  it  is  obvious  that  they  constitute  a  geometric 
progression,  of  which  1-111  is  the  ratio.  For  65-6  x  Mil  =  72-9;  65-G 
X  (1-111)3  =  80-98;  65-6  X  (MH)8  =  89-96,  &LC.;— the  property  of  a  ge- 
ometrical series.  As  this  view  appeared  to  be  consistent  with  actual  obser- 
vation, Newton  inferred  as  a  general  law  of  cooling,  that  while  the  times 


HEAT.  15 

of  cooling  form  an  arithmetical  series,  the  velocities  of  cooling  are   in  a 
geometric  progression. 

This  subject  has  been  experimentally  investigated  with  remarkable  in- 
genuity and  success  by  Dulong  and  Petit.  (An.  of  Phil.  xiii.  112.)  They 
have  demonstrated  that  Newton's  law  of  refrigeration  may  be  adopted  with- 
out material  error  when  a  body  is  but  slightly  hotter  than  the  surrounding 
medium,  and  the  whole  decrease  of  its  temperature  is  inconsiderable  ;  but 
when  the  range  of  cooling  is  extensive,  or  the  original  excess  of  heat  was 
great,  the  law  is  found  to  be  very  defective.  They  have  examined,  with  con- 
summate skill,  the  various  circumstances  by  which  the  cooling  of  a  hot  body 
in  a  vacuum,  and  when  surrounded  by  an  elastic  fluid,  is  influenced ;  but 
their  inquiry  is  too  mathematical  and  abstruse  for  the  purposes  of  an  ele- 
mentary treatise. 

EFFECTS  OF  HEAT. 

The  phenomena  that  may  be  ascribed  to  this  agent,  and  which  may, 
therefore,  be  enumerated  as  its  effects,  are  numerous.  With  respect  to  ani- 
mals, it  is  the  cause  of  the  feelings  of  cold,  agreeable  warmth,  and  burning, 
according  to  its  intensity.  It  excites  the  system  powerfully,  and  without  a 
certain  degree  of  it,  the  vital  actions  would  entirely  cease.  Over  the  vegeta- 
ble world  its  influence  is  obvious  to  every  eye.  By  its  stimulus  co-operating 
with  air  and  moisture,  the  seed  bursts  its  envelope  and  yields  a  new  plant, 
the  buds  open,  the  leaves  expand,  and  the  fruit  arrives  at  maturity.  With 
the  declining  temperature  of  the  seasons  the  circulation  of  the  sap  ceases, 
and  the  plant  remains  torpid  till  it  is  again  excited  by  the  stimulus  of  heat. 

The  dimensions  of  every  kind  of  matter  are  regulated  by  this  principle. 
Its  increase,  with  a  few  exceptions,  separates  the  particles  of  bodies  to  a 
greater  distance  from  each  other,  producing  expansion,  so  that  the  same 
quantity  of  matter  is  thus  made  to  occupy  a  larger  space ;  and  the  diminu- 
tion of  heat  has  an  opposite  effect.  Were  the  repulsion  occasioned  by  this 
agent  to  cease  entirely,  the  atoms  of  bodies  would  come  into  actual  contact. 

The  form  of  bodies  is  dependent  on  heat.  By  its  increase  solids  are  con- 
verted into  liquids,  and  liquids  are  dissipated  in  vapour ;  by  its  decrease 
vapours  are  condensed  into  liquids,  and  these  become  solid.  If  matter 
ceased  to  be  under  the  influence  of  heat,  all  liquids,  vapours,  and  doubtless 
even  gases,  would  become  permanently  solid ;  and  all  motion  on  the  surface 
of  the  earth  would  be  arrested. 

When. heat  is  accumulated  to  a  certain  extent  in  bodies,  they  shine  or 
become  incandescent.  On  this  important  property  depend  all  our  methods 
of  artificial  illumination. 

Heat  exerts  a  powerful  influence-  over  chemical  phenomena.  There  is, 
indeed,  scarcely  any  chemical  action  which  is  not  in  some  degree  modified 
by  this  principle;  and  hence  a  knowledge  of  its  laws  is  indispensable  to  the 
chemist.  By  its  means  bodies  previously  separate  are  made  to  combine,  and 
the  elements  of  compounds  are  disunited.  An  undue  proportion  of  it  is 
destructive  to  all  organic  and  many  mineral  compounds ;  and  it  is  essen- 
tially concerned  in  combustion,  a  process  so  necessary  to  the  wants  and 
comforts  of  man. 

Of  the  various  effects  of  heat  above  enumerated,  several  will  be  discussed 
in  other  parts  of  the  work.  In  this  place  it  is  proposed  to  treat  only  of  its 
influence  over  the  dimensions  and  form  of  bodies,  a  subject  which  will  be 
conveniently  studied  under  the  three  heads  of  expansion,  liquefaction,  and 
vaporization. 

EXPANSION. 

One  of  the  most  remarkable  properties  of  heat  is  the  repulsion  which  exists 
among  its  particles,  a  property  which  enables  it,  on  entering  into  a  body, 
to  remove  the  integrant  molecules  of  the  substance  to  a  greater  distance 


16  HEAT. 

from  each  other.  The  body,  therefore,  becomes  less  compact  than  before, 
occupies  a  greater  space,  or,  in  other  words,  expands.  This  effect  of  heat 
is  opposed  to  cohesion — that  force  which  tends  to  make  the  particles  of 
matter  approximate,  and  which  must  be  overcome  before  any  expansion  can 
ensue.  It  may  be  expected,  therefore,  that  a  small  addition  of  heat  will  occa- 
sion a  small  expansion,  and  a  greater  addition  of  heat  a  greater  expansion  ; 
because  in  the  latter  case  the  cohesion  will  be  more  overcome  than  in  the 
former.  It  may  be  anticipated,  also,  that  whenever  heat  passes  out  of  a 
body,  the  cohesion  being  then  left  to  act  freely,  a  contraction  will  necessarily 
follow ;  so  that  expansion  js  only  a  transient  effect,  occasioned  solely  by  the 
accumulation  of  heat.  It  follows,  moreover,  from  this  view,  that  heat  should 
produce  the  greatest  expansion  in  those  bodies  which  are  least  influenced  by 
cohesion,  an  inference  fully  justified  by  observation.  Thus  the  force  of  co- 
hesion is  greatest  in  solids,  less  in  liquids,  and  least  of  all  in  aeriform  sub- 
stances ;  while  the  expansion  of  solids  is  trifling,  that  of  liquids  much  more 
considerable,  and  that  of  elastic  fluids  far  greater. 

It  may  be  laid  down  as  a  rule,  the  reason  of  which  will  now  be  obvious, 
that  all  bodies  are  expanded  by  heat,  and  that  the  expansion  of  the  same 
body  increases  with  the  quantity  of  heat  which  enters  it.  But  this  law  does 
not  apply,  unless  the  form  and  chemical  constitution  of  the  body  be  pre- 
served. For  if  a  change  in  either  be  occasioned,  then  the  reverse  of  expan- 
sion may  ensue ;  not,  however,  as  the  direct  consequence  of  an  augmented 
temperature,  but  as  the  result  of  a  change  in  form  or  composition. 

In  proof  of  the  expansion  of  solids,  we  need  only  take  the  exact  dimen- 
sions in  length,  breadth,  and  thickness,  of  any  substance  when  cold,  and 
measure  it  again  while  strongly  heated,  when  it  will  be  found  to  have  in- 
creased in  every  direction.  A  familiar  demonstration  of  the  fact  may  be 
afforded  by  adapting  a  ring  to  an  iron  rod,  the  former  being  just  large 
enough  to  permit  the  latter  to  pass  through  it  while  cold.  The  rod  is  next 
heated,  and  will  then  no  longer  pass  through  the  ring.  This  dilatation  from 
heat  and  consequent  contraction  in  cooling  takes  place  with  a  force  which 
appears  to  be  irresistible. 

The  expansion  of  s-olids  has  engaged  the  attention  of  several  experimenters, 
whose  efforts  have  been  chiefly  directed  towards  ascertaining  the  exact 
quantity  by  which  different  substances  are  lengthened  by  a  given  increase 
of  heat,  and  determining  whether  or  not  their  expansion  is  equable  at  dif- 
ferent temperatures.  The  Philosophical  Transactions  contain  various  dis- 
sertations on  the  subject  by  Ellicot,  Smeaton,  Troughton,  and  General  Roy ; 
and  M.  Biot,  in  his  Traite  de  Physique,  has  given  the  results  of  experiments 
performed  with  great  care  by  Lavoisier  and  Laplace.  Their  experiments 
establish  the  following  points : — 1.  Different  solids  do  not  expand  to  the  same 
degree  from  equal  additions  of  heat.  2.  A  body  which  has  been  heated  from 
the  temperature  of  freezing  to  that  of  boiling  water,  and  again  allowed  to 
cool  to  32°  F.,  recovers  precisely  the  same  volume  which  it  possessed  at  first. 
3.  The  dilatation  of  the  more  permanent  or  infusible  solids  is  very  uniform 
within  certain  limits;  their  expansion,  for  example,  from  the  freezing  point 
of  water  to  122°,  is  equal  to  \Vhat  tal^s  place  betwixt  122°  and  212°.  The 
subsequent  researches  of  Dulong  and  Petit,  (An.  de  C.  et  de  P.  vii.)  prove 
that  solids  do  not  dilate  uniformly  at  high  temperatures,  but  expand  in  an 
increasing  ratio;  that  is,  the  higher  the  temperature  beyond  212°  the  greater 
the  expansion  for  equal  additions  of  heat.  It  is  manifest,  indeed,  from  their 
experiments,  that  the  rate  of  expansion  is  an  increasing  one  even  between 
32°  and  212°;  but  the  differences  which  exist  within  this  small  range  are 
so  inconsiderable  as  to  escape  observation,  and,  therefore,  for  most  practical 
purposes  may  be  disregarded. 

The  subjoined  table  includes  the  most  interesting  results  of  Lavoisier  and 
Laplace.  (Biot,  vol.  i.  p.  158.) 


17 


Elongation  when  heated 
from  32°  to  212°. 


TT 


T5T 


sir 


yl-4 


Names  of  Substances. 

Glass  tube  without  lead,  a  mean  of 

three  specimens 
English  flint  glass 
Copper 

Brass — mean  of  two  specimens     - 
Soft  iron  forged     - 
Iron  wire 
Untempered  steel 
Tempered  steel 
Lead 

Tin  of  India 
Tin  of  Falmouth 
Silver 

Gold — mean  of  three  specimens 
Platinum,  determined  by  Borda     - 

Knowing  the  elongation  of  any  substance  for  a  given  number  of  degrees 
of  the  thermometer,  its  total  increase  in  bulk  may  in  general  be  calculated 
by  trebling  the  number  which  expresses  its  increase  in  length.  Thus  if  a 
tube  of  flint  glass  elongates  by  T~^>  when  heated  from  the  freezing  to  the 
boiling  point  of  water,  its  cubic  space  will  have  increased  by  y-g^g-  °r  -yj-g- 
of  its  former  capacity.  Strictly  speaking  this  rule  is  not  exact ;  but  when 
the  expansion  of  any  substance,  corresponding  to  the  observed  increase  of 
temperature,  is  a  minute  fraction  of  its  volume,  the  formula  may  be  applied 
with  safety.  The  error  is  then  so  small  that  it  may  be  disregarded.* 

The  expansion  of  glass,  iron,  copper,  and  platin'um,  has  been  particularly 
investigated  by  MM.  Dulong  and  Petit.  The  following  table  contains  the 
result  of  their* observations  on  glass.  (An.  de  Ch.  et  de  Ph.  vii.  138.)  It 
appears  from  the  third  column  that  at  temperatures  beyond  212°,  glass  ex- 
pands in  a  greater  ratio  than  mercury. 


Temperature    by  an  air 
thermometer. 

Mean     absolute   dilata- 
tion of  glass  for  each  de- 
gree. 

Temperature  by  a  ther- 
mometer made  of  glass. 

Fahr. 

From  32°  to  212° 

qo    fn    QQo 

6T6"Fo~ 

Fahr. 

212° 
\   .        415.8 
667.2 

qo    fn    ^70 

F5T4TT 

T-9  V^ 

The  second,  fourth,  and  sixth  columns  of  the  following  table  show  the 
mean  total  expansion  of  iron,  copper,  and  platinum,  when  heated  from  32° 
to  212°  and  from  32°  to  572°,  for  each  degree.  The  third,  fifth,  and  sev- 


*  The  reason  of  this  is  easily  explained  on  gdometric  principles.  Let  1  be 
the  length  of  a  cold  metallic  bar,  and  v  its  volume  or  solidity  ;  let  l-\-d  be 
its  length  when  heated,  and  v'  its  volume  in  that  state.  As  its  breadth  and 
thickness  increase  in  the  same  proportion  as  its  length,  the  expanded  bar 
will  have  precisely  the  same  figure,  that  is,  the  same  proportion  of  its  dimen- 
sions, as  the  cold  one  ;  and  since,  by  Euclid,  the  solidity  of  similar  figures 
is  as  the  cube  of  homologous  sides,'  it  follows  that  v  :  v'  :  :  1  :  (l-f-rf)s  or 
l-f-3e?-f-3d2-{-d3.  When,  in  solids,  liquids,  or  gases,  d  happens  to  be  a  very 
small  fraction,  d  »  and  even  3d2  are  extremely  minute,  and  may  hence  be 
altogether  neglected. 

2* 


18 


cnth  columns  indicate  the  degrees  on  a  thermometer  of  iron,  copper,  and 
plantinum,  corresponding  to  a  temperature  of  572°  on  an  air  thermometer. 
It  is  obvious  that  platinum  is  much  more  uniform  in  its  expansion  than 
either  of  the  other  metals. 


Temp,  by 
air  ther- 
mome- 
ter. 

Mean    Dil. 
of  iron  in 
volume  for 
each  degree 

Temp,      by 
iron       rod 
thermome- 
ter. 

Mean  dilat.  of 
copper  in  vo- 
lume for  each 
degree. 

Temp,     by 
copper   rod 
thermome- 
ter. 

Mean     dilat 
of     platinum 
in  volume  for 
each  degree. 

Temp,     by 
platinum 
rod      ther- 
mometer. 

Fahr. 

212° 

572° 

ToTiST 
To  (TT5- 

Fahr. 

212° 
702.5 

•3T9TOT 

TTginr 

Fahr. 

212° 
623.8 

eTFFo 
FFnaTT 

Fahr. 

212° 
592.9 

The  expansion  of  liquids  is  readily  proved  by  putting  a  common  thermo- 
meter, made  with  mercury  or  alcohol,  into  warm  water  ;  when  the  dilatation 
of  the  liquid  will  be  shown  by  its  ascent  in  the  stem.  The  experiment  is  in- 
deed illustrative  of  two  other  facts.  It  proves,  first,  that  the  dilatation  in- 
creases with  the  temperature  ;  for  if  the  thermometer  be  plunged  into  several 
portions  of  water  heated  to  different  degrees,  the  ascent  will  be  greatest  in 
the  hottest  water,  and  least  in  the  coolest  portions.  It  demonstrates,  se- 
condly, that  liquids  expand  more  than  solids.  The  glass  bulb  of  the  thermo- 
meter is  itself  expanded  by  the  hot  water,  and,  therefore,  is  enabled  to  contain 
more  mercury  than  before;  but  the  mercury  being  dilated  to  a  much 
greater  extent,  not  only  occupies  the  additional  space  in  the  bulb,  but  like- 
wise rises  in  the  stem.  Its  ascent  marks  the  difference  between  its  own  dila- 
tation and  that  of  the  glass,  and  is  only  the  apparent,  not  the  actual,  expan- 
sion of  the  liquid. 

Different  liquids  do  not  expand  to  the  same  degree  from  an  equal  increase 
of  temperature.  Alcohol  expands  much  more  than  water,  and  water  than 
mercury.  From  the  frequency  with  which  the  latter  is  employed  in  philo- 
sophical experiments,  it  is  important  to  know  the  exact  amount  of  its  expan- 
sion. This  subject  has  been  investigated  by  several  philophosers,  but  the 
experiments  of  Lavoisier  and  Laplace,  and  especially  of  Dulong  and  Petit, 
from  the  extreme  care  with  which  they  were  made,  are  entitled  to  the 
greatest  confidence.  According  to  the  former,  the  actual  dilatation  of  mer- 
cury, in  passing  from  the  freezing  to  the  boiling  point  of  water,  amounts  to 
_LP_P_of  its  volume;  but  the  result  obtained  by  Dulong  and  Petit,  who  found 
it  -1-°-^5-»  is  probably  still  nearer  the  truth.  Adopting  the  last  estimate,  this 
metal  dilates,  for  every  degree  of  Fahrenheit's  thermometer,  -9  9^0  of  the 
bulk  which  it  occupied  at  the  temperature  of  32°.  If  the  barometer,  for  in- 
stance, stand  at  30  inches  when  the  thermometer  is  at  32°,  we  may  calcu- 
late what  its  elevation  ought  to  be  when  the  latter  is  at  60°,  or  at  any  other 
temperature.*  The  apparent  expesasion  of  mercury  contained  in  glass  is  of 


*The  pressure  exerted  by  equal  columns  of  a  fluid,  or  fluids,  is  as  the 
density  of  the  columns;  and  as  the  density  of  mercury  diminishes  with  in- 
crease of  temperature,  it  follows  that  a  30-inch  column  of  mercury  at  32°  F. 
has  a  greater  weight,  or  presses  more,  than  a  mercurial  column  of  equal 
base  and  height  at  60°,  It  is  hence  necessary,  in  estimating  atmospheric 
pressure  by  the  barometer,  either  to  have  the  mercurial  column  always  at 
the  same  temperature,  or  to  correct  the  error  arising  from  difference  of  tem- 
perature by  calculation.  This  correction  is  effected  by  finding  the  length  or 
height  of  a  mercurial  column  at  some  standard  temperature,  as  at  60°,  which 
shall  exert  the  same  pressure  as  another  column  at  any  other  temperature. 
The  formula  is  thus  deduced : — Let  H,  D,  V,  be  the  height,  density,  and  vo- 
lume of  a  mercurial  column  at  32°  ;  and  H',  IK,  V,  its  height,  density,  and 
volume  when  the  temperature  rises  above  32°  by  any  number  of  degrees  ex- 
pressed by  T'.  Now  it  is  a  principle  in  hydrostatics  that  the  height  of  fluid 

TT  TV 

columns  of  equal  pressure  is  inversely  as  their  density,  so  that—.-— — ;   and 

H      D 


HEAT.  19 

course  less  than  the  absolute  expansion.  Between  the  limits  of  32°  and 
212°  F.,  Lavoisier  and  Laplace  estimate  the  apparent  expansion  at  g-1-^,  and 
Dulong  and  Petit  at  g-J.-g-  of  its  volume,  being-  TTBT  T  *°r  eac^  degree  of 
Fahrenheit's  thermometer.  Dulong  and  Petit  state,  that  the  mean  total  ex- 
pansion of  mercury  from  32°  to  572°  F.  for  each  degree  is  -j-j^rB1  ;  and  that 
the  mean  apparent  expansion  in  glass  from  32°  to  572°  F.  for  each  degree  is 
TT5TJ'  The  temperature  in  their  experiments  was  estimated  by  an  air 
thermometer,  which  they  consider  more  uniform  in  its  rate  of  expansion 
than  one  of  mercury.  The  temperature  of  572°  F.  on  the  air  thermometer 
corresponds  to  586°  in  the  mercurial  one. 

All  experimenters  agree  that  liquids  expand  in  an  increasing  ratio,  or  that 
equal  increments  of  heat  cause  a  greater  dilatation  at  high  than  at  low  tem- 
peratures. Thus,  if  a  fluid  is  heated  from  32°  to  122°,  it  will  not  expand  so 
much  as  it  would  do  in  being  heated  from  122°  to  212°  ;  though  an  equal 
number  of  degrees  is  added  in  both  cases.  In  mercury  the  first  expansion, 
according  to  Deluc,  is  to  the  second  as  14  to  15  ;  in  olive  oil  as  13.4  to  15  ;  in 
alcohol  as  10,9  to  15  ;  and  in  pure  water  as  4.7  to  15.  Attempts  have  been 
made  to  discover  a  law  by  which  this  progression  is  regulated,  and  Dalton 
conceives  that  the  expansion  observes  the  ratio  of  the  square  of  the  tempera- 
ture estimated  from  the  point  of  congelation,  or  of  greatest  density;  but  this 
opinion  is  merely  hypothetical,  and  has  been  shown  by  Dulong  and  Petit  to 
be  inconsistent  with  the  facts  established  by  their  experiments. 

There  is  a  peculiarity  in  the  effect  of  heat  upon  the  bulk  of  some  fluids  ; 
namely,  that  at  a  certain  temperature,  increase  of  heat  causes  them  to  con- 
tract, and  its  diminution  makes  them  expand.  This  singular  exception  to  the 
general  effect  of  heat  is  only  observable  in  those  liquids  which  acquire  an  in- 
crease of  bulk  in  passing  from  the  liquid  to  the  solid  state,  and  is  remarked 
only  within  a  few  degrees  of  temperature  above  their  point  of  congelation. 
Water  is  a  noted  example  of  it.  Ice,  as  every  one  knows,  swims  upon  the 
surface  of  water,  and,  therefore,  must  be  lighter  than  it,  which  is  a  con- 
vincing proof  that  water,  at  the  moment  of  freezing,  must  expand.  The  in- 
crease is  estimated  by  Boyle  at  about  -J-th  of  its  volume,  which  gives  900  as 
the  specific  gravity  of  ice,  that  of  water  being  1000.  (Experiments  on  Cold.) 
Dalton  estimates  the  specific  gravity  of  ice  at  9.42. 

The  most  remarkable  circumstance  attending  this  expansion,  is  the  prodi- 
gious force  with  which  it  is  effected.  Boyle  filled  a  brass  tube,  three  inches 
in  diameter,  with  water,  and  confined  it  by  means  of  a  moveable  plug;  the 
expansion,  when  it  froze,  took  place  with  such  violence  as  to  push  out  the 
plug,  though  preserved  in  its  situation  by  a  weight  equal  to  74  pounds.  The 

V     IX 

since  the  volume  of  the  same  liquid  is  also  inversely  as  its  density,  —  —  — 

H     V 

Consequently,  the  heights  are  directly  as  the  volumes,  or  _/===—  .     Since, 


is,  of  course,  found  by  the  formula  H=H' 

9990 
(99904^)'   If%'  in  the  formula  for  H  '  we  substitute  for  H  and  T'  their  va- 

lue as  stated  in  the  text,  we  shall  find  H'=30.  ("Qf  ("t     )=30-084,  which 

y  j  j(j 

is  the  length  of  a  mercurial  column  at  60°,  having  the  same  pressure  as  a 
column  of  mercury  at  32°. 

The  rate  of  the  actual  and  not  apparent  expansion  is  used  in  these  for- 
mulae, because  the  length  of  the  mercurial  column,  depending  on  atmo- 
spheric pressure,  is  not  affected  by  the  expansion  or  contraction  of  the  tube. 


20  HEAT. 

Florentine  Academicians  burst  a  hollow  brass  globe,  whose  cavity  was  only 
an  inch  in  diameter,  by  freezing  the  water  with  which  it  was  filled ;  and  it 
has  been  estimated  that  the  expansive  power  necessary  to  produce  such  an 
effect  was  equal  to  a  pressure  of  27,720  pounds  weight.  Major  Williams 
gave  ample  confirmation  of  the  same  fact  by  some  experiments  which  he 
performed  at  Quebec  in  the  years  1784  and  1785.  (Philosophical  Transac- 
tions of  Ed.  ii.  23.) 

But  it  is  not  merely  during  the  act  of  congelation  that  water  expands ; 
for  it  begins  to  dilate  considerably  before  it  actually  freezes.  Dr.  Croune  no- 
ticed this  phenomenon  so  early  as  the  year  1683,  and  it  has  since  been  ob- 
served by  various  philosophers.  It  may  be  rendered  obvious  to  any  one  by 
the  following  experiment.  Fill  a  flask,  capable  of  holding  three  or  four 
ounces,  with  water  at  the  temperature  of  60°,  and  adapt  to  it  a  cork,  through 
which  passes  a  glass  tube  open  at  both  ends,  about  the  eighth  of  an  inch 
wide,  and  ten  inches  long.  After  having  filled  the  flask,  insert  the  cork  and 
tube,  and  pour  a  little  water  into  the  latter  till  the  liquid  rises  to  the  middle 
of  it.  On  immersing  the  flask  into  a  mixture  of  pounded  ice  and  salt,  the 
water  will  fall  in  the  tube,  marking  contraction ;  but  in  a  short  time  an  op- 
posite movement  will  be  perceived,  indicating  that  dilatation  is  taking  place, 
while  the  water  within  the  flask  is  at  the  same  time  yielding  heatTto  the 
freezing  mixture  in  which  it  is  immersed. 

To  the  inference  deduced  from  this  experiment,  it  was  objected  by  some 
philosophers,  that  the  ascent  of  the  water  in  the  tube  did  not  arise  from  any 
expansion  in  the  liquid  itself,  but  from  a  contraction  of  the  flask,  by  which 
its  capacity  was  diminished.  In  fact,  this  cause  does  operate  to  a  certain  ex- 
tent, but  it  is  by  no  means  sufficient  to  account  for  the  whole  effect;  and, 
accordingly,  it  has  been  proved  by  an  elegant  and  decisive  experiment  of  Dr. 
Hope,  that  water  does  really  expand  previous  to  congelation.*  He  believes 
the  greatest  density  of  water  to  be  between  thirty-nine  and  a  half  and  forty 
degrees  of  Fahrenheit's  thermometer  :  that  is,  boiling  water  obeys  the  usual 
law  till  it  has  cooled  to  the  temperature  of  about  40°,  after  which  the  ab- 
straction  of  heat  produces  increase  instead  of  diminution  of  volume.  Ac- 
cording to  Hallstrom,  whose  experiments  are  the  most  recent,  and  appear  to 
have  been  conducted  with  great  care,  the  maximum  density  of  water  is 
39.39°  F.  (An.  de  Ch.  et  de  Ph.  xxviii.  90.) 

The  cause  of  the  expansion  of  water  at  the  moment  of  freezing  is  attri- 
buted to  a  new  and  peculiar  arrangement  of  its  particles.  Ice  is  in  reality 
crystallized  water,  and  during  its  formation  the  particles  arrange  themselves 
in  ranks  and  lines,  which  cross  each  other  at  angles  of  60°  and  120°,  and 
consequently  occupy  more  space  than  when  liquid.  This  may  be  seen  by 
examining  the  surface  of  water  while  freezing  in  a  saucer.  No  very  satis- 
factory reason  can  be  assigned  for  the  expansion  which  takes  place  previous 
to  congelation.  It  is  supposed,  indeed,  that  the  water  begins  to  arrange  itself 
in  the  order  it  will  assume  in  the  solid  state,  before  actually  laying  aside  the 
liquid  form ;  and  this  explanation  is  generally  admitted,  not  so  much  because 
it  has  been  proved  to  be  true,  but  because  no  better  one  has  been  offered. 

Water  is  not  the  only  liquid  which  expands  under  a  reduction  of  tempera- 
ture; as  the  same  effect  has  been  observed  in  a  few  others  which  assume  a 
highly  crystalline  structure  on  becoming  solid.  Fused  iron,  antimony,  zinc, 
and  bismuth  are  examples  of  it.  Mercury  is  a  remarkable  instance  of  the 
reverse;  for  when  it  freezes,  it  suffers  a  very  great  contraction. 

As  the  particles  of  air  and  of  aeriform  substances  are  not  held  together  by 
cohesion,  it  follows  that  increase  of  temperature  must  occasion  a  considera- 
ble dilatation  of  them  ;  and,  accordingly,  they  are  found  to  dilate  fijom  equal 
additions  of  heat  much  more  than  solids  or  liquids.  Now,  chemists  are  in 
the  habit  of  estimating  the  quantity  of  the  gases  employed  in  their  experi- 
ments by  measuring  them ;  and  since  the  volume  occupied  by  any  gas  is  so 

*  Philosophical  Transactions  of  Edinburgh,  v.  379. 


HEA.T.  21 

much  influenced  by  temperature,  it  is  essential  to  accuracy  that  a  due  cor- 
rection be  made  for  the  variations  arising  from  this  cause ;  that  they  should 
know  how  much  dilatation  is  produced  by  each  degree  of  the  thermometer, 
whether  the  rate  of  expansion  is  uniform  at  all  temperatures,  and  whether 
that  ratio  is  the  same  in  all  gases. 

This  subject  had  been  unsuccessfully  investigated  by  several  philosophers, 
who  failed  in  their  object  chiefly  because  they  neglected  the  precaution  of 
drying  the  gases  upon  which  they  operated ;  but  at  last  the  law  of  dilatation 
was  detected  by  Dalton  and  Gay-Lussac  nearly  at  the  same  time.  Dalton's 
method  of  operating  (Manchester  Memoirs,  vol.  v.)  was  exceedingly  simple. 
He  filled  with  dry  mercury  a  graduated  tube,  closed  at  one  end  and  care- 
fully dried ;  and  then,  plunging  the  open  end  of  the  tube  into  a  mercurial 
trough,  introduced  a  portion  of  dry  air.  After  having  marked  the  bulk 
and  temperature  of  the  air,  he  exposed  it  to  a  gradually  increasing  heat,  the 
exact  amount  of  which  was  regulated  by  a  thermometer,  and  observed  the 
dilatation  occasioned  by  each  increase  of*  temperature.  The  apparatus  of 
Gay-Lussac  (An.  de  Ch.  v.  43)  was  the  same  in  principle,  but  more  com- 
plicated, in  consequence  of  the  precautions  he  took  to  avoid  every  possible 
source  of  fallacy. 

It  is  proved  by  the  researches  of  these  philosophers,  that  all  gases  undergo 
equal  expansions  by  the  same  addition  of  heat,  supposing  them  placed  under 
the  same  circumstances ;  so  that  it  is  sufficient  to  ascertain  the  law  of  ex- 
pansion observed  by  any  one  gas,  in  order  to  know  the  law  for  all.  Now  it 
appears  from  the  experiments  of  Gay-Lussac,  that  100  parts  of  air,  in  being 
heated  from  32°  to  212°  F.,  expand  to  137.5  parts.  The  increase  for  180  de- 
grees is,  therefore,  0.375  or  *.^  ths  of  its  bulk ;  and  by  dividing  this  number 
by  180,  it  is  found  that  a  given  quantity  of  dry  air  dilates  to  ^-^-th  of  the 
volume  it  occupied  at  32°,  for  every  degree  of  Fahrenheit's  thermometer. 
The  result  of  Dalton's  experiments  corresponds  very  nearly  with  the  foregoing. 

This  point  being  established,  it  is  easy  to  ascertain  what  volume  any  given 
quantity  of  gas  should  occupy  at  any  given  temperature.  Suppose  a  certain 
portion  of  gas  to  occupy  20  measures  of  a  graduated  tube  at  32°,  it  may  be 
desirable  to  determine  what  would  be  its  bulk  at  42°.  For  every  degree  of 
heat  it  has  increased  by  _ -J^-th  of  its  original  volume,  and,  therefore,  since 
the  increase  amounts  to  ten  degrees,  the  20  measures  will  have  dilated  by 
_Yo-ths.  The  expression  will,  therefore,  be  20-f-20_y^==20.416.  It  must 
not  be  forgotten  that  the  volume  which  the  gas  occupies  at  32°  is  a  neces- 
sary element  in  all  such  calculations.  Thus,  having  20.416  measures  of  gas 
at  42°,  the  corresponding  bulk  for  52°  cannot  be  calculated  by  the  formula 
20.4164-20x^/0-;  the  real  expression  is  20.41 6+20  X-^W  because  the 
increase  is  only  .JJLths  of  the  space  occupied  at  32°,  which  is  20  measures.* 

*  The  following  are  convenient  general  formula  for  these  calculations : — 
Let  P'  be  the  volume  of  gas  at  any  temperature  above  32°,  T'  the  num- 
ber of  degrees  above  that  point,  and  P  its  volume  at  32°.  Then  P'=P 

rp/  /( QC\   I    T*f 

0+480)  =P  (' — 4g0 — );  and  if  P  is  unknown>  its  value,  deduced  from 

AQ(\ 

the  last  equation,  may  be  calculated  from  the  formula  P=P'  (  \ 

It  frequently  happens,  in  the  employment  of  Fahrenheit's  thermometer, 
that  when  P'  for  the  above  formula  is  known,  it  is  not  P  itself  which  is 
wanted,  but  the  volume  of  gas  at  some  other  temperature,  as  at  60°  F.  This 
value  may  be  obtained  without  first  calculating  wjiat  P  is.  Thus,  retain- 
ing the  value  of  P'  and  T'  as  in  the  preceding  formula,  let  P"  be  the  corre- 
sponding quantity  of  gas  at  some  other  temperature,  the  degrees  of  which 

above  32°  may  be  expressed  by  T".    Now  P"=- — -~ — '  xP;  but  as  P 


A  similar  remark  applies  to  the  formula  for  estimating  the  effect  of  heat  on 
the  height  of  the  barometer. 

The  rate  of  expansion  of  atmospheric  air  at  temperatures  exceeding  212° 
has  been  examined  by  Dulong  and  Petit,  and  the  following  table  contains 
the  result  of  their  observations.  (An.  de  Ch.  et  de  Ph.  vii.  120.) 


Temperature  by  the 
Mercurial  Thermometer. 

Corresponding 
volumes   of  a 
given  volume 
of  air. 

Fahrenheit. 

Centigrade. 

—  33 
32 
212 
302 
392 
482 
572 
Mercury  boils  680 

—  36 
0 
100 
150 
200 
250 
300 
360 

0.8650 
1.0000 
1.3750 
1.5576 

1.7389 
1.8189 
2.0976 
2.3125 

is  unknown,  let  its  value  in  P'  be  substituted.     Thus,  P" 


P'480 


,    . 

Mrnipn    triVPQ    P"  — 


4802P'+480T"P' 

-  _        — 


480+  T" 
(      480      )  X 


480 
P'  480  N  (480+  T") 

- 


-  _  —  - 

4802+480  T'   "  480  (480  +  T') 


F  (480+  T") 

480+T' 

Suppose,  for  example,  a  portion  of  gas  occupies  100  divisions  of  a  gra- 
duated tube  at  48°,  how  many  will  it  fill  at  60°  F.  ?  Here  P'=100  ;  T'=48— 

32,  or  16  ;  T"=  60—32,  or  28.  The  number  sought,  or  the  P"  .J00*508 


102.42.* 


496 


*  To  those  who  are  not  algebraists,  the  following  explanation  and  calcu- 
lation may  be  useful.  As  every  gas  expands  1 -480th  of  the  volume  it  would 
occupy  at  32°,  for  every  degree  of  Fahrenheit's  thermometer,  it  is  clear  that 
it  will  expand  l-481st  part  of  its  volume  at  33°,  l-482d  part  of  its  volume  at 
34°,  and  so  on  for  each  successive  addition  of  one  degree  of  caloric.  In  order 
to  know,  therefore,  the  fractional  dilatation  of  a  gas  at  any  temperature  above 
32°,  for  a  single  degree,  it  is  only  necessary  to  add  to  the  denominator  of  the 
fraction  1-480,  a  number  of  units  equal  to  the  number  of  degrees  that  the 
gas  exceeds  the  temperature  of  32°.  Thus  a  gas  at  the  temperature  of  42° 
will  expand  l-490th,  at  52°  l-500th  of  its  volume,  for  every  increment  of  heat 
equal  to  one  degree.  Knowing  in  this  simple  manner  the  fractional  amount 
of  expansion  of  a  gas  at  any  temperature  for  one  degree,  we  multiply  this 
amount  by  the  difference  between  the  existing  temperature  and  the  tempera- 
ture for  which  we  wish  to  calculate  the  volume.  If  the  calculation  is  for  a 
higher  temperature,  this  product  is  added  to  the  existing  volume;  if  for  a 
lower,  subtracted.  Thus,  to  calculate  the  example  which  Dr.  Turner  has 
selected,  namely,  100  measures  of  a  gas  at  48°,  what  will  be  its  bulk  at  60°, 
we  proceed  as  follows :  as  the  existing  temperature  is  16°  above  32°,  its 
fractional  expansion  for  one  degree  will  be  1-480+16=1-496.  Taking  the 
496th  part  of  one  hundred,  the  given  volume,  we  have  the  actual  expansion 


HEAT.  23 

Hydrogen  gas  was  found  to  expand  in  the  same  proportion ;  so  that  all 
gases  may  be  inferred  to  expand  to  the  same  extent,  for  equal  increments  of 
heat,  between  — 33°  F.  and  680° ;  and  the  same  law  probably  prevails  at  all 
temperatures.* 

THERMOMETERS. 

The  influence  of  heat  over  the  bulk  of  bodies  is  better  fitted  for  estimating 
a  change  in  the  quantity  of  that  agent  than  any  other  of  its  properties ;  for 
substances  not  only  expand  more  and  more  as  the  temperature  increases,  but 
in  general  return  exactly  to  their  original  volume  when  the  heat  is  with- 
drawn.  The  first  attempt  to  measure  the  intensity  of  heat  on  this  principle 
was  made  early  in  the  17th  century,  and  the  honour  of  the  invention  is  by 
some  bestowed  on  Sanctorius,  by  others  on  Cornelius  Drebel,  and  by  others 
on  the  celebrated  Galileo.  The  material  used  by  Sanctorius  was  atmosphe- 
ric air.  The  construction  of  the  thermometer  itself,  or  thermoscope  as  it  was 
sometimes  called,  is  exceedingly  simple.  A  glass  tube  is  to  be  selected  for 
the  purpose,  and  one  end  of  it  is  blown  out  into  a  spherical  cavity,  while  its 
other  extremity  is  left  open.  After  expelling  a  small  quantity  of  air  by  heat- 
ing the  ball  gently,  the  open  end  of  the  tube  is  plunged  into  coloured  water, 
and  a  portion  of  the  liquid  is  forced  up  into  the  tube  by  the  pressure  of  the 
atmosphere,  as  the  air  within  the  ball  contracts.  In  this  state  it  indicates 
changes  of  temperature  with  extreme  delicacy,  the  alternate  expansion  and 
contraction  of  the  confined  air  being  rendered  visible  by  the  corresponding 
descent  and  ascent  of  the  coloured  water  in  the  stem.  The  material  used 
in  its  construction,  also,  is  peculiarly  appropriate;  because  air,  like  all  gases, 
expands  uniformly  by  equal  increments  of  heat.  There  are,  however,  two 
forcible  objections  to  the  general  employment  of  this  thermometer.  In  the 
first  place,  its  dilatations  and  contractions  are  so  great,  that  it  is  inconve- 
nient to  measure  them  when  the  change  of  tempera-ture  is  considerable;  and, 
secondly,  its  movements  are  influenced  by  pressure  as  well  as  by  heat,  so 
that  4he  instrument  would  be  affected  by  variations  of  the  barometer, 
though  the  temperature  should  be  quite  stationary. 

For  the  reasons  just  stated,  the  common  air  thermometer  is  rarely  em- 
ployed; but  a  modification  of  it,  described  in  1804  by  Sir  J.  Leslie,  in  his 
Essay  on  Heat,  under  the  name  of  Differential  Thermometer,  is  entirely  free 
from  the  last  objection,  and  is  admirably  fitted  for  some  special  purposes. 
This  instrument  was  invented  a  century  and  a  half  ago  by  Sturmius,  Profes- 
sor of  Mathematics  at  AltdorfF,  who  has  left  a  description  and  sketch  of 
it  in  his  Collegium  Curiosum,  p.  54,  published  in  the  year  1676;  but 
like  other  air  thermometers  it  had  fallen  into  disuse,  till  it  was  again 
brought  into  notice  by  Leslie.  As  now  made  it  consists  of  two  thin  glass 


for  one  degree.  This,  upon  calculation,  will  be  found  to  be  .2016,  which 
multiplied  by  12,  the  difference  between  the  actual  temperature  and  the  tem- 
perature of  the  volume  sought,  will  give  2.419,  as  the  actual  expansion,  cor- 
responding to  12  degrees.  As  the  temperature  of  the  volume  sought  is  above 
the  original  temperature,  this  number  must  be  added  to  the  given  volume. 
So  that  100-1-2-419=  102-419  will  be  the  volume  sought.  Ed. 

*  The  law  of  the  equable  expansion  or  contraction  of  gases  by  equal  incre- 
ments or  decrements  of  heat  is  a  very  curious  one;  but  it  becomes  particularly 
so  when  viewed  in  connexion  with  a  descending  temperature.  If  gases  expand 
or  contract  l-480th  of  the  volume  they  occupy  at  the  freezing  point,  for  every 
change  of  temperature  equal  to  one  degree,  it  is  obvious  that  a  given  volume 
of  any  gas  at  32°  will  be  expanded  by  a  volume  equal  to  itself,  by  having  its 
temperature  raised  480°.  But  the  converse  of  the  proposition  would  seem 
to  involve  a  paradox ;  for  by  the  application  of  the  same  law,  a  given  volume 
of  any  gas  at  32°,  if  diminished  in  temperature  480°,  would  be  contracted 
by  a  volume  equal  to  itself,  that  is,  reduced  to  nothing !  Ed. 


o 


24  HEAT. 

balls  joined  together  by  a  tube,  bent  twice  at  a 
right  angle,  as  represented  in  the  annexed  figure./ 
Both  balls  contain  air,  but  the  greater  part  of  the 
tube  is  filled  with  sulphuric  acid  coloured  with 
carmine.  It  is  obvious  that  this  instrument  can- 
not be  affected  by  any  change  of  temperature 
acting  equally  on  both  balls ;  for  as  long  as  the 
air  within  them  expands  or  contracts  to  the  same 
extent,  the  pressure  on  the  opposite  surfaces  of 
the  liquid,  and  consequently  its  position,  will 
continue  unchanged.  Hence  the  differential 
thermometer  stands  at  the  same  point,  however 
different  may  be  the  temperature  of  the  medium. 
But  the  slightest  difference  between  the  tempera- 
ture of  the  two  balls  will  instantly  be  detected  ; 
for  the  elasticity  of  the  air  on  one  side  being 
then  greater  than  that  on  the  other,  the  liquid 
will  retreat  towards  the  ball  whose  temperature 
is  the  lowest. 

Solid  substances  are  not  better  suited  to  the  con- 
struction of  a  thermometer  than  gases ;  for  while 
the  expansion  of  the  latter  is  too  great,  that  of  the 
former  is  so  small  that  it  cannot  be  measured  ex- 
cept by  the  adaptation  of  complicated  machinery. 
Liquids  which  expand  more  than  the  one  and  less 
than  the  other,  are  exempt  from  both  extremes ;  and,  consequently,  we  must 
search  among  them  for  a  material  with  which  to  construct  a  thermometer. 
The  principle  of  selection  is  plain.  A  material  is  required  whose  expan- 
sions are  uniform,  and  whose  boiling  and  freezing  points  are  very  remote 
from  one  another.  Mercury  fulfils  these  conditions  better  than  any  other 
liquid.  No  fluid  can  support  a  greater  degree  of  heat  without  boiling  than 
mercury,  and  none,  except  alcohol  and  ether,  can  endure  a  more  intense 
cold  without  freezing.  It  has,  besides,  the  additional  advantage  of  being 
more  sensible  to  the  action  of  heat  than  other  liquids,  while  its  dilatations 
between  32°  and  212°  are  almost  perfectly  uniform.  Strictly  speaking,  the 
same  quantity  of  heat  does  occasion  a  greater  dilatation  at  high  than  at  low 
temperatures;  so  that,  like  other  fluids,  it  expands  in  an  increasing  ratio. 
But  it  is  remarkable  that  this  ratio,  within  the  limits  assigned,  is  exactly  the 
same  as  that  of  glass ;  and,  therefore,  if  contained  in  a  glass  tube,  the  in- 
creasing expansion  of  the  vessel  compensates  for  that  of  the  mercury. 

The  first  object  in  constructing  a  thermometer  is  to  select  a  tube  with  a 
very  small  bore,  which  is  of  the  same  diameter  through  its  whole  length ; 
and  then,  by  melting  the  glass,  to  blow  a  small  ball  at  one  end  of  it.  The 
mercury  is  introduced  by  rarefying  the  air  within  the  ball,  and  then  dipping 
the  open  end  of  the  tube  into  that  liquid.  As  the  air  cools  and  -contracts, 
the  mercury  is  forced  up,  entering  the  bulb  to  supply  the  place  of  the  air 
which  had  been  expelled  from  it.  Only  a  part  of  the  air,  however,  is  re- 
moved by  this  means  ;  the  remainder  is  driven  out  by  the  ebullition  of  the 
mercury. 

Having  thus  contrived  that  the  bulb  and  about  one-third  of  the  tube  shall 
be  full  of  mercury,  the  next  step  is  to  seal  the  open  end  hermetically.  This 
is  done  by  heating  the  bulb  till  the  mercury  rises  very  near  the  summit,  and 
then  suddenly  darting  a  fine  pointed  flame  from  a  blow-pipe  across  the  open- 
ing, so  as  to  fuse  the  glass  and  close  the  aperture  before  the  mercury  has 
had  time  to  recede  from  it. 

The  construction  of  a  thermometer  is  now  so  far  complete  that  it  affords 
a  means  of  ascertaining  the  comparative  temperature  of  bodies ;  but  it  is 
deficient  in  one  essential  point,  namely,  the  observations  made  with  different 
instruments  cannot  be  compared  together.  To  effect  this  object,  the  ther- 
mometer must  be  graduated,  a  process  which  consists  of  two  parts.  The 


HEAT.  25 

first  and  most  important  is  to  obtain  two  fixed  points  which  shall  be  the 
same  in  every  thermometer.  The  practice  now  generally  followed  for  this 
purpose  was  introduced  by  Newton,  and  is  founded  on  the  fact,  that  when  a 
thermometer  is  plunged  into  ice  that  is  dissolving,  and  into  water  which  is 
boiling,  it  constantly  stands  at  the  same  elevations  in  all  countries,  provided 
there  is  a  certain  conformity  of  circumstances.  The  point  of  congelation 
is  easily  determined.  The  instrument  is  to  be  immersed  in  snow  or  pound- 
ed ice,  which  is  liquefying  in  a  moderately  warm  atmosphere,  till  the  mer- 
cury becomes  stationary.  To  fix  the  boiling  point  is  a  more  delicate  opera- 
tion ;  since  the  temperature  at  which  water  boils  is  affected  by  various  cir- 
cumstances which  will  be  more  particularly  mentioned  hereafter.  It  is 
sufficient  to  state  the  general  directions  at  present; — that  the  water  be  per- 
fectly pure,  free  from  any  foreign  particles,  and  not  above  an  inch  in  depth, 
— the  ebullition  brisk,  and  conducted  in  a  deep  metallic  vessel,  so  that  the 
stem  of  the  thermometer  may  be  surrounded  by  an  atmosphere  of  steam, 
and  thus  exposed  to  the  same  temperature  as  the  bulb — the  vapour  be  allow- 
ed to  escape  freely — and  the  barometer  stand  at  30  inches. 

(The  second  part  of  the  process  of  graduation  consists  in  dividing  the  in- 
terval between  the  freezing  and  boiling  points  of  water  into  any  number  of 
equal  parts  or  degrees,  which  may  be  either  marked  on  the  tube  itself,  by 
means  of  a  diamond,  or  first  drawn  upon  a  piece  of  paper,  ivory,  or  metal, 
and  afterwards  attacneoj  to  the  thermomete^/  The  exact  number  of  degrees 
into  which  the  space  is  divided,  is  not  very  material,  though  it  would  be 
more  convenient  did  all  thermometers  correspond  in  this  respect.  Unfor- 
tunately this  is  not  the  case./  In  Britain  we  use  Fahrenheit's  scale,  and  ac- 
cordingly in  this  treatise  the  degrees  always  refer  to  that  scale,  except  when 
the  contrary  is  directly  expressed ;)  whereas  the  continental  philosophers 
employ  either  the  centigrade,  or  that  of  Reaumur.  (.The  centigrade  is  the 
most  convenient  in  practice)  its  boiling  point  is  100,  that  of  melting  snow 
is  the  zero,  or  ^beginning  of  the  scale,  and  thef  interval  is  divided  into  100 
equal  parts.*?  The  interval  in  the  scale  of  Reaumur  is  divided  into  80  parts, 
and  in  that  of  Fahrenheit  into  180^  but  the  zero  of  Fahrenheit  is  placed 
32  degrees  below  the  temperature  of  melting  snow,  and  on  this  account  the 
point  of  ebullition  is  212°.) 

It  is  easy  to  reduce  the  temperature  expressed  by  one  thermometer  to 
that  of  another,  by  knowing  the  relation  which  exists  between  their  degrees. 
Thus,  180  is  to  100  as  9  to  5,  and  to  80  as  9  to  4;  so  that  nine  degrees  of 
Fahrenheit  are  equal  to  five  of  the  centigrade,  and  four  of  Reaumur's  ther- 
mometer. Fahrenheit's  is,  therefore,  reduced  to  the  centigrade  scale,  by  mul- 
tiplying by  five,  and  dividing  by  nine,  or  to  that  of  Reaumur,  by  multiplying 
by  four  instead  of  five.  Either  of  these  may  be  reduced  to  Fahrenheit  by 
reversing  the  process  ;  the  multiplier  is  nine  in  both  cases,  and  the  divisor 
four  in  the  one  and  five  in  the  other.  But  it  must  be  remembered  in  these 
reductions,  that  the  zero  of  Fahrenheit's  thermometer  is  32  degrees  lower 
than  that  of  the  centigrade  or  Reaumur,  and  a  due  allowance  must  be  made 
for  this  circumstance.  An  example  will  best  show  how  this  is  done.  To 
reduce  212°  F.  to  the  centigrade,  first  subtract  32,  which  leaves  180 ;  and 
this  number  multiplied  by  £,  gives  the  corresponding  expression  in  the  cen- 
tigrade scale.  Or  to  reduce  100°  C.  to  Fahrenheit,  multiply  by  |,  and  then 
add  32.  To  save  the  trouble  of  such  reductions,  I  have  subjoined  a  table, 
which  shows  the  degrees  on  the  centigrade  scale  and  that  of  Reaumur,  cor- 
responding to  the  degrees  of  Fahrenheit's  thermometer. 


26 

HEAT. 

Fahr. 

Cent 

Reaum 

Fahr. 

Cent. 

Reaum. 

Fahr. 

Cent 

Reaum. 

212 

100 

80 

113 

45 

36 

14 

-10 

-  8 

203 

95 

76 

104 

40 

32 

5 

-15 

-12 

194 

90 

72 

95 

35 

28 

-4 

-20 

-16 

185 

85 

68 

86 

30 

24 

-13 

-25 

-20 

176 

80 

64 

77 

25 

20 

-22 

-30 

-24 

167 

75 

60 

68 

20 

16 

-31 

-35 

-28 

158 

70 

56 

59 

15 

12 

-40 

-40 

-32 

149 

65 

52 

50 

10 

8 

140 

60 

48 

41 

5 

4 

131 

55 

44 

32 

0 

0 

122 

50 

40 

23 

-5 

-4 

The  mercurial  thermometer  may  be  made  to  indicate  temperatures  which 
exceed  212°,  or  fall  below  zero,  by  continuing  the  degrees  above  and  below 
those  points.  But  as  mercury  freezes  at  39  degrees  below  zero,  it  cannot 
indicate  temperatures  below  that  point ;  and  indeed  the  only  liquid  which 
has  been  used  for  such  purposes  is  alcohol.  Our  means  of  estimating  high 
degrees  of  heat  are  as  yet  very  unsatisfactory.  Mercury  is  preferable  to 
any  other  liquid ;  but  even  its  indications  cannot  be  altogether  relied  on. 
For,  in  the  first  place,  its  expansion  for  equal  increments  of  heat  is  greater 
at  high  than  at  low  temperatures ;  and,  secondly,  glass  expands  at  tempera- 
tures  beyond  212°  in  a  more  rapid  ratio  than  mercury,  and  consequently, 
from  the  proportionally  greater  capacity  of  the  bulb,  the  apparent  expansion 
of  the  metal  is  considerably  less  than  its  actual  dilatation.  Thus  Dulong 
and  Petit  observed,  that  when  the  air  thermometer  is  at  572°,  the  common 
mercurial  thermometer  stands  at  586° ;  but  when  corrected  for  the  error 
caused  by  the  glass,  it  indicates  a  temperature  of  597.5°.  No  liquid  can  be 
employed  for  temperatures  which  exceed  662°,  since  all  of  them  are  then 
either  dissipated  in  vapour,  or  decomposed. 

M.  Bellain  has  observed  that  mercurial  thermometers  slowly  change  their 
point  of  zero,  which  uniformly  becomes  higher  than  at  the  time  of  gradua- 
tion. This  phenomenon  appears  owing  to  a  diminished  capacity  of  the 
bulb  due  to  the  atmosphere  continually  pressing  on  its  exterior,  while  a 
vacuum  exists  in  the  interior  of  the  tube;  for  it  has  not  been  noticed  either 
in  mercurial  thermometers  which  are  unsealed,  or  in  thermometers  made 
with  alcohol.  The  principal  contraction  ensues  soon  after  the  tube  is 
sealed,  and  hence  some  months  should  be  permitted  to  elapse  between  the 
sealing  and  graduation  of  a  thermometer.  (An.  de  Ch.  et  de  Ph.  xxi.  330.) 

The  instruments  for  measuring  intense  degrees  of  heat  are  called  py- 
rometers, and  must  be  formed  either  of  solid  or  gaseous  substances.  The 
former  alone  have  been  hitherto  employed,  though  the  latter,  from  the 
greater  uniformity  with  which  they  expand,  are  better  calculated  for  the 
purpose.  The  action  of  most  pyrometers  depends  on  the  elongation  of  a 
metallic  bar  by  heat ;  and  the  difficulty  in  their  construction  consists  in  rind- 
ing an  infusible  metal  of  uniform  expansibility,  and  in  measuring  the  de- 
gree ef  expansion  with  exactness.  This  subject  has  for  some  time  occupied 
the  attention  of  Professor  Daniell,  who  has  at  last  succeeded  in  forming  a 
pyrometer  which,  with  a  little  practice,  may  be  used  with  facility,  and  ap- 
pears susceptible  of  very  great  precision.  (Phil.  Trans.  1830  and  31.) 
This  instrument  consists  of  two  parts,  the  Register  and  Scale ;  the  former 
designed  for  exposure  to  the  heat  to  be  estimated,  and  the  latter  for  measur- 
ing the  exact  amount  of  expansion.  The  first  consists  of  a  bar  of  black- 
lead  earthenware,  in  which  is  drilled  a  hole  3-10ths  of  an  inch  in  diameter, 
and  7£  inches  deep.  Into  this  hole  a  cylindrical  bar  of  platinum  or  soft 
iron,  of  nearly  the  same  diameter,  and  6£  inches  long,  is  introduced,  so  as 
to  rest  against  the  solid  end  of  the  hole ;  and  upon  the  outer  or  free  end  of 
the  metallic  bar  rests  a  cylindrical  piece  of  porcelain,  called  the  index,  1£ 
inches  long,  and  is  kept  firmly  in  its  place  by  a  strap  of  platinum  and  a 


HEAT.  27 

little  wedge  of  earthenware.  The  object  of  this  arrangement  is,  that  when 
the  register  is  heated,  the  metal  expanding  at  each  temperature  more  than 
the  earthenware  case,  presses  forward  the  index;  and  as  this  last  moves  with 
friction  in  consequence  of  the  strap  and  wedge,  it  remains  in  its  place  when 
the  register  is  removed  from  the  fire  and  cooled.  The  scale  is  an  instru- 
ment designed  for  measuring  with  minute  accuracy  the  precise  extent  to 
which  the  index  has  been  pushed  forward  by  the  metallic  bar.  It  thus  in- 
dicates the  apparent  elongation  of  the  bar,  that  is,  the  difference  between 
its  elongation  and  that  of  the  black-lead  case  which  contains  it.  For  its  in- 
dications to  be  correct,  that  is,  in  order  that  equal  dilatations  should  indi- 
cate equal  increments  of  heat,  it  is  necessary  that  the  bar  and  its  case  should 
both  expand  uniformly,  or  both  vary  at  the  same  rate.  Now  in  regard  to 
the  black-lead  case,  its  total  expansion  is  so  very  small,  that  any  want  of 
uniformity  at  intermediate  points  cannot  be  detected;  but  since,  as  will 
shortly  be  more  fully  stated,  all  earthenware  and  other  argillaceous  sub- 
stances contract  when  first  heated,  the  case  must  not  be  used  in  pyrometry, 
until  it  has  been  exposed  in  close  vessels  to  at  least  as  high  a  temperature 
as  that  which  will  afterwards  be  employed.  As  for  the  expansions  of  the 
metallic  bar,  these  are  not  exactly  uniform  (page  18) ;  but  still  they  afford  a 
good  practical  index  of  the  relative  intensity  of  different  fires,  and  will  be 
an  exact  measure  of  temperature  when  the  precise  rate  of  expansion  shall 
have  been  determined. 

The  pyrometer  of  Wedgwood  acts  on  a  different  principle,  being  founded 
on  the  property  which  clay,  a  compound  of  aluminous  earth  and  water,  pos- 
sesses of  gradually  losing  its  water  when  exposed  to  an  increasing  tempera- 
ture, and  of  contracting  as  the  water  is  dissipated.  The  contraction  even 
continues  after  every  trace  of  water  has  been  removed,  owing  to  partial  vitrifi- 
cation occurring,  which  tends  to  bring  the  particles  of  the  clay  into  still  nearer 
proximity.  The  intensity  of  the  heat  may,  therefore,  in  some  measure  be 
estimated  by  the  degree  of  contraction  which  it  has  occasioned. 

The  apparatus  consists  of  a  metallic  groove,  24  inches  long,  the  sides  of 
which  converge,  being  half  an  inch  wide  above,  and  three-tenths  below.  The 
clay,  well  washed,  is  made  up  into  little  cylinders  or  truncated  cones  which 
fit  the  commencement  of  the  groove,  after  having  been  heated  to  redness  ; 
and  their  subsequent  contraction  by  heat  is  determined  by  allowing  them  to 
slide  from  the  top  of  the  groove  downwards,  till  they  arrive  at  a  part  of  it 
through  which  they  cannot  pass.  Mr.  Wedgwood  divided  the  whole  length 
of  the  groove  into  240  degrees,  each  of  which  he  supposed  equal  to  130  of 
Fahrenheit ;  and  he  fixed  the  zero  of  his  scale  at  the  1077th  degree  of  Fah- 
renheit's thermometer. 

Wedgwood's  pyrometer  is  no  longer  employed  by  scientific  men,  because 
its  indications  cannot  be  relied  on.  Every  observation  requires  a  separate 
piece  of  clay,  and  the  observer  is  never  sure  that  the  contraction  of  the  se- 
cond piece,  from  the  same  heat,  will  be  exactly  similar  to  that  of  the  first; 
especially  as  it  is  difficult  to  procure  specimens  of  the  earth,  the  composition 
of  which  is  in  every  respect  the  same.  It  is  doubtful,  too,  if  its  point  of 
zero  has  been  correctly  estimated;  and  Guyton  de  Morveau  has  shown  that 
each  degree  corresponds  rather  to  62,5  than  to  130  degrees  of  Fahrenheit. 

For  some  purposes,  especially  in  making  meteorological  observations,  it  is 
a  very  desirable  object  to  ascertain  the  highest  and  lowest  temperature 
which  has  occurred  in  a  given  interval  of  time,  during  the  absence  of  the 
observer.  The  instrument  employed  with  this  intention  is  called  a  Register 


tense  cold  is  made  with  alcohol,  and  the  bulb  is  bent  at  a  right  angle  to  the 
stem,  so  that  the  latter  may  conveniently  be  placed  in  a  horizontal  position. 
In  the  spirit  is  immersed  a  cylindrical  piece  of  black  enamel,  of  such  size 
as  to  move  freely  within  the  tube.  In  order  to  make  an  observation,  the 
enamel  should  be  brought  down  to  the  surface  of  the  spirit,  an  object  easily 
effected  by  slight  percussion  while  the  bulb  is  inclined  upwards.  When 


28  HEAT. 

the  thermometer  sinks  by  exposure  to  cold,  the  enamel  likewise  retreats  to- 
wards the  bulb,  owing  to  its  adhesion  to  the  spirit;  but,  on  expanding,  the 
spirit  passes  readily  beyond  the  enamel,  leaving  it  at  the  extreme  point  to 
which  it  had  been  conveyed  by  the  previous  contraction. 

For  registering  the  highest  temperature,  a  common  mercurial  thermome- 
ter of  the  same  form  as  the  preceding  is  employed,  having  a  small  cylin- 
drical piece  of  black  enamel  at  the  surface  of  the  mercury.  When  the 
mercury  expands,  the  enamel  is  pushed  forward ;  and  as  the  stem  of  the 
thermometer  is  placed  horizontally,  it  does  not  recede  when  the  mercury 
contracts,  but  remains  at  the  spot  to  which  it  had  been  conveyed  by  the 
previous  dilatation.  The  enamel  is  easily  restored  to  the  surface  of  the 
mercury  by  slight  percussion  while  the  bulb  is  inclined  downwards;  but  this 
should  be  performed  with  care,  lest  the  enamel,  in  falling  abruptly,  should 
interrupt  the  continuity  of  the  mercurial  column,  and  interfere  with  the  in- 
dications of  the  instrument.  The  risk  of  this  accident  is  lessened  by  putting 
some  pure  naphtha  in  the  tube  beyond  the  mercury,  and  its  presence  is  like- 
wise of  use  in  preventing  the  oxidation  of  the  mercury.  The  above  descrip- 
tion applies  to  an  improvement  on  Dr.  Rutherford's  thermometer,  made  by 
Mr.  Adie  of  Edinburgh. 

Though  the  thermometer  is  one  of  the  most  valuable  instruments  of  phi- 
losophical research,  it  must  be  confessed  that  the  sum  of  information  which 
it  conveys  is  very  small.  It  does  indeed  point  out  a  difference  in  the  tem- 
perature of  two  or  more  substances  with  great  nicety  ;  but  it  does  not  indi- 
cate how  much  heat  any  body  contains.  It  does  not  follow,  because  the  ther- 
mometer stands  at  the  same  elevation  in  any  two  bodies,  that  they  contain 
equal  quantities  of  heat ;  nor  is  it  right  to  infer  that  the  warmer  possesses 
more  of  this  principle  than  the  colder.  The  thermometer  gives  the  same 
kind  of  information  which  maybe  discovered,  though  less  accurately,  by 
the  feelings;  it  recognizes  in  bodies  that  state  of  caloric  alone,  which  affects 
the  senses  with  an  impression  of  heat  or  cold, — the  condition  expressed  by 
the  word  temperature.  All  we  learn  by  this  instrument  is,  whether  the 
temperature  of  one  body  is  greater  or  less  than  that  of  another;  and  if  there 
is  a  difference,  it  is  expressed  numerically,  namely,  by  the  degrees  of  the 
thermometer.  But  it  must  be  remembered  that  these  degrees  are  parts  of 
an  arbitrary  scale,  selected  for  convenience,  without  any  reference  whatever 
to  the  actual  quantity  of  heat  present  in  bodies. 

Very  little  reflection  will  evince  the  propriety  of  these  remarks.  If  two 
glasses  of  unequal  size  be  filled  with  water  just  taken  from  the  same  spring, 
the  thermometer  will  stand  in  each  at  the  same  height,  though  their  quan- 
tities of  heat  are  certainly  unequal.  This  observation  naturally  suggests  the 
inquiry,  whether  different  kinds  of  substances,  whose  temperatures  as  esti- 
mated by  the  thermometer  are  the  same,  contain  equal  quantities  of  heat, — 
if,  for  example,  a  pound  of  iron  contains  as  much  heat  as  a  pound  of  water 
or  mercury.  The  foregoing  remark  shows  that  equality  of  temperature  is 
not  necessarily  connected  with  equality  in  quantity  of  heat;  and  the  in- 
ference has  been  amply  confirmed  by  experiment.  If  equal  quantities  of 
water  are  mixed  together,  one  portion  being  at  100°  and  the  other  at  50°, 
the  temperature  of  the  mixture  will  be  the  arithmetical  mean  or  75° ;  that 
is,  the  25  degrees  lost  by  the  warm  water  will  exactly  suffice  to  heat  the 
cold  water  by  the  same  number  of  degrees.  It  is  hence  inferred,  that  equal 
weights  or  measures  of  water  of  the  same  temperature  contain  equal  quan- 
tities of  heat;  and  the  same  is  found  to  be  true  of  other  bodies.  But  if  equal 
weights  or  equal  bulks  of  different  substances  are  employed,  the  result  will  be 
different.  Thus  if  a  pint  of  mercury  at  100°  be  mixed  with  a  pint  of  water  at 
40°,  the  mixture  will  have  a  temperature  of  60°,  so  that  the  40  degrees  lost  by 
the  former,  heated  the  latter  by  20  degrees  only;  and  when,  reversing  the  expe- 
riment, the  water  is  at  100°  and  the  mercury  at  40°,  the  mixture  will  be  at 
80°,  the  20  degrees  lost  by  the  former  causing  a  rise  of  40  in  the  latter.  The 
fact  is  still  more  strikingly  displayed  by  substituting  equal  weights  for  mea- 
sures. For  instance,  on  mixing  a  pound  of  mercury  at  160°  with  a  pound 


HEAT.  HI 

of  water  at  40°,  a  thermometer  placed  in  the  mixture  will  stand  at  45°  ;  but 
if  the  mercury  be  at  40°  and  the  water  at  160°,  the  mixture  will  have  a 
temperature  of  155°.  If  water  at  100°  be  mixed  with  an  equal  weight  of 
spermaceti  oil  at  40°,  the  mixture  will  be  found  at  80°;  and  when  the  oil 
is  at  100^  and  the  water  at  40°,  the  temperature  of  the  mixture  will  be 
only  60°. 

It  appears  from  the  facts  just  stated,  that  the  same  quantity  of  heat  im- 
parts twice  as  high  a  temperature  to  mercury  as  to  an  equal  volume  of 
water ;  that  a  similar  proportion  is  observed  with  respect  to  equal  weights  of 
spermaceti  oil  and  water;  and  that  the  heat  which  gives  5  degrees  to  water 
will  raise  an  equal  weight  of  mercury  by  115  degrees,  being  the  ratio  of  1  to 
23.  Hence  if  equal  quantities  of  heat  be  added  to  equal  weights  of  water, 
spermaceti  oil,  and  mercury,  their  temperatures  in  relation  to  each  other  will 
be  expressed  by  the  numbers,  1,  2,  arid  23 ;  or,  what  amounts  to  the  same, 
in  order  to  increase  the  temperature  of  equal  weights  of  those  substances  to 
the  same  extent,  the  water  will  require  23  times  as  much  heat  as  the  mer- 
cury, and  twice  as  much  as  the  oil.  The  peculiarity  exemplified  by  these 
substances,  and  which  it  would  be  easy  to  illustrate  by  other  examples,  was 
first  noticed  by  Dr.  Black.  It  is  a  law  admitted  to  be  universal,  and  may 
be  thus  expressed  ;  that  equal  quantities  of  different  bodies  require  unequal 
quantities  of  heat  to  heat  them  equally.  This  difference  in  bodies  was  ex- 
pressed in  the  language  of  Dr.  Black  by  the  term  capacity  for  heat,  a  word 
apparently  suggested  by  the  idea  that  the  heat  present  in  any  substance  is 
contained  within  its  pores,  or  in  the  spaces  left  between  its  particles,  and 
that  the  quantity  of  heat  is  regulated  by  the  size  of  the  pores.  And  indeed 
at  first  view  there  appear  sufficient  grounds  for  this  opinion ;  for  it  is  ob- 
served, that  very  compact  bodies  have  the  smallest  capacities  for  heat,  and 
that  the  capacity  of  the  same  substance  often  increases  as  its  density  be- 
comes less.  But,  as  Black  himself  pointed  out,  if  this  were  the  real  cause 
of  the  difference,  the  capacities  of  bodies  for  heat  should  be  inversely  as 
their  densities.  Thus,  since  mercury  is  thirteen  times  and  a  half  denser 
than  water,  the  capacity  of  the  latter  for  heat  ought  to  be  only  thirteen 
times  and  a  half  greater  than  the  former,  whereas  it  is  twenty-three  times 
as  great.  Oil  occupies  more  space  than  an  equal  weight  of  water,  and  yet 
the  capacity  of  the  latter  for  heat  is  double  that  of  the  former.  The  word 
capacity,  therefore,  is  apt  to  excite  a  wrong  notion,  unless  it  be  carefully 
borne  in  mind,  tfyat  it  is  merely  an  expression  of  the  fact  without  allusion 
to  its  cause ;  and  to  avoid  the  chance  of  error  from  this  source,  the  term 
specific  heat  has  been  proposed  as  a  substitute  for  it,  and  is  flow  very  gene- 
rally employed. 

The  singular  fact  of  substances  of  equal  temperature  containing  unequal 
quantities  of  heat  naturally  excites  speculation  about  its  cause,  and  various 
attempts  have  been  made  to  account  for  it.  The  explanation  deduced  from 
the  views  of  Black  is  the  following :  he  conceived  that  heat  exists  in  bodies 
in  two  opposites  states :  in  one  it  is  supposed  to  be  in  chemical  combina- 
tion, exhibiting  none  of  its  ordinary  characters,  and  remaining  as  it  were 
concealed,  without  evincing  any  signs  of  its  presence ;  in  the  other,  it  is 
free  and  uncombined,  passing  readily  from  one  substance  to  another,  affect- 
ing the  senses  in  its  passage,  determining  the  height  of  the  thermometer, 
and  in  a  word,  giving  rise  to  all  the  phenomena  which  are  attributed  to  this 
active  principle. 

Though  it  would  be  easy  to  start  objections  to  this  ingenious  conjecture, 
it  has  the  merit  of  explaining  phenomena  more  satisfactorily  than  any  view 
that  has  been  proposed  in  its  place.  It  is  entirely  consistent  with  analogy. 
For  since  heat  is  regarded  as  a  material  substance,  it  would  be  altogether 
anomalous  were  it  not  influenced,  like  other  kinds  of  matter,  by  chemical 
affinity;  and  if  this  be  admitted,  it  ought  certainly,  in  combining,  to  lose 
some  of  the  properties  by  which  it  is  distinguished  in  its  free  state.  Accord- 
ing to  this  view,  it  is  intelligible  how  two  substances,  from  being  in  the  same 
condition  with  respect  to  free  heat,  may  have  the  same  temperature ;  and 

3* 


30  HEAT. 

yet  that  their  actual  quantities  of  heat  may  be  very  different,  in  consequence 
of  one  containing  more  of  that  principle  in  a  combined  or  latent  state  than 
the  other.  But  in  admitting  the  plausibility  of  this  explanation,  it  is  proper 
to  remember  that  it  is  at  present  entirely  hypothetical ;  and  that  the  lan- 
guage suggested  by  an  hypothesis  should  not  be  unnecessarily  associated 
with  the  phenomena  to  which  it  owes  its  origin.  Accordingly,  the  word 
sensible  is  better  than  free  heat,  and  insensible  preferable  to  combined  or 
latent  heat ;  for  by  such  terms  the  fact  is  equally  well  expressed,  and  philo- 
sophical propriety  strictly  preserved.* 

It  is  of  importance  to  know  the  specific  heat  of  bodies.  The  most  con- 
venient method  of  discovering  it,  is  by  mixing  different  substances  together 
in  the  way  just  described,  and  observing  the  relative  quantities  of  heat 
requisite  for  heating  them  by  the  same  number  of  degrees.  Thus  the  caloric 
required  to  heat  equal  quantities  of  water,  spermaceti  oil,  and  mercury  by 
one  degree,  is  in  the  ratio  of  23,  11.5,  and  1,  and,  therefore,  their  specific 
heats  are  expressed  by  those  numbers.  Water  is  commonly  one  of  the 
materials  employed  in  such  experiments ;  as  it  is  customary  to  compare  the 
specific  heat  of  other  bodies  with  that  of  water.t 

*  The  theory  of  latent  heat  of  Dr.  Black,  as  applied  to  the  explanation  of 
the  different  specific  heats  of  bodies,  would  seem  to  be  in  some  respects  un- 
philosophical.  If  Pictet's  theory  of  the  equilibrium  of  caloric  be  admitted, 
then  equality  of  temperature  in  any  two  bodies  merely  means  that  their 
caloric  has  no  tendency  to  pass  from  one  to  the  other,  without  the  idea 
having  any  necessary  connexion  with  the  absolute  quantity  of  caloric  con- 
tained in  them.  It  may  be  admitted  as  highly  probable  that  the  reason 
why  different  bodies  assume  to  themselves  unequal  quantities  of  heat, 
when  this  principle  has  assumed  a  state  of  rest,  is  that  their  affinities  for 
caloric  are  different ;  yet  it  by  no  means  follows,  that  the  caloric  in  such 
bodies  is  in  two  different  states,  sensible  or  /ree,  and  insensible  or  combined. 
If  we  impart  ten  degrees  of  heat  to  equal  weights  of  water  and  oil,  the 
water  will  have  received  twice  as  much  caloric  as  the  oil.  Here  the 
"  actual  quantities  of  heat"  received  are  "  very  different ;"  but  are  we  on 
this  account  to  suppose  that  part  of  the  caloric  received  by  the  water  is  in 
an  insensible  or  combined  state  ?  It  will  at  once  be  evident  that  this  cannot 
be  the  case ;  for  if  the  equal  weights  of  water  and  oil,  after  having  been  heated 
ten  degrees,  be  allowed  to  cool  equally,  the  water  will  lose  twice  as  much 
actual  caloric  as  the  oil.  Now  all  the  caloric  lost  during  the  cooling  becomes 
free  caloric ;  for  it  is  distributed  among  surrounding  bodies. 

The  fact  is,  that  the  quantity  of  caloric  gained  or  lost  by  any  number  of 
bodies,  in  being  heated  or  cooled  through  the  same  number  of  degrees,  bears 
a  constant  proportion  to  their  several  specific  heats.  Hence  to  maintain  an 
equality  of  temperature  among  any  set  of  bodies,  the  quantity  of  caloric 
contained  by  each  must  be  directly  proportional  to  its  specific  heat.  What- 
ever subverts  this  relation  will  necessarily  change  the  temperature. 

It  sometimes  happens  that  the  loss  or  gain  of  caloric  by  a  body  is  exactly 
proportional  to  the  change  it  may  undergo  in  specific  heat  or  capacity. 
Thus,  if  a  body  receive  caloric,  and  have,  at  the  same  time,  its  capacity  pro- 
portionably  increased,  its  temperature  remains  the  same,  though  it  be  con- 
stantly receiving  caloric ;  and  it  is  by  such  cases  as  these  that  the  doctrine 
of  insensible  or  combined  heat  is  most  plausibly  supported.  But,  upon 
taking  a  nearer  view  of  the  subject,  it  will  be  found  that  the  temperature 
remains  the  same  in  conformity  with  the  principles  laid  down  in  this  note ; 
for  the  capacity  and  heat  being  simultaneously  and  proportionably  increased, 
the  relation  between  them,  so  far  from  being  subverted,  is  maintained. — Ed. 

t  A  formula  for  such  calculations  is  thus  deduced  : — Let  10,  t,  and  s,  be 
the  weight,  temperature,  and  specific  heat  of  the  warmer  body ;  w',  *',  and  s', 
the  weight,  temperature,  and  specific  heat  of  the  colder  body ;  and  6  the 
temperature  of  the  mixture.  Then  the  temperature  lost  by  the  warmer 
body  will  be  expressed  by  (t — 0),  and  its  actual  loss  of  heat  by  s.  (t — 6).  w  ; 


HEAT.  31 

This  method  was  first  suggested  by  Black,  and  was  afterwards  practised  to  a 
great  extent  by  Drs.  Crawford  and  Irvine.*  But  the  same  knowledge  may  be 
obtained  by  reversing  the  process, — by  noting  the  relative  quantities  of  heat 
which  bodies  give  out  in  cooling ;  for  if  water  require  23  times  more  heat 
than  mercury  to  raise  its  temperature  by  one  or  more  degrees,  it  must  also 
lose  23  times  as  much  in  cooling.  The  calorimeter,  invented  and  employed 
by  Lavoisier  and  Laplace,  acts  on  this  principle.  The  apparatus  consists  of  a 
wire  cage,  suspended  in  the  centre  of  a  metallic  vessel  so  much  larger  than 
itself,  that  an  interval  is  left  between  them,  which  is  filled  with  fragments  of 
ice.  The  mode  of  estimating  the  quantity  of  heat  which  is  emitted  by  a  hot 
body  placed  in  the  wire  cage,  depends  upon  the  fact,  that  ice  cannot  be  heated 
beyond  32°  ;  since  every  particle  of  heat  which  is  then  supplied  is  employed 
in  liquefying  it,  without  in  the  least  affecting  its  temperature.  If,  therefore, 
a  flask  of  boiling  water  be  put  into  the  cage,  it  will  gradually  cool,  the  ice 
will  continue  at  32°,  and  a  portion  of  ice-cold  water  will  be  formed;  and  the 
same  change  will  happen  when  heated  mercury,  oil,  or  any  other  substance 
is  substituted  for  the  hot  water.  The  sole  difference  will  consist  in  the 
quantity  of  ice  liquefied,  which  will  be  proportional  to  the  heat  lost  by  those 
bodies  while  they  cool;  so  that  their  capacity  is  determined  merely  by 
measuring  the  quantity  of  water  produced  by  each  of  them.  This  is  done 
by  allowing  the  water,  as  it  forms,  to  run  out  of  the  calorimeter  by  a  tube 
fixed  in  the  bottom  of  it,  and  carefully  weighing  the  liquid  which  issues. 

There  is  one  obvious  source  of  fallacy  in  this  mode  of  operating,  against 
which  it  is  necessary  to  provide  a  remedy  ;  namely,  the  ice  not  only  receives 
heat  from  the  substance  in  the  central  cage,  but  must  also  receive  it  from 
the  air  of  the  apartment  in  which  the  experiment  is  conducted.  This  in- 
convenience  is  avoided  by  surrounding  the  whole  apparatus  by  a  larger 
metallic  vessel  of  the  same  form  as  the  smaller  one,  and  of  such  a  size  that 
a  certain  space  is  left  between  them,  which  is  to  be  filled  with  pounded  ice 
or  snow.  No  external  heat  can  now  penetrate  to  the  inner  vessel ;  because 
all  the  heat  derived  from  the  apartment  is  absorbed  by  the  outer  one,  and  is 
employed,  not  in  elevating  its  temperature,  but  in  dissolving  the  pounded  ice 
within  it. 

Notwithstanding  this  precaution,  however,  the  accuracy  of  the  calorimeter 
may  fairly  be  questioned.  For  it  is  essential,  in  order  to  obtain  correct  re- 
sults, that  all  the  water  which  is  produced  should  flow  out  and  be  collected. 
But  there  is  reason  to  suspect  that  some  of  the  water  is  apt  to  freeze  again 
before  it  has  had  time  to  escape ;  and  if  this  be  true,  as  a  priori  is  very 
probable,  then  the  information  given  by  the  calorimeter  must  be  rejected  as 
useless. 

The  determination  of  the  specific  heat  of  gaseous  substances  is  a  problem 
of  importance,  and  has  accordingly  occupied  the  attention  of  several  experi- 
menters of  great  science  and  practical  skill ;  but  the  inquiry  is  beset  with 
so  many  difficulties  that,  in  spite  of  the  talent  which  has  been  devoted  to  it, 
our  best  results  can  be  viewed  as  approximations  only,  requiring  to  be  correct- 
ed by  future  research.  Dr.  Crawford,  to  whom  we  are  indebted  for  the  first 
elaborate  investigation  of  the  subject,  conducted  his  experiments  in  the  fol- 
lowing manner.  He  obtained  two  copper  vessels,  made  as  light  as  possible, 
and  exactly  of  the  same  form,  size,  and  weight,  exhausted  one  of  them,  and 


while  the  temperature  acquired  by  the  colder  body  will  be  (6 — t' ),  and 
the  whole  heat  gained  will  be  represented  by  s'.  (8 — t1}.  w'.  As  the  heat 
gained  by  the  one  is  equal  to  that  lost  by  the  other,  it  follows  that  s.  (t — 6). 

w=s'.  (Q — t').w';  and  consequently  — ;  =  - ^- — .    In  case  of  the  weights 

being  equal,  or  w=w',  then— -  = ;  that  is,  for  equal  weights,  the  spe- 
cific heats  are  inversely  as  the  variations  of  temperature. 
*  Crawford  on  Animal  Heat,  and  Irvine's  Chemical  Essays. 


32  HEAT. 

filled  the  other  with  the  gas  to  be  examined.  They  were  next  heated  to 
the  same  extent  by  immersion  in  hot  water,  and  then  plunged  into  equal 
quantities  of  cold  water  of  the  same  temperature.  Each  flask  heated  the 
water;  but  while  the  exhausted  flask  communicated  solely  the  heat  of  the 
copper,  the  other  gave  out  an  equal  quantity  of  heat  from  the  metal  of  which 
it  was  made,  together  with  that  derived  from  the  gas  in  its  interior.  The 
effect  produced  by  the  former  deducted  from  that  of  the  latter  gave  the  heat- 
ing power  of  the  confined  gas,  the  precise  information  wanted.  By  repeat- 
ing the  experiment  with  air  and  different  gases,  their  comparative  heating 
powers,  or  their  specific  heats,  were  ascertained.  But  correct  as  is  the 
leading  principle  on  which  these  experiments  were  founded,  the  results  are 
now  universally  admitted  to  be  very  wide  of  the  truth,  and,  therefore,  it  can 
answer  no  useful  purpose  to  cite  them.  The  fallacy  is  attributable  to  the 
circumstances  of  the  heat  derived  from  the  containing  vessel  being  so  great 
compared  to  that  emitted  by  the  confined  gas,  that  the  effect  ascribed  to  the 
latter  is  confounded  with,  and  materially  influenced  by,  the  unavoidable  errors 
of  manipulation. 

The  same  subject  was  investigated  by  Lavoisier  and  Laplace  by  means  of 
their  calorimeter.  A  current  of  gas  was  transmitted  in  a  serpentine  tube 
through  boiling  water  in  order  to  be  heated,  and  was  then  made  to  circulate 
within  the  calorimeter  in  a  similar  tube  surrounded  with  ice.  Its  tempera- 
ture in  entering  and  quitting  the  calorimeter  was  ascertained  by  thermome- 
ters, and  the  heat  lost  by  each  gas  was  estimated  by  the  quantity  of  ice  lique- 
fied. Their  experiments  are  of  course  liable  to  the  objections  already  made 
to  the  use  of  ice ;  but  a  similar  train  of  experiments,  not  exposed  to  this 
fallacy,  was  conducted  in  the  year  1813  with  extreme  care  by  Delaroche  and 
Berard.  (An.  de  Chimie,  LXXXV.  and  Annals  of  Phil,  n.)  They  transmitted 
known  quantities  of  gas,  heated  to  212°,  in  a  uniform  current  through  the 
calorimeter;  and,  instead  of  ice,  surrounded  the  serpentine  tube  with  water, 
the  temperature  of  which,  as  well  as  of  the  gas  at  its  exit,  was  ascertained 
during  the  course  of  the  process  by  delicate  thermometers.  By  operating 
with  a  considerable  quantity  of  gas,  they  avoided  the  error  into  which 
Crawford  fell ;  and  the  experiments,  though  complicated  and  involving 
various  sources  of  error,  were  conducted  with  such  skill  and  caution  that 
they  inspired  great  confidence,  and  are  still  admitted  to  be  more  accurate 
than  any  which  have  been  made  on  this  difficult  subject.  Their  results 
are  contained  in  the  following  table ;  the  specific  heat  of  the  gases  being 
referred  to  atmospheric  air  as  unity  in  the  two  first  columns,  and  to  water  in 
the  third. 


Names  of  Substances. 

Under  equal 
Volumes. 

Under  equal  Weights. 

Atmospheric  air  . 
Hydrogen  gas  .        .     ?   . 
Oxygen  gas          .         .  •  ,•  4,} 
Nitrogen  gas    .         .        , 
Nitrous  oxide  gas 
Olefiant  gas      . 
Carbonic  oxide  gas 
Carbonic  acid  gas     . 
Water          .... 

1.0000 
8.9033 
0.9765 
1.0000 
1.3503 
1.5530 
1.0340 
1.2583 

1.0000     .     . 
12.3400     .     . 

0.8848    .    . 
1.0318    .    . 
0.8878    .    . 
1.5763    .    . 
1.0805    .    . 
0.8280    .    . 

0.2669 
3.2936 
0.2361 
0.2754 
0.2369 
0.4207 
0.2884 
0.2210 
1.0000 
0.8470 

Aqueous  vapour 

.    .    . 

Some  experiments  performed  by  Clement  and  Desormes,  and  published  in 
the  year  1819  in  the  Journal  de  Physique,  LXXXIX.  320,  were  confirmatory 
of  the  foregoing  results ;  and  Dalton,  in  the  second  volume  of  his  Chemical 
Philosophy,  page  282,  states  that  he  has  repeated  the  experiment  of  Delaroche 
and  Berard  on  the  specific  heat  of  atmospheric  air,  and  is  convinced  of  their 


HEAT.  33 

estimate  being  very  near  the  truth.  But  the  accuracy  of  their  results  has 
been  questioned  by  others,  and  some  of  the  objections  are  by  no  means  de- 
ficient in  force.  One  of  these  was  stated  by  Mr.  Hay  craft  in  the  Edinburgh 
Phil.  Trans,  for  1824,  namely,  that  the  gases  were  employed  in  a  moist  in- 
stead of  a  dry  state,  a  circumstance  which  would  doubtless  in  some  measure 
modify  the  result ;  and  others  have  been  mentioned  by  De  la  Rive  and  Mar- 
cet.  (An.  de  Ch.  et  de  Ph.  xxxv.  5.  and  XLI.  78.)  For  example,  the  precise 
temperature  of  the  gases  used  in  their  experiments  was  not  ascertained  in 
an  unexceptionable  manner ;  because  a  thermometer  surrounded  by  gaseous 
matter  is  affected,  not  only  by  contact  with  the  gas  itself,  but  likewise  by 
the  radiant  heat  emitted  or  absorbed  by  the  containing  vessel.  It  is  also  to 
be  remarked  that  the  heated  gases,  in  passing  through  the  calorimeter, 
diminished  in  volume  in  proportion  as  they  cooled.  Now  it  is  found  in- 
variably that  whenever  the  bulk  of  a  gas  is  diminished,  a  certain  portion  of 
insensible  heat  becomes  sensible ;  so  that  in  the  experiments  of  Delaroche 
and  Berard,  the  heating  influence  of  the  gases  was  a  complex  phenomenon, 
partly  dependent  on  the  heat  lost  in  cooling,  and  partly  on  that  developed 
by  the  accompanying  diminution  in  volume.  This  last  source  of  heat 
ought  to  have  been  avoided,  and  in  the  experiments  of  Crawford  it  was  so ; 
for  the  heated  gases  with  which  he  operated,  being  confined  in  a  close  ves- 
sel, underwent  no  change  of  volume  while  they  cooled,  though  of  course 
their  elasticity  was  thereby  diminished. 

These  considerations  induced  De  la  Rive  and  Marcet  to  undertake  this 
difficult  inquiry.  In  their  experiments  the  gases  were  confined  in  a  thin 
globe  of  glass,  and  the  temperature  was  estimated,  not  by  a  thermometer, 
but  by  the  elastic  force  communicated  by  the  heat,  according  to  the  law  of 
Dalton  and  Gay-Lussac  already  mentioned.  (Page  21.)  The  glass  vessel 
was  placed  in  the  centre  of  a  very  thin  copper  globe,  the  inner  surface  of 
which  was  made  to  radiate  freely  by  a  coating  of  lamp-black,  and  the  air 
between  it  and  the  glass  globe  was  withdrawn  by  an  air-pump.  The  whole 
apparatus  being  brought  to  the  temperature  of  68°,  was  immersed  during 
exactly  five  minutes  in  water  kept  steadily  at  86° ;  and  the  heat  imparted  to 
the  copper  was  radiated  from  its  inner  surface,  and  thus  reached  the  glass 
globe  in  the  centre.  By  always  operating  exactly  in  the  same  manner,  it 
was  conceived  that  the  same  volume  of  each  gas  would  receive  equal  quanti- 
ties of  heat  in  equal  times ;  and  that  from  the  temperature  thus  communi- 
cated to  each,  its  specific  heat  might  be  inferred.  In  two  sets  of  experiments 
thus  conducted,  they  found  that  each  gas  acquired  the  same  elasticity,  or 
was  heated  to  the  same  degree ;  and  thence  they  inferred  that  gases  in  gene- 
ral, for  equal  volumes  and  pressures,  have  the  same  capacity  for  heat.  They 
also  operated  with  the  same  gas  at  different  densities  ;  and  concluded  that 
the  specific  heat  of  each  gas,  for  equal  volumes,  diminishes  slowly  as  its 
density  decreases. 

In  the  An.  de  Ch.  et  de  Ph.  XLI.  113,  Dulong  has  published  some  critical 
remarks  on  these  experiments.  He  argues,  in  the  first  place,  that  the  quan- 
tity of  gas  employed  was  so  small,  that  any  effect  arising  from  a  difference 
in  specific  heat  could  not  be  appreciated.  He  contends,  further,  that  the 
temperature  acquired  by  a  gas  in  such  experiments  is  not  influenced  by  its 
specific  heat  only,  but  in  part  by  the  relative  facility  with  which  heat  is 
transmitted  through  the  gas.  It  has  been  already  observed  that  heat  is 
conducted  by  gaseous  matter  with  extreme  slowness,  but  is  rapidly  diffused 
through  it  in  consequence  of  the  mobility  of  its  particles.  Now  gases  differ 
considerably  under  this  point  of  view.  Hydrogen  acquires  the  temperature 
of  a  hot  body  placed  in  it  much  more  rapidly  than  carbonic  acid  ;  and,  there- 
fore, were  the  same  volume  of  these  gases  exposed  for  an  equal  short  period 
to  equal  sources  of  heat,  the  former  would  acquire  a  higher  temperature 
simply  from  its  conveying  heat  more  readily.  The  validity  of  these  stric- 
tures can  scarcely,  I  apprehend,  be  denied.  It  may,  therefore,  be  inferred 
from  the  foregoing  observations,  that  the  specific  heats  of  the  gases  are  not 
yet  accurately  known,  and  that  the  numbers  stated  by  Delaroche  and  Berard 
are  probably  the  best  approximations  hitherto  published. 


34  HEAT. 

The  circumstances  which  merit  particular  notice,  concerning  the  specific 
heat  of  bodies,  may  be  arranged  under  the  eight  following  heads : — 

1.  Every  substance  has  a  specific  heat  peculiar  to  itself;  whence  it  follows, 
that  a  change  of  composition  will  be  attended  by  a  change  of  capacity  for 
heat. 

2.  The  specific  heat  of  a  body  varies  with  its  form.     A  solid  has  a  smaller 
capacity  for  heat  than  the  same  substance  when  in  the  state  of  a  liquid  ;  the 
specific  heat  of  water,  for  instance,  being  9  in  the  solid  state,  and  10  in  the 
liquid.     Whether  the  same  weight  of  a  body  has  a  greater  specific  heat  in  the 
solid  or  liquid  form  than  in  that  of  vapour,  is  a  circumstance  not  yet  decided. 
The  only  experiments  in  point  are  those  of  Crawford,  and   Delaroche  and 
Berard.     The  former  estimated  the  specific  heat  of  vapour  at  1.55,  and  the 
French  philosophers  at  0.847,  compared  to  that  of  water  as  unity;  nor  is  it 
possible  to  say  which  of  these  widely  discordant  results  is  nearer  the  truth, 
as  neither  can  be  relied  on  with  confidence.* 

3.  When  a  given  weight  of  any  gas  is  made  to  vary  in  density  and 
volume  while  its  elasticity  is  unchanged,  as  when  air  confined  in  a  tube  over 
mercury  is  heated  and  suffered  to  expand  without  variation  of  pressure,  the 
specific  heat  is  believed  to  remain  constant.     Gaseous  matter,  being  free 
from  the  disturbing  agency  of  cohesion,  is  very  equably  influenced  by  heat : 
according  to  our  best  observations,  equal  increments  of  heat,  when  the  elas- 
ticity is  constant,  give  rise  both  to  equal  increments  of  temperature  and 
equal  expansions. 

4.  Of  the  specific  heat  of  equal  volumes  of  the  same  gas  at  a  varying 
density  and  elasticity,  as  when  air  is  forced  into  a  bottle  with  different  de- 
grees offeree,  nothing  certain  has  been  established;  for  the  experiments  of 
De  la  Rive  and  Marcet,  above  described,  have  led  to  no  decisive  conclusion. 

5.  The  specific  heat  of  equal  weights  of  the  same  gas  varies  as  the  density 
and  elasticity  vary.     Thus,  when  100  measures  of  air  expand  by  diminished 
pressure  to  200  measures,  its  specific  heat  is  increased ;  and  when  the  same 
quantity  of  air  is  compressed  into  the  space  of  50  measures,  its  specific  heat 
is  diminished.    The  exact  rate  of  increase  is  unknown ;  but  according  to 
Delaroche  and  Berard,  the  ratio  is  less  rapid  than  the  diminution  in  density ; 
that  is,  the  specific  heat  of  any  gas  being  one,  it  is  not  two,  but  between  one 
and  two,  when  its  volume  is  doubled. 

6.  The  specific  heat  of  solids  and  liquids  was  formerly  thought,  especially 
by  Drs.  Crawford  and  Irvine,  to  be  constant  at  all  temperatures,  so  long  as 
they  suffer  no  change  of  form  or  composition.     Dr.  Dalton,  however,  (Che- 
mical Philosophy,  part  I.  p.  50,)  endeavours  to  show  that  the  specific  heat  of 
such  bodies  is  greater  in  high  than  at  low  temperatures ;  and  Petit  and  Du- 
long,  in  the  essay  already  quoted,  have  proved  it  experimentally  with  respect 
to  several  of  them.     Thus  the  mean  specific  heat  of  iron  between 

0°  Centigrade  and  100°  Centigrade  is  0.1098 

0°  .  .  200°  .          .  0.1150 

0°  .  "/'  300°  .          .  0.1218 

GO  .        --/  350°  .          .  0.1255 

*  The  question  here  referred  to  may  not  be  decided  experimentally  with 
rigid  accuracy,  and  yet  it  is  decided  with  much  plausibility  by  the  admitted 
doctrine  of  the  formation  of  vapours  from  liquids,  and  the  increased  specific 
heat  of  vapours  by  rarefaction.  Dr.  Turner  admits  that  the  specific  heat  of 
water  in  the  liquid  state  is  greater  than  in  that  of  ice.  Is  it  not  probable 
then  that  the  specific  heat  of  steam  is  greater  than  that  of  an  equal  weight 
of  water?  Conceding  that  the  increased  capacity  that  takes  place  as  water 
changes  into  steam,  is  not  conclusive  as  to  the  increased  specific  heat  of  the 
steam  itself  after  having  been  formed ;  yet  as  a  separation  of  the  particles 
of  steam  by  rarefaction  is  admitted  to  increase  its  specific  heat,  &  fortiori  the 
greater  separation  of  the  aqueous  particles  in  passing  from  water  to  steam 
might  be  supposed  to  be  attended  with  the  same  result. — Ed. 


HEAT.  35 

And  the  same  is  true  of  the  substances  contained  in  the  following  table. 


Mean  Capacity 
between  0°  and  100°  C. 

Mean  Capacity 
between  0°  and  300°  C. 

Mercury 
Zinc 
Antimony     . 
Silver 
Copper 
Platinum  . 
Glass      .       .       . 

0.0330 
0.0927 
0.0507 
0.0557 
0.0949 
0.0335 
0.1770 

0.0350 
0.1015 
0.0549 
0.0611 
0.1013 
0.0355 
0.1900 

It  is  difficult  to  determine  whether  the  increased  specific  heat  observed  in 
solids  and  liquids  at  high  temperatures  is  owing  to  the  accumulation  of  heat 
within  them,  or  to  their  dilatation.  It  is  ascribed  in  general  to  the  latter, 
and  I  believe  correctly ;  because  the  expansion  and  contraction  of  gases  by 
change  of  pressure,  without  the  aid  of  heat,  is  attended  with  corresponding 
changes  of  specific  heat. 

7.  Change  of  specific  heat  always  occasions  a  change  of  temperature. 
Increase  in  the  former  is  attended  by  diminution  of  the  latter ;  and  decrease 
in  the  former  by  increase  of  the  latter.     Thus  when  air,  confined  within  a 
flaccid  bladder,  is  suddenly  dilated  by  means  of  the  air-pump,  a  thermometer 
placed  in  it  will  indicate  the  production  of  cold.     On  the  contrary,  when  air 
is  compressed,  the  corresponding  diminution  of  its  specific  heat  gives  rise  to 
increase  of  temperature ;  nay,  so  much  heat  is  evolved  when  the  compression 
is  sudden  and  forcible,  that  tinder  may  be  kindled  by  it.    The  explanation 
of  these  facts  is  obvious.     In  the  first  case,  a  quantity  of  heat  becomes  in. 
sensible,  which  was  previously  in  a  sensible  state ;  in  the  second,  heat  is 
evolved,  which  was  previously  latent. 

8.  A  curious  relation  between  the  specific  heat  of  some  elementary  sub- 
stances and  their  atomic  weight  was  discovered  by  Dulong and  Petit;  namely, 
that  the  product  of  the  specific  heat  of  each  element  by  the  weight  of  its 
atom  is  a  constant  quantity.     This  relation,  if  general,  would  be  of  great 
interest,  as  leading  directly  to  the  inference  that  the   atoms  of  elementary 
substances  have  the  same  specific  heat,  and  enabling  chemists  to  calculate 
either  the  specific  heat  of  elements  from  their  atomic  weight,  or  conversely 
their  atomic  weight  from  their  specific  heat.     (An.  de  Ch.  et  de  Ph.  x.  403.) 
The  relation  above   alluded  to  was  exemplified  by  Dulong  and  Petit  by  a 
table  similar  to  the  subjoined. 


Product  of  the  Sp.  Hea* 
Relative  Weights               of  each  Element  by  the 
Specific  Heat.              of  Atoms.                         Weight  of  its  Atom. 

Lead    . 

0.0293 

X 

103.6 

= 

3.0354 

Tin 

0.0514 

X 

58.9 

BB 

3.0274 

Zinc     . 

0.0927 

X 

32.3 

:=; 

2.9942 

Tellurium 

0.0912 

X 

32.3 

— 

2.9457 

Copper 

0.0949 

X 

31.6 

= 

2.9988 

Nickel     . 

0.1035 

X 

29.5 

— 

3.0532 

Iron     . 

0.1100 

X 

28 

— 

3.0800 

Sulphur   . 

0.1880 

X 

16.1 

= 

3.0268 

Platinum      . 

0.0335 

X 

98.8 

mm 

3.3098 

Bismuth  . 

0.0288 

X 

71 

mm 

2.0448 

Cobalt 

0.1498 

X 

29.5 



4.4191 

Mercury  . 

0.0330 

X 

202 

KB 

6.6660 

Silver  . 

0.0557 

X 

108 

= 

6.0156 

Gold 

0.0298 

X 

199.2 

= 

5.9361* 

*  Professor  A.  D.  Bache,  President   of  Girard  College,   pointed  out  in 
1829,  that  the  coincidences  between  the  specific  heats   of  the   atoms  of 


36  HEAT. 

It  will  be  observed,  on  inspecting  the  last  column  of  the  table,  that  the  pro- 
duct of  the  specific  heat  into  the  atomic  weight  is  very  nearly  3  for  the  first 
eight  substances.  Platinum  deviates  visibly  from  the  law,  and  bismuth  and 
cobalt  strikingly.  The  three  last  metals  would  nearly  coincide  with  the  law, 
were  their  respective  atomic  weights  estimated  at  half  the  numder  given  in 
the  table.  It  is  singular  that  the  tabular  view  originally  framed  by  Dulong 
and  Petit  exhibited  a  more  perfect  coincidence  than  appears  in  my  table,  and 
that  the  difference  arises  from  the  substitution  of  the  atomic  weights  now 
used  for  the  less  correct  ones  employed  by  them.  This  circumstance  is  so 
far  unfavourable  to  the  notion  of  a  law ;  but  still  the  cases  which  do  coincide 
appear  too  numerous  to  be  the  result  of  chance.  Dr.  Dalton,  in  his  Chemical 
Philosophy  (ii.  293,)  contends  that  the  law  cannot  be  true  ;  since,  as  Dulong 
and  Petit  have  shown,  the  specific  heat  of  a  substance  is  not  constant,  but 
varies  both  from  a  change  of  form,  and  even  with  variation  of  temperature 
without  change  of  form.  To  the  latter  part  of  the  criticism,  Dulong  and 
Petit  are  certainly  exposed ;  but  they  have  anticipated  the  former  by  remark- 
ing,  that  the  law  is  not  affected  by  change  of  form,  provided  the  substances 
compared  are  taken  in  the  same  state.  Future  observation  must  decide  on 
the  validity  of  this  position. 

LIQUEFACTION. 

All  bodies  hitherto  known,  are  either  solid,  liquid,  or  gaseous ;  and  the 
form  they  assume  depends  on  the  relative  intensity  of  cohesion  and  repul- 
sion. Should  the  repulsive  force  be  comparatively  feeble,  the  particles  will 
adhere  so  firmly  together,  that  they  cannot  move  freely  upon  one  another, 
thus  constituting  a  solid.  If  cohesion  is  so  far  counteracted  by  repulsion, 
that  the  particles  move  on  each  other  freely,  a  liquid  is  formed.  And  should 
the  cohesive  attraction  be  entirely  overcome,  so  that  the  particles  not  only 
move  freely  on  each  other,  but  would,  unless  restrained  by  external  pressure, 
separate  from  one  another  to  an  almost  indefinite  extent,  an  aeriform  sub- 
stance will  be  produced. 

Now  the  property  of  repulsion  is  manifestly  owing  to  heat ;  and  as  it  is 
easy  within  certain  limits  to  increase  or  diminish  the  quantity  of  this  prin- 
ciple in  any  substance,  it  follows  that  the  form  of  bodies  may  be  made  to 
vary  at  pleasure :  that  is,  by  heat  sufficiently  intense  every  solid  may  be 
converted  into  a  fluid,  and  every  fluid  into  vapour.  This  inference  is  so  far 
justified  by  experience,  that  it  may  safely  be  considered  as  a  law.  The  con- 
verse ought  also  to  be  true,  and,  accordingly,  several  of  the  gases  have 
already  been  condensed  into  liquids  by  means  of  pressure,  and  liquids  have 
been  solidified  by  cold.  The  temperature  at  which  liquefaction  takes  place 
is  called  the  melting  point,  or  point  of  fusion ;  and  that  at  which  liquids 
solidify,  their  point  of  congelation.  Both  these  points  are  different  for  dif- 
ferent substances,  but  uniformly  the  same,  under  similar  circumstances,  in 
the  same  body. 

The  most  important  circumstance  relative  to  liquefaction  is  the  discovery 
of  Dr.  Black,  that  a  large  quantity  of  heat  disappears,  or  becomes  insensible 
to  the  thermometer,  during  the  process.  If  a  pound  of  water  at  32°  be 
mixed  with  a  pound  of  water  at  172°,  the  temperature  of  the  mixture  will 
be  intermediate  between  them,  or  102°.  But  if  a  pound  of  water  at  172°  be 

bodies  are  far  less  striking  when  the  corrected  atomic  weights  are  employed, 
than  they  appear  to  be  in  Dulong  and  Petit's  table,  in  which  the  old  atomic 
numbers  are  used.  Dr.  Turner  here  gives  a  new  table,  as  a  substitute  for 
Dulong  and  Petit's,  adopting  the  atomic  weights  according  to  the  latest 
determinations,  and  confirms  Professor  Baehe's  view.  A  number  of  errors 
in  the  atomic  weights  and  calculations  of  Dr.  Turner's  table  have  been  cor- 
rected. The  old  equivalent  for  tellurium,  however,  has  not  been  changed. 
See  Prof.  Bache's  paper  in  the  Journ.  of  the  Acad.  of  Nat.  Sciences  of  Phila- 
delphia, for  Jan.  1829.— Ed. 


HEAT.  37 

added  to  a  pound  of  ice  at  32°,  the  ice  will  quickly  dissolve,  and  on  placing 
a  thermometer  in  the  mixture,  it  will  be  found  to  stand,  not  at  102°,  but  at 
32°.  In  this  experiment,  the  pound  of  hot  water,  which  was  originally  at 
172°,  actually  loses  140  degrees  of  heat,  all  of  which  enters  into  the  ice,  and 
causes  its  liquefaction,  but  without  affecting  its  temperature ;  whence  it  fol- 
lows that  a  quantity  of  heat  becomes  insensible  during  the  melting  of  ice, 
sufficient  to  raise  the  temperature  of  an  equal  weight  of  water  by  140  de- 
grees of  Fahrenheit.  This  explains  the  well  known  fact,  on  which  the  gra- 
duation of  the  thermometer  depends, — that  the  temperature  of  melting  ice 
or  snow  never  exceeds  32°  F.  All  the  heat  which  is  added  becomes  insen- 
sible, till  the  liquefaction  is  complete. 

The  loss  of  sensible  heat  which  attends  liquefaction  seems  essentially 
necessary  to  the  change,  and  for  that  reason  is  frequently  called  the  heat  of 
fluidity.  The  actual  quantity  of  heat  required  for  this  purpose  varies  with 
the  substance,  as  is  proved  by  the  following  results  obtained  by  Irvine. 
The  degrees  indicate  the  extent  to  which  an  equal  weight  of  each  material 
may  be  heated  by  the  heat  of  fluidity  which  is  proper  to  it. 

Sulphur  . 
Spermaceti 
Lead  .  . 


Heat  of  Fluidity. 
.     143.68°  F. 
.     145° 

Zinc  .  . 
Tin  .  .  . 

Heat  of  Fluidity, 
.    .    493°  F. 
500° 

.    162o 
.     175° 

Bismuth  . 

'.    .    550° 

As  so  much  heat  disappears  during  liquefaction,  it  follows  that  heat  must 
be  evolved  when  a  liquid  passes  into  a  solid.  This  may  easily  be  proved. 
The  temperature  of  water  in  the  act  of  freezing  remains  at  32°,  though  ex- 
posed to  an  atmosphere  in  which  the  thermometer  is  at  zero.  In  order  that 
the  water  under  such  circumstances  should  preserve  its  temperature,  it  is 
necessary  that  heat  should  be  supplied  as  fast  as  it  is  abstracted ;  and  it  is 
obvious  that  the  only  source  of  supply  is  the  heat  of  fluidity.  Further,  if 
pure  recently  boiled  water  be  cooled  very  slowly,  and  kept  very  tranquil,  its 
temperature  may  be  lowered  to  21°  without  any  ice  being  formed ;  but  the 
least  motion  causes  it  to  congeal  suddenly,  and  in  doing  so  its  temperature 
rises  to  32°.  (Sir  C.  Blagden  in  Phil.  Trans.  1788.) 

The  explanation  which  Dr.  Black  gave  of  these  phenomena  constitutes 
what  is  called  his  doctrine  of  latent  heat,  which  was  partially  explained  on 
a  former  occasion.  (Page  29.)  He  conceived  that  heat  in  causing  fluidity 
loses  its  property  of  acting  on  the  thermometer,  in  consequence  of  combining 
chemically  with  the  solid  substance,  and  that  liquefaction  results,  because 
the  compound  so  formed  does  not  possess  that  degree  of  cohesive  attraction 
on  which  solidity  depends.  When  a  liquid  is  cooled  to  a  certain  point,  it 
parts  with  its  heat  of  fluidity,  heat  is  set  free  or  becomes  sensible,  and  the 
cohesion  natural  to  the  solid  is  restored.  The  same  mode  of  reasoning  was 
applied  by  Dr.  Black  to  the  conversion  of  liquids  into  vapours,  a  change 
during  which  a  large  quantity  of  heat  disappears. 

A  different  explanation  of  these  phenomena  was  proposed  by  Dr.  Irvine. 
Observing  that  a  solid  has  a  smaller  specific  heat  than  the  same  substance 
when  in  a  liquid  state,  he  argued  that  this  circumstance  alone  accounts  for 
heat  becoming  insensible  during  liquefaction.  For  since  the  specific  heat  of 
ice  and  water,  or  in  other  words,  the  quantity  of  heat  required  to  raise  their 
temperature  by  the  same  number  of  degrees,  was  found  to  be  as  9  to  10,  Dr. 
Irvine  inferred  that  ice  must  contain  one-tenth  less  heat  than  water  of  the 
same  temperature;  and  that  as  this  difference  must  be  supplied  to  the  ice 
when  it  is  converted  into  water,  the  change  must  necessarily  be  accompa- 
nied with  the  disappearance  of  heat.  Dr.  Irvine  applied  the  same  argument 
to  the  liquefaction  of  all  solids,  and  likewise  to  account  for  the  heat  which  is 
rendered  insensible  during  the  formation  of  vapour. 

Two  objections  may  properly  be  urged  against  the  opinion  of  Dr.  Irvine. 
In  the  first  place,  no  adequate  reason  is  assigned  for  the  liquefaction.  It 
accounts  for  the  disappearance  of  heat  which  accompanies  liquefaction,  but 

4 


38  HEAT. 

does  not  explain  why  the  body  becomes  liquid ;  whereas  the  hypothesis  of 
Black  affords  an  explanation  both  of  the  change  itself,  and  of  the  phenomena 
that  attend  it,  But  the  second  objection  is  still  more  conclusive.  Dr,  Ir* 
vine  argued  on  the  belief  that  a  liquid  has  in  every  case  a  greater  specific 
heat  than  when  in  the  solid  state;  and  though  this  point  has  not  been  de- 
monstrated in  a  manner  entirely  decisive,  yet  from  the  experiments  hitherto 
made,  it  appears  that  liquids  in  general  have  a  greater  specific  heat  than  so- 
lids, and  that,  therefore,  Irvine's  assumption  is  probably  correct.  In  like 
manner  he  believed  vapours  to  have  a  greater  specific  heat  than  the  liquids 
that  yield  them,  and  his  opinion  was  supported  by  the  experiments  of  Craw- 
ford on  the  specific  heat  of  water  and  watery  vapour.  But  no  reliance 
whatever  can  be  placed  on  the  researches  of  Crawford  on  this  subject ;  not 
only  because  his  result  is  so  different  from  that  obtained  by  Delaroche  and 
Berard,  but  because  all  his  other  experiments  on  the  specific  heat  of  elastic 
fluids  are  decidedly  erroneous.  (Page  32.)  Indeed  from  the  fact  of  most 
gases  having  a  smaller  specific  heat  than  liquids,  it  is  probable  that  the  spe- 
cific heat  of  elastic  fluids  in  general  is  inferior  to  that  of  the  liquids  from 
which  they  are  derived.*  The  disappearance  of  heat  during  vaporization  is, 
therefore,  not  explicable  on  the  views  of  Irvine ;  it  is  necessary  to  employ 
the  theory  of  Dr.  Black  to  account  for  that  change,  and,  therefore,  the  same 
doctrine  should  be  applied  to  the  analogous  phenomenon  of  liquefaction. 

In  speculating  on  the  cause  of  the  specific  heat  of  bodies,  at  page  29,  I 
had  recourse  to  the  doctrine  of  latent  or  combined  heat.  Black  restricted 
the  use  of  this  hypothesis  to  explain  the  phenomena  of  liquefaction  and  va- 
porization ;  but  I  apprehend  it  may  be  applied  without  impropriety  to  all 
cases  where  heat  passes  from  a  sensible  to  an  insensible  state.  That  this 
may  happen,  when  heat  enters  a  body,  without  change  of  form,  is  easily  de- 
monstrated. Thus,  in  order  to  raise  an  equal  weight  of  water  and  mercury 
by  the  same  number  of  degrees,  it  is  necessary  to  add  23  times  as  much 
heat  to  the  water  as  to  the  mercury  ;  a  fact  which  proves  that  a  quantity  of 
heat  becomes  insensible  to  the  thermometer  when  the  temperature  of  water 
is  raised  by  one  degree,  just  as  happens  when  ice  is  converted  into  water,  or 
water  into  vapour.t  The  phenomena  are  in  this  point  of  view  identical ; 
and,  therefore,  the  same  mode  of  reasoning  by  which  one  of  them  is  explain- 
ed, may  be  employed  to  account  for  the  other. 

The  loss  of  sensible^  heat  in  liquefaction  is  the  basis  of  many  artificial 
processes  for  producing  cold.  All  of  them  are  conducted  on  the  principle  of 
liquefying  solid  substances  without  the  aid  of  heat.  For,  the  heat  of  fluidity 
being  then  derived  chiefly  from  that  which  had  previously  existed  within 
the  solid  itself  in  a  sensible  state,  the  temperature  necessarily  falls.  The 
degree  of  Gold  thus  produced  depends  upon  the  quantity  of  heat  which  dis- 
appears, and  this  again  is  dependent  on  the  quantity  of  solid  matter  lique- 
fied, and  on  the  rapidity  of  liquefaction. 

The  most  common  method  of  producing  cold  is  by  mixing  together  equal 
parts  of  snow  and  salt.  The  salt  causes  the  snow  to  melt  by  reason  of  its 
affinity  for  water,  and  the  water  dissolves  the  salt;  so  that  both  of  them  be- 
come liquid.  The  cold  thus  generated  is  32  degrees  below  the  temperature 
of  freezing  water ;  that  is,  a  thermometer  placed  in  the  mixture  would  stand 
at  zero.  This  is  the  way  originally  proposed  by  Fahrenheit  for  determining 
the  commencement  of  his  scale. 

Any  other  substances  which  have  a  strong  affinity  for  water  may  be  sub- 
stituted for  the  salt ;  and  those  have  the  greatest  effect  in  producing  cold 
whose  affinity  for  that  liquid  is  greatest,  and  which  consequently  produce 
the  most  rapid  liquefaction.  The  crystallized  chloride  of  calcium,  proposed 
by  Lowitz,  is  by  far  the  most  convenient  in  practice.  It  may  be  made  by 
dissolving  marble  in  muriatic  acid,  and  concentrating  the  solution  by  evapo- 

*  See  note,  page  34,  relating  to  this  point. — Ed. 

t  See  note,  page  30,  where  this  view  of  the  subject  is  controverted. — Ed. 


HEAT.  39 

ration,  till,  upon  letting  a  drop  of  it  fall  upon  a  cold  saucer,  it  becomes  a  so. 
lid  mass.  It  should  then  be  withdrawn  from  the  fire,  and  when  cold  be 
speedily  reduced  to  a  fine  powder.  From  its  extreme  deliquescence  it  must 
be  preserved  in  well-stopped  vessels.  The  following  table,  from  Mr.  Walker's 
paper  in  the  Philosophical  Transactions  for  1801,  contains  the  best  propor. 
tions  for  producing  intense  cold. 

FRIGORIFIC  MIXTURES  WITH  SNOW.* 


MIXTURES. 
Parts  bv 
Weight. 
Sea-salt         ...       1 
Snow  .           ...       2 

from  any  temperature  1 

M 

hermometer  sinks 
to—  5° 

Degree  of  Cold 
produced. 

Sea-salt          ...       2 
Muriate  of  ammonia     .       1 
Snow    ....       5 

to  —12^ 

Sea-salt          .         .         .10 
Muriate  of  ammonia     .       5 
Nitrate  of  potassa          .       5 
Snow    .         .         .         .24 

to  —18° 

Sea-salt          ...       5 
Nitrate  of  ammonia       .      5 
Snow    .        .         .         .12 

to—  25° 

Diluted  sulphuric  acidt        2 
Snow    ....      3 

from  +32°  to  T23° 

55  degrees. 

Concentrated  muriatic  acid  5 

Snow    ....       8 

from  +32°  to  —27° 

59 

Concentrated  nitrous  acid   4 
Snow    ....       7 

from  +32°  to  —30° 

62 

Chloride  of  calcium       .       5 
Snow    ....      4 

from  +32°  to  —40° 

72 

Crystallized  chloride  of 
calcium     ...       3 
Snow    ....       2 

from  +32°  to  —50° 

82 

Fused  potassa        .         .       4 
Snow    ....       3 

from  +32°  to—  51° 

83 

But  freezing  mixtures  may  be  made  by  the  rapid  solution  of  salts,  without 
the  use  of  snow  or  ice ;  and  the  following  table,  taken  from  Walker's  Essay 
in  the  Philosophical  Transactions  for  1795,  includes  the  most  important  of 
them.  The  salts  must  be  finely  powdered  and  dry. 


*  The  snow  should  be  freshly  fallen,  dry,  and  uncompressed.  If  snow 
cannot  be  had,  finely  powdered  ice  may  be  substituted  for  it. 

t  Made  of  strong  acid,  diluted  with  half  its  weight  of  snow  or  distilled 
water, 


40 


MIXTURES. 
'4 

Muriate  of  ammonia 
Nitrate  of  potassa 
Water 

Parts  by 
Weight. 
.       5 
.      5 
.     16 

Temperature  falls 
from  +50°  to  +10° 

Degree  of  Cold 
produced. 

40  degrees. 

Muriate  of  ammonia 
Nitrate  of  potassa 
Sulphate  of  soda  . 
Water 

.      5 
.      5 

.      8 
.    16 

from  4-50°  to  +4° 

46 

Nitrate  of  ammonia 
Water 

.      1 
.      1 

from  4-50°  to  +4° 

46 

Nitrate  of  ammonia 
Carbonate  of  soda 
Water 

.      1 
.      1 
.      1 

from  -f  50°  to  —7° 

57 

Sulphate  of  soda 
Diluted  nitrous  acid* 

.      3 
2 

from  +50°  to  —3° 

53 

Sulphate  of  soda 
Muriate  of  ammonia 
Nitrate  of  potassa 
Diluted  nitrous  acid 

.       6 
.      4 
.      2 
.      4 

from  4-50°  to  —10° 

60 

Sulphate  of  soda 
Nitrate  of  ammonia 
Diluted  nitrous  acid 

.      6 
.      5 
.      4 

from  +50°  to  —14° 

64 

Phosphate  of  soda 
Diluted  nitrous  acid 

.      9 
.      4 

from  4-50°  to  —12° 

62 

Phosphate  of  soda 
Nitrate  of  ammonia 
Diluted  nitrous  acid 

.      9 
.      6 
.       4 

from  4-50°  to  —21° 

71 

Sulphate  of  soda 
Muriatic  acid 

.      8 
.      5 

from  4-50°  to  0° 

50 

Sulphate  of  soda           .       5 
Diluted  sulphuric  acidf      4 

from  4-50°  to  4-3° 

47 

These  artificial  processes  for  generating  cold  are  much  more  effectual 
when  the  materials  are  previously  cooled  by  immersion  in  other  frigorific 
mixtures.  One  would  at  first  suppose  that  an  unlimited  degree  of  cold 
might  be  thus  produced ;  but  it  is  found  that  when  the  difference  between 
the  mixture  and  the  air  becomes  very  great,  the  communication  of  heat  from 
one  to  the  other  becomes  so  rapid,  as  to  put  a  limit  to  the  reduction.  The 
greatest  cold  produced  by  Mr.  Walker  did  not  exceed  100  degrees  below  the 
zero  of  Fahrenheit. 

Though  it  is  unlikely  that  we  shall  ever  succeed  in  depriving  any  sub- 
stance of  all  its  heat,  it  is  presumed  that  bodies  do  contain  a  certain  definite 
quantity  of  this  principle,  and  various  attempts  have  been  made  to  calculate 
its  amount.  'Ike  mode  of  conducting  such  a  calculation  may  be  shown  by 
the  process  of  Dr.  Irvirie.  That  ingenious  chemist  proceeded  on  the  as- 
sumption, that  the  actual  quantity  of  heat  in  bodies  is  proportional  to  their 
specific  heat,  and  that  the  specific  heat  remains  the  same  at  all  temperatures, 
provided  no  change  of  form  takes  place.  Thus,  as  the  specific  heat  of  ice 

*  Composed  of  fuming  nitrous  acid  two  parts  in  weight,  and  one  of  water; 
the  mixture  being  allowed  to  cool  before  being  used. 

t  Composed  of  equal  weights  of  strong  acid  and  water»  being  allowed  to. 
cool  before  use. 


HEAT.  //  41 

to  that  of  water  as  9  to  10,  it  follows,  according^  to  the  hypothesis,  that 
ice  contains  l-10th  less  heal  than  water,  at  the  sa'ttie  temperature.  Now 
Dr.  Black  ascertained  that  this  tenth,  which  is  the  heat  of  fluidity,  is  equal 
to  140  degrees ;  whence  it  was  inferred  that  water  at  32°  contains  IQ.timei 
140,  or  1400  degrees  of  heat.  ^•BMC^ 

To  be  satisfied  that  such  calculations  cannot  be  trusted,  it  is  sufficient  to 
know,  that  the  estimates  made  by  different  chemists  respecting  the  absolute 
quantity  of  heat  in  water  vary  from  900  to  nearly  8000  degrees.*  Besides, 
did  even  the  estimates  agree  with  each  other,  the  principle  of  the  calculation 
would  still  be  unsatisfactory ;  for,  in  the  first  place,  there  is  no  proof  that 
the  quantity  of  heat  in  bodies  is  in  the  ratio  of  their  specific  heats ;  and, 
secondly,  the  assumption  that  the  specific  heat  of  a  body  is  the  same  at  all 
temperatures,  so  long  as  it  does  not  experience  a  change  of  form,  has  been 
proved  to  be  erroneous  by  the  experiments  of  Dulong  and  Petit, 

VAPORIZATION. 

Aeriform  substances  are  commonly  divided  into  vapours  and  gases.  The 
character  of  the  former  is,  that  they  may  be  readily  converted  into  liquids 
or  solids,  either  by  a  moderate  increase  of  pressure,  the  temperature  at 
which  they  were  formed  remaining  the  same,  or  by  a  moderate  diminution 
of  that  temperature,  without  change  of  pressure.  Gases,  on  the  contrary, 
retain  their  elastic  state  more  obstinately ;  they  are  always  gaseous  at  com- 
mon  temperatures,  and,  with  one  or  two  exceptions,  cannot  be  made  to 
change  their  form,  unless  by  being  subjected  to  much  greater  pressure  than 
they  are  naturally  exposed  to.  Several  of  them,  indeed,  have  hitherto  re- 
sisted every  effort  to  compress  them  into  liquids.  The  only  difference  be- 
tween gases  and  vapours  is  in  the  relative  forces  with  which  they  resist 
condensation. 

Heat  appears  to  be  the  cause  of  vaporization,  as  well  as  of  liquefaction, 
and  it  is  a  general  opinion  that  a  sufficiently  intense  heat  would  convert 
every  liquid  and  solid  into  vapour.  A  considerable  number  of  bodies,  how- 
ever, resist  the  strongest  heat  of  our  furnaces  without  vaporizing.  These 
are  said  to  be  fixed  in  the  fire :  those  which,  under  the  same  circumstances, 
are  converted  into  vapour,  are  called  volatile. 

The  disposition  of  various  substances  to  yield  vapour  is  very  different ; 
and  the  difference  depends  doubtless  on  the  relative  power  of  cohesion  with 
which  they  are  endowed.  Liquids  are,  in  general,  more  easily  vaporized 
than  solids,  as  would  be  expected  from  the  weaker  cohesion  of  the  former. 
Some  solids,  such  as  arsenic  and  sal  ammoniac,  pass  at  once  into  vapour 
without  being  liquefied ;  but  most  of  them  become  liquid  before  assuming 
the  elastic  condition. 

Vapours  occupy  more  space  than  the  substances  from  which  they  were 
produced.  According  to  the  experiments  of  Gay-Lussac,  water,  at  its  point 
of  greatest  density,  in  passing  into  vapour,  expands  to  1696  times  its  vo- 
lume, alcohol  to  659  times,  and  ether  to  443  times,  each  vapour  being  at  the 
temperature  of  212°  F.  and  under  a  pressure  of  29.92  inches  of  mercury. 
This  shows  that  vapours  differ  in  density.  Watery  vapour  is  lighter  than 
air  at  the  same  temperature  and  pressure,  in  the  proportion  of  1000  to  1604; 
or  the  density  of  air  being  1000,  that  of  watery  vapour  is  625.  The  vapour 
of  alcohol,  on  the  contrary,  is  half  as  heavy  again  as  air;  and  that  of  ether 
is  more  than  twice  and  a  half  as  heavy.  As  alcohol  boils  at  a  lower  tempe- 
rature than  water,  and  ether  than  alcohol,  it  was  conceived  that  the  density 
of  vapours  might  be  in  the  direct  ratio  of  the  volatility  of  the  liquids  which 
produced  them.  But  Gay-Lussae  has  shown  that  this  law  does  not  hold 
generally  ;  since  bisulphuret  of  carbon  boils  at  a  higher  temperature  than 
ether,  and  nevertheless  yields  a  heavier  vapour, 

*  Palton's  New  System  of  Chemical  Philosophy 


42  HEAT. 

The  dilatation  of  vapours  by  heat  was  found  by  Gay-Lussae  to  follow  the 
same  law  as  gases ;  that  is,  for  every  degree  of  Fahrenheit,  they  increase  by 
^g-Q-th  of  the  volume  they  occupied  at  32°.  But  the  law  does  not  hold  un- 
less the  quantity  of  vapour  continue  the  same.  If  the  increase  of  tempera- 
ture cause  a  fresh  portion  of  vapour  to  riser  then  the  expansion  will  be 
greater  than  ^cth  f°r  eacn  degree ;  because  the  heat  not  only  dilates  the 
vapour  previously  existing  to  the  same  extent  as  if  it  were  a  real  gas,  but 
augments  its  bulk  by  adding  a  fresh  quantity  of  vapour.  The  contraction 
of  a  vapour  on  cooling  will  likewise  deviate  from  the  above  law,  whenever 
the  cold  converts  any  of  it  into  a  liquid ;  an  effect  which  must  happen,  if 
the  space  had  originally  contained  its  maximum  of  vapour.  The  circum- 
stances just  explained  should  be  held  in  view,  whenever  the  influence  o£ 
heat  over  the  bulk  of  vapours  is  estimated  by  calculation.  The  formula  of 
page  21,  when  applied  to  vapours,  often  leads  to  a  result  which  would  be 
correct  for  any  gas,  but  which  may  be  untrue  in  the  case  of  vapour,  by  rea- 
son of  its  light  condensibility.  Thus  100  measures  of  steam  at  212°,  and 
when  the  barometer  is  at  30  inches,  would  theoretically  occupy  nearly  73  mea- 
sures at  32°,  and  at  the  same  pressure  j  but  this  estimate  is  practically  un- 
true, because,  under  the  conditions  specified,  water  cannot  exist  in  the  state 
of  vapour.  The  calculated  result,  being  deduced  from  correct  principles,  is 
sometimes  employed  in  effecting  other  calculations. 

The  volume  of  vapour  varies  under  varying  pressure  according  to  the 
same  law  as  that  of  gases,  provided  always  that  the  gaseous  state  is  pre- 
served. This  law,  discovered  by  Boyle  and  Mariotte,  is  more  fully  ex- 
plained in  the  section  on  atmospheric  air,  and  merely  expresses  the  fact  that 
the  volume  of  gaseous  substances  at  a  constant  temperature  is  inversely  as 
the  pressure  to  which  they  are  subject.  If  100  measures  of  steam  at  212°, 
and  under  the  atmospheric  pressure,  be  exposed  to  a  pressure  of  two  atmo- 
spheres, the  vapour  will  be  entirely  condensed,  affording  an  instance  of  fail- 
ure in  the  law,  in  consequence  of  the  gaseous  state  being  entirely  destroyed ; 
but  if  the  pressure  be  halved  instead  of  doubled,  the  100  measures  retain- 
ing  the  gaseous  form,  and  hence  acting  as  a  gas,  will  expand  to  200  mea- 
sures, In  fact,  if  v  be  the  volume  corresponding  to  any  pressure  p,  express- 
ed in  inches  of  mercury,  we  shall  have  rb~o=~p~'*  anc*  nence  0=100.  — . 
This  formula  gives  the  change  of  volume  due  to  a  change  of  pressure  from 
30  to/),  the  temperature  being  supposed  at  212°  in  both  cases.  To  render 
the  preceding  paragraph  intelligible  to  the  young  student,  it  should  be  men- 
tioned, that  pressure,  in  reference  to  the  volume  of  gaseous  matter,  is  usual- 
ly expressed  by  the  length  of  a  column  of  mercury :  a  mercurial  column, 
30  inches  in  length,  presses  on  a  given  surface  with  the  same  force  as  the 
atmosphere  in  its  ordinary  state;  and  hence  a  60-inch  column  is  equal  to 
two  atmospheres,  15  inches  to  half  an  atmosphere,  and  one  inch  to  l-30th  of 
the  atmospheric  pressure. 

Vaporization  is  conveniently  studied  under  two  heads, — Ebullition  and 
Evaporation.  In  the  first,  the  production  of  vapour  is  so  rapid  that  its  es- 
cape gives  rise  to  a  visible  commotion  in  the  liquid ;  in  the  second,  it  passes 
off  quietly  and  insensibly. 

Ebullition. — The  temperature  at  which  vapour  rises  with  sufficient  free- 
dom for  causing  the  phenomena  of  ebullition,  is  called  the  boiling  point.  The 
heat  requisite  for  this  effect  varies  with  the  nature  of  the  liquid.  Thus,  sul- 
phuric ether  boils  at  96°  F.,  alcohol  at  176°,  and  pure  water  at  212°; 
while  oil  of  turpentine  must  be  raised  to  316°,  and  mercury  to  662°,  before 
either  exhibits  marks  of  ebullition.  The  boiling  point  of  the  same  liquid  is 
constant,  so  long  as  the  necessary  conditions  are  preserved ;  but  it  is  liable 
to  be  affected  by  several  circumstances.  The  nature  of  the  vessel  has  some 
influence  upon  it.  Thus  Gay-Lussac  observed  that  pure  water  boils  precisely 
at  212°  in  a  metallic  vessel,  and  at  214°  in  one  of  glass,  owing  apparently  to 
its  adhering  to  glass  more  powerfully  than  to  a  metal.  It  is  likewise  affected 
by  the  presence  of  foreign  particles.  The  same  accurate  experimenter  found, 


HEAT.  43 

that  when  a  few  iron  filings  are  thrown  into  water,  boiling  in  a  glass  vessel, 
its  temperature  quickly  falls  from  214°  to  212°,  and  remains  stationary  at 
the  latter  point.  But  the  circumstance  which  has  the  greatest  influence  over 
the  boiling  point  of  fluids  is  variation  of  pressure.  All  bodies  upon  the  earth 
are  constantly  exposed  to  considerable  pressure;  for  the  atmosphere  itself 
presses  with  a  force  equivalent  to  a  weight  of  15  pounds  on  every  square 
inch  of  surface.  Liquids  are  exposed  to  this  pressure  as  well  as  solids,  and 
their  tendency  to  take  the  form  of  vapour  is  very  much  counteracted  by  it. 
In  fact,  they  cannot  enter  into  ebullition  at  all,  till  their  particles  have  ac- 
quired such  elastic  force  as  enables  them  to  overcome  the  pressure  upon  their 
surfaces ;  that  is,  till  they  press  against  the  atmosphere  with  the  same  force 
as  the  atmosphere  against  them.  Now  the  atmospheric  pressure  is  variable, 
and  hence  it  follows  that  the  boiling  point  of  liquids  must  also  vary. 

The  pressure  of  the  atmosphere  is  equal  to  a  weight  of  15  pounds  on  every 
square  inch  of  surface,  when  the  barometer  stands  at  30  inches,  and  then 
only  does  water  boil  at  212°  F.  If  the  pressure  be  less,  that  is,  if  the  baro- 
meter fall  below  30  inches,  then  the  boiling  point  of  water,  and  of  every  other 
liquid,  will  be  lower  than  usual ;  or  if  the  barometer  rise  above  30  inches, 
the  temperature  of  ebullition  will  be  proportionally  increased.  This  is  the 
reason  why  water  boils  at  a  lower  temperature  on  the  top  of  a  hill  than  in 
the  valley  beneath  it;  for  as  the  column  of  air  diminishes  in  length  as  we 
ascend,  its  pressure  must  likewise  suffer  a  proportional  diminution.  The 
ratio  between  the  depression  of  the  boiling  point  and  the  diminution  of  the 
atmospheric  pressure  is  so  exact,  that  it  has  been  proposed  as  a  method  for 
determining  the  height  of  mountains.  An  elevationsof  530  feet  makes  a 
diminution  of  one  degree  of  Fahrenheit.  (Mr.  Wollaston  in  Phil.  Trana.for 
1817.) 

The  influence  of  the  atmosphere  over  the  point  of  ebullition  is  best  shown 
by  removing  its  pressure  altogether.  The  late  Professor  Robison  found  that 
liquids  boil  in  vacuo  at  a  temperature  140  degrees  lower  than  in  the  open 
air.  (Black's  Lectrfres,  p.  151.)  Thus  water  boils  in  vacuo  at  72°,  alcohol 
at  36°,  and  ether  at  —44°  F.  This  proves  that  a  liquid  is  not  necessarily 
hot,  because  it  boils.  The  heat  of  the  hand  is  sufficient  to  make  water  boil 
in  a  vacuum,  as  is  exemplified  by  the  common  pulse-glass ;  and  ether,  under 
the  same  circumstances,  will  enter  into  ebullition,  though  its  temperature  be 
low  enough  for  freezing  mercury. 

Water  cannot  be  heated  under  common  circumstances  beyond  212°  ;  be- 
cause it  then  acquires  such  expansive  force  as  enables  it  to  overcome  the 
atmospheric  pressure,  and  fly  off  in  the  form  of  vapour.  But  if  subjected  to 
sufficient  pressure,  it  may  be  heated  to  any  extent  without  boiling.  This  is 
best  done  by  heating  water  while  confined  in  a  strong  copper  vessel,  called 
Papin's  digester.  In  this  apparatus,  on  the  application  of  heat,  a  large  quan- 
tity of  vapour  collects  above  the  water,  and  checks  ebullition  by  the  pressure 
which  it  exerts  upon  the  surface  of  the  liquid.  There  is  no  limit  to  the  de- 
gree to  which  water  may  thus  be  heated,  provided  the  vessel  is  strong 
enough  to  confine  the  vapour ;  but  the  expansive  force  of  steam  under  these 
circumstances  is  so  enormous  as  to  overcome  the  greatest  resistance. 

In  estimating  the  power  of  steam  it  should  be  remembered  that  vapour,  if 
separated  from  the  liquid  which  produced  it,  does  not  possess  greater  elasti- 
city than  an  equal  quantity  of  air.  If,  for  example,  the  digester  were  full  of 
steam  at  212°,  no  water  in  the  liquid  state  being  present,  it  might  be  heated 
to  any  degree,  even  to  redness,  without  danger  of  bursting.  But  if  water  be 
present,  then  each  addition  of  heat  causes  a  fresh  portion  of  steam  to  rise, 
which  adds  its  own  elastic  force  to  that  of  the  vapour  previously  existing ; 
and,  in  consequence,  an  excessive  pressure  is  soon  exerted  against  the  inside 
of  the  vessel.  Professor  Robison  (firewater's  edition  of  his  works,  p.  25) 
found  that  the  tension  of  steam  is  equal  to  two  atmospheres  at  244°,  and  to 
three  at  270°  F.  The  results  of  Mr.  Southern's  experiments,  given  in  the 
same  volume,  fix  upon  250.3°  as  the  temperature  at  which  steam  has  the 


44  HEAT. 

force  of  two  atmospheres,  on  293.4°  for  four,  and  343.6°  for  eight  atmo- 
spheres. 

This  subject  has  been  lately  examined  by  a  commission  appointed  by  the 
Parisian  Academy  of  Sciences,  and  Dulong  and  Arago  took  a  leading  part 
in  the  inquiry.  The  results,  which  are  given  in  the  following  table,  were 
obtained  by  experiment  up  to  a  pressure  of  25  atmospheres,  and  at  higher 
pressures  by  calculation.  (Brande's  Journal,  N.  S.  vii.  191.) 


Temperature  ac- 
cording to 
Fahrenheit. 

380.66° 

386.94 

392.86 

398.48 

403.82 

408.92 

413.78 

418.46 

422.96 

427.28 

431.42 

435.56 

439.34 

457.16 

472.73 

486.59 

491.14 

510.60 


The  elasticity  of  steam  is  employed  as  a  moving  power  in  the  steam- 
engine.  The  construction  of  this  machine  depends  on  two  properties  of  steam, 
namely,  the  expansive  force  communicated  to  it  by  heat,  and  its  ready  con- 
version  into  water  by  cold.  The  effect  of  both  these  properties  is  well  shown 
by  a  little  instrument  devised  by  Dr.  Wollaston.  It  consists  of  a  cylindrical 
glass  tube,  six  inches  long,  nearly  an  inch  wide,  and  blown  out  into  a  spheri- 
cal enlargement  at  one  end.  A  piston  is  accurately  fitted  to  the  cylinder,  so 
as  to  move  up  and  down  the  tube  with  freedom.  When  the  piston  is  at  the 
bottom  of  the  tube,  it  is  forced  up  by  causing  a  portion  of  water,  previously 
placed  in  the  bair,  to  boil  by  means  of  a  spirit-lamp.  On  dipping  the  ball 
into  cold  water,  the  steam  which  occupies  the  cylinder  is  suddenly  condensed, 
and  the  piston  forced  down  by  the  pressure  of  the  air  above  it.  By  the  alter- 
nate application  of  heat  and  cold,  the  same  movements  are  reproduced,  and 
may  be  repeated  for  any  length  of  time. 

The  moving  power  of  the  steam-engine  is  the  same  as  in  this  apparatus. 
The  only  essential  difference  between  them  is  in  the  mode  of  condensing  the 
steam.  In  a  steam-engine,  the  steam  is  condensed  in  a  separate  vessel, 
called  the  condenser,  where  there  is  a  regular  supply  of  cold  water  for  the 
purpose.  By  this  contrivance,  which  constitutes  the  great  improvement  of 
Watt,  the  temperature  of  the  cylinder  never  falls  helow  212°. 

The  formation  of  vapour  is  attended,  like  liquefaction^  with  loss  of  sensible 
heat.  This  is  proved  by  the  well-known  fact  that  the  temperature  of  steam 
is  precisely  the  same  as  that  of  the  boiling  water  from  which  it  rises ;  so 
that  all  the  heat  which  enters  into  the  liquid  is  solely  employed  in  convert- 
ing a  portion  of  it  into  vapour,  without  affecting  the  temperature  of  either  in 
the  slightest  degree,  provided  the  latter  is  permitted  to  escape  with  freedom-. 
The  heat  which  then  becomes  latent,  to  use  the  language  of  Black,  is  again 
set  free  when  the  vapour  is  condensed  into  water.  The  exact  quantity  of 


Elasticity  of  the 

Elasticity  of  the 

vapour,  taking 
atmospheric 

Temperature  ac- 
cording to 

vapour,  taking 
atmospheric 

pressure  as 

Fahrenheit. 

pressure  as 

unity. 

unity. 

1 

212° 

13 

1£ 

233.96 

14 

2 

250.52 

15 

2£ 

263.84 

16 

3 

275.18 

17 

3^ 

285.08 

18 

4 

293.72 

19 

4^ 

300.28 

20 

5 

307.5 

21 

5£ 

314.24 

22 

6 

320.36 

23 

6£ 

326.26 

24 

7 

331.70 

25 

7£ 

336.86 

30 

8 

341.78 

35 

9 

350.78 

40 

10 

358.88 

45 

11 

366.85 

50 

12 

374.00 

HEAT.  45 

heat  rendered  insensible  by  vaporization,  may,  therefore,  be  ascertained  by 
condensing  the  vapour  in  cold  water,  and  observing  the  rise  of  temperature 
which  ensues.  From  the  experiments  of  Black  and  Watt,  conducted  on  this 
principle,  it  appears  that  steam  of  212°,  in  being-  condensed  into  water  of 
212°,  gives  out  as  much  heat  as  would  raise  the  temperature  of  an  equal 
weight  of  water  by  950  degrees,  all  of  which  had  previously  existed  in  the 
vapour  without  being  sensible  to  a  thermometer. 

The  latent  heat  of  steam  and  several  other  vapours  has  been  examined  by 
Dr.  Ure,  whose  results  are  contained  in  the  following  table.  (Phil.  Trans, 
for  1818.) 

Latent  Heat. 

Vapour  of  Water  at  its  boiling  point        .        .        •        .  967° 

Alcohol .  442 

Ether 302.379 

Petroleum 177.87 

Oil  of  turpentine 177.87 

Nitric  acid 531.99 

Liquid  ammonia 837.28 

Vinegar       .......  875 

The  disappearance  of  heat  that  accompanies  vaporization  was  explained 
by  Black  and  Irvine,  in  the  way  already  mentioned  under  the  head  of  lique- 
faction ;  and  as  the  objections  to  the  views  of  the  latter  ingenious  chemist 
were  then  stated,  it  is  unnecessary  to  mention  them  on  the  present  occasion. 

The  variation  of  volume  and  elasticity  in  vapours  is  attended,  as  in  gases, 
with  a  change  of  specific  heat  and  a  consequent  variation  of  temperature. 
(Page  35.)  Thus  when  steam,  highly  heated  and  compressed  in  a  strong 
boiler,  is  permitted  to  escape  by  a  large  aperture,  the  sudden  expansion  is 
attended  with  a  great  loss  of  sensible  heat :  its  temperature  instantly  sinks 
so  much,  that  the  hand  may  be  held  in  the  current  of  vapour  without  incon- 
venience. The  same  principle  accounts  for  the  fact,  first  ascertained  by 
Watt,  that  distillation  at  a  low  temperature  is  not  attended  with  any  saving 
of  fuel.  For  when  water  boils  at  a  low  temperature  in  a  vacuum,  the  vapour 
is  in  a  highly  expanded  state,  and  contains  more  insensible  heat  than  steam 
of  greater  density.  From  some  experiments  by  Mr.  Sharpe  in  the  Man- 
chester Memoirs,  and  also  by  Clement  and  Desormes,  (Thenard's  Chemistry, 
i.  79,  5th  Ed.)  it  appears  that  the  sum  of  the  sensible  and  insensible  heat 
contained  in  equal  weights  of  steam  is  exactly  the  same  at  all  temperatures. 
Thus,  steam  at  212°,  when  condensed  and  reduced  to  32°,  gives  out  950 
degrees  of  insensible  and  180  of  sensible  heat,  the  sum  of  which  is  1130. 
The  same  weight  of  steam  at  250°,  on  being  condensed  and  cooled  to  32°, 
gives  out  likewise  1130  degrees,  of  which  218  are  sensible  and  912  insensible 
heat;  whereas  at  100°  its  sensible  heat  is  only  68°,  and  insensible  1062°, 
forming  the  constant  sum  of  1130.  The  same  is  found  by  Despretz  to  be 
true  of  various  other  vapours,  such  as  that  of  alcohol,  ether,  and  turpentine. 

Evaporation.  Evaporation  as  well  as  ebullition  consists  in  the  formation 
of  vapour,  and  the  only  assignable  difference  between  them  is,  that  the  one 
takes  place  quietly,  the  other  with  the  appearance  of  boiling.  Evaporation 
occurs  at  common  temperatures.  This  fact  may  be  proved  by  exposing 
water  in  a  shallow  vessel  to  the  air  for  a  few  days,  when  it  will  gradually 
diminish,  and  at  last  disappear  entirely.  Most  liquids,  if  not  all  of  them,  are 
susceptible  of  this  gradual  dissipation  ;  and  it  may  also  be  observed  in  some 
solids,  as  for  example  in  camphor.  Evaporation  is  much  more  rapid  in 
some  liquids  than  in  others,  and  it  is  always  found  that  those  liquids,  the 
boiling  point  of  which  is  lowest,  evaporate  with  the  greatest  rapidity.  Thus 
alcohol,  which  boils  at  a  lower  temperature  than  water,  evaporates  also  more 
freely ;  and  ether,  whose  point  of  ebullition  is  yet  lower  than  that  of  alcohol, 
evaporates  with  still  greater  rapidity. 

The  chief  circumstances  that  influence  the  process  of  evaporation  are  ex- 
tent of  surface,  and  the  state  of  the  air  as  to  temperature,  dryness,  stillness, 
and  density. 


46  HEAT. 

1.  Extent  of  surface.     Evaporation  proceeds  only  from  the  surface  of 
liquids,  and,  therefore,  cateris  paribus,  must  depend  upon  the  extent  of  sur- 
face exposed. 

2.  Temperature.    The  effect  of  heat  in  promoting  evaporation  may  easily 
be  shown  by  putting  an  equal  quantity  of  water  into  two  saucers,  one  of 
which  is  placed  in  a  warm,  the  other  in  a  cold  situation.     The  former  will 
be  quite  dry  before  the  latter  has  suffered  appreciable  diminution. 

3.  State  of  the  air  as  to  dryness  or  moisture.    When  water  is  covered  by 
a  stratum  of  dry  air,  the  evaporation  is  rapid  even  when  its  temperature  is 
low.     Thus  in  dry  cold  days  in  winter,  the  evaporation  is  exceedingly  rapid  ; 
whereas  it  goes  on  very  tardily,  if  the  atmosphere  contain  much  vapour, 
even  though  the  air  be  very  warm. 

4.  Evaporation  is  far  slower  in  still  air  than  in  a  current,  and  for  an  ob- 
vious reason.     The  air  immediately  in  contact  with  the  water  soon  becomes 
moist,  and  thus  a  check  is  put  to  evaporation.     But  if  the  air  be  removed 
from  the  surface  of  the  water  as  soon  as  it  has  become  charged  with  vapour, 
and  its  place  supplied  with  fresh  dry  air,  then  the  evaporation  continues 
without  interruption. 

5.  Pressure  on  the  surface  of  liquids  has  a  remarkable  influence  over  eva- 
poration.    This  is  easily  proved  by  placing  ether  in  the  vacuum  of  an  air- 
pump,  when  vapour  rises  so  abundantly  as  to  produce  ebullition. 

As  a  large  quantity  of  heat  passes  from  a  sensible  to  an  insensible  state 
during  the  formation  of  vapour,  it  follows  that  cold  should  be  generated  by 
evaporation.  The  fact  may  readily  be  proved  by  letting  a  few  drops  of  ether 
evaporate  from  the  hand,  when  a  strong  sensation  of  cold  will  be  excited1; 
or  if  the  bulb  of  a  thermometer,  covered  with  lint,  be  moistened  with  ether, 
the  production  of  cold  will  be  marked  by  the  descent  of  the  mercury.  But 
to  appreciate  the  degree  of  cold  which  may  be  produced  by  evaporation,  it 
is  necessary  to  render  it  very  rapid  and  abundant  by  artificial  processes ; 
and  the  best  means  of  doing  so,  is  by  removing  pressure  from  the  surface  of 
volatile  liquids.  Water  placed  under  the  exhausted  receiver  of  an  air-pump 
evaporates  with  great  rapidity,  and  so  much  cold  is  generated  as  would 
freeze  the  water,  did  the  vapour  continue  to  rise  for  some  time  with  the  same 
velocity.  But  the  vapour  itself  soon  fills  the  vacuum,  and  retards  the  eva- 
poration by  pressing  upon  the  surface  of  the  water.  This  difficulty  may  be 
avoided  by  putting  under  the  receiver  a  substance,  such  as  sulphuric  acid, 
which  has  the  property  of  absorbing  watery  vapour,  and  consequently  of 
removing  it  as  quickly  as  it  is  formed.  Such  is  the  principle  of  Leslie's 
method  for  freezing  water  by  its  own  evaporation.* 

The  action  of  the  cryophorus,  an  ingenious  contrivance  of  the  late  Dr. 
Wollaston,  depends  on  the  same  principle.  It  consists  of  two  glass  balls, 
perfectly  free  from  air,  and  joined  together  by  a  tube  as  here  represented. 


One  of  the  balls  contains  a  portion  of  distilled  water,  while  the  other  parts 
of  the  instrument,  which  appear  empty,  are  full  of  aqueous  vapour,  which 
checks  the  evaporation  from  the  water  by  the  pressure  it  exerts  upon  its 
surface.  But  when  the  empty  ball  is  plunged  into  a  freezing  mixture,  all 
the  vapour  within  it  is  condensed ;  evaporation  commences  from  the  surface 
of  the  water  in  the  other  ball,  and  it  is  frozen  in  two  or  three  minutes  by 
the  cold  thus  produced. 

Liquids  which  evaporate  more  rapidly  than  water,  cause  a  still  greater 
reduction  of  temperature.    The  cold  produced  by  the  evaporation  of  ether 

*  See  art.  Cold,  in  the  Supplement  to  the  Encyclopaedia  Britannica. 


HEAT,  47 

in  the  vacuum  of  the  air-pump,  is  so  intense  as,  under  favourable  circum- 
stances, to  freeze  mercury.* 

Scientific  men  have  differed  concerning  the  cause  of  evaporation.  It  was 
once  supposed  to  be  owing  to  chemical  attraction  between  the  air  and  water, 
and  the  idea  is  at  first  view  plausible,  since  a  certain  degree  of  affinity  does 
to  all  appearance  exist  between  them.  But  it  is  nevertheless  impossible  to 
attribute  the  effect  to  this  cause.  For  evaporation  takes  place  equally  in 
vacua  as  in  the  air ;  nay,  it  is  an  established  fact,  that  the  atmosphere  posi- 
tively retards  the  process,  and  that  one  of  the  best  means  of  accelerating  it, 
is  by  removing  the  air  altogether.  The  experiments  of  Dalton  prove  that 
heat  is  the  true  and  only  cause  of  the  formation  of  vapour.  He  finds  that 
the  actual  quantity  of  vapour,  which  can  exist  in  any  given  space,  is  de- 
pendent solely  upon  the  temperature.  If,  for  instance,  a  little  water  be  put 
into  a  dry  glass  flask,  a  quantity  of  vapour  will  be  formed  proportionate  to 
the  temperature.  If  a  thermometer  placed  in  it  stands  at  32°,  the  flask  will 
contain  a  very  small  quantity  of  vapour.  At  40°,  more  vapour  will  exist  in 
it ;  at  50°  it  will  contain  still  more ;  and  at  60°,  the  quantity  will  be  still 
further  augmented.  If,  when  the  thermometer  is  at  60°,  the  temperature  of 
the  flask  be  suddenly  reduced  to  40°,  then  a  certain  portion  of  vapour  will 
be  converted  into  water ;  the  quantity  which  retains  the  elastic  form  being 
precisely  the  same  as  when  the  temperature  was  originally  at  40°. 

It  matters  not  with  regard  to  these  changes,  whether  the  flask  is  full  of 
air,  or  altogether  empty ;  for  in  either  case,  it  will  eventually  contain  the 
same  quantity  of  vapour,  when  the  thermometer  is  at  the  same  height.  The 
only  effect  of  a  difference  in  this  respect,  is  in  the  rapidity  of  evaporation. 
The  flask,  if  previously  empty,  acquires  its  full  complement  of  vapour,  or,  in 
common  language,  becomes  saturated  with  it,  in  an  instant ;  whereas  the 
presence  of  air  affords  a  mechanical  impediment  to  its  passage  from  one 
part  of  the  flask  to  another,  and,  therefore,  an  appreciable  time  elapses  before 
the  whole  space  is  saturated. 

Dalton  found  that  the  tension  or  elasticity  of  vapour  is  always  the  same, 
however  much  the  pressure  may  vary,  so  long  as  the  temperature  remains 
constant,  and  there  is  liquid  enough  present  to  preserve  the  state  of  satura- 
tion proper  to  the  temperature.  If,  for  example,  in  a  flaccid  bladder  contain- 
ing a  little  water,  the  pressure  on  its  surface  be  diminished,  the  vapour  in 
the  interior  will  expand  proportionally,  and  consequently  for  the  moment 
will  diminish  in  elasticity,  because  the  tension  of  gaseous  substances  at  a 
constant  temperature  diminishes  in  the  same  ratio  as  the  volume  increases, 
or,  in  other  words,  the  elasticity  varies  inversely  as  the  volume ;  but  the  va- 
pour in  the  bladder  will  speedily  recover  its  original  tension,  since  the  water 
will  yield  an  additional  quantity  of  vapour,  proportional  to  the  increase  of 
space.  Again,  if  the  pressure  on  the  bladder  be  increased  so  as  to  diminish 
its  capacity,  the  temperature  remaining  constant,  the  tension  of  the  confined 
vapour  will  still  continue  unchanged,  because  a  portion  of  it  will  be  con- 
densed proportional  to  the  diminution  of  space ;  so  that,  in  fact,  the  remain- 
ing space  contains  the  very  same  quantity  of  vapour  as  it  did  originally. 
The  same  law  holds  good,  whether  the  vapour  is  pure,  or  mixed  with  air  or 
any  other  gas. 

The  elasticity  of  watery  vapour  at  temperatures  below  212°  was  carefully 
examined  by  Dalton,  (Manchester  Memoirs,  vol.  v.) ;  and  his  results,  toge- 
ther with  those  since  published  by  Dr.  Ure  in  the  Philosophical  Transac- 
tions for  1818,  are  presented  in  a  tabular  form  at  the  end  of  the  volume. 
They  were  obtained  by  introducing  a  portion  of  water  into  the  vacuum  of  a 
common  barometer,  and  estimating  the  tension  of  its  vapour  by  tfce  extent 
to  which  it  depressed  the  column  of  mercury  at  different  temperatures.  But 
Dalton  did  not  confine  his  researches  to  water;  he  extended  them  to  the 
vapour  of  various  liquids,  such  as  ether,  alcohol,  ammonia,  and  solution  of 

*  See  a  paper  by  the  late  Dr.  Marcet,  in  Nicholson's  Journal,  vol.  xxxiv. 


48  HEAT. 

chloride  of  calcium,  and  he  inferred  from  them  the  following1  law  :  —  that  the 
force  of  vapour  from  all  liquids  is  the  same,  at  equal  distances  above  or  be- 
low the  several  temperatures  at  which  they  boil  in  the  open  air.  Subse- 
quent observations  by  Dr.  Ure,  Despretz,  and  others,  have  proved  that  the 
law  is  far  from  universal,  and  that  it  fails  remarkably  at  temperatures  dis- 
tant from  the  point  of  ebullition  :  it  has,  indeed  been  abandoned  by  Dalton 
himself. 
A  knowledge  of  the  influence  of  heat  and  pressure  over  the  volume  of 

faseous  matter  is  elegantly  employed  in  calculating  the  density  of  vapour  ; 
ut  before  giving  the  mode  of  making  the  calculation,  it  will  be  useful  to 
explain  what  is  meant  by  density.  This  term  is  generally  used  synony- 
mously with  specific  gravity,  and  indicates  the  compactness  of  a  substance, 
or  the  quantity  of  ponderable  matter  contained  in  a  body  compared  with  the 
space  which  it  occupies.  The  density  of  a  substance  is  found  by  dividing 
its  weight  by  its  volume.  Thus,  if  d,  10,  v,  represent  the  density,  weight, 
and  volume  of  aqueous  vapour,  and  d't  w',  v',  the  density,  weight,  and  volume 

of  air,  then  d=  —  ,  andd'=—  7.     Hence,  comparing  these  densities,  d  : 
v  v 

d'  :  :  —  :—  rj  if  the  volumes  are  equal,  then  d  :  d'  :  :  w  :  w'  :  and  if  the 
v  v'  if 

weights   are   equal,   did':  :  —  :—  -.     Consequently,  the   density  of  sub- 
v    v 

stances  which  have  an  equal  volume,  is  directly  as  their  weight;  and  when 
the  weights  are  equal,  the  densities  are  inversely  as  the  volumes.  Accord- 
ingly, if  we  weigh  an  equal  volume  of  any  number  of  substances,  tempera- 
ture and  pressure  being  the  same  in  all,  the  density  of  each  respectively  will 
be  represented  by  its  weight.  Thus  Gay-Lussac  ascertained  that  if  a  cer- 
tain volume  of  air  at  212°  and  30  Bar.  weigh  1000  grains,  an  equal  volume 
of  aqueous  vapour,  at  the  same  temperature  and  pressure,  will  weigh  625 
grains  ;  and,  therefore,  the  density  of  steam  is  625  compared  to  that  of  air 
as  1000.  Atmospheric  air  is  universally  taken  as  a  term  of  comparison  for 
the  density  of  gaseous  substances,  and  pure  water  for  that  of  liquids  and 
solids. 

As  gases  expand  and  contract,  from  varying  temperature  and  pressure, 
according  to  the  same  laws,  it  follows  that  the  densities  found  at  any  one 
temperature  and  pressure  are  constant  for  all  others.  Thus  if  air  is  twice 
as  heavy  as  an  equal  volume  of  a  certain  gas,  both  being  weighed  at  32° 
and  30  Bar.,  the  same  ratio  will  be  found  at  32°  and  15  Bar,,  and  at  212° 
and  30  Bar.  The  same  remark  applies  to  vapours,  except  when  they  suffer 
condensation.  For  example,  the  density  of  air  and  stearn,  both  being  weigh- 
ed at  212°  and  30  Bar.,  is  expressed  by  1000  and  625  :  the  same  ratio  is  pre- 
served at  212°  and  at  any  other  pressure  less  than  30  Bar.,  because  in  that 
case  the  vapour  will  expand  like  air  ;  but  if  the  pressure  be  increased,  or  the 
temperature  diminished,  condensation  occurs,  and  the  density  of  the  vapour 
falls  below  625.  Hence  it  happens  that  the  density  of  vapours  varies  with 
the  temperature,  as  is  exemplified  by  the  following  table,  showing  the 
greatest  density  of  aqueous  vapour  at  the  temperatures  stated,  the  corre- 
sponding elasticities  agreeably  to  Dalton's  table,  and  the  weight  of  100  cubic 
inches  of  the  vapour. 

Elasticity  in  Weight  of 

Temp.  inches  of  mercury.  Density.  100  cubic  inches. 

32°  F.  0.2  5.7292  0.13716  grains. 

5Qo  0.375  103539  0.2478 

60°  0.524  14.18306  0.3394 

lOQo  j.860  46.6697  1.117 

150°  7.42  170.61  4.084 

30  625  14.96 


In  calculating  these  densities,  it  is  assumed  that  the  laws  of  gaseous  ex- 
pansion by  varying  heat  and  pressure  are  true,  —  that  the  density  of  steam  at 


HEAT.  49 

212°  F.  and  30  Bar.  is  625,  compared  to  air  at  the  same  temperature  and 
pressure  as  1000, — and  that  100  cubic  inches  of  air  at  212°  and  30  Bar. 
weigh  23.94  grains.  The  formula  for  the  calculation  is  thus  deduced : — If 
d  is  the  density  of  aqueous  vapour  at  any  pressure  p,  then  since  both  the 
density  and  elasticity  of  gaseous  substances  vary  inversely  as  their  volume, 
the  density  and  elasticity  are  proportional  to  each  other ;  so  that  d  :  625  :  : 

p:  30,  and  hence  eZ=625.|Jr.     This  gives  the  density  of  aqueous  vapour  at 
oU 

212°,  and  with  an  elasticity  equal  to  p.  In  this  state  the  vapour  is  rarefied, 
and  will  admit  of  being  cooled  down  to  a  certain  point,  but  not  lower,  say  to 
t  degrees  above  32°,  without  condensation ;  and  when  it  has  reached  that 
point,  its  density  has  acquired  a  maximum.  Its  elasticity  remains  un- 
changed, because  the  loss  of  tension  due  to  loss  of  heat  is  compensated  for 
by  diminution  of  volume.  Its  density  has  increased  exactly  in  the  same 
ratio  as  its  volume  has  diminished,  and,  therefore,  the  formula  of  page  21  in- 
verted will  give  the  increased  density  owing  to  decrease  of  temperature. 

Hence  we  shall  have  d =625.|p- .    For  example,  if  we  wish  to  cal- 

oU  4oU— |—  t 

culate  the  greatest  density  of  aqueous  vapour  at  100°  F.,  then  <=68,  and  the 
elasticity  of  that  vapour  by  Dalton's  table  is  1.86.  Inserting  these  values  of 

1  on  £cn 
t  and  p  in  the  preceding  formula,  we  shall  find  </=625.-^.— -==  46.6697. 

It  admits  of  inquiry  whether  liquids  of  weak  volatility,  such  as  mercury 
and  oil  of  vitriol,  give  off  any  vapour  at  common  temperatures.  An  opinion 
has  prevailed,  that  evaporation  not  only  takes  place  from  the  surface  of  these 
and  similar  liquids  at  all  times,  but  that  vapour  of  exceedingly  weak  ten- 
sion is  emitted  at  common  temperatures  from  all  substances  however  fixed 
in  the  fire,  even  from  the  earths  and  metals,  when  they  are  either  in  a  va- 
cuum, or  surrounded  by  gaseous  matter.  It  has  accordingly  been  supposed, 
that  the  atmosphere  contains  diffused  through  it  minute  quantities  of  the  va- 
pours of  all  the  bodies  with  which  it  is  in  contact ;  and  this  idea  has  been 
made  the  basis  of  a  theory  of  the  origin  of  meteorolites.  But  this  doctrine  has 
been  successfully  combated  by  Mr.  Faraday,  in  his  essay  on  the  Existence 
of  a  Limit  to  Vaporization,  published  in  the  Philosophical  Transactions  for 
1826.  The  argument  employed  by  Mr.  Faraday  is  founded  on  the  principle 
by  which  the  late  Dr.  Wollaston  accounted  for  the  limited  extent  of  the  at- 
mosphere. Since  the  volume  of  gaseous  substances  is  dependent  on  the 
pressure  to  which  they  are  subject,  the  air  in  the  higher  regions  of  the  atmo- 
sphere must  be  much  more  rare  than  that  in  the  lower,  because  the  former 
sustains  the  pressure  of  a  shorter  atmospheric  column  than  the  latter ;  so 
that  in  ascending  upwards  from  the  earth,  each  successive  stratum  of  air, 
being  less  compressed  than  the  foregoing,  is  likewise  more  attenuated.  Now 
it  is  found  experimentally,  that  the  elasticity  or  tension  of  any  gaseous  mat- 
ter diminishes  in  the  same  ratio  as  its  volume  increases ;  and,  accordingly, 
whenever  the  tenuity  of  a  portion  of  air,  owing  to  its  distance  from  the 
earth's  surface,  or  any  other  cause,  is  exceedingly  great,  its  tension  is  ex- 
ceedingly small.  Reasoning  on  this  principle,  Wollaston  conceived  that  at 
a  certain  altitude,  probably  at  a  distance  of  40  or  50  miles  from  the  surface 
of  the  earth,  the  rarefaction  and  consequent  loss  of  elastic  force  is  so  extreme, 
that  the  mere  gravity  of  the  particles  becomes  equal  to  their  elasticity,  and 
thus  puts  a  limit  to  their  separation. 

What  Wollaston  suggested  of  aerial  particles,  Mr.  Faraday  supposes  to 
occur  in  all  substances ;  and  this  supposition  is  perfectly  legitimate,  because 
gaseous  matter  in  general  is  subject  to  the  same  law  of  expansion,  and  is 
likewise  under  the  influence  of  gravity.  He  infers  that  every  kind  of  mat- 
ter ceases  to  assume  the  elastic  form,  whenever  the  gravitation  of  its  parti- 
cles is  stronger  than  the  elasticity  of  its  vapour.  The  loss  of  tension  ne- 
cessary for  effecting  this  object  may  be  accomplished  in  two  ways,  either 
by  extreme  dilatation,  or  by  cold.  For  substances  of  great  volatility,  such 

o 


50  HEAT. 

as  air,  and  most  gases,  the  former  condition  is  necessary  ;  because  the  de- 
gree of  cold  which  we  can  command  at  the  earth's  surface  diminishes  their 
tension  in  a  degree  quite  insufficient  to  destroy  their  elasticity.  But  the  vo* 
latility  of  numerous  bodies  is  so  small,  that  their  vapour  at  common  tempe- 
ratures approximates  in  rarity  to  the  air  at  the  limits  of  the  atmosphere,  and 
a  small  degree  of  cold  may  suffice  for  rendering  its  elasticity  a  force  inferior 
to  its  opponent,  gravity.  In  that  case,  the  vapour  would  be  entirely  con- 
densed. Mr.  Faraday  found  that  mercury,  at  a  temperature  varying  from 
60°  to  80°,  yields  a  small  quantity  of  vapour ;  but  in  winter  no  trace  of  va- 
pour could  be  detected.  Hence  it  is  inferred,  that  at  the  former  tempera- 
ture, the  elasticity  of  mercurial  vapour  is  slightly  superior  to  the  gravity  of 
its  particles,  and  that  in  cold  weather  the  latter  power  preponderates,  and 
puts  an  entire  check  to  the  evaporation  of  mercury.  The  earths  and  metals, 
which  are  more  fixed  than  mercury,  have  vapours  of  such  feeble  tension, 
that  the  highest  natural  temperature  is  unable  to  convert  them  into  vapour. 
Another  force,  which  co-operates  with  gravity  in  overcoming  elasticity,  is  the 
attraction  of  aggregation,  or  the  attraction  exerted  by  a  solid  or  liquid  on  the 
contiguous  particles  of  the  same  substance  in  the  gaseous  form.  This  argu- 
ment affords  very  sufficient  grounds  for  believing  that  the  vapours  of  earthy 
and  metallic  substances  are  never  present  in  the  atmosphere ;  and  Mr.  Fara- 
day has  proved  that  several  chemical  agents,  kept  in  a  confined  space  with 
moisture  during  four  years,  did  not  undergo  the  slightest  evaporation.  (Jour- 
nal of  the  R.  Inst.  i.  N.  S.) 

The  presence  of  vapour  has  a  considerable  influence  over  the  bulk  of 
gases ;  and  as  chemists  generally  determine  the  quantity  of  gaseous  sub- 
stances by  measure,  it  is  important  to  estimate  the  increase  of  volume  due 
to  the  presence  of  moisture.  The  mode  by  which  a  vapour  acts  is  obvious. 
When  tsvo  gases,  which  do  not  act  chemically  on  each  other,  are  intermin- 
gled, each  retains  the  elasticity  suited  to  its  volume,  exactly  as  if  the  other 
gas  were  absent ;  so  that  the  elasticity  of  the  mixture  is  the  sum  of  the 
elastic  forces  of  its  ingredients.  The  same  remark  applies  to  the  mixture 
of  gases  and  vapours.  If  a  few  drops  of  water  are  added  to  a  portion  of  dry 
air,  confined  in  a  glass  tube  over  mercury,  the  air  will  speedily  become 
saturated  with  vapour,  and  must  in  consequence  be  increased  in  bulk.  For 
the  elastic  power  of  the  vapour  being  added  to  that  previously  exerted  by 
the  gas  alone,  the  mixture  will  necessarily  exert  a  stronger  pressure  upon 
the  mercury  that  confines  it,  and  will  therefore  occupy  a  greater  space.  It 
is  equally  clear  that  the  degree  of  augmentation  will  depend  on  the  tempera- 
ture ;  for  it  is  the  temperature  alone  which  determines  the  elasticity  of  the 
vapour. 

As  the  elasticity  of  vapour  is  not  at  all  affected  by  mere  admixture  with 
gases,  it  is  easy  to  correct  the  fallacy  to  which  its  presence  gives  rise,  by 
means  of  the  data  furnished  by  the  experiments  of  Dalton.  The  formula 
for  the  correction  is  thus  deduced.  Let  n  be  the  bulk  of  dry  air  or  other 
gas  expressed  in  the  degrees  of  a  graduated  tube ;  p  the  elasticity  of  the 
dry  air,  equal  to  the  atmospheric  pressure  as  measured  by  a  barometer;  n' 
the  bulk  of  the  air  when  saturated  with  watery  vapour,  and  /  the  elasticity 
of  that  vapour.  (Biot's  Traite  de  Phys.  i.  303.)  Now  as  the  elasticity  of  a 
gas  for  equal  temperatures  is  inversely  as  its  volume,  it  follows  that  when 
the  dry  air  increases  in  bulk  from  n  to  w',  its  elasticity  will  diminish  in  the 
ratio  of  nr  to  n.  Hence  its  elasticity  ceases  to  be  =  p,  and  is  expressed  by 

^—f :  p  is  then  =^-?~j-/;  that  is,  the  elasticity  of  the  moist  air,  added  to 

the  elasticity  of  the  vapour  present,  is  equal  to  the  pressure  of  the  atmo- 
sphere.    From  this  last  equation  are  deduced  the  following  values :  pn-\~fnr 

^pnf ;  pn=pn' — fn1;  andw  =  — — — ~.    One  example  will  suffice  for 

showing  the  use  of  this  formula.     Having  100  measures  of  air  saturated 
with  watery  vapour  at  60°  F.,  the  barometer  standing  at  30  inches,  how 


HEAT.  51 

many  measures  would  the  air  occupy  if  quite  dry  ?     ri  =  100 ;  p  —  30 ;  /  = 
0.524,  the  tension  of  watery  vapour  at  60°,  according  to  Dalton's  table. 

100  X  (30—0.524)         100X29.476 
Hence  n  =  —5 = ^ =  98.25,  which  is  the  an- 

swer  required. 

The  preceding  formula  is  true  only  when  the  gas  is  confined  in  a  space 
which  readily  enlarges  proportionally  to  the  additional  pressure,  as  when  a 
tiibe  full  of  air  is  inverted  over  mercury.  If  the  gas  is  contained  in  a  space 
which  does  not  admit  of  enlargement,  and  a  drop  of  water  is  admitted,  the 
aqueous  vapour  adds  its  elastic  force /to  that  of  the  gas  p,  causing  the  pres- 
sure against  the  containing  vessel  to  be  equal  to  p-\-f> 

The  presence  of  aqueous  vapour  in  the  atmosphere  is  owing  to  evapora- 
tion. All  the  accumulations  of  water  upon  the  surface  of  the  earth  are  sub- 
jected by  its  means  to  a  natural  distillation  ;  the  impurities  with  which  they 
are  impregnated  remain  behind,  while  the  pure  vapour  ascends  into  the  air, 
gives  rise  to  a  multitude  of  meteorological  phenomena,  and  after  a  time 
descends  again  upon  the  earth.  As  evaporation  goes  on  to  a  certain  extent 
even  at  low  temperatures,  it  is  probable  that  the  atmosphere  is  never  abso- 
lutely free  from  vapour. 

The  quantity  of  vapour  present  in  the  atmosphere  is  very  variable,  in  con- 
sequence of  the  continual  change  of  temperature  to  which  the  air  is  subject. 
But  even  when  the  temperature  is  the  same,  the  quantity  of  vapour  is  still 
found  to  vary ;  for  the  air  is  not  always  in  a  state  of  saturation.  At  one 
time  it  is  excessively  dry,  at  another  it  is  fully  saturated ;  and  at  other  times 
it  varies  between  these  extremes.  This  variable  condition  of  the  atmosphere 
as  to  saturation  is  ascertained  by  the  hygrometer. 

A  great  many  hygrometers  have  been  invented ;  but  they  may  all  be  re- 
ferred to  three  principles.  The  construction  of  the  first  kind  of  hygrometer 
is  founded  on  the  property  possessed  by  some  substances  of  expanding  in  a 
humid  atmosphere,  owing  to  a  deposition  of  moisture  within  them ;  and  of 
parting  with  it  again  to  a  dry  air,  and  in  consequence  contracting.  Almost 
all  bodies  have  the  power  of  attracting  moisture  from  the  air,  though  in  dif- 
ferent proportions.  A  piece  of  glass  or  metal  weighs  sensibly  less  when 
carefully  dried,  than  after  exposure  to  a  moist  atmosphere ;  though  neither 
of  them  is  dilated,  because  the  water  cannot  penetrate  into  their  interior. 
Dilatation  from  the  absorption  of  moisture  appears  to  depend  on  a  deposition 
of  it  within  the  texture  of  a  body,  the  particles  of  which  are  moderately  soft 
and  yielding.  The  hygrometric  property,  therefore,  belongs  chiefly  to 
organic  substances,  such  as  wood,  the  beard  of  corn,  whalebone,  hair,  and 
animal  membranes.  Of  these,  none  is  better  than  the  human  hair,  which 
not  only  elongates  freely  from  imbibing  moisture,  but,  by  reason  of  its 
elasticity,  recovers  its  original  length  on  drying.  The  hygrometer  of  Saus- 
sure  is  made  with  this  material. 

The  second  kind  of  hygrometer  points  out  the  opposite  states  of  dryness 
and  moisture  by  the  rapidity  of  evaporation.  Water  does  not  evaporate  at 
all  when  the  atmosphere  is  completely  saturated  with  moisture ;  and  the 
freedom  with  which  it  goes  on  at  other  times,  is  in  proportion  to  the  dryness 
of  the  air.  The  hygrometric  condition  of  the  air  may  be  determined,  there- 
fore, by  observing  the  rapidity  of  evaporation.  The  most  convenient  method 
of  doing  this  is  by  covering  the  bulb  of  a  thermometer  with  a  piece  of  silk 
or  linen,  moistening  it  with  water,  and  exposing  it  to  the  air.  The  descent 
of  the  mercury,  or  the  cold  produced,  will  correspond  to  the  quantity  of 
vapour  formed  in  a  given  time.  Leslie's  hygrometer  is  of  this  kind. 

The  third  kind  of  hygrometer  is  on  a  principle  entirely  different  from  the 
foregoing.  When  the  air  is  saturated  with  vapour,  and  any  colder  body  is 
brought  into  contact  with  it,  deposition  of  moisture  immediately  takes  place 
on  its  surface.  This  is  often  seen  when  a  glass  of  cold  spring  water  is 
carried  into  a  warm  room  in  summer;  and  the  phenomenon  is  witnessed 
during  the  formation  of  dew,  the  moisture  appearing  on  those  substances  only 
which  are  colder  than  the  air.  The  degree  indicated  by  the  thermometer 


52  HEAT. 

when  dew  begins  to  be  deposited,  is  called  the  dew-point.  If  the  saturation 
be  complete,  the  least  diminution  of  temperature  is  attended  with  the  forma- 
tion of  dew ;  but  if  the  air  is  dry,  a  body  must  be  several  degrees  colder 
before  moisture  is  deposited  on  its  surface;  and  indeed  the  drier  the  atmo- 
sphere, the  greater  will  be  the  difference  between  its  temperature  and  the 
dew-point.  Attempts  were  made  to  estimate  the  hygrometric  state  of  the 
air  on  this  principle  by  the  Florentine  Academicians,  but  the  first  accurate 
method  was  introduced  by  M.  le  Roi,  and  since  adopted  by  Dalton.  It  con- 
sists simply  in  putting  cold  water  into  a  glass  vessel,  the  outside  of  which 
is  carefully  dried,  and  marking  the  temperature  of  the  liquid  at  which  dew 
begins  to  be  deposited  on  the  glass.  The  water  when  necessary  is  cooled 
either  by  means  of  ice  or  a  freezing  mixture.  A  convenient  form  of  appa- 
ratus is  a  small  cup  made  of  thin  silver,  nicely  gilt  on  the  outside,  capable 
of  holding  about  half  an  ounce  of  water,  and  fitted  into  a  case  of  turned 
wood  lined  with  cloth,  which  serves  as  a  stand  for  the  cup  during  an  ob- 
servation. The  water  is  cooled  by  successively  adding  a  few  grains  of  a 
powder  made  of  equal  parts  of  nitre  and  sal  ammoniac  intimately  mixed, 
stirring  with  the  bulb  of  a  small  thermometer.  As  soon  as  dew  is  deposited, 
the  temperature  is  noted ;  and  the  first  observation  is  corrected  by  waiting 
until  the  cup  and  its  contents  grow  warmer,  and  observing  the  temperature 
at  which  the  dew  begins  to  disappear.  The  last  observation  is  the  most 
trustworthy.  This  method,  when  deliberately  performed,  so  that  the  cup, 
the  solution,  and  the  thermometer,  should  have  time  to  acquire  the  same 
temperature,  is  susceptible  of  great  precision. 

The  hygrometer  of  Professor  Daniell,  described  in  his  Meteorological 
Essays,  acts  on  the  same  principle.  It  consists  of  a  cryophorus,  as  described 
at  page  46,  but  modified  somewhat  in  form,  and  containing  ether  instead  of 
water.  Within  one  of  its  balls  is  fixed  a  delicate  thermometer,  the  bulb  of 
which  is  partially  immersed  in  the  ether  so  as  to  indicate  its  temperature, 
and  the  other  ball  is  covered  with  muslin.  When  the  instrument  is  used, 
the  muslin  is  moistened  with  ether,  and  the  cold  produced  by  its  evaporation 
condenses  the  vapour  within  the  cryophorus,  and  causes  the  ether  to  evapo- 
rate rapidly  in  the  other  ball.  The  cold  thus  generated  chills  the  ether  itself 
and  the  ball  containing  it ;  and  in  a  short  time  its  temperature  descends  so 
low,  that  dew  is  deposited  on  the  surface  of  the  glass.  As  soon  as  this  takes 
place,  the  temperature  is  observed  by  the  thermometer. 

The  same  object  is  attained  in  a  still  easier  way  by  means  of  a  contri- 
vance described  by  Mr.  Jones  of  London,  in  the  Philos.  Trans,  for  1826,  and 
soon  after  in  the  Edin.  Philos.  Journal,  No.  xvii.  p.  155,  by  Dr.  Coldstream 
of  Leith.  It  consists  of  a  delicate  mercurial  thermometer,  the  bulb  of  which 
is  made  of  thin  black  glass,  and,  excepting  about  a  fourth  of  its  surface,  is 
covered  with  muslin.  On  moistening  the  muslin  with  ether,  the  temperature 
of  the  bulb  and  mercury  falls,  and  the  uncovered  portion  of  the  bulb  is  soon 
rendered  dim  by  the  deposition  of  moisture.  The  temperature  indicated  at 
that  instant  by  the  thermometer  is  the  dew-point.  It  appears  from  some 
remarks  by  Professor  Daniell  in  the  Quarterly  Journal  of  Science,  that  this 
hygrometer  was  originally  invented  in  Germany,  so  that  Mr.  Jones  and  Dr. 
Coldstream  are  second  inventors.  Professor  Daniell  considers  the  instru- 
ment inaccurate,  believing  that,  as  the  ether  is  applied  to  a  part  only  of  the 
bulb,  the  mercury  within  will  be  cooled  unequally ;  that  the  portion  corre- 
sponding to  the  covered  part  of  the  bulb  will  be  colder  than  the  mercury  op- 
posite to  the  exposed  part ;  and,  consequently,  that  the  dew-point  will  appear 
lower  than  it  ought  to  be.  This  objection  certainly  applies  when  the  muslin 
is  rendered  very  moist  with  ether,  and  the  temperature  of  the  bulb  is  rapidly 
reduced;  but  when  the  cooling  is  slowly  effected,  I  believe  the  indications  of 
this  hygrometer  to  be  at  least  as  correct  as  those  afforded  by  the  very  elegant, 
yet  more  costly  and  less  portable,  apparatus  of  Professor  Daniell.  For  facts 
confirmatory  of  this  opinion  the  reader  may  consult  an  essay  in  the  Edin- 
burgh Journal  of  Science,  No.  xiii.  p.  36,  by  Mr.  Foggo,  junior,  of  Leith. 

Jt  is  desirable  on  some  occasions,  not  merely  to  know  the  hygrometric 


HEAT.  53 

condition  of  air  or  gases,  but  also  to  deprive  them  entirely  of  their  vapour. 
This  may  be  done  to  a  great  extent  by  exposing  them  to  intense  cold ;  but 
the  method  now  generally  preferred  is  by  bringing  the  moist  gas  in  contact 
with  some  substance  which  has  a  powerful  chemical  attraction  for  water 
Of  these  none  is  preferable  to  chloride  of  calcium. 

CONSTITUTION  OF  GASES  WITH  RESPECT  TO  HEAT. 

The  experiments  of  Mr.  Faraday  on  the  liquefaction  of  gaseous  substances, 
appear  to  justify  the  option  that  gases  are  merely  the  vapours  of  extremely 
volatile  liquids.  Most  of  these  liquids,  however,  are  so  volatile,  that  their 
boiling  point,  under  the  atmospheric  pressure,  is  lower  than  any  natural 
temperature;  and  hence  they  are  always  found  in  the  gaseous  state.  By 
subjecting  them  to  great  pressure,  their  elasticity  is  so  far  counteracted  that 
they  become  liquid.  But  even  when  thus  compressed,  a  very  moderate  heat 
is  sufficient  to  make  them  boil ;  and  on  the  removal  of  pressure  they  resume 
the  elastic  form,  most  of  them  with  such  violence  as  to  cause  a  report  like 
an  explosion,  and  others  with  the  appearance  of  brisk  ebullition.  Inten«e 
cold  is  produced  at  the  same  time,  in  consequence  of  their  heat  passing  from 
a  sensible  to  an  insensible  state. 

The  process  for  condensing  gases  (Philos.  Trans,  for  1823)  consists  in  ex- 
posing  them  to  the  pressure  of  their  own  atmospheres.  The  materials  for 
producing  the  gas  are  put  into  a  strong  glass  tube,  which  is  afterwards 
sealed  hermetically,  and  bent  in  the 
middle,  as  represented  by  the  figure. 
The  gas  is  generated,  if  necessary,  by 
the  application  of  heat,  and  when  the 
pressure  becomes  sufficiently  great,  the  liquid  is  formed  and  collects  in  the 
free  end  of  the  tube,  which  is  kept  cool  to  facilitate  the  condensation.  Most 
of  these  experiments  are  attended  with  danger  from  the  bursting  of  the  tubes, 
against  which  the  operator  must  protect  himself  by  the  use  of  a  mask. 

The  pressure  required  to  liquefy  gases  is  very  variable,  as  will  appear  from 
the  following  table  of  the  results  obtained  by  Mr.  Faraday. 


Sulphurous  acid  gas    .         .        2  atmospheres  at            45°  F. 

Sulphuretted  hydrogen  gas 
Carbonic  acid  gas 

17 
36 

50° 
32° 

Chlorine  gas 

4 

60o 

Nitrous  oxide  gas 

50 

45o 

Cyanogen  gas 

3.6 

45o 

Arnmoniacal  gas 

6.5 

50° 

Muriatic  acid  gas 

40 

50o* 

*  The  general  law  in  regard  to  the  elasticity  or  tension  of  gases  is  that 
this  property  is  directly  proportional  to  the  compressing  force.  Oersted,  how- 
ever, has  shown,  that  it  does  not  always  hold ;  for  he  ascertained  that  con- 
densable  gases,  subjected  to  a  pressure  approaching  to  that  at  which  their 
condensation  would  take  place,  undergo  a  greater  diminution  of  volume  than 
is  proportional  to  the  pressure.  Berzelius  accounts  for  this  fact  by  supposing 
that  the  close  proximity  of  the  molecules  of  a  gas,  occasioned  by  great  pres- 
sure, brings  the  particles  more  completely  within  the  sphere  of  each  other's 
attraction,  and  thus  counteracts  the  separating  power  of  the  caloric,  which 
he  conceives  to  act  under  unfavourable  circumstances,  unless  the  ponderable 
particles  are  at  a  certain  distance  asunder.  (Berzelius,  Traite  de  Chimie,  i. 
83,  86.)  These  views  have  a  bearing  on  the  experiments  of  Mr.  Faraday 
cited  in  the  text. — Ed. 

5* 


54  LIGHT. 

SOURCES  OF  HEAT. 

The  sources  of  heat  maybe  reduced  to  six.  1.  The  sun.  2.  Combustion. 
3.  Electricity.  4.  The  bodies  of  animals  during  life.  5.  Chemical  action. 
6.  Mechanical  action.  All  these  means  of  procuring1  a  supply  of  heat,  ex- 
cept the  last,  will  be  more  conveniently  considered  in  other  parts  of  the  work. 

The  mechanical  method  of  exciting  heat  is  by  friction  and  percussion. 
When  parts  of  heavy  machinery  rub  against  one  another,  the  heat  excited, 
if  the  parts  of  contact  are  not  well  greased,  is  sufficient  for  kindling  wood. 
The  axletree  of  carriages  has  been  burned  from  this  cause,  and  the  sides  of 
ships  are  said  to  have  taken  fire  by  the  rapid  descent  of  the  cable.  Count 
Rumford  has  given  an  interesting  account  of  the  heat  excited  in  boring  can- 
non,  which  was  so  abundant  as  to  heat  a  considerable  quantity  of  water  to  its 
boiling  point.  It  appeared  from  his  experiments  that  a  body  never  ceases  to 
give  out  heat  by  friction,  however  long  the  operation  may  be  continued ;  and 
he  inferred  from  this  observation,  that  heat  cannot  be  a  material  substance, 
but  is  merely  a  property  of  matter.  Pictet  observed  that  solids  alone  produce 
heat  by  friction,  no  elevation  of  temperature  taking  place  from  the  mere  agi- 
tation of  fluids  with  one  another.  He  found  that  the  heat  excited  by  friction 
is  not  in  proportion  to  the  hardness  and  elasticity  of  the  bodies  employed. 
On  the  contrary,  a  piece  of  brass  rubbed  with  a  piece  of  cedar  wood,  produced 
more  heat  than  when  rubbed  with  another  piece  of  metal ;  and  the  heat  was 
still  greater  when  two  pieces  of  wood  were  employed. 


SECTION    II. 

LIGHT. 

OPTICS,  from  o:TTO<aa/,  I  see,  is  the  science  which  treats  of  light  and  vision. 
Of  the  nature  of  light  two  rival  theories  are  entertained.  According  to  some, 
and  this  was  the  theory  sanctioned  by  the  great  authority  of  Newton,  light 
is  an  emanation  from  luminous  bodies,  such  as  the  sun,  the  fixed  stars,  and 
incandescent  substances;  and  consists  of  inconceivably  minute  particlos, 
which  are  too  subtile  to  exhibit  the  common  properties  of  matter,  travel  in 
straight  lines  with  immense  velocity,  and  produce  the  sensation  of  light  by 
passing  into  the  eye,  and  striking  against  the  expanded  nerve  of  vision,  the 
retina.  Others  deny  to  light  a  separate  material  existence,  and  ascribe  its 
effects  to  the  vibrations  or  undulations  of  a  subtile  ethereal  medium  universal- 
ly present  in  nature,  the  pulses  of  which,  in  some  way  excited  by  luminous 
objects,  pass  through  space  and  transparent  bodies,  and  give  rise  to  vision  by 
impressing  the  retina,  in  the  same  way  as  pulsations  of  air  impress  the  nerve 
of  hearing  and  produce  the  sensation  of  sound.  The  latter,  the  undulatory 
theory  of  light,  which  was  formerly  maintained  by  Descartes,  Huygens,  and 
Euler,  but  subsequently  fell  into  disuse,  has  of  late  reeeived  powerful  support 
from  .Sir  John  Herschel  and  Professor  Airy,  who  in  their  analytic  researches 
on  polarized  light  find  the  phenomena  more  fully  explicable  on  the  undula- 
tory than  by  the  Newtonian  theory.  In  this,  however,  as  in  some  other  de- 
partments of  science,  either  of  two  theories  serves  the  purpose  of  classifying 
facts  and  explaining  most  of  the  phenomena*  the  advantage  lying  sometimes 
on  one  side  and  sometimes  on  the  other.  At  present,  the  strongest  evidence 
is  in  favour  of  the  undulatory  theory ;  but  as  the  views  of  Newton  are  still 
generally  used  and  understood,  and  readily  apply  to  all  the  subjects  which 
the  design  of  this  work  admits  of  being  noticed  here,  I  shall  continue  to 
adopt  it,  referring  those  who  are  prepared  to  study  the  undulatory  theory  to 
Sir  J.  HerschePs  article  on  light  in  the  Encyclopedia  Metropolitan^  and  to 
the  Mathematical  Tracts,  2d  edition,  of  Professor  Airy. 


LIGHT.  55 

Diffusion  of  Light. — Light  is  emitted  by  every  visible  point  of  a  luminous 
object,  and  is  equally  distributed  on  all  sides,  if  not  intercepted,  diverging 
like  radii  drawn  from  the  centre  to  the  circumference  of  a  circle.  Thus,  if 
a  single  luminous  point  were  placed  in  the  centre  of  a  hollow  sphere,  every 
point  of  its  concavity  would  be  illuminated,  and  equal  areas  would  receive 
equal  quantities  of  light.  The  smallest  portion  of  light  which  can  be  sepa- 
rated from  contiguous  portions,  is  called  a  ray  of  light.  Each  ray,  when  not 
interrupted  in  its  course,  and  while  it  remains  in  the  same  medium,  moves 
in  a  straight  line  ;  as  is  obvious  by  the  appearance  of  shadows  cast  by  the 
side  of  a  house,  or  of  a  sun-beam  admitted  through  a  small  aperture  into  a 
dark  room.  Owing  to  these  modes  of  distribution,  it  follows  that  the  quan- 
tity of  light  which  falls  upon  a  given  surface  decreases  as  the  square  of  its 
distance  from  the  luminous  object  increases,  the  same  law  which  regulates 
the  heating  power  of  a  hot  body.  (Page  9.) 

The  passage  of  light  is  progressive,  time  being  required  for  its  motion 
from  one  place  to  another.  By  astronomical  observations  it  is  found  that 
light  travels  at  the  rate  of  nearly  195,000  miles  in  a  second  of  time,  and 
would  require  about  eight  minutes  to  pass  from  the  sun  to  the  earth.  Owing 
to  this  prodigious  velocity,  the  light  emitted  in  the  firing  of  a  cannon  or  a 
sky-rocket  is  seen  by  different  spectators  at  the  same  instant,  whatever  may 
be  their  respective  distances  from  the  rocket,  the  time  required  for  light  to 
travel  100  or  1000  miles  being  inappreciable  to  our  senses. 

When  light  falls  upon  any  body,  it  may,  like  radiant  heat  (page  9,)  dis- 
pose of  itself  in  three  different  ways,  being  reflected,  refracted,  or  absorbed. 
The  phenomena  connected  with  the  two  former  modes  of  distribution  I  shall 
proceed  to  consider  in  succession;  while  those  of  absorbed  light  will  be  in- 
cluded under  the  head  of  Decomposition  of  Light. 

REFLECTION  OF  LIGHT. 

Light,  so  far  as  is  known,  is  not  reflected  by  purely  gaseous  bodies ;  but  it 
is  reflected  by  air  containing  floating  particles  of  moisture  in  the  form  of 
clouds,  and  by  all  solids  and  liquids,  though  in  very  different  degrees.  Bright 
metallic  surfaces,  such  as  polished  brass  and  silver,  or  clean  mercury,  reflect 
nearly  all  the  rays  which  fall  upon  them ;  while  those  which  are  dull  and 
rough,  reflect  but  few  of  the  rays.  The  reflection  of  light,  like  that  of  heat, 
takes  place  at  the  surface  of  bodies,  and  appears  influenced  rather  by  the 
condition  of  the  surface  than  by  the  nature  of  the  reflecting  body.  The  di- 
rection of  the  reflected  ray,  whatever  may  be  the  nature  or  figure  of  the  re- 
flecting surface,  is  regulated  by  these  two  laws. 

I.  The  incident  and  reflected  ray  always  lie  in  the  same  plane,  which 
plane  is  perpendicular  to  the  reflecting  surface. 

II.  The  incident  and  reflected  ray  always  form  equal  angles  with  the  re- 
flecting surface ;  or,  what  amounts  to  the  same,  the  angle  of  incidence  is 
always  equal  to  the  angle  of  reflection. 

Let  AB,  figure  1,  represent  a  plane  mirror,  ID  the  direction  of  a  ray  falling 
on  AB  at  the  point  D,  and  DP  a  line  perpendicular 
to  the  mirror  AB.   Then  a  plane  passing  through  j~ 
IDP  will  be  perpendicular  to  AB,  and,  by  the  first     x 
law,  the  reflected  ray  DR  will  lie  somewhere  in 
that  plane.     Also,  by  the  second  law,  the  angle 
of  reflection  RDP  must  be  equal  to  the  angle  of 
incidence  IDP.     Hence,  as  soon  as  the  direction 

of  the  incident  ray  is  given,  that  of  the  reflected 

ray  is  known  also.  /-\_  ID  IB 

These  laws  apply  equally  to  convex  and  concave  mirrors.    A  circle  or  any 


56 


Fig.  3. 


curve  may  be  viewed  as  a  polygon  with  very  short  sides  circumscribing  the 
curve,  as  shown  in  ab,  fig.  2 ;  and  on  this  prin- 
ciple a  tangent  tt'  at  any  point  D  of  a  curve  AB, 
may  be  taken  as  identical  at  the  touching  point 
with  the  curve  itself.  Similarly,  may  a  plane,  tan- 
gent to  a  curved  surface,  be  considered  as  part  of 
that  surface  at  the  point  of  contact.  The  action 
of  a  curved  mirror  may  hence  be  referred  to  that 
of  a  number  of  tangent  planes,  which  will  reflect 
light  agreeably  to  the  two  laws  above  mentioned. 
Thus,  let  AB,  fig.  3,  be  a  convex  mirror,  being  a  segment  of  a  sphere,  the 
centre  of  which  is  c;  let  ID,  if  D'  «-•-  n 

be  parallel  rays,  incident  at  D,  D'. 
The  dotted  lines  DP,  D'  p'  will  be 
respectively  perpendicular  to  the 
tangent  at  D,  D'  ;  the  angles  of  in- 
cidence are  IDP,  I'D'P'  ;  and  PDR, 
P'D'R',  the  angles  of  reflection. 
Parallel  rays  falling  on  a  convex 
mirror  are  obviously  scattered  or 
made  to  diverge. 

On  the  same  principle  must 
parallel  rays  falling  on  a  concave 
spherical  mirror,  as  represented 
by  fig.  4,  be  so  reflected  as  to  con- 
verge and  meet  together  at  one  point  F,  which  is  called  its  focus  for  .parallel 
rays,  or  its  principal  focus,  and  is  situated  midway  between  the  centre  c,  and 
the  axis  of  the  mirror  E.  The 
dotted  lines  represent  the 
perpendicular  to  the  tangent 
at  the  respective  points  of 
incidence,  D,  D'  d,  d'.  From 
the  same  figure  it  is  obvious 
that  the  diverging  rays  emit- 
ted by  a  light  placed  in  the 
focus  of  a  concave  mirror 
are  rendered  parallel  by  re- 
flection. If  the  light  be  pla- 
ced between  E  and  F,  then 
the  rays  will  continue  divergent  after  reflection.  On  placing  the  light  be- 
tween F  and  c,  the  incident  rays,  diverging  less  rapidly  than  when  the  light 
was  at  F,  will  converge  after  reflection,  and  meet  at  some  point  beyond  c, 
which  point  is  more  remote  from  c  the  nearer  the  light  is  to  F.  When  the 
light  is  at  c,  all  the  rays  are  reflected  back  to  c ;  since  each  ray  will  then  be 
perpendicular  to  the  tangent  at  its  point  of  incidence.  The  student  will 
easily  comprehend  these  statements,  if  he  will  but  take  rule  and  compass, 
and  draw  a  few  figures  for  himself. 

The  statement  above  made,  that  parallel  rays  are  collected  into  one  point 
by  reflection  from  a  concave  spherical  mirror,  is  not  strictly  correct.  When 
the  mirror  is  very  flat,  being  a  Fig.  5. 

small  segment  of  a  large  sphere, 
the  rays  meet  very  nearly  in  one 
point ;  but  they  are  far  from  doing 
so  when  the  curvature  of  the  mir-  < 
ror  is  considerable.  This  defect 
of  spherical  mirrors,  which  arises 
from  their  form,  and  is  termed 


Fig.  4. 


-x' 


spherical  aberration,  is  exhibited 
in  fig.  5,  where  the  rays  id,  i'  d' , 
near  the  axis,  meet  at  F;  whereas 
the  remoter  rays  ID,  i'  D'  are  collected  at  /.  The  consequence  of  such  aber- 


LIGHT.  57 

ration  is  a  confused  image,  a  defect  which  is  remedied  by  diminishing  cur- 
vature, and  cutting  off  by  screens  the  rays  most  distant  from  the  axis.  Pa- 
rabolic reflectors,  when  accurately  made,  are  entirely  free  from  this  incon- 
venience. 

The  position  in  which  objects  are  seen  after  being  reflected  will  now  be 
easily  understood.  Let  MN,  fig.  6,  be  an  arrow 
placed  before  a  plane  mirror  AB,  E  the  eye  of 
an  observer,  MC  Me  rays  emanating  from  the 
point  of  the  arrow,  and  N/  xd  rays  proceed- 
ing from  its  shaft.  The  only  reflected  rays 
which  reach  the  eye  are  those  that  fall  be- 
tween the  points  c  and  d.  Those  issuing 
from  any  single  point,  M,  continue  to  diverge 
at  the  same  rate  after  as  before  reflection; 
and,  though  they  are  reflected  and  enter  the 
eye  separately,  they  are  collected  together  by 
the  refracting  power  of  that  organ,  and  ap- 
pear to  the  observer  to  issue  from  a  point  m, 
at  which,  if  continued  back,  they  would  in- 
tersect. The  same  is  true  of  rays  issuing 
from  N,  and  from  all  points  intermediate  between  M  and  N.  By  inspecting 
the  figure  it  will  be  seen  that  each  part  of  the  image  mn  is  at  the  same  dis- 
tance behind  the  mirror  as  the  object  MN  is  before  it,  and  that  the  image  and 
object  have  the  same  length ;  consequences  which  flow  necessarily  from  the 
laws  of  reflection  and  the  known  properties  of  triangles. 

Again,  let  the  arrow  MN,  fig.  7,  represent  a  high  distant  object,  towards 

Fig.  7. 


which  a  spherical  mirror  AB  is  directed.  Rays  emanating  from  M  and  falling 
on  the  mirror  at  A,  E,  and  B,  will  be  so  reflected  that  they  all  meet  at  a  point 
m ;  rays  diverging  from  N,  and  reaching  the  same  points  of  the  mirror,  will 
be  collected  at  n  ;  and  all  points  intermediate  between  M  and  N  will  be  repre- 
sented along  the  line  mn,  forming  a  small  inverted  image  of  the  object.  As 
the  rays  prior  to  reflection  were  divergent,  their  focal  points  will  be  nearer 
the  centre  c  than  the  focus  for  parallel  rays.  The  image  mn,  will  be  much 
smaller  than  the  object,  the  ratio  of  their  lengths  being  directly  as  their  dis- 
tances from  the  mirror,  a  relation  which  the  geometric  reader  will  discover 
for  himself  by  inspecting  the  figure :  if  MN  be  1000  feet  from  the  mirror, 
and  mn  at  one  foot,  the  image  will  be  diminished  in  length  1000  times. 
Hence,  as  the  size  and  position  of  the  image  can  be  measured,  the  distance  of 
the  object  may  be  calculated  if  we  know  its  size ;  or  its  size  may  be  inferred 
from  a  knowledge  of  its  distance. 

The  construction  of  the  simple  reflecting  telescope  depends  on  the  prin- 
ciple just  explained.  The  small  size  of  the  image  is  compensated  for,  partly 
by  its  brightness,  since  each  point  is  formed  by  the  concentration  of  many 
rays,  and  partly  by  the  advantage  of  placing  the  eye  close  to  it.  In  order 
to  see  the  image  mn,  the  observer  may  place  in  the  focus  a  piece  of  ground- 
glass  or  tissue-paper ;  or,  a  hole  being  cut  in  the  mirror  at  E,  the  image 
may  be  received  on  a  small  plane  mirror  placed  in  the  focus,  and  be  reflect- 
ed to  the  observer  at  E.  Instead  of  using  a  plane  mirror  for  this  purpose, 
mn  may  be  considered  as  a  new  object,  and  be  reflected  by  a  second  smaller 


58 


concave  mirror  placed  between  mn  and  c,  and  in  front  of  AB  ;  for  the  con- 
verging rays  which  meet  at  any  point  m  of  the  image,  cross  each  other  at 
that  point,  and  then  diverge  exactly  as  though  the  place  of  the  image  were 
occupied  by  a  real  arrow.  The  second  mirror  may  be  so  placed  as  to  mag- 
nify the  image  mn  ;  and  the  second  image  may  be  still  further  enlarged  by 
a  convex  lens.  Compound  reflecting  telescopes  are  constructed  on  this  prin- 
ciple. 

The  arrangement  displayed  by  figure  7  is  exactly  that  of  a  simple  reflect- 
ing microscope,  provided  mn  be  viewed  as  a  small  real  object,  and  MN  as 
its  magnified  inverted  image.  If  mn  were  placed  in  the  principal  focus,  the 
reflected  rays  would  be  parallel,  and  hence  could  not  meet  to  form  an 
image  ;  but  if  situated  rather  beyond  the  principal  focus,  as  in  the  figure, 
then  the  rays  converge  after  reflection,  and  give  an  enlarged  image  of  the 
small  object.  The  ratio  of  the  length  of  the  object  and  image  will,  as  before, 
be  as  their  respective  distances  from  the  mirror. 

REFRACTION  OF  LIGHT. 

Light  traverses  the  same  transparent  medium,  such  as  air,  water,  or 
glass,  in  a  straight  line,  provided  no  reflection  occurs,  and  there  is  no 
change  of  density  ;  but  when  it  passes  from  one  medium  into  another,  or 
from  one  part  of  the  same  medium  into  another  of  a  different  density,  a 
change  of  direction  always  ensues  at  the  place  of  junction  of  the  media, 
except  when  the  ray  is  perpendicular  to  that  plane.  For  instance,  let 
AB  A'B',  fig.  8,  represent  a  vertical  Pigt  g. 

section  of  a  vessel  full  of  water,  and 
pp'  the  perpendicular  to  the  surface 
of  the  water  at  the  point  c.  Should 
a  ray  of  light  enter  the  water  perpen- 
dicularly to  its  surface,  as  in  the  line 


of  PC,  it  will  continue  on  its  course  j\ 
to  P'  without  deviation ;  but  if  it  de- 
scend obliquely,  as  in  the  direction  of 
ic,   it   will   suffer  a   bend  at  c,  and     j 
proceed   to   E,  instead   of  advancing  •**• 
along  the  dotted  line  to  F.     Converse- 


-n 


TO  '  /"*     " 


IB' 


ly,  were  a  ray  of  light  to  emanate  from  E  and  emerge  at  c,  it  would  not  ad- 
vance to  e,  but  take  the  direction  of  cr.  By  comparing-  the  direction  of  the 
refracted  ray  in  these  two  cases  in  relation  to  the  vertical  PP',  it  will  be  seen 
that  the  ray  approaches  the  perpendicular  in  entering  from  air  into  water, 
and  recedes  from  it  in  passing  out  of  water  into  air.  The  same  remark  ap- 
lies  to  the  passage  of  light  from  or  into  air  into  or  out  of  solid  or  liquid 
media  in  general. 

Bodies  differ  in  their  power  of  refracting  light.  In  general,  the  denser  a 
substance  is,  the  greater  is  the  deviation  which  it  produces.  If  in  fig.  8,  sul- 
phuric acid  were  mixed  with  the  water,  the  ray  ic  would  be  refracted  to  some 
point  between  E  and  G  ;  and  if  a  solid  cake  of  glass  were  substituted  for 
that  liquid,  the  refracted  ray  would  be  bent  down  to  eo.  But  this  is  far  from 
universal  :  —  alcohol,  ether,  and  olive  oil,  which  are  lighter  than  water,  have 
a  higher  refractive  power.  Observation  has  shown  it  to  be  a  law,  to  which 
no  exception  is  yet  known,  that  oils  and  other  highly  inflammable  bodies, 
such  as  hydrogen,  diamond,  phosphorus,  sulphur,  amber,  olive  oil,  and  cam- 
phor, have  a  refractive  power  which  is  from  two  to  seven  times  greater  than 
that  of  incombustible  substances  of  equal  density.  But  whatever  may  be  the 
refractive  power  of  bodies  in  relation  to  each  other,  refraction  is  always  go- 
verned by  the  two  following  laws,  discovered  in  1618  by  Snell,  though  usually 
ascribed  to  Descartes. 

1.  The  direction  of  the  incident  and  refracted  ray  is  always  in  a  plane 
perpendicular  to  the  surface  common  to  the  media. 


LIGHT.  59 

2.  The  sine  of  the  angle  of  incidence  and  the  sine  of  the  angle  of  refrac- 
tion are  in  a  constant  report  for  the  same  media. 

The  first  law  is  similar  to  the  first  law  of  reflection  already  explained. — 
(Page  55.)  To  explain  the  second  law, 
let  ABE,  fig.  9,  be  a  vertical  section  of  a 
refracting  medium,  pp7  the  perpendicular 
to  it,  ic  a  ray  of  light  incident  at  c,  and 
CE  the  refracted  ray.  Then  ICP  is  the 
angle  of  incidence,  and  ECP'  the  angle  of 
refraction.  Also  from  c,  as  a  centre, 
with  any  radius  ci,  and  in  the  plane  of 
the  ray  ICE,  draw  a  circle ;  and  from  the 
points  i  and  E,  where  the  course  of  the 
ray  cuts  the  circle,  let  fall  ia,  EC  at  right 
angles  to  PP'.  Then  may  la  be  consider- 
ed  the  sine  of  the  angle  of  incidence, 
and  EC  the  sine  of  the  angle  of  refraction. 
The  second  law  denotes  that  these  lines  are  for  each  substance  in  a  constant 
ratio,  whatever  may  be  the  direction  of  the  incident  ray.  In  the  figure  the 
sine  of  the  angle  of  refraction  is  to  the  sine  of  the  angle  of  incidence  as 
1  to  2 ;  and  this  ratio  being  once  determined,  each  ray  must  conform  itself 
to  it,  so  that  any  angle  of  incidence  being  given,  the  direction  of  the  refract- 
ed ray  may  be  foretold.  Thus,  if  ic  be  a  second  ray  incident  at  c,  of  which 
ib  is  the  sine  of  the  angle  of  incidence,  the  ray  will  be  bent  into  such  a 
course,  that  ed  shall  be  to  ib  as  1  is  to  2.  This  ratio  is  nearly  that  observed 
in  glass  made  of  one  part  of  flint  to  three  of  oxide  of  lead.  In  common 
flint-glass  the  ratio  is  nearly  as  1  to  1.6;  in  water  it  is  as  1  to  1.336  ;  in  oil 
of  cassia  as  1  to  1.641 ;  in  diamond  as  1  to  2.755 ;  in  phosphorus  as  1  to 
2.224;  and  in  melted  sulphur  as  1  to  2.148.  By  thus  representing  the  sine 
of  the  angle  of  refraction  by  1,  the  sines  of  the  angle  of  incidence  in  all 
bodies  refer  to  the  same  unit  of  comparison,  and  are,  therefore,  at  once  com- 
parable with  each  other:  such  numbers  are  called  indices  of  refraction,  and 
indicate  the  degree  of  refractive  power.  For  example,  the  index  of  re/rac- 
tion  for  water  is  1.336;  for  flint-glass  1.6;  and  for  diamond  2.755. 

By  means  of  SnelPs  laws  of  refraction,  and  with  a  knowledge  of  the  in- 
dices of  refraction,  the  course  of  a  ray  of  light  through  any  medium  may  be 
indicated,  whatever  may  be  the  nature  or  figure  of  that  medium,  or  the 
direction  of  the  ray.  The  refracting  substance  most  used  in  optics  is  glass, 
which  is  ground  into  different  forms,  such  as  prisms  and  lenses,  according 
to  the  purpose  for  which  it  is  designed.  One  of  the  simplest  cases  is  the 
refraction  of  a  plane  glass,  such  as  the  pane  of  a  window. 


Fig.  10. 


Let  ic,  fig.  10,  be  a  ray  incident  on  the 
upper  side,  AB,  of  a  plane  glass,  and  CE  the 
refracted  ray  :  at  its  exit  at  the  under  side, 
A'B',  which  is  parallel  to  AB,  it  will  be  re- 
fracted to  the  same  amount  as  at  its  en- 
trance, and  will  pass  on  in  the  direction  of 
EC,  appearing  to  an  observer  at  e  to  have 
come  along  the  line  I'E,  parallel  to  its  real 
course  ic.  Hence,  in  looking  at  an  object 
through  a  window,  it  is  not  seen  in  its  real 
position;  but  as  all  the  rays  are  similarly 
affected,  the  object  is  not  distorted,  provided 
the  opposite  sides  of  the  glass  are  really 
parallel. 

In  studying  the  influence  of  curved  media  on  light,  the  same  rule  is  to  be 
observed  as  in  reflection  by  curved  mirrors  (page  56) :  a  plane,  tangent  to 
the  curved  surface  at  each  point  of  incidence,  is  to  be  drawn  or  imagined, 
and  the  direction  of  the  ray  deduced  in  reference  to  that  plane.  On  apply- 
ing this  rule  to  convex  and  concave  lenses,  it  is  found  that  the  former  act 


60 


like  concave  mirrors,  and  tend  to  collect  the  refracted  rays  together ;  whereas 
a  concave  lens,  like  a  convex  mirror,  tends  to  scatter  them.  Figure  11  re- 
presents parallel  rays  falling  upon 
a  doubly  convex  lens,  the  two  curv- 
ed surfaces  of  which  are  shown  by 
the  vertical  section  AB.  The  ray  GF, 
which  falls  perpendicularly,  goes 
without  deviation  through  the  mid- 
dle or  axis  of  the  lens.  The  other 
rays  enter  and  quit  the  lens  so  as  to 
form  a  smaller  angle  on  one  side 
than  on  the  other,  and  the  acute 
angle  obviously  lies  on  the  side  towards  the  axis ;  every  ray  is  bent  towards 
that  axis  by  both  surfaces;  and  as,  from  the  figure  of  the  lens,  the  rays  most 
distant  from  the  axis  approach  the  lens  at  the  smallest  angle,  they  also  suffer 
the  greatest  refraction.  The  result  is,  that  the  rays  converge  and  meet  at  a 
point  F,  termed  the  focus  of  parallel  rays,  or  the  principal  focus.  Its  dis- 
tance from  c  varies  both  with  the  curvature  of  the  lens  and  the  refracting 
power  of  the  glass  with  which  it  is  made.  With  glass  of  the  same  quality 
the  focal  distance  depends  on  the  figure  of  the  lens,  the  greatest  convexity 
giving  the  shortest  focal  distance. 

As  the  lens  in  figure  11  brings  parallel  rays  into  a  focus  at  F,  it  is  obvious 
that  rays  diverging  from  a  luminous  object  placed  at  F  will  be  rendered 
parallel  by  the  same  lens,  the  course  of  the  rays  being  simply  reversed. 
Were  a  light  situated  between  F  and  c,  its  rays  would  diverge  so  much  that 
the  lens  could  not  render  them  parallel,  and  they  would  continue  divergent 
after  refraction.  On  removing  the  light  to  the  right  of  F,  the  incident  rays 
have  such  diminished  divergence  that  they  converge  after  refraction,  and 
meet  at  a  certain  distance  to  the  left  of  the  lens,  which  distance  diminishes 
as  the  light  recedes  from  F  ;  until  at  length,  when  the  luminous  object  is  so 
far  on  the  right  side  of  the  lens  that  the  incident  rays  may  be  considered 
parallel,  they  will  be  bent  into  a  focus  at  F'. 

Convex  lenses  are  subject  to  the  defect  called  spherical  aberration  equally 
with  concave  mirrors  (page  56),  and  from  the  same  cause.  The  spherical 
figure  of  a  convex  lens  causes  undue  refraction  of  the  rays  incident  near  its 
margin,  so  that  such  rays  have  a  shorter  focal  distance  than  those  incident 
near  its  axis.  The  defect  is  more  conspicuous  in  lenses  of  considerable  cur- 
vature than  in  flat  ones ;  and  it  may  be  remedied  by  intercepting  the  mar- 
ginal rays  with  an  opaque  screen,  or  by  forming  such  a  combination  of  lenses, 
as  may  augment  the  convergence  of  the  rays  near  the  axis  without  equally 
acting  on  those  more  distant  from  it.  In  the  eye  this  evil  is  averted  by  the 
substance  of  the  lens  increasing  in  density  from  its  margin  to  the  axis. 

The  action  of  concave  lenses, 
fig.  1 2,  is  the  opposite  to  that 
of  convex  lenses.  Drawing  a 
tangent  to  any  point  of  the 
curve,  and  constructing  the 
sines  of  incidence  and  refrac- 
tion, as  in  figure  9,  it  will  be 
found  that  parallel  rays  will 
be  so  refracted  by  both  sur- 
faces of  a  doubly  concave  lens, 
that  they  will  diverge  as  if  they  had  emanated  from  a  common  point  F  be- 
fore the  lens,  termed  its  principal  focus,  the  position  of  which  depends  on 
the  refracting  power  of  the  substance  of  the  lens,  as  well  as  on  its  curva- 
ture. Conversely,  the  rays  D'  D,  d,  d\  converging  towards  the  principal 
focus  F  of  a  doubly  concave  lens,  will  be  rendered  parallel  by  such  lens :  if 
their  original  convergence  were  less  rapid,  they  would  diverge  after  refrac- 
tion ;  but  if  their  convergence  were  to  a  point  between  F  and  c,  they  would 
still  converge  after  refraction,  and  meet  somewhere  along  the  axis  FG,  at  a 
point  less  remote  the  greater  the  original  convergence.  Rays  already  di- 


61 


Fig.  33. 


vergent  will  diverge  still  more  after  passing  through  a  concave  lens.  Thus 
the  influence  of  concave  lenses,  whether  concave  on  both  sides  or  on  one 
only,  is  exactly  opposed  to  that  of  convex  lenses.  The  former  tend  to  dimi- 
nish or  destroy  convergence,  and  to  render  diverging  rays  still  more  diver- 
gent ;  whereas  the  latter  diminish  or  destroy  divergence,  and  give  increased 
convergence  to  rays  already  convergent. 

The  refracting  properties  of  convex 
lenses  are  extensively  applied  in  the  con- 
struction of  refracting  telescopes  and  micro- 
scopes, the  object  being,  as  in  reflecting 
telescopes  and  microscopes,  to  obtain  a  dis- 
tinct small  image  of  u  large  distant  object,  or 
a  magnified  representation  of  a  near  small 
object.  The  nature  of  such  combinations  is 
illustrated  by  the  annexed  wood-cut,  Fig.  13, 
in  which  ab  is  a  doubly  convex  lens  acting 
on  rays  from  a  distant  object  represented 
by  the  arrow  MN.  As  the  incident  rays  are 
not  parallel,  but  divergent,  the  rays  from 
each  point  of  MN  will  be  collected  into  a 
focus  at  a  distance  behind  afe,  somewhat 
greater  than  the  focus  of  parallel  rays  /; 
and  an  inverted  image  nm  will  be  produced. 
The  length  of  the  image  to  that  of  the 
object  will  be  directly  as  their  respective 
distances  from  the  centre  of  the  lens  «6, 
exactly  as  in  the  reflecting  telescope  (page 
57).  If  MN  is  well  illuminated,  its  image 
will  be  bright,  since  each  point  is  formed 
by  the  confluence  of  many  rays.  The 
image  will  be  inverted;  the  rays  which 
emanate  from  the  upper  part  of  the  object 
forming  the  lower  part  of  the  image,  and 
conversely.  The  direction  in  which  the 
rays  from  any  point  M  meet,  may  be  found 
by  drawing  a  straight  line  from  M  through 
the  centre  c  of  the  lens  ab ;  for  as  the  ray 
MC  enters  the  lens  above  the  axis  at  the 
same  distance  as  it  quits  it  below  the  axis, 
the  second  refraction  is  exactly  the  reverse 
of  the  first,  and  the  ray  emerges  as  though 
it  had  passed  through  a  plane  glass  (fig.  10), 
— moving  onwards,  not  strictly  in  the  same 
straight  line,  (though  for  convenience  it  is 
usually  represented  as  such,)  but  in  a  line 
parallel  to  it.  Figure  13  likewise  exhibits  the  application  of  a  convex  lens 
in  the  construction  of  a  microscope.  For  if  nm  be  a  small  object  placed  a 
little  beyond  the  principal  focus  of  the  lens  06,  the  rays  will  be  so  refracted 
as  to  form  a  large  inverted  image  MN,  the  size  of  which  is  determined  by 
the  rule  above  mentioned. 

A  convex  lens  fitted  into  the  wall  of  a  darkened  chamber  constitutes  the 
arrangement  of  a  camera  obscura,  the  inverted  images  of  external  objects 
being  received  on  a  disc  of  paper  or  a  white  board.  In  the  simple  telescope 
the  lens  is  placed  at  the  extremity  of  a  tube  of  such  length  that  the  image 
may  be  formed  within  the  tube,  and  the  observer  looks  from  the  other  end 
at  the  image  formed  in  the  air.  The  eye  acts  on  the  same  principle.  Lu- 
minous rays  entering  the  transparent  parts  of  the  eye  are  refracted  by  the 
cornea  and  crystalline  lens,  and  are  brought  into  a  focus  at  the  bottom  of 
the  eye ;  an  inverted  image  of  external  objects  being  formed  upon  the  retina 
as  on  the  table  of  a  camera  obscura.  For  distinct  vision  it  is  necessary  that 

6 


62  LIGHT. 

this  image  should  be  formed  exactly  on  the  retina.  Hence  were  the  eye  an 
ordinary  lens,  having  an  invariable  focus,  our  range  of  vision  would  be  very 
narrow :  an  eye  fitted  for  seeing  at  a  distance,  would  be  useless  for  near 
objects;  and  persons  who  could  see  near  objects,  would  be  blind  to  remote 
ones.  Two  rays  emanating  from  a  distant  point  cannot  both  fall  upon  so 
small  an  object  as  the  eye,  unless  they  are  nearly  parallel ;  for  if  they  di- 
verged by  even  a  very  small  angle,  they  would  before  reaching  the  eye  sepa- 
rate by  an  interval  exceeding  the  diameter  of  the  cornea.  On  the  contrary, 
rays  in  rapid  divergence  may  enter  the  eye,  provided  the  point  from  which 
they  emanate  be  close  to  it ;  and  the  nearer  the  object,  the  more  divergent 
the  rays  which  enter.  When,  therefore,  we  observe  a  distant  landscape, 
then  successively  notice  nearer  and  nearer  objects,  and  lastly  cast  the  eyes 
upon  the  page  of  a  book  only  six  inches  distant,  we  receive  rays  coming 
from  a  multitude  of  different  objects,  each  set  of  rays  having  its  own  pecu- 
liar divergence,  and  requiring  a  separate  focus  ;  and  yet,  so  wonderful  is  the 
adjusting  power  of  the  eye,  a  single  minute  suffices  for  distinctly  seeing  all 
the  objects  so  beheld,  without  the  consciousness  of  an  effort. 

The  adjustment  of  the  eye  for  different  distances  appears  to  depend  on  a 
power  of  increasing  or  decreasing  the  distance  between  the  posterior  part  of 
the  eye  and  the  lens,  though  the  mechanism  by  which  this  is  accomplished 
is  unknown.  Some  ascribe  it  to  a  change  in  the  figure  of  the  whole  eye- 
ball, produced  by  the  muscles  which  move  the  eye ;  but  Sir  D.  Brewster,  I 
think  with  better  reason,  considers  the  position  of  the  lens  to  be  varied  by 
the  same  contractile  tissue  which  determines  the  movements  of  the  iris  and 
the  size  of  the  pupil.  To  this  adjusting  power,  however,  there  is  a  limit. 
The  distance  at  which  most  persons  see  small  objects  distinctly  is  about  six 
inches  :  at  shorter  distances  the  rays  are  so  divergent,  that  their  focal  point 
falls  behind  the  retina,  and  indistinct  vision  is  the  consequence.  Persons 
called  long-sighted  are  unable  to  see  near  objects  distinctly,  owing  to  a  weak 
refracting  power  of  the  eye,  due  to  deficient  convexity  or  density  in  the  hu- 
mours of  the  eye.  This  is  the  infirmity  of  advancing  life,  and  is  remedied 
by  convex  glasses,  which  cause  diverging  rays  to  be  parallel  or  slightly  con- 
vergent. In  short-sighted  persons  the  refractive  power,  either  from  undue 
convexity  or  undue  density  of  the  cornea  and  lens,  is  so  powerful,  that  all 
rays  which  do  not  diverge  rapidly  are  brought  to  a  focus  before  they  reach 
the  retina.  Youth  is  the  period  most  obnoxious  to  this  imperfection,  and 
assistance  is  derived  from  a  concave  glass,  which  causes  parallel  rays  to 
diverge,  and  thereby  counteracts  the  refracting  influence  of  the  eye. 

Objects  are  seen  erect,  though  their  images  on  the  retina  are  inverted. 
The  direction  in  which  each  point  of  an  object  is  seen,  may  depend  either 
on  the  direction  of  the  rays  which  form  it,  or  on  the  part  of  the  retina  which 
is  impressed.  On  inspecting  the  image  wm,  figure  13,  it  will  be  seen  that 
any  point  n  is  formed  by  a  multitude  of  rays  lying  within  the  angle  bna, 
each  of  which  has  a  different  direction  from  the  others ;  and  yet  when  a 
similar  collection  of  rays  is  formed  on  the  retina,  the  observer  sees  only  one 
point  N,  situated  nearly  in  the  direction  of  ncN.  Such  and  similar  consi- 
derations justify  the  belief,  that  the  direction  in  which  a  luminous  point  is 
seen  depends  not  on  the  direction  of  the  rays  as  they  enter  the  eye,  but  on 
the  part  of  the  retina  which  is  impressed.  Sir  D.  Brewster  contends  that  the 
line  of  visible  direction  is  always  perpendicular  to  that  part  on  which  a  ray 
falls ;  and  that,  as  the  eye-ball  is  nearly  a  perfect  sphere,  these  perpendiculars 
must  all  pass  through  the  centre  of  the  eye,  which  he  regards  as  the  centre 
of  visible  direction.  To  me  his  arguments  do  not  appear  conclusive.  Were 
this  opinion  true,  the  point  M'  of  an  arrow  M'N',  figure  14,  would  be  seen 
along  the  dotted  line  mop,  appearing  at  a  spot  very  remote  from  its  real  posi- 
tion. It  seems  more  consistent  with  observation  to  take  the  centre  of  the 
crystalline  lens,  or  rather  of  the  collective  humours  of  the  eye  regarded  as 
one  lens,  as  the  centre  of  visible  direction.  Through  that  centre  c,  fig.  14, 
all  the  directions  pass  from  each  part  of  an  image,  and  these  cross  each 
other:  the  lowest  part  of  an  image  is  the  highest  of  the  object,  and  the 
highest  of  the  image  the  lowest  of  the  object.  It  has  been  supposed  that  in 


63 


infancy  we  actually  see  erect  objects  inverted,  and  only  discover  that  they 
are  not  so  by  the  habitual  correction  derived  from  experience ;  but  this  fal- 
lacy has  been  fully  corrected  by  observation  on  persons  born  blind,  who 
first  obtained  the  power  of  vision  when  of  an  age  to  express  what  they  saw. 

The   apparent  size  of  objects  depends  on  their  dis-  Fig.  14. 

tance  from  the  eye.     Let  MC,  NC,  fig.  14,  be  rays  from       „    _  g 

the  extreme  points  of  the  arrow  MN,  which  cross  within 
the  eye  at  c  :  then  the  angle  MCN  is  termed  the  visual 
angle.  Mere  inspection  of  the  figure  shows  that  the 
larger  that  angle  is,  the  greater  will  be  the  arc  on  the 
retina  occupied  by  the  image  mn  ;  and  also  the  greater 
that  image,  the  greater  will  be  the  angle  included  by 
the  lines  of  visible  direction.  The  visual  angle  in  fact 
varies  exactly  as  the  arc  of  the  image  ;  and  as  that  an- 
gle may  be  found  with  sufficient  accuracy  by  drawing 
lines  from  the  eye  to  the  extremity  of  an  object,  it  af- 
fords a  convenient  expression  for  the  length  of  the  image: 
when  the  angles  are  small,  the  linear  magnitudes  of  two 
objects  are  nearly  in  the  same  ratio  as  their  visual  an- 
gles. If  a  second  arrow  M'  N',  twice  as  long  as  MN,  be 
placed  parallel  to  MN,  and  at  double  its  distance  from  the 
eye,  then,  by  the  properties  of  similar  triangles,  their 
visual  angles  will  be  equal,  and  their  apparent  magni- 
tude identical.  Conversely,  if  the  two  arrows  be  paral- 
lel, have  the  same  visual  angle  or  apparent  magnitude, 
and  one  be  twice  as  distant  as  the  other,  the  more  re- 
mote one  must  be  twice  as  long  as  the  other.  The  ap- 
parent magnitude  of  the  same  object  at  different  dis- 
tances may  be  inferred  on  the  same  principles.  Thus 
if  M'N'  approach  the  eye,  remaining  upright  all  the  time, 
the  visual  angle  will  enlarge,  and  at  half  the  distance  its 
length  will  appear  double;  or  if  MN  recede  from  the  eye, 
it  will  be  seen  under  a  smaller  angle,  and  appear  pro- 
portionally smaller,  until  at  double  the  distance  it  will 
seem  to  be  half  of  its  original  length.  In  fact,  the  ap- 
parent length  of  an  object  increases  in  the  same  ratio  as 
its  distance  from  the  eye,  or  more  strictly  from  the  point  ^ 
c  within  the  eye,  decreases.  A  large  object  seems  a  ^J 
mere  speck  at  a  great  distance  ;  and  a  minute  object  is 
invisible  unless  brought  close  to  the  eye.  To  bring  an 
object  near  the  eye  is  to  magnify  it.  A  tower  which  ap. 
pears  100  feet  high  to  a  person  4  miles  distant,  will  seem  200  feet  high  at  2 
miles,  and  400  at  1  mile ;  and  the  type  of  a  book  which  at  12  inches  appears  a 
line  in  length,  will  appear  two  lines  at  6  inches.  In  these  cases  it  is  the  linear 
magnitude  which  varies  inversely  as  the  distance :  the  superficial  extent,  or 
area,  will  vary  inversely  as  the  square  of  the  distance. 

The  foregoing  considerations  account  for  many  optical  phenomena.  Short- 
sighted  persons  see  minute  objects  better  than  those  who  have  a  long  sight ; 
because,  from  the  greater  refractive  power  of  their  eyes  (page  62),  they  can 
bring  the  object  closer  to  the  eye  than  those  who  are  long-sighted,  and  there- 
fore see  it  under  a  greater  angle.  But  by  aid  of  a  convex  lens  a  long-sighted 
person  may  attain  the  same  end.  Let  him  place  the  object  in  the  focus  of  a 
convex  lens,  and  the  eye  at  a  distance  behind  convenient  for  receiving  all 
the  rays  which  pass  through  it :  the  diverging  rays,  rendered  parallel  by  the 
lens,  are  readily  formed  by  the  eye  into  an  image  on  the  retina,  and  the  ob- 
ject is  seen  under  the  same  angle  as  though  the  eye  had  occupied  the  posi- 
tion of  the  lens.  This  arrangement  is  shown  by  figure  13,  where  MN  is  the 
object,  AB  the  lens,  and  E  the  eye  of  the  observer.  If  the  focal  distance  of 
the  lens  be  1  inch,  we  gain  the  same  advantage  as  though  the  eye  itself  were 


64  LIGHT. 

placed  at  one  inch  ;  and  taking  6  inches  as  the  shortest  distance  of  distinct 
vision  with  the  unaided  eye,  the  apparent  length  of  the  arrow  will  be  in- 
creased in  the  ratio  of  1  to  6.  With  a  lens  of  half  an  inch  focus,  the  increase 
will  be  as  £  to  6,  or  1  to  12 ;  and  if  the  focus  is  -Ajth  of  an  inch,  the  increase 
will  be  as  ^L  to  6,  or  1  to  60.  Convex  lenses  are  hence  familiarly  known 
by  the  name  of  magnifying  glasses. 

Convex  lenses  are  similarly  employed  in  the  construction  of  compound, 
microscopes  and  telescopes.  In  figure  13,  let  nm  represent  a  small  object 
formed  by  the  lens  db  into  an  enlarged  image  MN  :  that  image  may  be  viewed 
by  the  eye  at  the  distance  of  6  inches ;  but  by  interposing  a  second  lens  AB 
of  1  inch  focal  distance,  the  effect  is  the  same  as  though  the  eye  were  at  1 
inch,  and  thus  the  image  is  further  increased  in  the  ratio  of  1  to  6.  The 
lens  AB  is  called  the  eye-glass ,  and  ab  the  object-glass.  Again,  in  a  telescope, 
a  large  distant  object  is  represented  as  a  minute  image,  and  so  far  its  mag- 
nifying power  depends  on  the  eye  being  able  to  inspect  a  small  image  at  6 
inches  instead  of  the  large  object  at  a  great  distance.  For  instance,  a  tower 
400  feet  high,  formed  into  an  image  1  foot  long,  is  thereby  shortened  400 
times ;  but  as  that  image  can  be  seen  distinctly  at  the  distance  of  £  a  foot 
instead  of  the  object  at  400  feet,  the  elongation  due  to  this  cause  alone  is  as 
1  to  800.  The  apparent  height  of  the  tower  is  thus  diminished  400  times 
by  one  cause,  and  increased  800  times  by  another  ;  so  that  the  compound 
effect  is,  that  it  is  doubled.  But  by  employing  a  second  lens  with  a  very 
short  focus,  the  image  may  be  still  further  magnified  to  a  great  extent. 

Double  Refraction. — If  on  a  piece  of  paper  with  a  black  line  on  its  sur- 
face we  place  a  rhombohedron  of  Iceland-spar,  and  then  look  at  the  line 
through  the  crystal,  it  will  be  found  that  in  a  certain  position  the  line  ap- 
pears single  as  when  seen  through  water  or  glass ;  but  in  other  positions  of 
the  crystal  two  lines  are  visible  parallel  to  each  other,  and  separated  by  a 
distinct  interval.  The  light  in  passing  through  the  crystal  is  divided  into 
two  portions,  one  of  which  obeys  the  laws  of  refraction  already  explained 
(page  58);  whereas  the  other  portion  proceeds  in  a  wholly  different  direc- 
tion, and  hence  gives  the  appearance  of  two  objects  instead  of  one.  The 
former  is  termed  the  ordinary,  the  latter  the  extraordinary  ray.  This  phe- 
nomenon is  known  by  the  name  of  double  refraction^  and  has  been  witnessed 
in  many  crystallized  substances,  as  in  minerals  and  artificial  salts. 

Light,  transmitted  through  Iceland-spar  or  other  doubly  refracting  sub- 
stances, is  found  to  have  suffered  a  remarkable  change.  In  this  state  it  is 
distinguished  from  common  light  by  the  circumstance,  that,  when  it  falls 
upon  a  plate  of  glass  at  an  angle  of  56°  11',  it  is  almost  completely  reflected 
in  one  position  of  the  glass,  and  is  hardly  reflected  at  all  in  another :  if  re- 
flected when  the  plane  of  reflection  is  vertical,  no  reflection  ensues  when  the 
reflecting  plane  is  horizontal,  the  incident  angle  being  maintained  at  56°  11'. 
This  curious  property,  so  different  from  common  light,  has  been  theoreti- 
cally ascribed  to  a  kind  of  polarity  of  such  sort,  that  each  side  of  a  ray  of 
light  is  thought  to  have  a  character  different  from  the  two  adjacent  sides  at 
right  angles  to  it;  and  hence  the  origin  of  the  term  polarized  lightly  which 
this  property  is  distinguished.  Light  is  polarized  by  reflection  from  many 
substances,  such  as  glass,  water,  air,  ebony,  mother-of-pearl,  and  many  crys- 
tallized substances,  provided  the  light  is  incident  at  a  certain  angle  peculiar 
to  each  surface,  and  which  is  called  the  polarizing  angle.  Thus,  the  polar- 
izing angle  for  glass  is  56°  11',  and  for  water  53°  14';  that  is,  common 
light  reflected  by  glass  and  water  at  the  angles  stated  will  be  polarized. 

The  phenomena  of  double  refraction  and  polarized  light  constitute  a  de- 
partment of  optics  of  great  and  increasing  interest ;  but  it  is  too  remote  from 
the  pursuits  of  a  chemical  student  to  be  treated  of  at  length  in  this  work. 
Those  interested  in  such  studies  will  find  an  excellent  guide  in  Sir  D.  Brew- 
ster's  Treatise  on  Optics  in  the  Cabinet  Cyclopedia. 


LIGHT. 

DECOMPOSITION  OF  LIGHT. 


65 


The  analysis  of  light  may  be  effected  either  by  refraction  or  absorption. 
Newton,  who  discovered  the  compound  nature  of  solar  light,  effected  its  de- 
composition by  refraction,  employing  a  solid  piece  of  glass  bounded  by  three 
plane  surfaces,  well  known  under  the  name  of  the  prism.  His  mode  of  ope- 
rating consisted  in  admitting  a  ray  of  light  IG,  fig.  15,  into  a  dark  chamber 

Fig.  15. 


JL, 


through  a  window-shutter  DEF,  and  interposing  the  prism  ACB,  so  that  the 
ray  should  pass  obliquely  through  two  surfaces,  and  be  refracted  by  both. 
On  receiving  the  refracted  ray  upon  a  piece  of  white  paper  LM,  there  ap- 
peared, instead  of  a  spot  of  white  light,  an  oblong  coloured  surface  composed 
of  seven  different  tints,  called  the  prismatic  or  solar  spectrum.  On  subject- 
ing each  of  these  colours  to  refraction,  no  further  separation  was  accomplish, 
ed ;  but  on  causing  the  rays  separated  by  one  prism  to  pass  through  a  second 
of  the  same  power  and  in  an  inverted  position  CB«,  the  seven  colours  disap- 
peared, and  a  spot  of  white  light  appeared  at  H,  in  the  very  position  which  it 
would  have  occupied  had  both  prisms  been  absent.  From  such  and  similar 
experiments,  Newton  inferred  that  white  light  is  a  mixture  of  seven  colorific 
rays, — red,  orange,  yellow, green,  blue,  indigo,  and  violet;  and  that  the  sepa- 
ration of  these  primary  or  simple  rays  depended  on  an  original  difference  of 
refrangibility,  violet  being  the  most  refrangible  and  red  the  least  so. 

Though  a  prism  is  the  most  convenient  instrument  for  decomposing  light, 
the  separation  of  the  coloured  rays  is  more  or  less  effected  by  refracting 
media  in  general.  Lenses,  accordingly,  disperse  the  colorific  rays  at  the 
same  time  that  they  refract  them  ;  and  this  effect  constitutes  one  of  the 
greatest  difficulties  in  the  construction  of  telescopes,  insomuch  as  the  sepa- 
ration or  dispersion,  as  it  is  termed,  of  these  rays  diminishes  the  distinctness 
of  the  image.  The  combinations  by  which  the  defect  is  remedied  are  called 
achromatic. 

Newton's  analysis  of  light  led  him  to  explain  the  origin  of  the  colours  of 
natural  objects.  Of  opaque  bodies,  those  are  black  which  absorb  all  the 
light  that  falls  upon  them,  and  those  white  which  reflect  it  unchanged ;  the 
various  combinations  of  tints  are  the  consequence  of  certain  rays  being  ab* 
sorbed,  while  those  alone  whose  intermixture  produces  the  observed  colour 
are  reflected.  The  same  applies  to  transparent  media,  which  are  colourless 
like  pure  water  when  the  light  passes  through  unchanged,  but  are  coloured 
when  some  rays  are  transmitted  and  others  absorbed.  This  absorption  of  cer- 
tain rays  by  coloured  media,  such  as  glass  of  different  tints,  affords  another 
mode  of  decomposing  light ;  and  Sir  D.  Brewster  has  ingeniously  applied  it  to 
analyze  the  seven  colours  which  compose  the  prismatic  spectrum,  He  has 
proved  by  such  experiments,  what  has  been  maintained  before,  that  the  seven 
colours  of  the  spectrum  are  occasioned  not  by  seven,  but  by  three  simple  or 
primary  rays ;  namely,  the  red,  yellow,  and  blue.  These  rays  are  concen- 

6* 


66  LIGHT. 

trated  in  those  parts  of  the  spectrum  where  each  primary  colour  respectively 
appears ;  but  each  spreads  more  or  less  over  the  whole  spectrum,  the  mix- 
ture of  red  and  yellow  giving  orange,  of  yellow  and  blue,  green,  and  red 
with  blue  and  a  little  yellow  causing  the  violet. 

The  prismatic  colours,  according  to  the  experiments  of  Sir  W.  Herschel, 
differ  in  their  illuminating  power :  the  orange  illuminates  in  a  higher  de- 
gree than  the  red,  the  yellow  than  the  orange.  The  maximum  of  illumina- 
tion lies  in  the  brightest  yellow  or  palest  green.  The  green  itself  is  almost 
equally  bright  with  the  yellow ;  but  beyond  the  full  deep  green  the  illumi- 
nating power  sensibly  decreases.  The  blue  is  nearly  equal  to  the  red,  the 
indigo  is  inferior  to  the  blue,  and  the  violet  is  the  lowest  on  the  scale.  (Phil. 
Trans.  1800.) 

Solar  light,  both  direct  and  diffused,  possesses  the  property  of  exciting 
heat  as  well  as  light.  This  effect  takes  place  only  when  the  ray  is  absorb- 
ed, the  temperature  of  transparent  substances  through  which  it  passes,  or  of 
opaque  ones  that  reflect  it,  remaining  unchanged.  Hence  the  burning-glass 
and  concave  reflector  are  themselves  nearly  or  quite  cool,  though  at  the 
same  time  intense  heat  is  developed  at  the  focus.  The  intense  coldness  of 
the  higher  strata  of  the  air  arises  from  the  same  cause :  the  sun's  rays  pass 
on  unabsorbed  through  the  atmosphere ;  and  its  lower  strata  would  also  be 
very  cold,  did  they  not  receive  heat  by  contact  from  the  earth. 

The  absorption  of  light  is  much  influenced  by  the  nature  of  the  surface 
on  which  it  falls ;  and  it  is  remarkable  that  those  substances  which  absorb 
radiant  heat  most  powerfully,  are  also  the  best  absorbers  of  light.  Difference 
of  colour  has  still  greater  influence  over  the  absorption  of  light -than  of  sim- 
ple heat.  That  dark-coloured  substances  acquire  in  sunshine  a  higher  tem- 
perature than  light  ones,  may  be  inferred  from  the  general  preference  given 
to  the  latter  as  articles  of  dress  during  the  summer  ;  and  this  practice, 
founded  on  the  experience  of  mankind,  has  been  justified  by  direct  experi- 
ment. Dr.  Hooke,  and  subsequently  Dr.  Franklin,  proved  the  fact  by 
placing  pieces  of  cloth  of  the  same  texture  and  size,  but  of  different  colours, 
upon  snow,  and  allowing  the  sun's  rays  to  fall  upon  them.  The  dark- 
coloured  specimens  always  absorbed  more  heat  than  the  light  ones,  the 
snow  beneath  the  former  having  melted  to  a  greater  extent  than  under  the 
others ;  and  it  was  remarked  that  the  effect  was  nearly  in  the  ratio  of  the 
depth  of  shade.  Sir  H.  Davy  also  examined  the  subject,  and  arrived  at  the 
same  conclusions. 

Calorific  Rays  of  the  Spectrum. — The  rays  of  the  prismatic  spectrum  dif- 
fer from  each  other  in  their  heating  power  as  well  as  in  colour,  a  fact  first 
observed  by  Sir  W.  Herschel,  whose  attention  was  attracted  to  it  by  the  cir- 
cumstance, that,  in  viewing  the  sun  with  large  telescopes  through  differently 
coloured  glasses,  he  sometimes  felt  a  strong  sensation  of  heat  with  little 
light,  and  at  other  times  he  had  a  strong  light  with  little  heat.  This  obser- 
vation  led  to  his  celebrated  researches  on  the  heating  power  of  the  prismatic 
colours.  (Phil.  Trans.  1800.)  The  experiments  were  made  by  transmitting 
a  solar  beam  through  a  prism,  receiving  the  spectrum  on  a  table,  and 
placing  the  bulb  of  a  very  delicate  thermometer  successively  in  the  different 
parts  of  it.  While  engaged  in  this  inquiry,  he  observed  not  only  that  the 
red  was  the  hottest  ray,  but  that  there  was  a  point  a  little  beyond  the  red, 
altogether  out  of  the  spectrum,  where  the  thermometer  stood  higher  than  in 
the  red  itself.  By  repeating  and  varying  the  experiment,  he  found  that  the 
most  intense  heating  power  was  always  beyond  the  red  ray,  where  there 
was-  no  light  at  all ;  and  that  the  heat  progressively  diminished  in  passing 
from  the  red  to  the  violet,  where  it  was  least.  He  hence  inferred  that  there 
exists  in  the  solar  beam  a  distinct  kind  of  ray,  which  causes  heat  but  not 
light ;  and  that  these  rays,  from  being  less  refrangible  than  the  luminous 
ones,  deviate  in  a  smaller  degree  from  their  original  direction  in  passing 
through  the  prism. 

All  succeeding  experimenters  confirm  the  statement  of  Sir  W.  Herschel, 
that  the  prismatic  colours  differ  in  heating  power  ;  but  they  do  not  agree  as 


LIGHT.  67 

to  the  spot  where  the  heat  is  greatest.  Sir  H.  Englefield,  Davy,  and  others 
affirmed  with  Herschel  that  it  is  beyond  the  red  ray;  while  others,  and  in 
particular  Leslie,  contended  that  it  is  in  the  red  itself.  The  observations  of 
the  late  Dr.  Seebeck  (Edin.  Journ.  of  Science,  i.  358),  have  explained  these 
contradictory  statements,  by  showing  that  the  point  of  greatest  heat  varies 
with  the  kind  of  prism  which  is  employed  for  forming  the  spectrum.  When 
he  used  a  prism  of  fine  flint-glass,  the  greatest  heat  was  uniformly  beyond 
the  red ;  with  a  prisrn  of  crown-glass,  the  red  itself  was  the  hottest  part ; 
and  with  a  prism  externally  of  glass,  but  containing  water  within,  the  maxi- 
mum heat  was  neither  in  the  red  itself,  nor  beyond  it,  but  in  the  yellow. 
These  experiments  have  been  confirmed  by  Melloni,  who  has  succeeded  with 
a  prism  of  rock-salt  in  separating  the  spot  of  maximum  heat  from  the  colour- 
ed part  of  the  spectrum  by  a  much  greater  interval  than  had  been  done  pre- 
viously :  his  curious  and  surprising  results  appear  to  me  to  dissipate  all  re- 
maining doubt  as  to  the  existence  in  solar  light  of  calorific  rays  distinct 
from  those  rays  which  produce  colour.  He  also  traces  the  cause  of  the  va- 
rying position  of  the  maximum  heat  to  the  unequal  absorptive  power  of  dif- 
ferent transparent  media.  Rock-salt  is  freely  transmissible  to  the  least  re- 
frangible calorific  rays  in  solar  light,  but  absorbs  a  greater  proportion  of 
those  which  are  more  refrangible;  whereas  the  latter  pass  more  easily 
through  flint-glass,  yet  more  readily  through  crown-glass,  and  with  still 
greater  freedom  through  water.  Hence  in  successively  employing  a  prism 
of  these  four  substances  in  the  order  stated,  the  spot  of  greatest  heat  is  found 
to  be  far  beyond  the  red,  then  approaches  the  red,  next  is  in  the  red  itself, 
and  lastly  in  the  yellow  part  of  the  spectrum. — The  preceding  facts  go  far  to 
prove  that  most,  if  not  all,  of  the  heating  power  ascribed  to  light  is  due,  not 
to  the  absorption  of  luminous  rays,  but  to  that  of  the  heat  by  which  they  are 
accompanied. 

Chemical  Rays. — It  has  long  been  known  that  solar  light  is  capable  of 
producing  powerful  chemical  changes.  One  of  the  most  striking  instances 
of  it,  is  its  power  of  darkening  the  white  chloride  of  silver,  an  effect  which 
takes  place  slowly  in  the  diffuFed  light  of  day,  but  in  the  course  of  two  or 
three  minutes  by  exposure  to  sunshine.  This  effect  was  once  attributed  to 
the  influence  of  the  luminous  rays ;  but  it  appears  from  the  observations  of 
Ritter  and  Wollaston,  that  it  is  owing  to  the  presence  of  certain  rays  that 
excite  neither  heat  nor  light,  and  which,  from  their  peculiar  agency,  are 
termed  chemical  rays.  It  is  found  that  the  greatest  chemical  action  is  ex- 
erted just  beyond  or  at  the  verge  of  the  violet  part  of  the  prismatic  spec- 
trum ;  that  the  spot  next  in  energy  is  the  violet  itself;  and  that  the  property 
gradually  diminishes  in  advancing  to  the  green,  beyond  which  it  seems 
wholly  wanting.  It  hence  follows  that  the  chemical  rays  are  still  more  re- 
frangible than  the  luminous  ones,  in  consequence  of  which  they  are  dis- 
persed in  part  over  the  blue,  indigo,  and  violet,  but  in  the  greatest  quantity 
at  the  extreme  border  of  the  latter. 

Magnetizing  Rays. — The  more  refrangible  rays  of  light  have  been  thought 
to  possess  the  property  of  rendering  steel  and  iron  magnetic.  The  existence 
of  this  property  was  first  asserted  by  Dr.  Morichini  of  Rome.  Other  ob- 
servers subsequently  failed  in  obtaining  the  same  results ;  but  in  the  year 
1826  the  fact  appeared  to  be  decisively  established  by  the  learned  and  ac- 
complished Mrs.  Somerville,  in  an  essay  published  in  the  Transactions  of 
the  Royal  Society.  Since  that  period  the  subject  has  been  re-examined  by 
MM.  Riess  and  Moser.  They  object  to  Mrs.  Somerville's  results,  that  her 
method  of  ascertaining  the  magnetic  state  of  the  needles  used  in  the  experi- 
ments was  not  sufficiently  precise  :  they  found  that  the  duration  of  the  oscil- 
lations of  needles  is  exactly  the  same  whether  they  are  made  to  oscillate  in 
the  shade  or  underexposure  to  the  concentrated  violet  ray  of  the  spectrum,  a 
result  which  could  not  occur  had  even  a  feeble  degree  of  magnetism  been 
excited  ;  and  they  accordingly  deny  the  supposed  magnetizing  power  of  light. 
(Edin.  Journ.  of  Science,  ii.  225.) 


68  LKSHT. 

TERRESTRIAL  LIGHT. 

Under  this  head  are  included  all  kinds  of  artificial  light.  The  common 
method  of  obtaining  such  light  is  by  the  combustion  of  inflammable  matter, 
which  gives  out  so  much  heat  that  the  burning  substance  is  rendered  lumi- 
nous in  the  act  of  being  burned.  All  bodies  begin  to  emit  light  when  heat 
is  accumulated  within  them  in  great  quantity  ;  and  the  appearance  of  glow- 
ing or  shining,  which  they  then  assume,  is  called  incandescence.  The  tem- 
perature at  which  solids  in  general  begin  to  shine  in  the  dark  is  between 
600°  and  700°  F.;  but  they  do  not  appear  luminous  in  broad  daylight  till 
they  are  heated  to  about  1000°.  Th«  colour  of  incandescent  bodies  varies 
with  the  intensity  of  the  heat.  The  first  degree  of  luminousness  is  an  ob- 
scure red.  As  the  heat  augments,  the  redness  becomes  more  and  more  vivid, 
till  at  last  it  acquires  a  full  red  glow.  If  the  temperature  still  increase,  the 
character  of  the  glow  changes,  and  by  degrees  it  becomes  white,  shining 
with  increasing  brilliancy  as  the  heat  augments.  Liquids  and  gases  likewise 
become  incandescent  when  strongly  heated ;  but  a  very  high  temperature  is 
required  to  render  a  gas  luminous,  more  than  is  sufficient  for  heating  a  solid 
body  even  to  whiteness.  The  different  kinds  of  flame,  as  of  the  fire,  candles, 
and  gas  light,  are  instances  of  incandescent  gaseous  matter. 

Artificial  lights  differ  in  colour,  and  accordingly  exhibit  different  appear- 
ances when  transmitted  through  a  prism.  The  white  light  of  incandescent 
charcoal,  which  is  the  principal  source  of  the  light  from  candles,  oils,  and 
the  illuminating  gases,  contains  the  three  primary  colorific  rays,  the  red, 
yellow,  and  green.  The  dazzling  light  emitted  by  lime  intensely  heated, 
first  proposed  by  Lieut.  Drummond  for  the  trigonometrical  survey  (Phil. 
Trans.  1830),  and  of  late  so  successfully  applied  by  Messrs.  Cooper  and  Carey 
for  their  gas  microscope,  gives  the  prismatic  colours  almost  as  bright  as  in 
the  solar  spectrum.  The  light  emitted  by  iron  feebly  incandescent  consists 
principally  of  the  blue  and  red  rays,  as  does  the  red  light  obtained  by  means 
of  strontia  and  lithia ;  that  from  ignited  boracic  acid  is  such  a  mixture  of  the 
blue  and  yellow  rays  as  constitutes  green ;  and  incandescent  soda  emits  a 
yellow  light,  almost  wholly  free  from  the  rays  which  cause  the  red  and  blue 
colours. 

Artificial  light  differs  from  solar  light  in  containing  heat  in  two  states.  It 
contains  simple  radiant  heat  like  that  radiated  from  a  body  not  luminous, 
and  which  may  be  separated  by  transmission  through  a  plate  of  moderately 
thick  glass ;  but  the  light  so  purified  still  heats  any  body  which  absorbs  it, 
and  is  thus  believed  to  possess  calorific  rays  associated  with  its  luminous 
rays  like  those  in  solar  light,  and  like  them  to  be  susceptible  of  refraction  by 
transparent  media.  Thus,  Mr.  Daniell  found  that  the  rays  from  incandes- 
cent lime  were  concentrated  by  convex  lenses,  and  set  fire  to  phosphorus 
placed  in  the  focus.  (Phil.  Mag.  N.  S.  ii.  59.)  The  heat  excited  under  such 
circumstances  may  of  course  be  ascribed  to  the  absorption  of  luminous  rays; 
but  the  experiments  of  Herschel  with  solar  light  suggest  the  idea  that  calori- 
fic rays  capable  of  transmission  through  glass,  may  also  exist  in  artificial 
light,  and  this  opinion  has  been  verified  by  the  late  researches  of  Melloni. 
Nothing  could  show  the  fact  in  a  more  distinct  point  of  view  than  the  disco- 
very, by  this  ingenious  experimenter,  that  transparent  media  are  unequally 
permeable  by  colorific  and  calorific  rays :  substances  almost  opaque  in  re- 
gard to  light,  were  found  to  give  free  passage  to  calorific  rays ;  while  others 
of  the  most  perfect  transparency  are  little  permeable  to  heat.  Melloni  has 
consequently  introduced  a  distinct  name,  diathermanous  (from  <f;d  and  3-«g- 
fjKttvci)  to  denote  free  permeability  to  heat,  just  as  diaphanous  is  formed  from 
ef/gt  and  QO.IVOO.  Rock-salt  is  remarkably  diathermanous  or  transcalent^ 
greatly  more  so  than  glass  of  far  greater  transparency.  Chloride  of  sulphur 
of  a  reddish-brown  tint  is  more  diathermanous  than  nut  and  olive  oil  of  a  light 
yellow  colour,  and  these  than  the  purest  ether,  alcohol,  and  water,  the  trans- 
parency of  these  substances  being  in  the  opposite  order.  A  great  many  facts 


LIGHT.  69 

of  a  like  kind  are  enumerated  in  Melloni's  essay,  which  is  highly  deserving 
of  attention.  The  source  of  heat  was  an  argand  oil-lamp,  and  the  tempera- 
ture measured  by  the  thermo-multiplier  (page  11).  (An.  de  Ch.  et  de  Ph. 
liii.  5.) 

The  chemical  agency  of  artificial  light  is  analogous  to  that  from  the  sun. 
In  general  the  former  is  too  feeble  for  producing  any  visible  effect ;  but  light 
of  considerable  intensity,  such  as  that  from  ignited  lime,  darkens  chloride  of 
silver,  and  seems  capable  of  exerting  the  same  chemical  agencies  as  solar 
light,  though  in  a  degree  proportionate  to  its  inferior  brilliancy.  (An.  of 
Phil,  xxvii.  451.) 

Light  is  emitted  by  some  substances  either  at  common  temperatures  or  at 
a  degree  of  heat  disproportioned  to  the  effect,  giving  rise  to  an  appearance 
which  is  called  phosphorescence.  This  is  exemplified  by  a  composition  termed 
Canton's  phosphorus,  made  by  mixing  three  parts  of  calcined  oyster-shells 
with  one  of  the  flowers  of  sulphur,  and  exposing  the  mixture  for  an  hour  to 
a  strong  heat  in  a  covered  crucible.  The  same  property  is  possessed  by 
chloride  of  calcium  (Homberg's  phosphorus),  anhydrous  nitrate  of  lime 
(Baldwin's  phosphorus),  some  carbonates  and  sulphates  of  baryta,  strontia,  and 
lime,  the  diamond,  some  varieties  of  fluor-spar  called  chlorophane,  apatite, 
boracic  acid,  borax,  sulphate  of  potassa,  sea-salt,  and  by  many  other  sub- 
stances. Scarcely  any  of  these  phosphori  act  unless  they  have  been  pre- 
viously exposed  to  light:  for  some,  diffused  day-light  or  even  lamp-light 
will  suffice ;  while  others  require  the  direct  solar  light,  or  the  light  of  an 
electric  discharge.  Exposure  for  a  few  seconds  to  sunshine  enables  Canton's 
phosphorus  to  emit  light  visible  in  a  dark  room  for  several  hours  afterwards. 
Warmth  increases  the  intensity  of  light,  or  will  renew  it  after  it  has  ceased ; 
but  it  diminishes  the  duration.  When  the  phosphorescence  has  ceased  it 
may  be  restored,  and  in  general  for  any  number  of  times,  by  renewed  expo- 
sure to  sunshine;  and  the  same  effect  may  be  produced  by  passing  electric 
discharges  through  the  phosphorus.  Some  phosphori,  as  apatite  and  chloro- 
phane, do  not  shine  until  they  are  gently  heated ;  and  yet  if  exposed  to  a  red 
heat,  they  lose  the  property  so  entirely  that  exposure  to  solar  light  does  not 
restore  it.  Mr.  Pearsall  has  remarked  that,  in  these  minerals,  the  phospho- 
rescence, destroyed  by  heat,  is  restored  by  electric  discharges ;  that  speci- 
mens of  fluor-spar,  not  naturally  phosphorescent,  may  be  rendered  so  by 
electricity ;  and  that  this  agent  exalts  the  energy  of  natural  phosphori  in  a 
very  remarkable  degree.  (R.  Inst.  Journal,  N.  S.  i.)  The  theory  of  these 
phenomena,  like  that  of  light  itself,  is  very  obscure.  They  have  been  attri- 
buted to  direct  absorption  of  light,  and  its  subsequent  evolution ;  but  the  fact, 
that  the  colour  of  the  light  emitted  is  more  dependent  on  the  nature  of  the 
phosphorescent  body  than  on  the  colour  of  the  light  to  which  it  was  exposed, 
seems  inconsistent  with  this  explanation.  Chemical  action  is  not  connected 
with  the  phenomena ;  for  the  phosphori  shine  in  vacuo,  and  in  gases  which 
do  not  act  on  them,  and  some  even  under  water. 

Another   kind   of  phosphorescence  is  observable   in  some  bodies  when 
strongly  heated.     A  piece  of  lime,  for  example,  heated  to  a  degree  which 
.   would  only  make  other  bodies  red,  emits  a  brilliant  white  light  of  such  in- 
tensity that  the  eye  cannot  support  its  impression. 

A  third  species  of  phosphorescence  is  observed  in  the  bodies  of  some  ani- 
mals, either  in  the  dead  or  living  state.  Some  marine  animals,  and  particu- 
larly fish,  possess  it  in  a  remarkable  degree.  It  may  be  witnessed  in  the 
body  of  the  herring,  which  begins  to  phosphoresce  a  day  or  two  after  death, 
and  before  any  visible  sign  of  putrefaction  has  set  in.  Sea-water  is  capable 
of  dissolving  the  luminous  matter ;  and  it  is  probably  from  this  cause  that 
the  waters  of  the  ocean  sometimes  appear  luminous  at  night  when  agitated. 
Tiiis  appearance  is  also  ascribed  to  the  presence  of  certain  animalcules, 
which,  like  the  glow-worm  of  this  country,  or  the  fire-fly  of  the  West  Indies, 
are  naturally  phosphorescent. 

Light  is  sometimes  envolved  during  the  process  of  crystallization.  This  is 
exemplified  by  a  tepid  solution  of  sulphate  of  potassa  in  the  act  of  crystal- 


70  LIGHT. 

lizing;  and  it  has  been  likewise  witnessed  under  similar  circumstances  in  a 
solution  of  fluoride  of  sodium  and  nitrate  of  strontia.  Another  instance  of 
the  kind  is  afforded  by  the  sublimation  of  benzoic  acid.  Allied  to  this  phe- 
nomenon is  the  phosphorescence  which  attends  the  sudden  contraction  of 
porous  substances.  Thus,  on  decomposing  by  heat  the  hydrates  of  zireonia, 
peroxide  of  iron,  and  green  oxide  of  chromium,  the  dissipation  of  the  water 
is  followed  by  a  sudden  increase  of  density  suited  to  the  changed  state  of  the 
oxide,  and  a  vivid  glow  appears  at  the  same  instant.  The  essential  conditions 
are,  that  a  substance  should  be  naturally  denser  after  decomposition  than  it 
was  previously,  and  that  the  transition  from  one  mechanical  state  to  the  other 
should  be  abrupt. 

It  is  sometimes  of  importance  to  measure  the  comparative  intensities  of 
light,  and  the  instrument  by  which  this  is  done  is  called  a  Photometer.  The 
only  photometer  which  is  employed  for  estimating  the  relative  strength  of  the 
sun's  light  is  that  of  Leslie.  It  consists  of  his  differential  thermometer, 
with  one  ball  made  of  black  glass.  The  clear  ball  transmits  all  the  rays  that 
fall  upon  it,  and,  therefore,  its  temperature  is  not  affected ;  they  are  all  ab- 
sorbed, on  the  contrary,  by  the  black  ball,  and  by  heating  and  expanding  the 
air  within,  cause  the  liquid  to  ascend  in  the  opposite  stem.  The  whole  in- 
strument is  covered  with  a  case  of  thin  glass,  the  object  of  which  is  to  pre. 
vent  the  balls  from  being  affected  by  currents  of  cold  air.  The  action  of 
this  photometer  depends  on  the  heat  produced  by  the  absorption  of  light. 
Leslie  conceives  that  light  when  absorbed  is  converted  into  heat;  but,  accord- 
ing to  the  experiments  already  referred  to,  the  effect  must  be  attributed,  not 
so  much  to  the  light  itself,  as  to  the  absorption  of  the  calorific  rays  by  which 
it  is  accompanied. 

Sir  J.  Leslie  recommended  his  photometer  also  for  determining  the  relative 
intensities  of  artificial  light,  such  as  that  emitted  by  candles,  oil,  or  gas. 
This  application  of  it  differs  from  the  foregoing,  because  light  proceeding 
from  terrestrial  sources  contains  heat  under  two  forms.  One  portion  is  ana- 
logous to  that  emitted  by  a  hot  body  which  is  not  luminous ;  the  other  is 
similar  to  that  which  accompanies  solar  light.  It  is  presumed  that  the  first 
form  of  heat  will  not  prove  a  source  of  error;  that  these  rays  are  wholly  in- 
tercepted by  the  outer  case  of  glass ;  or  that,  should  a  few  penetrate  into  the 
interior,  they  will  be  absorbed  equally  by  both  balls,  and  will  therefore  heat 
them  to  the  same  extent.  It  is  probable  that  this  reasoning  is  not  wide  of  the 
truth ;  and,  consequently,  the  photometer  will  give  correct  indications  so  far 
as  regards  the  new  element — non-luminous  heat.  But  it  is  not  applicable  to 
lights  which  differ  in  colour,  because  the  relation  between  the  heating  and 
illuminating  power  of  such  lights  is  exceedingly  variable.  Thus,  the  light 
emitted  by  burning  cinders  or  red-hot  iron,  even  after  passing  through  glass, 
contains  a  quantity  of  calorific  rays,  which  is  out  of  all  proportion  to  the 
luminous  ones ;  and,  consequently,  they  may  and  do  produce  a  greater  effect 
on  the  photometer  than  some  lights  whose  illuminating  powers  are  far 
stronger. 

The  second  kind  of  photometer  is  on  a  totally  different  principle.  It  de- 
termines the  comparative  strength  of  lights  by  a  comparison  of  their  sha- 
dows. This  instrument  was  invented  by  Count  Rumford,  and  is  described 
by  him  in  his  Essays.  It  is  susceptible  of  great  accuracy  when  employed 
with  the  requisite  care;*  but,  like  the  foregoing,  its  indications  cannot  be 
trusted  when  there  is  much  difference  in  the  colour  of  the  lights.  In  this 
case,  the  best  mode  of  obtaining  an  approximative  result,  is  by  observing 
the  distance  from  each  light  at  which  any  given  object,  as  a  printed  page, 
ceases  to  be  distinctly  visible.  The  illuminating  power  of  the  lights  so  com- 
pared is  as  the  squares  of  their  distances. 

*  See  an  Essay  on  the  construction  of  Coal  Gas  Burners,  &c.  in  the  Edin- 
burgh Philosophical  Journal  for  1825. 


ELECTRICITY.  71 


SECTION  III. 


ELECTRICITY. 

Elementary  Facts. — When  certain  substances,  such  as  amber,  glass,  seal- 
ing-wax  and  sulphur,  are  rubbed  with  dry  silk  or  cloth,  they  are  found  to 
have  acquired  a  property,  not  observable  in  their  ordinary  state,  of  causing 
contiguous  light  bodies  to  move  towards  them ;  or  if  the  substances  so  rubbed 
be  light  and  freely  suspended,  they  will  move  towards  contiguous  bodies. 
After  a  while  this  curious  phenomenon  ceases;  but  it  may  be  renewed  an 
indefinite  number  of  times  by  friction.  The  principle  thus  called  into  action 
is  known  by  the  name  of  electricity,  from  the  Greek  word  »XSJCT§OV,  amber, 
because  the  electric  property  was  first  noticed  in  it.  The  same  term  is 
applied  to  the  science  which  treats  of  the  phenomena  of  electricity. 

When  a  substance  by  friction  or  any  other  means  acquires  the  property 
just  stated,  it  is  said  to  be  electrified,  or  to  be  electrically  excited',  and  its 
motion  towards  other  bodies,  or  of  other  bodies  towards  it,  is  ascribed  to  a 
force  called  electric  attraction.  But  its  influence,  on  examination,  will  be 
found  to  be  not  merely  attractive ;  on  the  contrary,  light  substances,  after 
touching  the  electrified  body,  will  be  disposed  to  recede  from  it  just  as  actively 
as  they  approached  it  before  contact.  This  is  termed  electric  repulsion. 
By  aid  of  the  electrical  machine  these  phenomena  of  electric  attraction  and 
repulsion  may  be  displayed  by  a  great  variety  of  amusing  and  instructive 
experiments,  showing  how  readily  an  invisible  power  is  called  into  operation, 
and  how  wonderfully  inert  matter  is  subject  to  its  control.  But  the  student 
may  witness  these  effects  quite  satisfactorily  by  very  simple  apparatus.  Let 
him  suspend  a  thread  of  white  sewing  silk  from  the  back  of  a  chair  so  that 
one  end  may  hang  freely,  taking  the  precaution  to  moisten  that  end  slightly 
by  holding  it  between  the  fingers,  while  the  rest  of  the  thread  is  carefully 
dried  by  the  fire;  and  let  him  then  place  near  the  free  end  a  piece  of  sealing, 
wax  previously  rubbed  on  the  sleeve  of  his  coat.  The  silk  will  move  towards 
it ;  but  after  touching  the  excited  wax  two  or  three  times,  it  will  recede 
from  it. 

When  an  electrified  body  touches  another  which  is  not  electrified,  the 
electric  property  is  imparted  by  the  former  to  the  latter.  Thus,  on  touching 
the  free  end  of  the  suspended  silk  thread  with  the  excited  wax,  the  silk  will 
itself  be  excited,  as  shown  by  its  moving  towards  a  book,  a  knife,  or  other 
unexcited  object  placed  near  it.  But  though  electricity  is  always  imparted 
by  an  excited  to  an  unexcited  body  by  contact,  the  latter  does  not  always 
exhibit  electric  excitement.  If,  for  example,  the  suspended  silk  be  wetted 
along  its  whole  length,  it  will  be  strongly  attracted  by  the  excited  wax,  but 
after  contact  it  will  not  evince  the  least  sign  of  being  itself  electrified.  Never- 
theless, electricity  is  communicated  to  the  silk  in  both  cases,  only  it  is 
retained  by  silk  when  dry,  and  is  lost  as  soon  as  received  by  wet  silk.  Such 
observations  led  to  the  discovery  that  electricity  passes  with  great  ease  over 
the  surface  of  some  substances,  and  with  difficulty  over  that  of  others,  and 
hence  to  the  division  of  bodies  into  conductors  and  non-conductors  of  elec- 
tricity. If  electricity  be  imparted  to  one  end  of  a  conductor,  such  as  a  cop- 
per wire,  the  other  extremity  of  which  touches  the  ground,  or  is  held  by  a 
person  standing  on  the  ground,  the  electricity  will  pass  along  its  whole  length 
and  escape  in  an  instant,  though  the  wire  were  several  miles  long ;  whereas 
excited  glass  and  resin,  which  are  non-conductors,  may  be  freely  handled 
without  losing  any  electricity  except  at  the  parts  actually  touched.  To  the 
class  of  conductors  belong  the  rnetals,  charcoal,  plumbago,  water,  and  aqueous 
solutions,  and  substances  generally  which  are  moist  or  contain  water  in  its 


72  ELECTRICITY. 

liquid  state,  such  as  animals  and  plants,  and  the  surface  of  the  earth.  These, 
however,  differ  in  their  conducting  power :  of  the  metals,  Mr.  Harris  found 
silver  and  copper  £o  be  the  best  conductors,  and  after  these  follow  gold,  zinc, 
platinum,'  iron,  tin,  lead,  antimony,  and  bismuth.  (Phil.  Trans.  1827,  Part  i. 
21.)  Mr.  Forbes  has  lately  called  attention  to  the  fact  that  the  foregoing 
order  is  very  nearly  the  same  as  that  expressive  of  their  conducting  power 
for  heat.  Aqueous  solutions  of  acids  and  salts  conduct  much  better  than 
pure  water.  To  the  list  of  non-conductors  belong  glass,  resins,  sulphur, 
diamond,  dried  wood,  precious  stones,  earth  and  most  rocks  when  quite  dry, 
silk,  hair,  and  wool.  Air  and  gases  in  general  are  non-conductors  if  dry, 
but  act  as  conductors  when  saturated  with  moisture. 

This  knowledge  is  of  continual  application  in  electrical  experiments. 
When  it  is  wished  to  collect  electricity  on  a  metallic  surface,  the  metal  must 
be  insulated,  that  is,  cut  off  from  contact  with  the  earth,  and  with  conductors 
touching  the  ground,  by  means  of  some  non-conductor;  an  object  commonly 
effected  either  by  supporting  it  on  a  handle  of  glass,  or  by  placing  it  on  a 
stool  made  with  glass  feet.  Another  mode  of  insulating  is  to  suspend  a 
substance  by  silk  threads.  But  such  insulators  must  be  dry  ;  since  they  begin 
to  conduct  as  soon  as  they  grow  damp,  and  conduct  well,  as  in  the  experi- 
ment above  described,  when  wet.  Again,  electrical  experiments  are  very 
apt  to  fail  in  damp  weather,  because  the  moisture  both  carries  off  electricity 
directly,  and  by  being  deposited  on  the  glass  supports,  destroys  the  insulation. 

To  diminish  this  inconvenience  it  is  usual  to  keep  the  insulators  warm, 
and  to  coat  them  with  a  varnish  made  by  dissolving  the  resin  called  shell-lac 
in  alcohol ;  this  resinous  matter  being  much  less  prone  to  attract  moisture 
from  the  air  than  glass.  The  same  principles  account  for  an  error  once  pre- 
valent that  a  metal  cannot  be  excited  by  friction :  if  held  in  the  hand, 
indeed,  it  exhibits  no  sign  of  excitement  when  rubbed,  because  the  electricity 
is  carried  off  as  soon  as  excited  ;  but  if,  while  carefully  insulated,  it  is  rubbed 
with  a  dry  cat's  fur,  excitement  readily  ensues. 

On  comparing  the  electric  properties  manifested  by  glass  and  sealing-wax 
when  both  are  rubbed  by  a  woollen  or  silk  cloth,  they  will  be  found  essen- 
tially different ;  and  hence  it  is  inferred  that  there  are  two  kinds  or  states  of 
electricity,  one  termed  vitreous,  because  developed  on  glass,  and  the  other 
resinous  electricity,  from  being  first  noticed  on  resinous  substances.  These 
two  kinds  of  electricity,  one  or  other  of  which  is  possessed  by  every  elec- 
trified substance,  are  also  termed  positive  and  negative,  the  terms  vitreous 
and  positive  being  used  synonymously,  as  are  resinous  and  negative.  The 
mode  of  distinguishing  between  positive  and  negative  electricity  is  founded 
on  the  circumstance,  that  if  two  electrified  substances  are  both  positive  or 
both  negative,  they  are  invariably  disposed  to  recede  from  each  other,  that  is, 
to  exhibit  electric  repulsion  ;  but  if  one  be  positive,  and  the  other  negative, 
their  mutual  action  is  as  constantly  attractive.  The  end  of  a  silk  thread, 
after  contact  with  an  electrified  stick  of  sealing-wax,  is  repelled  by  the  wax, 
because  both  are  in  the  same  electric  state ;  but  if  a  dry  warm  wine-glass 
be  rubbed  with  cloth  or  silk,  and  then  presented  to  the  thread,  attraction 
will  ensue.  A  silk  thread,  in  a  known  electric  state,  thus  indicates  the  kind 
of  electricity  possessed  by  other  substances :  a  convenient  mode  of  doing 
this,  is  to  draw  a  thread  of  white  silk  rapidly  through  a  fold  of  coarse  brown 
paper  previously  warmed,  by  which  means  its  whole  length  will  be  rendered 
positive. 

When  two  substances  are  rubbed  together  so  as  to  electrify  one  of  them, 
the  other,  if  in  a  state  to  retain  electricity,  will  be  excited  also,  one  being 
always  negative  and  the  other  positive.  It  is  easy  to  be  satisfied  of  this  by 
very  simple  experiments.  Rub  a  stick  of  sealing-wax  on  warm  coarse  brown 
paper,  and  the  paper  will  be  found  to  repel  a  positively  excited  thread  of  silk, 
while  the  wax  will  attract  it ;  if  a  warm  wine-glass  be  rubbed  on  the  brown 
paper,  the  glass  will  be  positive,  as  shown  by  its  repelling  the  positive  thread, 
while  the  same  thread  will  be  attracted  by  the  negative  paper;  friction  of 


ELECTRICITY.  <-     ^        ^  ( 

^V  *    *• 

sealing-wax  on  a  silk  riband  renders  the  wax  negative  and  the  riband  positive, 
but  with  glass  the  riband  is  negative.  If  two  silk  ribands,  one  white  and 
the  other  black,  be  made  quite  warm,  placed  in  contact,  and  then  drawn 
quickly  through  the  closed  fingers,  they  will  be  found  on  separation  to  be 
highly  attractive  to  each  other,  the  white  being  positive  and  the  black  nega- 
tive. The  back  of  a  cat  is  positive  to  all  substances  with  which  it  has  been 
tried,  and  smooth  glass  is  positive  to  all  except  the  back  of  a  cat.  Sealing- 
wax  is  negative  to  all  the  substances  just  enumerated,  but  becomes  positive 
by  friction  with  most  of  the  metals.  The  reader  will  perceive  from  these 
facts  that  the  same  substance  may  acquire  both  kinds  of  electricity,  becom- 
ing positive  by  friction  with  one  body,  and  negative  with  another. 

THEORIES  OF  ELECTRICITY. 

The  nature  of  electricity,  like  that  of  heat  and  light,  is  at  present  involved 
in  obscurity.  All  these  principles,  if  really  material,  are  so  light,  subtile, 
and  diffusive,  that  it  has  hitherto  been  found  impossible  to  recognize  in  them 
the  ordinary  characteristics  of  matter  ;  and,  therefore,  electric  phenomena 
might  be  referred,  not  to  the  agency  of  a  specific  substance,  but  to  some  pro- 
perty or  state  of  common  matter,  just  as  sound  is  produced  by  a  vibrating 
medium.  But  the  effects  of  electricity  are  so  similar  to  those  of  a  mechani- 
cal agent ;  it  appears  so  distinctly  to  emanate  from  substances  which  contain 
it  in  excess,  and  rends  asunder  all  obstacles  in  its  course  so  exactly  like  a 
body  in  rapid  motion,  that  the  impression  of  its  existence  as  a  distinct  ma- 
terial substance  sui  generis  forces  itself  irresistibly  on  the  mind.  All  na- 
tions, accordingly,  have  spontaneously  concurred  in  regarding  electricity  as 
a  material  principle ;  and  scientific  men  give  a  preference  to  the  same  view, 
because  it  offers  an  easy  explanation  of  phenomena,  arid  suggests  a  natural 
language  easily  intelligible  to  all. 

Theory  of  Two  Electric  Fluids. — This  theory,  the  fundamental  facts  of 
which  were  supplied  partly  by  Dufay,  and  partly  by  Symmer,  is  founded  on 
the  assumed  existence  of  two  electric  fluids,  which  Dufay  distinguished  by 
the  terms  vitreous  and  resinous  electricity.  In  order  to  account  for  electric 
phenomena  by  this  supposition,  the  two  fluids  are  assumed  to  possess  the 
following  properties  : — They  are  both  equally  subtile  and  elastic,  universally 
diffused,  and,  therefore,  present  in  all  bodies,  possessed  of  the  most  perfect 
fluidity,  each  highly  repulsive  to  its  own  particles,  and  as  highly  attractive 
to  those  of  the  opposite  kind ;  these  attractive  and  repulsive  forces  being  ex- 
actly equal  at  the  same  distance,  and  both  varying  inversely  as  the  square  of 
the  distance  varies.  Electric  quiescence  is  ascribed  to  these  fluids  being 
combined  and  neutralized  with  each  other;  and  electric  excitation  is  the  con- 
sequence of  either  fluid  being  in  excess.  Their  combination  is  destroyed  by 
several  causes,  of  which  friction  is  one.  The  application  of  these  principles 
is  as  follows.  Two  unexcited  contiguous  bodies,  A  and  B,  are  electrically  in- 
different to  each  other ;  for,  though  each  electricity  in  A  repels  the  electricity 
of  the  same  name  in  B,  attraction  to  precisely  the  same  extent  is  exerted 
between  the  opposite  electricities,  and  no  change  results.  If  A  and  B  are 
rubbed  together,  a  portion  of  the  combined  electricities  in  both  is  decomposed, 
and  the  separated  resinous  fluid  is  transferred  to  one  of  them,  suppose  to  A, 
and  the  vitreous  to  B,  each  being  electrified  to  the  same  degree,  though  op- 
positely. The  free  particles  of  resinous  electricity  in  A  tend  by  their  repul- 
sion to  recede  from  each  other,  and  would  quit  A  altogether,  unless  their  pas- 
sage were  impeded  by  a  non-conductor :  the  atmosphere,  if  dry,  cuts  off  the 
retreat,  and  by  its  pressure  confines  the  resinous  fluid  to  the  surface  of  A. 
The  same  happens  to  the  vitreous  fluid  on  the  surface  of  B.  But  the  opposite 
electricities  fixed  on  A  and  B  exert  a  strong  mutual  attraction,  and  may  suc- 
ceed either  in  forcing  their  way  across  the  intervening  stratum  of  air,  or  of 
actually  drawing  A  and  B  into  contact.  In  either  case  the  free  electricities 
reunite,  and  the  electric  equilibrium  is  restored.  On  the  contrary,  if  A  and 


74  ELECTRICITY. 

B  are  similarly  electrified,  that  is,  possess  the  same  kind  of  free  electricity, 
the  effort  of  the  electric  fluid  to  escape  in  opposite  directions  causes  the  sub- 
stances themselves  to  fly  asunder,  if  the  repulsive  force  exceed  their  weight, 
and  thus  produces  electric  repulsion* 

This  theory,  as  commonly  stated,  takes  little  or  no  cognizance  of  any  at- 
traction between  the  electric  fluids  and  other  material  substances.  But  it 
would  be  against  all  analogy  to  suppose  no  such  influence  to  exist ;  and  in- 
deed the  supposition  of  an  attractive  force  acting  at  insensible  distances 
seems  necessary  to  account  for  the  impediment  caused  by  non-conductors  to 
the  free  movement  of  the  electric  fluids. 

Theory  of  a  Single  Fluid. — The  celebrated  American  philosopher,  Frank- 
lin, proposed  a  different  theory,  founded  on  the  supposition  of  a  single  elec- 
tric fluid,  the  particles  of  which  are  conceived  to  repel  each  other  with  a  force 
diminishing  as  the  squares  of  the  distance,  and  to  be  attracted  by  matter  in 
general  according  to  the  same  law.  Material  substance  in  its  unelectric 
state  is  regarded  as  a  compound  of  electricity  and  matter,  saturated  and  neu- 
tralized with  each  other.  It  is  also  an  assumption,  shown  to  be  necessary 
by  uEpinus  and  Cavendish,  that  ponderable  bodies  repel  each  other  with  the 
same  force  and  according  to  the  same  law  as  the  particles  of  electricity. 
From  the  nature  of  these  postulates  it  will  be  easy  to  anticipate  their  appli- 
cation. Unelectric  bodies  are  such  as  have  their  natural  quantity  of  elec- 
tricity, which  precisely  suffices  to  saturate  and  neutralize  the  matter  of  which 
they  consist.  They  are  then  electrically  indifferent ;  because  the  repulsion 
exerted  between  the  electricity  and  matter  of  contiguous  bodies  is  exactly 
counteracted  by  the  attraction  of  the  electric  fluid  in  each  for  the  matter  of 
the  other.  Electrical  excitement  is  occasioned  either  by  increase  or  diminu- 
tion of  the  natural  quantity  of  electricity.  On  rubbing  a  tube  of  glass  with 
a  woollen  cloth,  the  electric  condition  of  both  is  disturbed:  the  glass  ac- 
quires more  electricity  than  it  naturally  possesses,  or  is  overcharged  with 
electric  fluid ;  and  the  cloth,  losing  what  the  glass  gained,  contains  less  than 
its  natural  supply,  or  is  undercharged.  These  opposite  states  are  denoted 
by  the  algebraic  terms  positive  and  negative,  the  former  corresponding  to  the 
vitreous,  the  latter  to  the  resinous  electricity  of  Dufay.  Bodies,  positively 
excited,  repel  each  other  by  means  of  the  repulsion  among  the  particles  of 
the  electricity  with  which  they  are  surcharged  ;  and  the  equal  tendency  of 
negatively  excited  bodies  to  separate  is  ascribed  to  the  mutual  repulsion 
among  the  particles  of  matter.  The  electric  equilibrium  in  excited  sub- 
stances is  restored  by  the  electricity  escaping  from  those  where  it  is  in  ex- 
cess, and  passing  to  those  which  are  undercharged. 

To  the  theory  of  Franklin  it  is  objected  that  it  involves  an  assumption  at 
variance  with  the  laws  of  gravitation,  namely,  that  of  matter  being  repulsive 
to  itself;  but  in  fact  this  assumption,  if  admitted,  would  not  satisfactorily 
explain  the  unequal  distribution  of  the  electric  energy  over  the  surface  of  the 
electrified  bodies,  as  well  negative  as  positive,  dependent  on  their  form.  To 
account  for  this  phenomenon  the  theory  requires  a  repulsive  fluid  superadded 
to  matter,  and  freely  moveable  among  its  particles,  a  sort  of  resident  electric 
fluid,  capable  of  performing  all  the  functions  ascribed  to  resinous  electricity. 
With  such  addition,  however,  the  theory  of  Franklin  would  virtually  cease 
to  be  that  of  a  single  electric  fluid,  and  would  still,  I  suspect,  be  less  gene- 
rally applicable  than  the  theory  of  two  fluids.  I  feel  it  necessary,  accord- 
ingly, to  adopt  the  latter,  substituting,,  however,  agreeably  to  present  usage, 
the  terms  positive  and  negative  for  vitreous  and  resinous  electricity.* 

*  The  chief  objection  which  has  been  urged  against  the  Franklinian 
theory  of  one  electric  fluid  is,  that  it  fails  to  explain  the  repulsion  of  two 
negatively  electrified  bodies.  It  is  alleged  that  the  condition  of  two  bodies, 
the  essence  of  which  consists  in  the  absence  of  a  subtile  principle  called  elec- 
tricity, cannot  cause  them  to  repel  each  other;  for  this  would  be  attributing 
to  a  negation  the  possession  of  a  positive  property,  which  is  absurd.  It  was 


ELECTRICITY.  75 

CAUSES  OF  ELECTRIC  EXCITEMENT. 
4  \ 

Friction. — This  cause  of  electric  excitement  having  been  already  men- 
tioned,  it  here  only  remains  to  state  the  usual  modes  of  developing  electricity 

J  by  friction.  A  supply  of  negative  electricity  is  easily  obtained  by  rubbing 
a  stick  of  sealing-wax,  or  a  glass  tube  covered  with  sealing-wax,  with  silk  or 
woollen  cloth :  and  positive  electricity  is  freely  developed  when  a  dry  glass 

4  tube  is  rubbed  with  silk,  brown  paper,  or  flannel,  the  surface  of  which  is  co- 
vered with  a  little  amalgam.  But  for  obtaining  an  abundant  supply  of  elec- 
tricity it  is  necessary Hto  employ  an  electrical  machine,  which  is  a  mechani- 
cal contrivance  for  exposing  a  large  surface  of  glass  to  continuous  friction. 
As  now  constructed,  it  is  formed  either  with  a  cylinder  or  plate  of  glass 

^  which  is  made  to  revolve  upon  an  axis,  and  pressed  during  rotation  by  cush- 
ions or  rubbers  made  of  leather  stuffed  with  flannel,  and  covered  usually 
with  silk.  On  the  rubber  is  spread  an  amalgam  of  tin  and  zinc,  rendered 
adhesive  by  admixture  with  a  small  quantity  of  lard  or  tallow.  To  prepare 
the  amalgam,  melt  in  a  Hessian  crucible,  one  ounce  of  tin  and  three  of  zinc, 
then  add  two  ounces  of  mercury  heated  to  near  its  boiling  point,  stir  briskly 
with  a  stick  for  a  few  minutes,  and  pour  the  mixture  on  a  clean  dry  stone : 
when  cold  pulverize  and  sift,  and  preserve  the  fine  powder  in  a  well-corked 

|      dry  phial.     Another  essential  part  of  the  machine  is  the  prime  conductor, 
^*s     which  is  an  insulated  conductor,  commonly  made  of  brass,  placed  in  such 

*  immediate  proximity  to  the  revolving  glass,  that  the  electric  state  of  the  one 
is  instantly  imparted  to  the  other. 

The  electricity  developed  by  the  electrical  machine  is  due  partly  to  fric- 

r  tion,  which  disunites  the  combined  electric  fluids  of  the  glass  and  rubber, 
but  principally  to  the  oxidation  of  the  amalgam.  The  positive  fluid  is  trans- 
>,  ferred  to  the  glass,  from  it  to  the  contiguous  prime  conductor,  and  thence  to 
any  system  of  conductors  connected  with  the  prime  conductor ;  and  similarly 
the  negative  fluid  collects  upon  the  rubber,  whence  it  is  distributed  to  one  or 
more  conductors  with  which  the  rubber  may  be  in  connexion.  Thus  all 
insulated  conductors  in  contact  with  the  prime  conductor  are  positive,  and 
those  attached  to  the  rubber  are  negative.  When  once  the  glass  and  rubber 
are  excited,  it  is  necessary  that  the  electric  equilibrium  of  both  should  be 
restored  before  a  second  development  can  occur ;  and  accordingly  it  is  found 
that  very  little  electricity  is  obtained  when  the  prime  conductor  and  rubber's 
conductor  are  both  insulated.  On  taking  positive  electricity  from  the  prime 
conductor,  the  rubber  should  communicate  with  the  ground,  that  its  negative 
electricity  might  escape ;  and  when  negative  -electricity  is  taken  from  the 
rubber's  conductor,  the  prime  conductor  is  connected  with  the  ground.  The 
same  object  may  be  accomplished  by  connecting  the  prime  conductor  with 
the  rubber's  conductor,  though  in  experiments  it  is  commonly  inconvenient 
to  employ  this  arrangement. 

Change  of  Temperature. — The  operation  of  this  cause  of  electric  excite- 
ment was  first  noticed  in  certain  minerals,  such  as  tourmalin  and  boracite, 
not  possessed  of  that  symmetric  arrangement  of  parts  commonly  observed  in 
crystals,  and  which  are  electrified  by  the  application  of  heat.  But  a  far 
more  general  principle  was  detected  by  the  late  Dr.  Seebeck,  who  found  that 
the  electric  equilibrium  is  disturbed  in  certain  metallic  rods  or  wires  when 
one  extremity  has  a  different  temperature  from  that  of  the  other,  whether 

this  apparent  difficulty  which  induced  ^Epinus  and  Cavendish  to  assert  that 
the  theory  of  Franklin  required  the  assumption  that  matter  was  repulsive  to 
itself.  Loaded  with  this  postulate,  the  theory  may,  indeed,  be  untenable  ;  but 
the  question  arises,  whether,  in  point  of  fact,  the  postulate  mentioned  is  ne- 
cessary to  the  Franklinian  theory.  We  think  it  is  not;  but  are  inclined,  with 
Dr.  Hare,  to  refer  the  apparent  repulsion  of  negatively  electrified  bodies  to 
an  attraction  between  such  bodies  and  the  contiguous  air,  electrified  positively 
by  induction. — Ed, 


76  ELECTRICITY. 

the  difference  be  effected  by  the  application  of  heat  or  cold.  This  observa- 
tion has  been  since  shown  by  Professor  Camming  to  be  true  of  all  metals, 
(An.  of  'Phil.  N.  S.  v.  427.)  See  also  the  recent  experiments  by  Mr.  Pri- 
deaux.  (Phil.  Mag.  iii.)  The  experiment  is  usually  made  by  'heating  or 
cooling  the  point  of  junction  of  two  metallic  wires,  which  are  soldered  toge- 
ther ;  but  M.  Becquerel  has  proved  that  the  contact  of  different  metals  is  not 
essential.  (An.  de  Ch.  et  de  Ph.  xli.  353.) 

Chemical  Action. — Another,  and  very  fertile  source  of  electricity,  is  che- 
mical action.  This  was  strongly  denied  by  the  late  Sir  H.  Davy  in  his  Bake- 
rian  lecture  for  1826;  but  the  experiments  of  Becquerel,  De  la  Rive,  and 
Pouillet,  afford  decisive  proof  that  chemical  union  and  decomposition  are 
both  attended  with  electrical  excitement.  (An.  de  Ch.  et  de  Ph.  T.  35,  36, 
37,  38,  and  39.)  Pouillet,  in  particular,  has  demonstrated  that  the  gas  arising 
from  the  surface  of  burning  charcoal  is  positive,  while  the  charcoal  itself 
is  negative ;  and  he  has  proved  that  similar  phenomena  are  produced  by  the 
combustion  of  hydrogen,  alcohol,  oil,  and  other  inflammables  of  the  same 
kind.  In  all  these  instances  the  combustible,  in  the  act  of  burning,  renders 
contiguous  particles  negative;  while  the  oxygen  imparts  positive  electricity 
to  the  products  of  combustion.  The  fact,  with  respect  to  charcoal,  was  ori- 
ginally noticed  by  Volta,  La  Place,  and  Lavoisier,  but  was  subsequently  de- 
nied by  Saussure  and  Sir  H.  Davy.  Pouillet  has  reconciled  these  conflicting 
statements  by  showing  that  the  result  depends  on  the  mode  in  which  the 
experiment  is  conducted.  For  if  the  carbonic  acid  be  completely  removed 
from  the  burning  mass  at  the  instant  of  its  formation,  both  are  found  to  be 
electrical;  but  if  the  carbonic  acid  subsequently  flow  over  the  surface  of  the 
charcoal,  the  equilibrium  will  instantly  be  restored,  and  no  sign  whatever  of 
excitement  be  perceptible.  Decisive  evidence  of  the  same  kind  is  supplied 
by  the  amalgam  of  the  electrical  machine,  the  influence  of  which  is  pro- 
portional  to  the  degree  of  chemical  action,  and  which  ceases  to  be  useful  as 
soon  as  the  metals  are  oxidized.  Thus,  Wollaston  found  that  amalgams  of 
silver  and  platinum,  which  are  indisposed  to  oxidize,  are  of  no  use  when  ap- 
"plied  to  the  rubber;  and  that  an  amalgam  of  zinc  and  tin,  which  is  the  most 
oxidable,  is  also  the  best  amalgam  for  exciting  the  machine.  He  observed 
that  a  machine  in  good  action  ceased  to  act  when  surrounded  with  carbonic 
acid,  but  instantly  recovered  its  action  on  re-admitting  the  air.  (Phil. 
Trans.  1801.)  On  such  facts  is  founded  the  foregoing  statement,  that  the 
energy  of  the  electrical  machine  is  much  more  owing  to  chemical  action  than 
to  friction. 

Contact. — Another  reputed  source  of  electricity  is  contact  of  different  sub- 
stances, especially  of  metals ;  a  source  originally  suggested  by  Volta,  who 
founded  on  it  a  theory  of  galvanism.  The  facts  on  which  Volta  rested  his 
opinion  were  of  this  nature.  Well-cleaned  plates  of  zinc  and  copper  were 
furnished  with  glass  handles,  by  which  they  could  be  both  supported  and 
insulated  :  the  zinc  plate,  held  by  its  glass  handle,  was  laid  repeatedly  on  the 
copper,  which  at  the  time  need  not  be  insulated,  and  after  each  contact  the 
zinc  was  made  to  touch  the  instrument,  shortly  to  be  described,  called  the 
condenser.  A  positive  charge  was  gradually  accumulated  ;  and  on  operating 
in  the  same  manner  with  the  insulated  plate  of  copper,  it  was  found  to  com- 
municate a  negative  charge.  He  also  stated  that  if  one  end  of  a  zinc  plate 
communicate  with  the  condenser,  while  the  zinc  at  its  other  end  is  in  con- 
tact with  a  plate  of  copper,  a  positive  charge  is  communicated ;  and  that 
negative  electricity  is  indicated  when  a  copper  plate,  in  contact  with  zinc  at 
one  end,  rests  at  its  other  upon  the  condenser.  From  such  experiments  it 
was  inferred,  that  the  contact  of  zinc  and  copper  disturbs  the  electric  equili- 
brium in  both  metals,  the  latter  acquiring  an  excess  of  negative  and  the  for- 
mer of  positive  electricity. 

The  quantity  of  electricity  developed  by  contact  is  confessedly  so  small, 
that  it  requires  for  its  detection  the  aid  of  very  delicate  instruments  and  of 
very  careful  manipulation;  and  the  opinion  is  daily  gaining  grou^  *^a* 
mere  contact  is  incapable  of  causing  electric  excitation.  The  phe 


ground  that 
henomeua 


ELECTRICITY.  77 

referred  by  Volta  to  contact,  are  ascribed  by  others  to  chemical  action  and 
to  friction.  De  la  Rive  of  Geneva  contends  (An.  de  Ch.  et  de  Ph.  xxxix.  297,) 
that  the  feeble  charge  commonly  observed  from  the  contact  of  zinc  and  cop- 
per, is  due  to  slight  oxidation  caused  by  moisture  and  the  oxygen  of  the  air 
acting  on  the  plate  of  zinc.  When  he  prevented  such  oxidation  by  operating 
in  an  atmosphere  of  hydrogen  or  nitrogen,  no  electric  excitement  fol- 
lowed ;  and  when  he  purposely  increased  chemical  action,  as  by  exposing 
the  zinc  to  acid  fumes,  or  by  substituting  for  zinc  a  more  oxidable  metal, 
such  as  potassium,  the  electrical  effects  observable  on  contact  with  copper 
were  greatly  augmented.  Electric  excitation  and  chemical  action  were  ob- 
served to  be  strictly  proportional  to  each  other.  Again,  Parrot  of  St.  Peters- 
burgh  (An,  de  Ch.  et  de  Ph.  xlvi.  361,)  not  only  .confirms  the  statements  of 
De  la  Rive,  but  shows  that  in  those  instances  where  electric  excitement  has 
been  witnessed  under  circumstances  which  appear  to  exclude  chemical  action, 
the  phenomenon  may  be  ascribed  to  friction  of  the  metals.  He  gives  as  the 
result  of  numerous  experiments  made  with  strict  care,  that  the  contact  of 
zinc  and  copper,  if  unattended  by  friction  or  chemical  action,  causes  not  the 
least  development  of  electricity.  The  opposite  evidence  adduced  by  Volta 
and  others  must,  therefore,  I  apprehend,  be  rejected  ;  and  the  only  remain- 
ing facts  in  favour  of  Volta's  opinion  are  derived  from  certain  chemical 
agencies  evinced  by  metals  during  contact,  a  subject  which  will  be  discussed 
in  the  section  on  galvanism. 

Changes  of  Form. — The  changes  of  form  caused  in  a  substance  by  varia- 
tions of  temperature,  such  as  liquefaction  and  solidification,  the  formation 
and  condensation  of  vapour,  constitute  another  reputed  source  of  electricity. 
On  liquefying  sulphur  in  a  glass  vessel,  and  removing  the  cake  after  cool- 
ing, the  sulphur  is  found  to  be  negative  and  the  glass  positive ;  and  on  pour- 
ing water  into  a  hot  iron  vessel  or  on  a  hot  coal  communicating  with  a 
delicate  electrometer,  the  rapid  evaporation  of  the  water  is  attended  with 
decisive  indications  of  electrical  excitement.  To  processes  of  this  nature, 
continually  taking  place  in  the  atmosphere,  the  electricity  of  the  clouds  is 
generally  ascribed.  But  the  opinion  is  questioned  by  Pouillet,  who  has 
shown  that  in  most  of  the  experiments  adduced  in  its  favour,  chemical  ac- 
tions ensue  at  the  same  time,  and  that  the  greatest  part  of  the  effect  is  due 
to  such  changes.  If,  for  example,  evaporation  be  accompanied  by  chemical 
decomposition,  as  when  saline  solutions  are  evaporated,  the  water  being 
separated  from  the  salt  with  which  it  was  previously  united,  or  if  the  vessel 
consist  of  iron  or  oth£r  easily  oxidable  material,  which  is  more  or  less 
chemically  attacked  by  the  evaporating  water,  then  the  development  of 
electricity  is  very  decisive  ;  but  he  contends  that  pure  water,  evaporated  in 
a  clean  platinum  vessel,  gives  rise  to  no  electrical  excitement  whatever. 
From  such  experiments  Pouillet  concludes  that  the  electricity,  hitherto  re- 
ferred to  changes  of  form,  is  entirely  owing  to  the  chemical  action  by  which 
they  are  generally  attended ;  and  these  phenomena,  of  which  evaporation 
from  the  ocean,  rivers,  and  the  surface  of  the  earth,  affords  an  instance,  pure 
water  being  thereby  separated  from  its  saline  impregnation,  as  also  the  che- 
mical changes  attendant  on  the  growth  and  nutrition  of  plants,  he  regards 
as  a  fertile  source  of  atmospheric  electricity.  (An.  de  Ch.  et  de  Ph,  xxxv. 
401,  and  xxxvi.  5.)  In  these  views  there  is  much  truth.  I  have  repeatedly 
noticed  free  electric  excitement  on  pouring  a  solution  of  chloride  of  sodium 
or  sulphate  of  soda  into  a  heated  platinum  crucible,  and  also  when  pure 
water  was  dropped  on  red-hot  iron  or  a  glowing  cinder  ;  but  I  have  as  con. 
stantly  failed  of  procuring  any  indication  when  pure  water  was  evaporating 
on  platinum.  Mr.  Harris,  however,  informs  me  that  with  an  apparatus  of 
unusual  delicacy,  he  finds  evaporation  of  pure  water  from  platinum  to  be 
attended  with  distinct  development  of  electricity  < 

Proximity  to  an  Electrified  Body. — It  is  a  direct  consequence  of  the  at- 
tractive and  repulsive  powers  ascribed  to  the  electric  fluids,  that  an  unelec- 
trified  conductor  must  be  excited  by  the  vicinity  of  an.  electrified  body.  Let 

7* 


78  ELECTRICITY. 

AB,  fig.  1,  be  an  unexcited  conductor,  sup-  pig 

ported  on  an  insulated  glass  rod  be ;  and 
let  c,  containing  free  positive  electricity,  and  .  G  •**! 
similarly  insulated,  be  placed  near  it  on  the  I  -f"J  \ 
side  A.  The  free  positive  electricity  on  c  will 
both  repel  the  positive  fluid  of  AB,  and  attract 
its  negative  fluid,  and  the  result  of  these  con- 
curring forces  is  instantly  to  decompose  a 
portion  of  the  combined  electricities  of  AB, 
the  free  negative  fluid  approaching  as  close  as  possible  to  c,  and  the  positive 
fluid  receding  from  it.  The  relative  position  of  these  fluids  is  indicated  in 
the  figure  by  the  signs  -f-  and  — ,  the  former  denoting  positive  and  the  lat- 
ter negative  electricity.  The  opposite  ends  of  the  conductor  AB  are  thus 
oppositely  electrified,  and  in  an  equal  degree :  the  excitement  is  found,  as 
would  be  anticipated,  to  be  greatest  at  the  extremities,  and  to  diminish  gra- 
dually towards  the  middle  line  ab,  which  is  neutral.  The  quantity  of  elec- 
tricity thus  set  free  depends  on  the  extent  to  which  c  is  excited,  and  on 
its  distance  from  AB.  If  now  c  be  suddenly  withdrawn,  the  opposite  fluids 
at  A  and  B  coalesce,  and  the  equilibrium  of  AB  is  restored.  But  so  long  as  c 
retains  its  position,  A  will  be  negative,  even  were  it  uninsulated.  The  only 
effect  of  communication  with  the  ground  is  to  neutralize  the  positive  fluid 
at  B  by  supplying  to  it  negative  electricity  from  the  earth  :  if  after  having 
effected  this  by  touching  the  cylinder  for  an  instant  with  the  finger,  c  be 
withdrawn,  AB  is  left  with  an  excess  of  the  negative  fluid.  The  electricity 
thus  developed  by  the  contiguity  of  an  electrified  body  is  said  to  be  induced, 
or  to  be  excited  by  induction. 

It  is  essential  that  the  student  should  reflect  carefully  on  these  plain  con- 
sequences of  the  theory  of  electricity,  since  the  applications  of  this  knowledge 
are  numerous.  A  few  of  these  may  now  be  enumerated : — 

1.  An  electrified  body  attracts  light  objects  near  it,  because  it  induces  in 
them  a  state  opposite  to  itself.     The  attraction  is  most  lively  when  the  light 
object  is  a  conductor,  and  in  contact  with  the  ground,  since  it  then  more 
completely  assumes  an  electric  state  opposed  to  that  of  the  inducing  body. 
A  non-conductor  is  very  imperfectly  electrified  by  induction,  because  the 
electric  fluids  cannot  quit  each  other  from  inability  to  move  through  the 
non-conductor. 

2.  If  a  stick  of  sealing-wax,  strongly  negative,  be  presented  to  a  thread 
or  pith  ball,  which  is  also  negatively,  but  feebly,  excited,  repulsion  will  ensue 
at  a  considerable  distance,  followed  by  attraction  when  the  distance  is  small. 
This  attraction  is  due  to  the  strongly  excited  wax  acting  by  induction  on 
the  feebly  negative  thread,  thereby  causing  it  to  have  an  excess  of  positive 
electricity. 

3.  The  positive  electricity  collected  on  the  prime  conductor  of  an  electrical 
machine  is  by  some  ascribed,  not  to  a  transfer  of  that  fluid  from  the  glass 
to  the  prime  conductor,  but  to  a  part  of  the  combined  electricities  of  the 
prime  conductor  being  separated  by  induction,  and  the  negative  fluid  being 
imparted  to  the  positive  glass.     The  same  view  is  applicable  to  any  system 
of  conductors  in  contact  with  the  prime  conductor,  as  also  to  conductors  con- 
nected with  the  rubber.     It  is  difficult  to  say  which  explanation  is  the  more 
correct,  or  whether  both  may  not  be  true. 

4.  On  moving  the  hand  towards  the  prime  conductor  of  an  excited  elec- 
trical machine,  the  hand  becomes  negative  by  induction,  and  the  spark  ulti- 
mately obtained  restores  the  equilibrium.     In  like  manner  a  negatively  elec- 
trified cloud  renders  positive  a  contiguous  tree  or  tower,  and  then  a  stroke 
of  lightning  follows  as  a  consequence  of  attraction  between  the  two  accumu- 
lated fluids. 

5.  The  action  of  the  Leyden  Jar  depends  on  the  principle  of  induced 
electricity.     A  glass  jar  or  bottle  with  a  wide  mouth  is  coated  externally 
and  internally  with  tinfoil,  except  to  within  three  or  four  inches  of  its  sum- 
mit ;  and  its  aperture  is  closed  by  dry  wood  or  some  imperfect  conductor, 


ELECTRICITY.  79 

through  the  centre  of  which  passes  a  metallic  rod  communicating  with  the 
tinfoil  on  the  inside  of  the  jar.  On  placing  the  metallic  rod  in  contact  with 
the  prime  conductor  of  an  excited  electrical  machine,  while  the  outer  coat- 
ing communicates  with  the  ground,  the  interior  of  the  jar  acquires  a  charge 
of  positive  electricity,  and  the  exterior  becomes  as  strongly  negative.  If, 
the  jar  being  insulated,  the  metallic  rod  be  placed  close  to  the  prime  con- 
ductor, avoiding  actual  contact,  while  an  uninsulated  conductor  be  held  at 
an  equal  distance  from  the  outer  coating,  electric  sparks  in  equal  number 
and  of  equal  size  will  pass  between  both  intervals,  and  both  sides  of  the  jar 
are  found  to  be  in  the  same  condition  as  before ;  but  no  charge  will  be  re- 
ceived when  the  inner  coating  communicates  with  the  prime  conductor,  and 
the  outer  coating  is  strictly  insulated.  From  these  facts  it  is  inferred  that 
the  interior  of  the  jar  becomes  positive,  either  by  receiving  positive  electri- 
city directly  from  the  prime  conductor,  or,  as  is  more  probable,  by  commu- 
nicating to  it  negative  electricity ;  and  that  the  exterior  then  becomes  nega- 
tive by  the  loss  of  a  quantity  of  positive  electricity  equal  to  that  on  the 
interior.  Unless  means  be  afforded  for  the  escape  of  the  positive  electricity 
from  the  exterior,  no  charge  ought  to  be  received;  arid  this  conclusion  is 
quite  conformable  to  the  fact  above  stated. 

The  opposite  electric  fluids  accumulated  on  the  opposite  sides  of  a  charged 
Leyden  jar  exert  a  strong  mutual  attraction  through  the  substance  of  the 
glass,  and  the  presence  of  each  secures  the  continuance  of  the  other.  The 
exterior  of  the  jar  may  be  freely  handled,  and  its  coating  removed,  without 
destroying  the  charge,  provided  no  communication  be  made  at  the  same 
time  with  the  interior ;  and  if  the  exterior  be  insulated,  the  charge  will  be 
preserved,  though  the  tinfoil  of  the  interior  be  removed.  But  when  a  con- 
ductor communicates  with  both  surfaces  at  the  same  instant,  the  two  fluids 
rush  together  with  violence,  and  the  equilibrium  is  restored.  Whether  in 
this  and  similar  cases  the  two  fluids  coalesce  entirely  on  the  intermediate 
conductor,  or  whether  each  from  its  velocity  may  not  in  part  pass  the  other, 
and  be  projected  to  the  opposite  surface,  is  a  question  on  which  electricians 
are  not  agreed. 

The  Leyden  jar  affords  the  means  of  passing  through  bodies  a  large 
quantity  of  electricity.  For  not  only  may  jars  of  any  required  size  be  em- 
ployed, but  it  is  easy  so  to  arrange  any  number  of  such  jars,  that  they  shall 
all  be  charged  and  discharged  at  the  same  time,  constituting  what  is  termed 
an  Electrical  Battery.  The  arrangement  is  made  by  placing  a  number  of 
Leyden  jars  in  a  box  lined  with  tinfoil,  by  which  means  their  outer  surfaces 
have  free  metallic  communication  with  each  other,  and  connecting  their 
inner  surfaces  by  wires. 

The  explanation  above  given  of  the  action  of  a  Leyden  jar  suggests  a 
curious  point  of  theory.  A  jar  after  it  has  been  discharged  contains  a  smaller 
quantity  of  the  combined  fluids  than  before  it  was  charged ;  since  the  act  of 
charging  is  ascribed  to  loss  of  negative  electricity  by  the  inner  and  of  positive 
electricity  by  the  outer  surface  of  the  jar,  which  loss  is  not  restored  at  the 
moment  of  discharge.  Hence,  if  the  same  jar  were  charged  and  discharged 
many  times  in  succession,  the  total  quantity  of  electricity  remaining  in  the 
jar  ought  to  be  diminished  :  and  yet  a  Leyden  jar  does  not  seem  to  be  im- 
paired by  use,  but  is  equally  effective  at  last  as  at  first.  Several  kinds  of 
assumption  may  be  made  to  explain  this.  1.  It  is  possible  that  the  quantity 
of  electricity  present  in  bodies  may  be  so  enormous,  that  any  loss  obtained 
in  our  experiments  is  inappreciable.  2.  There  may  be  some  unknown 
mode  by  which  electricity  abstracted  from  a  substance  is  restored  to  it. 
3.  It  may  be  assumed  that  when  the  total  quantity  of  the  electricity  in  a 
jar  is  diminished  to  a  certain  extent,  the  excited  prime  conductor  no  longer 
charges  the  interior  by  decomposing  its  combined  fluids,  but  by  imparting 
to  it  positive  electricity  ;  and  that  the  outer  surface  of  the  jar  is  then  supplied 
with  a  corresponding  quantity  of  electricity  directly  from  the  earth. 


80  ELECTRICITY. 

6.  The  principle  of  induced  electricity  was  ingeniously  Fig.  2. 
applied   by  Volta  in  the  construction  of  the  Condenser. 

This  apparatus,  shown  in  fig.  2,  consists  of  two  brass 
plates,  A  and  B,  supported  on  a  common  stand  D.  One 
of  the  plates  B  is  attached  to  the  stand  by  means  of  a 
hinge  c,  so  that,  though  represented  upright,  it  may  be 
placed  horizontally,  and  thus  be  withdrawn  from  the  vici- 
nity of  the  plate  A,  the  support  of  which  is  made  of  glass. 
On  electrifying  the  insulated  plate  positively,  the  plate  B, 
expressly  placed  close  to  A,  is  rendered  negative  by  induc- 
tion; and,  as  happens  in  the  Leyden  jar,  the  excitement 
of  B  will  be  proportional  to  that  of  A.  The  negative  charge 
of  B  tends  to  preserve  the  positive  charge  of  A,  which  may 
consequently  receive  still  more  electricity  by  contact  with  any  positive  sur- 
face, without  losing  what  it  had  previously  acquired.  Thus  is  electricity 
accumulated  or  condensed  on  A  ;  so  that  a  substance  too  feebly  excited  to 
produce  any  appreciable  effects  of  itself,  may,  by  repeated  contact  with  the 
insulated  plate  of  a  condenser,  communicate  a  charge  of  considerable  inten- 
sity. The  effect  of  the  accumulation  is  made  apparent  by  withdrawing  B, 
and  bringing  A  in  contact  with  a  delicate  electrometer.  The  condenser  is 
much  employed  in  experiments  of  delicacy,  and  the  plate  A  is  often  perma- 
nently fixed  on  the  gold-leaf  electrometer. 

7.  The  Electrophorus  is  another  contrivance  of  Volta's,  which  acts  by  in- 
duced electricity.     It  consists  essentially  of  two  parts;  one  being  a  flat  cake 
of  resin,  made  by  pouring  melted  resin  into  a  shallow  plate  or  circular  dish 
of  tinned  iron,  and  the  other  a  disc  of  brass,  of  rather  smaller  diameter  than 
the  resin,  supplied  with  a  glass  handle.     The  surface  of  the  resin  is  nega- 
tively excited  by  friction  or  flapping  with  silk  or  flannel,  and  the  brass  disc 
is  laid  upon  it.     The  resin  being  a  non-conductor  retains  its  own  electricity 
in  spite  of  the  super-imposed  brass,  and  decomposes  the  combined  electri- 
cities of  the  latter,  causing  its  under  surface  to  be  positive,  and  its  upper 
negative.     On  touching  the  brass  with  the  finger,  its  upper  surface  is  neu- 
tralized, and  on  then  withdrawing  the  brass  plate,  it  is  found  to  have  an 
excess  of  positive  electricity.     On  replacing  the  brass  as  before,  the  resin, 
having  lost  none  of  its  electricity  in  the  process,  acts  again  upon  the  metallic 
disc  as  on   the  first  occasion,  and  will  continue  so  to  act  for  an  indefinite 
number  of  times.     Kept  in  a  dry  place  the  electrophorus  will  keep  in  action 
for  months. 

ELECTROSCOPES  AND  ELECTROMETERS. 

It  is  very  important,  in  experiments  on  electricity,  to  possess  easy  methods 
of  discovering  when  a  substance  is  electrified,  of  ascertaining  its  intensity  or 
the  degree  to  which  it  is  excited,  and  distinguishing  the  kind  of  excitement. 
The  means  for  effecting  these  objects  are  founded  on  electrical  attraction 
and  repulsion,  and  the  instruments  employed  for  the  purpose  are  called 
Electroscopes  and  Electrometers,  the  latter  denoting  the  intensity  of  elec- 
tricity, the  former  merely  indicating  excitement,  and  the  electrical  state  by 
which  it  is  produced.  The  term  electrometer,  however,  is  often  indiscrimi- 
nately applied  to  all  such  instruments,  since  the  methods  of  ascertaining  the 
kind  of  excitement  give  at  the  same  time  some  idea  of  its  intensity. 

Gold-leaf  Electrometer. — Several  simple  electroseopic  methods  have  al- 
ready been  indicated.  (Page  72.)  Small  balls  made  of  the  pith  of  elder  are 
used  for  the  same  purpose.  A  single  pith  ball,  suspended  by  a  cotton  thread, 
is  attracted  by  a  feebly  electrified  substance.  Also,  when  two  pith  balls  are 
suspended  from  the  same  point  by  cotton  threads  of  equal  lengths,  and  an 
electrified  body  is  placed  near  them,  the  two  balls  are  thrown  by  induction 


ELECTRICITY. 


81 


into  the  same  electric  state,  and  diverge,  The  gold-leaf  electro-  Fig.  3. 
meter,  figure  3,  invented  by  Mr.  Bennett,  acts  upon  the  same 
principle,  but  is  far  more  delicate.  It  consists  of  a  glass  cyl- 
inder cemented  below  upon  a  brass  plate  CD,  and  covered 
above  by  a  brass  plate  AB,  pierced  in  its  centre  for  the  inser- 
tion of  a  glass  tube  be,  the  top  of  which  is  closed  by  a  brass 
plate  a :  into  this  plate  is  screwed  a  thick  brass  wire,  which 
passes  through  the  glass  tube,  and  from  the  lower  end  d  of 
which  two  slips  of  gold-leaf  are  suspended.  These  different 
parts  are  put  together  while  quite  dry,  all  the  joinings  are  se- 
cured by  wax  cement,  and  the  glass  is  covered  by  lac  varnish. 

The  effect  of  these  arrangements  is  to  insulate  the  plate  a  with  its  wire 
and  gold  leaves,  while  the  latter  are  secure  against  being  moved  by  currents 
of  air.  The  approach  of  any  electrified  body,  even  though  feebly  excited, 
to  the  plate  a,  is  immediately  detected  by  the  divergence  of  the  leaves,  as 
shown  in  the  figure.  The  instrument  is  equally  useful  in  indicating  the 
kind  of  excitement,  provided  the  plate  and  leaves  be  permanently  electrified, 
which  may  easily  be  done  on  the  same  principle  as  in  charging  the  metal- 
lic disc  of  an  electrophorus.  Thus,  on  placing  a  negatively  excited  body, 
as  for  example  a  stick  of  sealing-wax  after  friction  on  woollen  cloth,  near 
the  brass  plate  of  the  electrometer,  the  electric  equilibrium  of  its  whole  me- 
tallic surface  is  disturbed  :  the  brass  plate  becomes  positive,  and  the  slips  of 
gold-leaf  diverge  from  being:  negative.  If  the  plate  be  then  touched  with  the 
finger,  the  equilibrium  of  the  gold  leaves  is  restored,  and  their  divergence 
ceases,  while  an  excess  of  positive  electricity  is  preserved  on  the  plate  by  the 
vicinity  of  the  negative  sealing-wax.  On  removing  Jirst  the  finger,  and  then 
the  sealing-wax,  the  brass  is  left  with  an  excess  of  positive  electricity,  which 
extends  over  the  whole  metallic  surface  of  the  electrometer,  and  thus  pro- 
duces a  divergence  which  continues  for  a  considerable  time  if  the  glass  be 
dry,  and  the  atmosphere  moderately  free  from  moisture.  The  approach  to 
the  brass  plate  of  a  positively  excited  body  increases  the  divergence  of  the 
gold-leaves ;  because  the  plate  becomes  negative  by  induction,  and  the  posi- 
tive fluid  retiring  to  the  extremities  of  the  leaves,  renders  tltem  still  more 
positive.  A  negatively  excited  body  has  an  exactly  opposite  effect,  by  at- 
tracting the  positive  fluid  towards  the  plate  and  from  the  leaves,  and  dimi- 
nishing divergence. 

Quadrant  Electrometer. — An  instrument  much  used  for  estimating  the 
degree  or  intensity  of  electricity  is  the  quadrant  electro-  Fig.  4. 

meter •,  figure  4,  invented  by  Mr.  Henley.  It  consists  of  a 
smooth  round  stem  of  wood  a  5,  about  seven  inches  long, 
to  the  upper  part  of  which,  and  projecting  from  its  side, 
is  attached  a  semicircular  piece  of  ivory.  In  the  centre 
c  of  the  semicircle  is  fixed  a  pin,  from  which  is  suspend-  90 
ed,  to  serve  as  an  index,  a  slender  piece  of  wood  or  cane 
d  e,  four  inches  in  length,  and  terminated  by  a  small 
ball.  When  the  apparatus  is  screwed  on  the  prime  con- 
ductor of  the  electrical  machine,  or  placed  on  any  elec- 
trified body,  it  indicates  differences  of  electric  intensity 
by  the  extent  to  which  the  index  recedes  from  the  stem ; 
and  in  order  to  express  the  divergence  in  numbers,  the 
lower  half  of  the  semicircle,  which  is  traversed  by  the  in- 
dex, is  divided  into  90  equal  parts  called  degrees.  This 
instrument,  though  convenient  for  experiments  of  illustra- 
tion, is  not  suited  to  those  of  research,  wherein  the  object  is  to  examine  the 
effects  of  substances  feebly  electrified,  and  ascertain  their  relative  forces  with 
accuracy. 

Torsion  Electrometer. — This  instrument,  invented  by  Coulomb,  is  pecu- 
liarly fitted  for  scientific  investigation.  It  consists  of  a  small  needle  of  gum- 


ELECTRICITY. 


Fig.  5. 


Fig.  6. 


lac  c  d,  fig.  5,  suspended  horizontally  by  a  silk  thread  as 
spun  by  the  silk  worm,  or  by  a  fine  silver  wire  a  b  ;  on  the 
point  of  the  needle  is  fixed  a  small  gilt  ball  made  of  the 
pith  of  elder ;  and  the  whole  is  covered  with  a  glass  case 
to  protect  it  from  moisture  and  currents  of  air.  The  pith 
ball,  when  the  apparatus  is  at  rest,  is  in  contact  with  the 
knob  e  of  a  metallic  conductor /e,  which  passes  through  a 
hole  in  the  glass  case,  and  is  secured  in  its  place  by  ce- 
ment; but  when  an  excited  body  is  made  to  touch  the  con- 
ductor, the  pith  ball  in  contact  with  it  is  similarly  excited, 
and  recedes  from  it  to  an  extent  proportional  to  the  degree 
of  excitement.  The  needle  consequently  describes  the  arc 
of  a  circle,  which  is  measured  on  the  graduated  arc  AB, 
and  in  its  revolution  twists  the  supporting  thread  more  or  less  according  to 
the  length  of  the  arc  described.  The  torsion  thus  occasioned  calls  into  play 
the  elasticity  of  the  thread, — a  feeble  but  constant  force,  which  opposes  the 
movement  of  the  needle,  measures  by  the  extent  to  which  it  is  overcome  the 
repulsive  force  exerted,  and  brings  back  the  needle  to  its  original  position 
as  soon  as  the  electric  equilibrium  is  restored.  It  has  been  proved  that  the 
force  which  causes  the  torsion  is  exactly  proportional  to  the  arc  described  by 
the  needle. 

Balance  Electrometer. — Mr.  Harris  of  Plymouth  has  made  a  happy  appli- 
cation of  the  common  balance  and  weights  to  estimate  the  mutual  attrac- 
tion of  oppositely  electrified  surfaces.  The  appa- 
ratus, figure  6,  consists  of  a  brass  beam  BB',  sup- 
ported by  a  conductor  CD  standing  on  a  wooden 
frame  AA'  ;  d  is  a  scale  for  holding  weights,  and  E 
its  support;  a,  6,  are  gilt  cones  made  of  light  wood, 
a  being  suspended  by  a  silver  wire  from  B'  and  b 
insulated  by  the  glass  support  A.fd'.  The  instrument 
is  prepared  for  use  by  placing  a  and  d  in  exact 
equipoise ;  the  cone  a  is  suspended  so  that  its  base 
shall  be  opposite  and  parallel  to  the  base  of  the  cone 
6,  as  may  be  done  by  means  of  three  adjusting 
screws  in  the  frame  AA'  ;  and  b  is  raised  by  help  of 
a  graduated  brass  slide  c,  until  the  bases  of  the 
cones  are  just  in  contact.  The  cone  b  is  then  de- 
pressed to  any  desired  distance,  which  may  be  va- 
ried at  will  during  an  experiment.  The  same  cone 
is  connected  with  the  inner  coating  of  a  Leyden 
jar,  the  outer  coating  of  which  communicates  with 
the  frame  of  AA',  and  along  CDS'  with  the  cone  a : 
these  cones  may  thus  be  made  parts  of  a  charged 
Leyden  jar,  and  be  oppositely  excited,  as  indicated  by  the  signs  -{-  and  — . 
The  attractive  forces  exerted  between  their  bases  tends  to  draw  down  the 
cone  a  into  contact  with  6,  discharging  the  jar ;  but  before  it  can  do  so,  it 
has  to  overcome  the  weight  which  may  be  in  the  scale  d.  By  this  ingenious 
contrivance  any  number  of  attractive  forces  are  estimated  by  a  common 
standard,  namely,  the  number  of  grains  which  each  is  able  to  raise. 

Unit  Jar. — This  is  another  contrivance  of  Mr.  Harris,  and  is  a  most  im- 
portant addition  to  our  stock  of  electrical  apparatus.  It  is  formed  of  a 
small  inverted  Leyden  jar,  figure  7,  supported  and  insulated  by  a  slender 
glass  rod  e/,  which  is  covered  with  lac  varnish,  and  fixed  into  a  wocde  i 
frame  A.  The  inner  coating  of  this  jar  is  in  metallic  contact  with  a  brass 
ball  d  and  a  wire  a,  which  wire  communicates  with  the  prime  conductor 
of  an  active  electrical  machine;  whereas  the  brass  ball  c  and  wire  6  are 
connected  with  its  outer  coating.  If  the  wire  b  be  held  in  the  hand  or 
otherwise  communicate  with  the  ground,  the  electrical  machine  being  in 
action,  the  jar  is  charged  in  the  usual  manner,  and  is  discharged  by  a 


ELECTRICITY. 


83 


spark  passing  between  the  two  brass  balls  c  and  d.  The  Fig.  7- 
interval  may  be  increased  or  diminished  by  causing  one  of 
the  balls  to  be  moveable  by  means  of  a  slide  or  screw.  It 
will  be  readily  conceived  that  successive  sparks  through 
the  same  interval  must  be  caused  by  equal  quantities  of 
electricity ;  and  experiment  shows  this  to  be  the  case,  pro- 
vided the  apparatus  is  clean  and  dry,  and  the  charges  are 
taken  nearly  at  the  same  time,  that  is,  while  the  air  in  re- 
lation to  temperature,  pressure,  and  moisture,  may  be  con- 
sidered constant.  On  taking  six  successive  sparks  we  em- 
ploy  six  times  as  much  electricity  as  for  one  charge,  and 
three  times  as  much  as  for  two  charges,  the  quantity  of 
electricity  being  proportional  to  the  number  of  charges. 
It  is  on  this  account  Mr.  Harris  introduced  the  term 
unit  jar. 

The  principal  use  of  the  unit  jar  is  in  charging  other 
Leyden  jars  with  known  proportions  of  electricity.  Thus, 
if  the  unit  jar  be  charged  by  the  prime  conductor,  while 
its  outside  communicates  through  the  wire  b  with  the  in- 
side of  a  large  Leyden  jar  standing  on  the  ground,  the 
positive  fluid  repelled  from  the  unit  jar  gives  an  equal  positive 
charge  to  the  inner  coating  of  the  large  jar,  and  its  outer 
coating  is  rendered  negative  by  induction.  Under  these  cir- 
cumstances the  effect  of  a  spark  between  c  and  d  is  merely 
to  neutralize  the  coatings  of  the  unit  jar,  without  affecting  the  state  of  the 
large  jar.  On  giving  a  second  charge  to  the  unit  jar,  the  large  jar  receives 
an  increment  equal  to  what  it  received  from  the  first  charge,  and  the  second 
spark  merely  restores  the  equilibrium  of  the  unit  jar  as  before.  A  third  and 
fourth  charges  of  the  unit  jar  act  on  the  same  principle;  and,  by  continuing 
the  process,  any  known  proportions  may  be  given.  If  the  opposite  coatings 
of  a  jar  so  charged  be  connected  with  the  cones  of  the  balance  electrometer, 
previously  described,  the  attractive  forces  due  to  known  relative  quantities 
of  electricity  may  be  precisely  determined. 

Electric  Intensity. — Before  concluding  this  account  of  electrometers,  it 
will  be  useful  to  .refer  to  the  kind  of  information  which  they  supply.  From 
the  mode  in  which  these  instruments  act,  it  is  plain  that  they  indicate  the 
degree  of  electric  excitement,  the  remoteness  from  the  unexcited  state,  a 
condition  expressed  by  the  terms  tension  and  intensity.  If  two  insulated 
brass  discs  of  equal  size  be  supplied  with  equal  quantities  of  free  electricity, 
they  will  affect  an  electrometer  equally,  and,  therefore,  their  intensity  or 
tension  is  equal ;  but  if  one  of  the  discs  be  larger  than  the  other,  the  smaller 
will  have  the  highest  tension.  In  fact,  one  square  inch  of  the  smaller  disc 
will  possess  more  free  electricity  than  the  larger,  and  that  is  precisely  the 
condition  which  constitutes  differences  of  intensity.  Of  any  number  of 
electrified  substances,  that  will  have  the  highest  intensity  which  has  the 
most  free  electric  fluid  on  unity  of  surface. 

LAWS  OF  ELECTRICAL  ACCUMULATION. 

1.  The  quantity  of  free  electricity  which  an  insulated  conductor  is  capa- 
ble of  receiving  is  independent  of  its  quantity  of  matter.     Thus,  two  brass 
spheres  of  the  sanrfe  size,  one  solid  and  the  other  hollow,  will  take  equal 
quantities  of  electricity,  and  possess  equal  intensities.     The  cause  of  this  is 
referable  to  the  second  law. 

2.  The  free  electricity  of  an  insulated  conductor  is  always  accumulated 
on  its  surface,  where  it  forms  a  layer  or  stratum  enveloping  the  substance 
on  every  side,  and,  therefore,  possessed  of  the  same  figure.     Thus,  an  ex- 
cited sphere,  the  surface  of  which  is  exactly  fitted  with  two  thin  metallic 
hemispheres,  loses  the  whole  charge,  when,  by  means  of  glass  handles,  the 
hemispheres  are  suddenly  removed ;  and  an  excited  hollow  cylinder,  open  at 


84  ELECTRICITY. 

the  ends,  will  admit  of  being-  touched  by  an  insulated  conductor,  cautiously 
introduced  into  its  interior,  without  any  loss  of  electricity.  The  cause  of 
free  electricity,  being  disposed  upon  the  surface  of  conductors  is  ascribed  to 
the  mutual  repulsion  of  its  particles,  which  gives  them  a  tendency  to  recede 
as  far  as  possible  from  each  other,  and  to  be  arrested  at  the  surface  solely 
by  some  counteracting  force,  such  as  the  interposition  of  an  imperfect  con- 
ductor. 

3.  The  mode  in  which  electricity  is  distributed  over  the  surface  of  a  con- 
ductor  is  dependent  on  its  figure.     On  a  sphere  it  forms  a  uniform  stratum 
of  equal  thickness  all  around,  that  is,  each  part  of  the  surface  has  the  same 
quantity  of  electricity  as  any  other  part  of  equal  size.     But  on  an  ellipsoid 
the  stratum  is  thickest  at  the  extremities  of  the  longer  axis,  and  the  accu- 
mulation at  those  parts  is  greater  and  greater  as  the  length  of  that  axis  be- 
comes  more  and   more  predominant.     In  all  conductors  which  are  much 
longer  than  broad,  as  in  a  narrow  metallic  bar,  as  also  in  those  which  have 
elongated  pointed  terminations,  the   principal   accumulation  is  at  the  ends 
and  projecting  points.     The  inequality  of  distribution  is  just  as  conspicuous 
in  a  negatively  as  in  a  positively  excited  conductor,  a  circumstance  which 
seems  utterly  irreconcilable  with  the  theory  of  a  single  fluid.    Coulomb 
proved  these  facts  experimentally  by  touching  the  different  parts  of  electri- 
fied conductors  by  a  proof-plane,  which  is  a  very  small  disc  of  gilt  paper 
insulated  by  a  handle  of  lac  resin,  and  estimating  the  tension  of  the  proof- 
plane  by  his  torsion  electrometer :  he  found  that  this  plane  always  took  from 
the  spot  touched  a  constant  proportion  of  the  electricity  accumulated  at  that 
spot,  and,  therefore,  the  relative  intensities  of  the  plane,  after  contact  with 
different  parts  of  an  electrified  conductor,  exactly  represented  the  electric 
accumulation  of  the  parts  so  touched.     For  these  and  other  experiments  of 
Coulomb  on  electrical   actions,  the  reader  may  consult  Biot's    Traite    de 
Physique. 

The  unequal  accumulation  of  electricity  on  conductors  is  a  direct  con- 
sequence of  the  law  of  electric  repulsion ;  and  M.  Poisson,  assuming  the 
truth  of  that  law,  has  arrived  by  calculation  at  the  very  same  conclusions 
which  Coulomb  obtained  by  experiment.  Those  who  are  prepared  to  follow 
such  very  high  mathematical  inquiries  are  referred  to  Poisson's  original 
Essay,  to  the  article  on  Electricity  by  Mr.  Whewell  in  the  Encyclopedia 
Metropolitana,  and  to  a  late  work  on  Electricity  by  Mr.  Murphy. 

4.  The  electric  fluid  accumulated  at  the  surface  of  conductors  tends  to  escape 
by  the  repulsion  of  its  particles.     Its  pressure  against  the  air  is  considered 
proportional  to  the  square  of  the  quantity;  so  that  if  the  electric  accumula- 
tion at  four  different  parts  of  an  excited  conductor  is  as  1,  2,  3,  and  4,  the 
pressure  against  the  air  at  those  parts  will  be  as  1,  4,  9,  and  16.     Hence 
electricity  passes  off  with  great  rapidity  from  the  ends  or  projecting  points 
of  conductors,  a  result  quite  conformable  to  experience.     But  the  equilibrium 
of  an  excited  conductor  is  perhaps  never  entirely  restored  by  the  direct  dif- 
fusion of  its  excess  due  to  its  own  repulsion ;  for  the  conductor  necessarily 
tends  to  induce  a  state  opposite  to  itself  in  contiguous  conductors  and  in  the 
circumambient  air,  and  then  the  attraction  of  oppositely  electrified  surfaces 
is  called  into  play. 

5.  Coulomb  proved  experimentally,  by  aid  of  his  torsion  electrometer,  that 
the  repulsion  of  two  similarly  electrified  bodies  varies  inversely  as  the  square 
of  their  distances.     If  the  electric  charge  on  one  of  them  vary,  while  that  on 
the  other  and  the  distance  are  constant,  the  repulsion  will  vary  simply  as  the 
quantity.     Thus,  let  the  free  electricity  on  A  be  expressed  by  4,  and  that  on 
B  by  1,  and  the  distance  be  always  1  inch,  then  if  the  charges  on  B  vary  as 
1,  2,  3,  and  4,  the  repulsion  will  also  vary  as  1,  2,  3,  and  4;  for  the  succes- 
sive additions  to  B  merely  act  by  augmenting  in  the  same  ratio  the  number 
of  repulsive  particles  influenced  by  the  constant  charge  on  A.     The  repulsion 
in  these  cases  may  be  denoted  by  the  product  of  the  two  charges.     For 
example,  when  the  charges  on  A  and  B  are  4  and  1,  the  repulsion  will  be 
4X1=4;  when  they  are  4  and  2,  the  repulsion  is  4X2=8,  or  twice  four 


ELECTRICITY*  85 

when  4  and  3,  it  is  4X3==12,  or  three  times  four;  and  when  4  and  4,  the 
repulsion  is  4X4== 16,  or  four  times  four.  If  in  the  last  case  the  charge  on 
B  fall  to  2,  the  repulsion  becomes  4X2=8  as  before;  and  then  should  the 
charge  on  A  be  also  reduced  to  2,  the  repulsion  will  be  2X2=4.  Hence 
when  the  whole  quantity  of  electricity  changes,  the  repulsion  varies  as  the 
square  of  the  quantity* 

6.  The  attraction  of  two  oppositely  electrified  bodies  varies  inversely  as 
the  square  of  the  distance  between  them.     Coulomb,  who  verified  this  law 
by  experiment,  also  showed  that  the  attractive  force,  the  distance  being  con- 
stant, varies  by  the  same  law  as  that  for  repulsion  just  stated.     If  A  and  B 
are  equally  and  oppositely  excited,  so  that  we  may  represent  the  free  elec- 
tricity on  each  by  4,  and  their  mutual  attraction  by  4X4=16,  then  if  the 
quantity  on  B  successively  become  3,  2,  and  1,  the  corresponding  attractions 
will  be  12,  8,  4 ;  and  should  the  quantity  on  A  and  on  B  vary  together,  so  as 
to  be  reduced  on  both  from  4  to  2,  and  from  2  to  1,  the  attractions  will  be 
16,4,  and   1.     Thus,  when   the  whole  quantity  of  electricity  changes,  the 
attraction  varies  as  the  square  of  the  quantity. 

Mr.  Harris  has  given  a  beautiful  demonstration  of  these  laws  by  means  of 
his  balance  electrometer  and  unit  jar  (pages  82,  83),  the  cones  a,  6,  of  figure 
6,  being  connected  respectively  with  the  outer  and  inner  coatings  of  a  large 
Leyden  jar.  On  giving  to  it  a  constant  charge  by  means  of  the  unit  jar, 
and  varying  the  distance,  the  weights  raised,  or  the  attractive  force,  were 
found  to  vary  exactly  as  the  square  of  the  distance  between  the  cones.  On 
preserving  the  distance  constant,  giving  a  charge  capable  of  raising  one 
grain,  and  then  successively  doubling,  trebling,  and  quadrupling  the  quan- 
tity first  given  to  the  inner  coating,  the  weights  raised  were  4,  9,  and  16 
grains.  This  strictly  conforms  with  the  foregoing  statement ;  for  on  doubling 
the  charge  to  the  inner  coating  of  the  Leyden  jar,  the  electricity  on  the 
cone  6,  connected  with  it,  is  also  doubled,  and  the  double  charge  on  b  doubles 
the  induced  charge  on  a.  Hence  the  quantity  on  both  cones  being  doubled, 
the  force  ought  to  be  quadrupled. 

7.  It  may  be  inferred  from  the  law  No.  6,  that  when,  in  two  oppositely 
excited  bodies,  the  whole  quantity  of  electricity  and  the  distance  vary  toge- 
ther and  at  the  same  rate,  the  attractive  force  will  be  unchanged.     This  has 
been  fully  proved  by  Mr.  Harris.     On   putting  5  grains  into  his  balance, 
giving  a  charge  sufficient  to  raise  that  weight  at  a  certain  distance,  and  then 
successively   doubling,  trebling,  and  quadrupling  that  distance,  it  will   be 
necessary,  in  order  to  raise  the  5  grains,  to  give  a  double,  treble,  and  quadru- 
ple charge  to  the  inner  coating  of  the  Leyden  jar  communicating  with  cone 
b.     In  fact,  doubling  the  electricity  on  both  cones,  is  to  quadruple  the  attrac- 
tive force  between  them  ;  and  doubling  the  distance,  diminishes  the  force  by 
four  times :  the  force  is  thus  diminished  by  one  cause  as  much  as  it  is 
increased  by  the  other,  and,  therefore,  continues  unchanged. 

Mr.  Harris  has  demonstrated  the  same  law  by  observing  the  striking  dis- 
tance of  a  charged  jar,  that  is,  the  interval  through  which  the  electricity  will 
pass  so  as  to  discharge  it.  For  this  purpose  the  inner  and  outer  coating  are 
separately  connected  with  a  conductor  terminating  in  a  brass  ball,  one  of 
which  is  attached  to  a  graduated  slide,  so  as  to  be  fixed  at  any  required  dis- 
tance from  the  other  ball.  On  causing  the  distances  between  the  balls  to  vary 
in  the  ratio  of  1,  2,  3,  4,  the  jar  will  discharge  itself  by  the  passage  of  a 
spark,  when  the  charge  on  each  coating  is  increased  in  the  same  ratio.  The 
obstacle  which  the  electricity  has  to  overcome  before  it  can  discharge  the 
jar,  is  the  interposed  air ;  and  that  obstacle  may  be  regarded  as  constant  in 
experiments  performed  at  the  same  time,  since  it  is  found  to  depend  on  the 
density  of  the  air. 

8.  Mr.  Harris  ascertained  the  nature  of  the  influence  exerted  by  the  atmo- 
sphere over  the  striking  distance  of  a  charged  Leyden  jar,  by  including  the 
balls  connected  with  its  outer  and  inner  coating  within  glass  vessels  sus- 
ceptible of  exhaustion.     He  then  found  that  the  resistance  to  the  passage  of 
a  charge  varies  as  the  square  of  the  density  of  the  air.    Thus,  when  the 


86  ELECTRICITY. 

density  was  made  to  vary  in  the  ratio  of  1,2, 4,  the  charge  passed  through  a 
constant  interval,  when  the  quantity  added  to  the  inner  coating  varied  in  the 
same  ratio.  Now,  when  the  charges  were  as  1,  2,  4,  the  attractive  forces, 
by  law  No.  6,  were  as  1,  4,  1G,  which  represent  the  corresponding  obstacles 
caused  by  the  air.  Agreeably  to  the  same  law,  the  striking  distance,  when 
the  charge  is  constant,  varies  inversely  as  the  density  of  the  air :  a  charge 
which  strikes  through  one  inch  of  air  when  the  barometer  is  at  30  inches, 
will  pass  through  two  inches  in  air  so  rarefied  as  to  support  only  15  inches 
of  mercury,  and  through  four  inches  when  the  mercurial  column  is  7.5 
inches.  Hence,  in  a  perfect  vacuum,  a  Leyden  jar  ought  to  discharge  itself 
through  any  interval ;  and  in  the  higher  parts  of  the  atmosphere,  where  the 
air  is  much  rarefied,  two  oppositely  excited  clouds  will  neutralize  each  other, 
though  separated  by  very  great  distances. 

It  is  not  apparent  from  the  preceding  remarks,  whether  the  striking  dis- 
tance is  influenced  by  change  of  the  density  or  the  elasticity  of  the  confined 
air ;  since  in  rarefying  air  by  the  air-pump,  the  rarefaction  increases,  and  the 
elasticity  decreases  at  the  same  rate.  Mr.  Harris  has  shown,  contrary  to 
what  one  might  anticipate,  that  the  influential  condition  is  density  and  not 
elasticity.  For  on  rarefying  air  by  heat  so  as  to  preserve  its  original  elasti- 
city, the  striking  distance  was  exactly  the  same  as  in  cold  air  rarefied  to  the 
same  degree  by  the  air-pump ;  and  in  air  first  rarefied  by  the  air-pump,  and 
then  heated  until  it  had  recovered  its  original  elasticity,  its  volume  and  den- 
sity being  kept  the  same,  the  varied  elasticity  had  no  influence  on  the  charge 
required  to  pass  through  a  constant  distance.  From  these  and  similar  expe- 
riments Mr.  Harris  infers  that  the  remarkable  conducting  power  known  to 
be  possessed  by  hot  air  is  due  to  its  rarity  alone. — Though  I  have  not  had 
occasion  to  repeat  these  experiments  on  hot  air,  I  have  entire  confidence  in 
their  accuracy ;  inasmuch  as,  not  to  mention  the  known  skill  and  exactness 
of  Mr.  Harris,  I  find  that  the  striking  distance  for  the  same  charge  is  greater 
in  air  than  in  carbonic  acid  gas,  and  greater  in  hydrogen  gas  than  in  air,  the 
elasticities  being  equal. 

9.  The  continuance  of  an  excited  charge  on  an  insulated  conductor  is  com- 
monly ascribed  to  the  pressure  of  the  air.  An  opposite  opinion,  however, 
has  been  maintained.  Mr.  Morgan  (Phil.  Trans.  1785)  published  some  ex- 
periments to  prove  that  a  space  entirely  free  from  air,  such  as  a  Torricellian 
vacuum,  is  a  non-conductor  of  electricity ;  and  Mr.  Cavallo  (Treatise  on 
Electricity)  showed  that  exhaustion  may  be  carried  very  far  within  the  bell- 
jar  of  an  air-purnp,  without  an  electrified  body  placed  under  it  losing  its 
charge.  On  repeating  these  experiments,  at  the  request  of  Mr.  Harris,  I 
obtained  similar  results.  A  slip  of  gold-leaf  diverging  at  an  angle  of  60°, 
continued  so  for  hours  in  air  expanded  100  times ;  and  in  air  rarefied  300 
times  a  feeble  charge  was  retained  for  a  whole  week.  The  loss  observed  in 
still  further  states  of  exhaustion,  may  be  ascribed  to  the  excited  body  inducing 
an  opposite  state  in  the  conducting  materials  of  the  air-pump,  thereby  calling 
into  activity  a  force  which  co-operates  with  the  repulsion  of  its  own  particles. 
The  preceding  phenomena  appear  to  indicate  the  existence  of  an  adhesive 
force  between  the  particles  of  electricity  and  the  surface  of  bodies  which 
causes  an  obstacle  to  their  escape. 

The  facts  which  I  have  given  in  the  few  preceding  pages  on  the  authority 
of  Mr.  Harris,  are  described  by  him  at  length  in  an  essay  just  read  before 
the  Royal  Society.  Owing  to  his  kindness  in  procuring  for  me  his  appara- 
tus, and  showing  me  his  method  of  operating,  I  have  been  enabled  to  repeat 
all  the  experiments  referred  to,  except  those  on  heated  air,  and  am  quite 
satisfied  of  their  accuracy. 

HISTORICAL  NOTICE. 

The  science  of  electricity  is  of  modern  origin.  The  knowledge  of  the 
ancients  was  confined  to  the  fact,  that  amber  and  the  lyncurium  (supposed  to 
be  tourmalin)  acquired  the  property  of  attracting  light  bodies  by  friction.  It 


GALVANISM.  87 

was  not  known  that  other  bodies  might  be  similarly  excited  until  the  com- 
mencement of  the  seventeenth  century,  when  Dr.  Gilbert  of  Colchester  de- 
tected the  same  property  in  a  variety  of  other  substances,  and  thereby  laid 
the  foundation  of  the  science  of  electricity.  A  few  additional  facts  were  no- 
ticed  during  the  same  century  by  Boyle,  Otto  de  Guericke,  and  Wall,  and 
in  1709  Hawkesbee  published  an  account  of  many  curious  electrical  expe- 
riments; but  no  material  progress  was  made  until  Stephen  Grey  (Phil. 
Trans.  1729  to  1733)  drew  the  distinction  between  conductors  and  non-con- 
ductors of  electricity,  and  illustrated  it  by  new  and  striking  experiments. 
Soon  after  Dufay  in  France  distinguished  between  the  two  kinds  of  electri- 
city ;  and  in  1759  (Phil.  Trans,  li.'  340)  Symmer  added  the  important  fact 
that  friction  develops  both  kinds  of  electricity  at  the  same  time,  an  obser- 
vation which  led  to  the  theory  of  two  electric  fluids  as  now  understood. 
These  discoveries,  added  to  the  confirmation  of  Franklin's  opinion  as  to 
the  identity  of  the  cause  of  lightning  and  electricity,  fixed  the  attention  of 
scientific  men  upon  the  new  study,  and  soon  acquired  for  it  a  high  rank 
among  the  sciences. 

For  further  details  respecting  its  origin  and  early  progress,  the  reader 
may  consult  the  history  of  electricity  by  Priestley. 


SECTION    IV. 

GALVANISM. 

THE  science  of  Galvanism  owes  its  name  and  origin  to  the  experiments 
on  animal  irritability  made  by  Galvani,  Professor  of  Anatomy  at  Bologna, 
in  the  year  1790.  In  the  course  of  the  investigation  he  discovered  the  fact, 
that  muscular  contractions  are  excited  in  the  leg  of  a  frog  recently  killed, 
when  two  metals,  such  as  zinc  and  silver,  one  of  which  touches  the  crural 
nerve,  and  the  other  the  muscles  to  which  it  is  distributed,  are  brought  into 
contact  with  one  another.  Galvani  imagined  that  the  phenomena  are  owing 
to  electricity  present  in  the  muscles,  and  that  the  metals  only  serve  the  pur- 
pose of  a  conductor.  He  conceived  that  the  animal  electricity  originates  in 
the  brain,  is  distributed  to  every  part  of  the  system,  and  resides  particularly 
in  the  muscles.  He  was  of  opinion  that  the  different  parts  of  each  muscular 
fibril  are  in  opposite  states  of  electrical  excitement,  like  the  two  surfaces  of 
a  charged  Leyden  phial,  and  that  contractions  take  place  whenever  the  elec- 
tric equilibrium  is  restored.  This  he  supposed  to  be  effected  during  life 
through  the  medium  of  the  nerves,  and  to  have  been  produced  in  his  experi- 
ments by  the  intervention  of  metallic  conductors. 

The  views  of  Galvani  had  several  opponents,  one  of  whom,  the  celebrated 
Volta,  Professor  of  Natural  Philosophy  at  Pavia,  succeeded  in  pointing  out 
their  fallacy.  Volta  maintained  that  electric  excitement  is  due  solely  to  the 
metals,  and  that  the  muscular  contractions  are  occasioned  by  the  electricity 
thus  developed  passing  along  the  nerves  and  muscles  of  the  animal.  To  the 
experiments  instituted  by  Volta,  we  are  indebted  for  the  first  voltaic  appara- 
tus, which  was  described  by  him  in  the  Philosophical  Transactions  for  1800, 
and  which  has  properly  received  the  name  of  the  voltaic  pile;  and  to  the 
eame  distinguished  philosopher  belongs  the  real  merit  of  laying  the  founda- 
tion of  the  science  of  Galvanism. 

The  identity  of  the  agent  concerned  in  the  phenomena  of  galvanism  and  of 
the  common  electrical  machine,  is  now  a  matter  of  demonstration.  Voltaic  and 
common  electricity  are  due  to  the  same  force,  excited  by  different  conditions, 
operating  in  general  in  a  different  manner  and  under  different  circumstances. 
The  effects  of  the  latter  are  caused  by  a  comparatively  small  quantity  of  elec- 
tricity brought  into  a  state  of  insulation,  in  which  state  it  exerts  a  high  inten- 


88  GALVANISM. 

sity,  as  evinced  by  its  remarkable  attractive  and  repulsive  energies,  and  by 
its  power  to  force  a  passage  through  obstructing  media.  In  galvanism  the 
electric  agent  is  more  intimately  associated  with  other  substances,  is  deve- 
loped in  large  quantity,  but  never  attains  a  high  tension,  and  produces  its 
peculiar  effects  while  flowing  along  conductors  in  a  continuous  current. 

VOLTAIC  ARRANGEMENTS  OR  CIRCLES. 

Arrangements  for  exciting  galvanism  are  divided  into  simple  and  com- 
pound, the  former  being  voltaic  circles  in  their  most  elementary  form,  and 
the  latter  a  collection  of  simple  circles  acting  together:  it  will  hence  be  pro- 
per to  commence  the  description  of  them  with  the  most  simple. 

Simple  Voltaic  Circles. — When  a  plate  of  zinc  and  a  plate  of  copper  are 
placed  in  a  vessel  of  water,  and  the  two  metals  are  made  to  touch  each 
other,  either  directly  or  by  the  intervention  of  a  metallic  wire,  galvanism  is 
excited.  The  action  is,  indeed,  very  feeble,  and  not  to  be  detected  by  ordi- 
nary methods  ;  but  if  a  little  sulphuric  acid  be  added  to  the  water,  numerous 
globules  of  hydrogen  gas  will  be  evolved  at  the  surface  of  the  copper.  This 
phenomenon  continues  uninterruptedly  while  metallic  contact  between  the 
plates  continues,  in  which  state  the  circuit  is  said  to  be  closed;  but  it  ceases 
when  the  circuit  is  broken,  that  is  when  metallic  contact  is  interrupted. 
The  hydrogen  gas  which  arises  from  the  copper  plate  results  from  water  de- 
composed by  the  electric  current,  and  its  ceasing  to  appear  indicates  the 
moment  when  the  current  ceases.  In  this  case  the  voltaic  circle  consists  of 
zinc,  copper,  and  interposed  dilute  acid  ;  and  the  circle  gives  rise  to  a  cur- 
rent, only  when  the  two  metals  are  in  contact.  This  arrangement  is  shown 
in  figure  1,  where  metallic  contact  is  readily  made  Figj 

or  broken  by  means  of  copper  wires  soldered  to  the 
plates.  By  employing  a  galvanometer  (page  110), 
it  is  found  that  a  current  of  positive  electricity  con- 
tinually circulates  in  the  closed  circuit  from  the 

zinc  through  the  liquid  to  the  copper,  and  from  the  ^v       fiOTl^^  fa 

copper  along  the  conducting  wires  to  the  zinc,  as   ^\     lallM  IT 

indicated  by  the  arrows  in  the  figure.     A  current      VV _^/$ 

of  negative  electricity,  agreeably  to  the  theory  of 
two  electric  fluids,  ought  to  traverse  the  apparatus  in  a  direction  precisely 
reversed ;  but  for  the  sake  of  simplicity  I  shall  hereafter  indicate  the  course 
of  the  positive  current  only. 

It  matters  not,  so  far  as  voltaic  action  is  concerned,  at  what  part  the 
plates  of  fig.  1  touch  each  other.  A  current  takes  place,  whether  contact 
between  the  plates  is  made  below  where  covered  with  liquid,  above  where 
uncovered,  or  along  the  whole  length  of  the  plates,  provided  both  plates  are 
immersed  in  the  same  vessel  of  dilute  acid.  Immersion  of  one  plate  only  in 
the  acid  solution,  however  contact  between  the  plates  may  be  made,  does 
not  excite  voltaic  action ;  nor  does  it  suffice  to  have  one  plate  in  one  vessel, 
and  the  other  plate  in  another  vessel,  A  plate  of  zinc  spidered  to  one  of 
copper,  and  plunged  into  dilute  acid,  gives  a  current  passing  from  the  zinc 
through  the  fluid  round  to  the  copper:  but  if  the  soldered  plates  are  cement- 
ed into  a  box  with  a  wooden  bottom  and  metallic  sides,  Fi  10 
so  as  to  form  two  separate  cells,  as  shown  in  a  vertical 

section  by  figure  Q,  then  the  introduction  of  dilute  acid     , • • 

to  the  cells  will  not  excite  a  current,  unless  the  fluid  I 

of  the  cells  be  made  to  communicate   by  means  of  fk'-j          2£          (-^ 
moistened  fibres  of  twine,  cotton,  or  some  porous  mat- 
ter, or,  as  in  the  figure,  by  wires,  a  6,  soldered  to  the 
metallic  sides  which  contain  the  dilute  acid,  or  dipping 

into  the  acid  itself.     Then  the  positive  current  circu-       , __- 

lates  in  the  direction  shown  by  the  arrows.  <*  « 


GALVANISM. 


Fig.  4. 


Instead  of  a  pair  of  plates  being  soldered  to- 
gether, they  may  be  connected  by  a  wire,  and 
plunged  into  separate  cells,  a  e,  b  e,  figure  3,  in 
which  d  e  acts  as  a  partition ;  provided  the  positive 
current  issuing  from  the  zinc  plate  z,  is  conveyed 
by  a  wire,  /  g  h  i,  or  some  conducting  medium, 
into  the  cell,  6  e,  in  which  the  copperplate,  c,  is 
immersed. 

A  simple  voltaic  circle  may  be  formed  of  one 
metal  and  two  liquids,  provided  the  liquids  are  such 
that  a  stronger  chemical  action  is  induced  on  one  side  than 
on  the  other.  Thus,  on  cementing  a  plate  of  zinc,  z,  into  a 
box,  figure  4,  and  putting  a  solution  of  salt  into  the  cell,  b  6', 
and  dilute  nitric  acid  into  the  cell,  a  a',  a  positive  current 
will  be  excited  in  the  direction  of  the  arrows,  provided  the 
circuit  be  completed  by  a  wire,  a  6,  attached  to  the  metallic 
sides  of  the  box,  or  dipped  into  the  liquid  of  the  cells,  Nay, 
the  same  acid  solution  may  occupy  both  cells,  provided  some 
condition  be  introduced  which  shall  cause  one  side  of  the 
zinc  to  be  more  rapidly  dissolved  than  the  other;  as  by  the  plate  being  rough 
on  one  side  and  polished  on  the  other,  or  by  the  acid  being  hot  in  one  cell 
and  cold  in  the  other.  In  this  case,  however,  the  result  is  the  same  as 
though  two  different  liquids  were  used. 

An  interesting  kind  of  simple  voltaic  circle  is  afforded  by  commercial  zinc. 
This  metal,  as  sold  in  the  shops,  contains  traces  of  tin  and  lead,  with  rather 
more  than  one  per  cent,  of  iron,  which  is  mechanically  diffused  through  its 
substance :  on  immersion  in  dilute  sulphuric  acid,  these  small  particles  of 
iron  and  the  adjacent  zinc  form  numerous  voltaic  circles,  transmitting  their 
currents  through  the  acid  which  moistens  them,  and  disengaging  a  large 
quantity  of  hydrogen  gas.  Pure  distilled  zinc  is  very  slowly  acted  on  by 
dilute  sulphuric  acid  of  sp.  gr.  ranging  from  1.068  to  1.215 ;  but  if  fused 
with  about  2  per  cent.,  or  rather  less,  of  iron  filings,  it  is  as  readily  dissolved 
as  commercial  zinc.  In  like  manner,  pure  iron  or  steel  is  less  readily  acted 
on  by  dilute  sulphuric  acid  than  the  same  substances  after  fusion  with  small 
quantities  of  platinum  or  silver.  Mr.  Sturgeon  has  remarked  that  commer- 
cial zinc,  with  its  surface  amalgamated,  which  may  be  done  by  dipping  a 
zinc  plate  into  nitric  acid  diluted  with  two  or  three  parts  of  water,  and  then 
rubbing  it  with  mercury,  resists  the  action  of  dilute  acid  fully  as  well  as  the 
purest  zinc.  This  fact,  of  which  Faraday  in  his  late  researches  has  made 
excellent  use,  appears  due  to  the  mercury  bringing  the  surface  of  the  zinc 
to  a  state  of  perfect  uniformity,  preventing  those  differences  between  one 
spot  and  another,  which  are  essential  to  the  production  of  minute  currents; 
one  part  has  the  same  tendency  to  combine  with  electricity  as  another,  and 
cannot  act  as  a  discharger  to  it  (Faraday). 

While  the  current  formed  by  the  contact  of  two  metals  gives  increased  ef- 
fect to  the  affinity  of  one  of  them  for  some  element  of  the  solution,  the  ability 
of  the  other  metal  to  undergo  the  same  change  is  proportionally  diminished. 
Thus,  when  plates  of  zinc  and  copper  touch  each  other  in  dilute  acid,  the 
zinc  oxidizes  more,  and  the  copper  less,  rapidly  than  without  contact.  This 
principle  was  beautifully  exemplified  by  the  attempt  of  Davy  to  preserve 
the  copper  sheathing  of  ships.  A  sheet  of  copper  immersed  in  sea-water, 
or  a  solution  of  chloride  of  sodium,  in  an  open  vessel,  undergoes  rapid  cor- 
rosion ;  and  a  green  powder  commonly  termed  submuriate  of  copper,  but 
which  is  really  an  oxy-chloride,  is  formed :  atmospheric  oxygen  dissolved  in 
sea-water  unites  both  with  copper  and  sodium,  the  latter  yields  its  chlorine 
to  another  portion  of  copper,  and  the  oxide  and  chloride  of  copper  unite. 
But  if  the  copper  be  in  contact  with  zinc,  or  some  metal  more  electro-posi. 
tive  than  itself,  the  zinc  undergoes  the  same  change  as  the  copper  did,  an4 


90  GALVANISM. 

the  latter  is  preserved.  Davy  found  that  the  quantity  of  zinc  required  thus 
to  form  an  efficient  voltaic  circle  with  copper  was  very  small.  A  piece  of 
zinc  as  large  as  a  pea,  or  the  head  of  a  small  round  nail,  was  found  fully 
adequate  to  preserve  40  or  50  square  inches  of  copper ;  and  this  wherever  it 
was  placed ;  whether  at  the  top,  bottom,  or  middle  of  the  sheet  of  copper, 
or  under  whatever  form  it  was  used.  And  when  the  connexion  between 
different  pieces  of  copper  was  completed  by  wires,  or  thin  filaments  of  the 
40th  or  50th  of  an  inch  in  diameter,  the  effect  was  the  same ;  every  side, 
every  surface,  every  particle  of  the  copper  remained  bright,  whilst  the  iron 
or  the  zinc  was  slowly  corroded.  Sheets  of  copper  defended  by  l-40th  to 
l-1000th  part  of  their  surface  of  zinc,  malleable  arid  cast  iron,  were  exposed 
during  many  weeks  to  the  flow  of  the  tide  in  Portsmouth  harbour,  and  their 
weight  ascertained  before  and  after  the  experiment.  When  the  metallic 
protector  was  from  l-40th  to  l-150th,  there  was  no  corrosion  nor  decay  of 
the  copper;  with  smaller  quantities,  such  as  1 -200th  to  l-460th,  the  copper 
underwent  a  loss  of  weight  which  was  greater  in  proportion  as  the  protector 
was  smaller ;  and  as  a  proof  of  the  universality  of  the  principle,  it  was 
found  that  even  1-]  000th  part  of  cast-iron  saved  a  certain  proportion  of  the 
copper  (Phil.  Trans.  1824). 

Unhappily,  for  the  application  of  this  principle  in  practice,  it  is  found  that 
unless  a  certain  degree  of  corrosion  takes  place  in  the  copper,  its  surface 
becomes  foul  from  the  adhesion  of  sea-weeds  and  shell-fish.  The  oxy-chlo- 
ride  of  copper,  formed  when  the  sheathing  is  unprotected,  is  probably  inju- 
rious to  these  plants  and  animals,  and  thus  preserves  the  copper  free  from 
foreign  bodies. 

Simple  voltaic  circles  may  be  formed  of  very  various  materials;  but  the 
combinations  usually  employed  consist  either  of  two  perfect  and  one  imper- 
fect conductor  of  electricity,  or  of  one  perfect  and  two  imperfect  conductors. 
The  substances  included  under  the  title  of  perfect  conductors  are  metals  and 
charcoal,  and  the  imperfect  conductors  are  water  and  aqueous  solutions.  It 
is  essential  to  the  operation  of  the  first  kind  of  circle,  that  the  imperfect  con- 
ductor act  chemically  on  one  of  the  metals;  and  in  case  of  its  attacking  both, 
the  action  must  be  greater  on  one  metal  than  on  the  other.  It  is  also  found 
generally,  if  not  universally,  that  the  metal  most  attacked  is  positive  with 
respect  to  the  other,  or  bears  to  it  the  same  relation  as  zinc  to  copper  in 
figures  1,  2,  and  3.  Davy,  in  his  Bakerian  lecture  for  1826  (Phil.  Trans.), 
gave  the  following  list  of  the  first  kind  of  arrangements,  the  imperfect  con- 
ductor being  either  the  common  acids,  alkaline  solutions,  or  solutions  of 
metallic  sulphurets,  such  as  sulphuret  of  potassium.  The  metal  first  men- 
tioned is  positive  to  those  standing  after  it  in  the  series. 

With  common  acids. — Potassium  and  its  amalgams,  barium  and  its 
amalgams,  amalgam  of  zinc,  cadmium,  tin,  iron,  bismuth,  antimony,  lead, 
copper,  silver,  palladium,  tellurium,  gold,  charcoal,  platinum,  iridium,  rho- 
dium. 

With  alkaline  solutions. — The  alkaligenous  metals  and  their  amalgams, 
zinc,  tin,  lead,  copper,  iron,  silver,  palladium,  gold,  and  platinum. 

With  solutions  of  metallic  sulphurets. — Zinc,  tin,  copper,  iron,  bismuth, 
silver,  platinum,  palladium,  gold,  charcoal. 

Mr.  Faraday  has  shown  that  the  presence  of  water  is  not  essential.  A 
battery  may  be  composed  of  other  liquid  compounds,  such  as  a  fused  me- 
tallic chloride,  iodide,  or  fluoride,  provided  il  is  decomposable  by  galvanism, 
and  acts  chemically  on  one  metal  of  the  circle  more  powerfully  than  on  the 
other. 

The  following  table  of  voltaic  circles  of  tha  second  kind  is  from  Davy's 
Elements  of  Chemical  Philosophy  : — 


GALVANISM. 


91 


Solution  of  sulphuret  of  potassium, 

Copper, 
Silver, 
Lead, 
Tin, 
Zinc, 
Other  metals, 
Charcoal. 

Nitric  acid, 
Sulphuric  acid, 
Hydrochloric  acid, 
Any  solutions  con- 
taining acid. 

The  most  energetic  of  these  combinations  is  that  in  which  the  metal  is 
chemically  attacked  on  one  side  by  sulphuret  of  potassium,  and  on  the  other 
by  an  acid.  The  experiment  may  be  made  by  pouring  dilute  nitric  acid 
into  a  cup  of  copper  or  silver,  which  stands  in  another  vessel  containing 
sulphuret  of  potassium.  The  following  arrangements  may  also  be  employ- 
ed : — Let  two  pieces  of  thick  flannel  be  moistened,  one  with  dilute  acid  and 
the  other  with  the  sulphuret,  and  then  placed  on  opposite  sides  of  a  plate  of 
copper,  completing  the  circuit  by  touching  each  piece  of  flannel  with  a  con- 
ducting wire:  or,  take  two  discs  of  copper,  each  with  its  appropriate  wire, 
immerse  one  disc  into  a  glass  filled  with  dilute  acid,  and  the  other  into  a 
separate  glass  with  alkaline  solution,  and  connect  the  two  vessels  by  a  few 
threads  of  amianthus  or  cotton  moistened  with  a  solution  of  salt.  A  similar 
combination  may  be  disposed  in  this  order  :  let  one  disc  of  copper  be  placed 
on  a  piece  of  glass  or  dry  wood  ;  on  its  upper  surface  lay  in  succession  three 
pieces  of  flannel,  the  first  moistened  with  dilate  acid,  the  second  with  solu- 
tion of  salt,  and  the  third  with  sulphuret  of  potassium,  and  then  cover  the 
last  with  the  other  disc  of  copper. 

Metallic  bodies  are  not  essential  to  the  production  of  galvanic  phenomena. 
Combinations  have  been  made  with  layers  of  charcoal  and  plumbago,  of 
slices  of  muscle  and  brain,  and  beet-root  and  wood  ;  but  the  force  of  these 
circles,  though  accumulated  by  the  union  of  numerous  pairs,  is  extremely 
feeble,  and  they  are  very  rarely  employed  in  practice. 

Of  the  simple  voltaic  circles  above  described,  the  only  one  used  for  ordi- 
nary purposes  is  that  composed  of  a  pair  of  zinc  and  copper  plates  excited 
by  an  acid  solution  arranged  as  in  figure  1.  The  form  and  size  of  the  ap- 
paratus are  exceedingly  various.  Instead  of  actually  immersing  the  plates 
in  the  solution,  a  piece  of  moistened  cloth  may  be  placed  between  them. 
Sometimes  the  copper  plate  is  made  into  a  cup  for  con-  Fig  5. 

taining  the  liquid,  and  the  zinc  is  fixed  between  its  two 
sides,  as  shown  by  the  accompanying  transverse  verti- 
cal section,  figure  5 ;  care  being  taken  to  avoid  actual 
contact  between  the  plates,  by  interposing  pieces  of 
wood,  cork,  or  other  imperfect  conductor  of  electricity. 
Another  contrivance,  which  is  much  more  convenient, 
because  the  zinc  may  be  removed  at  will  and  have  its 
surface  cleaned,  is  that  represented  by  the  annexed 
wood-cut.  (Fig.  6.)  C  is  a  cup  made  with  two  cylind-ers  of  sheet  copper 
of  unequal  size,  placed  one  within  the  Fig.  g. 

other,1  and  soldered  together  at  bottom,  £  -» 

so  as  to  leave  an  intermediate  space  **•* 

a  a  a,  for  containing  the  zinc  cylinder 
z  and  the  acid  solution.  The  small 
copper  cups  b  b  are  useful  appendages; 
for  by  filling  them  with  mercury,  and 
inserting  the  ends  of  a  wire,  the  vol- 
taic circuit  may  be  closed  or  broken 
with  ease  and  expedition.  This  appa- 
ratus is  very  serviceable  in  experiments 
on  electro-magnetism. 

Another  kind  of  circle  may  be  formed  by  coiling  a  sheet  of  zinc  and  cop- 
per round  each  other,  so  that  each  surface  of  the  zinc  may  be  opposed  to  one  of 


GALVANYS3I. 


copper,  and  separated  from  it  by  a  small  interval.  The  London  Institution 
possesses  a  very  large  apparatus  of  this  sort,  made  under  the  direction  of 
Mr.  Pepys,  each  plate  of  which  is  60  feet  long  and  two  wide.  The  plates  are 
prevented  from  coming1  into  actual  contact  by  interposed  ropes  of  horsehair; 
and  the  coil,  when  used,  is  lifted  by  ropes  and  pulleys,  and  let  down  into  a 
tub  containing  dilute  acid.  The  contrivance  of  opposing  one  large  connect- 
ed surface  of  zinc  to  a  similar  surface  of  copper,  originated  with  Dr.  Hare  of 
Philadelphia,  who,  from  its  surprising  power  of  igniting  metals,  gave  it  the 
name  of  Calorimotor. 

Compound  Voltaic  Circles. — This  expression  is  applied  to  voltaic  arrange- 
ments which  consist  of  a  series  of  simple  circles.  The  first  combinations  of 
the  kind  were  described  by  Volta,  and  are  now  well  known  under  the  names 
of  voltaic  pile  and  crown  of  cups.  The  voltaic  pile  is  made  by  placing  pairs 
of  zinc  and  copper,  or  zinc  and  silver  plates,  one  above  the  other,  as  shown 
in  figure  7,  each  pair  separated  from  those  adjoining  by  pieces  Fig.  7. 
of  cloth,  rather  smaller  than  the  plates,  and  moistened  with  a 
saturated  solution  of  salt.  The  relative  position  of  the  metals 
in  each  pair  must  be  the  same  in  the  whole  series ;  that  is,  if 
the  zinc  be  placed  below  the  copper  in  the  first  pair,  the  same 
order  should  be  observed  in  all  the  others.  Without  such  pre- 
caution the  apparatus  would  give  rise  to  opposite  currents, 
which  would  neutralize  each  other  more  or  less  according  to 
their  relative  forces.  The  pile,  which  may  consist  of  any  con- 
venient number  of  combinations,  should  be  contained  in  a 
frame  formed  of  glass  pillars  fixed  into  a  piece  of  thick  dry 
wood,  by  which  it  is  both  supported  and  insulated.  Any  num- 
ber of  these  piles  may  be  made  to  act  in  concert  by  establish- 
ing metallic  communication  between  the  positive  extremity  of  each  pile,  and 
the  negative  extremity  of  the  pile  immediately  following. 

The  voltaic  pile  is  now  rarely  employed,  because  we  possess  other  modes 
of  forming  galvanic  combinations  which  are  far  more  powerful  and  conve- 
nient. The  galvanic  battery  proposed  by  Mr.  Cruickshank,  consists  of  a 
trough  of  baked  wood,  about  30  inches  long,  in  which  are  placed  at  equal 
distances  50  pairs  of  zinc  and  copper  plates  previously  soldered  together,  and 
so  arranged  that  the  same  metal  shall  always  be  on  the  same  side.  Each 
pair  is  fixed  in  a  groove  cut  in  the  sides  and  bot- 
tom of  the  box,  the  points  of  junction  being  made 
water-tight  by  cement.  The  apparatus  thus  con- 
structed is  always  ready  for  use,  and  is  brought 
into  action  by  filling  the  cells  left  between  the 
pairs  of  plates  with  some  convenient  solution, 
which  serves  the  same  purpose  as  the  moistened 
cloth  in  the  pile  of  Volta.  By  means  of  the  ac- 
companying wood-cut,  the  mode  in  which  the 
plates  are  arranged  will  easily  be  understood. 

Other  modes  of  combination  are  now  in  use,  which  facilitate  the  employ- 
ment of  the  voltaic  apparatus  and  increase  its  F-  9 
energy.  Most  of  these  may  be  regarded  as 
modifications  of  the  crown  of  cups.  In  this 
apparatus  the  exciting  solution  is  contained 
in  separate  cups  or  glasses,  disposed  circular- 
ly or  in  a  line  :  each  glass  contains  a  pair  of 
plates;  and  each  zinc  plate  is  attached  to  the 
copper  of  the  next  pair  by  a  metallic  wire,  as 
represented  in  figure  9.  Instead  of  glasses,  it 
is  more  convenient  in  practice  to  employ  a 
trough  of  baked  wood  or  glazed  earthenware,  divided  into  separate  cells  by 
partitions  of  the  same  material ;  and  in  order  that  the  plates  may  be  im- 
mersed into  and  taken  out  of  the  liquid  conveniently  and  at  the  same  moment, 
they  are  all  attached  to  a  bar  of  dry  wood,  the  necessary  connexion  between 


GALVANISM.  93 

the  zinc  of  one  cell  and  the  copper  of  the  adjoining  Fig.  10. 

one  being-  accomplished,  as  shown  in  figure  10,  by 
a  slip  or  wire  of  copper. 

A  material  improvement  in  the  foregoing  appa- 
ratus was  suggested  by  Dr.  Wollaston  (Mr.  Chil- 
dren's Essay  in  Phil.  Trans,  for  1815),  who  recom- 
mended that  each  cell  should  contain  one  zinc  and 
two  copper  plates,  so  that  both  surfaces  of  the  for- 
mer metal  might  be  opposed  to  one  of  the  latter. 
The  two  copper  plates  communicate  with  each 
other,  and  the  zinc  between  them  with  the  copper 
of  the  adjoining  cell.  An  increase  of  one-half  the 
power  is  said  to  be  obtained  by  this  method. 

A  variation  of  this  contrivance,  which  appears  to  me  advantageous,  has 
been  suggested  by  Mr.  Hart  of  Glasgow,  who  proposes  to  have  the  double 
copper  plates  of  the  preceding  battery  made  with  sides  and  bottoms,  so  that, 
as  in  figure  5,  they  may  contain  the  exciting  liquid.  The  plates  are  attached, 
as  in  figure  10,  to  a  bar  of  wood,  and  supported  above  the  ground  by  vertical 
columns  of  the  same  material,  by  which  they  are  insulated.  The  cells  are 
filled  by  dipping  the  whole  battery  into  a  trough  of  the  same  form,  full  of  the 
exciting  liquid.  (Brewster's  Journal,  iv.  19.) 

The  size  and  number  of  the  plates  may  be  varied  at  pleasure.  The  largest 
battery  ever  made  is  that  of  Mr.  Children,  described  in  the  essay  above  re- 
ferred to,  the  plates  of  which  were  six  feet  long,  and  two  feet  eight  inches 
broad.  The  common  and  most  convenient  size  for  the  plates  is  four  or  six 
inches  square  ;  and  when  great  power  is  required,  a  number  of  different  bat- 
teries are  united  by  establishing  metallic  communication  between  the  posi- 
tive extremity  or  pole  of  one  battery  and  the  negative  pole  of  the  adjoining 
one.  A  very  effective  battery  was  described  by  Dr.  Hare  under  the  name 
of  Deflagrator,  which  consisted  of  80  zinc  plates,  9  inches  by  6  in  size, 
and  80  copper  plates,  14  inches  by  6,  coiled  together,  and  so  connected  that 
the  whole  could  be  immersed  into  the  exciting  liquid,  or  removed  from  it,  at 
the  same  instant  (An.  of  Phil.  xvii.  329).  The  great  battery  of  the  Royal 
Institution,  with  which  Davy  made  his  celebrated  discovery  of  the  compound 
nature  of  the  alkalies,  was  composed  of  2000  pairs  of  plates,  each  plate  having 
32  square  inches  of  surface.  It  is  now  recognised,  however,  that  such  large 
compound  batteries  are  by  no  means  necessary.  Increasing  the  number  of 
plates  beyond  a  very  moderate  limit  gives,  for  most  purposes,  no  proportion- 
ate increase  of  power  ;  so  that  a  battery  of  50  or  100  pairs  of  plates,  thrown 
into  vigorous  action,  will  be  just  as  effective  as  one  of  far  greater  extent. 

The  electrical  condition  of  compound  voltaic  arrangements  is  similar  to  that 
of  the  simple  circle.  In  the  broken  circuit  no  electric  current  can  be  traced ; 
but  in  the  closed  circuit,  that  is,  when  the  wires  from  the  opposite  ends  of  the 
battery  are  in  contact,  the  galvanometer  indicates  a  positive  electric  current 
through  the  battery  itself  and  along  the  wires,  as  shown  by  the  arrows  in 
figures  8  and  9.  The  direction  of  the  current  appears  at  first  view  to  be 
different  from  that  of  the  simple  circle ;  since  in  the  latter  the  positive  elec- 
tric current  flows  from  the  zinc  through  the  liquid  to  the  copper,  while  in 
the  compound  circle  its  direction  is  from  the  extreme  copper  through  the 
battery  to  the  extreme  zinc  plate.  This  apparent  difference  arises  from  the 
compound  circle  being  usually  terminated  by  two  superfluous  plates.  The 
extreme  copper  and  extreme  zinc  plate  of  figure  8  are  not  in  contact  with  the 
exciting  fluid,  and  therefore  contribute  nothing  to  the  galvanic  action :  re- 
moving these  superfluous  plates,  which  are  solely  conductors,  there  will  re- 
main four  simple  circles,  namely,  the  3  pair  of  soldered  plates  marked  2,  3, 
4,  which  act  as  in  figure  2,  and  the  then  extreme  plates,  1, 1,  which  are  related 
to  each  other  as  the  plates  in  fig.  1.  When  thus  arranged,  the  direction  of 
the  current  will  be  seen  to  correspond  with  that  of  the  simple  circle. 

During  the  action  of  a  simple  circle,  as  of  zinc  and  copper,  excited  by  di- 


94  GALVANISM. 

lute  sulphuric  acid,  all  of  the  hydrogen  developed  in  the  voltaic  process  is 
evolved  at  the  surface  of  the  copper.  This  fact  is  not  apparent  when  com- 
mon zinc  plates  are  used,  owing  to  the  numerous  currents  which  form  on  the 
surface  of  the  zinc  (page  89);  but  when  a  plate  of  amalgamated  zinc  and 
another  of  platinum  are  introduced  into  dilute  sulphuric  acid  of  sp.  gr.  1.068 
or  a  little  higher,  no  gas  whatever  appears  until  contact  between  the  plates 
is  made,  and  then  hydrogen  gas  rises  solely  from  the  platinum,  while  zinc 
is  tranquilly  dissolved.  On  weighing  the  amalgamated  plate  before  and 
after  the  action  has  continued  for  half  an  hour  or  an  hour,  and  collect- 
ing the  hydrogen  gas  evolved  during  that  interval,  the  weight  of  the  hydro- 
gen set  free  and  of  zinc  dissolved  will  be  as  I  to  32.3,  being  the  ratio  of  their 
chemical  equivalents.  Mr.  Faraday,  who  has  lately  proved  this,  has  also 
shown  that  in  a  compound  voltaic  circle,  say  of  10  amalgamated  zinc  plates 
and  10  of  platinum,  each  of  the  former  during  a  given  period  of  action  loses 
exactly  the  same  weight,  and  from  each  of  the  latter  an  equivalent  quantity 
of  hydrogen  gas  is  evolved.  This  separation  of  one  ingredient  of  the  excit- 
ing solution  at  one  plate,  while  the  element  previously  combined  with  it 
unites  with  the  other  plate,  seems  essential  to  voltaic  action.  It  is  in  some 
way  connected  with  the  passage  of  the  current  across  the  exciting  liquid. 
Oxygen  in  a  free  state  may,  by  oxidizing  zinc,  cause  electric  excitement; 
but  the  voltaic  current  is  not  established,  unless  the  oxygen  formed  part  of 
a  previous  liquid  compound  in  contact  or  communication  with  both  the 
plates. 

Among  the  different  kinds  of  voltaic  apparatus  is  usually  placed  the  elec- 
tric column  of  De  Luc,  which  is  formed  of  successive  pairs  of  silver  and 
zinc,  or  silver  and  Dutch-metal  leaf,  separated  by  pieces  of  paper,  arranged 
as  in  a  voltaic  pile.  It  is  remarkable  for  its  power  of  exhibiting  attractions 
and  repulsions  like  common  electricity,  but  cannot  produce  chemical  decom- 
position or  any  of  the  effects  most  characteristic  of  a  voltaic  current,  and  is 
rather  an  electrical  than  a  voltaic  instrument.  It  is  quoted  as  a  proof  of  elec- 
tric development  by  contact,  since  it  will  continue  in  action  for  years  with- 
out being  cleaned  or  taken  to  pieces.  True  it  is  that  the  more  oxidable 
metal  of  the  column  is  slowly  corroded,  and  that  no  electricity  is  excited 
when  the  paper  is  quite  or  nearly  free  from  hygrometric  moisture,  the  pre- 
sence of  which  is  necessary  to  the  oxidation  of  the  zinc  and  copper;  but  at 
the  same  time  the  quantity  of  electricity  excited  seems  so  disproportioned 
to  the  corrosion,  that  the  one  can  scarcely  be  assigned  as  the  cause  of  the 
other. 

THEORIES  OF  GALVANISM. 

Of  the  theories  proposed  to  account  for  the  developement  of  electricity  in 
voltaic  combinations,  three  in  particular  have  attracted  the  notice  of  philoso- 
phers. The  first  originated  with  Volta,  who  conceived  that  electricity  is  set 
in  motion,  and  the  supply  kept  up,  solely  by  contact  or  communication  be- 
tween the  metals  (page  87).  He  regarded  the  interposed  solutions  merely 
as  conductors,  by  means  of  which  the  electricity  developed  by  each  pair  of 
plates  is  conveyed  from  one  part  of  the  apparatus  to  the  other.  Thus,  in  the 
pile  or  ordinary  battery,  represented  by  the  following  series, 


-f.     zinc  copper     fluid     zinc  copper     fluid     zinc  copper    — 

Volta  considered  that  contact  between  the  metals  occasions  the  zinc  in  each 
pair  to  be  positive,  and  the  corresponding  copper  plate  to  be  negative  ;  that 
the  positive  zinc  in  each  pair  except  the  last,  being  separated  by  an  interven- 
ing stratum  of  liquid  from  the  negative  copper  of  the  following  pair,  yields 
to  it  its  excess  of  electricity  ;  and  that  in  this  way  each  zinc  plate  communi- 


GALVANISM.  95 

cates,  not  only  the  electricity  developed  by  its  own  contact  with  copper,  but 
also  that  which  it  had  received  from  the  pair  of  plates  immediately  before  it. 
Thus,  in  the  three  pairs  of  plates  contained  in  brackets,  the  second  pair  re- 
ceives electricity  from  the  first  only,  while  the  third  pair  draws  a  supply 
from  the  first  and  second.  Hence  electricity  is  most  freely  accumulated  at 
one  end  of  the  battery,  and  is  proportionally  deficient  at  the  opposite  ex- 
tremity. The  intensity  is,  therefore,  greatest  in  the  extreme  pairs,  gradually 
diminishes  in  approaching  the  centre,  and  the  central  pair  itself  is  neither 
positively  nor  negatively  excited.  In  batteries  constructed  on  the  principle 
of  the  crown  of  cups  (fig.  9),  the  electro-motion,  as  Volta  called  it,  is  ascribed 
to  metallic  communication  between  the  zinc  of  one  glass  and  the  copper  of 
the  adjoining  one. 

The  second  is  the  chemical  theory,  proposed  by  Wollaston.  Volta  attached 
little  importance  to  the  chemical  changes  which  never  fail  to  occur  in  every 
voltaic  circle,  whether  simple  or  compound,  considering  them  as  casual  or 
unessential  phenomena,  and  therefore  neglected  them  in  the  construction  of 
his  theory.  The  constancy  of  their  occurrence,  however,  soon  attracted 
notice.  In  the  earlier  discussions  on  the  cause  of  spasmodic  movements  in 
the  frog  (page  87),  Fabroni  contended,  in  opposition  to  Volta,  that  the  effect 
was  not  owing  to  electricity  at  all,  but  to  the  stimulus  of  the  metallic  oxide 
formed,  or  of  the  heat  evolved  during  its  production.  More  extended  re- 
searches soon  proved  the  fallacy  of  this  doctrine ;  but  Fabroni  made  a  most 
ingenious  use  of  the  facts  within  his  knowledge,  and  paved  the  way  to  the 
chemical  theory  of  Wollaston. 

The  late  Dr.  Wollaston,  fully  admitting  electricity  as  the  voltaic  agent, 
assigned  chemical  action  as  the  cause  by  which  it  is  excited.  The  repeti- 
tion and  extension  of  Volta's  experiments  by  the  English  chemists,  speedily 
detected  the  error  he  had  committed  in  overlooking  the  chemical  phenomena 
which  occur  within  the  pile.  It  was  observed  that  no  sensible  effects  are 
produced  by  a  combination  of  conductors  which  do  not  act  chemically  on 
each  other;  that  the  action  of  the  pile  is  always  accompanied  by  the  oxidation 
of  the  zinc ;  ano\  that  the  energy  of  the  pile  in  general  is  proportional  to  the 
activity  with  which  its  plates  are  corroded.  Observations  of  this  nature 
induced  Wollaston  to  conclude  that  the  process  begins  with  the  oxidation  of 
the  zinc, — that  oxidation,  or  in  other  terms,  chemical  action  was  the  primary 
cause  of  the  development  of  electricity, — that  the  fluid  of  the  circle  served 
both  to  oxidize  the  zinc  and  to  conduct  the  electricity  which  was  excited, — 
and  that  contact  between  the  plates  served  only  to  conduct  electricity,  and 
thereby  complete  the  circuit. 

The  third  theory  of  the  pile  was  proposed  by  Davy,  and  is  intermediate 
between  the  two  former.  He  adduced  many  experiments  in  support  of  the 
fact  originally  stated  by  Volta,  that  the  electric  equilibrium  is  disturbed  by 
the  contact  of  different  substances,  without  any  chemical  action  taking  place 
between  them.  He  acknowledged,  however,  with  Wollaston,  that  the  che- 
mical changes  contribute  to  the  general  result;  arid  he  maintained  that, 
though  not  the  primary  movers  of  the  electric  current,  they  are  essential  to 
the  continued  and  energetic  action  of  every  voltaic  circle.  The  electric 
excitement  was  begun,  he  thought,  by  metallic  contact,  and  maintained  by 
chemical  action. 

The  progress  of  inquiry  since  these  theories  first  came  into  notice,  has 
gradually  given  more  and  more  support  to  the  views  of  Wollaston,  and  has 
at  last,  I  apprehend,  established  them  to  the  entire  exclusion  of  the  theory  of 
Volta.  The  very  fundamental  position,  that  electricity  is  excitable  as  a  pri- 
mary result  by  the  contact  of  different  substances,  is  warmly  contested,  and, 
as  some  think  with  strong  reason,  has  been  disproved  (page  76) ;  but  admit- 
ting, for  the  sake  of  argument,  that  a  small  effect,  which  is  all  that  can  now 
be  contended  for,  may  thus  be  produced,  it  is  altogether  insignificant  when 
contrasted  with  the  astonishing  phenomena  exhibited  by  a  voltaic  circle.  The 
experiments  of  A.  De  la  Rive,  in  reference  to  this  question,  appear  irrecon- 


96 


GALVANISM. 


cilable  with  the  theory  of  Volta  (An.  de  Ch.  et  de  Ph.  xxxviii.  225.)  This 
ingenious  philosopher  contends  that  the  direction  of  a  voltaic  current  is  not 
-determined  by  metallic  contact,  nor  even  by  the  nature  of  the  metals  rela- 
tively to  each  other,  but  by  their  chemical  relation  to  the  exciting  liquid. 
As  the  result  of  his  inquiries  he  states,  that  of  two  metals  composing  a  vol- 
taic circle,  that  one  which  is  most  energetically  attacked  will  be  positive 
with  respect  to  the  other.  Thus,  when  tin  and  copper  are  placed  in  acid 
solutions,  the  former,  which  is  most  rapidly  corroded,  gives  a  positive  current 
through  the  liquid  to  the  copper,  as  the  zinc  does  in  the  circle  in  fig.  1 ;  but, 
if  they  are  put  into  a  solution  of  ammonia,  which  acts  most  on  the  copper, 
the  direction  of  the  current  will  be  reversed.  Copper  is  positive  in  relation 
to  lead  in  strong  nitric  acid,  which  oxidizes  the  former  most  freely ;  whereas 
in  dilute  nitric  acid,  by  which  the  lead  is  most  rapidly  dissolved,  the  lead  is 
positive.  Even  two  plates  of  copper,  immersed  in  solutions  of  the  same  acid, 
but  of  different  strength,  will  form  a  voltaic  circle,  the  plate  on  which  che- 
mical action  is  most  free  giving  a  current  of  positive  electricity  to  the  other : 
nay,  it  is  possible  to  construct  a  compound  circle  solely  with  zinc  plates  and 
one  acid  solution  (page  89),  provided  the  same  side  of  each  plate  be  more 
rapidly  oxidized  than  the  other. 

Conclusive  evidence  against  the  theory  of  Volta  has  very  recently  been 
obtained  by  Faraday.  And  here,  to  prevent  repetition  and  frequent  reference, 
I  may  at  once  state  that  the  Philosophical  Transactions  for  1833  and  1834 
contain  a  succession  of  essays  on  voltaic  electricity  from  the  pen  of  Mr.  Fara- 
day, in  which  numerous  errors  have  been  exposed  and  new  views  of  deep 
interest  established.  It  is  much  to  affirm,  but  not  more,  I  conceive,  than  is 
strictly  true,  that  these  researches,  whether  viewed  in  reference  to  their 
intrinsic  value  to  science,  or  to  the  energy  and  talent  displayed  by  the  author, 
are  equal  to  any  of  his  most  successful  contributions.  In  respect  to  the  present 
question,  Faraday  proves  metallic  contact  not  to  be  essential  to  voltaic  action, 
by  procuring  that  action  quite  characteristically  without  Fig.  11. 
contact.  A  plate  of  zinc,  er,  fig.  11,  about  8  inches  long  by  %  c 

an  inch  wide,  was  cleaned  and  bent  at  a  right  angle :  and  a 
plate  of  platinum,  of  the  same  width  and  3  inches  long,  was 
soldered  to  a  platinum  wire,  b  s  x,  the  point  of  which,  or, 
rested  on  a  piece  of  bibulous  paper  lying  upon  the  zinc,  and 
moistened  with  a  solution  of  iodide  of  potassium.  On  intro- 
ducing the  plates  into  a  vessel,  c,  filled  with  dilute  sulphuric 
and  nitric  acid,  a  positive  electric  current  instantly  ensued 
in  the  direction  of  the  arrow,  as  testified  by  the  hydrogen 
evolved  at  the  plate  a,  by  the  decomposed  iodide  of  potassium, 
and  by  a  galvanometer.  We  have  thus  a  simple  circle  of  the 
same  construction  and  action  as  in  figure  1,  except  in  the 
absence  of  metallic  contact.  ^sss^zsz? 

Another  proof,  aptly  cited  by  Faraday,  of  electric  excitement  being  inde- 
pendent of  contact,  is  afforded  by  the  spark  which  appears,  when  the  wires 
of  a  pair  of  plates  in  vigorous  action  are  brought  into  contact.  The  spark  is 
occasioned  by  the  passage  of  electricity  across  a  thin  stratum  of  air,  and, 
therefore,  its  production  proves  that  electro-motion  really  occurred  while 
the  wires  were  yet  separated  by  a  thin  stratum  of  air,  which  permitted  the 
electric  current  to  pass,  and  anterior  to  their  actual  contact. 

The  arrangement  of  figure  11,  however,  though  good  for  establishing  a  prin- 
ciple, is  not  adapted  for  ordinary  practice.  The  moist  paper  at  #  is  a  much  less 
perfect  conductor  than  a  metal,  and  thus  obstructs  the  passage  of  the  current; 
nay,  it  does  more,  for  it  tends  to  establish  an  opposite  current.  In  fact,  on  re- 
moving the  dilute  acid  from  c,  and  putting  the  zinc  plate,  a,  in  contact  with  the 
plate  of  platinum,  an  ordinary  simple  circle  would  be  formed,  in  which  a  posi- 
tive current  would  flow  from  the  zinc  at  x  through  the  solution  to  and  along 
the  wire  x  s  b.  This  current,  in  Faraday's  experiment,  was  so  feeble  compared 
with  the  one  excited  by  the  acid  solution,  that  its  influence  was  scarcely  appre- 


t 


a 


GALVANISM.  97 

ciable ;  but  if  the  opposed  currents  had  been  of  the  same  force,  no  action 
would  have  ensued.     To  illustrate  this  still  fur-  Fig.  12. 

ther,  Faraday  fixed  a  plate  of  platinum,  p,  figure  p 

12,  parallel  and  near  to  a  plate  of  amalgamated  v  •          *          '      \ 

zinc,  z.     On  placing  a  drop  of  dilute  sulphuric  ^~"1    J          ^ \ 

acid  at  y,  and  making  metallic  contact  between 

the  plate  at  z  P,  a  positive  electric  current  flowed  in  the  direction  of  the  ar- 
rows.    If  in  the  same  plates,  fig.  13,  the  acid  be  Fig.  13. 

introduced  at  x,  and  metallic  contact  made  at  P  z,      p ^__ 

the  current,  passing  as  before  from  zinc  through  s  |      > 

the  liquid  to  the  platinum,  has  a  direction  op-   \g ~ x 

posed  to  that  of  figure  2,  owing  to  the  reversed 

position  of  the  acid.    If,  then,  in  the  same  plates,  figure  14,  a  drop  of  acid  be 

introduced  at  y  and  at  x,  the  conditions  are  ob-  Fig.  14. 

viously  fulfilled  for  producing  two  opposite  cur-  .     -p 

rents  of  positive  electricity,  each  fluid  acting  as  ^  "~ —  \ 

a  substitute  for  metallic   contact  in  conducting  \\.  V  I     l'\ 

the  current  which  the  other  tends  to  generate.     If     •?  z 

these  opposing  currents  happen  to  be  equal,  they  will  annihilate  the  effects 

each  separately  would  produce;  and  if  unequal,  the  stronger  current,  as  in 

figure  11,  will  annihilate  the  weaker,  and,  though  with  diminished  power, 

impress  its  character  on  the  circuit. 

These  considerations,  made  in  reference  to  a  simple  circle,  lead  at  once  to 
the  theory  of  the  compound  circle.  For  if,  in  figure  14,  a  drop  of  dilute  acid, 
which  acts  solely  on  the  zinc,  be  introduced  at  y,  and  a  different  liquid  at  #, 
capable  of  corroding  platinum  and  not  zinc,  then  the  chemical  action  at  y  will 
cause  a  positive  current  from  zinc  to  platinum,  and  that  at  x  a  similar  cur- 
rent from  platinum  to  zinc.  The  two  currents  tend  to  circulate  in  the  same 
direction,  and  each  promotes  the  progress  of  the  other.  The  same  state  of 
things  exists  in  the  batteries  represented  by  figures  8  and  9.  Chemical  ac- 
tion taking  place  on  the  zinc  of  each  pair  of  plates,  there  is  a  tendency  to 
establish  an  equal  number  of  positive  currents  all  in  the  same  direction ;  and 
the  simultaneous  effort  of  all  urges  on  the  current  with  a  force  which  it  could 
not  derive  from  a  single  pair  of  plates.  It  is  now,  also,  apparent  that  all  the 
zinc  plates  should  have  their  surfaces  towards  one  side,  and  those  of-  copper 
towards  the  other :  one  reversed  pair  tends  to  establish  a  counter-current, 
which  enfeebles  the  influence  of  the  rest.  On  the  same  principle,  the  exciting 
liquid  of  a  voltaic  circle  should  act  exclusively  on  one  of  the  plates :  if  the 
copper  is  oxidized  as  fast  as  the  zinc,  opposite  currents  will  be  excited,  which 
more  or  less  completely  counteract  each  other.  For  this  reason,  platinum 
and  zinc  act  better  than  copper  and  zinc,  especially  when  nitric  acid  is  em- 
ployed. 

LAWS  OF  THE  ACTION  OF  VOLTAIC  CIRCLES. 

Electricians  distinguish  between  quantity  and  intensity  in  galvanism  as  in 
ordinary  electricity.  Quantity,  in  reference  to  a  voltaic  circle,  signifies  the 
quantity  of  electric  fluid  set  in  motion ;  and  by  tension  or  intensity  is  meant 
the  energy  or  effort  with  which  a  current  is  impelled.  In  the  broken  circuit 
there  is  a  strain  to  establish  an  electric  current  as  a  condition  necessary  for 
oxidation :  there  exists  between  the  exciting  fluid  and  the  zinc,  a  desire,  as  it 
were,  for  chemical  action,  which  cannot  be  gratified  until,  by  closing  the 
circuit,  a  door  or  exit  is  opened  for  the  escape  and  circulation  of  electricity. 
This  strain  or  tension  is  great,  according  as  the  affinity  between  the  exciting 
fluid  and  zinc  is  great,  and  the  current  derives  a  character  from  this  tension. 
Nitric  acid,  from  its  great  oxidizing  power,  causes  a  greater  tendency  to 
chemical  action,  and,  therefore,  to  the  formation  of  electric  currents,  than 
sulphuric  acid,  and  this  acid  than  a  solution  of  salt.  Currents  of  high  tension 

9 


98  GALVANISM. 

are  urged  forward  with  greater  impetuosity  than  feeble  ones,  more  readily 
overcoming  obstacles  to  their  passage,  whether  derived  from  the  small  size 
of  conducting  wires,  or  the  imperfect  conduction  of  the  liquids  of  the  battery. 

The  current  of  a  single  pair  of  plates,  though  variable  in  intensity  accord- 
ing  as  the  nature  and  strength  of  the  exciting  liquid  varies,  never  attains  a 
high  tension.  For  if  the  plates  are  far  apart,  the  current  is  unable  to  pass 
at  all,  or  at  most  but  feebly,  owing  to  the  quantity  of  interposed  liquid  ;  and 
if  close,  the  obstacle  to  be  overcome  in  passing  through  a  thin  stratum  of 
fluid  is  too  small  to  admit  of  the  tension  being  considerable,  The  condition 
which  causes  high  intensity  is  an  extended  liquid  conductor  to  be  traversed, 
along  the  whole  line  of  which,  as  in  a  compound  circle,  are  ranged  successive 
pairs  of  plates,  each  acting  chemically  on  the  exciting  liquid,  and  urging  on 
a  current  in  the  same  direction.  Under  these  circumstances  the  tension  be* 
comes  very  high,  and  the  free  circulation  of  electricity  thereby  occasioned 
enables  the  quantity  set  in  motion  to  be  also  increased ;  but  Faraday  has 
given  sufficient  reasons  for  believing  that  the  quantity  of  electricity  trans- 
mitted  along  the  wires  of  a  closed  compound  circle  is  exactly  equal  in  amount 
to  that  which  passes  through  one  of  its  cells.  A  compound  circle  does  not 
act  by  directly  increasing  the  quantity  of  electricity,  but  by  giving  impetus 
or  tension  to  that  which  is  excited. 

The  energy  of  a  voltaic  circle  is  usually  estimated  either  by  the  deflection 
which  it  causes  on  a  magnetic  needle,  or  by  its  power  of  chemical  decompo- 
sition. Using  the  former,  Dr.  Ritchie  has  obtained  some  interesting  numerical 
results,  of  which  the  principal  are  as  follows  (Phil.  Trans.  1832-33). 

1.  The  power  of  a  single  pair  of  plates  in  deflecting  the  magnetic  needle  is 
directly  proportional  to  the  surface  of  the  plates  which  is  covered  with  dilute 
acid;  that  is,  a  given  deflection,  produced  by  covering  one  square  inch  of 
each  plate  with  liquid,  will  be  doubled  when  two  square  inches  are  immersed. 

2.  A  plate  of  zinc  introduced  into  a  rectangular  cup  of  copper,  as  in  figure 
5,  page  91,  deflects  the  needle  twice  as  much  as  when  one  side  of  the  zinc 
and  the  adjacent  surface  of  copper  are  protected  by  a  coating  of  cement  from 
the  action  of  the  acid  solution. — The  varying  conditions  of  the  experiments 
were  calculated  to  affect  the  quantity  of  electricity  set  in  motion,  without 
changing  the  intensity ;  and,  therefore,  the  results,  proving  the  deflection  to 
depend  on  quantity  and  not  on  tension,  entirely  conform  to  general  experience. 

3.  The  deflection  produced  by  a  pair  of  plates,  in  an  acid  solution  of  uni- 
form strength,  varies  inversely  as  the  square  root  of  the  distance  between 
them, — a  law  previously  established  by  Professor  Gumming.    Thus,  if  a  plate 
of  zinc  be  placed  successively  at  one,  four,  and  nine  inches  from  a  plate  of 
copper,  the  deflecting  powers  will  be  in  the  ratio  of  3,  2,  and  1 ;  that  is,  only 
twice  as  great  at  one  inch  as  at  four,  and  only  three  times  as  great  at  one 
inch  as  at  nine  inches. 

4.  The  same  law,  as  previously  deduced  by  Professors  Cumming  and  Bar- 
low, applies  to  variations  in  the  length  of  the  wire  by  which  the  zinc  and 
copper  plate  are  connected.     If,  all  other  circumstances  being  uniform,  the 
conducting  wire  varies  from  four  feet  to  one  foot  in  length,  the  deflecting 
power  will  vary  in  the  ratio  of  1  to  2.     Dr.  Ritchie  informs  me  that  with 
short  metallic  wires,  the  deflection  varies  inversely  as  the  square  root  of  the 
length  of  the  whole  circuit,  that  is,  of  the  solid  and  liquid  conductors  taken 
together.     The  wire  in  these  experiments  must  be  single,  and  not  coiled  as 
in  the  multiplier  of  Schweigger :  large  wires  should  be  used  capable  of  freely 
conveying  all  the  electricity  which  is  developed. 

Ritchie  has  also  shown,  agreeably  to  general  observation,  that  the  deflect- 
ing power  of  a  compound  circle  is  not  increased  by  increasing  the  number 
of  its  plates.  A  single  pair  of  plates  with  a  good  conducting  liquid  within 
the  cell,  and  supplied  with  large  conducting  wires  capable  of  carrying  off  the 
whole  quantity  of  electricity  set  in  motion,  deflects  the  needle  nearly  or  quite 
as  much  as  a  battery  composed  of  several  pairs  of  plates  of  the  same  size. 
This  is  another  proof  that  the  main  influence  of  a  number  of  plates  is  to  in- 


GALVANISM.  99 

crease  the  intensity  and  not  the  quantity  of  electricity  ;  for  the  prevailing 
opinion  that  the  magnetic  needle  takes  no  cognizance  of  intensity  is  fully 
borne  out  by  the  experiments  of  Faraday.  The  magnetic  needle  may  be 
viewed  as  an  exact  measure  of  the  quantity  of  electricity  in  motion,  without 
any  reference  to  its  tension. 

Chemical  decomposition  depends  on  quantity  and  intensity  together,  and 
affords  a  criterion  of  the  increased  tension  of  a  compound  circle  due  to  an 
increase  in  the  number  of  its  plates.  The  quantity  of  hydrogen  gas  evolved 
by  a  compound  circle  in  a  given  time  does  not  vary  in  the  simple  ratio  of 
the  number  of  plates ;  that  is,  the  volume  of  the  gas  is  not  doubled  when  the 
number  of  plates  is  doubled  :  the  effect  increases  at  a  slower  rate,  owing  to 
the  additional  obstacle  to  the  current  caused  by  the  increased  length  of  the 
circuit.  Ritchie  considers  the  ratio  to  be  as  the  square  root  of  the  number 
of  plates ;  so  that  when  the  number  varies  as  1  to  4,  the  gas  evolved  is  as  1 
to  2. 

In  discussing  the  preceding  theoretical  questions,  I  have  gone  on  the  as- 
sumption of  electricity,  as  explained  in  the  last  section,  being  an  indepen- 
dent principle  susceptible  of  rapid  motion  from  one  body  to  another ;  and  I 
have  here  supposed  that  the  condition  of  a  voltaic  conducting  wire  is  similar 
to  that  of  a  wire  leading  from  the  ground  to  the  prime  conductor  of  an  elec- 
trical machine,  or  which  connects  the  inner  and  outer  surface  of  a  charged 
'Leyden  phial,  except  that  the  voltaic  current  moves  slowly,  owing  to  its 
lower  tension  and  the  interposed  imperfect  conductor.  Some  conceive  that 
what  is  called  an  electric  current  is  not  an  actual  transfer  of  any  thing,  but 
a  process  of  induction  among  the  molecules  of  a  conductor  passing  progres- 
sively along  it.  Others,  denying  independent  materiality  to  electricity,  may 
ascribe  it  to  a  wave  of  vibrating  matter,  just  as  the  phenomena  of  optics  are 
explained  by  the  undulatory  theory.  But  whatever  theory  of  the  nature  of 
electricity  may  be  adopted,  it  seems  necessary,  after  the  experiments- of  Fa- 
raday on  the  identity  of  voltaic  and  common  electricity,  that  the  nature  of 
an  electric  and  voltaic  current  is  essentially  the  same. 

•  -  jjfc ;  • ' 

EFFECTS  OF  GALVANISM. 

When  a  zinc  and  copper  plate  are  immersed  in  dilute  acid,  and  the  wire 
attached  to  the  former  is  connected  with  a  gold-leaf  electrometer  of  sufficient 
delicacy,  the  leaves  diverge  with  negative  electricity;  and  on  testing  the 
wire  of  the  copper  plate  in  a  similar  manner,  divergence  from  positive  elec- 
tricity is  obtained.  The  effect  is  so  feeble  with  a  single  pair  of  plates,  as  to 
be  scarcely  appreciable ;  but  with  a  battery  of  many  pairs  it  is  very  distinct, 
though  never  powerful.  This  would  of  course  be  expected;  since  two  oppo- 
sitely electrified  conductors,  immersed  in  the  same  liquid,  would  necessarily 
neutralize  each  other,  unless  their  intensity  was  too  feeble  to  find  a  passage 
through  the  solution.  The  condition  of  a  battery  which  gives  the  greatest 
divergency  to  an  electrometer  is  that  of  numerous  plates;  small  plates  an 
inch  square  being  just  as  effectual  as  large  ones.  The  free  electricity  on 
the  wires  is  apparently  an  effect  of  the  tension  of  the  unbroken  circuit,  and 
is  proportional  to  it;  though  the  mode  in  which  the  effect  arises  is  of  difficult 
explanation.  It  is  due,  perhaps,  to  a  disturbed  electric  equilibrium  in  the 
zinc  plate,  the  chemical  relation  of  which  to  the  acid  renders  that  metal  posi- 
tive at  the  expense  of  the  attached  wire ;  while  the  copper  plate,  induced  by 
the  contiguous  zinc,  becomes  negative  at  the  expense  of  its  wire,  which  is 
thus  rendered  positive. 

A  Leyden  jar  may  be  charged  from  either  wire  of  an  unbroken  circuit, 
provided  the  battery  be  in  a  state  to  supply  a  large  quantity  of  electricity  of 
high  tension,  as  when  formed  of  numerous  four-inch  plates  excited  by  dilute 
acid.  When  the  wires  from  such  a  battery  are  brought  near  each  other,  a 
spark  is  seen  to  pass  between  them;  and  on  establishing  the  communication 
by  means  of  the  hands,  previously  moistened,  a  distinct  shock  is  perceived. 


100  GALVANISM, 

On  sending  the  current  through  fine  metallic  wires  or  slender  pieces  of 
plumbago  or  compact  charcoal,  these  conductors  become  intensely  heated, 
the  wires  even  of  the  most  refractory  metals  are  fused,  and  a  vivid  white  light 
appears  at  the  points  of  the  charcoal,  equal,  if  not  superior  in  intensity  to 
that  emitted  during  the  burning  of  phosphorus  in  oxygen  gas  ;  and  as  this 
phenomenon  takes  place  in  an  atmosphere  void  of  oxygen,  or  even  under  the 
surface  of  water,  it  manifestly  cannot  be  ascribed  to  combustion.  If  the 
communication  be  established  by  metallic  leaves,  the  metals  burn  with  vivid 
scintillations.  Gold-leaf  burns  with  a  white  light  tinged  with  blue,  and 
yields  a  dark  brown  oxide ;  and  the  light  emitted  by  silver  is  exceedingly 
brilliant,  and  of  an  emerald-green  colour.  Copper  emits  a  bluish-white 
light  attended  with  red  sparks,  lead  a  beautiful  purple  light,  and  zinc  a  bril- 
liant white  light  inclining  to  blue,  and  fringed  with  red.  (Singer.)  In  burn- 
ing metallic  leaf,  fusing  wire,  and  igniting  charcoal,  a  large  quantity  of  elec- 
tricity is  the  only  requisite.  The  phenomena  seem  to  arise  from  the  cur- 
rent passing  along  these  substances  with  difficulty ;  a  circumstance  which, 
as  they  are  perfect  conductors,  can  only  happen  when  the  quantity  to  be 
transmitted  is  out  of  proportion  to  the  extent  of  surface  over  which  it  has  to 
pass.  It  is,  therefore,  an  object  to  excite  as  large  a  quantity  of  electricity  in 
a  given  time  as  possible,  and  for  this  purpose  a  few  large  plates  answer  bet- 
ter than  a  great  many  small  ones.  A  strong  acid  solution  should  also  be 
used ;  since  energetic  action,  though  of  short  continuance,  is  more  important 
than  a  moderate  one  of  greater  permanence.  A  mixture  of  ten  or  twelve 
parts  of  water  to  one  of  nitric  acid  is  applicable;  or,  for  the  sake  of  economy, 
a  mixture  of  one  part  of  nitric  to  two  parts  of  sulphuric  acid  may  be  substi- 
tuted for  pure  nitric  acid.  The  large  battery  of  Mr.  Children,  though  capa- 
ble of  fusing  several  feet  of  platinum  wire,  had  an  electric  tension  so  feeble, 
that  it  did  not  affect  the  gold-leaves  of  the  electrometer,  gave  a  shock  scarce- 
ly perceptible  even  when  the  hands  were  moist,  communicated  no  charge  to 
a  Leyden  jar,  and  could  not  produce  chemical  decomposition.* 

Among  the  effects  of  galvanism,  produced  like  most  of  the  former  by  a 
closed  circuit  only,  and  caused  by  electric  currents,  none  are  more  surpris- 
ing or  so  important  as  its  chemical  and  magnetic  effects.  These  will  be 
studied  successively  under  separate  heads.  For  deflecting  a  magnetic  nee- 
dle, the  only  required  condition  is  quantity  of  electricity,  the  amount  of 
which  is  exactly  measured  by  the  degree  of  deflection ;  but  for  chemical  de- 
composition quantity  and  tension  must  be  combined :  for  the  former  a  single 
pair  of  large  plates  is  best  fitted ;  for  the  latter  a  compound  circle  is  almost 
essential. 

Most  of  the  effects  of  galvanism  above  described  are  so  similar  to  those 

*  Dr.  Hare  has  broached  an  ingenious  theory  to  account  for  the  heat  excited 
by  galvanic  action.  He  does  not  consider  it  probable  that  the  heat  extricated 
by  galvanic  combinations  is  the  effect  of  the  current  of  electricity  passing 
with  difficulty  along  conductors,  in  consequence  of  the  quantity  to  be  trans- 
mitted being  out  of  proportion  to  the  extent  of  the  surfaces  over  which  it 
has  to  pass.  On  the  contrary,  he  believes  that  caloric,  like  electricity,  is  an 
original  product  of  galvanic  action.  According  to  his  views,  the  relative 
proportion  of  the  two  principles  evolved  depends  upon  the  construction  of 
the  apparatus;  the  caloric  being  in  proportion  to  the  extent  of  the  generating 
surface,  and  the  electricity  to  the  number  of  the  series.  In  the  case  of 
batteries,  in  which  the  size  and  number  of  the  plates  are  very  considerable, 
both  electricity  and  caloric  are  presumed  by  him  to  be  generated  in  large 
quantities.  When  the  number  of  the  plates  is  very  great,  and  their  size 
insignificant,  as  in  De  Luc's  column,  electricity  is  the  chief  product ;  and 
conversely,  where  the  size  is  very  great  and  the  number  of  the  series 
small,  caloric  is  abundantly  produced,  and  the  electrical  effects  are  at  a  mi- 
nimum.— Ed. 


GALVANISM.  101 

of  the  electrical  machine,  that  it  is  impossible  to  witness  and  compare  both 
series  of  phenomena  without  ascribing-  them  to  the  same  agent.  The  ques- 
tion of  identity  early  occupied  the  attention  of  Wollaston,  who  made  some 
very  beautiful  and  conclusive  experiments  to  prove  that  the  chemical  effects 
of  galvanism  may  be  characteristically  produced  by  a  current  from  the  elec- 
trical machine  (Phil.  Trans.  1801).  The  subject  has  been  examined  anew 
by  Faraday,  who  has  subjected  the  effects  of  electricity  and  galvanism  to  a 
minute  and  critical  comparison:  he  has  obtained  ample  proof  of  the  decom- 
posing- power  of  an  electric  current  from  an  electrical  machine,  both  by  re- 
peating- the  experiments  of  Wollaston  and  devising  new  ones  of  his  own. 
He  has  also  completed  the  chain  of  evidence  by  deflecting  a  magnetic  needle 
with  an  electric  current  from  the  machine,  an  observation,  indeed,  which 
had  been  previously  made  by  Colladon.  These  researches  have  led  to  a  re- 
markable contrast  between  the  quantity  of  electricity  concerned  in  the  pro- 
duction of  voltaic  and  ordinary  electrical  phenomena.  Faraday  states,  that 
the  quantity  of  electric  fluid  employed  in  decomposing-  a  single  grain  of  wa- 
ter is  equal  to  that  of  a  very  powerful  flash  of  lightning;  and  this  statement, 
surprising  as  it  is,  is  supported  by  such  strong  evidence,  that  it  is  difficult 
to  withhold  assent  to  the  assertion. 

Chemical  Action  of  Galvanism. — The  chemical  agency  of  the  voltaic  ap- 
paratus, to  which  chemists  are  indebted  for  their  most  powerful  instrument 
of  analysis,  was  discovered  by  Messrs.  Carlisle  and  Nicholson,  soon  after  the 
invention  was  made  known  in  this  country.  The  substance  first  decompos- 
ed by  it  was  water.  When  two  gold  or  platinum  wires  are  connected  with 
the  opposite  ends  of  a  buttery,  and  their  free  extremities  are  plunged  into 
the  same  cup  of  water,  but  without  touching  each  other,  hydrogen  gas  is 
disengaged  at  the  negative,  and  oxygen  at  the  positive  wire.  By  collecting 
the  gases  in  separate  tubes  as  they  escape,  they  are  found  to  be  quite  pure, 
and  in  the  exact  ratio  of  two  measures  of  hydrogen  to  one  of  oxygen.  When 
wires  of  a  more  oxidable  metal  are  employed,  the  result  is  somewhat  differ- 
ent. The  hydrogen  gas  appears  as  usual  at  the  negative  wire ;  but  the 
oxygen,  instead  of  escaping-,  combines  with  the  metal,  and  converts  it  into 
an  oxide. 

This  important  discovery  led  many  able  experimenters  to  make  similar 
trials.  Other  compound  bodies,  such  as  acids  and  salts,  were  exposed  to  the 
action  of  galvanism,  and  all  of  them  were  decomposed  without  exception, 
one  of  their  elements  appearing  at  one  side  of  the  battery,  and  the  other  at 
its  opposite  extremity.  An  exact  uniformity  in  the  circumstances  attending 
the  decomposition  was  also  remarked.  Thus,  in  decomposing  water  or 
other  compounds,  the  same  kind  of  body  was  always  disengaged  at  the 
same  side  of  the  battery.  The  metals,  inflammable  substances  in  general, 
the  alkalies,  earths,  and  the  oxides  of  the  common  metals,  were  found  at 
the  negative  wire;  while  oxygen,  chlorine,  arid  the  acids,  went  over  to  the 
positive  surface. 

In  performing  some  of  these  experiments,  Davy  observed,  that  if  the  con- 
ducting wires  were  plunged  into  separate  vessels  of  water,  made  to  commu- 
nicate by  some  moist  fibres  of  cotton  or  amianthus,  the  two  gases  were  still 
disengaged  in  their  usual  order,  the  hydrogen  in  one  vessel,  and  the  oxygen 
in  the  other,  just  as  if  the  wires  had  been  immersed  into  the  same  portion 
of  that  liquid.  This  singular  fact,  and  another  of  the  like  kind  observed  by 
Hisinger  and  Berzelius,  induced  him  to  operate  in  the  same  way  with  other 
compounds,  and  thus  gave  rise  to  his  celebrated  researches  on  the  transfer 
of  chemical  substances  from  one  vessel  to  another  (Phil.  Trans.  1807). 
In  these  experiments  two  agate  cups,  N  and  P,  were  employed,  the  first 
communicating  with  the  negative,  the  second  with  the  positive  wire  of  the 
battery,  and  connected  together  by  moistened  amianthus.  On  putting  a 
solution  of  sulphate  of  potassa  or  soda  into  N,  and  distilled  water  into  P, 
the  acid  very  soon  passed  over  to  the  latter,  while  the  liquid  in  the  former, 
which  was  at  first  neutral,  became  distinctly  alkaline.  The  process  was  re- 

9* 


102  GALVANISM. 

versed  by  placing  the  saline  solution  in  P,  and  the  distilled  water  in  N,  when 
the  alkali  went  over  to  the  negative  cup,  leaving  free  acid  in  the  other. 
That  the  acid  in  the  first  experiment,  and  the  alkaline  base  in  the  second, 
actually  passed  along  the  amianthus,  was  obvious;  for  on  one  occasion, 
when  nitrate  of  oxide  of  silver  was  substituted  for  the  sulphate  of  potassa, 
the  amianthus  leading  to  N  was  coated  with  a  film  of  metal.  A  similar 
transfer  was  effected  by  putting  distilled  water  into  N  and  P,  and  a  saline 
solution  in  a  third  cup  placed  between  the  two  others,  and  connected  with 
each  by  moistened  amianthus.  In  a  short  time  the  acid  of  the  salt  appeared 
in  P,  and  the  alkali  in  N.  It  was  in  pursuing  these  researches  that  Davy 
made  his  great  discovery  of  the  decomposition  of  the  alkalies  and  earths, 
which  till  then  had  been  regarded  as  elementary.  (Phil.  Trans.  1808.) 

Such  is  a  statement  of  the  principal  phenomena  of  electro-chemical  de- 
composition according  to  the  earlier  experiments.  The  facts  then  observed 
were  received  as  established  truths  of  science,  and  passed  current  without 
suspicion  or  scrutiny  till  the  present  time.  But  Mr.  Faraday,  in  his  revi- 
sion of  this  part  of  the  science,  has  not  only  added  much  new  matter,  but 
proved  that  several  points,  which  were  considered  as  fundamental  maxims, 
are  erroneous.  Before  describing  his  results,  however,  I  will  define  the 
new  terms  which  he  has  had  occasion  to  introduce. — In  order  to  decompose 
a  compound,  it  is  necessary  that  it  should  be  liquid,  and  that  an  electric 
current  should  pass  through  it,  an  object  easily  effected  by  dipping  into  the 
liquid  the  ends  of  the  metallic  wires  which  communicate  with  the  voltaic 
circle.  These  extremities  of  the  wires  are  commonly  termed  poles,  from  a 
notion  of  their  exerting  attractive  and  repulsive  energies  towards  the  ele- 
ments of  the  decomposing  liquid,  just  as  the  poles  of  a  magnet  act  towards 
iron  ;  and  eajph  is  further  distinguished  by  the  term  positive  or  negative,  ac- 
cording as  it  affects  an  electrometer  with  positive  or  negative  electricity. 
Now  Faraday  contends  that  these  poles  have  not  any  attractive  or  repulsive 
energy,*  and  act  simply  as  a  path  or  door  to  the  current :  he  hence  calls 
them  electrodes,  from  nhtxr^v,  and  oefos,  a  way.  The  electrodes  are  the 
surfaces,  whether  of  air,  water,  metal,  or  any  other  substance,  which  serve 
to  convey  an  electric  current  into  and  from  the  liquid  to  be  decomposed. 
The  surfaces  of  this  liquid  which  are  in  immediate  contact  with  the  elec- 
trodes, and  where  the  elements  make  their  appearance,  are  termed  anode 
and  cathode,  from  avct,  upwards,  and  oefcf,  the  way  in  which  the  sun  rises, 
and  wra.,  downwards,  the  way  in  which  the  sun  sets.  The  anode  is  where 
the  positive  current  is  supposed  to  enter,  and  the  cathode  where  it  quits,  the 

*  Mr.  Faraday  here  proves  experimentally,  what  we  threw  out  as  a  sur- 
mise, in  a  note  contained  in  the  fourth  American  edition  of  this  work,  as  to 
the  indispensableness  of  a  galvanic  current  to  the  production  of  chemical 
decomposition,  independently  of  the  agency  of  any  attractive  or  repulsive 
energy  exercised  by  the  poles,  as  supposed  by  Davy.  The  note  referred  to 
is  in  the  following  words  :^ — 

"  If  the  explanation"  given  by  Davy,  "  of  the  chemical  agencies  of  the 
voltaic  apparatus  were  well  founded,  then  it  would  follow  that  decomposi- 
tion should  take  place,  if  the  same  portion  of  water  was  placed  in  connex- 
ion, at  the  same  time,  with  the  positive  pole  of  one  batter}'  and  the  negative 
pole  of  another.  Thus  the  negative  oxygen  being  attracted  more  strongly 
by  the  positive  or  zinc  pole  than  by  the  positive  hydrogen  with  which  it  is 
combined,  would  have  its  union  with  the  latter  severed,  a  result  which 
would  be  favoured  by  the  repulsion  exercised  by  the  positive  pole  on  the 
hydrogen.  Again,  the  positive  hydrogen  would  be  attracted  by  the  negative 
pole,  and  the  oxygen  be  repelled.  But  I  doubt  very  much  whether  any  de- 
composition would  take  place  under  such  circumstances ;  and  hence  I  believe 
that  a  current  of  the  galvanic  fluid  through  compounds  is  essential  to  its 
decomposing  powers." — Ed, 


GALVANISM.  103 

decomposing  liquid,  its  direction,  whe'n  the  electrodes  are  placed  east  and 
west,  corresponding  with  that  of  the  positive  current  which  is  thought  to 
circulate  on  the  surface  of  the  earth  (page  117).  To  electrolyze  a  com- 
pound, is  to  decompose  it  by  the  direct  action  of  galvanism,  its  name  being 
formed  from  »\«eTgc,v  and  At/a>,  to  unloose  or  set  free;  and  an  electrolyte  is 
a  compound  which  may  be  electrolyzed.  The  elements  of  an  electrolyte 
are  called  ions,  from  /oy,  going,  neuter  participle  of  the  verb  to  go.  Anions 
are  the  ions  which  appear  at  the  anode,  and  are  usually  termed  the  electro- 
negative ingredients  of  a  compound,  such  as  oxygen,  chlorine,  and  acids ; 
and  the  electro-positive  substances,  hydrogen,  metals,  alkalies,  which  appear 
at  the  cathode,  are  cations.  Whatever  may  be  thought  of  the  necessity  for 
some  of  these  terms,  the  words  electrode,  electrolyze,  and  electrolyte,  are 
peculiarly  appropriate. 

The  principal  facts  determined  by  Mr.  Faraday  may  be  arranged  under 
the  following  propositions: —      *-£- 

1.  All  compounds,  contrary  to  what  has  been  hitherto  supposed,  are  not 
electrolytes,  that  is,  are  n-»t  directly  decomposed  by  an   electric  current. 
But  in  making  this  assertion  it  is  necessary  to  distinguish  between  primary 
and  secondary  decomposition.     Water  is  an  electrolyte,  its  hydrogen  being 
delivered  up  at  the  negative,  and  its  oxygen  at  the   positive  electrode.     A 
solution  of  hydrochloric  acid  is  likewise  an  electrolyte,  being  resolved  into 
chlorine  and  hydrogen.     But  nitric  and  sulphuric  acids  and  ammonia  are 
not  electrolytes,  though  the  first  and   last  are  :  decomposed  by  secondary 
action.     Thus,  on  subjecting  nitric  acid  to  voltaic  action,  the  water  of  the 
solution  is  electrolyzed,  and  its  hydrogen  arriving  at  the  negative  electrode 
decomposes  the  nitric  acid,  water  being  there  reproduced  and  nitrous  acid 
formed.     So,  in  a  solution  of  ammonia,  the  oxygen  of  decomposed  water 
unites  at  the   positive  electrode   with  the  hydrogen  of  the  ammonia,  and 
nitrogen  gas  is  evolved.     Very  numerous  secondary  actions  are  occasioned 
in  this  way,  because  the  disunited  elements  are  presented  in  a  nascent  form, 
which  is  peculiarly  favourable  to*  chemical  action ;  and  in  many  instances 
the   electrode   itself,  which  is  commonly  metallic,  is  chemically  attacked. 
By   slow  secondary  actions   of  this  nature,  effected    by  very  feeble   cur- 
rents, Becquerel  has  procured  several  crystalline  compounds  analogous  to 
minerals. 

2.  Most  of  the  salts  which  have  been  examined  are  resolvable  into  acid 
and  oxide,  apparently  without  reference  to  their  proportions.     But  in  Com- 
pounds of  two  elements,  the  ratio  of  combination  has  an  influence  which 
has  hitherto  been  wholly  overlooked.     No  two  elements  appear  capable  of 
forming  more  than  one  electrolyte.     Hydrochloric  acid,  and  fused  metallic 
protochlorides,  such  as  the  chlorides  of  lead  and  silver,  and  protochloride  of 
tin,  are  readily  decomposed ;  while  bichloride  of  tin  and  other  perchlorides 
resist  decomposition.    Substances  which  consist  of  a  single  equivalent  of  one 
element  and  two  or  more  equivalents  of  some  other  element,  are  not  electro- 
lytes :  this  is  the  reason  why  sulphuric  and  nitric  acid  and  ammonia  do  not 
yield  primarily  to  voltaic  action.     This  principle  bids  fair  to  become  very 
important  in  determining  which  of  several  compounds  of  two  elements 
contains  single  equivalents.     Water,  which  is  remarkable  for  its  easy  de- 
composition, may  hence  be  inferred  to  be  a  true  binary  compound. 

3.  It  has  been  ascertained  that  most  of  the  elements  are  ions,  and  it  is 
probable  that  all  of  them  are  so ;  but  there  are  several  important  elements, 
such  as  nitrogen,  carbon,  phosphorus,  boron,  aluminium,  and  silicium,  which 
have  not  yet  been  proved  to  be  ions.     This  arises  from  the  difficulty  of 
obtaining  these  elements  in  compounds  fitted  for  electrolytic  action. 

4.  A  single  ion,  that  is,  one  ion  not  in  combination  with  another,  has  no 
tendency  to  pass  to  either  of  the  electrodes,  and  is  quite  indifferent  to  the 
passing  current,  unless  it  be  itself  a  compound  ion,  and  therefore  electroly- 
zable.     The  character  of  true  electrolytic  action  consists  in  the  separation  of 
ions,  one  passing  to  one  electrode  and  another  to  the  opposite  electrode,  and 


104  GALVANISM. 

appearing  there  at  the  same  instant,  unless  the  appearance  of  one  or  both  be 
prevented  by  some  secondary  action. 

5.  There  is  no  such  thing  as  a  transfer  of  ions  in  the  sense  usually  under- 
stood.    In  order  that  the  elements  of  decomposed  water  should  appear  at 
the  opposite  electrodes,  there  must  be  water  between  the  electrodes;  and  for 
the  similar  separation  of  sulphuric  acid  and  soda,  there   must  be  a  line  of 
particles  of  sulphate  of  soda   extending  from  one  electrode  to  the  other. 
Thus,  if  a  solution  of  sulphate  of  magnesia  be  covered  with  pure  water, 
care  being  taken  to  avoid  all  admixture  of  particles,  and  the  positive  metallic 
termination  or  pole  touch  the  magnesian  solution  only,  while  the  negative 
pole  is  in  contact  with  the  water  only,  a  deposite  of  magnesia  occurs  just 
where  the  pure  water  and  the  rnagnesiari  solution  meet,  and  none  reaches 
the  negative  pole.     In   Davy's  experiment,  where  sulphuric  acid  and  soda 
appeared  to  quit  each  other,  and  pass  over  separately  into  a  vessel  of  pure 
water,  there  was  certainly  by  capillary  attraction  an  actual  transfer  of  the 
salt  before  decomposition  occurred. 

6.  In  the  foregoing  experiment,  a  surface  of  water  acts  as  the  negative 
electrode,  clearly  showing  the  contact  of  a  metallic  conductor  with  the  de- 
composing liquid  not  to  be  essential.     Faraday  has  proved  that  even  air  may 
serve  as  an  electrode.     A  current  from  the  prime  conductor  of  an  electrical 
machine  was  made  to  pass  from  a  needle's  point  through  air  to  a  pointed 
piece  of  litmus  paper  moistened  with  sulphate  of  soda,  and  then  to  issue  from  a 
similarly  moistened  point  of  turmeric  paper.     True  electrolytic  action  took 
place,  the  litmus  becoming  red  and  the  turmeric  paper  brown ;  though  both 
extremities  of  the  decomposing  solution  communicated  solely  with  a  stratum 
of  air. 

7.  The  electro-chemical  decomposition  of  a  compound  cannot  occur  unless 
an  electric  current  is  actually  transmitted  through  it ;  or,  in  other  terms,  an 
electrolyte  is  always  a  conductor  of  electricity.  Water,  which  conducts  an  elec- 
tric current,  ceases  to  do  so  when  it  passes  into  ice,  and  then  also  resists  de- 
composition— an  observation  equally  true  of  all  electrolytes  in  becoming  solid. 
Moreover,  liquids  which  resist  electro-chemical  decomposition  do  not  permit 
the  current  of  a  voltaic  circle  to  pass.     The   alliance  between  conduction 
and  decomposition   is  so  constant,  that  the  latter  may  be   regarded  as  a 
means  by  which  voltaic  currents  are  transmitted  through  liquid  compounds. 
Agreeably  to  this  notion,  solidity  may  interfere  with  conduction  by  chaining 
down  the  elements  of  a  compound,  and  thereby  preventing  their  transfer 
to  the  electrodes.     Improving  the  conduction  of  a  liquid,  as  by  adding  sul- 
phuric acid  to  pure  water,  increases  the  decomposing  power  of  a  voltaic 
circle,  the  exciting  fluid  within  the  apparatus  remaining   the  same ;  and 
Faraday  has  proved  that  the  quantity  of  a  compound  decomposed  is  exactly 
proportional  to  the  quantity  of  electricity  which  passes,  however  much  other 
circumstances,  such  as  the  size  of  electrodes  and  conducting  wires,  number 
and  size  of  plates,  and   nature  of  exciting  fluid,  may  vary.     Changes  in 
these  conditions  do,  indeed  influence  the  quantity  of  electricity  transmitted ; 
but  then  the  degree  of  chemical  decomposition  varies  in  the  same  propor- 
tion.    The  foregoing  facts  at  first  led  to  the  opinion  that  the  current  of  a 
voltaic  circle  cannot  pass  through  liquids,  except  those  of  a  metallic  nature, 
unless  decomposition  ensues  at  the  same  time;  but  Faraday  has  noticed 
that  when  the  intensity  is  too  feeble  to  effect  decomposition,  a  small  quan- 
tity of  electricity  may  be  transmitted,  sufficient  to  be  discovered   by  a  gal- 
vanometer.    This  does  not,  however,  essentially  interfere  with  the  law  just 
announced. 

8.  Chemical  compounds  differ  in  the  electrical  force  required  for  decom- 
position.    A  current  of  very  feeble  tension  suffices  to  decompose  iodide  of 
potassium,  while  a  much  higher  intensity  is  required  for  disuniting  the  ele- 
ments of  water.     The  order  of  easy  decomposition  in  the  annexed  substances 
is  as  follows : — Solution  of  iodide  of  potassium ;  fused  chloride  of  silver ; 
fused  protochloride  of  tin ;  fused  chloride  of  lead ;  fused  iodide  of  lead ;  solu- 


GALVANISM.  105 

lion  of  hydrochloric  acid ;  and  water  acidulated  with  sulphuric  acid.  By 
extending  tables  of  this  kind,  a  ready  method  will  be  known  for  comparing 
the  tension  of  voltaic  circles. 

9.  The  conduction  of  the  electric  currents  within  the  cells  of  a  voltaic  cir- 
cle depends  on  chemical  decomposition  equally  with  that  between  platinum 
electrodes.     No  substance  not  an  electrolyte  can  serve  to  excite  a  voltaic  ap- 
paratus ;  and  for  the  passage  of  electricity  from  plate  to  plate  through  the 
intervening  solution,  the  separation  of  substances  previously  combined  in  the 
required  ratio  is  essential.     Neither  free  oxygen  nor  a  solution  of  chlorine 
can  excite  a  current,  though  they  attack  the  zinc;  and  in  a  voltaic  circle  ex- 
cited by  dilute  sulphuric  acid,  the  electricity  set  in  motion  is  due  to  decom- 
posed water  and  oxidized  zinc,  and  not  at  all  to  the  union  of  the  oxide  of  zinc 
with  sulphuric  acid.     The  platinum  electrodes  and  intervening  liquid  may 
be  viewed  as  one  of  the  cells  of  the  circle,  except  that  the  plates  act  merely 
as  conductors,  without  any  oxidation,  the  current  passing  in  virtue  of  the 
decomposed  solution.     Thus,  in  figure  9,  page  92,  the  zinc  and  copper  plate 
of  either  of  the  glasses  may  be  replaced  by  two  plates  of  platinum  ;  or  several 
pairs  of  such  plates  may  be  introduced  in  any  part  of  a  compound  circle,  in 
which  case  the  intervening  spaces  are  cells  of  decomposition  only.  But  such 
plates  diminish  very  much  the  power  of  a  battery.     In  the  zinc  and  copper 
cells,  the  current  is  urged  on  by  the  appetency  of  the  zinc  and  oxygen  to 
unite;  whereas,  in  passing  between  the  electrodes,  the  electricity  has  to  sur- 
mount the  mutual  attraction  of  oxygen  and  hydrogen,  or  some  similar  force, 
without  the  assistance  of  any  opposing  affinity.   In  overcoming  this  obstacle, 
the  electric  current  is  enfeebled ;  and  if  its  tension  is  insufficient  for  decora- 
posing  the  interposed  liquid,  it  is  almost  completely  arrested.    Hence,  in  ex- 
periments on  decomposition,  the  course  of  the  electricity  should  be  facilitated 
by  employing  large  electrodes  and  wires,  and  placing  them  at  a  short  distance 
from  each  other  in  a  good  conducting  solution. 

The  principles  above  established  show  the  importance  of  exciting  all  the 
cells  of  a  voltaic  circle  with  a  liquid  of  the  same  strength.  The  electricity 
circulating  in  a  voltaic  apparatus  with  the  conducting  wires  in  contact,  is 
equal  to  that  which  the  feeblest  cell  is  able  to  transmit,  any  chemical  action 
in  other  cells  more  than  sufficient  for  exciting  that  quantity  being  wasted; 
and  in  a  circle  with  several  decomposing  cells,  the  current  which  traverses 
the  cell  of  lowest  conducting  power  determines  the  quantity  circulating 
through  the  whole  apparatus. 

10.  In  a  voltaic  circle  in  which  no  zinc  is  oxidized  but  what  contributes  to 
excite  an  electric  current,  the  quantity  of  zinc  dissolved  in  a  given  time  from 
each  plate  is  in  a  constant  ratio,  not  only  to  the  hydrogen  gas  evolved  from 
the  corresponding  copper  plate  (page  94),  but  to  the  hydrogen  set  free  at  the 
negative  electrode.     The  ratio  is  such,  that  32.3  parts  of  zinc  are  dissolved 
during  the  evolution  of  1  part  of  hydrogen  gas ;  and  the  conclusion  which 
Mr.  Faraday  has  drawn  from  this  and  numerous  similar  experiments  is,  that 
the  quantity  of  electricity  set  in  motion  by  the  oxidation  of  32.3  grains  of 
zinc  exactly  suffices  for  resolving  9  grains  of  water  into  its  elements.   If  the 
same  current,  by  means  of  4  pairs  of  electrodes,  be  made  to  decompose  water, 
chloride  of  silver,  chloride  of  lead,  and  chloride  of  tin,  all  in  the  liquid  state, 
the  quantities  of  hydrogen,  silver,  lead,  and  tin  eliminated  at  the  4  negative 
electrodes  will  be  in  the  ratio  of  1,  108,  103.6,  and  58.9 ;  while,  at  one  posi- 
tive electrode,  oxygen,  and  at  the  three  others  chlorine,  in  the  ratio  of  8  to 
35.42,  are  separated.     Similar  facts  were  ascertained  of  many  other  com- 
pounds.   It  thus  distinctly  appears — and  it  is  a  new  and  important  discovery 
— that  electro-chemical  decomposition  is  perfectly  definite,  a  given  quantity 
of  electricity  evolving  the  ingredients  of  compound  bodies  in  well-defined  and 
invariable  proportions,  to  which  Faraday  has  given  the  name  of  electro-che- 
mical equivalents.    The  reader  will  at  once  see  that  these  numbers  are  iden- 
tical with  the  chemical  equivalents  (see  table  page  141).  Another  connexion, 
then,  closer  than  any  before  traced,  is  established  between  electricity  and 


106  GALVANISM. 

chemical  attraction,  showing-  a  mutual  dependence  and  similarity  of  effect  be- 
tween two  agencies,  such  as  almost  forces  a  belief  in  their  identity. 

The  definite  nature  of  electro-chemical  action  suggests  a  ready  mode  of 
estimating  the  quantity  of  electricity  circulating  in  a  voltaic  apparatus.  It 
is  only  necessary  to  collect  the  gas  evolved  from  acidulated  water,  in  order 
to  obtain  a  measure  of  the  quantity  of  electricity  which  has  passed  during  a 
given  interval :  a  tube  divided  into  equal  measures  will  thus  serve  to  express 
degrees  of  electricity,  just  as  the  expansion  of  a  liquid  in  a  thermometer  in- 
dicates degrees  of  temperature.  The  instrument  as  constructed  for  this  ob- 
ject, is  called  by  Faraday  a  volta '-electrometer.  Various  forms  of  it  have  been 
described  by  him,  according  as  it  is  wished  to  collect  oxygen  or  hydrogen 
separately,  or  both  together.  One  of  the  most  convenient  forms,  which  col- 
lects the  gases  together  is  ex-  -Fig- 15. 
hibited  by  figure  15.  It  consists 
of  a  glass  tube  closed  at  bottom, 
where  it  fits  into  a  support  of 
wood  A ;  the  wires  p  n  serve  to 
connect  it  with  a  closed  circle ; 
and  a  b  are  large  platinum  elec- 
trodes, placed  close  together, 
but  prevented  from  contact  by 
interposed  beads  of  glass.  The 
tube  when  prepared  for  use,  is 
filled  up  to  the  bend  with  dilute 
sulphuric  acid  of  sp.  gr.  1.336;  x 
and  the  gas  evolved,  escaping  " 
from  the  open  extremity  c,  is  col- 
lected in  a  tube  and  measured. 

Theory  of  Electro-chemical  Decomposition. — The  most  celebrated  attempt 
to  explain  the  phenomena  of  galvanism  was  made  by  Davy  in  his  essay  on 
Some  Chemical  Agencies  of  Electricity  (Phil.  Trans.  1807),  by  means  of  an 
hypothesis  which  has  received  the  appellation  of  the  electro-chemical  theory. 
The  views  of  Davy,  which  in  some  form  or  other  have  been  adopted  by  most 
persons  who  have  speculated  on  this  subject,  are  founded  on  the  assumption, 
now  rendered  so  much  more  plausible  than  in  his  day,  that  electrical  and 
chemical  attractions  are  owing  to  one  and  the  same  agent.  He  considered 
chemical  substances  to  be  endowed  with  natural  electric  energies ;  meaning 
thereby,  that  a  certain  electric  condition,  either  positive  or  negative,  is  natu- 
ral to  the  atoms  or  combining  molecules  of  bodies ;  that  chemical  union  is 
the  result  of  electrical  attraction  taking  place  between  oppositely  excited  atoms, 
just  as  masses  of  matter  when  oppositely  excited  are  mutually  attracted ;  and 
that  ordinary  chemical  decomposition  arises  from  two  combined  atoms  being 
drawn  asunder  by  the  electric  energies  of  other  atoms  more  potent  than  those 
by  which  they  were  united.  Electro-chemical  decomposition  was  at  once 
explained  by  Davy  on  the  same  principles.  He  regarded  the  metallic  ter- 
minations or  poles  of  a  voltaic  circle  (page  102)  as  two  centres  of  electrical 
power,  each  acting  repulsively  to  particles  in  the  same  electric  state  as  itself, 
and  by  attraction  on  those  which  were  oppositely  excited.  The  necessary 
result  was,  that  if  the  electric  energy  of  the  battery  exceeded  that  by  which 
the  elements  of  any  compound  subject  to  its  action  were  held  together,  de- 
composition followed,  and  each  element  was  transferred  bodily  to  the  pole 
by  which  it  was  attracted,  passing  through  solutions  not  containing  the  ori- 
ginal compound,  and  refusing  to  unite  with  substances  with  which  under 
other  circumstances  it  would  have  combined.  Substances  which  appeared  at 
the  positive  pole,  such  as  oxygen,  chlorine,  and  acids,  were  termed  electro- 
negative substances ;  and  those,  electro-positive  bodies  which  were  separated 
at  the  negative  pole. 

The  views  of  Davy,  both  in  his  original  essay  and  his  subsequent  expla- 
nations (Phil.  Trans.  1826),  were  so  generally  and  obscurely  expressed,  that 
chemists  have  never  fully  agreed,  as  to  some  points  of  the  doctrine,  about 


GALVANISM. 


«107 


his  real  meaning.  If  he  meant  that  a  particle  of  free  oxygen  or  free  chlorine 
is  in  a  negatively  excited  state ;  then  his  opinion  is  contrary  to  the  fact  that 
neither  of  those  gases  affect  an  electrometer  with  negative  or  any  kind  of  elec- 
tricity, any  more  than  hydrogen  gas  or  potassium  alone  exhibit  any  evidence 
of  positive  excitement.  If  sulphur  unites  with  oxygen  because  it  has  a  posi- 
tive electric  energy,  why  should  it  unite  with  potassium,  which  confessedly 
is  far  more  positive  than  itself?  The  only  mode  in  which  such  facts  as  these 
seem  reconcilable  with  the  electro-chemical  theory,  is  to  suppose  all  bodies  in 
their  uncornbined  state  to  be  electrically  indifferent,  but  that  they  have  a  na- 
tural appetency  to  assume  one  state  in  preference  to  another.  Electro-negative 
bodies  are  such  as  assume  negative  excitement  under  a  certain  approximation 
to  others  which  at  the  same  time  become  positively  excited,  chemical  union 
being  the  consequence.  On  this  supposition,  it  is  intelligible  that  sulphur  may 
be  positive  in  relation  to  oxygen,  and  negative  to  potassium,  just  as  black  silk 
is  positively  electrified  by  friction  with  sealing-wax,  and  negatively  by  white 
silk.  It  is  obvious,  from  the  following  table  constructed  by  Berzelius,  that  this 
chemist  takes  the  same  view  of  the  electric  energies  of  bodies  as  that  just  given. 
He  has  given  it  as  approximative  only,  and  not  as  rigidly  representing  the  exact 
electrical  relations  of  the  elements.  Nitrogen  and  hydrogen  scarcely  occupy 
their  true  position  in  the  series,  the  former  being  electro-negative  in  a  lower 
degree  than  chlorine  and  fluorine;  while  hydrogen,  I  think,  should  be  in  a 
prominent  station  among  the  electro-positive  elements.  All  the  bodies  enume- 
rated in  the  first  column  are  negative  to  those  of  the  second.  In  the  first  column 
each  substance  is  negative  to  those  below  it ;  and  in  the  second,  each  element 
is  positive  with  reference  to  those  which  occupy  a  lower  place  in  the  series. 


1. 

Negative  Electrics 
Oxygen. 
Sulphur. 
Nitrogen. 
Chlorine. 
Bromine. 
Iodine. 
Fluorine. 
Phosphorus. 
Selenium. 
Arsenic. 
Chromium. 
Molybdenum. 
Tungsten. 
Boron. 
Carbon. 
Antimony. 
Tellurium. 
Columbium. 
Titanium. 
Silicium. 
Osmium. 
Hydrogen. 


2. 

Positive  Electrics. 
Potassium. 
Sodium. 
Lithium. 
Barium. 
Strontium. 
Calcium. 
Magnesium. 
Glucinium. 
Yttrium. 
Aluminium. 
Zirconium. 
Thorium. 
Manganese. 
Zinc. 

Cadmium. 
Iron. 
Nickel. 
Cobalt. 
Cerium. 
Lead. 
.       Tin. 

Bismuth. 
Uranium. 
Copper. 
Silver. 
Mercury. 
Palladium. 
Platinum. 
Rhodium. 
Iridium. 
%Gold* 


*  The  statements  made  in  the  text  are,  perhaos.  not  expressed  with  suf- 


108  GALVANISM. 

It  requires  but  little  reflection  on  the  facts  described  in  this  section,  to 
perceive  that  they  are  inconsistent  with  the  electro-chemical  theory  as  un- 
derstood by  Davy.  It  gives  not  the  shadow  of  a  reason  for  a  voltaic  battery, 
which  can  decompose  the  protochloride  or  protiodide  of  a  metal,  being 
powerless  with  the  perchloride  and  periodide  of  the  same  metal.  The  fact 
itself  was  not  contemplated  by  Davy,  and  his  theory  was  designed  to  show 
why  all  such  compounds  should  be  decomposed.  Moreover,  there  is  no 
proof  that  the  poles  of  a  battery  do  exert  attractive  or  repulsive  forces. 
There  is  no  need  of  a  metallic  conductor  in  contact  with  the  decomposing 
body  (page  104);  nor  do  the  elements  reach  the  poles  at  all,  unless  they 
happen  to  be  in  contact  with  the  substance  under  decomposition  (page  104). 
When  hydrogen  reaches  the  negative  electrode,  it  is  freely  disengaged  as 
gas,  the  electrode  evincing  no  tendency  whatever  to  retain  it :  the  combina- 
tion of  the  elements  of  a  decomposed  body  with  the  matter  of  the  electrodes, 
does  not  prove  attraction,  but  may,  and  I  presume  does,  arise  from  the  sub- 
stances being  presented  in  a  state  favourable  for  chemical  union  (page  103). 
But  while  Davy's  theory  fails,  there  is  no  other  which  can  render  a  reason 
for  all  the  phenomena.  Faraday  has  done  much  by  showing  the  fallacy  of 
the  former  theory,  and  by  stating  the  facts  of  the  case  as  they  are.  He  con- 
tends that,  between  the  electrodes  and  acting  in  right  lines,  there  is  an  axis  of 
power  which  urges  the  electro-negative  element  of  an  electrolyte  towards  the 
side  from  which  the  positive  current  moves,  and  gives  an  opposite  impulse  to 
the  electro-positive  element.  He  adopts  the  opinion  of  Grotthus,  that  the  de- 
composing influence  is  not  exerted  on  any  single  particle  of  the  electrolyte, 
but  that  rows  of  particles  lying  between  the  electrodes  are  equally  subject 
to  its  action.  When  a  particle  of  oxygen  is  evolved  at  the  positive  electrode, 
the  hydrogen  with  which  it  had  been  combined  is  not  transferred  at  once  to 
the  opposite  electrode,  but  unites  with  the  oxygen  of  a  contiguous  particle  of 
water,  on  the  side  towards  which  the  positive  current  is  moving ;  the  second 
particle  of  hydrogen  decomposes  a  portion  of  water  still  nearer  to  the  nega- 
tive electrode ;  and  the  same  process  of  decomposition  and  reproduction  of 
water  continues  until  it  reaches  the  water  in  immediate  contact  with  the  ne- 
gative electrode,  the  hydrogen  of  which  is  disengaged.  This  operation,  de- 
scribed as  commencing  at  one  electrode,  takes  place  simultaneously  at  both  : 
a  row  of  particles  of  oxygen  suddenly  lose  their  affinity  for  the  hydrogen 
situated  on  the  side  next  the  negative  electrode,  in  favour  of  those  respec- 
tively adjacent  to  each  on  the  other  side  ;  while  the  affinity  of  a  similar  row 
of  particles  of  hydrogen  is  diminished  for  the  oxygen  on  the  side  of  the  posi- 
tive electrode,  and  is  increased  for  those  on  their  opposite  side.  Hence,  as 

ficient  clearness  for  the  comprehension  of  the  student.  The  doctrine  laid 
down  by  Dr.  Turner  is,  that  substances,  considered  singly,  are  neither  posi- 
tive nor  negative ;  or  in  other  words,  that  they  are  in  a  neuter  state  like  the 
earth.  Nevertheless,  they  are  capable  of  exciting  each  other  by  being  first 
brought  in  contact,  and  then  separated.  If  two  substances  touch  each  other, 
and  are  then  separated,  one  will  become  positive  and  the  other  negative ;  but 
the  result  is  not  conclusive  as  to  the  electric  energy  of  either,  because  the 
electric  state  of  each  may  possibly  be  reversed  by  contact  with  some  other 
substance.  These  positions- are  rigidly  exact  with  respect  to  all  the  simple 
substances,  except  oxygen  and  potassium ;  for,  as  the  former  yields  electri- 
city to  all  other  substances,  it  must  always  be  negative,  and  as  the  latter 
takes  electricity  from  all  other  substances,  it  must  be  invariably  positive. 
Thus  it  is  plain  that  the  electric  energy  of  none  of  the  simple  bodies  is  abso- 
lute, except  that  of  oxygen  and  potassium  ;  while  the  electric  energy  of  the 
remaining  simple  bodies  is  relative,  and  is  either  positive  or  negative,  ac- 
cording to  the  substance  with  which  each  may  be  compared.  It  is  for  these 
reasons  that  I  have  thought  that  the  arrangement  of  bodies  into  negative  and 
positive  electrics,  as  Dr.,  Turner  has  done,  after  Berzelius,  is  objectionable, 
as  leading  the  student  into  the  error  of  supposing  that  each  group  is  in  its 
own  nature  either  negative  or  positive. — Ed. 


GALVANISM.  109 

is  the  fact,  for  the  elimination  of  the  elements  of  fcn  electrolyte  at  the  elec- 
trode, it  is  essential  that  the  electrolyte  itself  should  occupy  the  space  be- 
tween the  electrodes,  and  be  in  contact  with  them.  The  theory,  however,  is 
at  present  incomplete :  it  affords  no  reason  for  the  disturbed  order  of  affini- 
ties in  the  elements  of  an  electrolyte;  nor  is  it  apparent  how  the  chemical 
changes  between  the  electrodes  are  so  essential  as  they  seem  to  be  (page 
104)  to  the  passage  of  the  currents. 

Magnetic  Effects  of  Galvanism. — The  power  of  lightning  in  destroying 
and  reversing  the  poles  of  a  magnet,  and  in  communicating  magnetic  pro- 
perties to  pieces  of  iron  which  did  not  previously  possess  them,  was  noticed 
at  an  early  period  of  the  science  of  electricity,  and  led  to  the  supposition  that 
similar  effects  may  be  produced  by  the  common  electrical  and  voltaic  appa- 
ratus. Attempts  were  accordingly  made  to  communicate  the  magnetic  virtue 
by  means  of  electricity  and  galvanism  ;  but  no  results  of  importance  were 
obtained  till  the  winter  of  1819,  when  Professor  Oersted  of  Copenhagen 
made  his  famous  discovery,  which  forms  the  basis  of  a  new  branch  of 
science.  (Annals  of  Philosophy,  xvi.  273). 

The  fact  observed  by  Professor  Oersted  was,  that  the  metallic  wire  of  a 
closed  voltaic  circle,  and  the  same  is  true  of  charcoal,  saline  fluids,  and  any 
conducting  medium  which  forms  part  of  a  closed  circle,  causes  a  magnetic 
needle  placed  near  it  to  deviate  from  its  natural  position,  and  assume  a  new 
one,  the  direction  of  which  depends  upon  the  relative  position  of  the  needle 
and  the  wire.  On  placing  the  wire  above  the  magnet  and  parallel  to  it,  the 
pole  next  the  negative  end  of  the  battery  always  moves  westward ;  and  when 
the  wire  is  placed  under  the  needle,  the  same  pole  goes  towards  the  east, 
If  the  wire  is  on  the  same  horizontal  plane  with  the  needle,  no  declination 
whatever  takes  place ;  but  the  magnet  shows  a  disposition  to  move  in  a  ver- 
tical direction,  the'  pole  next  the  negative  side  of  the  battery  being  depressed 
when  the  wire  is  to  the  west  of  it,  and  elevated  when  it  is  placed  on  the 
east  side.  Ampere  has  suggested  a  useful  aid  for  recollecting  the  direction 
of  these  movements.  Let  the  observer  regard  himself  as  the  conductor,  and 
suppose  a  positive  electric  current  to  pass  from  his  head  towards  his  feet,  in 
a  direction  parallel  to  a  magnet ;  then  its  north  pole  in  front  of  him  will 
move  to  his  right  side,  and  its  south  pole  to  his  left.  The  plane  in  which 
the  magnet  moves  is  always  parallel  to  the  plane  in  which  the  observer  sup- 
poses himself  to  be  placed.  If  the  plane  of  his  chest  is  horizontal,  the  plane 
of  the  magnet's  motion  will  be  horizontal;  but  if  he  lie  on  either  side  of  the 
horizontally  suspended  magnet,  his  face  being  towards  it,  the  plane  of  his 
chest  will  be  vertical,  and  the  magnet  will  tend  to  move  in  a  vertical  plane. 

The  extent  of  the  declination  occasioned  by  a  voltaic  circle  depends  upon 
its  power,  and  the  distance  of  the  connecting  wire  from  the  needle.  If  the 
apparatus  be  powerful,  and  the  distance  small,  the  declination  will  amount 
to  an  angle  of  45°.  But  this  deviation  does  not  give  an  exact  idea  of  the 
real  effect  which  may  be  produced  by  galvanism  ;  for  the  motion  of  the 
magnetic  needle  is  counteracted  by  the  magnetism  of  the  earth.  When 
the  influence  of  this  power  is  destroyed  by  means  of  another  magnet,  the 
needle  will  place  itself  directly  across  the  connecting  wire ;  so  that  the  real 
tendency  of  a  magnet  is  to  stand  at  right  angles  to  an  electric  current. 

The  communicating  wire  is  also  capable  of  attracting  and  repelling  the 
poles  of  a  magnet.  This  is  easily  demonstrated  by  permitting  a  horizontally 
suspended  magnet  to  assume  the  direction  of  north  and  south,  and  placing 
near  it  the  conducting  wire  of  a  closed  circle,  held  vertically  and  at  right 
angles  to  the  needle,  the  positive  current  being  supposed  to  flow  from  below 
upwards.  When  the  wire  is  exactly  intermediate  between  the  magnetic 
poles,  no  effect  is  observed ;  on  moving  the  wire  nearly  midway  towards  the 
north  pole,  that  is,  to  the  pole  which  points  to  the  north,  the  needle  will  be 
attracted ;  and  repulsion  will  ensue  when  the  wire  is  moved  close  to  the  north 
pole  itself.  Similar  effects  occur  on  advancing  the  wire  towards  the  south 
pole.  Such  are  the  phenomena  if  the  positive  current  ascend  on  the  west 
side  of  the  needle ;  but  they  are  reversed  when  the  wire  is  placed  vertically 

10 


110  GALVANISM. 

on  the  east  side.     Attractions  and  repulsions  likewise  take  place  in  a  dip- 
ping needle,  when  the  current  flows  horizontally  across  it. 

The  discovery  of  Oersted  was  no  sooner  announced,  than  the  experiments 
were  repeated  and  varied  by  philosophers  in  all  parts  of  Europe,  and,  as  was 
to  be  expected,  new  facts  were  speedily  brought  to  light.  Among  the  most 
successful  of  those  who  early  distinguished  themselves  were  Ampere,  Biot 
and  Arago,  of  Paris,  and  Davy  and  Faraday  in  this  country.  A  host  of  other 
able  men  have  since  added  their  contributions ;  and  their  joint  labours  have 
established  an  altogether  new  science,  Electro-Dynamics,  which  has  already 
become  one  of  the  most  important  branches  of  physical  knowledge,  and  still 
offers  a  rich  harvest  of  discovery  to  its  cultivators.  Those  who  wish  to  enter 
deeply  into  the  study  of  this  subject  should  consult  the  Recucil  ^Observa- 
tions Electro- Dynamiques,  by  Ampere,  Professor  Cumming's  Manual  of  Elec- 
tro-Dynamics, Mr.  Murphy's  Treatise  on  Electricity,  and  the  second  edition 
of  Mr.  Barlow's  Essay  on  Magnetic  Attractions.  A  less  mathematical,  and, 
therefore,  more  generally  intelligible  treatise  has  been  drawn  up  with  great 
ability  by  Dr.  Roget,  and  published  as  part  of  the  Library  of  Useful  Know- 
ledge ;  and  a  Popular  Sketch  of  Electro-Magnetism  has  been  given  by  Mr. 
Watkins  of  Charing-cross.  To  these  works  I  refer  as  supplying  that  detail 
of  the  facts  and  theories  of  electro-dynamics,  which,  as  belonging  more  to 
the  province  of  physics  than  chemistry,  is  unsuited  to  the  design  of  this  vo- 
lume. My  object  is  merely  to  give  an  outline  of  the  discoveries  in  electro- 
dynamics, and  to  convey  an  idea  of  the  nature  and  present  state  of  the  Science. 

The  phenomena  of  electro-dynamics  are  solely  produced  by  electricity  in 
motion.  Accumulated  electricity  giving  rise  to  tension,  which  acts  so  es- 
sential a  part  in  experiments  with  the  electrical  machine,  has  no  influence 
whatever  on  a  magnetic  needle.  The  passage  of  electricity  through  solid  or 
liquid  conductors  is  essential ;  and  it  is  remarkable  that  the  more  freely  the 
current  is  transmitted,  that  is,  the  more  perfect  the  conducting  substance, 
the  more  energetic  is  its  deflecting  power.  In  fact,  a  magnetic  needle  is  a 
Galvanoscopei  by  which  means  the  existence  and  direction  of  an  electric  cur- 
rent may  be  detected.  It  was  early  employed  with  this  intention  by  Ampere, 
who  found  that  a  voltaic  apparatus  itself  acts  on  a  magnetic  needle  placed 
upon  or  near  it  in  the  same  manner  as  the  wire  which  unites  its  two  extre- 
mities ;  but  as  the  deflection  took  place  only  when  the  opposite  ends  of  the 
battery  were  in  communication,  and  ceased  entirely  when  the  circuit  was 
broken,  he  inferred  that  electricity  passes  uninterruptedly  through  the  battery 
itself  when  the  circuit  is  closed,  and  not  at  all  in  the  interrupted  circuit. 

But  a  magnetic  needle  will  not  only  indicate  the  existence  and  direction 
of  an  electric  current :  it  may  even  serve,  by  the  degree  of  deflection,  as  an 
exact  measure  of  its  force.  When  used  for  this  purpose,  under  the  name  of 
Galvanometer,  some  peculiar  arrangements  are  required  in  order  to  ensure 
the  requisite  delicacy  and  precision.  Experiment  proves  that  a  magnet  is 
equally  affected  by  every  point  of  a  conductor  along  which  an  electric  cur- 
rent is  passing,  so  that  a  wire  transmitting  the  same  current  will  act  with 
more  or  less  energy,  according  as  the  number  of  its  parts  contiguous  to  the 
needle  is  made  to  vary.  On  this  principle  is  constructed  the  Galvanometer 
or  Multiplier  of  Schweigger.  A  copper  wire  is  bent  into  a  retangular  form 
consisting  of  several  coils,  and  in  the  centre  of  the  rectangle  is  placed  a  de- 
licately suspended  needle,  as  shown  in  figure  16.  Each  coil  adds  its  in- 
fluence to  that  of  the  others ;  and  as  the  current,  in  its  progress  along  the 
wire,  passes  repeatedly  above  and  below  the  needle  in  opposite  directions, 
their  joint  action  is  the  same.  In  order  to  prevent  the  electricity  from  pass- 
ing laterally  from  one  coil  to  another  in  con-  F-  16 
tact  with  it,  the  wire  should  be  covered  with 
silk.  The  ends  of  the  wire,  a  and  6,  are  left 
free  for  the  purpose  of  communication  with 
the  opposite  ends  of  the  voltaic  circle.  When 
a  single  needle  is  employed,  as  shown  in  the 
figure,  its  movements  arc  influenced  partly  by  the  earth's  magnetism,  and 
partly  by  the  electric  current.  The  indications  are  much  more  delicate  when 


GALVANISM, 


111 


the  needle  is  rendered  astatic,  that  is,  when  its  directive  property  is  destroyed 
by  the  proximity  of  another  needle  of  equal  magnetic  intensity,  fixed  paral- 
lel to  it,  and  in  a  reversed  position,  each  needle  having  its  north  pole  adjacent 
to  the  south  pole  of  the  other:  in  this  state  the  needles,  neutralizing-  each 
other,  are  unaffected  by  the  magnetism  of  the  earth,  while  they  are  still  sub- 
ject to  the  influence  of  galvanism.  If,  as  in  the  last  figure,  the  lower  needle 
lie  within  the  rectangle,  and  the  upper  needle  just  above  it,  the  electric  cur- 
rent flowing  between  will  act  on  both  in  the  same  manner.  For  researches 
of  delicacy  the  needle  should  be  suspended  by  a  slender  long  thread  of  glass, 
and  the  deflecting  force  measured,  not  by  the  length  of  the  arc  traversed  by 
the  needle,  but  by  the  torsion  required  to  keep  the  needle  at  a  constant  dis- 
tance from  the  wire,  as  in  the  torsion  electrometer  of  Coulomb  (page  81.) 
A  very  valuable  instrument  on  this  principle  has  been  described  by  my  col- 
league Dr.  Ritchie  (Royal  Inst.  Journal,  N.  S.  i.  31.) 

The  mutual  influence  of  a  magnetic  pole  and  a  conducting  wire  changes 
with  the  distance  between  them.  Experiment  shows  that  the  action  of  a 
magnetic  pole  and  a  continuous  conductor,  every  point  of  which  exerts  a  se- 
parate energy  on  the  pole,  varies  inversely  as  the  distance.  This  result  jus- 
tifies the  opinion  that  the  force  of  a  magnetic  pole  on  a  single  point  of  a 
conductor  varies  as  the  square  of  the  distance,  the  same  law  which  regulates 
the  distribution  of  heat  and  light,  as  well  as  the  effects  due  to  electricity. 

From  some  of  the  experiments  of  Oersted  above  mentioned,  it  was  at  first 
believed  that  a  force,  one  while  attractive  and  at  another  repulsive,  acted  in. 
straight  lines  between  the  magnet  and  conducting  wire  ;  but  on  examination 
all  the  phenomena  are  found  referable  to  a  force  acting  tangentially  upon  the 
poles  of  a  magnet,  and  in  a  plane  perpendicular  to  the  direction  of  the  current. 
Place,  for  instance,  a  blank  card  flat  on  the  table,  and  fix  a  wire  A  C  upright 
in  its  centre.  If,  then,  a  positive  electric  current  pass  up  or  down  the  wire,  a 
magnetic  pole  resting  on  the  card,  will  be  inclined  to  move  in  the  plane  of  the 
card,  and,  therefore,  at  right  angles,  to  the  current,  and  to  describe  a  circle  round 


Fig.  17. 

A 


C  as  its  centre.  If  a  north  pole  be  at  n  and  n',  and 
a  south  pole  at  s  and  s',  and  a  positive  current 
descend  as  shown  by  the  arrow  in  figure  17,  let 
fall  from  each  pole  a  dotted  line  perpendicular  to 
the  wire  at  C,  and  each  dotted  line  will  be  the 
radius  of  the  circle  in  which  the  corresponding  -™ 
pole  will  rotate.  All  the  north  poles  will  move  ^ 
in  the  line  of  the  tangent  directed  to  the  right  of 
the  radius,  and  will  have  the  same  course  as  the 
"hands  of  a  watch  when  it  is  placed  on  a  table 
with  the  dial  plate  upwards ;  and  the  south  poles  ^ 
will  rotate  in  the  opposite  direction.  Should  the  -^ 
electric  current  be  ascending,  the  rotation  of  each 
pole  will  be  reversed.  If  the  current  move  hori- 
zontally, the  plane  of  rotation  will  be  vertical ; 
and  if  figure  17  be  moved  into  this  position,  the  positive  current  still  flowing 
from  A  to  C,  the  arrows  on  the  card  will  still  indicate  the  course  of  rotation. 
The  movements  first  observed  by  Oersted  (page  109)  are  referable  to  this 
principle.  When  a  magnetic  needle, 
moveable  round  the  middle  of  its  axis, 
is  acted  on  by  a  parallel  current,  its 
poles  receive  an  equal  but  contrary 
impulse,  and  the  needle  consequently 
comes  to  rest  across  the  direction  of 
the  current.  If  a  vertical  positive 
current  be  placed,  as  shown  in  figure 
18,  at  w,  on  the  right  side  of  a  hori- 
zontal needle  N  S,  moveable  round  C, 
the  pole  N  will  move  towards  it ;  but 
if  the  current  continue  at  to  while  the 
magnet  occupies  the  position  of  N'  S;, 


Fig.  18. 


112 


GALVANISM. 


Fig.  19. 


the  pole  N'  will  recede  from  the  cur- 
rent  :  thus  there  is  the  appearance  of 
repulsion  in  one  case  and  of  attraction 
in  the  other. 

If  a  similar  current  were  without 
the  circle  in  which  a  horizontal  mag- 
net moves,  as  at  w  in  figure  19,  then 
the  magnet,  stationary  at  N  S,  would 
at  first  have  its  poles  impelled  in  op- 
posite  directions;  but  when  it  reaches 
the  position  N'  S',  the  force  at  each 
pole  acts  on  the  same  side  of  the  mag- 
net's axis.    The  poles  also,  being  equi- 
distant from  w,  and  having  the  same 
inclination,  will  be  influenced  by  equal 
forces  acting  at  the  same  mechanical 
advantage.  They  will,  therefore,  by  the  laws 
of  equilibrium,  have  a  resultant  which  will 
pass  directly  through  the  centre  of  motion. 
This  resultant,  represented  as  applied  at  </, 
will  tend  to  draw  the  wire  w  and  the  middle 
of  the  magnet  C  directly  towards  each  other. 
If  the  conducting  wire  w  were  on  the  right 
instead  of  the  left  side  of  the  magnet,  as 
in  figure  20;  then  the  resultant,  passing 
as  before  through  the  centre  of  motion,  but 
in  an  opposite  direction,  tends  to  draw  the 
magnet  and  wire  directly  from  each  other, 
and  to  give  the  appearance  of  repulsion. 

The  same  principle  accounts  for  the  rotation  of  a 
magnetic  pole  round  a  current,  discovered  l)y  Fara- 
day. Into  the  centre  of  the  bottom  of  a  cup,  as  in  the 
vertical  section,  figure  21,  a  copper  wire  c  d  was  in- 
serted, a  cylindrical  magnet  n  s  was  attached  by  a 
thread  to  the  copper  wire  c,  and  the  cup  was  nearly 
filled  with  mercury,  so  that  the  pole  n  only  of  the 
magnet  projected.  A  conductor  a  b  was  then  fixed 
in  the  mercury  perpendicularly  over  the  wire  c.  On 
connecting  the  conducting  wires  with  the  opposite 
ends  of  a  battery,  a  current  was  transmitted  from  one 
wire  through  the  mercury  to  the  other.  If  the  posi- 
tive current  descend,  the  north  pole  of  the  magnet,  if 
uppermost,  will  rotate  round  the  wire  a  b,  passing 
from  east  through  the  south  to  west,  like  the  move-  ci 
ments  in  the  hands  of  a  watch  ;  and  if  the  current 
ascend,  the  line  of  rotation  will  be  reversed.  Under 
similar  circumstances  the  south  pole  would  in  each 
case  rotate  in  the  opposite  direction. 

If  a  magnetic  pole  rotate  round  a  conductor,  a  con- 
ductor will  be  equally  disposed  to  rotate  round  a  mag- 
netic pole,  just  as  a  magnet  moves  towards  iron  or 
iron  towards  a  magnet,  according  as  one  or  other 
is  free  to  move.  Accordingly,  on  fixing  a  magnet 
vertically  in  the  middle  of  a  cup  of  mercury,  fig.  22, 
and  transmitting  a  current  by  the  moveable  conductor 
a  b  through  the  mercury,  and  along  a  second  con- 
ductor d,  fixed  as  before  in  -the  bottom  of  the  cup, 
Faraday  found  that  the  free  extremity  b  of  the  wire 
moved  round  the  pole  of  the  magnet  in  a  direction 
similar  to  the  last. 

It  is  obvious  that  the  direction  of  rotation  imparted 


Fig.  20. 


Fig.  21 


GALVANISM. 


113 


by  a  fixed  current  to  the  moveable  pole,  will  be  identical  with  that  which 
the  same  pole  tends  to  impart  to  the  same  current.  Thus  let  w  in  figure 
23  represent  the  section  of  a  wire  along  which  a  positive  electric  current  is 
descending,  and  n  the  north  pole  of  a  magnet.  If  w  impel 
n  towards  the  right  side,  n  will  give  an  impulse  to  w  in  the 
opposite  direction,  as  indicated  by  the  arrows.  Each  is  dis- 
posed to  describe  a  circle  round  the  other  as  a  centre,  moving 
in  the  same  direction  as  the  hands  of  a  watch  with  its  dial 
upwards ;  and  if  w  and  n  were  equally  free  to  move,  they 
would  act  as  a  couple  in  statics,  and  tend  to  rotate  round  the 
middle  of  the  dotted  line  which  joins  them. 

The  advantage  of  the  rectangular  form  in  the  construction  ^  ^ 

of  a  galvanometer  (page  110)  will  now  be  intelligible.  A  magnetic  needle 
N  S,  pointing  north  and  south,  and  suspended  by  the  point  C  horizontally 
within  the  rectangle,  Fig.  24. 

figure  24,  will  be  in- 
fluenced in  the  same  i\ 
manner  by  each  of 
its  sides.  If  the  posi- 
tive electric  current 
flow  from  A  horizon- 
tally above  the  nee- 
dle from  north  to 
south,  and  then  suc- 
cessively along  the 
other  three  sides  up 
to  B,  the  separate  influence  of  each  side,  agreeably  to  the  principle  above 
illustrated,  will  impel  the  north  pole  eastward,  and  the  south  to  the  west. 
The  little  cups  A  B  are  designed  to  contain  mercury,  and  afford  a  ready 
means  of  connecting  the  rectangle  with  the  opposite  sides  of  a  galvanic 
combination. 

If  the  rectangle,  in  the  last  combination,  have  the  property  of  impelling 
the  north  pole  of  a  magnet  to  its  right  side,  the  north  pole,  when  placed  on 
that  side,  will  give  an  opposite  impulse  to  the  rectangle.  This  may  be  shown 
by  an  elegant  apparatus  of  De  la  Rive,  which  consists  of  a  circular  copper 
wire,  the  extremities  of  which  are  passed  through  a  cork,  and  soldered  to  a 

Elate  of  zinc  and  copper.     On  placing  the  arrangement  in  a  vessel  of  acidu- 
ited  water,  a  positive  electric  current  passes  from  the  copper  plate  round 


Fig.  25. 


the  circle  to  the  zinc,  as  shown  in  figure 
25 ;  and  as  the  cork  renders  the  apparatus 
buoyant,  a  very  slight  force  will  throw  it 
into  motion.  It  will  exhibit  various  phe- 
nomena of  attraction  and  repulsion,  all 
explicable  on  the  principle  already  ex- 
plained, according  to  the  relative  position 
of  the  magnetic  pole  which  is  presented, 
The  apparatus  will  be  more  powerful  if 
the  conducting  wire,  covered  with  silk  to  prevent  lateral  communication,  be 
formed  into  several  circles  of  the  same  diameter,  on  the  principle  of  the 
multiplier. 

A  current  of  voltaic  electricity  Fig.  26. 

not  only  determines  the  position 
of  a  magnet,  but  renders  steel 
permanently  magnetic.  This 
was  observed  nearly  at  the  same 
time  by  Arago  and  Davy,  who 
found  that  when  needles  are 
placed  at  right  angles  to  the 
conducting  wire,  permanent 
magnetism  is  communicated ; 

10* 


114 


GALVANISM. 


and  Davy  also  succeeded  in  producing  this  effect  even  with  a  shock  of 

electricity  from  a  Leyden  phial.  Arago,  at  the  suggestion  of  Ampere,  made 

a   voltaic  conductor  into  the  form  of  a  helix,   into  the  axis  of  which  he 

placed  a  needle,  as  in  figure  26.     As  in  this  arrangement  the  current  nearly 

in  every  part  of  its  course  is  at  right  angles  to  the  needle,  and  as  each  coil 

adds  its  effect  to  that  of  the  others,  the  united  action  of  the   helix  is  ex- 

tremely powerful.     The  needle  was  thus  fully  magnetized  in  an  instant. 
Though  soft  iron  does  not   retain    magnetism,  its   magnetic   properties 

while  under  the  influence  of  an  electric  current  are  very  surprising.  A  piece 

of  soft  iron  about  a  foot  long  and  an  inch  in  diameter  is  bent  into  the  form 

of  a  horse-shoe,  a  copper  wire  is  twisted  round  the  bar  at  right  angles  to  its 

axis,  and  an  armature  of  soft  iron,  to  which  a  weight  may  be  attached,  is 

fitted  to  its  extremities,  as  in  Fig.  27. 

figure  27.    On  connecting  the 

ends  of  the  wire  with  a  simple 

voltaic   circle,  even    of  small 

size,  the  soft  iron  instantly  be- 

comes a  powerful  magnet,  and 

will  support  a  weight  of  50, 

60,  or    even   70  pounds.     In- 

creasing  the  number  of  coils 

gives  a  great  increase  of  pow- 

er ;  but  as  the  length  of  wire 

required   for  that  purpose  di- 

minishes the  influence  of  the  " 

current  (page  97),  the  follow- 

ing arrangement  has  been  suc- 

cessfully   adopted.     The  total 

length  of  copper  wire  intended 

to  be  used  is  cut  into  several 

portions,  each  of  which,  cover- 

ed with  silk  or  cotton  thread 

to  prevent  lateral  communica- 

tion, is  coiled  separately  on  the 

iron.     The  ends  of  all  the  wires  are  then  collected  into  two  separate  parcels, 

and  are  made  to  communicate  with  the  same   voltaic  battery,  taking  care 

that  the  positive  current  shall  pass  along  each  wire  in  the  same  direction. 

The  current  is  thus  divided  into  a  number  of  branches,  and  has  only  a  short 

passage  from  one  end  of  the  battery  to  the  other,  though  it  gives  energy  to 
a  multitude  of  coils.  A  combination  of  this  kind,  connected  with  a  battery 
of  five  feet  square,  supported  2063  pounds,  or  nearly  a  ton  weight. 

In  witnessing  the  influence  of  voltaic  conductors  over  the  directive  pro- 
perty of  magnets,  and  in  inducing  magnetism,  it  is  difficult  to  divest  one's 
self  of  the  conviction  that  these  conductors,  while  transmitting  a  current, 
are  themselves  magnetic.  This  belief  was  early  entertained  by  those  who 
repeated  the  experiments  of  Oersted,  and  experimental  evidence  of  its  truth 
was  speedily  adduced.  Arago  and  Davy  found  that  a  copper  wire  connect- 
ing the  end  of  a  voltaic  combination  attracted  iron  filings,  but  that  they  in- 
stantly fell  off  as  soon  as  the  circuit  was  broken  ;  and  a  conductor,  when 


its  movements  were  not  imped- 
ed by  friction  or  gravity,  was 
proved  by  Amphere  to  be  obe- 
dient, like  an  ordinary  magnet, 
to  the  magnetic  agency  of  the 
earth.  Though  these  properties 
may  be  exhibited  by  a  single 
wire,  the  action  is  more  conspi- 
cuous when,  on  the  principle 
of  the  multiplier,  the  con- 
ductor is  twisted  into  a  spiral, 
as  A,  figure  S8,  or  into  a  rect- 


Fig.  28. 


:B 


P 


p 


GALVANISM. 


115 


angular  form  as  represented  by  B  in  the  same  figure.  When  the  arrange- 
ment is  connected  with  a  floating  galvanic  combination  as  in  figure  25,  or  is 
very  delicately  suspended,  the  plane  of  the  spiral  places  itself  east  and  west, 
the  positive  current  ascending  on  the  west  side,  and  descending  on  the  east : 
the  positive  current,  in  fact,  takes  the  same  course  as  the  hands  of  a  watch, 
when  it  is  held  on  edge  with  the  plane  of  the  dial  lying  east  and  west,  facing 
the  south.  That  side  of  the  spiral  which  is  towards  the  north,  consistently 
with  an  experiment  already  mentioned  (page  113),  acts  as  the  north  pole ;  and 
the  south  side  of  the  spiral  has  an  opposite  polarity.  Each  side  is  power- 
fully attractive  to  iron  filings.  Another  convenient  form  of  the  conductor 
is  the  helix,  figure  26.  Each  coil  of  the  helix  is  a  separate  magnet,  and 
tends  to  place  itself  in  the  same  position  as  the  spiral  or  rectangle;  but  the 
multiplied  effect  of  all  the  coils  causes  north  and  south  polarity  to  be  accu- 
mulated at  the  opposite  ends  of  the  helix,  and,  therefore,  to  be  separated,  not 
by  the  mere  thickness  of  the  wire,  but  by  the  whole  length  of  the  helix. 

Since,  therefore,  the  conductors  just  described  may  be  regarded  as  mag- 
nets, such  magnetized  conductors  ought  mutually  to  repel  or  attract  each 
other,  when  poles  of  the  same  or  a  different  nature  are  adjacent;  and  as  the 
action  of  a  whole  spiral  or  rectangle  is  merely  the  accumulated  effect  of 
its  individual  parts,  it  is  fair  to  presume  that  each  small  portion  of  a  con- 
ductor has  its  opposite  sides  in  a  state  of  opposite  polarity,  and  that  two 
such  contiguous  portions  should  attract  or  repel  each  other  on  the  same 
principle  as  the  spirals  of  which  they  constitute  a  part.  Nay,  even  different 
parts  of  the  same  conductor  ought  to  be  mutually  attractive  or  repulsive. 
These  inferences  from  the  facts  already  detailed,  were  fully  demonstrated 
by  Ampere  soon  after  the  discovery  of  Oersted.  He  proved  that  two  vol- 
taic conductors,  or  two  portions  of  the  same  conductor,  attract  each  other 
when  the  currents  have  the  same  direction,  and  are  mutually  repulsive 
when  they  are  traversed  by  opposite  currents ;  which  is  exactly  what  would 
be  anticipated  from  the  magnetic  in- 
fluence of  conductors.  Thus,  in  the 
two  parallel  positive  currents,  AB  and 
CD,  figure  29,  which  flow  in  the  same 
direction,  the  contiguous  sides  are  af- 
fected with  an  opposite  polarity,  one 
being  south  and  the  other  north  ; 
whereas  in  the  two  contrary  currents, 
EF  and  GH,  the  adjacent  sides  have 
the  same  polarity,  and  therefore  repel 
each  other. 


Fig.  29- 

n 


'"' 


|S 


Fig.  30. 


-A. 


n  -7z7 


Similarly  when  two  currents  cross  each 
other,  as  AB  and  CD,  figure  30,  it  is  ob- 
vious that  at  two  of  the  four  corners,  AD 
and  CB,  similar  poles  are  contiguous; 
while  at  the  other  corners  different  poles 
concur.  Hence  the  wires  tend  to  revolve 
round  E,  and  place  themselves  parallel  to 
the  currents,  so  that  both  may  flow  in  the 
same  direction. 

If  a  rnoveable  conductor  C  D  be  wholly  on  one  side  of  A  B,  as  in  figure 
31,  repulsion  will  ensue  on  one  side  and  attraction  on  the  other.  The  di- 
rection in  which  these  forces  act  is  indicated  by  the  dotted  arrows,  e  b  and 
e  g\  and  they  give  a  resultant  e  r,  which  tends  to  draw  C  D  to  the  right 
side. 


116 


GALVANISM. 


Fig,  32. 


Figure  32  shows  the  effect  of  reversing  the  current  in  C  D,  which  will 
consequently  be  drawn  by  a  force  at  right  angles  to  itself  to  the  left  side. 

If  in  the  last  case  the  conductor 
CD  were  moveable  round  C  as  a 
centre,  then  the  resultant  e  r  would 
draw  D  towards  F,  figure  33 ;  but 
if  the  current  in  either  conductor 
were  reversed,  C  D  would  tend  to 
rotate  towards  G. 

These  are  a  few  examples  of  the 
numerous  facts  experimentally  prov- 
ed by  Ampere  concerning  the  action 
of  voltaic  conductors  on  each  other.  It  is  to  this  branch  of  the  subject,  the 
term  of  Electro- Dynamics,  or  the  science  of  electricity  in  motion,  is  some- 
times restricted,  while  the  mutual  action  of  conductors  and  magnets  is 
called  Electro-Magnetism ;  but  these  two  branches  are  so  entirely  parts  of 
the  same  science,  that  I  have  included  both  under  Ampdre's  term  of  Electro- 
Dynamics.  Any  one  who  has  studied  the  few  preceding  pages  with  mode- 
rate care,  cannot  fail  to  trace  a  close  analogy  between  a  helix  traversed  by 
an  electric  current  and  a  magnet.  The  former  is  affected  by  other  voltaic 
conductors,  by  the  poles  of  a  magnet,  and  by  the  magnetism  of  the  earth, 
in  the  same  manner  as  the  latter.  It  was  this  similarity,  or  rather  identity, 
of  action  which  led  Ampere  to  his  theory  of  magnetism.  He  supposes  that 
the  polarity  of  every  magnet  is  solely  owing  to  the  circulation,  within  its 
substance  and  at  its  surface,  of  electric  currents,  which  continually  pass 
around  all  its  particles  in  planes  perpendicular  to  its  axis.  On  placing  a 
magnet  in  its  natural  position  of  north  and  south,  the  direction  of  its  cur- 
rents is  exactly  the  same  as  in  the  conductors  of  figure  28,  descending  on 
the  east  side,  passing  under  the  magnet  from  east  to  west,  and  ascending  on 
the  side  next  the  west.  In  like  manner  are  currents  supposed  to  circulate 
within  the  earth,  especially  near  its  surface,  passing  from  east  to  west  in 
planes  parallel  to  the  magnetic  equator.  These  terrestrial  currents  cause  all 
bodies,  which  are  freely  suspended,  and  are  possessed  of  electric  currents,  to 
place  themselves  in  such  a  position  that  the  current  on  their  under  side 
should  flow  in  parallelism,  and  in  the  same  direction,  with  that  in  the  earth 
immediately  beneath.  That  the  existence  of  such  currents  will  account  for 
the  directive  property  of  the  earth,  follows  from  the  mutual  action  of  con- 
ductors; and  Mr.  Barlow,  to  render  the  analogy  still  more  complete,  con- 
structed  a  hollow  sphere  of  wood,  in  which  electric  currents  were  made  to 
circulate  in  the  same  direction  as  they  are  thought  to  do  in  the  earth ;  and 
by  placing  an  astatic  needle  on  different  parts  of  its  surface,  he  found  that 
all  the  phenomena  of  terrestrial  magnetism  might  be  imitated.  Observation 
has  even  supplied  a  cause  for  the  existence  of  currents  in  the  earth,  moving 
in  the  direction  which  theory  requires.  The  diurnal  rotation  of  our  planet 
on  its  axis  exposes  its  surface  to  be  heated  in  a  direction  passing  from  east 
to  west;  and  the  discoveries  which  have  been  made  in  thermo-electricity 
(page  75)  sufficiently  prove  the  probability  of  electric  currents  being  esta- 
blished in  the  conducting  matter  of  the  earth  by  the  successive  heating  of 


GALVANISM.  117 

its  parts.  In  short,  the  theory  of  Ampere  connects  the  facts  of  electro- 
dynamics with  the  phenomena  of  terrestrial  magnetism,  and  affords  a 
splendid  instance  of  the  application  of  mathematical  analysis  to  physical 
research. 

Volta-electric  Induction, — The  development  of  electricity  by  the  vicinity 
of  an  excited  body,  already  described  under  the  name  of  induced  electricity 
(page  78),  led  Mr.  Faraday  to  inquire  whether  electricity  in  motion,  as  well 
as  that  of  tension  and  at  rest,  may  not  be  excited  by  induction.  Though 
baffled  in  his  early  attempts,  he  at  last  succeeded  in  laying  open  a  new 
branch  of  electro-dynamics,  which  vies  in  interest  and  importance  with  the 
fundamental  discovery  of  Oersted  (Phil.  Trans.  1831).  A  copper  wire  203 
feet  long  was  passed  in  form  of  a  helix  round  a  large  block  of  wood,  and  an 
equal  length  of  a  similar  wire  was  wound  on  the  same  block  and  in  the 
same  direction,  so  that  the  coils  of  each  helix  should  be  interposed,  but 
without  contact,  between  the  coils  of  the  other.  The  ends  of  one  of  the 
helices  were  connected  with  a  galvanometer,  and  the  other  with  a  strong 
galvanic  battery,  with  the  view  of  ascertaining  whether  the  passage  of  an 
electric  current  through  one  helix  would  induce  a  current  in  the  adjoining 
helix.  It  was  found  that  the  galvanometer  needle  indicated  a  current  at  the 
moment  both  of  completing  and  breaking  the  circuit,  but  that  in  the  interval 
no  deflection  took  place;  and  similarly  the  induced  currents  readily  mag- 
netized a  sewing  needle,  while  the  electric  current  along  the  inducing  helix 
was  in  the  act  of  beginning  or  ceasing  to  flow,  but  at  no  other  period.  By 
varying  the  experiment  the  same  result  was  obtained ;  an  electric  current 
transmitted  from  a  voltaic  battery  through  a  conducting  helix  does  not  in- 
duce a  current  in  an  adjoining  helix,  except  at  the  moment  of  making  or 
breaking  the  voltaic  circuit.  In  the  former  case  the  direction  of  the  in- 
duced  current  is  opposite  to  that  of  the  inducing  current,  and  in  the  latter 
case  it  is  the  same.  This  phenomenon  is  distinguished  by  Faraday  under 
the  name  of  Volta-electric  induction. 

The  inducing  power  of  a  magnet  greatly  exceeds  that  of  an  electric  cur- 
rent. A  ring  of  soft  iron  was  covered  to  nearly  half  its  extent  by  several 
helices,  the  ends  of  which  were  brought  together  so  as  to  constitute  a  com- 
pound helix  terminating  in  the  conductors  a  6, 
figure  24 ;  and  on  the  other  half  of  the  ring 
were  arranged  similar  helices  which  commu-  /^ 
nicated  by  c  d  with  a  galvanometer.  The  two 
sets  of  helices  were  thus  separated  from  each 
other  by  portions  of  the  ring  M  M',  and  were 
protected  by  cloth  from  direct  contact  with  the 
ring  itself.  At  the  moment  the  wires  a  b 
touched  the  ends  of  a  voltaic  combination,  the 
galvanometer  was  strongly  affected :  the  needle 
then  returned  to  its  former  position  and  remained  there  until  the  voltaic 
circuit  was  broken,  when  the  needle  was  again  deflected  as  strongly  as  be- 
fore, but  in  the  opposite  direction.  The  action  was  still  greater  when  both 
compound  helices  were  on  the  same  part  of  the  ring,  the  induction  being 
increased  apparently  by  the  closer  contiguity  of  the  helices.  Another  of 
Faraday's  arrangements,  which  was  in  several  respects  more  convenient 
than  the  ring,  consisted  of  a  hollow  cylinder  of  pasteboard,  round  which  two 
compound  helices  were  adjusted.  On  connecting  one  helix  with  a  voltaic 
combination,  the  other  deflected  the  galvanometer  and  magnetized  a  needle, 
as  in  the  experiments  of  volta-electric  induction  at  first  described;  but  when 
a  cylinder  of  soft  iron  was  introduced  into  the  pasteboard  case,  and  a  voltaic 
current  transmitted  as  before,  the  effect  on  the  galvanometer  was  much 
greater.  The  action  in  this  last  experiment  and  with  the  iron  ring  is  distin- 
guished by  the  name  of  Magneto -electric  induction. 

The  phenomena  arising  from  magneto-electric  and  volta-electric  induction 
are  manifestly  owing  to  the  same  condition  of  the  induced  wire :  the  action 
on  the  needle,  though  different  in  force,  is  identical  in  kind.  It  is  equally 


118  GALVANISM. 

clear  that  the  agent  brought  into  operation  in  the  induced  wire  is  an  elec- 
tric current,  or,  to  dismiss  the  language  of  theory,  that  the  induced  wire  is 
in  the  same  electric  state  as  the  conducting  wire  in  a  closed  voltaic  circle. 
Its  power  in  magnetizing  steel  and  deflecting  a  magnet  is  sufficient  evi- 
dence of  this ;  but  Faraday,  by  magneto-electric  induction,  succeeded  in 
throwing  a  frog's  leg  into  spasms  by  connecting  it  with  the  induced  wire ; 
and  by  arming  the  ends  of  that  wire  with  points  of  charcoal,  and  separating 
them  at  the  instant  the  galvanic  circuit  of  the  inducing  wire  was  broken  or 
restored,  sparks  of  electricity  were  obtained.  The  mode  in  which  soft  iron 
contributes  to  the  effect  is  likewise  obvious.  An  electric  current  circulating 
round  a  bar  of  soft  iron  has  been  shown  to  convert  it  into  a  temporary 
magnet  possessed  of  surprising  power  (page  114);  and  it  is  doutless  to  this 
magnet,  called  into  temporary  existence  by  the  electric  current,  most  of 
the  induced  electricity  is  to  be  ascribed.  Faraday  reduced  this  to  certainty 
by  surrounding  a  cylinder  of  soft  iron  with  one  helix  connected  with  the 
galvanometer,  and  converting  the  soft  iron  into  a  temporary  magnet,  not  by 
a  voltaic  battery,  but  by  placing  at  each  end  of  the  cylinder  the  opposite 
pole  of  a  magnet.  During  the  act  of  applying  the  magnetic  poles  to  the 
iron,  the  galvanometer  needle  was  deflected ;  and  the  deflection  was  repro- 
duced, but  in  the  opposite  direction,  when  the  magnetism  of  the  iron  was 
ceasing  by  the  removal  of  the  magnet.  Similarly  when  a  helix  was  wound 
on  a  hollow  cylinder  of  pasteboard,  and  a  real  magnet  was  introduced,  the 
galvanometer  was  deflected :  the  needle  then  remained  quiescent  so  long  as 
the  magnet  was  left  in  the  cylinder ;  but  in  the  act  of  its  removal,  the  needle 
was  again  deflected,  though  as  usual  in  the  opposite  direction. 

These  singular  phenomena,  which  establish  such  new  and  intimate  rela- 
tions between  voltaic,  and  magnetic  action,  arid  supply  additional  evidence 
in  favour  of  Ampere's  beautiful  theory  of  magnetism,  have  led  to  an  experi- 
ment by  which,  at  first  view,  an  electric  spark  appeared  to  be  derived  from 
the  magnet  itself.  After  Faraday  had  announced  his  experiment,  above 
mentioned,  of  obtaining  a  spark  from  the  induced  wire,  other  attempts  were 
made  to  effect  the  same  object  with  a  magnet,  without  the  aid  of  galvanism. 
The  first  person  who  succeeded  in  this  country  was  Professor  Forbes,  who 
operated  with  a  powerful  loadstone  which  had  been  presented  to  the  Univer- 
sity of  Edinburgh  by  Dr.  Hope.  (Phil.  Trans,  of  Ed.  1832.)  A  helix  of 
copper  wire  was  formed  round  the  middle  of  a  cylinder  of  soft  iron,  which 
was  of  such  length  that  its  extremities  reached  from  one  pole  of  the  loadstone 
to  the  other.  On  applying  and  withdrawing  the  soft  iron  cylinder  to  and 
from  the  poles  of  the  loadstone,  magnetism  was  alternately  created  and  de- 
stroyed within  it.  At  these  periods  of  transition,  electric  currents  were  in- 
duced in  the  helix  surrounding  the  soft  iron ;  and  when,  at  these  instants, 
metallic  contact  between  the  conducting  wires  of  the  helix  was  broken,  an 
electric  spark  was  visible.  Mr.  Forbes  succeeded  best  by  connecting  one 
wire  with  a  cup  of  mercury,  and  removing  the  other  wire  from  contact  with 
its  surface  at  the  instant  when  an  assistant  withdrew  the  armature  of  soft 
iron  from  the  loadstone.  In  this  experiment,  therefore,  the  electricity  was 
obtained  from  the  helix,  and  was  induced  in  it  by  the  soft  iron  while  in  the 
act  of  acquiring  or  losing  magnetism.  The  same  experiment  was  perform- 
ed by  Mr.  Faraday  with  a  loadstone  belonging  to  Professor  Daniell ;  and 
shortly  before  the  experiment  of  Mr.  Forbes,  Nobili  and  Antinori  succeeded 
with  an  ordinary  steel  magnet.  Pixii  in  Paris  afterwards  performed  this 
experiment  with  great  effect  by  causing  a  strong  horse-shoe  magnet  to  re- 
volve upon  an  axis,  its  poles  passing  in  rapid  succession  in  front  of  a  soft 
iron  armature  of  the  same  form ;  and  a  still  better  arrangement  is  to  cause 
the  armature  to  revolve  in  front  of  the  poles  of  a  powerful  magnet,  as  in  the 
instrument  fitted  up  by  Mr.  Saxton,  and  exhibited  at  the  Adelaide-rooms, 
London.  The  voltaic  currents  are  induced  in  one  direction  as  the  armature 
approaches  the  magnetic  poles,  and  are  reversed  as  it  quits  them ;  so  that 
the  currents  change  their  direction  twice  in  each  revolution.  On  all  these 
occasions  the  source  of  the  electricity  is  the  same,  being  always  induced  in 


GALVANISM.  119 

the  helix  by  a  temporary  mag-net;  and  it  has  all  the  characters  of  a  voltaic 
current.  It  produces  brilliant  sparks,  renders  platinum  wire  red-hot,  and 
gives  a  strong  shock.  It  readily  explodes  gunpowder;  and  Dr.  Ritchie  has 
fitted  up  an  apparatus  for  exploding  with  it  a  mixture  of  oxygen  and  hydro- 
gen gases.  It  decomposes  water  rapidly;  and  though  from  the  rapid  re- 
versal in  the  direction  of  the  currents,  both  gases  are  given  off  at  the  same 
wire,  Pixii  succeeded  in  collecting  them  separately.  (An.  de  Ch.  et  de  Ph. 
1L  72.) 

Intimately  associated  with  magneto-electric  induction,  if  not  referable  to 
the  very  same  origin,  is  the  induction  of  electric  currents  by  movement. 
On  introducing  a  magnet  into  a  hollow  helix  of  copper  wire,  as  also  on 
withdrawing  the  magnet  after  its  introduction,  an  electric  current  was  mo- 
mentarily induced  in  the  wire;  and  if,  the  magnet  being  stationary,  the 
helix  were  moved  in  its  vicinity,  an  electric  current  is  likewise  induced. 
The  action  is  not  confined  to  magnets  and  copper  wire ;  but  in  all  solid  con- 
ductors of  electricity,  when  moved  near  the  pole  of  a  magnet,  an  electric 
current  is  generated,  and  the  most  perfect  conductors  act  with  the  greatest 
effect.  The  direction  of  the  movement  is  not  immaterial :  it  is  essential 
that  the  plane  in  which  the  conductor  moves  should  form  an  angle  with  the 
axis  of  the  magnet ;  and  the  most  powerful  currents  were  induced,  when 
the  plane  of  motion  was  at  right  angles  to  that  axis,  and  hence  parallel  to 
the  electric  currents  which  Ampere  supposes  to  exist  in  the  magnet.  The 
direction  of  the  currents  depends  on  the  direction  of  motion.  If  the  move- 
ment of  a  wire  from  right  to  left  cause  a  certain  current,  an  opposite  cur- 
rent will  be  induced  when  the  wire  is  moved  from  left  to  right.  In  short, 
with  regard  to  the  direction  of  an  induced  current,  Mr.  Faraday's  researches 
establish  this  law,  deduced  by  Dr.  Ritchie :  if  a  wire,  conducting  voltaic 
electricity,  produce  on  magnets  or  conductors  certain  motions,  whether  re- 
pulsive, attractive,  or  rotatory  ;  and  if  the  battery  be  removed,  the  ends  of  the 
wires  brought  into  metallic  contact,  and  the  same  motions  be  produced  by 
mechanical  means,  the  conductor  will  have  the  same  electric  state  induced 
in  it  as  it  had  when  connected  with  the  battery.  (Phil.  Mag.  3d  series, 
iv.  12.) 

Mr.  Faraday  has  applied  this  principle  in  a  most  happy  manner  to  ex- 
plain the  phenomena  of  rotation  discovered  by  M.  Arago.  If  a  plate  of 
copper  be  revolved  close  to  a  magnetic  needle  suspended  so  that  it  may 
rotate  in  a  plane  parallel  to  the  plate,  the  needle  will  rotate  in  the  same 
direction ;  and,  reciprocally,  a  rotating  magnet  tends  to  give  rotation  to  a 
contiguous  copper  plate.  The  same  effects  are  produced  by  the  rotation 
not  only  of  all  metals,  but,  according  to  Arago,  of  all  bodies,  whether  solid, 
liquid,  or  gaseous.  These  effects,  which  Faraday  has  principally  examined 
in  reference  to  the  rotation  of  metals,  are  entirely  owing  to  electric  currents 
induced  by  the  rotation,  and  flowing  at  right  angles  to  the  direction  of  mo- 
tion. Suppose  a  b  d,  figure  35,  to  be  a  circular  metallic  - 
plate,  placed  horizontally,  and  capable  of  revolving  round 
its  centre  c ;  and  let  n  be  the  north  pole  of  a  magnet 
situated  above  the  plate  near  its  circumference  at  a.  If 
a  positive  electric  current  were  to  flow  along  the  plate 
from  c  to  a,  the  pole  n  would  be  impelled  at  right  angles 
in  the  direction  indicated  by  the  arrow ;  and  hence  if 
the  plate  were  made  to  revolve  in  the  same  direction,  in- 
dicated by  the  arrows  at  6  and  d,  an  induced  positive 
current  would  instantly  flow  from  c  to  a.  Its  direction 
would  be  constantly  in  that  line,  being  at  right  angles  to  the  dotted  arrow, 
which  indicates  the  direction  in  which  that  part  of  the  plate  nearest  to  the 
pole  is  moving.  Hence  the  pole,  acted  on  by  the  induced  current,  would 
receive  an  impulse  in  the  same  direction. 

If  motion  in  the  vicinity  of  a  magnet  induce  an  electric  current,  the  same 
effect  would  be  anticipated  from  the  magnetic  influence  of  the  earth ;  and 
this  fact  has  been  proved  by  Mr.  Faraday  by  most  decisive  and  interesting 


120  GALVANISM. 

experiments.  When  a  bar  of  soft  iron  is  held  in  the  position  of  the  dipping 
needle,  the  direction  of  which,  in  regard  to  terrestrial  magnetism,  is  analo- 
gous to  the  axis  of  a  common  magnet,  it  acquires  magnetic  properties ;  and, 
accordingly,  on  introducing  a  soft  iron  cylinder  into  a  hollow  helix  of  cop- 
per placed  in  the  line  of  the  dip,  a  galvanometer  connected  with  the  helix 
was  instantly  affected.  But  the  use  of  iron  may  be  dispensed  with  altoge- 
ther ;  for  when  a  helix  of  copper  wire  was  simply  moved  at  right  angles  to 
the  dipping  needle,  electric  currents  were  induced  by  the  magnetism  of  the 
earth.  The  form  of  a  helix  is  not  even  necessary  :  the  movement  of  a  piece 
of  copper  wire  across  the  line  of  dip  developed  currents  in  the  wire.  The 
same  effect  was  produced  by  the  rotation  of  a  copper  plate  placed  horizon- 
tally so  as  to  be  nearly  at  right  angles  to  the  line  of  dip ;  and  the  revo- 
lution of  a  copper  globe  acted  in  the  same  manner.  Faraday  concludes  that 
the  rotation  of  the  earth  on  its  axis  ought  similarly  to  influence  the  conduct- 
ing matters  of  its  surface ;  and  that  electric  currents  should  be  thereby  in- 
duced from  the  equatorial  regions  to  either  pole.  He  throws  out  the  sugges- 
tion whether  the  aurora  borealis  and  australis  may  not  be  produced  by  the 
returning  currents  passing  from  the  poles  of  the  earth  into  the  atmosphere, 


PART   II. 

INORGANIC  CHEMISTRY. 


PRELIMINARY  REMARKS. 

IN  teaching  a  science  such  as  chemistry,  the  details  of  which  are  nume- 
rous and  complicated,  it  would  be  injudicious  to  follow  the  order  of  disco- 
very, and  proceed  from  individual  facts  to  the  conclusions  which  have  been 
deduced  from  them.  An  opposite  course  is  indispensable.  It  is  necessary 
to  discuss  general  principles  in  the  first  instance,  in  order  to  aid  the  begin- 
ner in  remembering  insulated  facts,  and  in  comprehending  the  explanations 
connected  with  them.  I  shall,  accordingly,  commence  the  second  part  of  the 
work  by  explaining  the  leading  doctrines  of  the  science.  One  inconvenience, 
indeed,  arises  from  this  method.  It  is  often  necessary,  by  way  of  illustra- 
tion, to  refer  to  facts  of  which  the  beginner  is  ignorant;  and,  therefore,  on 
some  occasions  more  knowledge  will  be  required  for  understanding  a  sub- 
ject fully,  than  the  reader  may  have  at  his  command.  But  these  instances 
will,  it  is  hoped,  be  rarely  met  with ;  and  when  they  do  occur,  the  reader  is 
advised  to  quit-the  point  of  difficulty,  and  return  to  the  study  of  it  when  he 
shall  have  acquired  more  extensive  knowledge  of  the  details. 

To  the  chemical  history  of  each  substance,  its  chief  physical  characters 
will  be  added.  A  knowledge  of  these  properties  is  not  only  advantageous  in 
assisting  the  chemist  to  distinguish  one  body  from  another,  but  in  many 
instances  it  is  applied  to  uses  still  more  important.  The  character  called 
specific  gravity,  the  meaning  of  which  was  explained  at  page  48,  is  of  so 
much  importance  that  the  mode  of  determining  it  will  be  mentioned  in  this 
place.  The  process  consists  in  weighing  a  body  carefully,  and  then  deter- 
mining the  weight  of  an  equal  bulk  of  water,  the  latter  being  regarded  as 
unity.  If,  for  example,  a  portion  of  water  weigh  9  grains,  and  the  same 
bulk  of  another  body,  20  grains,  its  specific  gravity  is  determined  by  this 
formula: — as  9  :  20  :  :  1  (assumed  as  the  specific  gravity  of  water)  to  the 
fourth  proportional  2.2222  ;  so  that  the  specific  gravity  of  any  substance  is 
found  by  dividing  its  weight  by  the  weight  of  an  equal  volume  of  water.  It 
is  easy  to  discover  the  weight  of  equal  bulks  of  water  and  any  other  liquid 
by  filling  a  small  bottle  of  known  weight  with  each  successively,  and  weigh- 
ing them.*  The  method  of  obtaining  the  necessary  data  in  case  of  a  solid 
is  somewhat  different.  The  body  is  first  weighed  in  air,  is  next  suspended 
in  water  by  means  of  a  hair  attached  to  the  scale  of  the  balance,  and  is  then 
weighed  again.  The  difference  between  the  two  weights  gives  the  weight  of 
a  quantity  of  water  equal  to  the  bulk  of  the  solid.  This  rule  is  founded  on 
the  hydrostatic  law,  that  a  solid  body,  immersed  in  any  liquid,  not  only 
weighs  less  than  it  does  in  air,  but  the  difference  corresponds  exactly  to  the 


*  Bottles  are  prepared  for  this  purpose  by  the  philosophical  instrument 
makers. 

11 


122  PRELIMINARY  REMARKS. 

weight  of  liquid  which  it  displaces ;  and  it  is  obvious  that  the  liquid  so  dis- 
placed is  exactly  of  the  same  dimensions  as  the  solid.  Another  method  is 
by  the  use  of  the  bottle  recommended  for  taking  the  specific  gravity  of 
liquids.  After  weighing  the  bottle  filled  with  water,  a  known  weight  of  the 
solid  is  put  into  it,  which  of  course  displaces  a  quantity  of  water  precisely 
equal  to  its  own  volume.  The  exact  weight  of  the  displaced  water  is  found 
by  weighing  the  bottle  again,  after  its  outer  surface  is  made  perfectly  dry. 

The  determination  of  the  specific  gravity  of  gaseous  substances  is  an  ope- 
ration  of  much  greater  delicacy.  From  the  extreme  lightness  of  gases,  it 
would  be  inconvenient  to  compare  them  with  an  equal  bulk  of  water,  and, 
therefore,  atmospheric  air  is  taken  as  the  standard  of  comparison.  The  first 
step  of  the  process  is  to  ascertain  the  weight  of  a  given  volume  of  air.  This 
is  done  by  weighing  a  very  light  glass  flask,  furnished  with  a  good  stopcock, 
while  full  of  air;  and  then  weighing  it  a  second  time,  after  the  air  has  been 
withdrawn  by  means  of  the  air-pump.  The  difference  between  the  two 
weights  gives  the  information  required.  According  to  the  observation  of  Dr. 
Prout,  100  cubic  inches  of  pure  and  dry  atmospheric  air,  at  the  temperature 
of  60°  F.  and  when  the  barometer  stands  at  30  inches,  weigh  31.0117  grains. 
By  a  similar  method  the  weight  of  any  other  gas  may  be  determined,  and 
its  specific  gravity  be  inferred  accordingly.  For  instance,  suppose  100  cubic 
inches  of  oxygen  gas  are  found  to  weigh  34.1872  grains,  its  specific  gravity 
will  be  thus  deduced  :  as  31.0117  :  34.1872  :  :  1  (the  sp.  gr.  of  air)  :  1.1024, 
the  specific  gravity  of  oxygen. 

There  are  four  circumstances  to  which  particular  attention  must  be  paid 
in  taking  the  specific  gravity  of  gases: — 

1.  The  gas  should  be  perfectly  pure,  otherwise  the  result  cannot  be  ac- 
curate. 

2.  Due  regard  must  be  had  to  its  hygrometric  condition.  If  it  is  saturated 
with   moisture,  the   necessary  correction   may  be   made  by  the  formula  of 
page  50  ;  or  it  may  be  dried  by  the  use  of  substances  which  have  a  power- 
ful attraction  for  moisture,  such  as  chloride  of  calcium,  quicklime,  or  fused 
potassa. 

3.  As  the  bulk  of  gaseous  substances,  owing  to  their  elasticity  and  com- 
pressibility, is  dependent  on  the  pressure  to  which  they  are  exposed,  no  two 
observations  admit  of  comparison,  unless  made  under  the  same  elevation  of 
the  barometer.     It  is  always  understood,  in  taking  the  specific  gravity  of  a 
gas,  that  the  barometer  must  stand  at  thirty  inches,  by  which  means  the 
operator  is  certain  that  each  gas  is  subject  to  equal  degrees  of  compression. 
An  elevation  of  thirty  inches  is,  therefore,  called  the  standard  height;  and 
if  the  mercurial  column  be  not  of  that  length  at  the  time  of  performing  the 
experiment,  the  error  arising  from  this  cause  must  be  corrected  by  calcula- 
tion.    It  has  been  established  by  careful  experiment,  that  the  bulk  of  gases 
is  inversely  as  the  pressure  to  which  they  are  subject.     Thus,  100  measures 
of  air,  under  the  pressure  of  a  thirty-inch  column  of  mercury,  will  dilate  to 
200  measures,  if  the  pressure  be  diminished  by  one-half;  and  will  be  com- 
pressed to  fifty  measures,  when  the  pressure  is  double,  or  equal  to  a  mercu- 
rial column  of  sixty  inches.     The  correction  for  the  effect  of  pressure  may, 
therefore,  be  made  by  the  rule  of  three,  as  will  appear  by  an  example.     If 
a   certain   portion   of  gas  occupy  the  space  of  100    measures    at    twenty- 
nine  inches  of  the  barometer,  its  bulk  at  thirty  inches  may  be   obtained   by 
the  following  proportion ;  as  30  :  29  :  :  100  :  96.G6.     It  is  understood  that 
the  temperature  of  the  mercurial  column  is  constant;  if  not  so,  correction 
must  be  made  agreeably  to  the  note  at  page  18. 

For  a  similar  reason  the  temperature  should  always  be  the  same.  The 
standard  or  mean  temperature  is  60°;  and  if  the  gas  be  admitted  into  the 
weighing-flask  when  the  thermometer  is  above  or  below  that  point,  the  for- 
mula of  page  21  should  be  employed  for  making  the  necessary  correction. 

Chemistry  is  indebted  for  its  nomenclature  to  the  labours  of  four  celebrated 
chemists,  Lavoisier,  Berthollet,  Guyton-Morveau,  and  Fourcroy.  The  pjrin- 

/  ; 


PRELIMINARY  REMARKS.  123 

ciples  which  guided  them  in  its  construction  are  exceedingly  simple  and  in- 
genious. The  known  elementary  substances,  and  the  more  familiar  com- 
pound  ones,  were  allowed  to  retain  the  appellation  which  general  usage  had 
assigned  to  them.  The  newly-discovered  elements  were  named  from  some 
striking  property.  Thus,  as  it  was  supposed  that  acidity  was  always  owing 
to  the  presence  of  the  vital  air  discovered  hy  Priestley  and  Scheele,  they  gave 
it  the  name  of  oxygen,  from  o£uc  acid,  and  ytvvsiv  to  generate;  and  they 
called  inflammable  air  hydrogen,  from  vJa>£  water,  and  ^m«/y,  because  it 
enters  into  the  composition  of  water. 

Compounds,  of  which  oxygen  forms  a  part,  were  called  acids  or  oxides^ 
according  as  they  do  or  do  not  possess  acidity.  An  oxide  of  iron  or  copper 
signifies  a  combination  of  those  metals  with  oxygen,  which  has  no  acid  pro- 
perties. The  name  of  an  acid  was  derived  from  the  substance  acidified  by 
the  oxygen,  to  which  was  added  the  termination  in  ic.  Thus,  sulphuric 
and  carbonic  acids  signify  acid  compounds  of  sulphur  and  carbon  with  oxygen. 
If  sulphur  or  any  other  body  should  form  two  acids,  that  which  contains  the 
least  quantity  of  oxygen  is  made  to  terminate  in  OMS,  as  sulphurows  acid. 
The  termination  in  uret  was  intended  to  denote  combinations  of  the  simple 
non-metallic  substances  either  with  one  another,  with  a  metal,  or  with  a  me- 
tallic oxide.  Sulphwref  and  carbwreJ  of  iron,  for  example,  signify  compounds 
of  sulphur  and  carbon  with  iron.  The  different  oxides  or  sulphurets  of  the 
same  substance  were  distinguished  from  one  another  by  some  epithet,  which 
was  commonly  derived  from  the  colour  of  the  compound,  such  as  the  black 
and  red  oxides  of  iron,  the  black  and  red  sulphurets  of  mercury.  Though 
this  practice  is  still  continued  occasionally,  it  is  now  more  customary  to  dis- 
tinguish degrees  of  oxidation  by  the  use  of  derivatives  from  the  Greek  or 
Latin.  Protoxide  signifies  the  first  degree  of  oxidation,  oinoxide  the  second, 
and  Peroxide  the  third  ;  and  the  term  peroxide  is  often  applied  to  the  highest 
degree  of  oxidation.  The  Latin  word  sesqui,  one  and  a  half,  is  used  as  an 
affix  to  an  oxide,  the  oxygen  in  which  is  to  that  in  the  first  oxide,  as  I  %  to 
1,  or  as  3  to  2.  The  sulphurets,  carburets,  &,c,  of  the  same  substance  are 
designated  in  a  similar  way.  Compounds  consisting  of  acids  in  combination 
with  metallic  oxides,  or  any  alkaline  bases,  are  termed  salts,  the  names  of 
which  are  so  contrived  as  to  indicate  the  substances  contained  in  them.  If 
the  acidified  substance  contain  a  maximum  of  oxygen,  the  name  of  the  salt 
terminates  in  ate;  if  a  minimum,  the  termination  in  ite  is  employed.  Thus, 
the  sulphate,  phosphate,  and  arseniate  of  potassa,  are  salts  of  sulphuric  phos- 
phoric and  arsenic  acids  ;  while  the  terms  sulphite,  phosphite,  and  arsenite 
of  potassa,  denote  combinations  of  that  alkali  with  the  sulphurous,  phosphor- 
ous, and  arseniows  acids. 

The  advantage  of  a  nomenclature  which  disposes  the  different  parts  of  a 
science  in  so  systematic  an  order,  and  gives  such  powerful  assistance  to  the 
memory,  is  incalculable.  The  principle  has  been  acknowledged  in  all  conn- 
tries  where  chemical  science  is  cultivated,  and  its  minutest  details  have  been 
adopted  in  Britain.  It  must  be  admitted,  indeed,  that  in  some  respects  the 
nomenclature  is  defective.  The  erroneous  idea  of  oxygen  being  the  general 
acidifying  principle,  has  exercised  an  injurious  influence  over  the  whole 
structure.  It  would  have  been  convenient  also  to  have  had  a  different  name 
for  hydrogen.  But  it  is  now  too  late  to  attempt  a  change;  for  the  confusion 
attending  such  an  innovation  would  more  than  counterbalance  its  advantages. 
The  original  nomenclature  has,  therefore,  been  preserved,  and  such  additions 
have  been  made  to  it  as  the  progress  of  the  science  rendered  necessary.  The 
most  essential  improvement  was  suggested  by  the  discovery  of  the  laws  of 
chemical  combination.  The  different  salts  formed  of  the  same  constituents 
were  formerly  divided  into  neutral,  super,  and  swo-salts.  They  were  called 
neutral  if  the  acid  and  alkali  were  in  such  proportion  that  one  neutralized 
the  other;  super-salts,  if  the  acid  prevailed;  and  sub-salts,  if  the  alkali  was 
in  excess.  The  name  is  now  regulated  by  the  atomic  constitution  of  the 
salt.  If  it  is  a  compound  of  an  equivalent  of  the  acid  and  the  alkali,  the 
generic  name  of  the  salt  is  employed  without  any  other  addition ;  but  if  two 
or  more  equivalents  of  the  acid  are  attache^  to  one  of  the  base,  or  two  OF 


124  AFFINITY. 

more  equivalents  of  the  base  to  one  of  the  acid,  a  numeral  is  prefixed  so  as 
to  indicate  its  composition.  The  two  salts  of  sulphuric  acid  and  potassa  are 
called  sulphate  and  /;f  sulphate;  the  first  containing-  an  equivalent  of  the  acid 
and  the  alkali,  and  the  second  salt,  two  of  the  former  to  one  of  the  latter. 
The  three  salts  of  oxalic  acid  and  potassa  are  termed  the  oxalate,  fo'woxalate, 
and  quadroxail&te  of  potassa ;  because  one  equivalent  of  the  alkali  is  united 
with  one  equivalent  of  acid  in  the  first,  with  two  in  the  second,  and  with  four 
in  the  third  salt.  As  the  numerals  which  denote  the  equivalents  of  the  acid 
in  a  super-salt  are  derived  from  the  Latin  language,  Dr.  Thomson  proposes 
to  employ  the  Greek  numerals,  dis,  iris,  tetrakis,  to  signify  the  equivalents  of 
alkali  in  a  sub-salt;  and  I  shall  not  only  adopt  his  proposition,  but  give  it  the 
following  extension.  Since,  agreeably  to  the  electro-chemical  theory,  the 
elements  of  a  compound  may  in  relation  to  each  other  be  considered  oppo- 
sitely electric,  I  shall  distinguish  two  or  more  equivalents  of  the  negative 
element  by  Latin  numerals,  and  apply  Greek  numerals  to  that  element 
which  is  regarded  as  positive.  Thus  a  bichloride  denotes  a  compound 
which  contains  two  equivalents  of  the  negative  element  chlorine ;  whereas 
a  bichloride  indicates  that  one  equivalent  of  chlorine  is  combined  with  two 
of  some  positive  body. 


SECTION   I. 

AFFINITY. 

ALL  chemical  phenomena  are  owing  to  Affinity  or  Chemical  Attraction. 
It  is  the  basis  on  which  the  science  of  chemistry  is  founded.  It  is,  as  it 
were,  the  instrument  which  the  chemist  employs  in  all  his  operations,  and 
hence  it  forms  the  first  and  leading  object  of  his  study. 

Affinity  is  exerted  between  the  minutest  particles  of  different  kinds  of 
matter,  causing  them  to  combine  so  as  to  form  new  bodies  endowed  with  new 
properties.  It  acts  only  at  insensible  distances ;  in  other  words,  apparent 
contact,  or  the  closest  proximity,  is  necessary  to  its  action.  Every  thing 
which  prevents  such  contiguity  is  an  obstacle  to  combination ;  and  any  force 
which  increases  the  distance  between  particles  already  combined,  tends  to 
separate  them  permanently  from  each  other.  In  the  former  case,  they  do 
not  come  within  the  sphere  of  their  mutual  attraction  ;  in  the  latter,  they  are 
removed  out  of  it.  It  follows,  therefore,  that  though  affinity  is  regarded  as  a 
specific  power  distinct  from  the  other  forces  which  act  on  matter,  its  action 
may  be  promoted,  modified,  or  counteracted  by  them ;  and  consequently,  in 
studying  the  phenomena  produced  by  affinity,  it  is  necessary  to  inquire  into 
the  conditions  that  influence  its  operation. 

The  most  simple  instance  of  the  exercise  of  chemical  attraction  is  afforded 
by  the  admixture  of  two  substances.  Water  and  sulphuric  acid,  or  water 
and  alcohol,  combine  readily.  On  the  contrary,  water  shows  little  disposition 
to  unite  with  sulphuric  ether,  and  still  less  with  oil;  for  however  intimately 
their  particles  may  be  mixed  together,  they  are  no  sooner  left  at  rest  than  the 
ether  separates  almost  entirely  from  the  water,  and  a  total  separation  takes 
place  between  that  fluid  and  the  oil.  Sugar  dissolves  very  sparingly  in  al- 
cohol, but  to  any  extent  in  water;  while  camphor  is  dissolved  in  a  very  small 
degree  by  water,  and  abundantly  by  alcohol.  It  appears,  from  these  examples, 
that  chemical  attraction  is  exerted  between  different  bodies  with  different  de- 
grees of  force.  There  is  sometimes  no  proof  of  its  existence  at  all ;  between 
some  substances  it  acts  very  feebly,  and  between  others  with  great  energy. 

Simple  combination  of  two  substances  is  a  common  occurrence;  of  which 
the  solution  of  salts  in  water,  the  combustion  of  phosphorus  in  oxygen  gas, 
and  the  neutralization  of  a  pure  alkali  by  an  acid,  are  instances.  But  the 


AFFINITY.  125 

phenomena  arc  often  more  complex.  The  formation  of  a  new  compound  is 
often  attended  by  the  destruction  of  a  pre-existing  one;  as  when  some  third 
body  acts  on  a  compound,  for  one  element  of  which  it  has  a  greater  affinity 
than  they  have  for  one  another.  Thus,  oil  has  an  affinity  for  the  volatile  al- 
kali, ammonia,  and  will  unite  with  it,  forming  a  soapy  substance  called  a 
liniment.  But  the  ammonia  has  a  still  greater  attraction  for  sulphuric  acid ; 
and  hence  if  this  acid  be  added  to  the  liniment,  the  alkali  will  quit  the  oil, 
and  unite  by  preference  with  the  acid.  It*  a  solution  of  camphor  in  alcohol 
be  poured  into  water,  the  camphor  will  be  set  free,  because  the  alcohol  corn- 
bines  with  the  water.  Sulphuric  acid,  in  like  manner,  separates  baryta  from 
nitric  acid.  Combination  and  decomposition  occur  in  each  of  these  cases ; 
— combination  of  sulphuric  acid  with  ammonia,  of  water  with  alcohol,  and 
of  baryta  with  sulphuric  acid; — decomposition  of  the  compounds  formed  of 
oil  and  ammonia,  of  alcohol  and  camphor,  and  of  nitric  acid  and  baryta. 
These  are  examples  of  what  Bergmann  called  single  elective,  affinity ; — elec- 
tive, because  a  substance  manifests,  as  it  were,  a  choice  for  one  of  two  others, 
uniting  with  it  by  preference,  and  to  the  exclusion  of  the  other.  Many  of 
the  decompositions  that  occur  in  chemistry  arc  instances  of  single  elective 
affinity. 

The  order  in  which  these  decompositions  take  place  has  been  expressed 
in  tables,  of  which  the  following,  drawn  up  by  Geoffroy,  is  an  example;— 

Sulphuric  acid. 

Baryta, 

Strontia, 

Potassa, 

Soda, 

Lime, 

Ammonia, 

Magnesia. 

This  table  signifies,  first,  that  sulphuric  acid  has  an  affinity  for  the  sub- 
stances  placed  below  the  horizontal  line,  and  may  unite  separately  with 
each ;  and,  secondly,  that  the  base  of  the  salts  so  formed  will  be  separated 
from  the  acid  by  adding  any  of  the  alkalies  or  earths  which  stand  above  it 
in  the  column.  Thus  ammonia  will  separate  magnesia,  lime  ammonia,  and 
potassa  lime;  but  none  can  withdraw  baryta  from  sulphuric  acid,  nor  can 
ammonia  or  magnesia  decompose  sulphate  of  lime,  though  strontia  or  baryta 
will  do  so.  Bergmann  conceived  that  these  decompositions  are  solely  deter- 
mined by  chemical  attraction,  and  that  consequently  the  order  of  decompo- 
sition  represents  the  comparative  forces  of  affinity;  and  this  view,  from  the 
simple  and  natural  explanation  it  affords  of  the  phenomenon,  was  for  a  time 
very  generally  adopted.  But  Bergmann  was  in  error.  It  does  not  necessa 
rily  follow,  because  lime  separates  ammonia  from  sulphuric  acid,  that  the 
lime  hae  a  greater  attraction  for  the  acid  than  the  volatile  alkali.  Other 
causes  are  in  operation  which  modify  the  action  of  affinity  to  such  a  degree, 
that  it  is  impossible  to  discover  how  much  of  the  effect  is  owing  to  that 
power.  It  is  conceivable  that  ammonia  may  in  reality  have  a  stronger  at- 
traction for  sulphuric  acid  than  lime,  and  yet  that  the  latter,  from  the  great 
influence  of  disturbing  causes,  may  succeed  in  decomposing  sulphate  of  am- 
monia. 

The  propriety  of  the  foregoing  remark  will  be  made  obvious  by  the  fol. 
lowing  example.  When  a  stream  of  hydrogen  gas  is  passed  over  oxide  of 
iron  heated  to  redness,  the  oxide  is  reduced  to  the  metallic  state,  and  water 
is  generated.  On  the  contrary,  when  watery  vapour  is  brought  into  contact 
with  red-hot  metallic  iron,  the  oxygen  of  the  water  quits  the  hydrogen  and 
combines  with  the  iron.  It  follows  from  the  result  of  the  first  experiment, 
according  to  Bergmann,  that  hydrogen  has  a  stronger  attraction  than  iron 
for  oxygen ;  and  from  that  of  the  second,  that  iron  has  a  greater  affinity  for 
oxygen  than  hydrogen.  But  these  inferences  are  incompatible  with  each 

11* 


126  AFFINITY. 

other.  The  affinity  of  oxygen  for  the  two  elements,  hydrogen  and  iron? 
must  either  be  equal  or  unequal.  If  equal,  the  result  of  both  experiments 
was  determined  by  modifying  circumstances;  since  neither  of  these  sub- 
stances ought  on  this  supposition  to  take  oxygen  from  the  other.  But  if 
the  forces  are  unequal,  the  decomposition  in  one  of  the  experiments  must 
have  been  determined  by  extraneous  causes,  in  direct  opposition  to  the  ten- 
dency of  affinity. 

To  Berthollet  is  due  the  honour  of  pointing  out  the  fallacy  of  Bergrnann's 
opinion.  He  was  the  first  to  show  that  the  relative  forces  of  chemical  at- 
traction cannot  always  be  determined  by  observing  the  order  in  which  sub- 
stances separate  each  other  when  in  combination,  and  that  the  tables  of 
Geoffroy  are  merely  tables  of  decomposition,  not  of  affinity.  He  likewise 
traced  all  the  various  circumstances  that  modify  the  action  of  affinity,  arid 
gave  a  consistent  explanation  of  the  mode  in  which  they  operate.  Berthollet 
went  even  a  step  further.  He  denied  the  existence  of  elective  affinity  as  an 
invariable  force,  capable  of  effecting  the  perfect  separation  of  one  body  from 
another;  he  maintained  that  all  the  instances  of  complete  decomposition  at- 
tributed to  elective  affinity  are  in  reality  determined  by  one  or  more  of  the 
collateral  circumstances  that  influence  its  operation.  But  here  this  acute 
philosopher  went  too  far.  Bergmann  erred  in  supposing  the  result  of  che- 
mical action  to  be  in  every  case  owing  to  elective  affinity  ;  but  Berthollet 
ran  into  the  opposite  extreme  in  declaring  that  the  effects  formerly  ascribed 
to  that  power  are  never  produced  by  it.  That  chemical  attraction  is  exerted 
between  bodies  with  different  degrees  of  energy  is,  I  apprehend,  indisputa- 
ble. Water  has  a  much  greater  affinity  for  hydrochloric  acid  and  ammo- 
niacal  gases  than  for  carbonic  and  hydrosulphuric  acids,  and  for  these  than 
for  oxygen  and  hydrogen.  The  attraction  of  lead  for  oxygen  is  greater  than 
that  of  silver  for  the  same  substance.  The  disposition  of  gold  and  silver  to 
combine  with  mercury  is  greater  than  the  attraction  of  platinum  and  iron 
for  that  fluid.  As  these  differences  cannot  be  accounted  for  by  the  opera- 
tion of  any  modifying  causes,  we  must  admit  a  difference  in  the  force  of 
affinity  in  producing  combination.  It  is  equally  clear  that  in  some  instances 
the  separation  of  bodies  from  one  another  can  only  be  explained  on  the  same 
principle.  No  one,  I  conceive,  will  contend  that  the  decomposition  of  hy- 
driodic  acid  by  chlorine,  or  of  hydrosulphuric  acid  by  iodine,  is  determined 
by  the  concurrence  of  any  modifying  circumstances. 

Affinity  is  the  cause  of  still  more  complicated  changes  than  those  which 
have  been  just  considered.  In  a  case  of  single  elective  affinity,  three  sub- 
stances only  are  present,  and  two  affinities  are  in  play.  But  it  frequently 
happens  that  two  compounds  are  mixed  together,  and  four  different  affinities 
brought  into  action.  The  changes  that  may  or  do  occur  under  these  cir- 
cumstances may  be  studied  by  aid  of  a  diagram,  a  method  which  was  first 
employed,  I  believe,  by  Dr.  Black,  and  has  since  been  generally  practised. 
Thus,  in  mixing  together  a  solution  of  carbonate  of  ammonia  and  hydro- 
chlorate  e£ Jime,  their  mutual  action  may  be  represented  in  the  following 
manner  : 

Carbonic  acid  Ammonia. 


Hydrochloric  acid  Lime. 

Each  of  the  acids  has  an  attraction  for  both  bases,  and  hence  it  is  possi- 
ble either  that  the  two  salts  should  continue  as  they  were,  or  that  an  inter- 
change of  principles  should  ensue,  giving  rise  to  two  new  compounds — 
carbonate  of  lime  and  hydrochlorate  of  ammonia.  According  to  the  views 
of  Bergmann,  the  result  is  solely  dependent  on  the  comparative  strength  of 
affinities.  If  the  affinity  of  carbonic  acid  for  ammonia,  and  of  hydrochloric 
acid  for  lime,  exceed  that  of  carbonic  acid  for  lime,  added  to  that  of  hydro- 


AFFINITY.  127 

chloric  acid  for  ammonia,  then  will  the  two  salts  experience  no  change 
whatever;  but  if  the  latter  affinities  preponderate,  then,  as  does  actually 
happen  in  the  present  example,  both  the  original  salts  will  be  decomposed, 
and  two  new  ones  generated.  Two  decompositions  and  two  combinations 
take  place,  being  an  instance  of  what  is  called  double  elective  affinity.  Mr. 
Kirwin  applied  the  terms  quiescent  and  divellent  to  denote  the  tendency  of 
the  opposing  affinities,  the  action  of  the  former  being  to  prevent  a  change, 
the  latter  to  produce  it. 

The  doctrine  of  double  elective  affinity  was  assailed  by  Berthollet  on  the 
same  ground  and  with  the  same  success  as  in  the  case  of  single  elective  at- 
traction. He  succeeded  in  proving  that  the  effect  cannot  always  be  ascribed 
to  the  sole  influence  of  affinity.  For,  to  take  the  example  already  adduced, 
if  carbonate  of  ammonia  decompose  hydrochlorate  of  lime  by  the  mere 
force  of  a  superior  attraction,  it  is  manifest  that  carbonate  of  lirne  ought 
never  to  decompose  hydrochlorate  of  ammonia.  But  if  these  two  salts  are 
mixed  in  a  dry  state  and  exposed  to  heat,  double  decomposition  does  take 
place,  carbonate  of  ammonia  and  hydrochlorate  of  lime  being  formed  ;  and, 
therefore,  if  the  change  in  the  first  example  was  produced  by  chemical  at- 
traction alone,  that  in  the  second  must  have  occurred  in  direct  opposition  to 
that  power.  It  does  not  follow,  however,  because  the  result  is  sometimes 
determined  by  modifying  conditions,  that  it  must  always  be  so.  I  appre- 
hend that  the  decomposition  of  the  solid  cyanuret  of  mercury  by  hydrosnl- 
phuric  acid  gas,  which  takes  place  even  at  a  low  temperature,  cannot  be 
ascribed  to  any  other  cause  than  a  preponderance  of  the  divellent  over  the 
quiescent  affinities. 

CHANGES  THAT  ACCOMPANY  CHEMICAL  ACTION. 

The  leading  circumstance  that  characterizes  chemical  action  is  the  loss  of 
properties  experienced  by  the  combining  substances,  and  the  acquisition  of 
new  ones  by  the  product  of  their  combination.  The  change  of  property  is 
sometimes  inconsiderable.  In  a  solution  of  sugar  or  salt  in  water,  and  in 
mixtures  of  water  with  alcohol  or  sulphuric  acid,  the  compound  retains  so 
much  of  the  character  of  its  constituents,  that  there  is  no  difficulty  in  recog- 
nising their  presence.  But  more  generally  the  properties  of  one  or  both  of 
the  combining  bodies  disappear  entirely.  One  would  not  suppose  from  its 
appearance  that  water  is  a  compound  body ;  much  less  that  it  is  composed 
of  two  gases,  oxygen  and  hydrogen,  neither  of  which,  when  uncombined, 
has  ever  been  compressed  into  a  liquid.  Hydrogen  is  one  of  the  most  in- 
flammable substances  in  nature,  and  yet  water  cannot  be  set  on  fire  ;  oxygen, 
on  the  contrary,  enables  bodies  to  burn  with  great  brilliancy,  and  yet  water 
extinguishes  combustion.  The  alkalies  and  earths  were  regarded  as  simple 
until  Sir  H.  Davy  proved  them  to  be  compound,  and  certainly  they  evince  no 
sign  whatever  of  containing  oxygen  and  a  metal.  Numerous  examples  of  a 
similar  kind  are  afforded  by  the  mutual  action  of  acids  and  alkalies.  Sul- 
phuric acid  and  potassa,  for  example,  are  highly  caustic.  The  former  is  in- 
tensely sour,  reddens  the  blue  colour  of  vegetables,  and  has  a  strong  affinity 
for  alkaline  substances ;  the  latter  has  a  pungent  taste,  converts  the  blue 
colour  of  vegetables  to  green,  and  combines  readily  with  acids.  On  adding 
these  principles  cautiously  to  each  other,  a  compound  results  called  a  neutral 
salt,  which  does  not  in  any  way  affect  the  colouring  matter  of  plants,  and  in 
which  the  other  distinguishing  features  of  the  acid  and  alkali  can  no  longer 
be  perceived.  They  appear  to  have  destroyed  the  properties  of  each  other, 
and  are  hence  said  to  neutralize  one  another. 

The  other  phenomena  that  accompany  chemical  action  are  changes  of 
density,  temperature,  form,  and  colour. 

1.  It  is  observed  that  two  bodies  rarely  occupy,  after  combination,  the 
same  space  which  they  possessed  separately.  In  general  their  bulk  is 
diminished,  so  that  the  specific  gravity  of  the  new  body  is  greater  than  the 
mean  of  its  components.  Thus  a  mixture  of  100  measures  of  water,  and  an 


128  AFFINITY. 

equal  quantity  of  sulphuric  acid  does  not  occupy  the  space  of  200  measures, 
but  considerably  less.  A  similar  contraction  frequently  attends  the  combi- 
nation of  solids.  Gases  often  experience  a  remarkable  condensation  when 
they  unite.  The  elements  of  olefiant  gas,  for  instance,  would  expand  to 
four  times  the  bulk  of  that  compound,  if  they  were  suddenly  to  become  free, 
and  assume  the  gaseous  form.  But  the  rule  is  not  without  exception.  The 
reverse  happens  in  some  metallic  compounds;  and  there  are  examples  of 
combination  between  gases  without  any  change  of  bulk. 

2.  A   change   of  temperature   generally  accompanies   chemical   action. 
Heat  is  evolved  either  when  there  is  a  diminution  in  the  bulk  of  the  com- 
bining substances  without  change  of  form,  or  when  a  gas  is  condensed  into 
a  liquid,  or  a  liquid  becomes  solid.     The  heat  caused  by  mixing  sulphuric 
acid  with  water  is  an  instance  of  the  former ;  and  the  common  process  of 
slaking   lime,  during  which  water  loses  its  liquid   form  in  combining  with 
that  earth,  is  an  example  of  the  latter.     The  rise  of  temperature  in   these 
cases  is  obviously  referable  to  diminution  in  the  capacity  of  the  new  com- 
pound for  heat;  but  intense  heat  sometimes   accompanies  chemical   action 
under   circumstances   in    which    an  explanation   founded   on  a  change   of 
specific  heat  is  quite  inadmissible.     At  present  it  is  enough  to   have  stated 
the  fact;  its  theory  will  be  discussed  under  the  subject  of  combustion.     The 
production  of  cold  seldom  or  never  takes  place  during  combination,  except 
when  heat  is  rendered  insensible  by  the  conversion  of  a  solid   into  a  liquid, 
or  a  liquid  into  a  gas.     All  the  frigorific  mixtures  act  in  this  way. 

3.  The  changes  of  form  that  attend  chemical    action    are   exceedingly 
various.     The  combination  of  gases  may  give  rise  to  a  liquid  or  a  solid ; 
solids  sometimes  become  liquid,  and  liquids  solid.    Several  familiar  chemical 
phenomena,  such  as  detonation,  effervescence,  and  precipitation,  are   owing 
to  these  changes.     The  sudden   evolution   of  a  large  quantity  of  gaseous 
matter  causes  an    explosion,  as  when  gunpowder  detonates.     The  slower 
disengagement  of  gas  produces  effervescence,  as  when  marble  is  put   into 
hydrochloric  acid.     A  precipitate  is  owing  to  the  formation  of  a  new  body 
which  happens  to  be  insoluble  in  the  liquid  in   which  its  elements  were 
dissolved. 

4.  Chemical   action  is  frequently  attended    by   change   of  colour.      No 
uniform  relation  has  been  traced  between  the  colour  of  a  compound  and  that 
of  its  elements.     Iodine,  whose  vapour  is  of  a  violet  hue,  forms  a  beautiful 
red  compound  with  mercury,  and  a  yellow  one  with  lead.    The  brown  oxide 
of  copper  generally  gives  rise  to  green  and   blue  coloured  salts;  while  the 
salts  of  the  oxide  of  lead,  which  is  itself  yellow,   are   for  the  most  part 
colourless.     The  colour  of  precipitates  is  a  very  important  study,  as  it  sup- 
plies  a  character  by  which  most  substances  may  be  distinguished. 

CIRCUMSTANCES  THAT  MODIFY  AND  INFLUENCE  THE 
OPERATION  OF  AFFINITY. 

Of  the  conditions  which  are  capable  of  promoting  or  counteracting  the 
tendency  of  chemical  attraction,  the  following  are  the  most  important; — 
cohesion,  elasticity,  quantity  of  matter,  and  gravity.  To  these  may  be  added 
the  agency  of  the  imponderables. 

Cohesion. — The  first  obvious  effect  of  cohesion  is  to  oppose  affinity,  by 
impeding  or  preventing  that  mutual  penetration  and  close  proximity  of  the 
particles  of  different  bodies,  which  is  essential  to  the  successful  exercise  of 
their  attraction.  For  this  reason,  bodies  seldom  act  chemically  in  their 
solid  state;  their  molecules  do  not  come  within  the  sphere  of  attraction,  and, 
therefore,  combination  cannot  take  place,  although  their  affinity  may  in  fact 
be  considerable.  Liquidity,  on  the  contrary,  favours  chemical  action ;  it 
permits  the  closest  possible  approximation,  while  the  cohesive  power  is  com- 
paratively so  trifling  as  to  oppose  no  appreciable  barrier  to  affinity. 

Cohesion  may  be  diminished  in  two  ways,  by  mechanical  division,  or  by 
the  application  of  heat.  The  former  is  useful  by  increasing  the  extent  of 


AFFINITY.  129 

surface ;  but  it  is  not  of  itself  in  general  sufficient,  because  the  particles, 
however  minute,  still  retain  that  degree  of  cohesion  which  constitutes 
solidity.  Heat  acts  with  greater  effect,  and  never  fails  in  promoting  combi- 
nation, whenever  the  cohesive  power  is  a  barrier  to  it.  Its  intensity  should 
always  be  so  regulated  as  to  produce  liquefaction.  The  fluidity  of  one  of 
the  substances  frequently  suffices  for  effecting  chemical  union,  as  is  proved 
by  the  facility  with  which  water  dissolves  many  salts  and  other  solid  bodies. 
But  the  cohesive  force  is  still  in  operation  ;  for  a  solid  is  commonly  dissolved 
in  greater  quantity  when  its  cohesion  is  diminished  by  heat.  The  reduction 
of  both  substances  to  the  liquid  state  is  the  best  method  for  ensuring  chemi- 
cal action.  The  slight  degree  of  cohesion  possessed  by  liquids  does  not 
appear  to  cause  any  impediment  to  combination ;  for  they  commonly  act  as 
energetically  on  each  other  at  low  temperatures,  or  at  a  temperature  just 
sufficient  to  cause  perfect  liquefaction,  as  when  their  cohesive  power  is  still 
further  diminished.  It  seems  fair  to  infer,  therefore,  that  very  little,  if  any, 
affinity  exists  between  two  bodies  which  do  not  combine  when  they  are 
intimately  mixed  in  a  liquid  state. 

The  phenomena  of  crystallization  are  owing  to  the  ascendency  of  cohesion 
over  affinity.  When  a  large  quantity  of  salt  has  been  dissolved  in  water  by 
the  aid  of  heat,  part  of  the  saline  matter  generally  separates  as  the  solution 
cools ;  because  the  cohesive  power  of  the  salt  then  becomes  comparatively  too 
powerful  for  chemical  attraction.  Its  particles  begin  to  cohere  together  and 
are  deposited  in  crystals,  the  process  of  crystallization  continuing  till  it  is 
arrested  by  the  affinity  of  the  liquid.  A  similar  change  happens  when  a 
solution  made  in  the  cold  is  gradually  evaporated.  The  cohesion  of  the 
saline  particles  is  no  longer  counteracted  by  the  affinity  of  the  liquid,  and 
the  salt,  therefore,  assumes  the  solid  form. 

Cohesion  plays  a  still  more  important  part,  It  sometimes  determines  the 
result  of  chemical  action,  probably  even  in  opposition  to  affinity.  Thus,  on 
mixing  together  a  solution  of  two  acids  and  one  alkali,  of  which  two  salts 
may  be  formed,  one  soluble,  and  the  other  insoluble,  the  alkali  will  unite 
with  that  acid  with  which  it  forms  the  insoluble  compound,  to  the  total 
exclusion  of  the  other.  This  is  one  of  the  modifying  circumstances  em- 
ployed by  Berthollet  to  account  for  the  phenomena  of  single  elective 
attraction,  and  is  certainly  applicable  to  many  of  the  instances  to  be  found 
in  the  tables  of  affinity.  When,  for  example,  hydrochloric  acid,  sulphuric 
acid,  and  baryta,  are  mixed  together,  sulphate  of  baryta  is  formed  in  conse- 
quence of  its  insolubility.  Lime,  which  yields  an  insoluble  salt  with  car- 
bonic acid,  separates  that  acid  from  ammonia,  potassa,  and  soda,  with  all 
of  which  it  makes  soluble  compounds. 

A  similar  explanation  may  be  given  of  many  cases  of  double  elective 
attraction.  On  mixing  together  in  solution  four  substances,  A,  B,  c,  D,  of 
which  it  is  possible  to  form  four  compounds,  AB  and  CD,  or  AC  and  BD,  that 
compound  will  certainly  be  produced,  which  happens  to  be  insoluble.  Thus 
sulphuric  acid,  soda,  nitric  acid,  and  baryta,  may  give  rise  either  to  sulphate 
of  soda  and  nitrate  of  baryta,  or  to  sulphate  of  baryta  and  nitrate  of  soda; 
but  the  first  two  salts  cannot  exist  together  in  the  same  liquid,  because  the 
insoluble  sulphate  of  baryta  is  instantly  generated,  and  its  formation  neces- 
sarily causes  the  nitric  acid  to  combine  with  the  soda.  In  like  manner,  a 
solution  of  nitrate  of  lime  is  decomposed  by  carbonate  of  ammonia,  in  con- 
sequence of  the  insolubility  of  carbonate  of  lime. 

To  comprehend  the  manner  in  which  cohesion  acts  in  these  instances,  it 
is  necessary  to  consider  what  takes  place  when  in  the  same  liquid  two  or 
more  compounds  are  brought  together,  which  do  not  give  rise  to  an  insolu- 
ble substance.  Thus  on  mixing  solutions  of  sulphate  of  potassa  and  nitrate 
of  soda,  no  precipitate  ensues;  because  the  salts  capable  of  being  formed  by 
double  decomposition,  sulphate  of  soda  and  nitrate  of  potassa,  are  likewise 
soluble.  In  this  case  it  is  possible  either  that  each  acid  may  be  confined  to 
one  base,  so  as  to  constitute  two  neutral  salts ;  or  that  each  acid  may  be  di- 
vided between  both  bases,  yielding  four  neutral  salts.  It  is  difficult  to  decide 


130  AFFINITY. 

this  point  in  an  unequivocal  manner:  but  judging  from  many  chemical 
phenomena,  there  can,  I  apprehend,  be  no  doubt  that  the  arrangement  last 
mentioned  is  the  most  frequent,  and  is  probably  universal  whenever  the 
relative  forces  of  affinity  are  not  very  unequal.  When  two  acids  and  two 
bases  meet  together  in  neutralizing  proportion,  it  may,  therefore,  be  inferred, 
that  each  acid  unites  with  both  the  bases  in  a  manner  regulated  by  their 
respective  forces  of  affinity,  and  that  four  salts  are  contained  in  solution.  In 
like  manner  the  presence  of  three  acids  and  three  bases  will  give  rise  to  nine 
salts;  and  when  four  of  each  are  present,  sixteen  salts  will  be  produced. 
This  view  affords  the  most  plausible  theory  of  the  constitution  of  mineral 
waters,  and  of  the  products  which  they  yield  by  evaporation. 

The  influence  of  insolubility  in  determining  the  result  of  chemical  action 
may  be  readily  explained  on  this  principle.  If  nitric  acid,  sulphuric  acid, 
and  baryta,  are  mixed  together  in  solution,  the  base  may  be  conceived  to  be 
at  first  divided  between  the  two  acids,  and  nitrate  and  sulphate  of  baryta  to 
be  generated.  The  latter  being  insoluble  is  instantly  removed  beyond  the 
influence  of  the  nitric  acid,  so  that  for  an  instant  nitrate  of  baryta  and  free 
sulphuric  acid  remain  in  the  liquid  ;  but  as  the  base  left  in  solution  is  again 
divided  between  the  two  acids,  a  fresh  quantity  of  the  insoluble  sulphate  is 
generated  ;  and  this  process  of  partition  continues,  until  either  the  baryta  or 
the  sulphuric  acid  is  withdrawn  from  the  solution.  Similar  changes  ensue 
when  nitrate  of  baryta  and  sulphate  of  soda  are  mixed. 

The  separation  of  salts  by  crystallization  from  mineral  waters  or  other  sa- 
line mixtures  is  explicable  by  a  similar  mode  of  reasoning.  Thus  on  mixing 
nitrate  of  potassa  and  sulphate  of  soda,  four  salts,  according  to  this  view,  are 
generated,  namely,  the  sulphates  of  soda  and  potassa,  and  the  nitrates  of  those 
bases;  and  if  the  solution  be  allowed  to  evaporate  gradually,  a  point  at  length 
arrives  when  the  least  soluble  of  these  salts,  the  sulphate  of  potassa,  will  be 
disposed  to  crystallize.  As  soon  as  some  of  its  crystals  are  deposited,  and 
thus  withdrawn  from  the  influence  of  the  other  salts,  the  constituents  of  these 
undergo  a  new  arrangement,  whereby  an  additional  quantity  of  sulphate  of 
potassa  is  generated ;  and  this  process  continues  until  the  greater  part  of 
the  sulphuric  acid  and  potassa  has  combined,  and  the  compound  is  removed 
by  crystallization.  If  the  difference  in  solubility  is  considerable,  the  separa- 
tion of  salts  may  be  often  rendered  very  complete  by  this  method. 

The  efflorescence  of  a  salt  is  sometimes  attended  with  a  similar  result. 
If  carbonate  of  soda  arid  chloride  of  calcium  are  mingled  together  in  solu- 
tion, the  insoluble  carbonate  of  lime  subsides.  But  if  carbonate  of  lime  and 
sea-salt  are  mixed  in  the  solid  state,  and  a  certain  degree  of  moisture  is 
present,  carbonate  of  soda  and  chloride  of  calcium  are  slowly  generated ; 
and  since  the  former,  as  soon  as  it  is  formed,  separates  itself  from  the 
mixture  by  efflorescence,  its  production  continues  progressively.  The 
efflorescence  of  carbonate  of  soda,  which  is  sometimes  seen  on  old  walls,  or 
which  in  some  countries  is  found  on  the  soil,  appears  to  have  originated  in 
this  manner. 

Elasticity. — From  the  obstacle  which  cohesion  puts  in  the  way  of  affinity, 
the  gaseous  state,  in  which  the  cohesive  power  is  wholly  wanting,  might  be 
expected  to  be  peculiarly  favourable  to  chemical  action.  The  reverse,  how- 
ever, is  the  fact.  Bodies  evince  little  disposition  to  unite  when  presented  to 
each  other  in  the  elastic  form.  Combination  does  indeed  sometimes  take 
place,  in  consequence  of  a  very  energetic  attraction ;  but  examples  of  an 
opposite  kind  are  much  more  common.  Oxygen  and  hydrogen  gases,  and 
chlorine  and  hydrogen,  though  their  mutual  affinity  is  very  powerful,  may 
be  preserved  together  for  any  length  of  time  without  combining.  This  want 
of  action  seems  to  arise  from  the  distance  between  the  particles  preventing 
that  close  approximation  which  is  so  necessary  to  the  successful  exercise  of 
affinity.  Hence  many  gases  cannot  be  made  to  unite  directly,  which  never- 
theless combine  readily  while  in  their  nascent  state;  that  is,  while  in  the  act 
of  assuming  the  gaseous  form  by  the  decomposition  of  some  of  their  solid  or 
fluid  combinations. 


AFFINITY.  131 

Elasticity  operates  likewise  as  a  decomposing  agent.  If  two  gases,  the 
reciprocal  attraction  of  which  is  feeble,  suffer  considerable  condensation 
when  they  unite,  the  compound  will  be  decomposed  by  very  slight  causes. 
Chloride  of  nitrogen,  which  is  an  oil-like  liquid,  composed  of  the  two  gases 
chlorine  and  nitrogen,  affords  an  apt  illustration  of  this  principle,  being 
distinguished  for  its  remarkable  facility  of  decomposition.  Slight  elevation 
of  temperature,  by  increasing  the  natural  elasticity  of  the  two  gases,  or 
contact  of  substances  which  have  an  affinity  for  either  of  them,  produces 
immediate  explosion. 

Many  familiar  phenomena  of  decomposition  are  owing  to  elasticity.  All 
compounds  that  contain  a  volatile  and  a  fixed  principle,  are  liable  to  be 
decomposed  by  a  high  temperature.  The  expansion  occasioned  by  heat 
removes  the  elements  of  the  compound  to  a  greater  distance  from  each 
other,  and  thus,  by  diminishing  the  force  of  chemical  attraction,  favours  the 
tendency  of  the  volatile  principle  to  assume  the  form  which  is  natural  to  it. 
The  evaporation  of  water  from  a  solution  of  salt  is  an  instance  of  this  kind. 
Many  solid  substances,  which  contain  water  in  a  state  of  intimate  com- 
bination, part  with  it  in  a  strong  heat,  in  consequence  of  the  volatile  nature 
of  that  liquid.  The  separation  of  oxygen  from  some  metals,  by  heat  alone, 
is  explicable  on  the  same  principle. 

From  these  and  some  preceding  remarks,  it  appears  that  the  influence  of 
heat  over  affinity  is  variable ;  for  at  one  time  it  promotes  chemical  union, 
and  opposes  it  at  another.  Its  action,  however,  is  always  consistent.  When- 
ever the  cohesive  power  is  an  obstacle  to  combination,  heat  favours  affinity 
either  by  diminishing  the  cohesion  of  a  solid,  or  by  converting  it  into  a 
liquid.  As  the  cause  of  the  gaseous  state,  on  the  contrary,  it  keeps  at  a 
distance,  particles  which  would  otherwise  unite;  or,  by  producing  expansion, 
it  tends  to  separate  from  one  another  substances  which  are  already  com- 
bined. There  is  one  effect  of  heat  which  seems  somewhat  anomalous ; 
namely,  the  combination  which  ensues  in  gaseous  explosive  mixtures  on  the 
approach  of  flame.  The  explanation  given  by  Berthollet  is  probably  correct, 
— that  the  sudden  dilatation  of  the  gases  in  the  immediate  vicinity  of  the 
flame,  acts  as  a  violent  compressing  power  to  the  contiguous  portions,  and 
thus  brings  them  within  the  sphere  of  their  attraction. 

Some  of  the  decompositions,  which  were  attributed  by  Bergmann  to  the 
sole  influence  of  elective  affinity,  may  be  ascribed  to  elasticity.  If  three 
substances  are  mixed  together,  two  of  which  can  form  a  compound  which  is 
less  volatile  than  the  third  body,  the  last  will,  in  general,  be  completely 
driven  off  by  the  application  of  heat.  The  decomposition  of  the  salts  of 
ammonia  by  the  pure  alkalies  or  alkaline  earths,  may  be  adduced  as  an 
example;  and ,  for  the  same  reason,  all  the  carbonates  are  decomposed  by 
hydrochloric  acid,  and  all  the  hydrochlorates  by  sulphuric  acid.  This  ex- 
planation applies  equally  well  to  some  cases  of  double  decomposition.  It 
explains,  for  instance,  why  the  dry  carbonate  of  lime  will  decompose  hydro- 
chlorate  of  ammonia  by  the  aid  of  heat;  for  carbonate  of  ammonia  is  more 
volatile  than  the  hydrochlorale  either  of  ammonia  or  lime. 

The  influence  of  elasticity  in  determining  the  result  of  chemical  action  in 
these  instances,  seems  owing  to  the  same  cause  which  enables  insolubility  to 
be  productive  of  similar  effects.  Thus,  on  mixing  hydrochlorate  of  ammonia 
with  lime,  the  acid  is  divided  between  the  two  bases  ;  some  ammonia 
becomes  free,  which,  in  consequence  of  its  elasticity,  is  entirely  expelled  by 
a  gentle  heat.  The  acid  of  the  remaining  hydrochlorate  of  ammonia  is 
again  divided  between  the  two  bases;  and  if  a  sufficient  quantity  of  lime  is 
present,  the  ammoniacal  salt  will  be  completely  decomposed.  In  like  man- 
ner the  decomposition  of  potassa  may  be  effected  by  iron,  though  the 
affinity  of  this  metal  for  oxygen  seems  much  inferior  to  that  of  potassium 
for  oxygen.  If  potassa  in  the  fused  state  be  brought  in  contact  with 
metallic  iron  at  a  white  heat,  the  oxygen  is  divided  between  the  two  metals, 
and  a  portion  of  potassium  set  at  liberty.  But  as  potassium  is  volatile  at  a 
white  heat,  it  is  expelled  at  the  instant  of  reduction:  and  thus,  by  its 
influence  being  withdrawn,  an  opportunity  is  given  for  the  decomposition  of 
an  additional  quantity  of  potassa. 


132  AFFINITY. 

Quantity  of  Matter.  The  influence  of  quantity  of  matter  over  affinity  is 
universally  admitted.  If  one  body  A  unites  with  another  body  B  in  several 
proportions,  that  compound  will  be  most  difficult  of  decomposition  which 
contains  the  smallest  quantity  of  B.  Of  the  three  oxides  of  lead,  for  instance, 
the  peroxide  parts  most  easily  with  its  oxygen  by  the  action  of  heat ;  a 
higher  temperature  is  required  to  decompose  the  red  oxide ;  and  the  pro- 
toxide will  bear  the  strongest  heat  of  our  furnaces  without  losing  a  particle 
of  its  oxygen. 

The  influence  of  quantity  over  chemical  attraction  may  be  further  illus- 
trated by  the  phenomena  of  solution.  When  equal  weights  of  a  soluble  salt 
are  added  in  succession  to  a  given  quantity  of  water,  which  is  capable  of 
dissolving  almost  the  whole  of  the  salt  employed,  the  first  portion  of  the  salt 
will  disappear  more  readily  than  the  second,  the  second  than  the  third,  the 
third  than  the  fourth,  and  so  on.  The  affinity  of  the  water  for  the  saline 
substance  diminishes  with  each  addition,  till  at  last  it  is  weakened  to  such  a 
degree  as  to  be  unable  to  overcome  the  cohesion  of  the  salt.  The  process 
then  ceases,  and  a  saturated  solution  is  obtained. 

Quantity  of  matter  is  employed  advantageously  in  many  chemical  opera- 
tions. If,  for  instance,  a  chemist  is  desirous  of  separating  an  acid  from  a 
metallic  oxide  by  means  of  the  superior  affinity  of  potassa  for  the  former^he 
frequently  uses  rather  more  of  the  alkali  than  is  sufficient  for  neutralizing 
the  acid.  He  takes  the  precaution  of  employing  an  excess  of  alkali,  in  order 
the  more  effectually  to  bring  every  particle  of  the  substance  to  be  decom- 
posed in  contact  with  the  decomposing  agent. 

But  Berthollet  has  attributed  a  much  greater  influence  to  quantity  of  mat- 
ter. It  was  the  basis  of  his  doctrine,  developed  in  the  Statique  Chimique, 
that  bodies  cannot  be  wholly  separated  from  each  other  by  the  affinity  of  a 
third  substance  for  one  element  of  a  compound ;  and  to  explain  why  a  su- 
perior chemical  attraction  does  not  produce  the  effect  which  might  be  ex- 
pected from  it,  he  contended  that  quantity  of  matter  compensates  for  a  weaker 
affinity.  From  the  co-operation  of  several  disturbing  causes,  Berthollet  per- 
ceived that  the  force  of  affinity  cannot  be  estimated  with  certainty  by  observ- 
ing the  order  of  decomposition ;  and  he,  therefore,  had  recourse  to  another 
method.  He  set  out  by  supposing  that  the  affinity  of  different  acids  for  the 
same  alkali,  is  in  the  inverse  ratio  of  the  ponderable  quantity  of  each  which 
is  necessary  for  neutralizing  equal  quantities  of  the  alkali.  Thus,  if  two  parts 
of  one  acid  A,  and  one  part  of  another  acid  B,  are  required  to  neutralize  equal 
quantities  of  the  alkali  C,  it  was  inferred  that  the  affinity  of  B  for  C  was  twice 
as  great  as  that  of  A.  He  conceived,  further,  that  as  two  parts  of  A  produce 
the  same  neutralizing  effect  as  one  part  of  B,  the  attraction  exerted  by  any 
alkali  towards  two  parts  of  A  ought  to  be  precisely  the  same  as  for  the  one 
part  of  B ;  and  he  hence  concluded  that  there  is  no  reason  why  the  alkali 
should  prefer  the  small  quantity  of  one  to  the  large  quantity  of  the  other. 
On  this  he  founded  the  principle  that  quantity  of  matter  compensates  for 
force  of  attraction. 

Berthollet  has  here  obviously  confounded  two  things,  namely,  force  of  at- 
traction and  neutralizing  power,  which  are  really  different,  and  ought  to  be 
held  distinct.  The  relative  weights  of  hydrochloric  and  sulphuric  acids  re- 
quired to  neutralize  an'equal  quantity  of  any  alkali,  or,  in  other  words,  their 
capacities  of  saturation,  are  as  3G.42  to  40.1,  a  ratio  which  remains  constant 
with  respect  to  all  other  alkalies.  The  affinity  of  these  acids,  according  to  Ber- 
thollet's  rule,  will  be  expressed  by  the  same  numbers.  But  in  taking  this 
estimate,  we  have  to  make  three  assumptions,  each  of  which  wis  disputable. 
There  is  no  proof,  in  the  first  place,  that  hydrochloric  acid  has  a  greater  af- 
finity for  an  alkali,  such  as  potassa,  than  sulphuric  acid.  Such  an  inference 
would  be  directly  opposed  to  the  general  opinion  founded  on  the  order  of  de- 
composition ;  and  though  that  order,  as  we  have  shown,  is  by  no  means  a 
satisfactory  test  of  the  strength  of  affinity,  it  would  be  improper  to  adopt  an 
opposite  conclusion  without  having  good  reasons  for  so  doing.  Secondly, 
were  it  established  that  hydrochloric  acid  has  the  greater  affinity,  it  does  not 


AFFINITY.  133 

follow  that  the  attraction  of  those  acids  for  potassa  is  in  the  ratio  of  36.42  to 
40.1.  And,  thirdly,  supposing  this  point  settled,  it  is  very  improbable  that  the 
ratio  of  their  affinities  for  one  alkali  will  apply  to  all  others;  analogy  would 
lead  us  to  anticipate  the  reverse.  Independently  of  these  objections,  M.  Du- 
long  has  found  that  the  principle  of  Berthollet  is  not  in  accord  with  the  results 
of  experiment. 

Gravity. — The  influence  of  gravity  is  perceptible  when  it  is  wished  to  make 
two  substances  unite,  the  densities  of  which  are  different.  In  a  case  of  sim- 
ple solution,  a  larger  quantity  of  saline  matter  is  found  at  the  bottom  than  at 
the  top  of  the  liquid,  unless  the  solution  shall  have  been  well  mixed  subse- 
quently to  its  formation.  In  making  an  alloy  of  two  metals,  which  differ 
from  one  another  in  density,  a  larger  quantity  of  the  heavier  metal  will  be 
found  at  the  lower  than  in  the  upper  part  of  the  compound ;  unless  great 
care  be  taken  to  counteract  the  tendency  of  gravity  by  agitation.  This  force 
obviously  acts,  like  the  cohesive  power,  in  preventing  a  sufficient  degree  of 
approximation. 

Imponderables. — The  influence  which  heat  exerts  over  chemical  phenomena, 
and  the  modes  in  which  it  operates,  have  been  already  discussed.  The  che- 
mical agency  of  galvanism  has  also  been  described.  The  effects  of  light 
will  be  most  conveniently  stated  in  other  parts  of  the  work.  Electricity  is 
frequently  employed  to  produce  the  combination  of  gases  with  one  another, 
and  in  some  instances  to  separate  them.  It  appears  to  act  by  the  heat  which 
it  occasions,  and,  therefore,  on  the  same  principle  as  flame. 

MEASURE  OF  AFFINITY. 

As  the  foregoing  observations  prove  that  the  order  of  decomposition  is  not 
always  a  satisfactory  measure  of  affinity,  it  becomes  a  question  whether  there 
are  any  means  of  determining  the  comparative  forces  of  chemical  attraction. 
When  no  disturbing  causes  operate,  the  phenomena  of  decomposition  afford 
a  sure  criterion ;  but  when  the  conclusions  obtained  in  this  way  are  doubtful, 
assistance  may  b?  frequently  derived  from  other  sources.  The  surest  indi- 
cations are  procured  by  observing  the  tendency  of  different  substances  to 
unite  with  the  same  principle,  under  the  same  circumstances,  and  subse- 
quently by  marking  the  comparative  facility  of  decomposition  when  the 
compounds  so  formed  are  exposed  to  the  same  decomposing  agent.  Thus, 
on  exposing  silver,  lead,  and  iron,  to  air  and  moisture,  the  iron  soon  rusts, 
the  lead  is  oxidized  in  a  slight  degree  only,  and  the  silver  resists  oxidation  al- 
together. It  is  hence  inferred  that  iron  has  the  greatest  affinity  for  oxygen, 
lead  next,  and  silver  the  least.  This  conclusion  is  supported  by  concurring 
observations  of  a  like  nature,  and  confirmed  by  the  circumstances  under 
which  the  oxides  of  those  metals  part  with  their  oxygen.  Oxide  of  silver  is 
reduced  by  heat  only ;  and  oxide  of  lead  is  decomposed  by  charcoal  at  a  lower 
temperature  than  oxide  of  iron. 

It  is  inferred  from  the  action  of  heat  on  the  carbonate  of  potassa,  baryta, 
lime,  and  oxide  of  lead,  that  potassa  has  a  stronger  attraction  for  carbonic 
acid  than  baryta,  baryta  than  lime,  and  lime  than  oxide  of  lead.  The  affinity 
of  different  substances  for  water  may  be  determined  in  a  similar  manner. 

Of  all  chemical  substances,  our  knowledge  of  the  relative  degrees  of  at- 
traction of  acids  and  alkalies  for  each  other  is  the  most  uncertain.  Their 
action  on  one  another  is  affected  by  so  many  circumstances,  that  it  is  in  most 
cases  impossible,  with  certainty,  to  refer  any  effect  to  its  real  cause.  The 
only  methods  that  have  been  hitherto  devised  for  remedying  this  defect  are 
those  of  Berthollet  and  Kirwan.  Both  of  them  are  founded  on  the  capacities 
of  saturation,  and  the  objections  which  have  been  urged  to  the  rule  suggested 
by  the  former  philosopher  apply  equally  to  that  proposed  by  the  latter.  But 
this  uncertainty  is  of  no  great  consequence  in  practice.  We  know  perfectly 
the  order  of  decomposition,  whatever  may  be  the  actual  forces  by  which  it  is 
effected. 

12 


134  LAWS  OF  COMBINATION. 


SECTION  II. 


PROPORTIONS  IN  WHICH  BODIES  UNITE,  AND  THE 
LAWS  OF  COMBINATION. 

THE  study  of  the  proportions  in  which  bodies  unite  naturally  resolves  itself 
into  two  parts.  The  first  includes  compounds  whose  elements  appear  to  unite 
in  a  great  many  proportions  ;  the  second  comprehends  those,  the  elements  of 
which  combine  in  a  few-  proportions  only. 

I.  The  compounds  contajned  in  the  first  division  are  of  two  kinds.     In 
one,  combination  takes  place  unlimitedly  in  all  proportions ;  in  the  other,  it 
occurs  in  every  proportion  within  a  certain  limit.     The  union  of  water  with 
alcohol  and  the  liquid  acids,  such  as  the  sulphuric,  hydrochloric,  and  nitric 
acids,  affords  instances  of  the  first  mode  of  combination  ;  the  solutions  of  salts 
in  water  are  examples  of  the  second.     One  drop  of  sulphuric  acid  may  be 
diffused  through  a  gallon  of  water,  or  a  drop  of  water  through  a  gallon  of  the 
acid;  or  they  may  be  mixed  together  in  any  intermediate  proportions;  and 
nevertheless  in  each  case  they  appear  to  unite  perfectly  with  each  other.     A 
hundred  grains  of  water,  on  the  contrary,  will  dissolve  any  quantity  of  sea- 
salt  which  does  not  exceed  forty  grains.     Its  solvent  power  then  ceases,  be- 
cause the  cohesion  of  the  solid  becomes  comparatively  too  powerful  for  the 
force  of  affinity.     The  limit  to  combination  is  in   such  instances  owing  to 
the  cohesive  power ;  and  but  for  the  obstacle  which  it  occasions,  the  salt 
would  most  probably  unite  with  water  in  every  proportion. 

All  the  substances  that  unite  in  many  propoitions,  give  rise  to  compounds 
which  have  this  common  character,  that  their  elements  are  united  by  a  fee- 
ble affinity,  and  preserve,  when  combined,  more  or  less  of  the  properties 
which  they  possess  in  a  separate  state.  In  a  scientific  point  of  view,  these 
combinations  are  of  minor  importance ;  but  they  are  exceedingly  useful  as 
instruments  of  research.  They  enable  the  chemist  to  present  bodies  to  each 
other  under  circumstances  peculiarly  favourable  for  acting  with  effect :  the 
liquid  form  is  thus  communicated  to  them;  while  the  affinity  of  the  solvent 
or  menstruum,  which  holds  them  in  solution,  is  not  sufficiently  powerful  to 
interfere  with  their  mutual  attraction. 

II.  The  most  interesting  series  of  compounds  is  produced   by  substances 
which  unite  in  a  few  proportions  only  ;  and  which,  in  combining,  lose  more 
or  less  completely  the  properties  that  distinguish  them  when  separate.     Of 
these  bodies,  some  form  but  one  combination.     Thus  there  is  only  one  com- 
pound of  boron  and  oxygen,  and  of  chlorine  and  hydrogen.     Others  combine 
in  two  proportions.     For  example,  two  compounds  are  formed   by  tin  and 
oxygen,  and  by  hydrogen  and  oxygen.     Other  bodies   again  unite  in  three, 
four,  five,  or  even  six  proportions,  which  is  the  greatest  number  of  com- 
pounds that  any  two  substances  are  known  to  produce,  except  perhaps  car- 
bon and  hydrogen,  and  those  which  belong  to  the  first  division. 

The  combination  of  substances  that  unite  in  a  few  proportions  only,  is  re- 
gulated by  the  three  following  remarkable  laws : — 

1.  The  first  of  these  laws  is,  that  the  composition  of  bodies  is  fixed  and 
invariable.  A  compound  substance,  so  long  as  it  retains  its  characteristic 
properties,  always  consists  of  the  same  elements  united  together  in  the  same 
proportion.  Sulphuric  acid,  for  example,  is  always  composed  of  sulphur  and 
oxygen  in  the  ratio  of  16.1  parts*  of  the  former  to  24  of  the  latter:  no  other 
elements  can  form  it,  nor  can  it  be  produced  by  its  own  elements  in  any 
other  proportion.  Water,  in  like  manner,  is  formed  of  1  part  of  hydrogen 

*  By  the  expression  4  parts'  I  always  mean  parts  by  weight. 


LAWS  OF  COMBINATION.  135 

and  8  of  oxygen  ;  and  were  these  two  elements  to  unite  in  any  other  pro- 
portion, some  new  compound,  different  from  water,  would  be  the  product. 
The  same  observation  applies  to  all  other  substances,  however  complicated, 
and  at  whatever  period  they  were  produced.  Thus,  sulphate  of  baryta, 
whether  formed  ages  ago  by  the  hand  of  nature,  or  quite  recently  by  the 
operations  of  the  chemist,  is  always  composed  of  40.1  parts  of  sulphuric  acid 
and  76.7  of  baryta.  This  law,  in  fact,  is  universal  and  permanent.  Its  im- 
portance is  equally  manifest :  it  is  the  essential  basis  of  chemistry,  without 
which  the  science  itself  could  have  no  existence. 

Two  views  have  been  proposed  by  way  of  accounting  for  this  law.  The 
explanation  now  universally  given  is  confined  to  a  mere  statement,  that  sub- 
stances are  disposed  to  combine  in  those  proportions  to  which  they  are 
so  strictly  limited,  in  preference  to  any  others ;  it  is  regarded  as  an  ultimate 
fact,  because  the  phenomena  are  explicable  on  no  other  known  principle. 
A  different  doctrine  was  advanced  by  Berthollet,  in  his  Statique  Chimique, 
published  in  1803.  Having  observed  the  influence  of  cohesion  and  elasticity 
in  modifying  the  action  of  affinity  as  already  described,  he  thought  he  could 
trace  the  operations  of  the  same  causes  in  producing  the  effect  at  present 
under  consideration.  Finding  that  the  solubility  of  a  salt  and  of  a  gas  in 
water  is  limited,  in  the  former  by  cohesion,  and  in  the  latter  by  elasticity, 
he  conceived  that  the  same  forces  would  account  for  the  unchangeable  com- 
position of  certain  compounds.  He  maintained,  therefore,  that  within  cer- 
tain limits  bodies  have  a  tendency  to  unite  in  every  proportion  ;  and  that 
combination  is  never  definite^and  invariable,  except  when  rendered  so  by 
the  operation  of  modifying  causes,  such  as  cohesion,  insolubility,  elasticity, 
quantity  of  matter,  and  the  like.  Thus,  according  to  Berthollet,  sulphate  of 
baryta  is  composed  of  40.1  parts  of  sulphuric  acid  and  76.7  of  baryta,  not 
because  those  substances  are  disposed  to  unite  in  that  ratio  rather  than  in 
another,  but  because  the  compound  so  constituted  happens  to  have  great 
cohesive  power. 

These  opinions,  which,  if  true,  would  shake  the  whole  science  of  chemis- 
try to  its  foundation,  were  founded  on  observation  and  experiment,  supported 
by  all  the  ingenuity  of  that  highly  gifted  philosopher.  They  were  ably  and 
successfully  combated  by  Proust  in  several  papers  published  in  the  Journal 
de  Physique,  wherein  he  proved  that  the  metals  are  disposed  to  combine 
with  oxygen  and  with  sulphur,  only  in  one  or  two  proportions,  which  are 
definite  and  invariable.  The  controversy  which  ensued  between  these  emi- 
nent chemists,  is  remarkable  for  the  moderation  with  which  it  was  con- 
ducted on  both  sides,  and  has  been  properly  quoted  by  Berzelius  as  a  model 
to  controversialists.  How  much  soever  opinion  may  have  been  divided  upon 
the  question  at  that  period,  the  controversy  is  now  at  an  end.  The  great  va- 
riety of  new  facts,  similar  to  those  observed  by  Proust,  which  have  since 
been  established,  has  proved  beyond  a  doubt  that  the  leading  principle  of 
Berthollet  is  erroneous.  The  tendency  of  bodies  to  unite  in  definite  propor- 
tions only,  is  indeed  so  great  as  to  excite  a  suspicion  that  all  substances 
combine  in  this  way;  and  that  the  exceptions,  thought  to  be  afforded  by  the 
phenomena  of  solution,  are  rather  apparent  than  real ;  for  it  is  conceivable 
that  the  apparent  variety  of  proportion,  noticed  in  such  cases,  may  arise  from 
the  mixture  or  combination  of  a  few  definite  compounds  with  each  other. 

2.  The  second  law  of  combination  is,  that  the  relative  quantities  in  which 
bodies  unite  may  be  expressed  by  proportional  numbers.  Thus,  8  parts  of 
oxygen  unite  with  1  part  of  hydrogen,  16.1  of  sulphur,  35.42  of  chlorine,  39.6 
of  selenium,  and  108  parts  of  silver.  Such  are  the  quantities  of  these  five 
bodies  which  are  disposed  to  unite  with  8  parts  of  oxygen ;  and  it  is  found 
that  when  they  combine  with  one  another,  they  unite  either  in  the  propor- 
tions expressed  by  those  numbers,  or  in  multiplies  of  them  according  to  the 
third  law  of  combination.  Hydrosulphuric  acid,  for  instance,  is  composed 
of  1  part  of  hydrogen  and  16.1  of  sulphur,  and  bisulphuret  of  hydrogen,  of  1 
part  of  hydrogen  to  32.2  of  sulphur;  35.42  of  chlorine  unite  with  1  of  hydro- 
gen, 16.1  of  sulphur,  and  108  of  silver ;  and  39.6  parts  of  selenium  with  1  of 
hydrogen,  and  16.1  of  sulphur. 


136  LAWS  OF  COMBINATION. 

From  the  occurrence  of  such  proportional  numbers  has  arisen  the  use  of 
certain  terms,  as  Proportion,  Combining  Proportion,  Proportional,  and  Che- 
mical Equivalent,  or  Equivalent,  to  express  them.  The  latter  term,  intro- 
duced by  Dr.  Wollaston,  and  which  I  shall  commonly  employ,  was  suggest- 
ed by  the  circumstance  that  the  combining  proportion  of  one  body  is,  as  it 
were,  equivalent  to  that  of  another  body,  and  may  be  substituted  for  it  in 
combination.  At  page  141  will  be  found  a  table  of  the  equivalents  of  ele- 
mentary substances. 

This  law  does  not  apply  to  elementary  substances  only  ;  since  compound 
bodies  have  their  combining  proportions  or  equivalents,  which  may  likewise 
be  expressed  in  numbers.  Thus,  since  water  is  composed  of  one  equivalent 
or  8  parts  of  oxygen,  and  one  equivalent  or  1  of  hydrogen,  its  combining 
proportion  or  equivalent  is  9.  The  equivalent  of  sulphuric  acid  is  40.1,  be- 
cause it  is  a  compound  of  one  equivalent  or  16.1  parts  of  sulphur,  and  three 
equivalents  or  24  parts  of  oxygen  ;  and  in  like  manner,  the  combining  pro- 
portion of  hydrochloric  acid  is  36.42,  because  it  is  a  compound  of  one  equiva- 
lent or  35.42  parts  of  chlorine,  and  one  equivalent  or  1  part  of  hydrogen.  The 
equivalent  number  of  potassium  is  39.15,  and  as  that  quantity  combines  with 
8  of  oxygen  to  form  potassa,  the  equivalent  of  the  latter  is  39. 15 -{-8=47.1 5. 
Now  when  these  compounds  unite,  one  equivalent  of  the  one  combines  with 
one,  two,  three,  or  more  equivalents  of  the  other,  precisely  as  the  simple 
substances  do.  The  hydrate  of  potassa,  for  example,  is  constituted  of  47.15 
parts  of  potassa  and  9  of  water,  and  its  equivalent  is  consequently  47.15-J-9, 
or  56.15.  The  sulphate  of  potassa  is  composed  of  40.1  sulphuric  acid-f-47.15 
potassa;  and  the  nitrate  of  the  same  alkali  of  54.15  nitric  acid+47.15  of  po- 
tassa. The  equivalent  of  the  former  salt  is,  therefore,  87.25,  and  of  the  lat- 
ter 101.3. 

The  composition  of  the  salts  affords  a  very  instructive  illustration  of  this 
subject;  and  to  exemplify  it  still  further,  a  list  of  the  equivalents  of  a  few 
acids  and  alkaline  bases  is  annexed : — 

Hydrofluoric  acid  19.68  Lithia  14.44 

Phosphoric  acid  71.4  Magnesia  20.7 

Hydrochloric  acid  36.42  Lime  28.5 

Sulphuric  acid  40.1  Soda  31.3 

Nitric  acid  54.15  Potassa  47.15 

Arsenic  acid  115.4  Strontia  51.8 

Selenicacid  63.6  Baryta  76.7 

It  will  be  seen  at  a  glance  that  the  neutralizing  power  of  the  different  alka- 
lies is  very  different ;  for  the  equivalent  of  each  base  expresses  the  quantity 
required  to  neutralize  an  equivalent  of  each  of  the  acids.  Thus  14.44  of  lithia, 
31.3  of  soda,  and  76.7  of  baryta,  combine  with  54.15  of  nitric  acid,  forming  the 
neutral  nitrates  of  lithia,  soda,  and  baryta.  The  same  fact  is  obvious  with 
respect  to  the  acids;  for  71.4  of  phosphoric,  40.1  of  sulphuric,  and  115.4  of 
arsenic  acid  unite  with  76.7  of  baryta,  forming  a  neutral  phosphate,  sul- 
phate, and  arseniate  of  baryta. 

These  circumstances  afford  a  ready  explanation  of  a  curious  fact,  first 
noticed  by  the  Saxon  chemist  Wenzel ;  namely,  that  when  two  neutral  salts 
mutually  decompose  each  other,  the  resulting  compounds  are  likewise  neu- 
tral. The  cause  of  this  fact  is  now  obvious.  If  71.4  parts  of  neutral  sul- 
phate of  soda  are  mixed  with  130.85  of  nitrate  of  baryta,  the  76.7  parts  of 
baryta  unite  with  40.1  of  sulphuric  acid,  and  the  54.15  parts  of  nitric  acid 
of  the  nitrate  combine  with  the  31.3  of  soda  of  the  sulphate,  not  a  particle 
of  acid  or  alkali  remaining  in  an  uncornbined  condition. 

Sulphate  of  Soda.  Nitrate  of  Baryta. 

Sulphuric  acid        40.1  54.15  Nitric  acid. 

Soda       .         .         31.3        .  76.7     Baryta. 

TU  130.85 


LAWS  OP  COMBINATION.  137 

It  matters  not  whether  more  or  less  than  71.4  parts  of  sulphate  of  soda 
are  added;  for  if  more,  a  small  quantity  of  sulphate  of  soda  will  remain  in 
solution ;  if  less,  nitrate  of  baryta  will  be  in  excess ;  but  in  either  case  the 
neutrality  will  be  unaffected. 

3.  The  third   law  of  combination  is,  that  when  one  body  A  unites  with 
another   body  B  in  two  or  more  proportions,  the  quantities  of  the  latter, 
united  with  the  same  quantity  of  the  former,  bear  to  each  other  a  very  sim- 
ple ratio.      The  progress  of  chemical  research,  in  discovering  new  com- 
pounds and  ascertaining-  their  exact  composition,  has  shown  that  these  ratios 
of  B  may  be  represented  by  one  or  other  of  the  two  following  series: — 
1st  Series.     A  unites  with  1,  2,  3,  4,  5,  &c.  of  B. 
2d  Series.     A  unites  with  1,  1£,  2,  2£,  &c.  of  B. 
The  first  series  is  exemplified  by  the  subjoined  compounds : — 
Water  is  composed  of  -         Hydrogen     1  Oxygen  8(1 

Binoxide  of  hydrogen  Do.  1  Do.    16(2 

Carbonic  oxide      -         -         -         Carbon          6.12  Do.      831 

Carbonic  acid        ...  Do.  6.12  Do.    16  >  2 

Nitrous  oxide        ...         Nitrogen      14.15  Do.      8"j  1 

Nitric  oxide          ...  Do.  14.15  Do."  16     2 

Hyponitrous  acid  -         -  Do.  14.15  PO.    24  }-3 

Nitrous  acid          ...  Do.  14.15  Do.    32  |  4 

Nitric  acid  ...  Do.  14.15  Do.   40  J  5 

It  is  obvious  that  in  all  these  compounds  the  ratios  of  the  oxygen  are  ex- 
pressed by  whole  numbers.  In  water  the  hydrogen  is  combined  with  half 
as  much  oxygen  as  in  the  binoxide  of  hydrogen ;  so  that  the  ratio  is  as  1  to 
2.  The  same  relation  holds  in  carbonic  oxide  and  carbonic  acid.  The 
oxygen  in  the  compounds  of  nitrogen  and  oxygen  is  in  the  ratio  of  1,  2,  3, 
4,  and  5.  In  like  manner  the  ratio  of  sulphur  in  the  two  sulphurets  of 
mercury,  and  that  of  chlorine  in  the  two  chlorides  of  mercury,  is  as  1  to  2. 
So,  in  bicarbonate  of  potassa,  the  alkali  is  united  with  twice  as  much  car- 
bonic acid  as  in  the  carbonate ;  and  the  acid  of  the  three  oxalates  of  potassa 
is  in  the  ratio  of  1,  2,  and  4. 

The  following  compounds  exemplify  the  second  series  : — 
Protoxide  of  iron  consists  of  Iron  28         Oxygen  8  J  1 

Sesquioxide  or  peroxide     -  -         Do.  28  Do.    12  £  1£ 

Protoxide  of  manganese     -  -     Manganese   27.7          Do.      8)1 

Sesquioxide  .  -         Do.  27.7          Do.    12  >  1£ 

Binoxide  -        Do.  27.7          Do.    16^2 

Arsenious  acid  -  -     Arsenic          37.7          Do.    12  >  1^ 

Arsenic  acid  <    -         Do.  37.7          Do.    20  $  2£ 

Hypophosphorous  acid      -  -     Phosphorus    15.7          Do.     4 )    £ 

Phosphorous  acid  -         Do.  15.7          Do.    12/1^ 

Phosphoric  acid  -         Do.  15.7          Do.   20 )  2*| 

Both  of  these  series,  which  together  constitute  the  third  law  of  combr 
nation,  result  naturally  from  the  operation  of  the  second  law.  The  first 
series  arises  from  one  equivalent  of  a  body  uniting  with  one,  two,  three,  or 
more  equivalents  of  another  body.  The  second  series  is  a  consequence  of  two 
equivalents  of  one  substance  combining  with  three,  five,  or  more  equivalents  of 
another.  Thus  if  two  equivalents  of  phosphorus  unite  both  with  three  and  with 
five  equivalents  of  oxygen,  we  obtain  the  ratio  of  1^  to  2j|;  and  should  one 
equivalent  of  iron  combine  with  one  of  oxygen,  and  another  compound  be 
formed  of  two  equivalents  of  iron  to  three  of  oxygen,  then  the  oxygen  united 
with  the  same  weight  of  iron  would  have  the  ratio,  as  in  the  table,  of  1  to 
1£.  The  compounds  of  manganese  and  phosphorus  with  oxygen  afford  ex- 
amples of  the  same  nature.  Still  more  complex  arrangements  will  be  readily 
conceived,  such  as  three  equivalents  of  one  substance  to  four,  five,  or  more  of  an, 
other.  But  it  is  remarkable  that  combinations  of  the  kind  are  very  rare;  and 
even  their  existence,  though  theoretically  possible,  has  not  been  decidedly  esla. 


138  LAWS  OF  COMBINATION. 

blished.  Even  some  of  the  compounds  which  are  usually  included  in  the 
second  series  belong  properly  to  the  first.  The  red  oxide  of  lead,  for  in- 
stance, appears  in  its  chemical  relations  not  so  much  as  a  direct  compound 
of  lead  and  oxygen,  but  as  a  kind  of  salt  formed  by  the  union  of  the  bin- 
oxide  of  lead  with  the  protoxide  of  the  same  metal.  On  this  supposition 
the  two  other  oxides  belong  to  the  first  series. 

The  merit  of  establishing  the  first  law  of  combination  seems  justly  due 
to  Wenzel,  a  Saxon  chemist ;  and  the  second  law  is  also  deducible  from  his 
experiments  on  the  composition  of  the  salts.  His  work,  entitled  Lehre  der 
Verwandtschaft,  was  published  in  1777.  Bergmann  and  Richter,  a  few 
years  after,  confirmed  the  observations  of  Wenzel,  though  without  adding 
materially  in  the  way  of  generalization.  The  late  Mr.  Higgins,  also,  in 
1789,  speculated  on  the  atomic  constitution  of  compound  bodies  in  a  man- 
ner which,  if  pursued,  would  have  led  to  the  discovery  of  Dalton.  It  is  to 
the  latter,  science  is  indebted  for  deducing  from  the  scattered  facts  which 
had  been  previously  collected,  a  theory  of  chemical  union,  embracing  the 
whole  science,  and  giving  it  a  consistency  and  form  which  before  his  time  it 
had  never  possessed.  In  his  hands  the  second  law  of  combination  first  at- 
tained its  full  generality ;  but  the  discovery  which  is  more  peculiarly  his 
own,  is  that  part  of  the  third  law  of  combination  which  is  contained  in  the 
first  of  the  two  series  above  mentioned.  The  first  public  announcement  of 
his  views  appears  to  have  been  made  to  the  Philosophical  Society  of  Man- 
chester in  1803;  and  in  1808  they  were  explained  in  his  New  System  of 
Chemical  Philosophy.  In  the  same  year  Dr.  Wollaston  and  Dr.  Thomson 
gave  their  evidence  in  support  of  the  new  doctrine,  and  other  chemists  have 
followed  in  the  same  path  of  inquiry.  But  of  all  who  have  successfully  la- 
boured in'  establishing  the  laws  of  combination,  the  most  splendid  contribu- 
tion is  that  of  the  celebrated  Berzelius.  Struck  with  the  perusal  of  the 
works  of  Richter,  he  commenced  in  1807  an  investigation  into  the  laws  of 
definite  proportion.  Since  that  period  his  labours  in  this  important  field 
have  been  incessant,  and  every  department  of  the  science  has  been  enrich- 
ed by  his  skill  and  iri'defatigable  industry.  Whether  we  look  to  pneumatic 
chemistry,  to  the  chemical  history  of  the  metals  and  of  the  salts,  or  to  the 
composition  of  minerals,  we  are  alike  indebted  to  Berzelius.  In  all  has  he 
traced  the  laws -of  definite  proportion,  and,  by  a  multitude  of  exact  analyses, 
given  to  the  laws  of  combination  that  certainty  which  accumulated  facts  can 
alone  convey. 

The  utility  of  being  acquainted  with  these  important  laws  is  almost  too 
manifest  to  require  mention.  Through  their  aid,  and  by  remembering  the 
equivalents  of  a  few  elementary  substances,  the  composition  of  an  extensive 
range  of  compound  bodies  may  be  calculated  with  facility.  Thus,  by  know- 
ing that  6.12  is  the  equivalent  of  carbon  and  8  of  oxygen,  it  is  easy  to  recollect 
the  composition  of  carbonic  oxide  and  carbonic  acid ;  the  first  consisting  of 
6.13  parts  of  carbon  4.  8  of  oxygen,  and  the  second  of  6,12  carbon  +  16  of 
oxygen.  The  equivalent  of  potassium  is  39.15;  and  potassa,  its  protoxide,  is 
composed  of  39.15  of  potassium  +  8  of  oxygen.  From  these  few  data,  we 
know  at  once  the  composition  of  carbonate  and  bicarbonate  of  potassa ;  the 
former  being  composed  of  22.12  parts  of  carbonic  acid  -f-  47.15  potassa,  and  the 
latter  of  44.24  carbonic  acid  +  47.15  potassa.  This  method  acts  as  an  artificial 
memory,  the  advantage  of  which,  compared  with  the  common  practice  of 
stating  the  composition  in  100  parts,  will  be  manifest  by  inspecting  the  fol- 
lowing quantities,  and  attempting  to  recollect  them. 

Carbonic  Oxide.  Carbonic  Acid. 

Carbon  42.86         ....        27.27 

Oxygen  57.14        ....        72.73 

Carbonate  of  Potassa.  Bicarbonate  of  Potassa. 

Carbonic  acid      31.43         ....        47.83 
Potassa  68.57        ....        52.17 


LAWS  OF  COMBINATION.  139 

From  the  same  data,  calculations,  which  would  otherwise  be  difficult  or 
tedious,  may  be  made  rapidly  and  with  ease,  without  reference  to  books,  and 
frequently  by  a  simple  mental  process.  The  exact  quantities  of  substances 
required  to  produce  a  given  effect  may  be  determined  with  certainty ;  thus 
affording  information  which  is  often  necessary  to  the  success  of  chemical 
processes,  and  of  great  consequence  both  in  the  practice  of  the  chemical 
arts,  and  in  the  operations  of  pharmacy. 

The  same  knowledge  affords  a  good  test  to  the  analyst  by  which  he  may 
judge  of  the  accuracy  of  his  result,  and  even  sometimes  correct  an  analysis 
which  he  has  not  the  means  of  performing  with  rigid  precision.  Thus  a 
powerful  argument  for  the  accuracy  of  an  analysis  is  derived  from  the  cor- 
respondence of  its  result  with  the  laws  of  chemical  union.  On  the  contrary, 
if  it  form  an  exception  to  them,  we  are  authorized  to  regard  it  as  doubtful ; 
and  may  hence  be  led  to  detect  an  error,  the  existence  of  which  might  not 
otherwise  have  been  suspected.  If  an  oxidized  body  be  found  to  contain 
one  equivalent  of  the  combustible  with  7.99  of  oxygen,  it  is  fair  to  infer  that 
8  or  one  equivalent  of  oxygen,  would  have  been  the  result,  had  the  analysis 
been  perfect. 

The  composition  of  a  substance  may  sometimes  be  determined  by  a  cal- 
culation, founded  on  the  laws  of  chemical  union,  before  an  analysis  of  it  has 
been  accomplished.  When  the  new  alkali  lithia  was  first  discovered,  che- 
mists did  not  possess  it  in  sufficient  quantity  for  determining  its  constitution 
analytically.  But  the  neutral  sulphates  of  the  alkalies  arid  alkaline  earths 
are  known  to  be  composed  of  one  equivalent  of  each  constituent,  and  the 
oxides  to  contain  one  equivalent  of  oxygen.  If  it  be  found,  therefore,  by 
analysis,  that  neutral  sulphate  of  lithia  is  composed  of  40.1  parts  of  sul- 
phuric acid  and  14.44  of  lithia,  it  may  be  inferred,  since  40.1  is  one  equiva- 
lent  of  the  acid,  that  14,44  is  the  equivalent  for  lithia;  and  that  this  oxide  is 
formed  of  8  parts  of  oxygen  and  6.44  of  lithium. 

The  method  of  determining  equivalent  numbers  will  be  anticipated  from 
what  has  already  been  said.  The  commencement  is  made  by  carefully  ana- 
lyzing a  definite  compound  of  two  simple  substances  which  possess  an  ex- 
tensive  range  of  affinity.  Thus  water,  a  compound  of  oxygen  and  hydrogen, 
is  found  to  contain  8  parts  of  the  former  to  1  of  the  latter ;  and  if  it  be  as- 
sumed that  water  consists  of  one  equivalent  of  oxygen  and  one  of  hydrogen, 
the  relative  weights  of  these  equivalents  will  be  as  8  to  1.  The  chemist  then 
selects  for  analysis  such  compounds  as  he  believes  to  contain  one  equivalent 
of  each  element,  in  which  either  oxygen  or  hydrogen,  but  not  both,  is  pre- 
sent. Carbonic  oxide  and  hydrosulphuric  acid  are  suited  to  his  purpose :  as 
the  former  consists  of  8  parts  of  oxygen  and  6,12  of  carbon,  and  the  latter  of 
I  part  of  hydrogen  and  ]  6.1  of  sulphur,  the  equivalent  of  carbon  is  inferred 
to  be  6.12,  and  that  of  sulphur  16.1.  The  equivalents  of  all  the  other 
elements  may  be  determined  in  a  similar  manner. 

In  researches  on  chemical  equivalents  there  are  two  kinds  of  difficulty, 
one  involved  in  the  processes  for  ascertaining  the  exact  composition  of  com- 
pounds, and  the  other  in  the  selection  of  the  compounds  which  contain  sin- 
gle equivalents.  Important  general  precautions  in  the  experimental  part  of 
the  subject  are  the  following : — 1,  to  exert  scrupulous  care  about  the  purity 
of  materials ;  2,  to  select  methods  which  consist  of  a  few  simple  operations 
only ;  3,  to  repeat  experiments,  and  with  materials  prepared  at  different 
times ;  4,  to  arrive  at  the  same  conclusion  by  two  or  more  processes  indepen- 
dent of  each  other.  In  the  selection  of  compounds  of  single  equivalents, 
there  are  several  circumstances  calculated  to  direct  the  judgment: — 

1.  If  two  substances  combine  in  several  proportions,  the  Jaw  of  multiples 
usually  affects  the  electro-negative  element  of  a  compound.  Thus,  in  the 
five  compounds  of  nitrogen  and  oxygen,  in  which  oxygen  is  the  negative  ele- 
ment, 14.15  parts  of  nitrogen  are  united  with  8,  16,  24,  32,  and  40  parts  of 
oxygen ;  whereas,  taking  the  quantity  of  oxygen  as  constant,  8  parts  of  oxy- 
gen are  united  with  14,  7,  4.66,  3.5,  and  2.8  parts  of  nitrogen,  in  which  the 
pimple  ratio  of  the  first  series  does  not  exist.  This  circumstance  induces  the 


140  LAWS  OF  COMBINATION. 

chemist  always  to  search  among  the  oxides  of  the  same  element  for  the  lowest 
grade  of  oxidation,  and  in  most  eases  to  consider  it  as  a  compound  of  single 
equivalents.  In  some  instances,  however,  the  second  degree  of  oxidation  is 
formed  of  single  equivalents,  while  the  lowest  oxide  consists  of  two  equiva- 
lents of  the  positive  element  and  one  of  oxygen.  Such  compounds  are  call- 
ed dioxides  (page  124)  and  sometimes  suboxides. 

2.  Metallic  oxides,  distinguished  for  strong  alkalinity  or  for  acting  as 
strong  alkaline  bases,  are  always  protoxides.     Dioxides  rarely,  if  ever,  unite 
definitely  with  acids,  and  are  remarkable  for  their  ready  conversion  into 
protoxides  with  separation  of  metal.     If  the  same  metal  yield  several  oxides, 
the  protoxide  is  the  strongest  base  ;  the  highest  grade  of  oxidation  is  frequent- 
ly an  acid,  and  the  intermediate  oxides  are  in  general  little  distinguished 
either  for  alkalinity  or  acidity.      Protoxides  usually  resist  decomposition 
more  obstinately  than  other  oxides. 

3.  When  a  metal  forms  two  oxides,  the  oxygen  of  which  is  in  the  ratio  of 
1  to  1^,  the  first  is  usually  the  protoxide,  and  the  second  a  compound  of  two 
equivalents  of  the  metal  to  three  of  oxygen.     The  oxides  of  iron  and  nickel 
are  examples. 

4.  If  two  compounds  resemble  each  other  in  their  modes  of  combination,  it 
is  a  strong  presumption  that  their  constitution  is  similar.     Alumina  and  the 
sesquioxide  of  iron,  commonly  called  the  peroxide,  are  remarkably  allied  in 
their  chemical  relations ;  and  hence  it  is  inferred,  since  the  latter  consists  of 
two  eq.  of  iron  and  three  eq.  of  oxygen,  that  the  former,  whose  composition 
would  otherwise  be  very  doubtful,  is  composed  of  two  eq.  of  aluminium  and 
three  eq.  of  oxygen. 

5.  Mitscherlich  has  found,  as  is  more  fully  stated  in  the  article  on  crys- 
tallization, that  certain  compounds  which  resemble  each  other  in  composition 
and  in  their  modes  of  combining,  are  likewise  disposed  in  crystallizing  to 
affect  the  same  form.     Hence  it  is  a  strong  presumption  that  compounds 
which  are  analagous  both  in  their  crystalline  figure  and  modes  of  combining, 
are  also  similar  in  their  composition.     In  the  oxide  and  acid  of  chromium, 
the  oxygen  is  in  the  ratio  1  to  2;  and  hence  it  was  at  first  supposed  that  one 
eq.  of  chromium  was  united  in  the  oxide  with  one  eq.  and  in  the  acid  with 
two  equivalents  of  oxygen.     But  the  chromates  resemble  the  sulphates  in 
form  and   modes  of  combining,  and  the  oxide  of  chromium  bears  the  same 
analogy  to  alumina  and  sesquioxide  of  iron.     The  inference  is  that  oxide  of 
chromium  consists  of  two  eq.  of  chromium  and  three  eq.  of  oxygen,  and 
chromic  acid,  of  one  eq.  of  chromium  and  three  eq.  of  oxygen. 

6.  Another  guide  in  these  inquiries  is  derived  from  the  relation  traced  by 
Dulong  and  Petit  between  the  equivalent  of  a  body  and  its  specific  heat.   The 
coincidences  pointed  out  at  page  35  are  sufficiently  numerous  to  show  an 
interesting  relation  which  is  sometimes  useful  in  selecting  between  doubtful 
numbers ;  but  the  instances  of  failure  are  at  present  too  frequent  to  admit  of 
this  principle  being  used  except  with  much  caution. 

7.  The  ready  decomposition  by  galvanism,  observed  by  Mr.  Faraday,  of 
compounds  which  consist  of  single  equivalents,  and  the  resistance  to  the 
same  agent  of  many  others  not  so  constituted,  promises  to  become  an  indi- 
cation of  great  value  in  determining  equivalent  numbers.     The  facts  as  yet 
known  respecting  it  will  be  found  in  the  section  on  galvanism. 

8.  Great  light  is  often  thrown  on  the  chemical  constitution  of  a  compound 
by  a  knowledge  of  the  volumes  of  the  substances  of  which  it  is  composed. 
This  subject,  however,  will  be  discussed  in  an  after  part  of  this  section. 

Since  the  equivalents  merely  express  the  relative  quantities  of  different 
substances  which  combine  together,  it  is  in  itself  immaterial  what  figures 
are  employed  to  express  them.  The  only  essential  point  is,  that  the  relation 
should  be  strictly  observed.  Thus,  the  equivalent  of  hydrogen  may  be  as- 
sumed as  10;  but  then  oxygen  must  be  80,  carbon  61.2,  and  sulphur  161. 
We  may  call  hydrogen  100  or  1000  ;  or,  if  it  were  desirable  to  perplex  the 
subject  as  much  as  possible,  some  high  uneven  number  might  be  selected, 
provided  the  due  relation  between  the  different  numbers  were  faithfully  pre- 
served. But  such  a  practice  would  effectually  do  away  with  the  advantage 


LAWS  OF  COMBINATION. 


141 


above  ascribed  to  the  use  of  equivalents  ;  and  it  is  the  object  of  every  one  to 
employ  such  as  are  simple,  that  their  relation  may  be  perceived  by  mere  in- 
spection.  Dr.  Thomson  makes  oxygen  1,  so  that  hydrogen  is  eight  times 
less  than  unity,  or  0.125,  carbon  0.75,  and  sulphur  2.  Dr.  Wollaston,  in  his 
scale  of  chemical  equivalents,  estimated  oxygen  at  10  ;  and  hence  hydrogen 
is  1.25,  carbon  7.5,  and  so  on.  According  to  Berzelius,  oxygen  is  100.  And 
lastly,  several  other  chemists,  such  as  Dalton,  Davy,  Henry,  and  others,  se- 
lected hydrogen  as  their  unit ;  and,  therefore,  the  equivalent  of  oxygen  is  8. 
One  of  these  series  may  easily  be  reduced  to  either  of  the  others  by  an  ob- 
vious and  simple  calculation.  The  numbers  adopted  in  this  work  refer  to 
hydrogen  as  unity,  and  are  given  in  the  subjoined  table. 

CHEMICAL  EQUIVALENTS  OF  ELEMENTARY  SUBSTANCES. 


Elements. 

Equivalents. 

Elements. 

Equivalents 

Elements. 

Equivalents. 

Aluminium 

13.7 

Gold 

199.2 

Potassium 

39.15 

Antimony 

64.6 

Hydrogen 

1 

Rhodium 

52.2 

Arsenic 

37.7 

Iodine 

126.3 

Selenium 

39.6 

Barium 

68.7 

Iridium 

98.8 

iSiHcitun 

7.5 

Bismuth 

71 

Iron 

28 

jSilver 

108 

Boron 

10.9 

Lead 

103.6 

|  Sodium 

23.3 

Bromine 

78.4 

Lithium 

6.44 

[Strontium 

43.8 

Cadmium 

55.8 

Magnesium 

12.7 

Sulphur 

16.1 

Calcium 

20.5 

Manganese 

27.7 

Tellurium 

64.2 

Carbon 

6.12 

Mercury 

202 

Thorium 

59.6 

Cerium 

46 

Molybdenum 

47.7 

Tin 

58.9 

Chlorine 

35.42 

Nickel 

29.5 

Titanium 

24.3 

Chromium 

28 

Nitrogen 

14,15 

Tungsten 

94.8 

Cobalt 

29.5 

Osmium 

99.7 

Uranium 

217 

Columbium 

185 

}xygen 

8 

Vanadium 

68.5 

Copper 

31.6 

Palladium 

53.3 

Yttrium 

32.2 

Fluorine 

18.68 

Phosphorus 

15.7 

Zinc 

32.3 

Glucinium 

17.7 

Platinum 

98.8 

Zirconium 

33.7 

The  preceding  table  is  constructed  principally  from  the  published  tables 
of  Berzelius,  and  partly  from  facts  supplied  by  my  own  researches.  The 
hypothesis  that  all  equivalent  numbers  are  simple  multiples  of  the  equivalent 
of  hydrogen,  has  been  elsewhere  shown  to  be  untenable.  (Phil.  Trans.  1833, 
Part  ii.  page  523.)  Whenever  the  experimental  quantity  is  nearly  a  whole 
number,  the  last  may  for  many  purposes  be  used  as  a  sufficient  approxima- 
tion ;  but  on  all  occasions  where  exact  calculations  are  concerned,  the  num- 
bers given  in  the  table  should  be  employed. 

The  useful  instrument,  known  by  the  name  of  the  Scale  of  Chemical  Equi- 
valents, was  originally  devised  by  Dr.  Wollaston,  and  is  a  table  of  equiva- 
lents, comprehending  all  those  substances  which  are  most  frequently  em- 
ployed by  chemists  in  the  laboratory ;  and  it  only  differs  from  other  tabular 
arrangements  of  the  same  .kind,  in  the  numbers  being  attached  to  a  sliding 
rule,  which  is  divided  according  to  the  principle  of  that  of  Gunter.  From 
the  mathematical  construction  of  the  scale,  it  not  only  serves  the  same  pur- 
pose as  other  tables  of  equivalents,  but  in  many  instances  supersedes  the  ne- 
cessity of  calculation.  Thus,  by  inspecting  the  common  table  of  equivalents, 
we  learn  that  87.25  parts,  or  one  equivalent,  of  sulphate  of  potassa  contain 
40.1  parts  of  sulphuric  acid  and  47.15  of  potassa  ;  but  recourse  must  be  had 
to  calculation,  when  it  is  wished  to  determine  the  quantity  of  acid  or  alkali 
in  any  other  quantity  of  the  salt.  This  knowledge,  on  the  contrary,  is  ob- 
tained directly  by  means  of  the  scale  of  chemical  equivalents.  For  example, 


142  LAWS  OF  COMBINATION. 

on  pushing  up  the  slide  until  100  marked  upon  it  is  in  a  line  with  the  name 
sulphate  of  potassa  on  the  fixed  part  of  the  scale,  the  numbers  opposite  to  the 
terms  sulphuric  acid  and  potassa  will  give  the  precise  quantity  of  each  con- 
tained in  100  parts  of  the  compound.  In  the  original  scale  of  Dr.  Wollaston, 
for  a  particular  account  of  which  I  may  refer  to  the  Philosophical  Transac- 
tions for  1614,  oxygen  is  taken  as  the  standard  of  comparison  ;  but  hydrogen 
may  be  selected  for  that  purpose  with  equal  propriety,  and  scales  of  this  kind 
have  been  prepared  for  sale  by  Dr.  Boswell  Reid  of  Edinburgh.  A  very 
complete  scale  of  equivalents  has  been  drawn  up  by  Mr.  Prideaux  of  Ply- 
mouth. (Phil.  Mag.  and  Annals,  viii.  430.) 

ATOMIC  THEORY. 

The  brief  sketch  which  has  been  given  of  the  laws  of  combination,  will, 
I  trust,  serve  to  set  in  its  true  light  the  importance  of  that  department  of 
chemical  science.  It  is  founded,  as  may  have  been  seen,  on  experiment 
alone ;  and  the  laws  which  have  been  stated  are  the  mere  expression  of  fact. 
It  is  not  necessarily  connected  with  any  speculation,  and  may  be  kept  wholly 
free  from  it.  The  error  which  students  of  chemistry  are  apt  to  commit  in 
Bupposing  that  the  laws  of  combination  involve  something  uncertain  or  hy- 
pothetical, may  easily  be  traced  to  its  source.  It  was  impossible  to  reflect 
on  the  regularity  and  constancy  with  which  bodies  obey  these  laws,  without 
speculating  about  the  cause  of  that  regularity :  and,  consequently,  the  facts 
themselves  were  no  sooner  noticed  than  an  attempt  was  made  to  explain 
them.  Accordingly,  when  Dr.  Dalton  published  his  discovery  of  those  laws, 
he  at  onee  incorporated  the  description  of  them  with  his  notion  of  their  phy- 
sical cause,  and  even  expressed  the  former  in  language  suggested  by  the  lat- 
ter. Since  that  period,  though  several  British  chemists  of  eminence,  and  in 
particular  Wollaston  and  Davy,  recommended  and  practised  an  opposite 
course,  both  subjects  have  been  too  commonly  comprised  under  the  head  of 
atomic  theory ;  and  hence  it  has  often  happened  that  beginners  have  rejected 
the  whole  as  hypothetical,  because  they  could  not  satisfactorily  distinguish 
those  parts  which  are  founded  on  fact,  from  those  which  are  conjectural. 
All  such  perplexity  would  have  been  avoided,  and  this  department  of  the 
science  have  been  far  better  understood,  and  its  value  more  justly  appre- 
ciated, had  the  discussion  concerning  the  atomic  constitution  of  bodies  been 
always  kept  distinct  from  that  of  the  phenomena  which  it  is  intended  to  ex- 
plain. When  employed  in  this  limited  sense,  the  atomic  theory  may  be  dis- 
cussed in  a  few  words. 

Two  opposite  opinions  have  long  existed  concerning  the  ultimate  elements 
of  matter.  It  is  supposed,  according  to  one  party,  that  every  particle  of 
matter,  however  small,  may  be  divided  into  smaller  portions,  provided  our 
instruments  and  organs  were  adapted  to  the  operation.  Their  opponents 
contend,  on  the  other  hand,  that  matter  is  composed  of  certain  ultimate  par- 
ticles or  molecules,  which  by  their  nature  are  indivisible,  and  hence  termed 
atoms  (from  A  not  and  rtftvtiv  to  cut].  These  opposite  opinions  have  from 
time  to  time  been  keenly  contested,  and  with  variable  success,  according  to 
t,he  acuteness  and  ingenuity  of  their  respective  champions.  But  it  was  at  last 
perceived  that  no  positive  data  existed  capable  of  deciding  the  question,  and 
its  interest,  therefore,  gradually  declined.  The  progress  of  modern  chemistry 
has  revived  the  general  attention  to  this  controversy,  by  affording  a  far 
stronger  argument  in  favour  of  the  atomic  constitution  of  bodies  than  was 
ever  advanced  before,  and  one  which  I  conceive  is  almost  irresistible.  We 
have  only  in  fact  to  assume  with  Dalton,  that  all  bodies  are  composed  of  ulti- 
mate atoms,  the  weight  of  which  is  different  in  different  kinds  of  matter,  and 
we  explain  at  once  the  foregoing  laws  of  chemical  union ;  and  this  mode  of 
reasoning  is  in  the  present  case  almost  decisive,  because  the  phenomena  do 
not  appear  explicable  on  any  other  supposition. 

According  to  the  atomic  theory,  every  compound  is  formed  of  the  atoms 


LAWS  OF  COMBINATION.  143 

of  its  constituents.  An  atom  of  A  may  unite  with  one,  two,  three,  or  more 
atoms  of  B.  Thus,  supposing-  water  to  be  composed  of  one  atom  of  hydro- 
gen and  one  atom  of  oxygen,  binoxide  of  hydrogen  will  consist  of  one  atom 
of  hydrogen  and  two  atoms  of  oxygen.  If  carbonic  oxide  is  formed  of  one 
atom  of  carbon  and  one  atom  of  oxygen,  carbonic  acid  will  consist  of  one 
atom  of  carbon  and  two  atoms  of  oxygen. 

If,  in  the  compounds  of  nitrogen  and  oxygen  enumerated  at  page  137,  the 
first,  or  protoxide  consist  of  one  atom  of  nitrogen  and  one  atom  of  oxygen, 
the  four  others  will  be  regarded  as  compounds  of  one  atom  of  nitrogen  to 
two,  three,  four,  and  five  atoms  of  oxygen.  From  these  instances  it  will 
appear,  that  the  law  of  multiple  proportion  is  a  necessary  consequence  of 
the  atomic  theory.  There  is  also  no  apparent  reason  why  two  or  more 
atoms  of  one  substance  may  not  combine  with  two,  three,  four,  five,  or  more 
atoms  of  another;  but,  on  the  contrary,  these  arrangements  are  necessary 
in  explanation  of  the  not  unfrequent  occurrence  of  half  equivalents,  as  for- 
merly stated.  (Page  137.)  Such  combinations  will  also  account  for  the 
complicated  proportion  noticed  in  certain  compounds,  especially  in  many  of 
those  belonging  to  the  animal  and  vegetable  kingdoms. 

In  consequence  of  the  satisfactory  explanation  which  the  laws  of  chemical 
union  receive  by  means  of  the  atomic  theory,  it  ha's  become  customary  to 
employ  the  term  atom  in  the  same  sense  as  combining  proportion  or  equiva- 
lent. For  example,  instead  of  describing  water  as  a  compound  of  one 
equivalent  of  oxygen  and  one  equivalent  of  hydrogen,  it  is  said  to  consist  of 
one  atom  of  each  element.  In  like  manner  sulphate  of  potassa  is  said  to  be 
formed  of  one  atom  of  sulphuric  acid  and  one  atom  of  potassa  ;  the  word  in 
this  case  denoting  as  it  were  a  compound  atom,  that  is,  the  smallest  integral 
particle  of  the  acid  or  alkali, — a  particle  which  does  not  admit  of  being 
divided,  except  by  the  separation  of  its  elementary  or  constituent  atoms. 
The  numbers  expressing  the  proportions  in  which  bodies  unite,  must  like- 
wise indicate,  consistently  with  this  view,  the  relative  weights  of  atoms ;  and 
accordingly  these  numbers  are  often  called  atomic  weights.  Thus,  as  water 
is  composed  of  8  parts  of  oxygen  and  1  of  hydrogen,  it  follows,  on  the  sup- 
position of  water  consisting  of  one  atom  of  each  element,  that  an  atom  of 
oxygen  must  be  eight  times  as  heavy  as  an  atom  of  hydrogen.  If  carbonic 
oxide  be  formed  of  an  atom  of  carbon  and  an  atom  of  oxygen,  the  relative 
weight  of  their  atoms  is  as  6.12  to  8;  and  in  short  the  chemical  equivalents 
of  all  bodies  may  be  considered  as  expressing  the  relative  weights  of  their 
atoms. 

The  foregoing  argument  in  favour  of  the  atomic  constitution  of  matter 
becomes  much  stronger,  when  we  trace  the  intimate  connexion  which  sub- 
sists, among  many  substances,  between  their  crystalline  form  and  chemical 
composition.  This  subject,  however,  now  known  under  the  name  of  isomor- 
phism will  be  more  conveniently  discussed  under  the  head  of  crystallization. 

Dalton  supposes  that  the  atoms  of  bodies  are  spherical ;  and  he  has  in- 
vented certain  symbols  to  represent  the  mode  in  which  he  conceives  they 
may  combine  together,  as  illustrated  by  the  following  figures. 

0   Hydrogen.  O   Oxygen. 

0   Nitrogen.  •  Carbon. 

BINARY  COMPOUNDS. 

O©  Water. 

O  •   Carbonic  oxide. 

TERNARY  COMPOUNDS. 

O  ©  O   Binoxide  of  hydrogen. 
O  •  O   Carbonic  acid. 
&c.  &c.  &c. 


144  LAWS  OF  COMBINATION. 

All  substances  containing  only  two  atoms  he  called  binary  compounds, 
those  composed  of  three  atoms  ternary  compounds,  of  four  quaternary,  and 
so  on. 

There  are  several  questions  relative  to  the  nature  of  atoms,  most  of  which 
will  perhaps  never  be  decided.  Of  this  nature  are  the  questions  which  re- 
late to  the  actual  form,  size,  and  weight  of  atoms,  and  to  the  circumstances 
in  which  they  mutually  differ.  All  that  we  know  with  any  certainty  is, 
that  their  weights  do  differ,  and  by  exact  analysis  the  relations  between 
them  may  be  determined. 

It  is  but  justice  to  the  memory  of  the  late  Mr.  Higgins  of  Dublin,  to 
state  that  he  first  made  use  of  the  atomic  hypothesis  in  chemical  reasonings. 
In  his  "Comparative  View  of  the  Phlogistic  and  Antiphlogistic  Theories," 
published  in  the  year  1789,  he  observes  (pages  36  and  37)  that  "in  volatile 
vitriolic  acid,  a  single  ultimate  particle  of  sulphur  is  intimately  united  only 
to  a  single  particle  of  dephlogisticated  air;  and  that,  in  perfect  vitriolic  acid, 
every  single  particle  of  sulphur  is  united  to  two  of  dephlogisticated  air, 
being  the  quantity  necessary  to  saturation;"  and  he  reasons  in  the  same 
way  concerning  the  constitution  of  water  and  the  compounds  of  nitrogen 
and  oxygen.  These  remarks  of  Mr.  Higgins  do  not  appear  to  have  had  the 
slightest  connexion  with  the  subsequent  views  of  Dr.  Dalton,  who  in  fact 
seems  to  have  never  seen  the  work  of  Higgins  till  after  he  had  given  an  ac- 
count of  his  own  doctrine.  The  observations  of  Higgins,  though  highly 
creditable  to  his  sagacity,  do  not  affect  Dalton's  merit  as  an  original  ob- 
server. They  were  made,  moreover,  in  so  casual  a  manner,  as  not  only  not 
to  have  attracted  the  notice  of  his  contemporaries,  but  to  prove  that  Higgins 
himself  attached  no  particular  interest  to  them.  Dalton's  chief  merit  con- 
sists in  having  formed  a  complete  theory  of  chemical  union,  and  in  the  dis- 
covery of  an  essential  and  most  important  part  of  the  doctrine,  a  merit 
which  is  solely  and  indisputably  his;  but  in  which  he  would  have  been 
anticipated  by  Higgins,  had  that  chemist  perceived  the  importance  of  his 
own  opinions. 

To  the  student  who  may  desire  a  more  ample  account  of  the  doctrine  of 
atoms  than  the  nature  and  limits  of  this  volume  admit  of  being  given  here, 
I  may  recommend  a  small  work  by  Dr.  Daubeny  on  the  atomic  theory, 
which  in  other  respects  will  be  found  well  worthy  of  perusal.  The  advanced 
student  may  also  consult  Dr.  Prout's  Bridgewater  Treatise,  where  he  will 
find  some  novel  speculations  on  the  agencies  which  give  rise  to  chemical 
union,  and  on  the  mode  in  which  the  combining  molecules  are  arranged ; 
speculations  which  may  well  open  a  path  to  important  views,  though  in 
their  present  form  they  will  scarcely  receive  the  general  assent  of  chemists. 

THEORY  OF  VOLUMES. 

Soon  after  the  publication  of  the  New  System  of  Chemical  Philosophy  in 
1808,  in  which  work  Dr.  Dalton  explained  his  views  of  the  atomic  constitution 
of  bodies,  a  paper  appeared  in  the  second  volume  of  the  Memoires  tfArcueil 
by  M.  Gay-Lussac,  on  the  "  Combination  of  Gaseous  Substances  with  one 
another."  He  there  proved  that  gases  unite  together  by  volume  in  very 
simple  and  definite  proportions.  In  the  combined  researches  of  himself  and 
Humboldt,  those  gentlemen  found  that  water  is  composed  precisely  of  100 
measures  of  oxygen  gas  and  200  measures  of  hydrogen;  and  Gay-Lussac, 
being  struck  by  this  peculiarly  simple  proportion,  was  induced  to  examine 
the  combinations  of  other  gases,  with  the  view  of  ascertaining  if  any  thing 
similar  occurred  in  other  instances. 

The  first  compounds  which  he  examined  were  those  of  ammoniacal  gas 
with  hydrochloric,  carbonic,  and  fluoboric  acid  gases.  100  volumes  of  the 
alkali  were  found  to  combine  with  precisely  100  volumes  of  hydrochloric 
acid  gas,  and  they  could  be  made  to  unite  in  no  other  ratio.  With  both  the 


LAWS  OF  COMBINATION. 


145 


other  acids,  on   the   contrary,  two   distinct   combinations   were   possible. 
These  are 

100  Fluoboric  acid  gas,  with  100  Ammoniacal  gas. 

100  do.  200          do. 

100  Carbonic  acid  gas,  100  do. 

100  do.  200          do. 

Various  other  examples  were  quoted,  both  from  his  own  experiments  and 
from  those  of  others,  all  demonstrating  the  same  fact.  Thus  ammonia  was 
found  by  A.  Berthollet  to  consist  of  100  volumes  of  nitrogen  gas  and  300 
volumes  of  hydrogen ;  sulphuric  acid  contains  100  volumes  of  sulphurous 
acid  and  50  volumes  of  oxygen  ;  and  carbonic  acid  is  formed  by  burning  a 
mixture  of  50  volumes  of  oxygen  and  100  volumes  of  carbonic  oxide. 

From  these  and  other  instances  Gay-Lussac  established  the  fact,  that 
gaseous  substances  unite  in  the  simple  ratio  of  1  to  1,  1  to  2,  1  to  3,  &c. ; 
and  this  original  observation  has  been  confirmed  by  such  a  multiplicity  of 
experiments,  that  it  may  be  regarded  as  one  of  the  best  established  laws  in 
chemistry.  Nor  does  it  apply  to  gases  merely,  but  to  vapours  also.  For 
example,  hydrosulphuric,  sulphurous,  and  hydriodic  acid  gases  are  com- 
posed of 

600  vol.  Hydrogen  gas  and  100  vol.  vapour  of  Sulphur. 
600         Oxygen  100         .         .         Sulphur. 

100         Hydrogen  100         .        .        Iodine. 

Another  remarkable  fact  established  by  Gay-Lussac  in  the  same  essay  is, 
that  the  volumes  of  compound  gases  and  vapours  always  bear  a  very  simple 
ratio  to  the  volumes  of  their  elements.  This  will  appear  from  the  follow- 
ing table,  in  which  all  the  substances  are  supposed  to  be  in  the  gaseous 
state  :— 

Volumes  of  resulting  Compounds, 
yield        200  Ammonia. 
100  Water. 

100  Protoxide  of  nitrogen. 
600  Hydrosulphuric  acid. 
600  Sulphurous  acid. 
200  Hydrochloric  acid. 
200  Hydriodic  acid. 
200  Hydrobrornic  acid. 
200  Hydrocyanic  acid. 
200  Binoxide  of  nitrogen. 


Volumes  of  Elements. 


100  Nitrogen 
50  Oxygen 
50  Oxygen 
100  Sulphur 
100  Sulphur 
100  Chlorine 
100  Iodine 
100  Bromine 
100  Cyanogen 
100  Oxygen 


300  Hydrogen 
100  Hydrogen 
100  Nitrogen 
600  Hydrogen 
600  Oxygen 
100  Hydrogen 
100  Hydrogen 
100  Hydrogen 
100  Hydrogen 
100  Nitrogen 


The  law  of  multiples  (page  137)  is  equally  demonstrable  by  means  of 
combining  volumes  as  by  combining  weights.  The  annexed  tabular  view 
will  justify  this  statement : — 

Volumes  of  Elements.  Resulting  Compounds, 

rogen          -f-      ^50  Oxygen        yield        Protoxide  of  nitrogen. 

Binoxide  of  nitrogen. 
Hyponitrous  acid. 
Nitrous  acid. 
Nitric  acid. 
Water. 

Binoxide  of  hydrogen. 
Carbonic  oxide. 
Carbonic  acid. 

It  thus  appears  that  the  laws  of  combination  may  equally  well  be  deduced 
from  the  volumes  as  from  the  weights  of  the  combining  substances,  and  that 
the  composition  of  gaseous  bodies  may  be  expressed  as  well  by  measure 
as  weight.  In  the  subjoined  table  is  a  comparative  view  of  equivalent 

lo 


1  00  Nitrogen    -}- 
100   do.      + 
100   do.      + 
100   do.      -f- 
100   do.      + 
100  Hydrogen   4- 
100   do.      + 
100  Carbon  vapour  -j- 
100   do.      -f- 

50  Oxygen 
100   do. 
150   do. 
200   do. 
250   do. 
50   do. 
100   do. 
50   do. 
100   do. 

146 


LAWS  OF  COMBINATION. 


weights  and  volumes,  to  which  are  added  the  respective  specific  gravities  in 
relation  both  to  air  and  hydrogen  :  the  facts  respecting  the  vapours  are 
drawn  from  an  important  essay  lately  published  by  Mitscherlich.  (An.  de 
Ch.  et  de  Ph.  Iv.  5.) 


GASES   AND   VAPOURS. 

Specific  Gravities. 

Chemical  Equivalents. 

Air  as  1. 

Hydrogenasl. 

By  Vol. 

By  Weight. 

i 

Hydrogen 

0.0689 

1.00 

100 

1 

Nitrogen       .         .         . 

0.9727 

14.15 

100 

14.15 

Chlorine    .... 

2.4700 

3542 

100 

35.42 

Carbon  (hypothetical)    . 

0.4215 

6.12 

100 

6.12 

T  j.        x  •*  *• 
Iodine 

8.7020 

126.30 

100 

126.3 

Bromine 

5.4017 

78.40 

100 

78.4 

Water       .... 

0.6201 

9.00 

100 

9 

Alcohol 

1.6009 

23.24 

100 

23.24 

Sulphuric  ether          .  *     . 

2.5817 

37.48 

100 

37.48 

Light  carburetted  hydrogen 
Olefiant  gas 

0.5593 

0.9808 

8.12 
14.24 

100 
100 

8.12 
14.24 

Carbonic  oxide 

0.9727 

14.12 

100 

14.12 

Carbonic  acid    . 

1.5239 

22.12 

100 

22.12 

Protoxide  of  nitrogen    . 

1.5239 

22.15 

100 

22.15 

Sulphurous  acid 

2.2117 

32.10 

100 

32.1 

Sulphuric  acid  (anhydrous) 

2.7629 

40.10 

100 

40.1 

Cyanogen 
Hydrosulphuric  acid 

1.8157 
1.1782 

26.39 
17.10 

100 
100 

26.39 
17.1 

Binoxide  of  nitrogen 

1.0375 

15.75 

200 

30.15 

Mercury 

6.9589 

101.00 

200 

202 

Ammonia 

0.5897 

8.75 

200 

17.15 

Hydrochloric  acid 
Hydriodic  acid 

1.2694 
4.3854 

18.21 
63.65 

200 
200 

36.42 
127.3 

Hydrobromic  acid 

2.7353 

39.70 

200 

79.4 

Hydrocyanic  acid 

0.9423 

13.95 

200 

27.39 

Arseriiu  retted  hydrogen 

2.7008 

39.20 

200 

78.4 

Sesquichloride  of  arsenic  . 
Sesquiodlde  of  arsenic  . 

6.3025 
15.6505 

90.83 
227.15 

200 
200 

181.66 
454.3 

Protochloride  of  mercury  . 

8.1939 

118.71 

200 

237.42 

Bichloride  of  mercury  . 

9.4289 

136.42 

200 

272.84 

Bromide  of  mercury 

9.6597 

140.20 

200 

280.4 

Bibromide  of  mercury  . 

12.3606 

179.40 

200 

358.8 

Biniodide  of  mercury 

15.6609 

227.30 

200 

454.6 

Oxygen         ... 

1.1024 

16.00 

50 

8 

Arsenious  acid 

13.6972 

198.80 

50 

99.4 

Phosphorus  . 

4.3269 

62.80 

25 

15.7 

Arsenic     .... 

10.3901 

150.80 

25 

37.7 

Sulphur        » 

6.6558 

96.60 

16.66 

16.1 

Bisulphuret  of  mercury     . 

5.3788 

78.06 

300 

234.2 

The  observations  which  more  immediately  flow  from  the  facts  in  the  pre- 
ceding table  are  these : — 

1.  The  combining  volumes  of  substances,  both  elementary  and  compound, 
are  either  equal,  or  have  the  simple  ratio  of  1  to  2, 1  to  3,  &c.     The  same 
simplicity  rarely  exists  among  the  equivalent  weights. 

2.  On  comparing  together  the  third  and  fifth  columns,  the  corresponding 


LAWS  OF  COMBINATION.  147 

numbers  for  the  first  18  substances  will  be  found  identical.  As  those 
substances  have  the  same  uniting  volume  as  hydrogen,  which  is  the  assumed 
unit  of  comparison,  and  as  the  specific  gravities  are  merely  the  weights  of 
equal  volumes,  the  numbers  of  the  third  column,  necessarily  coincide  with 
those  of  the  fifth. 

3.  The  identity  in  the  equivalent  volumes  of  the  elementary  gases,  hydro- 
gen, nitrogen,  and  chlorine,  led  to  the  notion  that  the  equivalent  volumes  of 
most  other  elements,  such  as  carbon,  sulphur,  and  phosphorus,  might  also  be 
identical.     Assuming  that  identity,  the  specific  gravity  which  those  elements 
ought  to  have  when  gaseous,  may  easily  be  calculated.    Thus,  taking  1,  6.12, 
and  16.1  as  the  equivalents  of  hydrogen,  carbon,  and  sulphur,  then  will  their 
specific  gravities  in  the  gaseous  state,  combining  volumes  being  supposed 
equal,  be  in  the  ratio  of  1,  6.12,  and  16.1.     This  method,  by  which  the  hypo- 
thetical specific  gravity  of  carbon,  as  stated  in  the  table,  was  obtained,  was 
first  indicate^  by  Dr.  Prout.     (An.  of  PhiL  vi.  321.)     But  though  such  hypo- 
thetical  numbers  may  sometimes  be  used  for  the  convenience  of  expressing 
the  relation  of  uniting  substances   by  measure,  recent  facts  show  how  dan- 
gerous it  would  be  to  confide  in  them  ;  for   by  the  table  it  appears  that  the 
equivalent  volume  of  sulphur  vapour  is  one-sixth  of  that  of  hydrogen,  which 
renders  the  specific  gravity  of  the  vapour  of  sulphur  six  times  greater  than 
the   hypothetical  number.      Similar  deviation  is  observable  in  phosphorus, 
arsenic,  and  mercury.     In  these  cases,  the  real  specific  gravity  of  a  vapour  is 
as  much  greater  than  the  hypothetical,  as  its  equivalent  volume  is  less  than 
that  of  hydrogen. 

4.  The  identity  in  the  equivalent  volumes  of  hydrogen,  nitrogen,  and  chlo- 
rine, suggested  the  idea  that  the  atoms  or  indivisible  molecules  of  all  the  ele- 
ments are  of  the  same  magnitude ;  and  this  coupled  with  the  supposition 
that  the  self-repulsive  energy  of  these  stoms  is  equal,  led  to  the  opinion  that 
equal  volumes  of  the  elements  in   the  gaseous  state  must  contain  an  equal 
number  of  atoms.     This  hypothesis,  recommended  by  its  simplicity,  and  sup- 
ported by  the  fact  that  the  volumes  of  gaseous  substances  vary  according  to 
the  same  law  by  varying  temperature  and  pressure,  was  accordingly  em- 
ployed as  a  mode  of  determining  the  relative  weights  of  atoms.    As  water 
consists  of  50  measures  of  oxygen  and  100  of  hydrogen  gas,  it  was  inferred 
to  be  a  compound  of  one  atom  of  oxygen  and  two  atoms  of  hydrogen ;  and 
consequently,  taking  8  as  the  weight  of  an  atom  of  oxygen,  the  weight  of 
one  atom  of  hydrogen  is  £,  instead  of  1  as  in  the  table ;  or  taking  hydrogen 
as  I,  the  atom  of  oxygen  is  16.     On  the  same  principle  may  the  numbers, 
which  in  the  table  represent  the  equivalent  weights  of  chlorine,  bromine, 
iodine,  and  nitrogen,  which  have  the  same  equivalent  volumes  of  hydrogen, 
be  considered  as  the  weights  of  two  equivalents.     The  equivalents  adopted 
by  Davy  in  his  Elements  of  Chemical  Philosophy,  as  well  as  those  of  Ber- 
zelius,  which  are  now  in  general  use  on  the  Continent,  were  framed  in  ac- 
cordance with  these  views.     This  the  British  chemist  requires  to  bear  in 
mind ;  since  the  same  numbers  which  Berzelius  uses  for  two  equivalents  of 
hydrogen,  nitrogen,  chlorine,  bromine,  and  iodine,  he  considers  as  one  equiva- 
lent.    But  the  opinion  of  Davy  and  Berzelius  must  now  either  be  abandoned, 
or   maintained   on    other  principles;  since   the   late  researches   of  Durnas, 
Jind  Mitscherlich  have  shown  experimentally  that  equal  volumes  of  the  ele- 
mentary gases  and  vapours  do  not  contain  the  same  number  of  atoms. 

5.  The  facts  contained  in  the  last  and    preceding  tables  supply  materials 
for  calculating  the  sp.  gravity  of  compound  gases,  by  which  means  the  ac- 
curacy of  other   conclusions  respecting  their  composition  may  be  verified. 
Thus  analysis  proves  that  amnroniacal  gas  is  composed  of  100  volumes  of 
nitrogen,  and  300  of  hydrogen  gases,  condensed  into  the  space  of  200  vol- 
umes ;  if  so,  its  sp.  gravity  will  be 

0.9727+3X0.0689     1.1794 

z -=  --r— =  0.5897. 


148  LAWS  OF  COMBINATION. 

The  near  agreement  of  this  calculated  number  with  that  found  by  weighing 
the  gas  itself,  proves  that  ammonia  has  really  the  constitution  above  assigned 
to  it,  and  gives  great  probability  that  the  sp.  gravity  of  nitrogen  and  hydro- 
gen gases  is  nearly  correct. 

Again,  hydrochloric  acid  gas  consists  of  100  volumes  of  hydrogen  and  100 
of  chlorine  gases,  united  without  any  change  of  bulk.  Hence  its  sp.  gravity 
ought  to  be 

2.47+0.0689 

5 =1.2694 

m 

Hydrocyanic  acid  vapour  is  formed  of  100  volumes  of  hydrogen  and  100 
of  cyanogen,  gases  united  without  change  of  volume ;  and,  therefore,  its  sp. 
gravity  should  be 

1.81574-0.0689 

g =0.9423. 

Considering  defiant  gas  as  a  compound  of  200  volumes  of  hydrogen  gas 
and  200  of  the  vapour  of  carbon,  condensed  into  100,  its  sp.  gravity  will  be 
2  x  0.0689  +  2  X  0.4215=  0.1378  +  0.8430  =0.9808. 

Aqueous  vapour  is  composed  of  100  volumes  of  hydrogen  and  50  of  oxy- 
gen gases,  condensed  into  the  space  of  100  volumes ;  and,  therefore,  its  sp. 
gravity  ought  to  be  0.0689  +  0.5512  (half  the  sp.  gr.  of  oxygen)  =0.6201. 

Protoxide  of  nitrogen  is  formed  of  100  volumes  of  nitrogen  and  50  of  oxy- 
gen gases,  condensed  into  100  volumes,  and  hence  its  sp.  gravity  should  be 
0.9727+0.5512=1.5239. 

Assuming  carbonic  oxide  to  be  a  compound  of  100  volumes  of  carbon  va- 
pour and  50  of  oxygen  gas,  contracted  in  uniting  into  100  volumes,  its  sp. 
gravity  should  be  0.4215  +  0.5512=0.9727. 

As  the  different  sp.  gravities  thus  calculated  are  very  nearly  those  found 
by  direct  experiment,  there  is  a  strong  presumption  that  the  elements  of  the 
calculations  are  correct. 

The  principle  of  these  calculations  is  sufficiently  obvious.  The  sp.  gra- 
vities represent  the  weights  of  equal  volumes  of  the  gases :  taking  100  as 
the  standard  volume  of  which  the  sp.  gravity  of  each  gas  denotes  the  weight, 
then  50  volumes  of  a  gas  may  be  indicated  by  half,  25  volumes  by  a  fourth, 
and  16.66  volumes  by  a  sixth  of  its  specific  gravity.  Thus  hydrosulphuric 
acid  is  a  compound  of  100  volumes  of  hydrogen  gas,  and  16.66  (^-^-)  of  the 
vapour  of  sulphur,  condensed  into  100  volumes,  and,  therefore,  its  sp.  gravity  is 

6.6558 
0.0689  +  —£—=0.0689  + 1.1093=  1.1782. 

Sulphurous  acid  consists  of  100  volumes  of  oxygen  gas  and  16.66  of  the  va- 
pour of  sulphur,  condensed  into  100  volumes ;  and  hence  its  sp.  gravity  is 

6.6558 
1.1024+— 6—  =1.1024  +  1.1093=2.2117. 

In  these  two  gases  the  volume  is  the  same  as  the  hydrogen  or  oxygen  which 
they  contain,  and,  therefore,  their  sp.  gravities  are  the  sum  of  the  sp.  gravi- 
ties of  their  elements.  The  same  applies  to  water,  protoxide  of  nitrogen, 
and  carbonic  oxide.  In  olefiant  gas  400  volumes  are  condensed  into  100,  and, 
therefore,  its  sp.  gravity  is  the  sum  of  the  sp.  gravities  of  its  elements.  Hy- 
drochloric acid  gas  occupies  the  same  space  as  its  elements,  and,  therefore, 
its  sp.  gravity  is  found  by  taking  the  mean  of  their  sp.  gravities.  The  same 
remark  applies  to  hydrocyanic  acid.  In  ammonia  400  volumes  are  con- 
densed into  200,  and,  therefore,  the  sum  of  the  sp.  gravities  is  halved.* 

*The  statements  in  this  paragraph  are  rather  loosely  expressed.  We  may, 
as  Dr,  Turner  remarks  in  a  preceding  paragraph,  assume  the  specific  gravity 


LAWS  OF  COMBINATION.  149 

As  vapours  are  easily  condensed  by  cold,  and  in  many  cases  exist  as  such 
only  at  high  temperatures,  their  sp.  gravities  may  often  be  obtained  by  cal- 
culation more  accurately  than  by  experiment.  Thus  it  is  easier  accurately 
to  ascertain  the  sp.  gravity  of  hydrogen  and  hydrosulphuric  acid  gases  than 
of  the  vapour  of  sulphur;  and,  therefore,  as  soon  as  experiment  has  shown 
that  the  sp.  gravity  of  that  vapour  is  somewhere  about  6.6558,  then  the  pre- 
cise number  may  be  calculated.  For  as  100  volumes  of  hydrosulphuric  acid 
gas  contain  100  of  hydrogen  gas,  the  sp.  gravity  of  the  latter  deducted  from 
that  of  the  former  (1*1782—0.0689,)  gives  1.1093  as  the  weight  of  combined 
sulphur.  If  the  equivalent  volume  of  sulphur  were  JOO,  then  must  1.1093 
be  its  sp,  gravity  ;  but  as  the  number  found  experimentally  is  nearly  six 
times  1.1093,  the  inference  is  that  the  real  sp.  gravity  is  6X1.1093=6.6558, 
and  that  its  equivalent  volume  is  only  one-sixth  of  100,  or  16.66.  The  only 
assumption  here  is,  that  if  the  equivalent  volume  of  the  vapour  is  not  100,  it 
must  be  some  multiple  or  submultiple  of  it  by  a  whole  number,  consistently 

of  the  different  gases  to  be  the  weight  of  some  standard  volume  of  each  of 
them,  as  for  example  100  volumes;  and,  on  this  assumption,  it  will  follow 
that  on  ascertaining  the  weight  of  100  volumes  of  any  gas,  we  shall  have  its 
specific  gravity.  The  general  formula  applicable  to  these  calculations,  there- 
fore, is  to  deduce  from  the  known  specific  gravities  of  certain  gases,  from  the 
proportion  in  which  they  unite  in  volume,  and  from  the  resulting  volume, 
the  weight  of  100  volumes  of  the  compound  gas  which  may  be  formed  ;  for 
if  the  known  sp.  gr.  in  all  cases  be  assumed  to  represent  the  weight  of  100 
volumes,  reciprocally  the  weight  of  100  volumes,  when  ascertained,  will  re- 
present the  sp.  gr.  In  ascertaining  then  the  weight  of  100  volumes  of  a  com- 
pound gas,  the  first  step  is  to  add  together  the  weights  of  the  known  volumes 
of  its  constituents  ;  these  weights  being  deduced  from  the  assumption  that  the 
weight  of  every  100  volumes  of  each  constituent  is  represented  by  its  specific 
gravity.  The  sum  thus  obtained  will  be  the  weight  of  the  resulting  volume, 
and,  if  this  happen  to  be  100  volumes,  the  answer  is  furnished  at  once.  But 
if  the  resulting  volume  should  not  be  100  volumes,  then,  by  the  rule  of  pro- 
portion, the  weight  of  100  volumes  of  the  compound  gas  is  to  be  ascertained 
thus  :  if  the  known  number  of  volumes  in  the  resulting  volume  weigh  the  sum 
obtained  as  above  mentioned,  what  will  100  volumes  weigh?  The  weight  of 
100  volumes  thus  ascertained  necessarily  represents  the  specific  gravity.  The 
simplest  case  under  the  rule  is  when  100  volumes,  respectively,  of  the  con- 
stituents  of  a  compound  gas  are  condensed  into  100  volumes;  for  here  thesp. 
gravities  of  the  constituent  gases  represent  at  once  the  entire  volume  of  each 
constituent  entering  into  combination;  and  their  sum  gives  the  sp.  gr.  of  the 
compound;  because  it  represents  the  weight  of  100  volumes.  An  instance  of 
this  simplest  case  is  afforded  by  carbonic  acid,  in  which  100  volumes  of  car- 
bon  vapour  and  100  volumes  of  oxygen  are  condensed  into  100  volumes 
Here  it  is  only  necessary  to  add  together  0.4215  (sp.  gr.  of  carb.  vap.)  and 
1.1024  (sp.  gr.  of  oxygen,)  and  the  sum,  1.5239,  is  the  sp.gr.  of  carbonic  acid. 
It  is  only  in  this  simplest  case  that  the  sp.  gr.  of  a  compound  gas  is  the  sum 
of  the  sp.  gravities  of  its  constituents.  Dr.  Turner  is  inaccurate,  therefore, 
when  he  states  that  hydrosulphuric  and  sulphurous  acid  gases  furnish  cases 
in  which  their  sp.  gravities  are  the  sum  of  the  sp.  gravities  of  their  elements : 
for  though,  in  the  instances  of  these  two  gases,  the  sp.  gravities  of  the  hydro- 
gen and  oxygen  may  be  taken,  since  these  elements  are  present  in  the  amount 
of  100  volumes ;  yet  the  sp.  gr.  of  the  sulphur  vapour  cannot  be  taken,  as  it 
is  not  the  weight  of  100  volumes  of  this  vapour  which  is  required,  but  the 
weight  of  one-sixth  of  100  volumes.  Dr.  Turner's  inaccuracy  consists  in 
this,  that  he  calls  the  weight  of  the  given  number  of  volumes  of  each  consti- 
tuent gas,  its  sp.  gr. ;  whereas  such  weight  is  to  be  assumed  to  be  the  sp.  gr., 
only  in  case  it  is  the  weight  of  100  volumes.  Thus,  in  the  case  of  defiant 
gas,  cited  by  Dr.  Turner/its  sp.  gr.  is  not  the  sum  of  the  sp.  gravities  of  its 
elements,  but  the  sum  of  double  the  sp.  gr.  of  its  elements. — Ed, 

13* 


150 


LAWS  OF  COMBINATION. 


with  the  theory  of  volumes.  In  the  construction  of  the  preceding  table  I 
have  given  the  sp.  gravities  of  vapours  calculated  on  these  principles  rather 
than  the  precise  numbers  given  by  experiment. 

CHEMICAL  SYMBOLS. 

The  impracticability  in  many  cases  of  contriving  convenient  names  ex- 
pressive of  the  constitution  of  chemical  compounds,  especially  of  minerals, 
suggested  the  employment  of  symbols  as  an  abbreviated  mode  of  denoting 
the  composition  of  bodies.  It  was  thought  that  the  names  of  elementary 
substances,  instead  of  being  written  at  full  length,  might  often  be  more  con- 
veniently  indicated  by  the  first  letter  of  their  names ;  and  that  the  combina- 
tion of  elements  with  each  other  might  be  expressed  by  placing  together,  in 
some  way  to  be  agreed  on,  the  letters  which  represent  them.  The  advantage 
of  such  a  symbolic  language  was  felt  so  strongly  by  Berzelius,  that  he  some 
years  ago  contrived  a  set  of  symbols,  which  he  has  since  used  extensively  in 
his  writings ;  and  other  eminent  chemists  as  well  as  mineralogists,  believing 
symbols  to  be  useful,  adopted  those  which  Berzelius  had  proposed.  The  con- 
sequence is,  that  symbolic  expressions,  called  chemical  formula,  are  now  so 
much  resorted  to,  and  are  so  identified  with  the  language  of  chemistry,  that 
essays  of  great  value  are  in  a  measure  as  sealed  books  to  those  who  cannot 
read  symbols.  It  is,  therefore,  important  that  the  chemical  student,  what- 
ever he  may  think  of  the  value  of  symbols,  should  not  be  unacquainted  with 
them.  Fortunately,  the  labour  of  a  few  minutes  will  enable  him  to  under- 
stand the  subject.  The  following  table  includes  the  symbols  of  all  the  ele- 
mentary substances  according  to  Berzelius. 


TABLE  OF  SYMBOLS. 


Elements. 

Symb 

Elements. 

Symb. 

Elements. 

Symb. 

Aluminium     .     . 

Al 

Gold  (Aurum) 

Au 

Potassium  (Kaliurn) 

K 

Antimony  (Stibium) 

Sb 

Hydrogen  .     . 

H 

Rhodium    .     .     . 

R 

Arsenic       .     .     . 

As 

Iodine   .     .     . 

I 

Selenium    .     .     . 

Se 

Barium  .... 

Ba 

Iridium      .     . 

Ir 

Silicium     .     .     . 

Si 

Bismuth     .     .     . 

Bi 

Iron  (Ferrum) 

Fe 

Silver  (  Argentum) 

Ag 

Boron     ...     . 

B 

Lead  (Plumbum) 

Pb 

Sodium  (Natrium) 

Na 

Bromine     .     .     . 

Br 

Lithium     .     . 

L 

Strontium  .     .     . 

Sr 

Cadmium    .     .     . 

Cd 

Magnesium    . 

Mg 

Sulphur      .     .     . 

S 

Calcium      .     .     . 

Ca 

Manganese     . 

Mn 

Tellurium  .    .    . 

Te 

Carbon  .... 

C 

Mercury  (Hy- 

Thorium   .     .     . 

Th 

Cerium  .... 

Ce 

drargyrum) 

Hg 

Tin  (Stannum)   . 

Sn 

Chlorine     .    .     . 

Cl 

Molybdenum  . 

Mo 

Titanium   .     .     . 

Ti 

Chromium  .     .     . 

Cr 

Nickel  .     .     . 

Ni 

Tungsten  (Wol- 

Cobalt   .... 

Co 

Nitrogen    .     . 

N 

fram)      .     .     . 

W 

Columbium  (Tan- 

Osmium    .     . 

Os 

Uranium    .     .     . 

U 

talum)     .     .     . 

Ta 

Oxygen      .     . 

O 

Vanadium  ... 

V 

Copper  (Cuprum) 

Cu 

Palladium  .     . 

Pd 

Yttrium     . 

Y 

Fluorine      .     .     . 

F 

Phosphorus    . 

P 

Zinc  ....  ,"*••  - 

Zn 

Glucinium  .     .    . 

G 

Platinum   .     . 

Pt 

Zirconium      .     . 

Zr 

For  the  sake  of  uniformity,  and  to  prevent  confusion,  it  is  much  to  be 
wished  that  these  symbols,  being  now  generally  known,  should  be  rigorously 
adhered  to.  Berzelius  has  properly  selected  them  from  Latin  names,  as 
being  known  to  all  civilized  nations ;  and  when  the  names  of  two  or  more 
elements  beg-in  with  the  same  letter,  the  distinction  is  made  by  means  of  an 
additional  letter. 


LAWS  OF  COMBINATION.  151 

The  foregoing  symbols  are  intended  to  represent  the  chemical  equivalents 
of  the  elements.  Thus,  the  letters  H,  I,  and  Ba,  stand  for  one  equivalent  of 
hydrogen,  iodine,  and  barium  ;  and  2H,  3H,  and  4H,  for  2,  3,  and  4  equiva- 
lents of  hydrogen.  Two  equivalents  of  an  element  are  often  denoted  by 
placing  a  dash  through  or  under  its  symbol :  for  instance,  H  or  H  means  2H, 
and  P  or  P  signifies  2P.  Certain  compounds  are  often,  for  the  sake  of 
brevity,  denoted  by  single  symbols  in  the  same  manner  as  the  elements; 
thus  an  equivalent  of  water,  ammonia,  and  cyanogen,  is  sometimes  expressed 
by  Aq,  Am,  and  Cy;  but  in  general  the  formulae  for  compound  bodies  are 
so  contrived  as  to  indicate  the  elements  they  contain,  and  the  mode  in  which 
they  are  united.  This  may  be  done  in  several  ways ;  but  that  which  first 
suggests  itself,  is  to  connect  together  the  symbols  by  the  same  signs  as  are 
used  in  algebra.  Thus  the  ^formulas  K+O,  Ca+O,  Ba+O,  Mn-j-O, 
Fe-j-O,  2Fe+30,  3H+N,  2H+2C,  C-f-2O,  N-f5O,  8+30),  and  H+C1, 
denote  single  equivalents  of  potassa,  lime,  baryta,  protoxide  of  manganese, 
protoxide  of  iron,  sesquioxide  of  iron,  ammonia,  olefiant  gas,  carbonic  acid, 
nitric  acid,  sulphuric  acid,  and  hydrochloric  acid.  The  formula  K-J-N-J-6O 
indicates  the  elements  which  are  contained  in  an  equivalent  of  nitrate  of 
potassa :  in  order  to  express  further  that  the  potassium  is  combined  with 
only  one  equivalent  of  oxygen,  the  remaining  oxygen  with  the  nitrogen,  and 
the  potassa  with  nitric  acid,  the  symbols  are  placed  thus, — (K-r-O)-}- 
(j\j_j_5O),  the  brackets  containing  the  symbols  of  those  elements  which  are 
supposed  to  be  united.  A  number  placed  on  the  outside  of  a  bracket  mul- 
tiplies the  compound  within  it:  thus  (K-|-O)+(S-i-3O)  is  sulphate  of 
potassa,  and  (K+O)-j-2(S-|-3O)  is  the  bisulphate.  All  the  elements  con- 
tained in  a  compound  are  thus  visibly  represented,  and  the  chemist  is  able 
readily  to  trace  all  possible  modes  of  combination,  and  to  select  that  which 
is  most  in  harmony  with  the  facts  and  principles  of  his  science.  He  may, 
and  often  does,  thereby  detect  relations  which  might  otherwise  have  escaped 
notice. 

Another  advantage  attributable  to  such  formulae  is,  that  they  facilitate 
the  comprehension  of  chemical  changes.  If  hydrosulphuric  acid  acts  upon 
the  protoxide  of  lead,  it  is  easy  to  say  that  the  sulphur  combines  with  the 
lead,  and  the  hydrogen  with  the  oxygen ;  but  the  exact  adaptation  of  the 
quantities  for  mutual  interchange  appears  to  me  more  clearly  shown  by 
symbols  than  by  a  description  or  a  diagram,  both  of  which  are  apt  to  pro- 
duce  confusion  where  the  change  to  be  explained  is  complex.  In  the  simple 
instance  alluded  to,  H-j-S  reacts  on  Pb-j-O,  and  the  products  are  Pb-|-S 
and  H-f-O.  When  hydrosulphuric  acid  acts  on  bicyanuret  of  mercury,  the 
result  is  bisulphuret  of  mercury  and  hydrocyanic  acid  :  the  substances 
which  interchange  elements  are  2(H-j-S)  and  Hg-[-2Cy ;  and  the  products 
are  Hg-f-2S,  and  2(H-r-Cy).  In  more  complicated  changes  the  advantage 
of  chemical  formulae  is  still  more  manifest,  examples  of  which  kind  will  be 
found  in  the  section  on  cyanogen,  and  in  other  parts  of  this  volume. 

Useful  as  the  algebraic  chemical  formula?  are  for  the  purpose  of  studying 
chemical  changes,  they  are  sometimes  found  inconveniently  long  where  the 
object  is  merely  to  express  the  composition  of  bodies,  and  accordingly 
Berzelius  has  introduced  several  abbreviations.  For  instance,  he  indicates 


degrees  of  oxidation  by  dots  placed  over  the  symbol,  writing  K,  C,  N, 
instead  of  K+O,  C-f-2O,  N-f-SO,  for  potassa,  carbonic  acid,  and  nitric  acid. 
In  like  manner  he  denotes  compounds  of  sulphur  by  commas,  writing 

K,  Hg,  H  instead  of  K+S,  Hg+2S,  H-fS,  for  sulphuret  of  potassium, 
bisulphuret  of  mercury,  and  hydrosulphuric  acid.  When  the  ratio  is  that 
of  2  to  3  he  employs  the  symbol  for  two  equivalents  above  stated ;  thus, 

Fe,  P,  As  is  used  instead  of  2Fe-f-3O,  2P-I-5O,  2As-f-5O,  for  an  equivalent 


152  LAWS  OF  COMBINATION. 

of  sesquioxide  of  iron,  phosphoric  acid,  and  arsenic  acid  ;  and  similarly  we 

»»»          »  •>   1 

have  As,  As,  instead  of  2As-|-3S,  2As+5S,  for  the  sesquisulphuret  and  per- 
sulphuret  of  arsenic.  These  last  formulae  are  sometimes  used  to  indicate 
two  equivalents  instead  of  one;  but  as,  agreeably  to  the  atomic  theory,  the 
smallest  possible  molecule  of  sesquioxide  of  iron  consists  of  two  atoms  of  iron 
and  three  of  oxygen,  the  formula  2Fe-j-3O  ought  to  stand  for  one  equivalent 
only. 

Berzelius  often  dispenses  with  the  sign  -}-,  and  writes  combined  elements 
side  by  side,  the  sign  of  addition  being  understood  instead  of  expressed. 

Thus  he  uses  KS,  CaC,  BaN,  KS-f-NiS,  instead  of  K-fS,  Ca+C,  Ba+N, 

(K-f-S)-r-(Ni-f-S),  for  sulphate  of  potassa,  carbonate  of  lime,  nitrate  of 
baryta,  and  the  double  sulphate  of  potassa  and  oxide  of  nickel.  Two  or 
more  equivalents  of  one  constituent  of  a  compound  are  denoted  by  numbers 
placed  in  the  same  position  as  the  indices  of  powers  in  algebra  :  thus  NH3, 

NO,  Fe_s  Hs,is  the  abbreviation  of  N-J-3H,  N-f-2C,  2Fe-|-3H,  for  ammonia, 
cyanogen,  and  sesquihydrate  of  iron,  a  compound  of  two  equivalents  of 
sesquioxide  of  iron  and  three  of  water.  A  number  used  before  symbols,  like 
co-efficients  in  algebra,  multiplies  all  the  following  symbols  not  separated 

from  it  by  a  +  sign.  Thus  in  SCaSis+K  Si<4-16  Aq  (which  is  the 
formula  for  the  mineral  called  apophyllite),  the  8  denotes  eight  equivalents  of 

Ca  Si3,  or  tersilicate  of  lime,  which  arc  united  with  one  equivalent  of  sexsili- 
cate  of  potassa,  and  sixteen  of  water. 

Berzelius  also  expresses  the  vegetable  and  animal  acids  by  the  first  letter 
of  their  name  with  a  dash  over  it.  Thus  T,  A,  C,  B,  G,  F,  are  the  sym- 
bols for  tartaric,  acetic,  citric,  benzoic,  gallic,  and  formic  acids. 

ISOMERIC  BODIES. 

It  was  formerly  thought  that  the  same  elements  united  in  the  same  ratio 
must  always  give  rise  to  the  same  compound  ;  but  within  these  few  years 
several  examples  have  been  discovered  of  two  or  even  more  substances  con- 
taining the  same  elements  in  the  same  ratio,  and  yet  exhibiting  chemical 
properties  distinct  from  each  other.  For  such  compounds  Berzelius  has 
suggested  the  general  appellation  of  isomeric,  from  uros  equal  and  pe^oc  part, 
expressive  of  equality  in  the  ingredients.  Interesting  instances  of  this  kind 
are  the  two  cyanic  acids,  which  consist  of  cyanogen  and  oxygen  in  the 
same  ratio,  and  have  the  same  equivalent,  yet  differ  widely  in  their  chemical 
properties;  and  a  similar  example  is  afforded  by  the  tartaric  and  para- 
tartaric  acids.  Berzelius  proposed  to  prefix  para  in  this  instance,  from 
7rtt£*  near  to,  as  indicative  of  the  close  alliance  between  the  two  compounds, 
a  principle  of  nomenclature  which  will  probably  be  found  applicable  on  other 
occasions. 

Unexpected  as  was  the  discovery  of  isomerism,  it  is  quite  consistent  with 
our  theories  of  chemical  union;  insomuch  as  the  same  elements  may  be 
grouped  or  combined  in  different  ways,  and  thereby  give  rise  to  compounds 
essentially  distinct.  Thus  the  elements  of  sulphate  of  potassa  may  perhaps 
be  united  indiscriminately  with  each  other,  as  expressed  by  the  formula 
KSO;  or  they  may  form  KO-r-SO3;  or  KS-f-CH;  or  KOH-SO;  and 
other  combinations  might  be  made.  The  second  of  these  is  doubtless  the 
real  one;  but  no  one  can  say  that  the  others  are  impracticable.  Again,  the 
elements  of  peroxide  of  tin,  Sn  and  2O,  may  either  form  SnO',  or  SnO-}-O; 
and  those  of  the  sesquioxide  of  iron,  2Fe  and  3O,  may  either  be  Fe2O3,  or 
FeO-j-FeO3,  not  to  mention  other  possible  combinations.  The  elements  of 


OXYGEN.  153 

alcohol  are  2C,  3H,  and  O,  which  may  be  united  indiscriminately  aa 
HSC2Q,  or  H3C3-f-O,  or  as  H2C2+HO,  besides  others:  it  is  commonly 
considered  a  compound  of  olefiant  gas  and  water,  as  indicated  by  the  last 
formula. 

Some  bodies  consist  of  the  same  elements  in  the  same  ratio,  and  yet  dif- 
fer in  their  equivalents.  A  marked  example  is  supplied  by  olefiant  gas  and 
etherine;  the  former  of  which  contains  200  volumes  of  carbon  vapour  and 
200  of  hydrogen  gas  condensed  into  100  volumes,  and  the  latter,  400  vo- 
lumes of  carbon  vapour  and  400  of  hydrogen  gas,  united  so  as  to  yield  100 
volumes  of  etherine.  The  equivalent  of  olefiant  gas  is  14.24,  and  that  of 
etherine  28.48,  or  exactly  double.  A  similar  case  will  be  found  in  the  de- 
scription of  cyanuric  acid.  The  nature  of  these  compounds  is  at  once  de- 
tected by  their  equivalents  being  unlike,  and  by  the  volume  which  they 
occupy  as  gases,  compared  with  the  volumes  of  the  elements  of  which  they 
consist.  Isomeric  bodies  of  this  kind  are  obviously  much  less  intimately 
allied  than  those  above  described. 


SECTION  III. 

OXYGEN. 

OXYGEN  gas  was  discovered  by  Priestley  in  1774,  and  by  Scheele  a  year  or 
two  after,  without  previous  knowledge  of  Priestley's  discovery.  Several  ap- 
pellations have  been  given  to  it.  Priestley  named  it  dephlogisticated  air ; 
it  was  called  empyreal  air  by  Scheele,  and  vital  air  by  Condorcet.  The 
name  it  now  bears,  derived  from  the  Greek  words  of y?  acid  and  yevvtiv  to 
generate,  was  proposed  by  Lavoisier,  who  considered  it  the  sole  cause  of 
acidity. 

Oxygen  gas  may  be  obtained  from  several  sources.  The  peroxides  of 
manganese,  lead,  and  mercury,  nitre,  and  chlorate  of  potassa,  yield  it  in 
large  quantities  when  they  are  exposed  to  a  red  heat.  The  substances  com- 
monly employed  for  the  purpose  are  peroxide  of  manganese  and  chlorate  of 
potassa.  It  may  be  procured  from  the  former  in  two  ways ;  either  by  heat- 
ing it  to  redness  in  a  gun-barrel,  or  in  a  retort  of  iron  or  earthenware ;  or 
by  putting  it  in  fine  powder  into  a  flask  with  about  an  equal  weight  of  con- 
centrated sulphuric  acid,  and  heating  the  mixture  by  means  of  a  lamp.  To 
understand  the  theory  of  these  processes,  it  is  necessary  to  bear  in  mind  the 
composition  of  the  three  following  oxides  of  manganese  : — 

Manganese.  Oxygen. 

Protoxide        .        27.7  or  1  equiv.  -+-    8  .        =35.7 

Sesquioxide     .        27.7         .            -f-  12  =39.7 

Peroxide         .        27.7        .           +  16  =43.7 

On  applying  a  red  heat  to  the  last,  it  parts  with  half  an  equivalent  of 
oxygen,  and  is  converted  into  the  sesquioxide.  Every  43.7  grains  of  the  per- 
oxide will,  therefore,  lose,  if  quite  pure,  4  grains  of  oxygen,  or  nearly  12 
cubic  inches  ;  and  one  ounce  will  yield  about  128  cubic  inches  of  gas.  The 
action  of  sulphuric  acid  is  different.  The  peroxide  loses  a  whole  equivalent 
of  oxygen,  and  is  converted  into  the  protoxide,  which  unites  with  the  acid, 
forming  a  sulphate  of  the  protoxide  of  manganese.  Every  43.7  grains  of 
peroxide  must  consequently  yield  8  grains  of  oxygen  and  35.7  of  protoxide, 
which  by  uniting  with  one  equivalent  (40.1)  of  the  acid,  forms  75.8  of  the 
sulphate.  The  first  of  these  processes  is  the  most  convenient  in  practice. 

The  gas  obtained  from  peroxide  of  manganese,  though  hardly  ever  quite 
pure,  owing  to  the  presence  of  iron,  carbonate  of  lime,  and  other  earthy  sub- 
stances, is  sufficiently  good  for  ordinary  purposes.  It  yields  a  gas  of  better 


154  OXYGEN. 

quality,  if  previously  freed  from  carbonate  of  lime  by  dilute  hydrochloric  or 
nitric  acid;  but  when  oxygen  of  great  purity  is  required,  it  is  better  to  ob- 
tain it  from  chlorate  of  potassa.  For  this  purpose,  the  salt  shoald  be  put 
into  a  retort  of  green  "glass,  or  of  white  glass  made  without  lead,  and  be 
heated  nearly  to  redness.  It  first  becomes  liquid,  though  quite  free  from  wa- 
ter, and  then,  on  increase  of  heat,  is  wholly  resolved  into  pure  oxygen  gas, 
which  escapes  with  effervescence,  and  into  a  white  compound,  called  chloride 
of  potassium,  which  is  left  in  the  retort.  The  composition  of  the  chloric 
acid  and  potassa  which  constitute  the  salt,  is  stated  below  ; — 

Chlorine      .      35.42  or  1  eq.  Potassium      .      39.15  or  1  eq. 

Oxygen       .40       or  5  eq.  Oxygen          .        8       or  1  eq. 

Chloric  acid      75.42  or  1  eq.  Potassa  .      47.15  or  I  eq. 

Hence  the  oxygen  which  passes  over  from  the  retort,  is  derived  partly 
from  the  potassa  and  partly  from  the  chloric  acid ;  while  chlorine  and  potas- 
sium enter  into  combination.  Thus  are  122.57  grains  of  the  chlorate  resolv- 
ed into  74.57  grains  of  chloride  of  potassium,  and  48  grains,  or  about  161 
cubic  inches,  of  pure  oxygen. 

Oxygen  gas  is  colourless,  has  neither  taste  nor  smell,  is  not  chemically  af- 
fected by  the  imponderables,  refracts  light  very  feebly,  and  is  a  non-con- 
ductor of  electricity.  It  is  the  most  perfect  negative  electric  that  we  possess, 
always  appearing  at  the  positive  pole,  when  any  compound  which  contains 
it  is  exposed  to  the  action  of  galvanism.  It  emits  light,  as  well  as  heat, 
when  suddenly  and  forcibly  compressed ;  but  Thenard  has  shown  that  the 
light  is  entirely  owing  to  the  combustion  of  the  oil  with  which  the  com- 
pressing tube  is  lubricated.  When  not  united  with  other  ponderable  mat- 
ter, it  is  always  in  the  form  of  gas ;  but  even  in  this  its  purest  state,  it  is 
probably  combined,  as  is  most  likely  true  of  all  elementary  principles,  with 
neat,  light,  arid  electricity. 

Oxygen  gas  is  heavier  than  atmospheric  air.  The  principal  estimates  vary 
from  1.1026,  that  of  Dulong  and  Berzelius,  to  1.1111  as  given  by  Dr.  Thom- 
son. Judging  from  the  care  devoted  to  the  inquiry,  the  observation  of  Du- 
long and  Berzelius  appears  to  me  most  deserving  of  confidence  as  an  ex- 
perimental result ;  but  it  is  so  important  to  know  the  exact  specific  gravity 
of  oxygen  gas,  that  chemists  anxiously  look  for  the  result  of  the  observations 
which  Dr.  Prout  is  understood  to  have  been  long  engaged  in  on  this  subject. 
Adopting  1.1024,  the  number  given  in  the  table,  page  146,  100  cubic  inches, 
when  the  thermometer  is  at  60°  F.  and  the  barometer  stands  at  30  inches, 
would  weigh  34.1872  grains. 

Oxygen  gas  is  very  sparingly  absorbed  by  water,  100  cubic  inches  of  that 
liquid  dissolving  only  three  or  four  of  the  gas.  It  has  neither  acid  nor  alka- 
line properties ;  for  it  does  not  change  the  colour  of  blue  flowers,  nor  does  it 
evince  a  disposition  to  unite  directly  either  with  acids  or  alkalies.  It  has  a 
very  powerful  attraction  for  most  simple  substances;  and  there  is  not  one  of 
them  with  which  it  may  not  be  made  to  combine.  The  act  of  combining 
with  oxygen  is  called  oxidation,  and  bodies  which  have  united  with  it  are 
said  to  be  oxidized.  The  compounds  so  formed  are  divided  by  chemists  into 
acids  and  oxides.  The  former  division  includes  those  compounds  which  pos- 
sess the  general  properties  of  acids  ;  arid  the  latter  comprehends  those  which 
not  only  want  that  character,  but  of  which  many  are  highly  alkaline,  and 
yield  salts  by  uniting  with  acids.  The  phenomena  of  oxidation  are  variable. 
It  is  sometimes  produced  with  great  rapidity,  arid  with  evolution  of  heat  and 
light.  Ordinary  combustion,  for  instance,  is  nothing  more  than  rapid  oxida- 
tion; and  all  inflammable  or  combustible  substances  derive  their  power  of 
burning  in  the  open  air  from  their  affinity  for  oxygen.  On  other  occasions 
it  takes  place  slowly,  and  without  any  appearance  either  of  heat  or  light,  as 
is  exemplified  by  the  rusting  of  iron  when  exposed  to  a  moist  atmosphere. 
Different  as  these  processes  may  appear,  oxidation  is  the  result  of  both ;  and 
both  depend  on  the  same  circumstance,  namely,  the  presence  of  oxygen  in 
the  atmosphere. 


OXYGEN.  155 

All  substances  that  are  capable  of  burning  in  the  open  air,  burn  with  far 
greater  brilliancy  in  oxygen  gas.  A  piece  of  wood,  on  which  the  least  spark 
of  light  is  visible,  bursts  into  flame  the  moment  it  is  put  into  a  jar  of  oxygen  ; 
lighted  charcoal  emits  beautiful  scintillations;  and  phosphorus  burns  with 
so  powerful  and  dazzling  a  light  that  the  eye  cannot  bear  its  impression. 
Even  iron  and  steel,  which  are  not  commonly  ranked  among  the  inflamma- 
bles, undergo  rapid  combustion  in  oxygen  gas. 

The  changes  that  accompany  these  phenomena  are  no  less  remarkable 
than  the  phenomena  themselves.  When  a  lighted  taper  is  put  into  a  vessel 
of  oxygen  gas,  it  burns  for  a  while  with  increased  splendour;  but  the  size 
of  the  flame  soons  begins  to  diminish,  and  if  the  mouth  of  the  jar  be  closed, 
the  light  will  in  a  short  time  disappear  entirely.  The  gas  has  now  lost  its 
characteristic  property ;  for  a  second  lighted  taper,  immersed  in  it,  is  in- 
stantly extinguished.  This  result  is  general.  The  burning  of  one  body  in 
a  given  portion  of  oxygen  unfits  it  more  or  less  completely  for  supporting 
the  combustion  of  another;  and  the  reason  is  manifest.  Combustion  is  pro- 
duced by  the  combination  of  inflammable  matter  with  oxygen.  The  quan- 
tity of  free  oxygen,  therefore,  diminishes  during  the  process,  and  is  at  length 
nearly  or  quite  exhausted.  The  burning  of  all  bodies,  however  inflamma- 
ble, must  then  cease,  because  the  presence  of  oxygen  is  necessary  to  its  con- 
tinuance.  For  this  reason  oxygen  £as  is  called  a  supporter  of  combustion. 
The  oxygen  often  loses  its  gaseous  form  as  well  as  its  other  properties.  If 
phosphorus  or  iron  be  burnt  in  a  jar  of  pure  oxygen  over  water  or  mer- 
cury, the  disappearance  of  the  gas  becomes  obvious  by  the  ascent  of  the 
liquid,  which  is  forced  up  by  the  pressure  of  the  atmosphere,  and  fills  the 
vessel.  Sometimes,  on  the  contrary,  the  oxygen  gas  suffers  diminution  of 
volume  only,  or  it  may  even  undergo  no  change  of  bulk  at  all,  as  is  exempli- 
fied by  the  combustion  of  the  diamond. 

The  changes  experienced  by  the  burning  body  are  equally  striking. 
While  the  oxygen  loses  its  power  of  supporting  combustion,  the  inflamma- 
ble substance  lays  aside  its  combustibility.  It  is  then  an  oxidized  body,  and 
cannot  be  made  to  burn  even  by  aid  of  the  purest  oxygen  gas.  It  has  also 
increased  in  weight.  It  is  an  error  to  suppose  that  bodies  lose  any  thing 
while  they  burn.  The  materials  of  our  fires  and  candles  do  indeed  disap- 
pear, but  they  are  not  destroyed.  Although  they  fly  off  in  the  gaseous  form, 
and  are  commonly  lost  to  us,  it  is  not  difficult  to  collect  and  preserve  all  the 
products  of  combustion.  When  this  is  done  with  the  required  care,  the  com- 
bustible matter  is  always  found  to  weigh  more  after  than  before  combus- 
tion ;  and  the  increase  in  weight  is  exactly  equal  to  the  quantity  of  oxygen 
which  has  disappeared  during  the  process. 

Oxygen  gas  is  necessary  to  respiration.  No  animal  can  live  in  an  atmo- 
sphere which  does  not  contain  a  certain  portion  of  uncombined  oxygen;  for 
an  animal  soon  dies  if  put  into  a  portion  of  air  from  which  the  oxygen  has 
been  previously  removed  by  a  burning  body.  It  may,  therefore,  be  antici- 
pated that  oxygen  is  consumed  during  respiration.  If  a  bird  be  confined  in 
a  limited  quantity  of  atmospheric  air,  it  will  at  first  feel  no  inconvenience; 
but  as  a  portion  of  oxygen  is  withdrawn  at  each  inspiration,  its  quantity  di- 
minishes rapidly,  so  that  respiration  soon  becomes  laborious,  and  in  a  short 
time  ceases  altogether.  Should  another  bird  be  then  introduced  into  the 
same  air,  it  will  die  in  the  course  of  a  few  seconds ;  or  if  a  lighted  candle 
be  immersed  in  it,  its  flame  will  be  extinguished.  Respiration  and  combus- 
tion have,  therefore,  the  same  effect.  An  animal  cannot  live  in  an  atmosphere 
which  is  unable  to  support  combustion ;  nor,  in  general,  can  a  candle  burn 
in  air  which  contains  too  little  oxygen  for  respiration. 

It  is  singular  that,  though  oxygen  is  necessary  to  respiration,  in  a  state  of 
purity  it  is  deleterious.  When  an  animal,  as  a  rabbit  for  example,  is  sup- 
plied with  an  atmosphere  of  pure  oxygen  gas,  no  inconvenience  is  at  first 
perceived;  but  after  the  interval  of  an  hour  or  more,  the  circulation  and  re- 
spiration become  very  rapid,  and  the  system  in  general  is  highly  excited. 
Symptoms  of  debility  subsequently  ensue,  followed  by  insensibility ;  and 


156  OXYGEN. 

death  occurs  in  six,  ten  or  twelve  hours.  On  examination  after  death,  the 
blood  is  found  highly  florid  in  every  part  of  the  body,  and  the  heart  acts 
strongly  even  after  the  breathing  has  ceased.  For  these  experiments  we  are 
indebted  to  Mr.  Broughton. 

THEORY  OF  COMBUSTION. 

The  only  phenomena  of  combustion  noticed  by  an  ordinary  observer,  are 
the  destruction  of  the  burning  body,  and  the  development  of  heat  and  light; 
but  it  has  been  demonstrated  that  in  addition  to  these  circumstances,  oxygen 
gas  invariably  disappears,  and  a  new  compound  consisting  of  oxygen  and 
the  combustible  is  generated.  The  term  combustion,  therefore,  in  its  com- 
mon signification,  implies  the  rapid  union  of  oxygen  gas  and  combustible 
matter,  accompanied  with  heat  and  light.  As  the  evolution  of  heat  and  light 
is  dependent  on  chemical  action,  the  same  phenomena  may  be  expected  in 
other  chemical  processes ;  and,  accordingly,  heat  and  light  are  frequently 
emitted  quite  independently  of  oxygen.  Thus  phosphorus  takes  fire,  and  a 
taper  burns  for  a  short  time,  in  a  vessel  of  chlorine;  and  several  of  the  com- 
mon metals,  such  as  copper,  antimony,  and  arsenic,  in  a  state  of  fine  divi- 
sion, become  red-hot  when  introduced  into  a  jar  of  that  gas.  Potassium 
takes  fire  in  cyanogen  gas;  and  copper-leaf  or  iron  wire,  if  moderately  heat- 
ed, undergoes  the  same  change  in  the  vapour  of  sulphur.  A  mixture  of  iron 
filings  and  sulphur,  when  heated  so  as  to  bring  the  latter  into  perfect  fusion, 
emits  intense  heat  and  light  at  the  instant  of  combination;  and  a  like  effect, 
though  in  a  far  less  degree,  is  produced  by  the  action  of  concentrated  sul- 
phuric acid  on  pure  magnesia.  Most  of  these  and  similar  examples,  espe- 
cially when  one  of  the  combining  substances  is  gaseous,  are  frequently  in- 
cluded under  the  idea  of  combustion ;  and  they  certainly  belong  to  the  same 
class  of  phenomena.  In  the  subsequent  observations,  however,  I  shall  em- 
ploy the  term  in  its  ordinary  sense  ;  but  the  remarks  concerning  increase  of 
temperature,  whether  with  or  without  light,  apply  equally  to  all  cases  where 
heat  is  developed  as  a  result  of  chemical  action. 

For  many  years  prior  to  the  discovery  of  oxygen  gas,  the  phenomena  of 
combustion  were  explained  on  the  Stahlian  or  phlogistic  hypothesis.  All 
combustible  bodies,  according  to  Stahl,  contain  a  certain  principle  which  he 
called  phlogiston,  to  the  presence  of  which  he  ascribed  their  combustibility. 
He  supposed  that  when  a  body  burns,  phlogiston  escapes  from  it ;  and  that 
when  the  body  has  lost  phlogiston,  it  ceases  to  be  combustible,  and  is  then  a 
dephlogisticated  or  incombustible  substance.  A  metallic  oxide  was  conse- 
quently regarded  as  a  simple  substance,  and  the  metal  itself  as  a  compound 
of  its  oxide  with  phlogiston.  The  heat  and  light  which  accompany  combus- 
tion were  attributed  to  the  rapidity  with  which  phlogiston  is  evolved  during 
the  process. 

The  discovery  of  oxygen  proved  fatal  to  the  Stahlian  doctrine.  Lavoisier 
had  the  honour  of  overthrowing  it,  and  of  substituting  in  its  place  the  anti- 
phlogistic theory.  The  basis  of  his  doctrine  has  already  been  stated, — that 
combustion  and  oxidation  in  general  consist  in  the  combination  of  combus- 
tible matter  with  oxygen.  This  fact  he  established  beyond  a  doubt.  On 
burning  phosphorus  in  a  jar  of  oxygen,  he  observed  that  a  considerable 
quantity  of  the  gas  disappeared,  that  the  phosphorus  gained  materially  in 
weight,  and  that  the  increase  of  the  latter  exactly  corresponded  to  the  loss 
of  the  former.  An  iron  wire  was  burnt  in  a  similar  manner,  and  the  weight 
of  the  oxidized  iron  was  found  equal  to  that  of  the  wire  originally  employed, 
added  to  the  quantity  of  oxygen  which  had  disappeared.  That  the  oxygen 
is  really  present  in  the  oxidized  body  he  proved  by  a  very  decisive  experi- 
ment. Some  liquid  mercury  was  confined  in  a  vessel  of  oxygen  gas,  and  ex- 
posed to  a  temperature  sufficient  for  causing  its  oxidation.  The  oxide  of 
mercury,  so  produced,  was  put  into  a  small  retort  and  heated  to  redness, 
when  it  was  reconverted  into  oxygen  and  fluid  mercury,  the  quantity  of 
the  oxygen  being  exactly  equal  to  that  which  had  combined  with  the  mer- 
cury in  the  first  part  of  the  operation. 


OXYGEN.  157 

To  account  for  the  production  of  heat  and  light  during  combustion,  La- 
voisier  had  recourse  to  Dr.  Black's  theory  of  latent  heat.  Heat  is  always 
evolved,  whenever  a  substance,  without  change  of  form,  passes  from  a  rarer 
into  a  denser  state,  and  also  when  a  gas  becomes  liquid  or  solid,  or  a  liquid 
solidifies ;  because  a  quantity  of  heat  previously  combined,  or  latent,  within 
it,  is  then  set  free.  Now  this  is  precisely  what  happens  in  many  instances 
of  combustion.  Thus  water  is  formed  by  the  burning  of  hydrogen,  in  which 
case  two  gases  give  rise  to  a  liquid ;  and  in  forming  phosphoric  acid  with 
phosphorus,  or  in  oxidizing  metals,  oxygen  is  condensed  into  a  solid.  When 
the  product  of  combustion  is  gaseous,  as  in  the  burning  of  charcoal,  the  evo- 
lution of  heat  is  ascribed  to  the  circumstance  that  the  oxidized  body  con- 
tains a  smaller  quantity  of  combined  heat,  or  has  a  smaller  specific  heat, 
than  the  substances  by  which  it  is  produced. 

This  is  the  weak  point  of  Lavoisier's  theory.  Chemical  action  is  very 
often  accompanied  by  increase  of  temperature,  and  the  heat  evolved  during 
combustion  is  only  a  particular  instance  of  it.  Any  theory,  therefore,  by 
which  it  is  proposed  to  account  for  the  production  of  heat  in  some  cases, 
ought  to  be  applicable  to  all.  When  combustion,  or  any  other  chemical  ac- 
tion, is  followed  by  considerable  condensation,  in  consequence  of  which  the 
new  body  contains  less  insensible  heat  than  its  elements  did  before  combina- 
tion, it  is  obvious  that  heat  will,  in  that  case,  be  disengaged.  But  if  this 
were  the  sole  cause  of  the  phenomenon,  a  rise  of  temperature  should  always 
be  preceded  by  a  corresponding  diminution  of  specific  heat ;  and  the  extent 
of  the  former  ought  to  be  in  a  constant  ratio  with  the  degree  of  the  latter.  Now 
Petit  and  Dulong  infer  from  their  researches  on  this  subject,  (Annales  de  Chim. 
et  de  Phys.  vol.  x.)  that  the  degree  of  heat  developed  during  combination, 
bears  no  relation  to  the  specific  heat  of  the  combining  substances ;  and  that 
in  the  majority  of  cases,  the  evolution  of  heat  is  not  attended  by  any  dimi- 
nution in  the  specific  heat  of  the  compound.  It  is  a  well  known  fact,  that 
increase  of  temperature  frequently  attends  chemical  action,  though  the  pro- 
ducts contain  much  more  insensible  heat  than  the  substances  from  which 
they  were  formed.  This  happens  remarkably  in  the  explosion  of  gunpow- 
der, which  is  attended  by  intense  heat;  and  yet  its  materials,  in  passing 
from  the  solid  to  the  gaseous  state,  expand  to  at  least  250  times  their  volume, 
and  consequently  render  latent  a  large  quantity  of  heat. 

These  circumstances  leave  no  doubt  that  the  evolution  of  heat  during 
chemical  action  is  owing  to  some  cause  quite  unconnected  with  that  as- 
signed by  Lavoisier  ;  and  if  this  cause  operates  so  powerfully  in  some  cases, 
it  is  fair  to  infer  that  part  of  the  effect  must  be  owing  to  it  on  those  occa- 
sions, when  the  phenomena  appear  to  depend  on  change  of  specific  heat 
alone.  A  new  theory  is,  therefore,  required  to  account  for  the  chemical 
production  of  heat.  But  it  is  easier  to  perceive  the  fallacies  of  one  doctrine, 
than  to  substitute  another  which  shall  be  faultless;  and  it  appears  to  me 
that  chemists  must,  for  the  present,  be  satisfied  with  the  simple  statement, 
that  energetic  chemical  action  does  of  itself  give  rise  to  increase  of  tempe- 
rature. Berzelius,  in  adopting  the  electro-chemical  theory,  regards  the  heat 
of  combination  as  an  electrical  phenomenon,  believing  it  to  arise  from  the 
oppositely  electrical  substances  neutralizing  one  another,  in  the  same  man- 
ner as  the  electric  equilibrium  is  restored  during  the  discharge  of  a  Leyden 
jar.  There  are  indeed  strong  grounds  for  believing  that  electrical  action  is 
an  essential  part  of  every  chemical  change,  and  it  is  probable  that  the  heat 
developed  during  the  latter  may  be  due  to  the  former;  but  this  part  of  sci- 
ence is  as  yet  too  imperfect  for  indicating  the  precise  mode  by  which  the 
effect  is  produced. 

The  heat  emitted  during  combustion  varies  with  the  nature  of  the  mate- 
rial. The  effect  of  the  combustible  gases  in  raising  the  temperature  of 
water,  according  to  the  experiments  of  Dr.  Dalton,  is  shown  in  the  follow- 
ing table. — (Chemical  Philosophy,  ii.  309.) 

14 


158  HYDROGEN. 

Hydrogen,  in  burning,  raises  an  equal  volume  of  water    .  5°  F. 

Carbonic  oxide  ......         4^ 

Light  carburetted  hydrogen  .  .  .  .  18 

Olefiant  gas  .  .  .  .  .27 

Coal  gas  varies  with  the  quality  of  the  gas  from   .  .  10  to  16 

Oil  gas  varies  also  with  the  quality  of  the  gas  from    .          12  to  20 

Dr.  Dalton  further  states  that  generally  the  combustible  gases  give  out 
heat  nearly  in  proportion  to  the  oxygen  which  they  consume. 

In  the  thirty-seventh  volume  of  the  An.  de  Ch.  et  de  Ph.,  page  180,  M. 
Despretz  has  given  a  notice  of  some  experiments  on  the  heat  developed  in 
combustion.  The  substances  burned  were  hydrogen,  carbon,  phosphorus, 
and  several  metals ;  and  so  much  of  each  was  employed,  as  to  require  the 
same  quantity  of  oxygen.  When  the  combustion  of  hydrogen  gas  pro- 
duced  2578  degrees  of  heat,  carbon  gave  out  2967,  and  iron  5325.  Phos- 
phorus, zinc,  and  tin  emit  quantities  of  heat  very  nearly  the  same  as  iron. 
Hence  it  follows  that,  for  equal  quantities  of  oxygen,  hydrogen  in  burning 
evolves  less  heat  than  most  other  substances.  These  results  do  not  accord 
with  those  of  Dalton. 


SECTION   IV. 

HYDROGEN. 

THIS  gas  was  formerly  termed  inflammable  air,  from  its  combustibility, 
and  phlogiston,  from  the  supposition  that  it  was  the  matter  of  heat ;  but  the 
name  hydrogen,  from  wfo>g  water,  and  ytvvtiv  to  generate,  has  now  become 
general.  Its  nature  and  leading  properties  were  first  pointed  out  in  the 
year  1766  by  Mr.  Cavendish.  (Philos.  Trans.  Ivi.  144.) 

Hydrogen  gas  may  be  easily  procured  in  two  ways.  The  first  consists 
in  passing  the  vapour  of  water  over  metallic  iron  heated  to  redness.  This 
is  done  by  putting  iron  wire  into  a  gun-barrel  open  at  both  ends,  to  one  of 
which  is  attached  a  retort  containing  pure  water,  and  to  the  other  a  bent 
tube.  The  gun-barrel  is  placed  in  a  furnace,  and  when  it  has  acquired  a 
full  red  heat,  the  water  in  the  retort  is  made  to  boil  briskly.  The  gas, 
which  is  copiously  disengaged  as  soon  as  the  steam  comes  in  contact  with 
the  glowing  iron,  passes  along  the  bent  tube,  and  may  be  collected  in  con- 
venient  vessels,  by  dipping  the  free  extremity  of  the  tube  into  the  water  of  a 
pneumatic  trough.  The  second  and  most  convenient  method  consists  in 
putting  pieces  of  iron  or  zinc  into  dilute  sulphuric  acid,  formed  of  one  part 
of  strong  acid  and  four  or  five  of  water.  Zinc  is  generally  preferred.  The 
hydrogen  obtained  in  these  processes  is  not  absolutely  pure.  The  gas 
evolved  during  the  solution  of  iron  has  an  offensive  odour,  ascribed  by  Ber- 
zelius  to  the  presence  of  a  volatile  oil,  which  may  be  almost  entirely  re- 
moved  by  transmitting  the  gaa  through  alcohol.  The  oil  appears  to  arise 
from  some  compound  being  formed  between  hydrogen,  and  the  carbon  which 
is  always  contained  even  in  the  purest  kinds  of  common  iron ;  and  it  is 
probable  that  a  little  carburetted  hydrogen  gas  is  generated  at  the  same 
time.  The  zinc  of  commerce  contains  sulphur,  and  almost  always  traces  of 
charcoal,  in  consequence  of  which  it  is  contaminated  with  hydrosulphuric 
acid,  and  probably  with  the  same  impurities,  though  in  a  less  degree,  as  are 
derived  from  iron.  A  little  metallic  zinc  is  also  contained  in  it,  apparently 
in  combination  with  the  hydrogen.  All  these  impurities,  carburetted  hydro- 
gen excepted,  may  be  removed  by  passing  the  hydrogen  through  a  solution  of 
pure  potassa.  To  obtain  hydrogen  of  great  purity,  distilled  zinc  should  be 
employed. 


HYDROGEN.  159 

Hydrogen  is  a  colourless  gas,  when  pure  has  neither  odour  nor  taste,  and 
is  a  powerful  refractor  of  light.  Like  oxygen,  it  cannot  be  resolved  into 
more  simple  parts,  and,  like  that  gas,  has  hitherto  resisted  all  attempts  to 
compress  it  into  a  liquid.  It  is  the  lightest  body  in  nature,  and  is  conse- 
quently the  best  material  for  rilling  balloons.  From  its  extreme  lightness 
it  is  difficult  to  ascertain  its  precise  density  by  weighing ;  because  the  pre- 
sence of  minute  quantities  of  common  air  or  watery  vapour  occasions  con- 
siderable error.  By  the  table  of  specific  gravities  (page  146),  it  appears 
that  hydrogen  gas  is  just  16  times  lighter  than  oxygen,  an  inference  de- 
rived from  the  composition  of  water  to  be  shortly  stated :  it  hence  follows 
that  100  cubic  inches  of  hydrogen  gas  at  60°  F.  and  30  inches  Bar.  should 
weigh  y1^  x  34.1872  =  2.1367  grains,  and  that  its  specific  gravity  is 
0.0689. 

Hydrogen  does  not  change  the  blue  colour  of  vegetables.  It  is  sparingly 
absorbed  by  water,  100  cubic  inches  of  that  liquid  dissolving  about  one  and 
a  half  of  the  gas.  It  cannot  support  respiration ;  for  an  animal  soon  pe- 
rishes when  confined  in  it.  Death  ensues  from  deprivation  of  oxygen  rather 
than  from  any  noxious  quality  of  the  hydrogen  ;  since  an  atmosphere 
composed  of  a  due  proportion  of  oxygen  and  hydrogen  gases  may  be  re- 
spired without  inconvenience.  Nor  is  it  a  supporter  of  combustion  ;  for 
when  a  lighted  candle  fixed  on  wire  is  passed  up  into  an  inverted  jar  full  of 
hydrogen  gas,  the  light  instantly  disappears. 

Hydrogen  gas  is  inflammable  in  an  eminent  degree,  though,  like  other 
combustibles,  it  requires  the  aid  of  a  supporter  of  combustion.  This  is  ex- 
emplified by  the  experiment  above  alluded  to,  in  which  the  gas  is  kindled 
by  the  flame  of  a  candle,  but  burns  only  where  it  is  in  contact  with  the  air. 
Its  combustion,  when  conducted  in  this  manner,  goes  on  tranquilly,  and  is 
attended  with  a  yellowish-blue  flame  and  a  very  feeble  light.  The  pheno- 
mena are  different  when  the  hydrogen  is  previously  mixed  with  a  due  quan- 
tity of  atmospheric  air.  The  approach  of  flame  not  only  sets  fire  to  the  gas 
near  it,  but  the  whole  is  kindled  at  the  same  instant ;  and  a  flash  of  light 
passes  through  the  mixture,  followed  by  a  violent  explosion.  The  best  pro- 
portion for  the  experiment  is  two  measures  of  hydrogen  to  five  or  six  of  air. 
The  explosion  is  far  more  violent  when  pure  oxygen  is  used  instead  of  at- 
mospheric air,  particularly  when  the  gases  are  mixed  together  in  the  ratio 
of  one  measure  of  oxygen  to  two  of  hydrogen. 

Oxygen  and  hydrogen  gases  cannot  combine  at  ordinary  temperatures, 
and  may,  therefore,  be  kept  in  a  state  of  mixture  without  even  gradual  com- 
bination taking  place  between  them.  Hydrogen  may  be  set  on  fire,  when 
in  contact  with  air  or  oxygen  gas,  by  flame,  by  a  solid  body  heated  to  bright 
redness,  and  by  the  electric  spark.  If  a  jet  of  hydrogen  gas  be  thrown  upon 
recently  prepared  spongy  platinum,  this  metal  almost  instantly  becomes 
red-hot,  and  then  sets  fire  to  the  gas,  a  discovery  which  was  made  in  the 
year  1824,  by  Professor  Doebereiner  of  Jena.  The  power  of  flame  and 
electricity,  in  causing  a  mixture  of  hydrogen  with  air  or  oxygen  gas  to 
explode,  is  limited.  Mr.  Cavendish  found  that  flame  occasions  a  very  feeble 
explosion  when  the  hydrogen  is  mixed  with  nine  times  its  bulk  of  air;  and 
that  a  mixture  of  four  measures  of  hydrogen  with  one  of  air  does  not  ex- 
plode at  all.  An  explosive  mixture,  formed  of  two  measures  of  hydrogen 
and  one  of  oxygen  gas,  explodes  from  all  the  causes  above  enumerated. 
Biot  found  that  sudden  and  violent  compression  likewise  causes  an  explo- 
sion, apparently  from  the  heat  emitted  during  the  operation  ;  for  an  equal 
degree  of  condensation,  slowly  produced,  has  not  the  same  effect.  The 
electric  spark  ceases  to  cause  detonation,  when  the  explosive  mixture  is 
diluted  with  twelve  times  its  volume  of  air,  fourteen  of  oxygen,  or  nine  of 
hydrogen ;  or  when  it  is  expanded  to  sixteen  times  its  bulk  by  diminished 
pressure.  Spongy  platinum  acts  just  as  rapidly  as  flame  or  the  electric 
spark  in  producing  explosion,  provided  the  gases  are  quite  pure  and  mixed 


160  HYDROGEN. 

in  the  exact  ratio  of  two  to  one.*  Mr.  Faraday  finds  that  platinum  foil,  if 
perfectly  clean,  produces  gradual  though  rather  rapid  combination  of  the 
gases,  often  followed  by  explosion.  (Phil.  Trans.  1834.) 

When  the  action  of  heat,  the  electric  spark,  and  spongy  platinum  no 
longer  cause  explosion,  a  silent  and  gradual  combination  between  the  gases 
may  still  be  occasioned  by  them.  Sir  H.  Davy  observed  that  oxygen  and 
hydrogen  gases  unite  slowly  with  one  another,  when  they  are  exposed  to  a 
temperature  above  the  boiling  point  of  mercury,  and  below  that  at  which 
glass  begins  to  appear  luminous  in  the  dark.  An  explosive  mixture, 
diluted  with  air  to  too  great  a  degree  to  explode  by  electricity,  is  made  to 
unite  silently  by  a  succession  of  electric  sparks.  Spongy  platinum  causes 
them  to  unite  slowly,  though  mixed  with  one  hundred  times  their  bulk  of 
oxygen  gas. 

A  large  quantity  of  heat  is  evolved  during  the  combustion  of  hydrogen 
gas.  Lavoisier  concludes  from  experiments  made  with  his  calorimeter, 
(Elements,  vol.  i.)  that  one  pound  of  hydrogen  occasions  as  much  heat  in 
burning  as  is  sufficient  to  melt  295.6  pounds  of  ice.  Dr.  Dalton  fixes  the 
quantity  of  ice  at  320  pounds,  and  Dr.  Crawford  at  480.  The  most  intense 
heat  that  can  be  produced,  is  caused  by  the  combustion  of  hydrogen  in 
oxygen  gas.  Dr.  Hare  of  Philadelphia,  who  first  burned  hydrogen  for  this 
purpose,  collected  the  gases  in  separate  gasholders,  from  which  a  stream  was 
made  to  issue  through  tubes  communicating  with  each  other,  just  before 
their  termination.  At  this  point  the  jet  of  the  mixed  gases  was  inflamed. 
The  effect  of  the  combustion,  though  very  great,  is  materially  increased  by 
forcing  the  two  gases  in  due  proportion  into  a  strong  metallic  vessel  by 
means  of  a  condensing  syringe,  and  setting  fire  to  a  jet  of  the  mixture  as  it 
issues.  An  apparatus  of  this  kind,  now  known  by  the  name  of  the  oxy- 
hydrogen  blowpipe,  was  contrived  by  Mr.  Newman,  and  employed  by 
the  late  Professor  Clarke  in  his  experiments  on  the  fusion  of  refractory 
substances.  On  opening  a  stop-cock  which  confines  the  compressed  gases, 
a  jet  of  the  explosive  mixture  issues  with  force  through  a  small  blowpipe- 
tube,  at  the  extremity  of  which  it  is  kindled.  In  this  state,  however,  the 
apparatus  should  never  be  used ;  for  as  the  reservoir  is  itself  full  of  an  ex- 
plosive  mixture,  there  is  great  danger  of  the  flame  running  back  along  the 
tube,  and  setting  fir.e  to  the  vhole  gas  at  once.  To  prevent  the  occurrence 
of  such  an  accident,  which  would  most  probably  prove  fatal  to  the  operator, 
Professor  Gumming  proposed  that  the  gas,  as  it  issues  from  the  reservoir, 
should  be  made  to  pass  through  a  cylinder  full  of  oil  or  water  before  reach- 
ing the  point  at  which  it  is  to  burn ;  and  Dr.  Wollaston  suggested  the 
additional  precaution  of  fixing  successive  layers  of  fine  wire  gauze  within 
the  exit  tube,  each  of  which  would  be  capable  of  intercepting  the  communi- 
cation of  flame.  A  modification  of  this  apparatus  has  been  devised  by  Mr. 
Gurney ;  but  both  his  and  Newman's  are  rendered  unnecessary  by  the  safety 
tube  lately  proposed  by  Mr.  Hemming.  It  consists  of  a  brass  cylinder, 
about  6  inches  long,  and  3-4ths  of  an  inch  wide,  filled  with  very  fine  brass 
wire  in  length  equal  to  that  of  the  tube.  A  pointed  rod  of  metal,  l-8th  of  an 
inch  thick,  is  then  forcibly  inserted  through  the  centre  of  the  bundle  of 
wires  in  the  tube,  so  as  to  wedge  them  tightly  together.  The  interstices 
between  the  wires  thus  constitute  very  fine  metallic  tubes,  the  conducting 
power  of  which  is  so  great  as  entirely  to  intercept  the  passage  of  flame. 
The  mixed  gases  are  supplied  from  a  common  bladder.  (Phil.  Mag.  3d 
S.  i.  82.)  A  very  intense  heat  may  be  safely  and  easily  procured  by  passing 

*  For  a  variety  of  facts  respecting  the  causes  which  prevent  the  action  of 
flame,  electricity,  and  platinum  in  producing  detonation,  the  reader  may 
consult  the  essay  of  M.  Grotthus  in  the  Ann.  de  Chimie,  vol.  Ixxxii. ;  Sir  H, 
Davy's  work  on  Flame;  Dr.  Henry's  essay  in  the  Philosophical  Transac- 
tions for  1824;  and  a  paper  by  myself  in  the  Edinburgh  Philosophical  Jour- 
nal for  the  same  year. 


HYDROGEN.  161 

a  jet  of  oxygen  gas  through  the  flame  of  a  spirit  lamp,  as  proposed  by 
the  late  Dr.  Marcet.  An  elegant  improvement  on  this  principle  has  been 
devised  by  Mr.  Daniell,  by  fixing  a  jet  for  conveying  oxygen  within 
another  jet  for  hydrogen  or  coal  gas,  so  that  a  current  of  oxygen  may  be 
introduced  into  the  middle  of  the  flame.  (Phil.  Mag.  ii.  57.  3d  Series.) 
The  heat  from  this  apparatus  is  quite  sufficient  for  most  purposes ;  and  it 
may  be  still  further  increased  by  causing  the  gases  to  pass  separately 
through  heated  tubes,  in  order  that  they  may  have  a  temperature  of  400°  or 
500°  on  issuing  from  the  jets. — On  this  principle  is  founded  the  patent  of 
Mr.  Dunlop,  of  the  Carron  Iron  Works,  for  increasing  the  temperature  of 
blast  furnaces:  the  air  which  supports  the  combustion  is  previously  heated 
by  transmission  through  iron  tubes  kept  at  a  low  red  heat,  whereby  the 
power  of  the  furnaces  is  surprisingly  increased,  and  a  great  saving  in  fuel 
and  time  is  accomplished. 

The  compounds  of  hydrogen  described  in  this  section  are  two  in  number, 
the  composition  of  which  is  as  follows  : — 

By  Weight.  By  Volume. 

Hydrogen.  Oxygen.         Equiv.  Hyd.  Oxy. 

Water  (protoxide  of  hydrogen)  1  or  1  eq.-|-    8  or  1  eq.=     9         100      50 
Peroxide  of  hydrogen  1  or  1  eq.-f  16  or  2  eq.=  17         100     100 

The  chemical  symbol  of  water  is  H+O,  or  H,  and  sometimes  aq,  from 
aqua ;  and  that  of  the  peroxide  is  H-j-SO,  or  H. 

WATER. 

Water  is  the  sole  product  of  the  combustion  of  hydrogen  gas.  For  this 
important  fact  we  are  indebted  to  Mr.  Cavendish.  He  demonstrated  it  by 
burning  oxygen  and  hydrogen  gases  in  a  dry  glass  vessel ;  when  a  quantity 
of  pure  water  was  generated,  exactly  equal  in  weight  to  that  of  the  gases 
which  had  disappeared.  This  experiment,  which  is  the  synthetic  proof  of 
the  composition  of  water,  was  afterwards  made  on  a  much  larger  scale  in 
Paris  by  Vauquelin,  Fourcroy,  and  Seguin.  Lavoisier  first  demonstrated  its 
nature  analytically,  by  passing  a  known  quantity  of  watery  vapour  over  me- 
tallic  iron  heated  to  redness  in  a  glass  tube.  Hydrogen  gas  was  disengaged, 
the  metal  in  the  tube  was  oxidized,  and  the  weight  of  the  former,  added  to 
the  increase  which  the  iron  had  experienced  from  combining  with  oxygen, 
exactly  corresponded  to  the  quantity  of  water  decomposed, 

A  knowledge  of  the  exact  proportions  in  which  oxygen  and  hydrogen 
gases  unite  to  form  water,  is  a  necessary  element  in  many  chemical  reason- 
ings. Its  composition  by  volume  was  demonstrated  very  satisfactorily  by 
Messrs.  Nicholson  and  Carlisle,  in  their  researches  on  the  chemical  agency 
of  galvanism.  On  resolving  water  into  its  elements  by  this  agent,  and  col- 
lecting them  in  separate  vessels,  they  obtained  precisely  two  measures  of 
hydrogen  and  one  of  oxygen,— a  result  which  has  been  fully  confirmed  by 
subsequent  experimenters.  The  same  fact  was  proved  synthetically  by  (*ay- 
Lussac  and  Humboldt,  in  their  Essay  on  Eudiometry,  published  in  the  Jour? 
nal  de  Physique  for  1805.  They  found  that  when  a  mixture  of  oxygen  and 
hydrogen  is  inflamed  by  the  electric  spark,  those  gases  always  unite  in  the 
exact  ratio  of  one  to  two,  whatever  may  be  their  relative  quantity  in  the 
mixture.  When  one  measure  of  oxygen  is  mixed  with  three  of  hydrogen, 
one  measure  of  hydrogen  remains  after  the  explosion ;  and  a  mixture  of  two 
measures  of  oxygen  and  two  of  hydrogen  leaves  one  measure  of  oxygen, 
When  one  volume  of  oxygen  is  mixed  with  two  of  hydrogen,  both  gases,  if 
quite  pure,  disappear  entirely  on  the  electric  spark  being  passed  through 
them.  The  composition  of  water  by  weight  was  determined  with  great  care 
by  Berzelius  and  Dulong ;  and  we  cannot  hesitate,  considering  the  known 
dexterity  of  the  operators,  and  the  principle  on  which  their  method  of  arja- 

14* 


162  HYDROGEN. 

lysis  was  founded,  to  regard  their  result  as  a  nearer  approximation  to  the 
truth  than  that  of  any  of  their  predecessors.  They  state,  as  a  mean  of  three 
careful  experiments,  (Ann.  de  Ch.  et  de  Ph.  vol.  xv.)  that  100  parts  of  pure 
water  consist  of  11.1  of  hydrogen  and  88.9  oxygen,  which  is  the  ratio  of  1  to 
8.009,  very  nearly  that  of  1  to  8  above  stated. 

The  processes  for  procuring  a  supply  of  hydrogen  gas  will  now  be  intelli- 
gible. The  first  is  the  method  by  which  Lavoisier  made  the  analysis  of  wa- 
ter. It  is  founded  on  the  fact,  that  iron  at  a  red  heat  decomposes  water,  the 
oxygen  of  that  liquid  uniting  with  the  metal,  and  the  hydrogen  gas  being 
set  free.  That  the  hydrogen  which  is  evolved  when  zinc  or  iron  is  put  into 
dilute  sulphuric  acid  must  be  derived  from  the  same  source,  is  obvious  from 
the  consideration,  that  of  the  three  substances,  iron,  sulphuric  acid,  and  wa- 
ter, the  last  is  the  only  one  which  contains  hydrogen.  The  product  of  the 
operation,  besides  hydrogen,  is  sulphate  of  the  protoxide  of  iron,  if  iron  is 
used,  or  of  the  oxide  of  zinc,  when  zinc  is  employed.  The  knowledge  of  the 
combining  proportions  of  these  substances  will  readily  give  the  exact  quan- 
tity of  each  product.  These  numbers  are — 

Water  (8  oxy.  +  1  hyd.)          ....        ,~ '-       9 

Sulphuric  acid 40.1 

Iron 28 

Protoxide  of  iron  (28  iron  -f-  8  oxygen)         .        «  36 

Sulphate  of  the  protoxide  of  iron  (40.1+36)     .        .  76.1 

Hence  for  every  9  grains  of  water  which  are  decomposed,  1  grain  of  hydro- 
gen will  be  set  free;  8  grains  of  oxygen  will  unite  with  28  grains  of  iron, 
forming  36  of  the  protoxide  of  iron ;  and  the  36  grains  of  protoxide  will  com- 
bine with  40.1  grains  of  sulphuric  acid,  yielding  76.1  of  sulphate  of  the  prot- 
oxide of  iron.  A  similar  calculation  may  be  employed  when  zinc  is  used, 
merely  by  substituting  the  equivalent  of  zinc  (32.3)  for  that  of  iron.  Ac- 
cording  to  Mr.  Cavendish,  an  ounce  of  zinc  yields  676  cubic  inches,  and  an 
equal  quantity  of  iron,  782  cubic  inches  of  hydrogen  gas. 

The  action  of  dilute  sulphuric  acid  on  metallic  zinc  affords  an  instance  of 
what  was  once  called  Disposing  Affinity.  Zinc  decomposes  pure  water  at 
common  temperatures  with  extreme  slowness  ;  but  as  soon  as  sulphuric  acid 
is  added,  decomposition  of  the  water  takes  place  rapidly,  though  the  acid 
merely  unites  with  oxide  of  zinc.  The  former  explanation  was,  that  the 
affinity  of  the  acid  for  oxide  of  zinc  disposed  the  metal  to  unite  with  oxygen, 
and  thus  eiiabled  it  to  decompose  water;  that  is,  the  oxide  of  zinc  was  sup- 
posed to  produce  an  effect  previous  to  its  existence.  The  obscurity  of  this 
explanation  arises  from  regarding  changes  as  consecutive,  which  are  in 
reality  simultaneous.  There  is  no  succession  in  the  process ;  the  oxide  of 
zinc  is  not  formed  previously  to  its  combination  with  the  acid,  but  at  the 
same  instant.  There  is,  as  it  were,  but  one  chemical  change,  which  con- 
sists in  the  combination  at  one  and  the  same  moment  of  zinc  with  oxygen, 
and  of  oxide  of  zinc  with  the  acid ;  and  this  change  occurs  because  these 
two  affinities,  acting  together,  overcome  the  attraction  of  oxygen  and  hydro- 
gen for  one  another. 

Water  is  a  transparent  colourless  liquid,  which  has  neither  smell  nor 
taste.  It  is  a  powerful  refractor  of  light,  conducts  heat  very  slowly,  and  is 
an  imperfect  conductor  of  electricity.  The  experiments  of  Oersted,  and  Cul- 
ladon  and  Sturm  have  proved  that  water  is  compressible  by  great  pressure ; 
and  according  to  the  latter  observers,  its  absolute  diminution  for  each  atmo- 
sphere is  51.3  millionths  of  its  volume.  (An.deCh.et  de  Ph.xxxvi.  140.)  The 
relations  of  water,  with  respect  to  heat,  are  highly  important ;  but  they  have 
already  been  discussed  in  the  first  part  of  the  work.  The  specific  gravity 
of  water  is  1,  the  density  of  all  solid  and  liquid  bodies  being  referred  to  it  as 
a  term  of  comparison.  One  cubic  inch,  at  62°  F.  and  30  inches  of  the  baro- 
meter, weighs  252.458  grains ;  so  tha£  it  is  815  times  as  heavy  as  atmo- 
spheric air. 

Watert  owing  partly  to  the  extensive  range  of  its  own  affinity,  and  partly 


HYDROGEN.  163 

to  the  nature  of  its  elements,  is  one  of  the  most  powerful  agents  which  we 
possess.  The  preparation  of  hydrogen  gas  is  an  example  of  this;  and  in- 
deed there  are  few  complex  changes,  where  oxygen  and  hydrogen  are  pre- 
sent, which  do  not  give  rise  either  to  the  production  or  decomposition  of 
water.  But,  independently  of  the  elements  of  which  it  is  composed,  it  com- 
bines directly  with  many  bodies.  Sometimes  it  is  contained  in  a  variable 
ratio,  as  in  ordinary  solution ;  in  other  compounds  it  is  present  in  a  fixed 
definite  proportion,  as  is  exemplified  by  its  union  with  several  of  the  acids, 
the  alkalies,  and  all  salts  that  contain  water  of  crystallization.  These  com- 
binations are  termed  hydrates.  Thus,  concentrated  sulphuric  acid  is  a  corn- 
pound  of  one  equivalent  of  the  real  acid  and  one  equivalent  of  water  ;  and 
its  proper  name  is  hydrous  sulphuric  acid,  or  hydrate  of  sulphuric  acid. 
The  adjunct  hydro  has  been  sometimes  used  to  signify  the  presence  of  water 
in  definite  proportion;  but  it  is  advisable,  to  prevent  mistakes,  to  limit  its 
employment  to  the  compounds  of  hydrogen. 

The  purest  water  which  can  be  found  as  a  natural  product,  is  procured  by 
melting  freshly  fallen  snow,  or  by  receiving  rain  in  clean  vessels  at  a  dis- 
tance from  houses.  But  this  water  is  not  absolutely  pure ;  for  if  placed 
under  the  exhausted  receiver  of  an  air-pump,  or  boiled  briskly  for  a  few 
minutes,  bubbles  of  gas  escape  from  it.  The  air  obtained  in  this  way  from 
snow  water  is  much  richer  in  oxygen  gas  than  atmospheric  air.  According 
to  the  experiments  of  Gay-Lussae  and  Humboldt,  it  contains  34.8  per  cent, 
of  oxygen,  and  the  air  separated  by  ebullition  from  rain  water  contains  32 
per  cent,  of  that  gas.  All  water  which  has  once  fallen  on  the  ground  be- 
comes impregnated  with  more  or  less  earthy  or  saline  matters,  and  it  can  be 
separated  from  them  only  by  distillation.  The  distilled  water,  thus  obtained, 
and  preserved  in  clean  well-stopped  bottles,  is  absolutely  pure.  Recent- 
ly boiled  water  has  the  property  of  absorbing  a  portion  of  all  gases,  when 
its  surface  is  in  contact  with  them ;  and  the  absorption  is  promoted  by  brisk 
agitation.  The  following  table,  from  Dr.  Henry's  Chemistry,  shows  the  ab- 
sorbability of  different  gases  by  water,  deprived  of  all  its  air  by  ebullition. 

100  cubic  inches  of  such  water,  at  the  mean  temperature  and  pressure, 
absorb  of 

Dalton  and  Henry.                        Saussure. 

Sulphuretted  hydrogen       100  cubic  inches.  253  cubic  inches. 

Carbonic  acid    .             .     100  .  .     106 

Nitrous  oxide           .100  .                           76 

Olefiantgas       .             .       12.5      .  .  .       15.3 

Oxygen        .                            3.7  ..               6.5 

Carbonic  oxide               .         1.56    .  .  V^v     6.2 

Nitrogen      .             .              1.56  '  .: '-"'.    ,' .:             4.1 

Hydrogen       "'^  ;    .^y        1.56    .  !;;«/;  w\     4.6 

The  estimate  of  Saussure  is  in  general  too  high.  That  of  Drs.  Dalton 
and  Henry  for  nitrous  oxide,  according  to  the  experiments  of  Sir  H.  Davy, 
is  considerably  beyond  the  truth. 


PEROXIDE  OF  HYDROGEN. 

The  binoxide  or  peroxide  of  hydrogen  was  discovered  by  Thenard  irf  the 
year  1818.  Before  describing  the  mode  of  preparing  this  compound,  it  must 
be  observed  that  there  are  two  oxides  of  barium  ;  and  that  when  the  per- 
oxide of  that  metal  is  put  into  a  dilute  acid,  oxygen  gas  is  set  at  liberty,  and 
the  peroxide  is  converted  into  protoxide  of  barium  or  baryta,  which  com- 
bines with  the  acid.  When  this  process  is  conducted  with  the  necessary 
precautions,  the  oxygen  which  is  set  free,  instead  of  escaping  in  the  form  of 
gas,  unites  with  the  hydrogen  of  the  water,  and  brings  it  to  a  maximum  of 
oxidation.  For  a  full  detail  of  all  the  minutise  of  the  process,  the  reader  may 


164  HYDROGEN. 

consult  the  original  memoir  of  Thenard;*  the  general  directions  are  the  fol- 
lowing : — To  six  or  seven  ounces  of  water  add  so  much  pure  concentrated 
hydrochloric  acid  as  is  sufficient  to  dissolve  230  grains  of  baryta ;  and  after 
having  placed  the  mixed  fluids  in  a  glass  vessel  surrounded  with  ice,  add  in 
successive  portions  185  grains  of  peroxide  of  barium  reduced  to  powder,  and 
stir  with  a  glass  rod  after  each  addition.  When  the  solution,  which  takes 
place  without  effervescence,  is  complete,  sulphuric  acid  is  added  in  sufficient 
quantity  for  precipitating  the  whole  of  the  baryta,  in  the  form  of  an  insoluble 
sulphate,  leaving  the  hydrochloric  acid  in  solution.  Another  portion  of  per- 
oxide of  barium,  amounting  to  185  grains,  is  then  put  into  the  liquid :  the 
free  hydrochloric  acid  instantly  acts  upon  it,  and  as  soon  as  it  is  dissolved, 
the  baryta  is  again  separated  as  a  sulphate  by  the  addition  of  sulphuric  acid. 
The  solution  is  then  filtered,  in  order  to  separate  the  insoluble  sulphate  of 
baryta ;  and  fresh  quantities  of  peroxide  of  barium  are  added  in  succession, 
till  about  three  ounces  have  been  employed.  The  liquid  then  contains  from 
25  to  30  times  its  volume  of  oxygen  gas.  The  hydrochloric  acid  which  has 
served  to  decompose  the  peroxide  of  barium  during  the  whole  process,  is  now 
removed  by  the  cautious  addition  of  sulphate  of  oxide  of  silver,  and  the  sul- 
phuric acid  afterwards  separated  by  solid  baryta. 

Peroxide  of  hydrogen,  as  thus  prepared,  is  still  diluted  with  a  considera- 
ble quantity  of  water.  To  separate  the  latter,  the  mixed  liquids  are  placed, 
with  a  vessel  of  strong  sulphuric  acid,  under  the  exhausted  receiver  of  an 
air-pump.  As  the  water  evaporates,  the  density  of  the  residue  increases, 
till  at  last  it  requires  the  specific  gravity  of  1.452.  The  concentration  can- 
not be  pushed  further ;  for  if  kept  under  the  receiver  after  reaching  this  point, 
the  peroxide  itself  gradually  but  slowly  volatilizes  without  change. 

Peroxide  of  hydrogen,  of  specific  gravity  1.452,  is  a  colourless  transparent 
liquid  without  odour.  It  whitens  the  surface  of  the  skin  when  applied  to  it, 
causes  a  pricking  sensation,  and  even  destroys  its  texture  if  the  application 
be  long  continued.  It  acts  in  a  similar  manner  on  the  tongue ;  in  addition 
to  which  it  thickens  the  saliva,  and  tastes  like  certain  metallic  solutions. 
Brought  into  contact  with  litmus  and  turmeric  paper,  it  gradually  destroys 
their  colour  and  makes  them  white.  It  is  slowly  volatilized  in  vacuo^  a  fact 
which  shows  that  its  vapour  is  much  less  elastic  than  that  of  water.  It  pre- 
serves its  liquid  form  at  all  degrees  of  cold  to  which  it  has  hitherto  been  ex- 
posed. At  the  temperature  of  59°  F.  it  is  decomposed,  being  converted  into 
water  and  oxygen  gas.  For  this  reason  it  ought  to  be  preserved  in  glass 
tubes  surrounded  with  ice. 

The  most  remarkable  property  of  peroxide  of  hydrogen  is  its  facility  of 
decomposition.  Diffused  daylight  does  not  seem  to  exert  any  influence  over 
it,  and  even  the  direct  solar  rays  act  upon  it  tardily.  It  effervesces  from 
escape  of  oxygen  at  59°  F.,  and  the  sudden  application  of  a  higher  tempera- 
ture, as  that  of  212°,  gives  rise  to  such  rapid  evolution  of  gas  as  to  cause  an 
explosion.  Water,  apparently  by  combining  with  the  peroxide,  renders  it  more 
permanent;  but  no  degree  of  dilution  can  enable  it  to  bear  the  heat  of  boil- 
ing water,  at  which  temperature  it  is  entirely  decomposed.  All  the  metals 
except  iron,  tin,  antimony,  and  tellurium,  have  a  tendency  to  decompose  the 
peroxide  of  hydrogen,  converting  it  into  oxygen  and  water.  A  state  of 
minute  mechanical  division  is  essential  for  producing  rapid  decomposition. 
If  the  metal  is  in  mass,  and  the  peroxide  diluted  with  water,  the  action  is 
slow.  The  metals  which  have  a  strong  affinity  for  oxygen  are  oxidized  at  the 
same  time,  such  as  potassium,  sodium,  arsenic,  molybdenum,  manganese,  zinc, 
tungsten,  and  chromium ;  while  others,  such  as  gold,  silver,  platinum,  iridium, 
osmium,  rhodium,  palladium,  and  mercury,  retain  the  metallic  state. 

Peroxide  of  hydrogen  is  decomposed  at  common  temperatures  by  many  of 


*  In  the  An.  de  Chim=  et  de  Phys.  vol.  viii.  ix.  x.  and  1. ;  Annals  of  Philo- 
sophy, vol.  xiii.  and  xiv. ;  and  M-  Thenard's  Traite  de  Chimie, 


HYDROGEN,  165 

the  metallic  oxides.  That  some  protoxides  should  have  this  effect,  would  be 
anticipated  in  consequence  of  their  tendency  to  pass  into  a  higher  state  of 
oxidation.  The  protoxides  of  iron,  manganese,  tin,  cobalt,  and  others,  act 
on  this  principle,  and  are  really  converted  into  peroxides.  The  peroxides  of 
barium,  strontium,  and  calcium  may  likewise  be  formed  by  the  action  of 
peroxide  of  hydrogen  on  baryta,  strontia,  and  lime.  But  it  is  a  singular 
fact,  and  I  am  not  aware  that  any  satisfactory  explanation  of  it  has  been 
given,  that  some  oxides  decompose  peroxide  of  hydrogen  without  passing 
into  a  higher  degree  of  oxidation.  The  peroxides  of  lead,  mercury,  gold, 
platinum,  manganese,  and  cobalt,  possess  this  property  in  the  greatest 
perfection,  acting  on  peroxide  of  hydrogen,  when  concentrated,  with  sur- 
prising energy.  The  decomposition  is  complete  and  instantaneous;  oxygen 
gas  is  evolved  so  rapidly  as  to  produce  a  kind  of  explosion,  and  such  intense 
temperature  is  excited,  that  the  glass  tnbe  in  which  the  experiment  is  con- 
ducted  becomes  red-hot.  The  reaction  is  very  great  even  when  the  per- 
oxide of  hydrogen  is  diluted  with  water.  Oxide  of  silver  occasions  very 
perceptible  effervescence  when  put  into  water  which  contains  only  l-50th  of 
its  bulk  of  oxygen.  All  the  metallic  oxides,  which  are  decomposed  by  a 
red  heat,  such  as  those  of  gold,  platinum,  silver,  and  mercury,  are  reduced 
to  the  metallic  state  when  they  act  upon  peroxide  of  hydrogen.  This  effect 
cannot  be  altogether  ascribed  to  heat  disengaged  during  the  action  ;  for 
oxide  of  silver  suffers  reduction  when  put  into  a  very  dilute  solution  of  the 
peroxide,  although  the  decomposition  is  not  then  attended  by  an  appreciable 
rise  of  temperature. 

While  the  tendency  of  metals  and  metallic  oxides  is  to  decompose  the 
peroxide  of  hydrogen,  acids  have  the  property  of  rendering  it  more  stable. 
In  proof  of  this,  let  a  portion  of  that  liquid,  somewhat  diluted  with  water,  be 
heated  till  it  begins  to  effervesce  from  the  escape  of  oxygen  gas;  let  some 
strong  acid,  as  the  nitric,  sulphuric,  or  hydrochloric,  be  then  dropped  into  it, 
and  the  effervescence  will  cease  on  the  instant.  When  a  little  finely 
divided  gold  is  put  into  a  weak  solution  of  peroxide  of  hydrogen,  containing 
only  10,  20,  or  30  times  its  bulk  of  oxygen,  brisk  effervescence  ensues ;  but 
on  letting  one  drop  of  sulphuric  acid  fall  into  it,  effervescence  ceases 
instantly ;  it  is  reproduced  by  the  addition  of  potassa,  and  is  again  arrested 
by  adding  a  second  portion  of  acid.  The  only  acids  that  do  not  possess  this 
property  are  those  that  have  a  low  degree  of  acidity,  as  carbonic  and  boracic 
acids ;  or  those  which  suffer  a  chemical  change  when  mixed  with  peroxide 
of  hydrogen,  such  as  hydriodic,  hydrosulphuric,  and  sulphurous  acids. 
Acids  appear  to  increase  the  stability  of  the  peroxide  in  the  same  way  as 
water  does,  namely,  by  combining  chemically  with  it.  Several  compounds 
of  this  kind  were  formed  by  Thenard,  before  he  was  aware  of  the  existence 
of  the  peroxide  of  hydrogen.  They  were  made  by  dissolving  peroxide  of 
barium  in  some  dilute  acid,  such  as  the  nitric,  and  then  precipitating  the 
baryta  by  sulphuric  acid.  As  nitric  acid  was  supposed  under  these  circum- 
stances to  combine  with  an  additional  quantity  of  oxygen,  Thenard  applied 
the  term  oxygenized  nitric  acid  to  the  resulting-  compound,  and  described 
several  other  new  acids  under  a  similar  title.  But  the  subsequent  discovery 
of  peroxide  of  hydrogen  put  the  nature  of  the  oxygenized  acids  in  a  clearer 
light;  for  their  properties  are  easily  explicable  on  the  supposition  that  they 

are  composed,  not  of  acids  and  oxygen  gas,  but  of  acids  united  with  per- 

•  j      /•  i     i 
oxide  ot  hydrogen. 

Peroxide  of  hydrogen  was  analyzed  by  diluting  a  known  weight  of  it 
with  water,  and  then  decomposing  it  by  toiling  the  solution.  According  to 
two  careful  analyses,  conducted  on  this  principle,  864  parts  of  the  peroxide 
are  composed  of  466  of  water,  and  398  of  oxygen  gas.  The  466  of  water 
contain  414  of  oxygen,  whence  it  may  be  inferred  that  peroxide  of  hydrogen 
contains  twice  as  much  oxygen  as  water.  A  small  deficiency  of  oxygen  in 
this  experiment  was  to  be  expected,  owing  to  the  difficulty  of  obtaining  per- 
oxide of  hydrogen  perfectly  free  from  water. 


1 66  .  NITROGEN. 

, 

SECTION   V. 

NITROGEN. 

THE  existence  of  nitrogen  gas,  as  distinct  from  every  other  gaseous  sub- 
stance, appears  to  have  been  first  noticed  in  the  year  1772  by  the  late  Dr. 
Rutherford  of  Edinburgh.  Lavoisier  discovered  in  1775  that  it  is  a  constitu- 
ent part  of  the  atmosphere;  and  the  same  discovery  was  made  soon  after,  or 
about  the  same  time,  by  Scheele.  Lavoisier  called  it  azote,  from  A  privative, 
and  g®b  life,  because  it  is  unable  to  support  the  respiration  of  animals ;  but 
as  it  possesses  this  negative  property  in  common  with  most  other  gases,  the 
more  appropriate  term  nitrogen  has  been  since  applied  to  it,  from  the  cir- 
cumstance of  its  being  an  essential  ingredient  of  nitric  acid. 

Nitrogen  is  most  conveniently  prepared  by  burning  a  piece  of  phosphorus 
in  a  jar  full  of  air  inverted  over  water.  The  strong  affinity  of  phosphorus 
for  oxygen  enables  it  to  burn  till  the  whole  of  that  gas  is  consumed.  The 
product  of  the  combustion,  metaphosphoric  acid,  is  at  first  diffused  through 
the  residue  in  the  form  of  a  white  cloud  ;  but  as  this  substance  is  rapidly 
absorbed  by  water,  it  disappears  entirely  in  the  course  of  half  an  hour. 
The  residual  gas  is  nitrogen,  containing  a  small  quantity  of  carbonic  acid 
and  vapour  of  phosphorus,  both  of  which  may  be  removed  by  agitating  it 
briskly  with  a  solution  of  pure  potassa.  Several  other  substances  may  be 
employed  for  withdrawing  oxygen  from  atmospheric  air.  A  solution  of 
protosulphate  of  iron,  charged  with  binoxide  of  nitrogen,  absorbs  the 
oxygen  in  the  space  of  a  few  minutes.  A  stick  of  phosphorus  produces  the 
same  effect  in  twenty-four  hours,  if  exposed  to  a  temperature  of  60°  F.  A 
solution  of  sulphuret  of  potassium  or  calcium  acts  in  a  similar  manner;  and 
a  mixture  of  equal  parts  of  iron  filings  and  sulphur,  made  into  a  paste  with 
water,  may  be  employed  with  the  same  intention.  Both  these  processes, 
however,  are  inconvenient  from  their  slowness.  Nitrogen  gas  may  likewise 
be  obtained  by  exposing  a  mixture  of  fresh  muscle  and  nitric  acid  of  speci- 
fic gravity  1.20  to  a  moderate  temperature.  Effervescence  then  takes  place, 
and  a  large  quantity  of  gaseous  matter  is  evolved,  which  is  nitrogen  mixed 
with  a  little  carbonic  acid.  The  latter  must  be  removed  by  agitation  with 
lime-water ;  but  the  residue  still  retains  a  peculiar  odour,  indicative  of  the 
presence  of  some  volatile  principle  which  cannot  be  wholly  separated  from 
it.  The  theory  of  this  process  is  somewhat  complex,  and  will  be  considered 
more  conveniently  in  a  subsequent  part  of  the  work. 

Pure  nitrogen  is  a  colourless  gas,  wholly  devoid  of  smell  and  taste.  It 
does  not  change  the  blue  colour  of  vegetables,  and  is  distinguished  from 
other  gases,  more  by  negative  characters  than  by  any  striking  quality.  It 
is  not  a  supporter  of  combustion ;  but,  on  the  contrary,  extinguishes  all 
burning  bodies  that  are  immersed  in  it.  No  animal  can  live  in  it ;  but  yet 
it  exerts  no  injurious  action  either  on  the  lungs  or  on  the  system  at  large, 
the  privation  of  oxygen  gas  being  the  sole  cause  of  death.  It  is  not  inflam- 
mable like  hydrogen;  though  under  favourable  circumstances,  it  may  be 
made  to  unite  with  oxygen.  Water,  when  deprived  of  air  by  ebullition, 
takes  up  about  one  and  a  half  per  cent  of  it.  Its  specific  gravity  is  esti- 
mated at  0.976  by  Dulong  and  Berzelius,  and  0.9722  by  Dr.  Thomson :  I 
have  adopted  0.9727  as  more  consistent  with  the  specific  gravity  of  air  and 
oxygen  gas.  Hence  100  cubic  inches  at  the  mean  temperature  and  pressure 
will  weigh  30.1650  grains. 

Considerable  doubt  exists  as  to  the  nature  of  nitrogen.  Though  ranked 
among  the  simple  non-metallic  bodies,  some  circumstances  have  led  to  the 
suspicion  that  it  is  compound ;  and  this  opinion  has  been  warmly  advocated 
by  Sir  H.  Davy  and  Berzelius.  The  chief  argument  in  favour  of  this  view 
is  drawn  from  the  phenomena  that  attend  the  formation  of  what  is  called 
the  ammoniacal  amalgam.  From  the  metallic  appearance  of  this  substance, 


it  was  supposed  to  be  a  compound  of  mercury  and  a  metal ;  and  as  the  only 
method  of  forming  it  is  by  the  action  of  galvanism  on  a  salt  of  ammonfe,  in 
contact  with  a  globule  of  mercury,  it  follows  that  the  metal,  if  present  at  all, 
must  have  been  supplied  by  the  ammonia.  Now  ammonia  is  composed  of 
hydrogen  and  nitrogen ;  and  as  the  former,  from  its  small  specific  gravity, 
can  hardly  be  supposed  to  contain  a  metal,  it  was  inferred  that  it  must  be 
present  in  the  latter.  Unfortunately  for  this  argument,  the  supposed  metal 
cannot  be  obtained  in  a  separate  state.  The  amalgam  no  sooner  ceases  to 
be  under  galvanic  influence  than  its  elements  begin  to  separate  spontaneous- 
ly, and  in  a  few  minutes  decomposition  is  complete,  the  sole  products  being 
ammonia,  hydrogen,  and  pure  mercury.  Sir  H.  Davy  accounted  for  this 
change  on  the  supposition  that  water  is  decomposed  ;  that  its  oxygen  repro- 
duces nitrogen  by  uniting  with  the  supposed  metal ;  and  that  one  part  of  its 
hydrogen  forms  ammonia  by  uniting  with  the  nitrogen,  while  the  remainder 
escapes  in  the  form  of  gas.  But  Gay-Lussac  and  Thenard  (Recherches 
Physico-Chimiques,  vol  i.)  declare  that  the  amalgam  resolves  itself  into 
mercury,  ammonia,  and  hydrogen,  even  though  perfectly  free  from  mois- 
ture ;  and  they  infer  from  their  experiments  that  it  is  composed  of  those 
three  substances  combined  directly  with  each  other.  It  hence  appears  that 
the  examination  of  the  ammoniacal  amalgam  affords  no  proof  of  the  com- 
pound nature  of  nitrogen  ;  nor  was  Sir  H.  Davy's  attempt  to  decompose  that 
gas  by  aid  of  potassium,  intensely  heated  by  a  galvanic  current,  attended 
with  better  success.  Berzelius  has  defended  the  idea  that  nitrogen  is  a 
compound  body  on  other  principles ;  but  as  his  arguments,  though  very  in- 
genious, are  merely  speculative,  they  cannot  be  admitted  as  decisive  of  the 
question. 

Chemists  are  not  agreed  about  the  equivalent  of  nitrogen.  In  this  coun- 
try 14  is  commonly  adopted ;  but  from  the  experiments  of  Berzelius,  with 
which  my  own  observations  correspond  (Phil.  Trans.  1833),  14.15  is  a  better 
estimate.  The  compounds  of  nitrogen  treated  of  in  this  section  are  the 
following,  exclusive  of  atmospheric  air,  which  is  regarded  as  a  mechanical 
mixture : — 


By  Volume. 
Nit.        Oxy. 
Nitrous  oxide         100    .      50 
Nitric  oxide            100     .    100 
Hyponitrous  acid    100     .     150 
Nitrous  acid           100     .    200 

By  Weight. 
Nit.       Oxy.     Equiv.      Symbols. 
14.15+   8  =  22.15    N  +  O  or  N. 
14.15  +  16  =  30.15    N+2OorN. 
14.15  +  24  =  38.15     N  +  3O  or  N. 
14.15  +  32  =  46.15     N  +  4O  or  N." 

Nitric  acid  100    .    250         14.15  +  40  =  54.15    N+5Oor¥. 

THE  ATMOSPHERE. 

The  earth  is  every  where  surrounded  by  a  mass  of  gaseous  matter  called 
the  atmosphere,  which  is  preserved  at  its  surface  by  the  force  of  gravity, 
and  revolves  together  with  it  around  the  sun.  It  is  colourless  and  invisible, 
excites  neither  taste  nor  smell  when  pure,  and  is  not  sensible  to  the  touch 
unless  when  it  is  in  motion.  It  possesses  the  physical  properties  of  elastic 
fluids  in  a  high  degree.  Its  specific  gravity  is  unity,  being  the  standard 
with  which  the  density  of  all  gaseous  substances  is  compared.  It  is  815 
times  lighter  than  water,  and  nearly  11065  times  lighter  than  mercury. 
The  knowledge  of  its  exact  weight  is  an  essential  element  in  many  physi- 
cal and  chemical  researches,  and  has  been  lately  determined  with  very  great 
care  by  Dr.  Prout.  According  to  his  observations  100  cubic  inches  of  pure 
and  dry  atmospheric  air,  at  60°  F.  and  30  B.,  weigh  31.0117  grains. 

The  pressure  of  the  atmosphere  was  first  noticed  early  in  the  seventeenth 
century  by  Galileo,  and  was  afterwards  demonstrated  by  his  pupil  Torricelli, 
to  whom  science  is  indebted  for  the  invention  of  the  barometer.  Its  pres- 


1 68  NITROGEN. 

sure  at  the  level  of  the  sea  is  equal  to  a  weight  of  about  15  pounds  on  every 
square  inch  of  surface,  and  is  capable  of  supporting  a  column  of  water  34 
feet  high,  and  one  of  mercury  of  30  inches  ;  that  is,  a  column  of  mercury 
one  inch  square  and  30  inches  long  has  the  same  weight  (nearly  15  pounds) 
as  a  column  of  water  of  equal  base  and  34  feet  long,  and  as  a  column  of  air 
of  equal  base,  reaching  from  the  level  of  the  sea  to  the  extreme  limit  of  the 
atmosphere.  By  the  use  of  the  barometer  it  was  discovered  that  the  atmo- 
spheric pressure  is  variable.  It  varies  according  to  the  elevation  above  the 
level  of  the  sea,  and  on  this  principle  the  height  of  mountains  is  estimated. 
Supposing  the  density  of  the  atmosphere  to  be  uniform,  a  fall  of  one  inch  in 
the  barometer  would  correspond  to  11065  inches,  or  922  feet  of  air;  but  in 
order  to  make  the  calculation  with  accuracy,  allowance  must  be  made  for 
the  increasing  rarity  of  the  air,  and  for  various  other  circumstances  which 
are  detailed  in  works  on  meteorology.  (DanielPs  Meteorological  Essays,  2d 
edit.  376.)  From  causes  at  present  not  understood,  the  pressure  varies  like- 
wise at  the  same  place.  On  this  depends  the  indications  of  the  barometer 
as  a  weather-glass ;  for  observation  has  fully  proved,  that  the  weather  is 
commonly  fair  and  calm  when  the  barometer  is  high,  and  usually  wet  and 
stormy  when  the  mercury  falls. 

Atmospheric  air  is  highly  compressible  and  elastic,  so  that  its  particles 
admit  of  being  approximated  to  a  great  extent  by  compression,  and  expand 
to  an  extreme  degree  of  rarity,  when  the  tendency  of  its  particles  to  separate 
is  not  restrained  by  external  force.  It  has  been  found  experimentally  that 
the  volume  of  air  and  all  other  gaseous  fluids,  so  long  as  they  retain  the 
elastic  state,  is  inversely  as  the  pressure  to  which  they  are  exposed.  Thus  a 
portion  of  air  whiah  occupies  100  measures  when  compressed  by  a  force  of 
one  pound,  will  be  diminished  to  50  measures  when  the  pressure  is  doubled, 
and  will  expand  to  200  measures  when  the  compression  is  equal  to  half  a 
pound.  This  law  was  first  demonstrated  in  1662  by  the  celebrated  Boyle, 
and  a  second  demonstration  of  it  was  given  some  years  afterwards  by  the 
French  philosopher  M.  Mariotte,  apparently  without  being  aware  that  the 
discovery  had  been  previously  made  in  England.  It  is  hence  frequently 
called  the  law  of  Mariotte.  Till  lately  it  had  not  been  verified  for  very 
great  pressures;  but  from  the  experiments  of  Oersted  in  1825,  who  extended 
his  observations  to  air  compressed  by  a  force  equal  to  110  atmospheres,  it 
may  be  inferred  to  be  quite  general,  except  when  the  gaseous  matter  as- 
sumes the  liquid  form.  (Edinburgh  Journal  of  Science,  iv.  224.)  It  has,  in- 
deed, been  recently  stated  by  M.  Despretz  that  the  easily  condensible  gases 
vary  from  this  law,  diminishing  under  increase  of  pressure  much  more 
rapidly  than  atmospheric  air ;  but  the  details  of  his  experiments  have  not,  I 
believe,  been  published.*  (An.  de  Ch.  et  de  Ph.  xxxiv.  335  and  433.)  At 
what  pressure  air  becomes  liquid  is  uncertain,  since  all  attempts  to  condense 
it  have  hitherto  been  unsuccessful. 

The  extreme  compressibility  and  elasticity  of  the  air  account  for  the  fa- 
cility with  which  it  is  set  in  motion,  and  the  velocity  with  which  it  is  capa- 
ble of  moving.  It  is  subject  to  the  laws  which  characterize  elastic  fluids  in 
general.  It  presses,  therefore,  equally  on  every  sitie ;  and  when  some  parts 
of  it  become  lighter  than  the  surrounding  portions,  the  denser  particles  rush 
rapidly  into  their  place  and  force  the  more  rarefied  ones  to  ascend.  The 
motion  of  air  gives  rise  to  various  familiar  phenomena.  A  stream  or  cur- 
rent of  air  is  wind,  and  an  undulating  vibration  excites  the  sensation  of 
sound. 

The  atmosphere  is  not  of  equal  density  at  all  its  parts.  This  is  obvious 
from  the  consideration,  that  those  portions  which  are  next  the  earth  sustain 
the  whole  pressure  of  the  atmosphere,  while  the  higher  strata  bear  only  a 
part.  The  atmospheric  column  diminishes  in  length  as  the  distance  from 
the  earth's  surface  increases ;  and,  consequently,  the  greater  the  elevation, 
the  lighter  must  be  the  air.  It  is  not  known  to  what  height  the  atmo- 

*  See  note,  page  53. — Ed. 


NITROGEN.  169 

sphere  extends.  From  calculations  founded  on  the  phenomena  of  refraction, 
its  height  is  supposed  to  be  about  45  miles ;  and  Dr.  Wollaston  estimated, 
from  the  law  of  expansion  of  gases,  that  it  must  extend  to  at  least  40  miles 
with  properties  unimpaired  by  rarefaction.  In  speculating  on  its  extent  be- 
yond that  distance,  it  becomes  a  question  whether  the  atmosphere  is  or  is 
not  limited  to  the  earth.  This  subject  was  discussed  with  his  usual  sagacity 
by  the  late  Dr.  Wollaston,  in  an  essay  on  the  Finite  Extent  of  the  Atmo- 
sphere, published  in  the  Philosophical  Transactions  for  1822.  On  the  sup- 
position that  the  atmosphere  is  unlimited,  it  would  pervade  all  space,  and 
accumulate  about  the  sun,  moon,  and  planets,  forming  around  each  an  at- 
mosphere, the  density  of  which  would  depend  on  their  respective  forces  of 
attraction.  Now  Dr.  Wollaston  inferred  from  astronomical  observations 
made  by  himself  and  Captain  Kater,  that  there  is  no  solar  atmosphere; 
and  the  observations  of  other  astronomers  appear  to  justify  the  same  infe- 
rence with  respect  to  the  planet  Jupiter.  If  the  accuracy  of  these  conclu- 
sions be  admitted,  it  follows  that  our  atmosphere  is  confined  to  the  earth ; 
and  it  may  next  be  asked,  by  what  means  is  its  extent  limited  ?  Dr.  Wol- 
laston accounted  for  it  by  supposing  the  air,  after  attaining  a  certain  degree 
of  rarefaction,  to  possess  such  feeble  elasticity,  that  the  tendency  of  its  par- 
ticles to  separate  further  from  each  other  is  counteracted  by  gravity.  The 
unknown  height  at  which  this  equilibrium  between  the  two  forces  of  elasti- 
city and  gravitation  takes  place,  is  the  extreme  limit  of  the  atmosphere. 

The  loss  of  elasticity  may  be  ascribed  to  two  powerful  and  concurring 
causes;  namely,  to  the  distance  between  the  particles  of  air  when  highly  rare- 
fied, and  to  the  extreme  cold  which  prevails  in  the  higher  strata  of  the  at- 
mosphere. 

The  temperature  of  the  atmosphere  varies  with  its  elevation.  Gaseous 
fluids  permit  radiant  matter  to  pass  freely  through  them  without  any  ab- 
sorption, and,  therefore,  without  their  temperature  being  influenced  by  its 
passage.  The  atmosphere  is  not  heated  by  transmitting  the  rays  of  the 
sun,  but  receives  its  heat  solely  from  the  earth,  and  chiefly  by  actual  con- 
tact; so  that  its  temperature  becomes  progressively  lower,  as  the  distance 
from  the  general  mass  of  the  earth  increases.  Another  circumstance  which 
contributes  to  the  same  effect,  is  the  increasing  tenuity  of  the  atmosphere ; 
for  the  temperature  of  rarefied  air  is  less  raised  by  a  given  quantity  of  heat, 
than  that  of  the  same  portion  of  air  when  compressed,  owing  to  its  specific 
heat  being  greater  in  the  former  state  than  in  the  latter.  From  the  joint  in- 
fluence of  both  these  causes  it  is  found  that,  in  ascending  into  the  atmo- 
sphere, the  temperature  diminishes  at  the  rate  of  one  degree  for  about  every 
352  feet.  The  rate  of  decrease  is  probably  much  slower  at  considerable 
distances  from  the  earth  ;  but  still  there  is  no  reason  to  doubt  that  the  tem- 
perature continues  to  decrease  with  the  increasing  elevation.  There  must 
consequently  in  every  latitude  be  a  point,  where  the  thermometer  never 
rises  above  32°,  and  where  ice  is  never  liquefied.  This  point  varies  with 
the  latitude,  being  highest  within  the  tropics  and  descending  gradually  as 
we  advance  towards  the  poles.  The  following  table,  from  the  Supplement 
to  the  Encyclopedia  Britannica,  page  190,  article  Climate,  shows  the  point 
of  perpetual  ice  corresponding  to  different  latitudes. 

English  feet  English  feet 

Latitude.                         in  height.  Latitude.                         in  height. 

0°            .            .        15,207  45°            .            .         7,671 

5°       .            .              15,095  50°  .             .               6,334 

10°            .            .       14,764  55°            .            .         5,034 

15°      .            .             14,220  60°  .            .               3,818 

20°            .            .        13,478  65°            .            .         2,722 

25°      .            .             12,557  70°  .            .               1,778 

30°            .            .        11,484  75°            .            .         1,016 

35°       .            .              10,287  80°  T           .                  457 

40°            .             .         9,001  85°            •             .            117 

15 


170  WTROGKtf, 

Air  was  one  of  the  four  elements  of  the  ancient  philosophers,  and  theif 
opinion  of  its  nature  prevailed  generally,  till  its  accuracy  was  rendered  ques- 
tionable by  the  experiments  of  Boyle,  Hooke,  and  Mayow,  The  discovery  of 
oxygen  gas  in  1774  paved  the  way  to  the  knowledge  of  its  real  composition^ 
which  was  discovered  about  the  same  time  by  Scheele  and  Lavoisier,  The 
former  exposed  some  atmospheric  air  to  a  solution  of  sulphuret  of  potassium, 
which  gradually  absorbed  the  whole  of  the  oxygen.  Lavoisier  effected  the 
same  object  by  the  combustion  of  iron  wire  and  phosphorus. 

The  earlier  analyses  of  the  air  did  not  agree  very  well  with  each  other. 
According  to  the  researches  of  Lavoisier,  it  is  composed  of  27  measures  of 
oxygen  and  73  of  nitrogen.  The  analysis  of  Scheele  gave  a  somewhat 
higher  proportion  of  oxygen.  Priestley  found  that  the  quantity  of  oxygen 
varies  from  20  to  25  per  cent;  and  Cavendish  estimated  it  only  at  20.  These 
discrepancies  must  have  arisen  from  imperfections  in  the  mode  of  analysis ; 
for  the  proportion  of  oxygen  has  been  found  by  subsequent  experiments  to 
be  almost,  if  not  exactly,  that  which  was  stated  by  Cavendish.  The  results  of 
Scheele  and  Priestley  are  clearly  referable  to  this  cause.  It  is  now  known 
that  the  processes  they  employed  cannot  be  relied  on,  unless  certain  precau- 
tions are  taken  of  which  those  chemists  were  ignorant.  Recently  boiled 
water  absorbs  nitrogen  ;  and,  consequently,  if  sulphuret  of  potassium  be 
dissolved  in  that  liquid  by  the  aid  of  heat,  the  solution,  when  agitated  with 
air,  takes  up  a  portion  of  nitrogen,  and  thereby  renders  the  apparent  absorp- 
tion of  oxygen  too  great.  This  inconvenience  may  be  avoided  by  dissolving 
the  sulphuret  in  cold  unboiled  water.  The  binoxide  of  nitrogen,  employed 
by  Priestley,  removes  all  the  oxygen  in  the  course  of  a  few  seconds ;  but  for 
reasons  which  will  soon  be  mentioned,  its  indications  are  very  apt  to  be  fal- 
lacious. The  combustion  of  phosphorus,  as  well  as  the  gradual  oxidation  of 
that  substance,  acts  in  a  very  uniform  manner,  and  removes  the  whole  of  the 
oxygen  completely.  The  residual  nitrogen  contains  a  little  of  the  vapour  of 
phosphorus,  which  increases  the  bulk  of  that  gas  by  l-40th,  for  which  an  al- 
lowance must  be  made  in  estimating  the  real  quantity  of  nitrogen. 

Since  chemists  have  learned  the  precautions  to  be  taken  in  the  analysis  of 
the  air,  a  close  correspondence  has  been  observed  in  the  results  of  their  ex- 
periments upon  it.  The  researches  of  Davy,  Dalton,  Gay-Lussac,  Thomson, 
and  others,  leave  no  doubt  that  100  measures  of  pure  atmospheric  air  con- 
sist of  20  or  21  volumes  of  oxygen,  and  80  or  79  of  nitrogen.  The  most  ap- 
proved mode  of  analysis  consists  in  mixing  with  the  air,  a  quantity  of  hydro- 
gen sufficient  to  convert  all  the  oxygen  present  into  water,  and  kindling  the 
mixture  by  the  electric  spark.  The  combination  may  also  be  effected  with- 
out detonation' by  means  of  spongy  platinum.  Water  is  formed  and  is  con- 
densed, and  since  that  liquid  is  composed  of  one  volume  of  oxygen  and  two 
of  hydrogen,  one  third  of  the  diminution  must  give  the  exact  quantity  of 
oxygen.  This  process  is  so  easy  of  execution,  and  so  uniform  in  its  indica- 
tions, that  it  is  now  employed  nearly  to  the  total  exclusion  of  all  others.* 

*  The  best  analyses  of  atmospheric  air  correspond  so  nearly  with  the  pro- 
portions of  two  volumes  of  nitrogen  to  half  a  volume  of  oxygen,  that  it 
seems  probable  that  these  proportions  (which  correspond  at  the  same  time 
with  the  theory  of  volumes)  would  be  obtained  exactly,  if  our  experiments 
could  be  performed  with  rigid  accuracy.  On  the  assumption  that  these  are 
the  true  proportions,  the  specific  gravity  of  oxygen  would  be  1.10192,  and  that 
of  nitrogen  0.97452;  numbers  which  correspond  very  nearly  with  those  con- 
tained in  the  table,  page  146,  and  with  the  experimental  results  of  Berzelius 
and  Dulong.  The  composition  of  atmospheric  air,  when  stated  in  volumes, 
gives  the  oxygen  at  20  per  cent.,  as  mentioned  by  Dr.  Turner ;  and  yet  the 
usual  analyses  make  it  21  per  cent.  This  discrepancy  will  probably  disap- 
pear when  the  analysis  is  performed  with  more  accuracy.  Dr.  Hare  found 
that  the  average  of  a  great  number  of  analyses  of  atmospheric  air  performed 
by  explosion  'with  hydrogen,  by  means  of  his  very  accurate  eudiometers, 
gave  the  proportion  of  oxygen  at  20.66  per  cent.,  which  approaches  very 
nearly  to  the  quantity  indicated  by  the  theory  of  volumes.— Ed. 


NITROGEN,  171 

Such  is  the  constitution  of  pure  atmospheric  air.  But  the  atmosphere  is 
never  absolutely  pure;  for  it  always  contains  a  certain  variable  quantity  of 
carbonic  acid  and  watery  vapour,  besides  the  odoriferous  matter  of  flowers 
and  other  volatile  substances,  which  are  also  frequently  present.  Saussure 
found  carbonic  acid  in  air  collected  at  the  top  of  Mont-Blanc ;  and  it  exists 
at  all  altitudes  which  have  been  hitherto  attained.  Saussure  in  a  recent 
essay,  states  the  proportion  of  this  gas  to  vary  at  the  same  place  within 
short  intervals  of  time.  It  is  greater  in  summer  than  in  winter ;  and  from 
observations  made  during  spring,  summer,  and  autumn,  in  the  open  fields 
and  in  calm  weather,  its  proportion  is  inferred  to  be  always  greater  at  night 
than  in  the  day,  and  to  be  more  abundant  in  gloomy  than  in  bright  weather. 
A  very  moist  state  of  the  ground,  as  after  much  rain,  diminishes  the  quan- 
tity of  carbonic  acid,  apparently  by  direct  absorption.  It  is  rather  more 
abundant  in  elevated  situations,  as  on  the  summits  of  high  mountains,  than 
in  the  plains ;  but  its  quantity  is  there  nearly  the  same  in  day  and  night,  in 
wet  and  dry  weather,  because  the  higher  strata  of  the  air  are  less  influenced 
by  vegetation,  and  the  state  of  the  soil.  Saussure  thinks  also  that  a  highly 
electrical  state  of  the  atmosphere  tends  to  diminish  the  quantity  of  carbonic 
acid.  He  found  that  10,000  parts  of  air  contain  4.9  of  carbonic  acid  as  a 
mean,  6.2'  as  a  maximum,  and  3.7  as  a  minimum*  (An.  de  Ch.  et  de  Ph. 
xxxviii.  411.  xliv.  5.) 

The  chief  chemical  properties  of  the  atmosphere  are  owing  to  the  presence 
of  oxygen  gas.  Air  from  which  this  principle  has  been  withdrawn  is  nearly 
inert.  It  can  no  longer  support  respiration  and  combustion,  and  metals  are 
not  oxidized  by  being  heated  in  it.  Most  of  the  spontaneous  changes  which 
mineral  and  dead  organized  matters  undergo,  are  owing  to  the  powerful 
affinities  of  oxygen.  The  uses  of  the  nitrogen  are  in  a  great  measure  un- 
known. It  was  supposed  to  act  as  a  mere  diluent  to  the  oxygen  ;  but  it 
most  probably  serves  some  useful  purpose  in  the  economy  of  animals,  the 
exact  nature  of  which  has  not  been  discovered. 

The  knowledge  of  the  composition  of  the  air,  and  of  the  importance  of 
oxygen  to  the  life  of  animals,  naturally  gave  rise  to  the  notion  that  the 
healthiness  of  the  air,  at  different  times,  and  in  different  places,  depends  on 
the  relative  quantity  of  this  gas.  It  was,  therefore,  supposed  that  the  purity 
of  the  atmosphere,  or  its  fitness  for  communicating  health  and  vigour,  might 
be  discovered  by  determining  the  proportion  of  oxygen ;  and  hence  the  ori- 
gin of  the  term  Eudiometer,  which  was  applied  to  the  apparatus  for  analyz- 
ing the  air.  But  this  opinion,  though  at  first  supported  by  the  discordant 
results  of  the  earlier  analysts,  was  soon  proved  to  be  fallacious.  It  appears, 
on  the  contrary,  that  the  composition  of  the  air  is  not  only  constant  in  the 
same  place,  but  is  the  same  in  all  regions  of  the  earth,  and  at  all  altitudes. 
Air  collected  at  the  summit  of  the  highest  mountains,  such  as  Mont-Blanc 
and  Chimborazo,  contains  the  same  proportion  of  oxygen  as  that  of  the  low- 
est valleys.  The  air  of  Egypt  was  found  by  Berthollet  to  be  similar  to  that 
of  France.  The  air  which  Gay-Lussac  brought  from  an  altitude  of  21,735 
feut  above  the  earth,  had  the  same  composition  as  that  collected  at  a  short 
distance  from  its  surface.  Even  the  miasmata  of  marshes,  and  the  effluvia 
of  infected  places,  owe  their  noxious  qualities  to  some  principle  of  too  subtile 
a  nature  to  be  detected  by  chemical  means,  and  not  to  a  deficiency  of  oxy- 
gen. Seguin  examined  the  infectious  atmosphere  of  an  hospital,  the  odour 
of  which  was  almost  intolerable,  arid  could  discover  no  appreciable  deficiency 
of  oxygen,  or  other  peculiarity  of  composition. 

The  question  has  been  much'discussed  whether  the  oxygen  and  nitrogen 
gases  of  the  atmosphere  are  simply  intermixed,  or  chemically  combined 
with  each  other.  Appearances  are  at  first  view  greatly  in  favour  of  the  lat- 
ter opinion.  Oxygen  and  nitrogen  gases  differ  in  density,  and,  therefore,  it 
might  be  expected,  were  they  merely  mixed  together,  that  the  oxygen  as  the 
heavier  gas  ought,  in  obedience  to  the  force  of  gravity,  to  collect  in  the 
lower  regions  of  the  air ;  while  the  nitrogen  should  have  a  tendency  to  oc- 
cupy the  higher,  Bqt  this  has  nowhere  been  observed.  If  air  be  confined  in 


172  NITROGEN. 

a  long  tube,  preserved  at  perfect  rest,  its  upper  part  will  contain  just  as  much 
oxygen  as  the  lower,  even  after  an  interval  of  many  months ;  nay,  if  the 
lower  part  of  it  be  filled  with  oxygen,  and  the  upper  with  nitrogen,  these 
gases  will  be  found  in  the  course  of  a  few  hours  to  have  mixed  intimately 
with  one  another.  The  constituents  of  the  air  are,  also,  in  the  exact  propor- 
tion for  combining.  By  measure  they  are  nearly  in  the  simple  ratio  of  1  to 
4,  which  agrees  with  the  law  of  combination  by  volume ;  and  by  weight  they 
are  as  8  to  28.3,  which  corresponds  to  one  equivalent  of  oxygen  and  two  of 
nitrogen. 

Strong  as  are  these  arguments  in  favour  of  the  chemical  theory,  it  is 
nevertheless  liable  to  objections  which  appear  insuperable.  The  atmosphere 
possesses  all  the  characters  that  should  arise  from  a  mechanical  mixture. 
There  is  not  as  in  all  other  cases  of  chemical  union,  any  change  in  the  bulk, 
form,  or  other  qualities  of  its  elements.  The  nitrogen  manifests  no  attraction 
for  the  oxygen.  All  bodies  which  have  an  affinity  for  oxygen  abstract  it  from 
the  atmosphere  with  as  much  facility  as  if  the  nitrogen  were  absent  alto- 
gether. Even  water  effects  this  separation;  for  the  air  which  is  expelled 
from  rain  water  by  ebullition,  contains  more  than  21  per  cent,  of  oxygen. 
When  oxygen  and  nitrogen  gases  are  mixed  together  in  the  ratio  of  1  to  4, 
the  mixture  occupies  precisely  5  volumes,  and  has  every  property  of  pure 
atmospheric  air.  The  refractive  power  of  the  atmosphere  is  precisely  such 
as  a  mixture  of  oxygen'  and  nitrogen  gases  ought  to  possess,  and  different 
from  what  would  be  expected  were  its  elements  chemically  united.  (Edin- 
burgh Journal  of  Science,  iv.  211.) 

Since  the  elements  of  the  air  cannot  be  regarded  as  in  a  state  of  actual 
combination,  it  is  necessary  to  account  for  the  steadiness  of  their  proportion 
on  some  other  principle.  It  has  been  conceived  that  the  affinity  of  oxygen 
and  nitrogen  for  one  another,  though  insufficient  to  cause  their  combination 
when  mixed  together  at  ordinary  temperatures,  might  still  operate  in  such  a 
manner  as  to  prevent  their  separation  ;  that  a  certain  degree  of  attraction  is 
even  then  exerted  between  them,  which  is  able  to  counteract  the  tendency  .of 
gravity.  An  opinion  of  this  kind  was  advanced  by  Berthollet,  in  his 
Statique  Ckimique,  and  defended  by  the  late  Dr.  Murray.  This  doctrine, 
however,  is  not  satisfactory.  It  is,  indeed,  quite  conceivable  that  oxygen 
and  nitrogen  may  attract  each  other  in  the  way  supposed  ;  and  it  may  be 
admitted  that  this  supposition  explains  why  these  two  gases  continue  in  a 
state  of  perfect  mixture.  But  still  the  explanation  is  unsatisfactory  ;  and 
for  the  following  reason  : — Dalton  took  two  cylindrical  vessels,  one  of  which 
was  filled  with  carbonic  acid,  the  other  with  hydrogen  gas ;  the  latter  was 
placed  perpendicularly  over  the  other,  and  a  communication  was  established 
between  them.  In  the  course  of  a  few  hours  hydrogen  was  detected  in  the 
lower  vessel,  and  carbonic  acid  gas  in  the  upper.  If  the  upper  vessel  be 
filled  with  oxygen,  nitrogen,  or  any  other  gas,  the  same  phenomena  will 
ensue ;  the  gases  will  be  'found,  after  a  short  interval,  to  be  in  a  state  of 
mixture,  and  will  at  last  be  distributed  equally  through  both  vessels.  Now 
this  result  cannot  be  ascribed  to  the  action  of  affinity.  Carbonic  acid  cannot 
be  made  to  unite  either  with  hydrogen,  oxygen,  or  nitrogen ;  and,  therefore, 
it  is  gratuitous  to  assert  that  it  •  has  an  affinity  for  them.  Some  other  power 
must  be  in  operation,  capable  of  producing  the  mixture  of  gases  with  each 
other,  independently  of  chemical  attraction;  and  if  this  power  can  cause 
carbonic  acid  to  ascend  through  a  gas  which  is  twenty-two  times  lighter  than 
itself,  it  will  surely  explain  why  oxygen  and  nitrogen  gases,  the  densities  of 
which  differ  so  little,  should  be  intermingled  in  the  atmosphere. 

The  explanation  which  Dalton  has  given  of  these  phenomena  is  founded 
on  the  assumption,  that  the  particles  of  one  gas,  though  highly  repulsive  to 
each  other,  do  not  repel  those  of  a  different  kind.  It  follows  from  this  sup- 
position, that  one  gas  acts  as  a  vacuum  with  respect  to  another;  and, 
therefore,  if  a  vessel  full  of  carbonic  acid  be  made  to  communicate  with 
another  of  hydrogen,  the  particles  of  each  gas  insinuate  themselves  between 
the  particles  of  the  other,  till  they  are  equally  diffused  through  both  vessels. 
The  particles  of  the  carbonic  acid  do  not  indeed  fill  the  space  occupied  by 


NITIIOGEN.  173 

the  hydrogen  with  the  same  velocity  as  if  it  were  a  real  vacuum  ;  because 
the  particles  of  the  hydrogen  afford  a  mechanical  impediment  to  their  pro- 
gress. The  ultimate  effect,  however,  is  the  same  as  if  the  vessel  of  hydrogen 
had  been  a  vacuum.  (Manchester  Memoirs,  vol.  v.) 

Though  it  would  not  be  difficult  to  find  objections  to  this  hypothesis,  it 
has  the  merit  of  being  applicable  to  every  possible  case  ;  which  cannot,  I 
conceive,  be  admitted  of  the  other.  It  accounts  not  only  for  the  mixture  of 
gases,  but  for  the  equable  diffusion  of  vapours  through  gases,  and  through 
each  other.  This  view  receives  support  from  the  experiments  of  Mr.  Gra- 
ham of  Glasgow  on  the  diffusion  of  gases.  (Phil.  Trans.  Edin.  1831.) 
When  a  gas  is  contained  in  a  glass  bell  jar  which  has  a  crack  or  fissure  in 
its  sides,  or  communicates  with  the  air  by  a  narrow  aperture,  or  is  contained 
in  a  porous  vessel,  the  gas  gradually  diffuses  itself  into  the  air,  and  air  into 
the  gas,  each  passing  through  the  chink  or  other  small  opening  at  the  same 
time,  but  in  opposite  directions.  On  ascertaining,  after  an  interval,  how 
much  gas  has  escaped  from,  and  how  much  air  entered  into,  the  vessel,  it 
will  be  found  that  the  respective  quantities  depend  on  the  relative  densities  ; 
and  the  same  principle  of  intermixture  equally  applies  when  the  apertures  of 
communication  are  large,  as  when  they  are  small.  Each  gas  has  a  dif- 
fusiveness peculiar  to  itself,  and  which  is  greater  as  its  density  is  less.  Mr. 
Graham  determined  the  rate  of  diffusion  for  different  gases  by  means  of 
what  he  calls  a  diffusion  tube,  which  is  simply  a  graduated  tube  closed  at 
one  end  by  plaster  of  Paris,  a  substance,  when  moderately  dry,  possessed  of 
the  requisite  porosity.  He  has  been  led  by  direct  experiment  to  the  follow, 
ing  conclusion,  —  that  "the  diffusion  or  spontaneous  intermixture  of  two 
gases  in  contact,  is  effected  by  an  interchange  in  position  of  indefinitely 
small  volumes  of  the  gases,  which  volumes  are  not  necessarily  of  equal  mag- 
nitude, being,  in  the  case  of  each  gas,  inversely  proportional  to  the  square 
root  of  the  density  of  that  gas."  The  relative  diffusiveness  of  each  gas  may 
hence  be  represented  by  the  reciprocal  of  the  square  root  of  its  density.  Thus, 
the  density  of  air  being  1,  its  diffusiveness  is  1  also;  that  of  hydrogen  is 


==3'807!  that  °f  °^en      =    =°-9524; 


and  that  of  nitrogen       -         =  1.014  ; 

so  that  the  relative  power  of  diffusion  of  air,  hydrogen,  oxygen,  and  nitro- 
gen, is  indicated  by  the  numbers,  1,  3.807,  0^9524,  and  1.014.  In  gases 
which  are  very  sparingly  soluble  in  water,  and  hence  not  condensible  by 
the  moisture  of  the  plaster  of  Paris,  the  results  of  experiment  coincide  so 
exactly  with  the  law,  that  Mr.  Graham  suggests  its  application  to  deter- 
mine the  density  of  gases.  Thus  if  g  denote  the  diffusiveness  of  a  gas,  as 
found  by  careful  experiment,  and  d  its  density  ;  then  since,  by  the  law  oi" 
diffusion, 


It  is  obvious  that  these  phenomena  cannot  be  referred  to  any  chemical 
principle,  but  are  dependent  on  the  mechanical  constitution  of  gases.  It  has 
been  lately  shown  in  a  very  clever  paper  by  Mr.  Thomas  Thomson  of  Cli- 
theroe  (Phil.  Mag.  3d  series,  iv.  321),  that  the  law  of  gaseous  diffusion  is 
included  under  Dalton's  hypothesis,  that  one  gas  is  as  a  vacuum  with  re- 
spect to  another.  For  it  is  a  law  deduced  from  the  physical  properties  of 
gaseous  bodies,  that  the  velocities  of  gases  flowing  under  like  circumstances 
into  a  vacuum  are  inversely  as  the  square  roots  of  their  densities,  which  is 
precisely  the  same  law  that  regulates  their  flow  into  each  other.* 

*  As  connected  with  this  subject,  the  reader  is  referred  to  an  important 
paper  on  the  "  Penetrativeness  of  Fluids,"  by  Dr.  J.  K.  Mitchell,  of  Phila- 
delphia, published  in  the  American  Journal  of  Medical  Sciences,  vol.  vii, 
p.  3G.—Ed.  15  * 


174  NITROGEN. 

There  is  still  one  circumstance  for  consideration  respecting  the  atmo- 
sphere. Since  oxygen  is  necessary  to  combustion,  to  the  respiration  of  ani- 
mals, and  to  various  other  natural  operations,  by  all  of  which  that  gas  is 
withdrawn  from  the  air,  it  is  obvious  that  its  quantity  would  gradually  dimi- 
nish, unless  the  tendency  of  those  causes  were  counteracted  by  some  com- 
pensating  process.  To  all  appearance  there  does  exist  some  source  of  com- 
pensation ;  for  chemists  have  not  hitherto  noticed  any  change  in  the  consti- 
tution of  the  atmosphere.  The  only  source  by  which  oxygen  is  known  to 
be  supplied,  is  the  action  of  growing  vegetables.  A  healthy  plant  absorbs 
carbonic  acid  during  the  day,  appropriates  the  carbonaceous  part  of  that  gas 
to  its  own  wants,  and  evolves  the  oxygen  with  which  it  was  combined. 
During  the  night,  indeed,  an  opposite  effect  is  produced.  Oxygen  gas  then 
disappears,  and  carbonic  acid  is  eliminated  ;  but  it  follows  from  the  experi- 
ments of  Priestley,  Davy,  and  Dr.  Daubeny,  that  plants  during  24  hours 
yield  more  oxygen  than  they  consume.  Whether  living  vegetables  make  a 
full  compensation  for  the  oxygen  removed  from  the  air  by  the  processes 
above  mentioned  is  uncertain.  From  the  great  extent  of  the  atmosphere, 
and  the  continual  agitation  to  which  its  different  parts  are  subject  by  the 
action  of  winds,  the  effects  of  any  deteriorating  process  would  be  very  gra- 
dual, and  a  change  in  the  proportion  of  its  elements  could  be  perceived  only 
by  observations  made  at  very  distant  intervals. 

PROTOXIDE  OF  NITROGEN.  ",^" 

This  gas  was  discovered  by  Priestley,  who  gave  it  the  name  of  depJilogis- 
ticated  nitrous  air.  Sir  H.  Davy  called  it  nitrous  oxide.  According  to  the 
principles  of  chemical  nomenclature,  its  proper  appellation  is  protoxide  of 
nitrogen.  It  may  be  formed  by  exposing  nitric  oxide  for  some  days  to  the 
action  of  iron  filings,  or  other  substances  which  have  a  strong  affinity  for 
oxygen,  when  the  nitric  oxide  loses  one-half  of  its  oxygen,  and  is  converted 
into  the  protoxide.  But  the  most  convenient  method  of  procuring  it  is  by 
means  of  nitrate  of  ammonia.  This  salt  is  prepared  by  neutralizing  with 
carbonate  of  ammonia  pure  nitric  acid  diluted  with  about  three  parts  of 
water,  and  concentrating  by  evaporation,  until  a  drop  of  the  liquid  let  fall  on 
a  cold  plate  becomes  a  firm  mass,  adding  a  little  ammonia  towards  the  close 
to  ensure  neutrality.  The  salt  after  cooling  is  broken  to  pieces,  introduced 
into  a  retort,  and  heated  by  a  lamp  or  pan  of  charcoal :  at  first,  below  400°, 
fusion  ensues;  and  as  the  heat  rises  to  480°  or  500°  rapid  decomposition 
sets  in,  which  continues  until  all  the  salt  disappears.  If  a  white  cloud  ap- 
pears within  the  retort,  due  to  some  of  the  salt  subliming  undecomposed,  the 
heat  should  be  checked. 

The  sole  products  of  this  operation,  when  carefully  conducted,  are  water 
and  protoxide  of  nitrogen.  The  nature  of  the  change  will  be  readily  under- 
stood by  comparing  the  composition  of  nitrate  of  ammonia  with  that  of  the 
products  derived  from  it.  These,  in  round  numbers,  are  as  follows : — 


Nitric  Acid.  Ammonia. 

Nitrogen  14  or  1  eq.  Nitrogen  14  or  1  eq. 

Oxygen    40  or  5  eq.  Hydrogen  3  or  3  eq. 

54  17 


Water.  Prot.  of  Nitrogen. 

Hyd.   3  or  3  eq.  Nit.  28  or  2  eq. 

Oxy.  24  or  3  eq.  Oxy.  16  or  2  eq. 

27  44 


The  same  expressed  in  symbols  is 

N+50;  N+3H;  |          3(H+O);  2(N+O). 

It  thus  appears  that  the  hydrogen  in  the  ammonia  takes  so  much  oxygen 
as  is  sufficient  for  forming  water,  and  the  residual  oxygen  converts  the  ni- 
trogen both  of  the  nitric  acid  and  of  the  ammonia  into  protoxide  of  nitrogen  : 
71  grains  of  the  salt  will  thus  yield  44  grains  of  protoxide  of  nitrogen  and 
£7  of  water. 

Protoxide  of  nitrogen  is  a  colourless  gas,  which  does  not  affect  the  blue 
vegetable  colours,  even  when  mixed  with  atmospheric  air.  Recently  boiled 


NITROGEN.  175 

water,  which  has  cooled  without  exposure  to  the  air,  absorbs  nearly  its  own 
bulk  of  it  at  60°  F.  and  gives  it  out  again  unchanged  by  boiling.  The  solu- 
tion, like  the  gas  itself,  has  a  faint  agreeable  odour  and  sweet  taste.  The  ac- 
tion of  water  upon  it  affords  a  ready  means  of  testing  its  purity;  removing 
it  readily  from  all  other  gases,  such  as  oxygen  and  nitrogen,  which  are 
sparingly  absorbed  by  that  liquid.  For  the  same  reason  it  cannot  be  pre- 
served over  cold  water ;  but  should  be  collected  either  over  hot  water  or 
mercury. 

Protoxide  of  nitrogen  is  a  supporter  of  combustion.  Most  substances 
burn  in  it  with  far  greater  energy  than  in  the  atmosphere.  When  a  recently 
extinguished  candle  with  a  very  red  wick  is  introduced  into  it,  the  flame  is 
instantly  restored.  Phosphorus,  if  previously  kindled,  burns  in  it  with  great 
brilliancy.  Sulphur,  when  burning  feebly,  is  extinguished  by  it;  but  if  im- 
mersed while  the  combustion  is  lively,  the  size  of  the  flame  is  considerably 
increased.  With  an  equal  bulk  of  hydrogen  it  forms  a  mixture  which  ex- 
plodes violently  by  the  electric  spark  or  by  flame.  In  all  these  cases,  the  pro- 
duct of  combustion  is  the  same  as  when  oxygen  gas  or  atmospheric  air  is 
used.  The  protoxide  is  decomposed  ;  the  combustible  matter  unites  with  its 
oxygen,  and  the  nitrogen  is  set  free.  Protoxide  of  nitrogen  suffers  decom- 
position when  a  succession  of  electric  sparks  is  passed  through  it,  and  a 
similar  effect  is  caused  by  conducting  it  through  a  porcelain  tube  heated  to 
incandescence.  It  is  resolved,  in  both  instances,  into  nitrogen,  oxygen,  and 
nitrous  acid. 

Sir  H.  Davy  discovered  that  protoxide  of  nitrogen  may  be  taken  into  the 
lungs  with  safety,  and  that  it  supports  respiration  for  a  few  minutes.  He 
breathed  nine  quarts  of  it,  contained  in  a  silk  bag,  for  three  minutes,  and 
twelve  quarts  for  rather  more  than  four  ;  but  no  quantity  could  enable  him  to 
bear  the  privation  of  atmospheric  air  for  a  longer  period.  Its  action  on  the 
system,  when  inspired,  is  very  remarkable.  A  few  deep  inspirations  are 
followed  by  most  agreeable  feelings  of  excitement,  similar  to  the  earlier 
stages  of  intoxication.  This  is  shown  by  a  strong  propensity  to  laughter, 
by  a  rapid  flow  of  vivid  ideas,  and  an  unusual  disposition  to  muscular  exer- 
tion. These  feelings,  however,  soon  subside;  and  the  person  returns  to  his 
usual  state  without  experiencing  the  languor  or  depression  which  so  univer- 
sally follows  intoxication  from  spirituous  liquors.  Its  effects,  however,  on 
different  persons  are  various;  and  in  individuals  of  a  plethoric  habit,  it 
sometimes  produces  giddiness,  headach,  and  other  disagreeable  symptoms. 
(Researches  on  the  Nitrous  Oxide.) 

Protoxide  of  nitrogen  was  analyzed  by  Sir  H.  Davy  by  means  of  hydro- 
gen gas.  He  mixed  39  measures  of  the  former  with  40  measures  of  hydro- 
gen, and  fired  the  mixture  by  the  electric  spark.  Water  was  formed ;  and 
the  residual  gas,  which  amounted  to  41  measures,  had  the  properties  of  pure 
nitrogen.  As  40  measures  of  hydrogen  require  20  of  oxygen  for  combus- 
tion, it  follows  that  39  volumes  of  the  protoxide  of  nitrogen  contain  41  of 
nitrogen  and  20  of  oxygen.  But  since  no  exception  has  hitherto  been  found 
to  Gay-Lussac's  law  of  gaseous  combination,  it  may  be  inferred  that  protoxide 
of  nitrogen  contains  its  own  volume  of  nitrogen  and  half  its  volume  of  oxygen. 
The  analysis  of  this  compound  by  Dr.  Henry,  (Annals  of  Phil.  viii.  299,  N.  S.) 
performed  by  means  of  carbonic  oxide  gas,  has  proved  beyond  a  doubt  that 
this  is  the  exact  proportion.  Now, 

100  cubic  inches  of  nitrogen  gas  weigh         .  30.1650  grains. 

50         do.  oxygen       ....         17.0936 

These  numbers  added  together  amount  to         .  47.2586 

which  must  be  the  weight  of  100  cubic  inches  of  the  protoxide;  and  Us  spe- 
cific gravity  is,  therefore,  1.5239.  Its  composition  by  weight  is  determined 
by  the  same  data,  being  17.0936  of  oxygen  to  30.1650  of  nitrogen,  or  as  8 
to  14.117,  nearly  the  number  already  stated.  (Page  167.) 


176  NITROGEN. 


BINOXIDE  OF  NITROGEN. 

This  compound  is  best  obtained  by  the  action  of  nitric  acid,  of  specific 
gravity  1.2,  on  metallic  copper.  Brisk  effervescence  takes  place  without  the 
aid  of  heat,  and  the  gas  may  be  collected  over  water  or  mercury.  The  cop- 
per gradually  disappears  during  the  process ;  the  liquid  acquires  a  beautiful 
blue  colour,  and  yields  on  evaporation  a  salt  which  is  composed  of  nitric 
acid  and  oxide  of  copper.  The  chemical  changes  that  occur  are  the  follow, 
ing. — One  portion  of  nitric  acid  suffers  decomposition :  part  of  its  oxygen 
oxidizes  the  copper ;  while  another  part  is  retained  by  the  nitrogen  of  the 
nitric  acid,  forming  binoxide  of  nitrogen.  The  oxide  of  copper  attaches 
itself  to  some  undecomposed  nitric  acid,  and  forms  the  blue  nitrate  of  cop- 
per. Many  other  metals  are  oxidized  by  nitric  acid,  with  disengagement  of 
a  similar  compound ;  but  none,  mercury  excepted,  yields  so  pure  a  gas  as 
copper. 

The  gas  derived  from  this  source  was  discovered  by  Dr.  Hales.  It  was 
first  carefully  studied  by  Priestley,  who  called  it  nitrous  air.  The  terms 
nitrous  gas  and  nitric  oxide  are  frequently  applied  to  it ;  but  binoxide  of  ni- 
trogen, as  indicative  of  its  nature,  is  the  most  suitable  appellation. 

Binoxide  of  nitrogen  is  a  colourless  gas.  When  mixed  with  atmospheric 
air,  or  any  gaseous  mixture  that  contains  oxygen  in  an  uncombined  state, 
dense,  suffocating,  acid  vapours,  of  a  red  or  orange  colour,  are  produced, 
called  nitrous  acid  vapours ;  which  are  copiously  absorbed  by  water,  and 
communicate  acidity  to  it.  This  character  serves  to  distinguish  the  binoxide 
from  every  other  substance,  and  affords  a  convenient  test  of  the  presence  of 
free  oxygen.  Though  it  gives  rise  to  an  acid  by  combining  with  oxygen, 
binoxide  of  nitrogen  itself  does  not  redden  the  blue  colour  of  vegetables ;  but 
for  this  experiment,  the  gas  must  be  previously  well  washed  with  water  to 
separate  all  traces  of  nitrous  acid.  Water  absorbs  the  binoxide  sparingly  ; 
100  measures  of  that  liquid,  cold  and  recently  boiled,  take  up  about  1 1  of 
the  gas. 

Very  few  inflammable  substances  burn  in  binoxide  of  nitrogen.  Burning 
sulphur  and  a  lighted  candle  are  instantly  extinguished  by  it.  Charcoal  and 
phosphorus,  however,  if  in  a  state  of  vivid  combustion  at  the  moment  of  be- 
ing immersed  in  it,  burn  with  increased  brilliancy.  The  product  of  the 
combustion  is  carbonic  acid  in  the  former  case,  and  metaphosphoric  acid  in 
the  latter,  nitrogen  being  separated  in  both  instances.  With  an  equal  bulk 
of  hydrogen,  it  forms  a  mixture  which  cannot  be  made  to  explode,  but  which 
is  kindled  by  contact  with  a  lighted  candle,  and  burns  rapidly  with  a  green- 
ish-white flame,  water  and  pure  nitrogen  gas  being  the  sole  products.  The 
action  of  freshly  ignited  spongy  platinum  on  a  mixture  of  hydrogen  and 
binoxide  of  nitrogen  gases  leads  to  the  slow  production  of  water  and  am- 
monia. 

Binoxide  of  nitrogen  is  quite  irrespirable,  exciting  strong  spasm  of  the 
glottis,  as  soon  as  an  attempt  is  made  to  inhale  it.  The  experiment,  how- 
ever, is  a  dangerous  one  ;  for  if  the  gas  did  reach  the  lungs,  it  would  there 
mix  with  atmospheric  air,  and  be  converted  into  nitrous  acid  vapours,  which 
are  highly  irritating  and  corrosive. 

Binoxide  of  nitrogen  is  partially  resolved  into  its  elements  by  being  passed 
through  red-hot  tubes.  A  succession  of  electric  sparks  has  a  similar  effect. 
It  is  converted  into  protoxide  of  nitrogen  by  substances  which  have  a  strong 
affinity  for  oxygen,  such  as  moist  iron  filings,  and  a  solution  of  sulphuret 
of  potassium.  Sir  H.  Davy  ascertained  its  composition  by  the  combustion 
of  charcoal.  (Elements  of  Chemical  Philosophy,  p.  200.)  Two  volumes  of 
the  binoxide  yielded  one  volume  of  nitrogen,  and  about  one  of  carbonic  acid; 
whence  it  was  inferred  to  consist  of  equal  measures  of  oxygen  and  nitrogen 
gases,  united  without  any  condensation.  Gay-Lussac,  in  his  essay  in  the 
Memoires  d'Arcueil,  proved  that  this  proportion  is  rigidly  exact.  He  decom- 
posed 100  measures  of  the  gas,  by  heating  potassium  in  it ;  when  50  raea- 


NITROGEN.  177 

sures  of  pure  nitrogen  were  left,  and  the  potassa  formed  corresponded  to  50 
measures  of  oxygen.  The  same  fact  has  been  proved  by  Dr.  Henry  (An.  of 
Phil.  N.  S.  viii.  299.)  Hence,  as 

50  cubic  inches  of  oxygen  gas  weigh 17.0936  grains. 

50          do.  nitrogen 15.0825 

100  cubic  inches  of  the  binoxide  must  weigh      .     .     32.1761 

Its  composition,  stated  at  page  167,  is  drawn  from  these  facts.  Its  density 
ought  to  be  1.0375,  which  closely  agrees  with  the  direct  experiments  of 
Davy,  Thomson,  and  Berard. 

From  the  invariable  formation  of  red-coloured  acid  vapours,  whenever 
binoxide  of  nitrogen  and  oxygen  are  mixed  together,  these  gases  detect  the 
presence  of  each  other  with  great  certainty;  and  since  the  product  is  wholly 
absorbed  by  water,  either  of  them  may  be  entirely  removed  from  any  gaseous 
mixture  by  adding  a  sufficient  quantity  of  the  other.  Priestley,  who  first 
observed  this  fact,  supposed  that  combination  takes  place  between  them  in 
one  proportion  only;  and  inferring,  on  this  supposition,  that  a  given  absorp- 
tion must  always  indicate  the  same  quantity  of  oxygen,  he  was  led  to  em- 
ploy  binoxide  of  nitrogen  in  eudiometry.  But  in  this  opinion  he  was  mis- 
taken. The  discordant  results  obtained  by  this  method,  soon  excited  suspi- 
cion of  their  accuracy ;  and  the  source  of  error  has  since  been  discovered  by 
the  researches  of  Dalton  and  Gay-Lussac.  It  appears  from  the  experiments 
of  Gay-Lussac,  and  his  results  do  not  differ  materially  from  those  of  Dalton, 
that  for  100  measures  of  oxygen,  400  of  the  binoxide  may  be  absorbed  as  a 
maximum,  and  133  as  a  minimum ;  and  that  between  these  extremes,  the 
quantity  of  the  binoxide,  corresponding  to  100  of  oxygen,  is  exceedingly  va- 
riable. It  does  not  follow  from  this,  that  oxygen  and  binoxide  of  nitrogen 
unite  in  every  proportion  within  these  limits.  The  true  explanation  is,  that 
the  mixture  of  these  gases  may  give  rise  to  three  compounds,  hyponitrous, 
nitrous,  and  nitric  acids;  and  that  either  may  be  formed  almost,  if  not  en- 
tirely, to  the  exclusion  of  the  others,  if  certain  precautions  are  adopted.  But 
in  the  usual  mode  of  operating,  two,  if  not  all,  are  generated  at  the  same 
time,  and  in  a  proportion  to  each  other  which  is  by  no  means  uniform.  The 
circumstances  that  influence  the  degree  of  absorption,  when  a  mixture  of 
oxygen  and  binoxide  of  nitrogen  is  made  over  water,  are  the  following  : — 
1,  The  diameter  of  the  tube;  2,  The  rapidity  with  which  the  mixture  is 
made ;  3,  The  relative  proportion  of  the  two  gases ;  4,  The  time  allowed  to 
elapse  after  mixing  them  ;  5,  Agitation  of  the  tube ;  and  lastly,  The  oppo- 
site conditions  of  adding  the  oxygen  to  the  binoxide,  or  the  binoxide  to  the 
oxygen. 

Notwithstanding  these  many  sources  of  error,  Dalton  and  Gay-Lussac 
maintain  that  binoxide  of  nitrogen  may  nevertheless  be  employed  in  eudio- 
metry ;  and  they  have  described  the  precautions  which  are  required  to  en- 
sure accuracy.  Dalton  has  given  his  process  in  the  Annals  of  Philosophy, 
x.  38 ;  and  further  directions  have  been  published  by  Dr.  Henfy  in  his  Ele- 
ments. The  method  of  Gay-Lussac,  to  which  my  own  observation  would 
lead  me  to  give  the  preference,  may  be  found  in  the  Memoires  d'Arcueil,  ii. 
247.  Instead  of  employing  a  narrow  tube,  such  as  is  commonly  used  for 
measuring  gases,  Gay-Lussac  advises  that  100  measures  of  air  should  be  in- 
troduced into  a  very  wide  tube  or  jar,  and  that  an  equal  volume  of  binoxide 
of  nitrogen  should  then  be  added.  The  red  vapours,  which  are  instantly 
produced,  disappear  very  quickly;  and  the  absorption  after  half  a  minute,  or 
a  minute  at  the  most,  may  be  regarded  as  complete.  The  residue  is  then 
transferred  into  a  graduated  tube  and  measured.  The  diminution  almost 
always,  according  to  Gay-Lussac,  amounts  to  84  measures,  one-fourth  of 
which  is  oxygen.*  Gay-Lussac  has  applied  this  process  to  the  analysis  of 

*  On  the  supposition  that  the  oxygen  and  binoxide  of  nitrogen  unite  in 
the  proportion  to  form  nitrous  acid,  one-third,  and  not  one-fourth,  of  the  di- 


1 78  NITROGEN. 

various  mixed  gases,  in  which  the  oxygen  was  sometimes  in  a  greater,  at 
others  in  a  less  proportion  than  in  the  atmosphere,  and  the  indications  were 
always  correct.  When  the  proportion  of  oxygen  is  great,  a  proportionally 
large  quantity  of  the  binoxide  must,  of  course,  be  employed,  in  order  that  an 
excess  of  it  may  be  present. 

There  is  another  mode  of  absorbing  oxygen  gas  by  means  of  binoxide  of 
nitrogen.  If  a  current  of  the  binoxide  be  conducted  into  a  solution  of  pro- 
tosulphate  of  iron,  the  gas  is  absorbed  in  large  quantity,  and  the  solution 
acquires  a  deep  olive-brown  colour,  which  appears  almost  black  when  fully 
saturated.  This  solution  absorbs  oxygen  with  facility.  But  it  cannot  be 
safely  employed  in  eudiometry ;  because  the  absorption  of  oxygen  is  accom- 
panied, or  at  least  very  soon  followed,  by  evolution  of  gas  from  the  liquid 
itself. 

Sir  H.  Davy  ascertained  that  binoxide  of  nitrogen  is  dissolved,  without  de- 
composition, by  a  cold  solution  of  protosulphate  of  iron  ;  and  that  when  the 
solution  is  heated,  the  greater  part  of  the  gas  is  disengaged,  and  the  remain- 
der decomposed.  The  decomposition  is  determined  chiefly  by  the  affinity  of 
protoxide  of  iron  for  oxygen  gas.  The  protoxide  of  iron  decomposes  a  por- 
tion of  water  and  binoxide  of  nitrogen  at  the  same  time,  and  unites  with  the 
oxygen  of  both  ;  while  the  hydrogen  of  the  water  and  nitrogen  of  the  bin- 
oxide  combine  and  generate  ammonia.  Nitric  acid  is  formed  when  the  so- 
lution is  exposed  to  the  air  or  oxygen  gas,  but  not  otherwise. 

It  is  singular  that  both  binoxide  and  protoxide  of  nitrogen,  notwithstand- 
ing the  absence  of  acidity,  are  capable  of  forming  compounds  of  considera. 
ble  permanence  with  the  pure  alkalies.  The  circumstances  which  give  rise 
to  the  formation  of  these  compounds  will  be  stated  in  the  description  of  nitre. 

HYPONITROUS  ACID. 

On  adding  binoxide  of  nitrogen  in  excess  to  oxygen  gas,  confined  in  a 
glass  tube  over  mercury,  Gay-Lussac  observed  that  the  absorption  is  always 
uniform,  provided  a  strong  solution  of  pure  potassa  is  put  into  the  tube  be- 
fore mixing  the  two  gases.  He  found  that  100  measures  of  oxygen  gas 
combine  under  these  circumstances  with  400  of  the  binoxide,  forming  an 
acid  which  unites  with  the  potassa.  The  compound  so  formed  is  hyponi- 
trous  acid,  the  composition  of  which  may  be  easily  inferred  from  the  pro- 
portions just  mentioned.  For  as  binoxide  of  nitrogen  contains  half  its  vo- 
lume of  oxygen  gas,  the  new  acid  must  be  composed  of  200  measures  of 
nitrogen  and  300  of  oxygen,  or  of  100  and  150,  as  already  stated  (page  167), 

minution  ought  to  be  due  to  oxygen  ;  for  nitrous  acid  is  composed  of  one 
volume  of  oxygen  and  two  volumes  of  binoxide  of  nitrogen.  It  may  be 
asked,  therefore,  what  are  the  real  products  of  the  experiment;  as  in  point  of 
fact,  one-fourth  of  the  gaseous  matter  which  disappears  represents  the  oxy- 
gen ?  The  late  Dr.  Dana  of  Boston  ingeniously  reconciled  this  result  with 
the  theory  of  volumes,  by  supposing  that  two-thirds  of  the  binoxide  of  nitro- 
gen become  hyponitrous  acid,  and  one-third  nitrous  acid.  Thus,  supposing 
six  volumes  of  the  binoxide  to  be  mixed  with  a  sufficient  quantity  of  oxygen, 
four  volumes  are  assumed  to  be  converted  into  hyponitrous  acid,  by  com- 
bining with  one  volume  of  oxygen,  and  the  remaining  two,  into  nitrous  acid, 
by  uniting  with  another  volume  of  oxygen.  In  this  manner  six  volumes  of 
binoxide  and  two  volumes  of  oxygen,  in  all  eight  volumes,  will  disappear, 
being  condensed,  as  above  explained,  into  hyponitrous  and  nitrous  acids. 
Now  of  these  eight  volumes,  one- fourth  is  oxygen. 

When  the  experiment  is  performed  with  certain  precautions,  nitrous  acid 
is  the  sole  product,  and  the  formula  for  calculating  the  quantity  of  oxygen  is 
of  course  to  divide  the  diminution  by  three.  I  had  the  pleasure  of  seeing 
this  proved  experimentally,  on  several  occasions,  by  Dr.  Hare  of  the  Univer- 
sity of  Pennsylvania, — Ed. 


NITROGEN.  179 

Another  method  of  forming  it  is  by  keeping  hinoxide  of  nitrogen  for  a  con- 
siderable time,  say  three  months,  in  a  glass  tube  over  mercury,  with  a 
strong  solution  of  pure  potassa.  The  binoxide  is  resolved  into  hyponitrous 
acid,  which  unites  with  the  alkali,  and  protoxide  of  nitrogen  remains  in  the 
tube.  It  is  also  said  to  be  formed  when  400  measures  of  binoxide  of  nitro- 
gen are  mixed  with  100  of  oxygen  gas,  both  quite  dry,  and  the  resulting 
orange  fumes  are  exposed  to  a  cold  of  0°  F.  when  it  is  condensed  into  a 
liquid. 

Anhydrous  liquid  hyponitrous  acid  is  colourless  at  0°  F.  and  green  at 
common  temperatures.  It  is  so  volatile,  that,  in  open  vessels,  the  green  fluid 
wholly  and  rapidly  passes  off  in  the  form  of  an  orange  vapour,  which  is  said 
by  Mitscherlich  to  have  a  density  of  1.72.  On  admixture  with  water  it  is 
converted  into  nitric  acid  and  binoxide  of  nitrogen,  the  latter  escaping  with 
effervescence;  but  when  much  nitric  acid  is  present,  the  hyponitrous  is 
changed  into  nitrous  acid,  the  presence  of  which  imparts  several  shades  of 
colour,  orange,  yellow,  green,  and  blue,  according  as  its  quantity  is  more  or 
less  predominant.  One  equivalent  of  hyponitrous  and  one  of  nitric  acid 
yield  two  equivalents  of  nitrous  acid:  thus  N-J-3O  and  N-f5O  obviously 
contain  the  elements  for  forming  2(N-f-4O). 

Hyponitrous  acid  does  not  unite  directly  with  alkalies,  being  then  resolv- 
ed principally  into  nitric  acid  and  binoxide  of  nitrogen ;  but  the  hyponi- 
trites  of  the  alkalies  and  alkaline  earths  may  be  obtained  by  subjecting  the 
corresponding  nitrates  to  a  gentle  red  heat;  and  the  hyponitrite  of  the  oxide 
of  lead  is  formed  by  boiling  a  solution  of  the  nitrate  of  that  oxide  with  me- 
tallic lead. 

Hyponitrous  acid  forms  with  water  and  sulphuric  acid  a  crystalline  com- 
pound, which  is  generated  in  large  quantity  during  the  manufacture  of  sul- 
phuric acid,  and  the  production  of  which  is  an  essential  part  of  that  process. 
It  is  generated  whenever  moist  sulphurous  acid  gas  and  nitrous  acid  vapour 
are  intermixed,  being  instantly  deposited  in  the  form  of  white  acicular  crys- 
tals; and  Gay-Lussac  discovered  that  it  may  also  be  made  by  the  direct  ac- 
tion of  anhydrous  nitrous  and  strong  sulphuric  acid.  The  first  attempt  to  de- 
termine its  composition  analytically  was  made  by  Dr.  Henry,  who  found  it  to 
consist  of  one  equivalent  of  hyponitrous  acid,  five  of  sulphuric  acid,  and  five 
of  water.  (Ann.  of  Phil,  xxvii.  367.)  Gaultier  de  Claubry  has  lately  repeated 
the  analysis  of  the  same  compound  in  a  state  of  more  perfect  dryness,  and 
by  what  he  considers  a  better  method ;  and  he  gives  as  its  constituents  two 
equivalents  of  hyponitrous  acid,  four  of  water,  and  five  of  sulphuric  acid. 
(An.  de  Ch.  et  de  Ph.  xlv.  284.)  The  theory  of  its  production  has  been  very 
carefully  studied  by  G.  de  Claubry.  It  appears  that  when  moist  sulphurous 
and  nitrous  acids  react  on  each  other,  the  former  is  converted  into  sulphuric 
and  the  latter  into  hyponitrous  acid,  the  oxygen  lost  by  one  being  gained  by 
the  other.  A  little  nitrogen  gas  is  always  disengaged  at  the  same  time, 
which  can  only  arise -from  a  small  portion  of  nitrous  acid  losing  the  whole 
of  its  oxygen.  The  action  of  sulphuric  on  nitrous  acid  is  different:  in  this 
case  the  nitrous  acid  is  resolved  into  nitric  and  hyponitrous  acids,  the  latter 
uniting  with  sulphuric  acid  and  most  of  its  water  to  produce  the  crystalline 
solid,  while  the  remainder  of  the  water  unites  with  the  nitric  acid.  When 
the  crystalline  matter  is  put  into  water,  the  hyponitrous  is  resolved  into  ni- 
trous acid  and  binoxide  of  nitrogen,  both  of  which  escape  with  effervescence. 
If  much  water  is  present,  more  or  less  of  the  nitrous  acid  is  converted  into 
nitric  acid  and  the  binoxide.  Similar  changes  ensue  when  the  crystals  are 
exposed  to  the  air,  humidity  being  rapidly  absorbed.  This  subject  has  also 
been  lately  examined  by  Bussy  with  similar  results. 

NITROUS  ACID. 

To  form  pure  nitrous  acid  by  the  mixture  of  oxygen  gas  with  binoxide  of 
nitrogen,  the  operation  should  not  be  conducted  over  water  or  mercury :  the 
presence  of  the  former  determines  the  production  of  nitric  acid,  and  the  lat- 


180  NITROGEN. 

ter  is  oxidized  by  the  nitrous  acid,  and,  therefore,  decomposes  it.  Davy 
showed,  by  making  the  mixture  in  a  dry  glass  vessel  previously  exhausted, 
that  nitrous  acid  vapour  is  formed  by  the  action  of  200  measures  of  binoxide 
of  nitrogen  on  100  of  oxygen  gas  ;  and  hence,  as  200  of  the  binoxide  contain 
100  of  nitrogen  and  100  of  oxygen,  nitrous  acid  was  inferred  to  consist  of 
100  measures  of  nitrogen  united  with  200  of  oxygen  gas,  as  stated  at  page 
167.  This  inference  has  been  confirmed  by  the  researches  of  Gay-Lussac 
and  Dulong  (An.  de  Ch.  et  de  Ph.  i.  and  ii.),  the  former  of  whom  also  proved 
that  its  elements  contract  to  l-3d  of  their  volume;  or  in  other  words,  100 
measures  of  nitrous  acid  vapour  contain  100  of  nitrogen  gas  and  200  of 
oxygen.  The  specific  gravity  of  this  vapour  ought  to  be  3,1775,  formed  of 
0.9727,  the  sp.  gr.  of  nitrogen,-}-2.2048,  twice  the  sp.  gr.  of  oxygen. 

Nitrous  acid  vapour  is  characterized  by  its  orange-red  colour,  acid  reaction 
to  test  paper,  and  by  being  absorbed  by  water  with  disengagement  of  bin- 
oxide  of  nitrogen  and  formation  of  nitric  acid.  It  is  quite  irrespirable,  ex- 
citing great  irritation  and  spasm  of  the  glottis,  even  when  moderately  diluted 
with  air.  A  taper  burns  in  it  with  considerable  brilliancy.  It  extinguishes 
burning  sulphur ;  but  the  combustion  of  phosphorus  continues  in  it  with 
great  vividness. 

Nitrous  acid  may  exist  in  the  liquid  as  well  as  in  the  gaseous  form.  Its 
vapour  may  be  condensed  by  a  freezing  mixture  ;  but  the  best  mode  of  pre- 
paring it,  is  by  exposing,  in  an  earthen  retort,  nitrate  of  lead,  carefully  dried, 
to  a  red  heat.  The  nitric  acid  of  the  salt  is  resolved  into  nitrous  acid  and 
oxygen;  and  on  receiving  these  products  in  a  dry  tube  surrounded  by  a 
mixture  of  ice  and  salt,  most  of  the  former  is  condensed.  The  liquid  as 
thus  obtained  is  anhydrous,  is  acid  and  pungent  to  the  taste,  gives  a  yellow 
stain  to  the  skin,  and  is  powerfully  corrosive.  At  common  temperatures  its 
colour  is  an  orange-red  ;  but  it  becomes  yellow  when  cooled  below  32°,  and 
at  0°  F.  is  nearly  colourless.  Its  density  is  1.451.  It  is  extremely  volatile, 
boiling  at  82° :  in  a  stoppered  bottle  it  preserves  its  liquid  form  at  common 
temperatures ;  but  when  exposed  to  the  atmosphere  it  is  rapidly  dissipated, 
forming  nitrous  acid  vapours  which,  when  once  mixed  with  air  or  other 
gases,  require  intense  cold  for  condensation. 

Nitrous  acid  is  a  powerful  oxidizing  agent,  readily  giving  oxygen  to  the 
more  oxidable  metals,  and  to  most  substances  which  have  a  strong  affinity 
for  it.  The  acid  is  decomposed  at  the  same  time,  being  commonly  changed 
into  binoxide  of  nitrogen ;  though  sometimes  the  protoxide  and  even  pure 
nitrogen  gas  are  evolved.  When  transmitted  through  a  red-hot  porcelain 
tube,  it  suffers  decomposition,  and  a  mixture  of  oxygen  and  nitrogen  gases 
is  obtained. 

When  nitrous  acid  is  mixed  with  a  considerable  quantity  of  water,  it  is 
instantly  resolved  into  nitric  acid,  which  unites  with  the  water,  and  binoxide 
of  nitrogen  which  escapes  with  effervescence.  Three  equivalents  of  nitrous 
acid  are  in  proportion  to  form  two  of  nitric  acid  and  one  of  the  binoxide ; 
for  3(N+  4O)  contain  2(N-f-5O)  and  N-f-2O.  When  a  rather  small  quan- 
tity of  water  is  used,  the  disengagement  of  binoxide  of  nitrogen,  at  first 
considerable,  becomes  less  and  less  as  successive  quantities  of  nitrous  acid 
are  added,  till  at  last  the  evolution  of  gas  ceases  altogether.  The  colour  of 
the  solution  varies  remarkably  during  the  process :  from  being  colourless, 
the  liquid  acquires  a  blue  tint,  then  passes  into  bluish-green,  green,  yellow, 
and  lastly  orange.  These  different  solutions  contain  different  relative  quan- 
tities of  nitric  acid,  nitrons  acid,  and  water,  on  which  circumstance  the 
varying  shades  of  colour  depend.  Nitric  and  nitrous  acids  are  disposed  to 
unite  with  each  other,  and  the  influence  of  this  attraction  enables  nitrous 
acid  to  sustain  admixture  with  water  without  decomposition.  Strong  nitric 
acid  will  unite  with  a  considerable  quantity  of  nitrous  acid,  and  thereby  ac- 
quires an  orange-red  tint.  In  a  weaker  nitric  acid  the  water  decomposes 
part  of  the  nitrous  acid,  and  the  colour  of  the  solution  is  orange  or  yellow. 
As  the  strength  of  the  nitric  acid  becomes  weaker  and  weaker,  the  quantity 
of  nitrous  acid  which  it  can  protect  from  decomposition  becomes  less  and 


NITROGEN.  181 

less,  and  the  colour  of  the  solution  varies  from  yellow,  green,  and  blue,  and 
is  at  length  colourless.  These  changes  may  be  witnessed,  not  only  by  add- 
ing successive  quantities  of  nitrous  acid  to  water,  and  thereby  at  length 
producing  a  strong  nitric  acid,  but  commencing  with  the  latter,  saturating 
it  with  nitrous  acid,  and  then  successively  diluting  with  water. 

When  nitrous  acid  is  mixed  with  a  very  small  quantity  of  water,  no  bin- 
oxide  of  nitrogen  is  disengaged ;  but  the  liquid  becomes  green,  like  the  co- 
lour of  hyponitrous  acid.  I  have  repeatedly  obtained  a  similar  liquid  in  pre- 
paring nitrous  acid  from  nitrate  of  lead,  when  the  materials  were  not 
adequately  dried;  and  that  green  liquid,  when  allowed  to  dissipate  In  the 
air,  leaves  some  nitric  acid  behind.  From  these  facts  it  seems  probable  that 
in  the  decomposition  of  nitrous  acid  by  water,  the  first  change  is  the  con- 
version of  nitrous  into  nitric  and  hyponitrous  acids,  which  last  is  subse- 
quently changed,  when  the  required  quantity  of  water  is  present,  into  nitric 
acid  and  binoxide  of  nitrogen.  It  may  thus  well  happen  that  hyponitrous 
acid  contributes  to  produce  the  varying  colours  above  described. 

Some  chemists  consider  nitrous  acid  as  a  compound  of  nitric  and  hypo- 
nitrous  acids,  rather  than  of  nitrogen  and  oxygen.  In  fact,  on  adding  nitrous 
acid  to  an  alkaline  solution,  we  obtain  a  nitrate  and  hyponitrite,  a  circum- 
stance which  has  given  rise  to  the  notion  that  nitrous  acid  cannot  act  as  a 
distinct  acid.  Berzelius  and  Mitscherlich  affirm  that  the  salts  commonly 
termed  nitrites,  such  as  nitrite  of  baryta  and  potassa,  made  by  heating  the 
corresponding  nitrates  to  gentle  redness,  contain  hyponitrous  acid. 

NITRIC  ACID. 

If  a  succession  of  electric  sparks  be  passed  through  a*rnixture  of  oxygen 
and  nitrogen  gases  confined  in  a  glass  tube  over  mercury,  a  little  water 
being  present,  the  volume  of  the  gases  will  gradually  diminish,  and  the 
water  after  a  time  will  be  found  to  have  acquired  acid  properties.  On  neu- 
tralizing the  solution  with  potassa,  or  what  is  better,  by  putting  a  solution 
of  that  alkali  instead  of  water  into  the  tube  at  the  beginning  of  the  experi- 
ment, a  salt  is  obtained  which  possesses  all  the  properties  of  nitrate  of 
potassa.  This  experiment  was  performed  in  1785  by  Mr.  Cavendish,  who 
inferred  from  it  that  nitric  acid  is  composed  of  oxygen  and  nitrogen.  The 
best  proportion  of  the  gases  was  found  to  be  seven  of  oxygen  to  three  of 
nitrogen ;  but  as  some  nitrous  acid  is  always  formed  during  the  process,  the 
exact  composition  of  nitric  acid  cannot  in  this  way  be  accurately  deter- 
mined. 

Nitric  acid  may  be  formed  much  more  conveniently  by  adding  binoxide 
of  nitrogen  slowly  over  water  to  an  excess  of  oxygen  gas.  Gay-Lussac 
proved  that  nitric  acid  may  in  this  manner  be  obtained  quite  free  from 
nitrous  or  hyponitrous  acid;  and  that  it  is  composed  of  100  measures  of 
nitrogen  and  250  of  oxygen.  This  result  has  been  confirmed  by  the  expe- 
riments of  Davy,  Henry,  Berzelius,  and  others,  fully  establishing  the  com- 
position as  already  stated. 

Nitric  acid  cannot  exist  in  an  insulated  state.  Binoxide  of  nitrogen  and 
oxygen  gases  never  form  nitric  acid  if  mixed  together  when  quite  dry;  and 
nitrous  acid  vapour  may  be  kept  in  contact  with  oxygen  gas  without  change, 
provided  no  water  is  present.  The  most  simple  form  under  which  chemists 
have  hitherto  procured  nitric  acid  is  in  solution  with  water;  a  liquid  which, 
in  its  concentrated  state,  is  the  nitric  acid  of  the  Pharmacopeias.  By  manu- 
facturers it  is  better  known  by  the  name  of  aquafortis. 

The  nitric  acid  of  commerce  is  procured  by  decomposing  some  salt  of 
nitric  acid  by  means  of  oil  of  vitriol ;  and  common  nitre,  as  the  cheapest  of 
the  nitrates,  is  employed  for  the  purpose.  This  salt,  previously  well  dried, 
is  put  into  a  glass  retort,  and  a  quantity  of  the  strongest  oil  of  vitriol  is 
poured  upon  it.  On  applying  heat,  ebullition  ensues,  owing  to  the  escape  of 
.  nitric  acid  vapours,  which  must  be  collected  in  a  cool  receiver.  The  h«at 

16 


182  NITROGEN. 

should  be  steadily  increased  during  the  operation,  and  continued  as  long  as 
any  acid  vapours  come  over. 

Chemists  differ  as  to  the  best  proportions  for  forming  nitric  acid.  The 
London  College  recommends  equal  weights  of  nitre  and  oil  of  vitriol;  and 
the  Edinburgh  and  Dublin  Colleges  employ  three  parts  of  nitre  to  two  of 
the  acid.  In  the  process  of  the  London  College,  the  alkali  of  the  nitre  is  left 
as  a  bisulphate  in  the  retort;  since  one  equivalent  of  nitre  (54.15  nitric  acid 
and  47.15  potassa)  is  101.3,  and  the  nearly  equal  number  98.2  corresponds 
to  two  equivalents  of  oil  of  vitriol,  which  contain  two  eq.  of  anhydrous  sul- 
phuric acid  and  two  eq.  of  water.  During  the  distillation  the  nitric  acid 
passes  over  along  with  one  and  a  half  eq.  of  water,  and  half  an  equivalent 
of  water  is  retained  by  the  bisulphate  of  potassa.  The  presence  of  water  is 
essential :  nitric  acid  of  sp.  gr.  ]  .5  consists  of  real  or  anhydrous  acid  and 
water,  in  the  ratio  of  one  eq.  to  one  and  a  half,  or  two  to  three ;  and  unless 
water  in  at  least  this  proportion  be  supplied,  a  proportional  quantity  of 
nitric  acid  is  resolved,  at  the  moment  of  quitting  the  potassa,  into  oxygen 
and  nitrous  acid  (Phillips,  in  Phil.  Mag.  ii.  430).  If  the  mixture  be  intro- 
duced into  the  retort  without  soiling  its  neck,  and  the  heat  be  cautiously 
raised,  the  product  will  be  quite  free  from  sulphuric  acid;  and,  therefore,  the 
second  distillation  from  nitre,  recommended  in  the  London  Pharmacopoeia,  is 
superfluous. 

The  proportions  of  the  Edinburgh  and  Dublin  Colleges  are  such,  that  the 
residual  salt  is  a  mixture  of  sulphate  and  bisulphate  of  potassa.  The  acid  • 
of  the  nitre  does  not  receive  from  the  oil  of  Vitriol  the  requisite  quantity  of 
water,  and  hence  part  of  it  is  decomposed,  yielding  towards  the  close  of  the 
operation  an  abundant  supply  of  nitrous  acid  fumes.  If  the  receiver  be  kept 
cool,  nearly  all  these  vapours  are  condensed,  and  the  product  is  a  mixture 
of  nitric  and  nitrous  acids,  of  a  deep  orange-red  colour,  very  strong  and 
fuming,  and  of  a  greater  specific  gravity,  though  proportionally  less  in  quan- 
tity, than  that  obtained  by  the  foregoing  process.  The  specific  gravity  of 
the  pale  acid  is  1.5 ;  while  that  of  the  red  acid  is  1.52,  or  by  previously  dry- 
ing the  nitre  and  boiling  the  sulphuric  acid,  Dr.  Hope  states  that  it  may  be 
made  so  high  as  1.54. 

Some  manufacturers  decompose  nitre  with  half  its  weight  of  sulphuric 
acid,  thus  employing  the  ingredients  in  the  proportion  of  one  equivalent  of 
each.  In  this  case  about  half  of  the  nitric  acid  is  decomposed,  and  con- 
siderable loss  sustained,  unless  the  requisite  quantity  of  water  is  previously 
mixed  with  the  sulphuric  acid,  or  water  be  placed  in  the  receiver  to 
condense  the  nitrous  acid.  Some  of  the  nitre  is  likewise  apt  to  escape 
decomposition;  and  the  residue,  consisting  of  neutral  sulphate,  which  is 
much  less  soluble  than  the  bisulphate,  is  removed  from  the  retort  with 
difficulty. 

In  none  of  the  preceding  processes,  not  even  in  the  first,  is  the  product 
quite  colourless ;  for  at  the  commencement  and  close  of  the  operation, 
nitrous  acid  fumes  are  disengaged,  which  communicate  a  straw-yellow  or 
an  orange-red  tint,  according  to  their  quantity.  If  a  very  pale  acid  is  re- 
quired, two  receivers  should  be  used ;  one  for  condensing  the  colourless  va- 
pours of  nitric  acid,  and  another  for  the  coloured  products.  The  coloured 
acid  is  called  nitrous  acid  by  the  Edinburgh  College ;  but  it  is  in  reality  a 
mixture  or  compound  of  nitric  and  nitrous  acids,  similar  to  what  may  be 
obtained  by  mixing  anhydrous  nitrous  with  colourless  nitric  acid.  It  is  easy 
to  convert  the  common  mixed  acid  of  the  College  into  colourless  nitric  acid, 
by  exposing  the  former  to  a  gentle  heat  for  some  time,  when  all  the  nitrous 
acid  will  be  expelled.  But  this  process  is  rarely  necessary  ;  as  the  coloured 
acid  may  be  substituted  in  most  cases  for  that  which  is  colourless.  Where 
an  acid  of  great  strength  is  required,  the  former  is  even  preferable. 

Nitric  acid  frequently  contains  portions  of  sulphuric  and  hydrochloric 
acid.  The  former  is  derived  from  the  acid  which  is  used  in  the  process ; 
arid  the  latter  from  sea-salt,  which  is  frequently  mixed  with  nitre.  These 
impurities  may  be  detected  by  adding  a  few  drops  of  a  solution  of  chloride 


NITROGEN.  183 

of  barium  and  nitrate  of  silver  to  separate  portions  of  nitric  acid,  diluted  with 
three  or  four  parts  of  distilled  water.  If  chloride  of  barium  cause  a  cloudi- 
ness or  precipitate,  sulphuric  acid  must  be  present ;  if  a  similar  effect  be 
produced  by  nitrate  of  silver,  the  presence  of  hydrochloric  acid  may  be  in- 
ferred. Nitric  acid  is  purified  from  sulphuric  acid  by  redistilling  it  from  a 
small  quantity  of  nitrate  of  potassa,  with  the  alkali  of  which  the  sulphuric 
acid  unites,  and  remains  in  the  retort.  To  separate  hydrochloric  acid,  it  is 
necessaiijj'  to  drop  a  solution  of  nitrate  of  silver  into  the  nitric  acid  as  long  as 
a  precipitate  is  formed,  and  draw,  off  the  pure  acid  by  distillation. 

Nitric  acid  possesses  acid  properties  in  an  eminent  degree.  A  few  drops 
of  it  diluted  with  a  considerable  quantity  of  water  form  an  acid  solution, 
which  reddens  litmus  paper  permanently.  It  unites  with  and  neutralizes 
alkaline  substances,  forming  with  them  salts  which  are  called  nitrates.  In 
it's  purest  and  most  concentrated  state  it  is  colourless,  and  has  a  specific  gra- 
vity of  1.5  or  1.51.  It  still  contains  a  considerable  quantity  of  water,  from 
which  it  cannot  be  separated  without  decomposition,  or  by  uniting  with 
some  other  body.  An  acid  of  density  1.5  contains  20  per  cent,  of  water, 
according  to  the  experiments  of  Mr.  Phillips,  and  20.3  per  cent,  accord- 
ing to  those  of  Dr.  Ure.*  Nitric  acid  of  this  strength  emits  dense,  white, 
suffocating  vapours  when  exposed  to  the  atmosphere.  It  attracts  watery  va- 
pour from  the  air,  whereby  its  density  is  diminished.  A  rise  of  temperature 
is  occasioned  by  mixing  it  with  a  certain  quantity  of  water.  Dr.  Ure  found 
that  when  58  measures  of  nitric  acid  of  density  1.5  are  suddenly  mixed  with 
42  of  water,  the  temperature  rises  from  60  to  140°  F. ;  and  the  mixture,  on 
cooling  to  60°,  occupies  the  space  of  92.65  measures  instead  of  100.  From 
its  strong  affinity  for  water,  it  occasions  snow  to  liquefy  with  great  rapidity ; 
and  if  the  mixture  is  made  in  due  proportion,  intense  cold  will  be  generated. 
(Page  39.) 

Nitric  acid  boils  at  248°F.,  and  may  be  distilled  without  suffering  mate- 
rial change.  An  acid  of  lower  density  than  1.42  becomes  stronger  by  being 
heated,  because  the  water  evaporates  more  rapidly  than  the  acid.  An  acid, 
on  the  contrary,  which  is  stronger  than  1.42  is  weakened  by  the  application 
of  heat. 

Nitric  acid  may  be  frozen  by  cold.  The  temperature  at  which  congelation, 
takes  place,  varies  with  the  strength  of  the  acid.  The  strongest  acid  freezes 
at  about  50°  below  zero.  When  diluted  with  half  its  weight  of  water,  it  be- 
comes solid  at  — 1^°  F.  By  the  addition  of  a  little  more  water,  its  freezing 
point  is  lowered  to — 45°  F. 

Nitric  acid  acts  powerfully  on  substances  which  are  disposed  to  unite  with 
oxygen ;  and  hence  it  is  much  employed  by  chemists  for  bringing  bodies  to 
their  maximum  of  oxidation.  Nearly  all  the  metals  are  oxidized  by  it;  and 
some  of  them,  such  as  tin,  copper,  and  mercury,  are  attacked  with  great  vio- 
lence. If  flung  on  burning  charcoal,  it  increases  the  brilliancy  of  its  com- 
bustion in  a  high  degree.  Sulphur  and  phosphorus  are  converted  into  acids 
by  its  action.  All  vegetable  substances  are  decomposed  by  it.  In  general 
the  oxygen  of  the  nitric  acid  enters  into  direct  combination  with  the  hydro- 
gen  and  carbon  of  those  compounds,  forming  water  with  the  former,  and 
carbonic  acid  with  the  latter.  This  happens  remarkably  in  those  compounds 
in  which  hydrogen  and  carbon  are  predominant,  as  in  alcohol  and  the  oils. 
It  effects  the  decomposition  of  animal  matters  also.  The  cuticle  and  nails 
receive  a  permanent  yellow  stain  when  touched  with  it;  and  if  applied  to  the 
skin  in  sufficient  quantity  it  acts  as  a  powerfnl  cautery,  destroying  the  or- 
ganization of  the  part  entirely. 

When  oxidation  is  effected  through  the  medium  of  nitric  acid,  the  acid 
itself  is  commonly  converted  into  binoxide  of  nitrogen.  This  gas  is  some- 
times given  off  nearly  quite  pure ;  but  in  general  some  nitrous  acid,  protox- 

*  See  his  table  in  the  Appendix,  showing  the  strength  of  diluted  acid  of 
different  densities. 


184  CARBON. 

ide  of  nitrogen,  or  pure  nitrogen,  is  disengaged  at  the  same  time.  The 
escape  of  nitrous  acid  in  these  cases  seerns  owing,  according  to  some  late 
observations  of  Mr.  Phillips,  not  so  much  to  its  direct  formation,  but  to  the 
binoxide  at  first  formed  acting  on  the  nitric  acid  of  the  solution.  Direct 
solar  light  deoxidizes  nitric  acid,  resolving  a  portion  of  it  into  oxygen  and 
nitrous  acid.  The  former  escapes  as  gas ;  the  latter  is  absorbed  by  the  nitric 
acid,  and  converts  it  into  the  mixed  nitrous  acid  of  the  shops.  When  the 
vapour  of  nitric  acid  is  transmitted  through  red-hot  porcelain  tubes,  it  suffers 
complete  decomposition,  and  a  mixture  of  oxygen  and  nitrogen  gases  is  the 
product. 

Nitric  acid  may  also  be  deoxidized  by  transmitting  a  current  of  binoxide 
of  nitrogen  through  it.  That  gas,  by  taking  oxygen  from  the  nitric,  is  con- 
verted into  nitrous  acid ;  and  a  portion  of  nitric  acid,  by  losing  oxygen,  passes 
into  the  same  compound.  The  nitrous  acid,  thus  derived  from  two  sources, 
gives  a  colour  to  the  nitric  acid,  the  depth  and  kind  of  which  depend  on  the 
strength  of  the  acid.  On  saturating  with  binoxide  of  nitrogen  four  separate 
portions  of  nitric  acid  of  the  densities  1.15,  1.35,  1.40,  and  1.50,  the  colour 
will  be  blue  in  the  first,  green  in  the  second,  yellow  in  the  third,  and  brown- 
ish-red in  the  fourth;  and  acio1  of  1.05  is  not  coloured  at  all.  Mr.  Phillips 
found  that  acid  of  density  1.497  acquired  a  density  1.541,  that  is,  was  made 
stronger,  by  saturation  with  the  binoxide ;  but  those  acids  which  become 
green  are  much  weakened,  because  nitrous  acid,  formed  at  the  expense  of 
the  nitric  acid,  is  decomposed  by  the  water  of  the  solution. 

All  the  salts  of  nitric  acid  are  soluble  in  water,  and,  therefore,  it  is  impos- 
sible to  precipitate  that  acid  by  any  reagent.  The  presence  of  nitric  acid, 
when  uncombined;  is  readily  detected  by  its  strong  action  on  copper  and 
mercury,  emitting  ruddy  fumes  of  nitrous  acid,  and  by  its  forming  with  po- 
tassa  a  neutral  salt,  which  crystallizes  in  prisms,  and  has  all  the  properties  of 
nitre.  Gold-leaf  is  a  still  more  delicate  test.  When  hydrochloric  acid  is  added 
to  the  solution  of  a  nitrate,  chlorine  is  disengaged,  and  the  liquid  hence  ac- 
quires the  property  of  dissolving  gold-leaf;  but  as  the  action  of  hydrochloric 
acid  on  the  salts  of  chloric,  bromic,  iodic,  and  selenic  acids  likewise  yields  a 
solution  capable  of  dissolving  gold,  no  inference  can  be  drawn  from  the  ex- 
periment, unless  the  absence  of  these  acids  shall  have  been  previously  de- 
monstrated. Another  character  which  may  be  useful  is  to  mix  the  supposed 
nitric  acid  or  nitrate  with  dilute  sulphuric  acid  in  a  tube,  add  a  few  frag- 
ments of  pure  zinc,  and  set  fire  to  the  hydrogen  as  it  issues  :  if  nitric  acid 
be  present,  the  flame  of  the  hydrogen  will  have  a  greenish-white  tint,  due  to 
admixture  with  binoxide  of  nitrogen.  This  test  occurred  to  my  assistant, 
Mr.  Belmain,  and  Mr.  Maitland  at  the  same  time  proposed  alcohol  instead 
of  zinc  with  the  same  intention.  A  very  delicate  test  has  been  proposed  by 
Dr.  O'Shaugnessy,  founded  on  the  orange-red  followed  by  a  yellow  colour, 
which  nitric  acid  communicates  to  morphia.  The  supposed  nitrate  is  heated 
in  a  test  tube  with  a  drop  of  sulphuric  acid,  and  then  a  crystal  of  morphia 
is  added.  (Lancet,  1829 — 30.)  It  is  advisable  to  try  the  process  in  a  sepa- 
rate tube  with  the  sulphuric  acid  alone,  in  order  to  prove  the  absence  of 
nitric  acid. 


SECTION   VI. 

CARBON. 

WHEN  wood  is  heated  to  a  certain  degree  in  the  open  air,  it  takes  fire,  and 
burns  with  the  formation  of  water  and  carbonic  acid  gas  till  the  whole  of 
it  is  consumed.  A  small  portion  of  ashes,  consisting  of  the  alkaline  and 
earthy  matters  which  had  formed  a  part  of  the  wood,  is  the  sole  residue. 
But  if  the  wood  be  heated  to  redness  in  close  vessels,  so  that  atmospheric 


CARBON.  185 

air  cannot  have  free  access  to  it,  a  large  quantity  of  gaseous  and  other  vola- 
lile  matters  is  expelled,  and  a  black,  hard,  porous  substance  is  left,  called 
charcoal. 

Charcoal  may  be  produced  from  other  sources.  When  the  volatile  matters 
are  driven  off  from  coal,  as  in  the  process  for  making  coal  gas,  a  peculiar 
kind  of  charcoal,  called  coke,  remains  in  the  retort.  Most  animal  and  vege- 
table substances. yield  it  when  ignited  in  close  vessels.  Thus,  a  very  pure 
charcoal  may  be  procured  from  starch  or  sugar;  and  from  the  oil  of  turpen- 
tine or  spirit  of  wine,  by  passing  their  vapour  through  tubes  heated  to  red- 
ness. When  bones  are  made  red-hot  in  a  covered  crucible,  a  black  mass  re- 
mains, which  consists  of  charcoal  mixed  with  the  earthy  matters  of  the 
bone.  It  is  called  ivory  black,  or  animal  charcoal. 

Charcoal  is  hard  and  brittle,  conducts  heat  very  slowly,  but  is  a  good  con- 
ductor of  electricity.  It  is  quite  insoluble  in  water,  is  attacked  with  difficulty 
by  nitric  acid,  and  is  little  affected  by  any  of  the  other  acids,  or  by  the  alkalies. 
It  undergoes  little  change  from  exposure  to  air  and  moisture,  being  less  in- 
jured under  these  circumstances  than  wood.  It  is  exceedingly  refractory  in 
the  fire,  if  excluded  from  the  air,  supporting  the  most  intense  heat  which 
chemists  are  able  to  produce  without  change. 

Charcoal  possesses  the  property  of  absorbing  a  large  quantity  of  air  or 
other  gases  at  common  temperatures,  and  of  yielding  the  greater  part  of 
them  again  when  it  is  heated.  It  appears  from  the  researches  of  Saussure, 
that  different  gases  are  absorbed  by  it  in  different  proportions.  His  experi- 
ments were  performed  by  plunging  a  piece  of  red-hot  charcoal  under  mer- 
cury, and  introducing  it  when  cool  into  the  gas  to  be  absorbed.  He  found 
that  charcoal  prepared  from  box- wood  absorbs,  during  the  space  of  24  or  36 
hours,  of 

Ammoniacal  gas         .  .  9i  times  its  volume. 

Muriatic  acid         ...  85 

Sulphurous  acid  .  .  .65 

Sulphuretted  hydrogen      .  .  55 

Nitrous  oxide .  .  .  .       40 

Carbonic  acid         ...  35 

defiant  gas     .  .  .  .35 

Carbonic  oxide       .  .  .  9.42 

Oxygen  ....         9.25 

Nitrogen  .  .  .  7.5 

Hydrogen        .  .  .  .1.75 

The  absorbing  power  of  charcoal,  with  respect  to  gases,  cannot  be  attri- 
buted to  chemical  action ;  for  the  quantity  of  each  gas,  which  is  absorbed, 
bears  no  relation  whatever  to  its  affinity  for  charcoal.  The  effect  is  in 
reality  owing  to  the  peculiar  porous  texture  of  that  substance,  which  enables 
it,  in  common  with  most  spongy  bodies,  to  absorb  more  or  less  of  all  gases, 
vapours,  and  liquids  with  which  it  is  in  contact.  This  property  is  most  re- 
markable in  charcoal  prepared  from  wood,  especially  in  the  compact  varie- 
ties of  it,  the  pores  of  which  are  numerous  and  small.  It  is  materially  di- 
minished by  reducing  the  charcoal  to  powder ;  and  in  plumbago,  which  has 
not  the  requisite  degree  of  porosity,  it  is  wanting  altogether. 

The  porous  texture  of  charcoal  accounts  for  the  fact  of  absorption  only; 
its  power  of  absorbing  more  of  one  gas  than  of  another,  must  be  explained 
on  a  different  principle.  This  effect,  though  modified  to  all  appearance  by 
the  influence  of  chemical  attraction,  seems  to  depend  chiefly  on  the  natural 
elasticity  of  the  gases.  Those  which  possess  such  a  great  degree  of  elasti- 
city as  to  have  hitherto  resisted  all  attempts  to  condense  them  into  liquids, 
are  absorbed  in  the  smallest  proportion ;  while  those  that  admit  of  being  con- 
verted into  liquids  by  compression,  are  absorbed  more  freely.  For  this  rea- 
son, charcoal  absorbs  vapours  more  easily  than  gases,  and  liquids  than 
either. 

Messrs.  Allen  and  Pepys  determined  experimentally  the  increase  in  weight 

16* 


186  CARBON. 

experienced  by  different  kinds  of  charcoal,  recently  ignited,  after  a  week's 
exposure  to  the  atmosphere.  The  charcoal  from  fir  gained  13  per  cent ;  that 
from  lignum  vita,  9.6 ;  that  from  box,  14;  from  beech,  16.3 ;  from  oak,  16.5  ; 
and  from  mahogany,  18.  The  absorption  is  most  rapid  during  the  first  24 
hours.  The  substance  absorbed  is  both  water  and  atmospheric  air,  which 
the  charcoal  retains  with  such  force,  that  it  cannot  be  completely  separated 
from  them  without  exposure  to  a  red  heat.  Vogel  has  observed  that  char- 
coal absorbs  oxygen  in  a  much  greater  proportion  from  the  air  than  nitro- 
gen. Thus,  when  recently  ignited  charcoal,  cooled  under  mercury,  was  put 
into  ajar  of  atmospheric  air,  the  residue  contained  only  8  per  cent,  of  oxy- 
gen gas ;  and  if  red-hot  charcoal  be  plunged  into  water,  and  then  introduced 
into  a  vessel  of  air,  the  oxygen  disappears  almost  entirely.  It  is  said  that 
pure  nitrogen  may  be  obtained  in  this  way.  (Schweigger's  Journal,  iv.) 

Charcoal  likewise  absorbs  the  odoriferous  and  colouring  principles  of 
most  animal  and  vegetable  substances.  When  coloured  infusions  of  this 
kind  are  digested  with  a  due  quantity  of  charcoal,  a  solution  is  obtained, 
which  is  nearly  if  not  quite  colourless.  Tainted  flesh  may  be  deprived  of  its 
odour  by  this  means,  and  foul  water  be  purified  by  filtration  through  char- 
coal. The  substance  commonly  employed  to  decolorize  fluids  is  animal 
charcoal  reduced  to  a  fine  powder.  It  loses  the  property  of  absorbing  co- 
louring matters  by  use,  but  recovers  it  by  being  heated  to  redness. 

Charcoal  is  highly  combustible.  When  strongly  heated  in  the  open  air,  it 
takes  fire,  and  burns  slowly.  In  oxygen  gas,  its  combustion  is  lively,  and 
accompanied  with  the  emission  of  sparks.  In  both  cases  it  is  consumed 
without  flame,  smoke,  or  residue,  if  quite  pure ;  and  carbonic  acid  gas  is 
the  product  of  its  combustion. 

The  pure  inflammable  principle,  which  is  the  characteristic  ingredient  of 
all  kinds  of  charcoal,  is  called  carbon.  In  coke  it  is  in  a  very  impure  form. 
Wood-charcoal  contains  about  1-50  of  its  weight  of  alkaline  and  earthy 
salts,  which  constitute  the  ashes  when  this  species  of  charcoal  is  burned.  In 
plumbago,  the  carbon  is  thought  to  be  combined  with  a  small  portion  of  me- 
tallic iron.  Charcoal  derived  from  spirit  of  wine  is  almost  quite  pure  ;  and 
the  diamond  is  carbon  in  a  state  of  absolute  purity. 

The  diamond  is  the  hardest  substance  in  nature.  Its  texture  is  crystalline 
in  a  high  degree,  and  its  cleavage  very  perfect.  Its  primary  form  is  the  oo- 
tohedron.  Its  specific  gravity  is  3.52.  Acids  and  alkalies  do  not  act  upon 
it;  and  it  bears  the  most  intense  heat  in  close  vessels  without  fusing  or  un- 
dergoing any  perceptible  change.  Heated  to  redness  in  the  open  air,  it  is 
entirely  consumed.  Newton  first  suspected  it  to  be  combustible  from  its 
great  refracting  power,  a  conjecture  which  was  rendered  probable  by  the  ex- 
periments of  the  Florentine  academicians  in  1694,  and  subsequently  con- 
firmed by  several  philosophers.  Lavoisier  first  proved  it  to  contain  carbon 
by  throwing  the  sun's  rays,  concentrated  by  a  powerful  lens,  upon  a  dia- 
mond contained  in  a  vessel  of  oxygen  gas.  The  diamond  was  consumed 
entirely,  oxygen  disappeared,  and  carbonic  acid  was  generated.  It  has  since 
been  demonstrated  by  the  researches  of  Guyton-Morveau,  Smithson  Ten- 
nant,  Allen  and  Pepys,  and  Davy,  that  carbonic  acid  is  the  product  of  its 
combustion,  Guyton-Morveau  inferred  from  his  experiments  that  the  dia- 
mond is  pure  carbon,  and  that  charcoal  is  an  oxide  of  carbon.  Tennant 
burned  diamonds  by  heating  them  with  nitre  in  a  gold  tube;  and  compar- 
ing his  own  results  with  those  of  Lavoisier  on  the  combustion  of  charcoal, 
he  concluded  that  equal  weights  of  diamond  and  pure  charcoal,  in  combin- 
ing with  oxygen,  yield  precisely  equal  quantities  of  carbonic  acid.  He  was 
thus  induced  to  adopt  the  opinion,  that  charcoal  and  the  diamond  are  che- 
mically the  same  substance ;  and  that  the  difference  in  their  physical  cha- 
racter is  solely  dependent  on  a  difference  of  aggregation.*  This  conclusion 
was  confirmed  by  the  experiments  of  Allen  and  Pepys,t  and  Davy,t  who 

*  Philos.  Trans,  for  1797.  t  Ibid.  1807.  I  Ibid.  1814. 


CARBON.  187 

compared  the  product  of  the  combustion  of  the  diamond  with  that  derived 
from  different  kinds  of  charcoal.  The  latter  chemist  did  indeed  observe  the 
production  of  a  minute  quantity  of  water  during-  the  combustion  of  the 
purest  charcoal,  indicative  of  a  trace* of  hydrogen;  but  its  quantity  is  so 
small,  that  it  cannot  be  regarded  as  a  necessary  constituent.  It  proves  only 
that  a  trace  of  hydrogen  is  retained  by  charcoal  with  such  force,  that  it  can- 
not be  expelled  by  the  temperature  of  ignition. 

Chemists  are  agreed  that  carbonic  acid  is  a  compound  of  one  equivalent  of 
carbon  and  two  equivalents  of  oxygen,  and  that  carbonic  acid  gas  contains 
its  own  volume  of  oxygen.  Hence  the  difference  between  the  densities  of 
carbonic  acid  and  oxygen  (1.5239 — 1.1024),  or  0.4215  is  the  quantity  of 
carbon  united  with  1.1024  of  oxygen,  being  the  ratio  of  6.12  to  16.  Dr. 
Thomson,  on  the  same  principles  but  different  facts,  considers  6  as  the  true 
equivalent ;  but  the  composition  of  vegetable  compounds  attests  that  6.12  is 
more  nearly  correct  than  6,  though  the  latter  is  often  a  sufficient  approxima- 
tion. The  hypothetical  density  of  the  vapour  of  carbon,  calculated  as  ex- 
plained at  page  147,  is  0.4215,  and  100  cubic  inches  of  it  should  weigh 
13.0714  grains. 

The  composition  of  the  compounds  of  carbon  described  in  this  section  is 
as  follows  : — 

Carbon.  Oxygen.       Equiv.  Formulae. 

Carbonic  oxide      .  6,12  or  1  eq.  -j-     8  or  I  eq.  =  14.12     C  +  O  or  C. 

Carbonic  acid  6.12  or  1  eq.  -f  16  or  2  eq.  =  22.12     C  -f-  2O  or  C. 

Carbonic  oxide  gas  is  theoretically  considered  as  a  compound  of  100  mea- 
sures of  the  vapour  of  carbon  and  50  of  oxygen  condensed  into  100  measures  ; 
and  carbonic  acid  gas,  of  100  measures  of  the  vapour  of  carbon  and  100  of 
oxygen  condensed  into  100  measures. 

CARBONIC  ACID. 

Carbonic  acid  was  discovered  by  Dr.  Black  in  1757,  and  described  by  him 
in  his  inaugural  dissertation  on  magnesia  under  the  name  of  fixed  air.  He 
observed  the  existence  of  this  gas  in  common  limestone  and  magnesia,  and 
found  that  it  may  be  expelled  from  these  substances  by  the  action  of  heat  or 
acids.  He  also  remarked  that  the  same  gas  is  formed  during  respiration, 
fermentation,  and  combustion.  Its  composition  was  first  demonstrated 
synthetically  by  Lavoisier,  who  burned  carbon  in  oxygen  gas,  and  obtained 
carbonic  acid  as  the  product.  The  same  experiment  has  been  repeated  by 
Davy,  Allen  and  Pepys,  and  others,  with  the  result  that  in  the  combustion 
of  diamond  or  other  pure  carbonaceous  matter,  the  oxygen  undergoes  no 
change  of  volume,  or  in  other  words  that  carbonic  acid  gas  contains  its  own 
volume  of  oxygen.  Smithson  Tennant  illustrated  its  nature  analytically  by 
passing  the  vapour  of  phosphorus  over  chalk,  or  carbonate  of  lime  heated  to 
redness  in  a  glass  tube.  The  phosphorus  took  oxygen  from  the  carbonic 
acid,  charcoal  in  the  form  of  a  light  black  powder  was  deposited,  and  the 
phosphoric  acid,  which  was  formed,  united  with  the  lime. 

Carbonic  acid  is  most  conveniently  prepared  for  the  purposes  of  experi- 
ment by  the  action  of  hydrochloric  acid,  diluted  with  two  or  three  times  its 
weight  of  water,  on  fragments  of  marble  ;  when  the  hydrochloric  acid  takes 
the  lirne,  and  carbonic  acid  gas  escapes  with  effervescence. 

Carbonic  acid,  as  thus  procured,  is  a  colourless,  inodorous,  elastic  fluid, 
which  possesses  all  the  physical  characters  of  the  gases  in  an  eminent 
degree,  and  requires  a  pressure  of  thirty-six  atmospheres  to  condense  it  into 
a  liquid.  The  exact  knowledge  of  its  density  is  still  an  important  desidera- 
tum :  it  is  estimated  at  1.524  by  Dulong  and  Berzelius,  and  at  1.5277  by 
Dr.  Thomson.  (First  Principles,  i.  143.)  .According  to  the  estimate  in  the 
table,  page  146,  its  sp.  gr.  is  1.5239,  and  assuming  this  number,  100  cubic 
inches  should  weigh  47.2586  grains. 

Carbonic  acid  extinguishes  burning  substances  of  all  kinds,  and  the  com. 
bustion  does  not  cease  from  the  want  of  oxygen  only.  It  exerts  a  positive 


188  CARBON. 

influence  in  checking  combustion;  as  appears  from  the  fact,  that  a  candle 
cannot  burn  in  a  gaseous  mixture  composed  of  four  measures  of  atmospheric 
air  and  one  of  carbonic  acid. 

It  is  not  better  qualified  to  support  the  respiration  of  animals;  for  its  pre- 
sence, even  in  moderate  proportion,  is  soon  fatal.  An  animal  cannot  live  in 
air  which  contains  sufficient  carbonic  acid  for  extinguishing  a  lighted 
candle ;  and  hence  the  practical  rule  of  letting  down  a  burning  taper  into 
old  wells  or  pits  before  any  one  ventures  to  descend.  If  the  light  is  extin- 
guished, the  air  is  certainly  impure ;  and  there  is  generally  thought  to  be 
no  danger,  if  the  candle  continues  to  burn.  But  some  instances  have  been 
known  of  the  atmosphere  being  sufficiently  loaded  with  carbonic  acid  to 
produce  insensibility,  and  yet  not  so  impure  as  to  extinguish  a  burning  can- 
dle. (Christison  on  Poisons,  2d  Ed.  707.)  When  an  attempt  is  made  to 
inspire  pure  carbonic  acid,  violent  spasm  of  the  glottis  takes  place,  which 
prevents  the  gas  from  entering  the  lungs.  If  it  be  so  much  diluted  with 
air  as  to  admit  of  its  passing  the  glottis,  it  then  acts  as  a  narcotic  poison  on 
the  system.  It  is  this  gas  which  has  often  proved  destructive  to  persons 
sleeping  in  a  confined  room  with  a  pan  of  burning  charcoal. 

Carbonic  acid  is  quite  incombustible,  and  cannot  be  made  to  unite  with  an 
additional  portion  of  oxygen.  It  is  a  compound,  therefore,  in  which  carbon 
is  in  its  highest  degree  of  oxidation. 

Lime-water  becomes  turbid  when  brought  into  contact  with  carbonic 
acid.  The  lime  unites  with  the  gas,  forming  carbonate  of  lime,  which,  from 
its  insolubility  in  water,  at  first  renders  the  solution  milky,  and  afterwards 
forms  a  white  flaky  precipitate.  Hence  lime-water  is  not  only  a  valuable 
test  of  the  presence  of  carbonic  acid,  but  is  frequently  used  to  withdraw  it 
altogether  from  any  gaseous  mixture  that  contains  it. 

Carbonic  acid  is  absorbed  by  water.  This  may  easily  be  demonstrated 
by.  agitating  the  gas  with  that  liquid,  or  by  leaving  a  jar  full  of  it  inverted 
over  water.  In  the  first  case  the  gas  disappears  in  the  course  of  a  minute  ; 
and  in  the  latter  it  is  gradually  absorbed.  Recently  boiled  water  dissolves 
its  own  volume  of  carbonic  acid  at  the  common  temperature  and  pressure; 
but  it  will  take  up  much  more  if  the  pressure  be  increased.  The  quantity 
of  the  gas  absorbed  is  in  exact  ratio  with  the  compressing:  force;  that  is, 
water  dissolves  twice  its  volume  when  the  pressure  is  doubled,  and  three 
times  its  volume  when  the  pressure  is  trebled. 

A  saturated  solution  of  carbonic  acid  may  be  made  by  transmitting  a 
stream  of  the  gas  through  a  vessel  of  cold  water  during  the  space  of  half  an 
hour,  or  still  better  by  the  use  of  a  Woulfe's  bottle,  or  Nooth's  apparatus,  so 
as  to  aid  the  absorption  by  pressure.  Water  and  other  liquids  which  have 
been  charged  with  carbonic  acid  under  great  pressure,  lose  the  greater  part 
of  the  gas  when  the  pressure  is  removed.  The  effervescence  which  takes 
place  on  opening  a  bottle  of  ginger  beer,  cider,  or  brisk  champaign,  is  owing 
to  the  escape  of  carbonic  acid  gas.  Water,  which  is  fully  saturated  with 
carbonic  acid  gas,  sparkles  when  it  is  poured  from  one  vessel  into  another. 
The  solution  has  an  agreeably  acidulous  taste,  and  gives  to  litmus  paper  a 
red  stain  which  is  lost  on  exposure  to  the  air.  On  the  addition  of  lime- 
water  to  it,  a  cloudiness  is  produced,  which  at  first  disappears,  because  the 
carbonate  of  lime  is  soluble  in  excess  of  carbonic  acid ;  but  a  permanent 
precipitate  ensues  when  the  free  acid  is  neutralized  by  an  additional  quan- 
tity of  lime-water.  The  water  which  contains  carbonic  acid  in  solution  is 
wholly  deprived  of  the  gas  by  boiling.  Removal  of  pressure  from  its  surface 
by  means  of  the  air-pump  has  a  similar  effect. 

The  agreeable  pungency  of  beer,  porter,  and  ale,  is  in  a  great  measure 
owing  to  the  presence  of  carbonic  acid ;  by  the  loss  of  which,  on  exposure  to 
the  air,  they  become  stale.  All  kinds  of  spring  and  well-water  contain 
carbonic  acid  absorbed  from  the  atmosphere,  and  to  which  they  are  partly 
indebted  for  their  pleasant  flavour.  Boiled  water  has  an  insipid  taste  from 
the  absence  of  carbonic  acid. 
Carbonic  acid  is  always  present  in  the  atmosphere,  even  at  the  summit 


CARBON.  189 

of  the  highest  mountains,  or  at  a  distance  of  several  thousand  feet  above  the 
ground.  Its  presence  may  be  demonstrated  by  exposing  lime-water  in  an 
open  vessel  to  the  air,  when  its  surface  will  soon  be  covered  with  a  pellicle, 
which  is  carbonate  of  lime.  The  origin  of  the  carbonic  acid  is  obvious. 
Besides  being  formed  abundantly  by  the  combustion  of  all  substances  which 
contain  carbon,  the  respiration  of  animals  is  a  fruitful  source  of  it,  as  may  be 
proved  by  breathing  for  a  few  minutes  into  lime-water;  and  it  is  also  genera- 
ted in  all  the  spontaneous  changes  to  which  dead  animal  and  vegetable  mat- 
ters are  subject.  The  carbonic  acid  proceeding  from  such  sources,  is  com- 
monly diffused  equably  through  the  air;  but  when  any  of  these  processes  oc- 
cur in  low  confined  situations,  as  at  the  bottom  of  old  wells,  the  gas'is  then  apt 
to  accumulate  there,  and  form  an  atmosphere  called  choke  damp,  which  is 
fatal  to  any  animals  that  are  placed  in  it.  These  accumulations  happily 
never  take  place,  except  when  there  is  some  local  origin  for  the  carbonic 
acid  ;  as,  for  example,  when  it  is  generated  by  fermentative  processes  going 
on  at  the  surface  of  the  ground,  or  when  it  issues  directly  from  the  earth,  as 
happens  at  the  Grotto  del  Cane  in  Italy,  and  at  Pyrmont  in  Westphalia. 
There  is  no  real  foundation  for  the  opinion  that  carbonic  acid  can  separate 
itself  from  the  great  mass  of  the  atmosphere,  and  accumulate  in  a  low  situa- 
tion, merely  by  the  force  of  gravity.  Such  a  supposition  is  contrary  to  the 
well-known  tendency  of  gases  to  diffuse  themselves  equally  through  each 
other.  It  is  also  contradicted  by  observation  ;  for  many  deep  pits,  which  are 
free  from  putrefying  organic  remains,  though  otherwise  favourably  situated 
for  such  accumulations,  contain  pure  atmospheric  air. 

Though  carbonic  acid  is  the  product  of  many  natural  operations,  chemists 
have  not  hitherto  noticed  any  increase  in  the  quantity  contained  in  the  atmos- 
phere. The  only  known  process  which  tends  to  prevent  increase  in  its  pro- 
portion, is  that  of  vegetation.  Growing  plants  purify  the  air  by  withdraw- 
ing carbonic  acid,  and  yielding  an  equal  volume  of  pure  oxygen  in  return  ; 
but  whether  a  full  compensation  is  produced  by.  this  cause,  has  not  yet  been 
satisfactorily  determined. 

Carbonic  acid  is  contained  in  the  earth.  Many  mineral  springs,  such  as 
those  of  Tunbridge,  Pyrmont,  and  Carlsbad,  are  highly  charged  with  it.  In 
combination  with  lime  it  forms  extensive  masses  of  rock,  which  geologists 
have  found  to  occur  in  all  countries,  and  in  every  formation. 

Carbonic  acid  unites  with  alkaline  substances,  and  the  salts  so  constituted 
are  called  carbonates.  Its  acid  properties  are  feeble,  so  that  it  is  unable  to 
neutralize  completely  the  alkaline  properties  of  potassa,  soda,  and  lithia.  For 
the  same  reason,  all  the  carbonates,  without  exception,  are  decomposed  by 
hydrocholoric  and  all  the  stronger  acids];  when  carbonic  acid  is  displaced, 
and  escapes  in  the  form  of  gas. 

CARBONIC  OXIDE  GAS. 

When  two  parts  of  well-dried  chalk  and  one  of  pure  iron  filings  are  mixed 
together,  and  exposed  in  a  gun  barrel  to  a  red  heat,  a  large  quantity  of 
aeriform  matter  is  evolved,  which  may  be  collected  over  water.  On  examina- 
tion, it  is  found  to  contain  two  compounds  of  carbon  and  oxygen,  one  of 
which  is  carbonic  acid,  and  the  other  carbonic  oxide.  By  washing  the 
mixed  gases  with  lime-water,  the  carbonic  acid  is  absorbed,  and  carbonic 
oxide  gas  is  left  in  a  state  of  purity.  A  very  elegant  mode  of  preparing 
carbonic  oxide  has  been  suggested  by  Dumas.  (Ed.  Journal  of  Science,  vi. 
350.)  The  process  consists  in  mixing  binoxalate  of  potassa  with  five  or  six 
times  its  weight  of  concentrated  sulphuric  acid,  and  heating  the  mixture  in 
a  retort  or  other  convenient  glass  vessel.  Effervescence  soon  ensues,  owing 
to  the  escape  of  gas,  consisting  of  equal  measures  of  carbonic  acid  and  car- . 
bonic  oxide  gases;  and  on  absorbing  the  former  by  an  alkaline. solution,  the 
latter  is  left  in  a  state  of  perfect  purity.  To  comprehend  the  theory  of  the 
process  it  is  necessary  to  premise,  that  oxalic  acid  is  a  compound  of  .equal 
measures  of  carbonic  acid  and  carbonic  oxide,  or  at  least  its  elements  are  in 


190  CARBON. 

the  proportion  to  form  these  gases;  and  that  it  cannot  exist  unless  in  com- 
bination with  water  or  some  other  substance.  Now  the  sulphuric  acid  unites 
both  with  the  potassa  and  water  of  the  binoxalate,  and  the  oxalic  acid,  being 
thus  set  free,  is  instantly  decomposed.  Oxalic  acid  may  be  substituted  in 
this  process  for  binoxalate  of  potassa. 

Priestley  discovered  this  gas  by  igniting  chalk  in  a  gun-barrel,  and  after- 
wards obtained  it  in  greater  quantity  from  chalk  and  iron  filings.  He  sup- 
posed it  to  be  a  mixture  of  hydrogen  and  carbonic  acid  gases.  Its  real  na- 
ture was  pointed  out  by  Mr.  Cruickshank,*  and  about  the  same  time  by  Cle- 
ment and  Desormes.t 

Carbonic  oxide  gas  is  colourless  and  insipid.  It  does  not  affect  the  blue 
colour  of  vegetables  in  any  way ;  nor  does  it  combine,  like  carbonic  acid, 
with  lime  or  any  of  the  pure  alkalies.  It  is  very  sparingly  dissolved  by 
water.  Lime-water  does  not  absorb  it,  nor  is  its  transparency  affected  by  it. 

Carbonic  oxide  is  inflammable.  When  a  lighted  taper  is  plunged  into  a 
jar  full  of  that  gas,  the  taper  is  extingushed ;  but  the  gas  itself  is  set  on  fire, 
and  burns  calmly  at  its  surface  with  a  lambent  blue  flame.  The  sole  product 
of  its  combustion,  when  the  gas  is  quite  pure,  is  carbonic  acid,  a  fact  which 
proves  that  it  does  not  contain  any  hydrogen. 

Carbonic  oxide  gas  cannot  support  respiration.  It  acts  injuriously  on  the 
system ;  for  if  diluted  with  air,  and  taken  into  the  lungs,  it  very  soon  occa- 
sions headach  and  other  unpleasant  feelings;  and  when  breathed  pure,  it 
almost  instantly  causes  profound  coma. 

A  mixture  of  carbonic  oxide  and  oxygen  gases  may  be  made  to  explode 
by  flame,  by  a  red-hot  solid  body,  or  by  the  electric  spark.  If  they  are 
mixed  together  in  the  ratio  of  100  measures  of  carbonic  oxide  and  rather 
more  than  50  of  oxygen,  and  the  mixture  is  inflamed  in  Volta's  eudiometer 
by  electricty,  so  as  to  collect  the  product  of  the  combustion,  the  whole  of  the 
carbonic  oxide,  together  with  50  measures  of  oxygen,  disappears,  and  100 
measures  of  carbonic  acid  gas  occupy  their  place.  From  this  fact,  first  ascer- 
tained by  Berthollet,  and  since  'confirmed  by  subsequent  observation,  it  fol- 
lows that  carbonic  oxide  contains  half  as  much  oxygen,  and  as  much  carbon, 
as  carbonic  acid.  Accordingly  its  density  should  be  0.4215  (sp.  gr.  of 
carbon  vapour)  -f-0.5512  (half  the  sp.  gr.  of  oxygen  gas)  =0.9727,  which  is 
the  number  found  experimentally  by  Dulong  and  Berzelius.  Hence  100  cubic 
inches  should  weigh  30.1650  grains. 

The  first  process  mentioned  for  generating  carbonic  oxide  will  now  be  in- 
telligible. The  principle  of  the  method  is  to  bring  carbonic  acid  at  a  red  heat 
in  contact  with  some  substance  which  has  a  strong  affinity  for  oxygen.  This 
condition  is  fulfilled  by  igniting  chalk,  or  any  carbonate  which  can  bear  a 
red  heat  without  decomposition,  such  as  the  carbonate  of  baryta,  strontia, 
soda,  potassa,  or  lithia,  with  half  its  weight  of  iron  filings  or  charcoal.  The 
carbonate  is  reduced  to  the  caustic  slate,  and  its  carbonic  acid  is  converted 
into  carbonic  oxide,  by  yielding  oxygen  to  the  iron  or  charcoal.  When  the 
former  is  used,  oxide  of  iron  is  the  product;  when  charcoal  is  employed,  the 
charcoal  itself  is  oxidized,  and  yields  carbonic  oxide.  This  gas  may  like- 
wise be  generated  by  heating  to  redness  a  mixture  of  almost  any  metallic 
oxide  with  one-sixth  of  its  weight  of  charcoal  powder.  The  oxides  of  zinc, 
iron,  and  copper  are  the  cheapest  and  most  convenient.  It  may  also  be 
formed  by  transmitting  a  current  of  carbonic  acid  gas  over  ignited  charcoal. 
In  all  these  processes,  it  is  essential  that  the  ingredients  be  quite  free  from 
moisture  and  hydrogen,  otherwise  some  carburetted  hydrogen  gas  would  be 
generated.  The  product  should  always  be  washed  with  lime-water  to  free  it 
from  carbonic  acid. 

Dr.  Henry  has  ascertained  that  when  a  succession  of  electric  sparks  is 


«  Nicholson's  Journal,  4to.  Ed.  vol.  v.    t  Annales  de  Chimie,  vol.  xxxix. 


SULPHUR.  191 

passed  through  carbonic  acid  confined  over  mercury,  a  portion  of  that  gas  is 
converted  into  carbonic  oxide  and  oxygen.  When  a  mixture  of  hydrogen 
and  carbonic  acid  gases  is  electrified,  a  portion  of  the  latter  yields  one-half 
of  its  oxygen  to  the  former,  water  is  generated,  and  carbonic  oxide  pro- 
duced. On  electrifying  a  mixture  of  equal  measures  of  carbonic  oxide  and 
protoxide  of  nitrogen,  both  gases  are  decomposed  without  change  of  volume, 
and  the  residue  consists  of  equal  measures  of  carbonic  acid  and  nitrogen 
gases.  The  carbonic  oxide  should  be  in  very  slight  excess,  in  order  to  en- 
sure the  success  of  the  experiment.  On  this  fact  is  founded  Dr.  Henry's 
method  of  analyzing  protoxide  of  nitrogen,  and  testing  its  purity,  as  will  be 
more  particularly  mentioned  in  the  fourth  part  of  the  work. 


SECTION    VII. 


SULPHUR. 

SULPHUR  occurs  as  a  mineral  production  in  some  parts  of  the  earth,  parti- 
cularly in  the  neighbourhood  of  volcanoes,  as  in  Italy  and  Sicily.  It  is  com- 
monly fou-nd  in  a  massive  state;  but  it  is  sometimes  met  with  crystallized  in 
the  form  of  an  oblique  rhombic  octohedron.  It  exists  much  more  abundant- 
ly in  combination  with  several  metals,  such  as  silver,  copper,  antimony,  lead, 
and  iron.  It  is  procured  in  large  quantity  by  exposing  iron  pyrites  to  a  red 
heat  in  close  vessels. 

Sulphur  is  a  brittle  solid  of  a  greenish-yellow  colour,  emits  a  peculiar 
odour  when  rubbed,  and  has  little  taste.  It  is  a  non-conductor  of  electricity, 
and  is  excited  negatively  by  friction.  Its  specific  gravity  is  1.99.  Its  point 
of  fusion  is  216°  F. ;  between  230°  and  280°  it  possesses  the  highest  degree 
of  fluidity,  is  then  of  an  amber  colour,  and  if  cast  into  cylindrical  moulds, 
forms  the  common  roll  sulphur  of  commerce.  It  begins  to  thicken  near 
320°,  and  acquires  a  reddish  tint ;  and  at  temperatures  between  428°  and 
482°,  it  is  so  tenacious  that  the  vessel  may  be  inverted  without  causing  it  to 
change  its  place.  From  482°  to  its  boiling  point  it  again  becomes  liquid, 
but  never  to  the  same  extent  as  when  at  248°.  When  heated  to  at  least 
428°,  and  then  poured  into  water,  it  becomes  a  ductile  mass,  which  may  be 
used  for  taking  the  impression  of  seals.  (Dumas.) 

Fused  sulphur  has  a  tendency  to  crystallize  in  cooling.  A  crystalline  ar- 
rangement is  perceptible  in  the  centre  of  common  roll  sulphur;  and 'by  good 
management  regular  crystals  may  be  obtained.  For  this  purpose  several 
pounds  of  sulphur  should  be  melted  in  an  earthen  crucible;  and  when  par- 
tially cooled,  the  outer  solid  crust  should  be  pierced,  and  the  crucible  quickly 
inverted,  so  that  the  inner  and  as  yet  fluid  parts  may  gradually  flow  out. 
On  breaking  the  solid  mass,  when  quite  cold,  crystals  of  sulphur  will  be 
found  in  its  interior. 

Sulphur  is  very  volatile.  It  begins  to  rise  slowly  in  vapour  even  before  it 
is  completely  fused.  At  550°  or  600°  F.  it  volatilizes  rapidly,  and  condenses 
again  unchanged  in  close  vessels.  Common  sulphur  is  purified  by  this  pro- 
cess;  and  if  the  sublimation  be  conducted  slowly,  the  sulphur  collects  in  the 
receiver  in  the  form  of  detached  crystalline  grains,  called  powers  of  sulphur. 
In  this  state,  however,  it  is  not  quite  pure ;  for  the  oxygen  of  the  air  within 
the  apparatus  combines  with  a  portion  of  sulphur  during  the  process,  and 
forms  sulphurous  acid.  The  acid  may  be  removed  by  washing  the  flowers 
repeatedly  with  water. 

The  density  of  sulphur  vapour  was  found  by  Dumas  to  lie  between  6  51 
and  6.617,  and  by  Mitscherlich  to  be  6.9  (An.  de  Ch.  et  do  Ph.  Iv.  8.):  its 


192  SULPHUR. 

density  by  calculation  (page  146)  is  6.6558.  Hence,  could  the  vapour  con- 
tinue  as  such  at  60°  F.  and  30  Bar.,  100  cubic  inches  should  weigh  206.4076 
grains. 

Sulphur  is  insoluble  in  water,  but  unites  with  it  under  favourable  circum- 
stances, forming  the  white  hydrate  of  sulphur,  termed  lac  sulphuris.*  It 
dissolves  readily  in~boiling  oil  of  turpentine.  The  solution  has  a  reddish- 
brown  colour  like  melted  sulphur,  and  if  fully  saturated  deposites  numerous 
small  crystals  in  cooling.  Sulphur  is  also  soluble  in  alcohol,  if  both  sub- 
stances are  brought  together  in  the  form  of  vapour.  The  sulphur  is  precipi- 
tated from  the  solution  by  the  addition  of  water. 

Sulphur,  like  charcoal,  retains  a  portion  of  hydrogen  so  obstinately  that  it 
cannot  be  wholly  freed  from  it  either  by  fusion  or  sublimation.  Sir  H-.  Davy 
detected  its  presence  by  exposing  sulphur  to  the  strong  heat  of  a  powerful 
galvanic  battery,  when  some  hydrosulphuric  acid  gas  was  disengaged.  The 
hydrogen,  from  its  minute  quantity,  can  only  be  regarded  in  the  light  of  an 
accidental  impurity,  and  as  in  no  wise  essential  to  the  nature  of  sulphur. 

When  sulphur  is  heated  in  the  open  air  to  300°  or  a  little  higher,  it  kin- 
dles spontaneously,  and  burns  with  a  faint  blue  light.  In  oxygen  gas  its 
combustion  is  far  more  vivid,  the  flame  is  much  larger,  and  of  a  bluish- 
white  colour.  Sulphurous  acid  is  the  product  in  both  instances ;  no  sul- 
phuric acid  is  formed  even  in  oxygen  gas,  unless  moisture  be  present. 

The  oxygen  in  the  oxide  and  acid  of  neutral  sulphates  is  in  the  ratio  of  1 
to  3  ;  so  that  when  the  composition  of  a  metallic  oxide,  and  the  quantity  of 
acid  by  which  it  is  neutralized  are  known,  the  equivalent  of  sulphur  may  be 
calculated.  On  this  principle  has  Berzelius  inferred,  from  the  composition 
of  sulphate  of  the  oxide  of  lead,  that  the  equivalent  of  sulphur  is  16.12;  and 
the  number  which  I  have  obtained  in  the  same  way  from  the  same  salt 
and  from  sulphate  of  baryta,  is  16.09.  As  a  mean  of  these  results,  16.1  may 
be  taken  as  the  equivalent  of  sulphur.  The  number  16,  adopted  in  this 
country,  is,  therefore,  for  many  purposes  a  sufficient  approximation. 

The  compounds  of  sulphur  described  in  this  section  are  composed  as  fol- 
lows : — 

Sulphur.  Oxygen.       Equiv.          Formulae 

Sulphurous  acid  16.1  or  1  eq.  +  16  or  2  eq.  =  32.1          S+2O  or  S 

Sulphuric  acid  1*6.1  or  1  eq.  +  24  or  3  eq.  =  40.1         S+3O  or  S 

Hyposulphurous  acid    32.2  or  2  eq.  4-  16  or  2  eq.  =  48.2       2S+2O  or  S 

Hyposulphuric  acid       32.2  or  2  eq.  +  40  or  5  eq.  =  72.2       2S+ 5O  or  S_ 

Taking  16.66  as  the  combining  volume  of  the  vapour  of  sulphur,  the  weight 
of  which  is  represented  by  1.1093  (page  149),  these  compounds  by  measure 
are  thus  constituted  :^ 

Sulph.     Oxy.  Condensed  into.  Densities. 

Sulphurous  acid  16.66  +  100  100  1.1093+1.1024=2.2117 

Sulphuric  acid  16.66  +  150  100  1.1093+1.6536=2.7629 

Hyposulphurous  acid  33.33  +  100         unknown. 
Hyposulphuric  acid     33.33  +  250        unknown. 

SULPHUROUS  ACID  GAS. 

Pure  sulphurous  acid,  at  the  common  temperature  and  pressure,  is  a  co- 
lourless transparent  gas,  which  was  first  obtained  in  a  separate  state  by 
Priestley.  It  is  the  sole  product  when  sulphur  is  burned  in  air  or  dry  oxy- 

*  Berzelius  asserts  that  the  lac  sulphuris  is  not  a  hydrate,  but  sulphur 
united  with  a  minute  portion  of  hydrogen. — Ed. 


SULPHUR.  193 

gen  ga&,  and  ia  freely  evolved,  mixed  with  carbonic  acid,  when  chips  of  wood, 
straw,  cork,  oil,  or  most  other  organic  matters  are  heated  in  strong  sulphuric 
•acid  which  yields  oxygen  to  the  carbon  and  hydrogen  of  those  substances, 
«nd  is  thereby  converted  into  sulphurous  acid.  Nearly  all  the  metals,  with 
the  aid  of  heat,  have  a  similar  effect :  one  portion  of  the  acid  yields  oxygen 
to  the  metal,  and  is  thus  reduced  to  sulphurous  acid ;  while  the  metallic  oxide, 
•at  the  moment  of  its  formation,  unites  with  sulphuric  acid.  A  very  pure  gas 
may  thus  be  obtained  by  means  of  copper  or  mercury. 

Sulphurous  acid  has  a  pungent  suffocating  odour,  being  that  emitted  by 
burning  sulphur;  its  taste  is  acid;  sp.  gr,  2.2117,  and  100  C.  I.  at  60°  and 
30  Bar.  weigh  68.5885  grains ;  it  is  liquid  at  45°  under  the  pressure  of  two 
atmospheres,  and  at  0°  under  that  of  one  atmosphere.  The  gas  extinguishes 
all  burning  bodies  which  are  immersed  into  it,  and  is  not  inflammable.  It 
does  not  support  respiration,  but  causes  violent  irritation  and  spasm  of  the 
glottis;  and  even  when  diluted  with  air,  it  excites  cough  when  inspired,  and 
causes  a  peculiar  uneasiness  about  the  chest.  Water,  at  60°  and  30  Bar. 
dissolves  33  times  its  volume,  the  solution  having  the  peculiar  odour  of  the 
gas.,  and  yielding  it  unchanged  by  ebullition.  It  has  considerable  bleaching 
properties  :  at  first  it  reddens  litmus  paper,  and  then  slowly  bleaches  it;  but 
most  vegetable  colours,  as  of  the  rose  and  violet,  are  speedily  removed  by  it 
without  being  first  reddened.  The  colouring  principle  is  not  destroyed,  but 
may  be  restored  by  a  stronger  acid,  or  by  an  alkali. 

Davy  proved  that  sulphurous  acid  gas  contains  exactly  its  own  volume  of 
oxygen  (Elements,  p.  273),  and  consequently  the  difference  in  the  weights  or 
sp.  gr.  of  these  gases  (2-2117  — 1-1024  =  1-1093)  gives  the  weight  of  sul- 
phur combined  with  the  oxygen.  The  sulphur  and  oxygen  are  thus  found 
to  be  in  the  ratio  of  H093  to  1-1024,  or  16-1  to  1<3. 

Liquid  sulphurous  acid  is  easily  obtained  by  transmitting  the  dry  pure 
gas  through  a  glass  tube  surrounded  by  a  freezing  mixture  of  snow  and  salt. 
Its  sp.  gr.  is  1-45 ;  it  boils  at  14°,  and  from  the  rapidity  of  its  evaporation 
causes  intense  cold;  it  conducts  electricity  (Kemp).  When  exposed  to  cold 
in  the  moist  state,  a  crystalline  solid  is  formed,  which  contains  20  per  cent, 
of  water,  and  probably  consists  of  one  equivalent  of  the  acid  to  one  equiva- 
lent of  water. 

Though  sulphurous  acid  cannot  be  made  to  burn  by  the  approach  of 
flame,  it  has  a  very  strong  attraction  for  oxygen,  uniting  with  it  under  fa- 
vourable circumstances,  and  forming  sulphuric  acid.  The  presence  of  mois- 
ture is  essential  to  this  change.  A  mixture  of  sulphurous  acid  and  oxygen 
gases,  if  quite  dry,  may  be  preserved  over  mercury  for  any  length  of  time 
without  chemical  action.;  but  if  a  little  water  be  admitted,  the  sulphurous 
acid  gradually  unites  with  oxygen,  and  sulphuric  acid  is  generated.  Many 
of  the  chemical  properties  of  sulphurous  acid  are  owing  to  its  affinity  for 
oxygen.  The  solutions  of  metals  which  have  a  weak  affinity  for  oxygen,  such 
as  gold,  platinum,  and  mercury,  are  completely  decomposed  by  it,  those  sub- 
stances being  precipitated  in  the  metallic  form.  Nitric  acid  converts  it  in- 
stantly into  sulphuric  acid  by  yielding  some  of  its  oxygen.  Peroxide  of  man- 
ganese causes  a  similar  change,  and  is  itself  converted  into  protoxide  of 
manganese,  which  unites  with  the  resulting  sulphuric  acid. 

Sulphurous  acid  gas  may  be  passed  through  red-hot  tubes  without  decom- 
position. Several  substances  which  have  a  strong  affinity  for  oxygen,  such 
as  hydrogen,  carbon,  and  potassium,  decompose  it  at  the  temperature  of 
ignition. 

Sulphurous  acid  combines  with  metallic  oxides,  and  forms  salts  called 
sulphites,  which  are  decomposed  by  sulphuric  acid,  and  then  emit  the  cm  - 
racteristic  odour  of  sulphurous  acid. 

Its  eq.  is  32-1 ;  eq.  vol.  —  100;  symb.  S  +  2O,  SO,  or  S. 

SULPHURIC  ACID. 

Hist,  and  Prep.— Sulphuric  acid,  or  oil  of  vitriol  as  it  is  often  called,  was 
discovered  by  Basil  Valentine  towards  the  close  of  the  15th  century.  It  is 

17 


194  SULPHUR. 

procured  for  the  purposes  of  commerce  by  two  methods.  One  of  these  has 
been  long  pursued  in  the  manufactory  at  Nordhausen  in  Germany,  and  con- 
sists in  decomposing  sulphate  of  oxide  of  iron  (green  vitriol)  by  heat.  This 
salt  contains  six  equivalents  of  water  of  crystallization  ;  and  when  strongly 
dried  by  the  fire,  it  crumbles  down  into  a  white  powder,  which,  accord- 
ing to  Thomson,  contains  one  equivalent  of  water.  On  exposing  this  dried 
protosulphate  to  a  red  heat,  its  acid  is  wholly  expelled,  the  greater  part  pass- 
ing over  unchanged  into  the  receiver,  in  combination  with  the  water  of  the 
salt.  Part  of  the  acid,  however,  is  resolved  by  the  strong  heat  employed 
in  the  distillation  into  sulphurous  acid  and  oxygen.  The  former  escapes  as 
gas  throughout  the  whole  process ;  the  latter  only  in  the  middle  and  latter 
stages  ;  since,  in  the  beginning  of  the  distillation,  it  unites  with  the  protoxide 
of  iron.  Peroxide  of  iron  is  the  sole  residue. 

The  acid,  as  procured  by  this  process,  is  a  dense,  oily  liquid  of  a  brown- 
ish tint.  It  emits  copious  white  vapours  on  exposure  to  the  air,  and  is  hence 
called  fuming  sulphuric  acid.  Its  sp.  gr.  is  1.896  or  1.90.  According 
to  Thomson  it  consists  of  80.2  parts  or  two  equivalents  of  anhydrous  acid, 
and  9  parts  or  one  equivalent  of  water.  On  putting  this  acid  into  a  glass  re- 
tort, to  which  a  receiver  surrounded  by  snow  is  securely  adapted,  and  heat- 
ing it  gently,  a  transparent  colourless  vapour  passes  over,  which  condenses 
into  a  white  crystalline  solid.  This  substance  is  pure  anhydrous  sulphu- 
ric acid.  It  is  tough  and  elastic,  liquefies  at  66°,  and  boils  at  a  temperature 
between  104°  and  122°,  forming,  if  no  moisture  is  present,  a  transparent 
vapour.  Exposed  to  the  air,  it  unites  with  watery  vapour,  and  flies  off  in 
the  form  of  dense  white  fumes.  The  residue  of  the  distillation  is  no  longer 
fuming,  and  is  in  every  respect  similar  to  the  common  acid  of  commerce. 

The  other  process  for  forming  sulphuric  acid,  which  is  practised  in  Bri- 
tain and  in  most  parts  of  the  Continent,  is  by  burning  sulphur  previously 
mixed  with  one-eighth  of  its  weight  of  nitrate  of  potassa.  The  mixture  is 
burned  in  a  furnace  so  contrived  that  the  current  of  air,  which  supports  the 
combustion,  conducts  the  gaseous  products  into  a  large  leaden  chamber,  the 
bottom  of  which  is  covered  to  the  depth  of  several  inches  with  water.  The 
nitric  acid  yields  oxygen  to  a  portion  of  sulphur,  and  converts  it  into  sul- 
phuric acid,  which  combines  with  the  potassa  of  the  nitre;  while  the  greater 
part  of  the  sulphur  forms  sulphurous  acid  by  uniting  with  the  oxygen  of 
the  air.  The  nitric  acid,  in  losing  oxygen,  is  converted,  partly  perhaps  into 
nitrous  acid,  but  chiefly  into  binoxide  of  nitrogen,  which,  by  mixing  with 
air  at  the  moment  of  its  separation,  gives  rise  to  the  red  nitrous  acid 
vapours.  The  gaseous  substances,  present  in  the  leaden  chamber,  are, 
therefore,  sulphurous  and  nitrous  acids,  atmospheric  air,  and  watery  va- 
pour. The  explanation  of  the  mode  in  which  these  substances  react  on  each 
other,  so  as  to  form  sulphuric  acid,  was  suggested  by  the  experiments  of 
Clement  and  Desormes,  (An.  de  Ch.  lix.)  and  Davy,  (Elements,  p.  276.) 
When  dry  sulphurous  acid  gas  and  nitrous  acid  vapour  are  mixed  to- 
gether in  a  glass  vessel  quite  free  from  moisture,  no  change  ensues ;  but  if 
a  few  drops  of  water  be  added,  in  order  to  fill  the  space  with  aqueous  vapour, 
the  white  crystalline  compound,  described  at  page  179,  is  immediately  pro- 
duced. Clement  and  D6sormes  believed  it  to  consist  of  sulphuric  acid,  bin- 
oxide  of  nitrogen,  and  water;  and  Davy,  of  sulphurous  acid,  nitrous  acid, 
and  water.  But  the  observation,  that  the  same  compound  may  be  made 
with  sulphuric  and  anhydrous  nitrous  acids,  and  that  when  decomposed  by 
water,  both  nitrous  acid  and  binoxide  of  nitrogen  are  disengaged,  led  Gay- 
Lussac  to  the  opinion  which  now  seems  to  be  fully  substantiated  by  experi- 
ment. (Page  179.)  A  consistent  account  may,  therefore,  be  given  of  what 
really  takes  place  within  the  leaden  chambers. — The  mutual  reaction  of  hu- 
midity, sulphurous  acid,  and  nitrous  acid,  gives  rise  to  the  crystalline  com- 
pound of  sulphuric  acid,  hyponitrous  acid,  and  water ;  and  when  this  solid 
falls  into  the  water  of  the  chamber,  it  is  instantly  decomposed,  sulphuric 
acid  is  dissolved,  and  nitrous  acid  and  binoxide  of  nitrogen  escape  with  ef- 
fervescence. The  nitrous  acid  thus  set  free,  as  well  as  that  reproduced  by 


-.  SULPHUR.  195 

the  binoxide  uniting  with  the  oxygen  of  the  atmosphere,  is  again  intermixed 
with  sulphurous  acid  and  humidity,  and  thus  gives  rise  to  a  second  portion 
of  the  crystalline  solid,  which  undergoes  the  same  change  as  the  first.  Acer- 
tain  portion  of  nitric  acid  is  usually  formed  by  the  action  of  water  on  the 
nitrous  acid ;  but  the  presence  of  sulphuric  acid  in  that  water  tends  to  pre- 
vent the  free  decomposition  of  nitrous  acid  which  pure  water  produces. 
Nay,  when  the  water  becomes  pretty  strongly  acid,  the  nitric  acid  at  first 
generated  is  reduced,  by  absorbed  sulphurous  acid,  into  the  hyponitrous, 
which  unites  with  sulphuric  acid,  and  remains  even  after  concentration :  it 
is  the  cause  of  the  evolution  of  binoxide  of  nitrogen  which  usually  ensues 
.when  common  oil  of  vitriol  is  diluted,  the  hyponitrous  acid  being  then  de- 
composed by  the  water  (Dana).  When  the  water  of  the  chamber  is  suffi- 
ciently charged  with  acid,  it  is  drawn  off,  and  concentrated  by  evaporation. 
It  hence  appears  that  the  oxygen,  by  which  the  sulphurous  is  converted 
into  sulphuric  acid,  is  in  reality  supplied  by  the  air ;  that  the  combination  is 
effected,  not  directly,  but  through  the  medium  of  nitrous  acid ;  and  that  a 
small  quantity  of  nitrous  acid  is  sufficient  for  the  production  of  a  large 
quantity  of  sulphuric  acid.  The  decomposition  of  the  crystalline  solid  by 
water  seems  owing  to  the  strong  affinity  of  that  liquid  for  sulphuric  acid. 

Besides  hyponitrous  acid  as  above  stated,  it  contains  potassa,  and  the  ox- 
ide of  lead,  and  sometimes  iron,  the  first  derived  from  the  nitre  employed  in 
making  it,  and  the  two  latter  from  the  leaden  chamber.  To  separate  them, 
the  acid  should  be  distilled  from  a  glass  or  platinum  retort.  The  former  may 
be  safely  used  by  putting  into  it  some  fragments  of  platinum  leaf,  which 
cause  the  acid  to  boil  freely  on  applying  heat,  without  danger  of  breaking 
the  vessel,  Arsenious  acid,  derived  from  arsenic  in  the  sulphur  used  in  the 
manufacture,  has  been  lately  detected  in  most  of  the  oil  of  vitriol  made  in 
Germany ;  and  from  that  source  arsenic  is  introduced  into  preparations  for 
which  such  acid  is  employed,  as  into  phosphorus  and  hydrochloric  acid. 
The  arsenic  is  discovered  by  diluting  with  water  and  transmitting  through 
the  solution  hydrosulphuric  acid  gas,  which  causes  orpiment  to  be  formed. 
The  oil  of  vitriol  may  be  purified  from  arsenious  acid  by  adding  a  little  hy- 
drated  peroxide  of  iron  before  distilling. 

Prop. — As  obtained  by  the  second  process,  pure  sulphuric  acid  is  a  dense, 
colourless,  oily  fluid,  which  boils  at  620°,  and  has  a  specific  gravity,  in  its 
most  concentrated  form,  of  1.847  or  a  little  higher,  never  exceeding  1.850. 
Mitscherlich  found  the  density  of  its  vapour  to  be  3 ;  but  the  calculated  num- 
ber 2.7629,  is  probably  nearer  the  truth.  It  is  one  of  the  strongest  acids  with 
which  chemists  are  acquainted,  and  when  undiluted  is  powerfully  corrosive. 
It  decomposes  all  animal  and  vegetable  substances  by  the  aid  of  heat,  caus- 
ing deposition  of  charcoal  and  formation  of  water.  It  has  a  strong  sour 
taste,  and  reddens  litmus  paper,  even  though  greatly  diluted.  It  unites  with 
alkaline  substances,  and  separates  all  other  acids  more  or  less  completely 
from  their  combinations  with  the  alkalies. 

In  a  very  concentrated  state  it  dissolves  small  quantities  of  sulphur, 
and  acquires  a  blue,  green,  or  brown  tint.  Tellurium  and  selenium  are 
also  sparingly  dissolved,  the  former  causing  a  crimson,  and  the  latter  a 
green  colour.  By  dilution  with  water,  these  substances  subside  unchanged  ; 
but  if  heat  is  applied,  they  are  oxidized  at  the  expense  of  the  acid,  and  sul- 
phurous acid  gas  is  disengaged.  Charcoal  also  appears  soluble  to  a  small  ex- 
tent in  sulphuric  acid,  communicating  at  first  a  pink,  and  then  a  dark  reddish- 
brown  tint. 

It  has  a  very  great  affinity  fo,r  water,  and  unites  with  it  in  every 
proportion.  The  combination  takes  place  with  production  of  intense 
heat.  When  four  parts  by  weight  of  the  acid  are  suddenly  mixed  with  one 
of  water,  the  temperature  of  the  mixture  rises,  according  to  Ure,  to 
300°.  By  its  attraction  for  water,  it  causes  the  sudden  liquefaction  of 
snow ;  and  if  mixed  with  it  in  due  proportion  (p.  39),  intense  cold  is  gene- 
rated ^  It  absorbs  watery  vapour  with  avidity  from  the  air,  and  on  this  ac- 
count is  employed  in  tfte.  process  for  freezing  water  by  its  own  evaporation. 


196  SULPHUR. 

Its  action  in  destroying  the  texture  of  the  skin,  and  in  decomposing  animal 
and  vegetable  substances  in  general,  seems  dependent  on  its  affinity  for 
water. 

To  ascertain  the  quantity  of  real  acid  present  in  liquid  acid  of  different 
strengths,  dilute  a  known  weight  of  the  acid  moderately  with  water,  andy 
while  warm,  add  pure  anhydrous  carbonate  of  soda,  until  the  solution  is 
exactly  neutral.  Every  53.42  parts  of  carbonate  of  soda,  required  to  pro- 
duce this  effect,  correspond  to  40.1  parts  of  real  sulphuric  acid.  If  minute 
precision  is  not  desi/fcd,  the  strength  of  the  acid  may  be  estimated  by  its  sp. 
gr.  according  to  the  table  of  Ure  inserted  in  the  Appendix. 

Sulphuric  acid  of  commerce  freezes  at —  15°.  Diluted  with  water  so 
as  to  have  a  specific  gravity  of  1.78  it  congeals  even  above  32°,  and  remains 
in  the  solid  state,  according  to  Keir,  till  the  temperature  rises  to  45°. 
When  mixed  with  rather  more  than  its  weight  of  water,  its  freezing  point  is 
lowered  to  — 36°. 

The  composition  of  sulphuric  acid  as  before  given  is  founded  on  the  ob- 
servation of  Gay-Lussac,  that  when  the  vapour  of  sulphuric  acid  is  passed 
through  a  small  porcelain  tube  heated  to  redness,  it  is  resolved  into  two- 
measures  of  sulphurous  acid  gas  and  one  of  oxygen.  Berzelius  has  confirmed 
this  conclusion  by  directly  converting  a  known  weight  of  sulphur  into  sul- 
phuric acid. 

Chemists  possess  an  unerring  test  of  the  presence  of  sulphuric  acid.  If  a 
solution  of  chloride  of  barium  is  added  to  a  liquid  containing  sulphuric  acid& 
it  causes  a  white  precipitate,  sulphate  of  baryta,  which  is  characterized  by 
its  insolubility  in  acids  and  alkalies. 

Sulphuric  acid  does  not  occur  free  in  nature,  except  occasionally  in  the- 
neighbourhood  of  volcanoes.  In  combination,  particularly  with  lime  and 
baryta,  it  is  very  abundant. 

Hy posit iphurous  Acid. — It  may  "be  formed  either  by  digesting  sulphur 
in  a  solution  of  any  sulphite,  or  by  transmitting  a  current  of  sulphurous 
acid  into  a  solution  of  sulphuret  of  calcium  or  strontium.  In  the  former  case, 
the  sulphurous  acid  takes  up  an  additional  quantity  of  sulphur,  and  a  salt  of 
hyposulphurous  acid  is  obtained;  and  in  the  latter,  the  sulphurous  acid 
gives  part  of  its  oxygen  to  the  metal,  and  its  remaining  oxygen  unites  with 
sulphur.  Three  equivalents  of  sulphurous  acid  and  two  of  sulphuret  of  cal- 
cium contain  the  elements  for  forming  two  equivalents  of  hyposulphite  of 
lime,  one  eq.  of  sulphur  being  deposited.  A  convenient  solution  for  this  pur- 
pose is  made  by  boiling  3  parts  of  slaked  lime  and  1  of  sulphur  with  20 
parts  of  water  for  one  hour,  and  decanting  the  clear  liquid  from  the  undis- 
solved  portions  ;  but  when  this  solution  is  used,  the  deposite  of  sulphur  is 
abundant.  Herschel  states  that  hyposulphurous  acid  may  be  formed  by  the 
action  of  sulphurous  acid  on  iron  filings;  but  the  nature  of  the  change 
is  not  well  understood. 

The  salts  of  hyposulphurous  acid  were  first  described  by  Gay-Lussac 
(An.  de  Ch.  Ixxxv.)  under  the  name  of  sulphuretted  sulphites.  Thomson,  in 
his  System  of  Chemistry,  suggested  that  the  acid  of  these  salts  might  be 
regarded  as  a  compound  of  one  equivalent  of  sulphur  and  one  of  oxygent 
and  proposed  for  it  the  name  of  hyposulphurous  acid :  and  the  subsequent 
researches  of  Herschel  (Phil.  Journal,  i.  8  and  396)  accorded  so  entirely 
with  this  opinion,  that  it  was  universally  adopted.  But  it  appears  from 
the  experiments  of  Rose,  that  though  the  ratio  of  its  elements  is  as  16  to  8, 
the  equivalent  of  the  acid,  or  the  quantity  required  to  neutralize  one  equiva- 
lent of  an  alkali,  is  riot  24,  but  48;  and  hence  that  its  smallest  molecule  must 
be  formed  of  two  atoms  of  sulphur  united  with  two  atoms  of  oxygen.  (Pog, 
Ann.  xxi.  431.) 

Prop. — It  cannot  exist  permanently  in  a  free  state.  On  decomposing  a 
hyposulphite  by  any  stronger  acid,  such  as  the  sulphuric  or  hydrochlo- 
ric, the  hyposulphurous  acid,  at  the  moment  of  quitting  the  base,  re- 
solves itself  into  sulphurous  acid  and  sulphur.  Herschel  succeeded  in 
obtaining  free  hyposulphurous  acid,  by  adding  a  slight  excess  of  sulphuric 


PHOSPHORUS. 


197 


acid  to  a  dilute  solution  of  hyposulphite  of  strontia  ;  but  its  decomposition 
very  soon  took  place,  even  at  common  temperatures,  and  was  instantly  ef- 
fected by  heat.  Most  of  the  hyposulphites  are  soluble  in  water,  and  have 
a  bitter  taste.  The  solution  precipitates  the  nitrates  of  the  oxides  of  silver 
and  mercury  black,  as  sulphuret  of  the  metals  ;  and  salts  of  baryta  and 
oxide  of  lead  are  thrown  down  as  white  insoluble  hyposulphites  of  those 
bases.  That  of  baryta  is  soluble  without  decomposition  in  water  acidulated 
with  hydrochloric  acid.  The  solution  of  all  the  neutral  hyposulphites  has 
the  peculiar  property  of  dissolving  recently  precipitated  chloride  of  silver  in 
large  quantity,  and  forming  with  it  a  liquid  of  an  exceedingly  sweet  taste. 

Hyposulphuric  Acid.  —  It  was  discovered  in  1819  by  Welter  and  Gay- 
Lussac.  (An.  de  Ch.  et  de  Ph.  x.)  It  is  formed  by  transmitting  a  cur- 
rent of  sulphurous  acid  gas  through  water  containing  peroxide  of  manganese 
in  fine  powder;  when,  by  a  new  arrangement  of  their  elements, 

2  eq.  sulph's  acid  &  1  eq.  perox.  mang.  2  1  eq.  protox.  mang.  &.  1  eq.  hyposulph'c  acid, 
2(S4-2O)  Mn+2O     ~  Mn+O  2  S+5O, 


hyposulphate  of  protoxide  of  manganese  remaining  in  solution.  During  the 
action  heat  is  freely  evolved,  and  in  consequence  sulphuric  acid  is  also  gene- 
rated ;  but  if  the  peroxide  of  manganese  be  pure  and  the  materials  kept 
cool,  the  formation  of  sulphuric  acid  is  almost  completely  prevented.  To 
the  liquid,  after  filtration,  a  solution  of  pure  baryta,  or  sulphuret  of  barium 
in  slight  excess,  is  added,  whereby  the  manganese  is  thrown  down  as  an 
oxide  or  sulphuret,  sulphuric  acid  as  sulphate  of  baryta,  and  a  solution  of 
hyposulphate  of  baryta  is  obtained  :  the  excess  of  baryta  is  got  rid  of  by  a 
free  current  of  carbonic  acid  gas,  and  then  heating  the  solution.  The  hypo- 
sulphate  of  baryta  crystallizes  by  evaporation,  and  on  decomposing  a  solu- 
tion of  that  salt  by  a  quantity  of  sulphuric  acid  exactly  sufficient  for  pre- 
cipitating the  baryta,  the  hyposulphuric  acid  is  left  in  sblution. 

Prop.  —  Taste  sour  ;  distinct  acid  reaction  ;  neutralizes  alkalies  ;  inodorous, 
and  thus  distinguished  from  sulphurous  acid  ;  forms  soluble  salts  with  baryta, 
strontia,  lime,  and  oxide  of  lead,  by  which  it  is  distinguished  from  sulphuric 
acid.  It  cannot  be  obtained  free  from  water.  Its  solution,  if  confined  with 
a  vessel  of  sulphuric  acid  under  the  exhausted  receiver  of  an  air-pump,  may 
be  concentrated  till  it  has  a  density  of  1.347;  but  if  an  attempt  w  made  to 
condense  it  still  further,  the  acid  is  decomposed,  sulphurous  acid  gas  escapes, 
and  sulphuric  acid  remains  in  solution.  A  similar  change  is  still  more 
readily  produced  if  the  evaporation  is  conducted  by  heat. 

Welter  and  Gay-Lussac  analyzed  hyposulphuric  acid  by  exposing  neutral 
hyposulphate  of  baryta  to  heat.  At  a  temperature  a  little  above  212°  this 
salt  suffers  complete  decomposition  ;  sulphurous  acid  gas  is  disengaged,  and 
neutral  sulphate  of  baryta  is  obtained.  It  was  thus  ascertained  that  72 
grains  of  hyposulphuric  acid  yield  32  grains  of  sulphurous,  and  40  of  sul- 
phuric acid  ;  from  which  it  is  inferred  that  hyposulphuric  acid  is  composed 
either  of  an  equivalent  of  each  of  those  acids  combined  with  each  other,Nor 
of  two  equivalents  of  sulphur  and  five  of  oxygen. 


SECTION   VIII. 

PHOSPHORUS. 

Hist,  and  Prep. — PHOSPHORUS  (<j>a>0-<j>9goc  from  <j>£s  light  and  <j>cg«y  to 
carry),  so  called  from  its  property  of  shining  in  the  dark,  was  discovered 
about  the  year  1669  by  Brandt,  an  alchemist  of  Hamburgh.  It  was  origi- 
nally prepared  from  urine ;  but  Scheele,  after  Gahn's  discovery  of  bones  con- 
taining  phosphate  of  lime,  extracted  it  from  that  source.  The  bones  are  first 

17* 


198  PHOSPHORUS. 

ignited  in  an  open  fire  till  they  become  white,  so  as  to  destroy  their  animaf 
matter,  and  burn  away  the  charcoal  derived  from  it,  in  which  state  they  con- 
tain nearly  4-5ths  of  phosphate  of  lime.  They  are  then  reduced  to  a  fine 
powder,  and  digested  for  a  day  or  two  with  half  their  weight  of  strong  sul- 
phuric acid,  with  the  addition  of  so  much  water  as  will  give  the  consistence 
of  a  thin  paste.  Decomposition  of  the  phosphate  of  lime  is  thus  effected,  and 
two  new  salts  formed,  the  sparingly  soluble  sulphate  and  a  soluble  superphos- 
phate of  lime.  The  latter  is  dissolved  in  warm  water,  and  the  solution,  after 
being  separated  by  filtration  from  the  sulphate  of  lime,  is  evaporated  to  the 
consistence  of  syrup,  mixed  with  a  fourth  of  its  weight  of  powdered  char- 
coal, and  strongly  heated  in  an  earthen  retort  well  luted  with  clay.  The 
beak  of  the  retort  is  put  into  water,  in  which  the  phosphorus,  as  its  vapour 
passes  over,  is  condensed.  When  first  obtained  it  is  usually  of  a  reddish- 
brown  colour,  owing  to  the  presence  of  phosphuret  of  carbon,  formed  during 
the  process.  It  may  be  purified  .by  fusion,  in  hot  water,  and  being  pressed 
while  liquid  through  chamois  leather,  or  by  a  second  distillation. 

In  this  process  the  oxygen  of  that  part  of  the  phosphoric  acid  which  con- 
stitutes the  superphosphate,  unites  with  charcoal,  giving  rise  to  carbonic 
acid  and  carbonic  oxide  gases ;  and  phosphate  of  lime  in  the  state  of  bone 
earth,  together  with  redundant  charcoal,  remains  in  the  retort.  The  lime 
acts  an  important  part  in  fixing  the  phosphoric  acid,  which,  if  not  so  com- 
bined, would  distil  over  before  the  heat  was  high  enough  for  its  decomposi- 
tion. In  extracting  phosphorus  from  urine,  the  phosphoric  acid  should  be 
thrown  down  by  acetate  of  the  oxide  of  lead,  and  the  insoluble  salt  converted 
by  the  action  of  sulphuric  acid  into  the  superphosphate,  which  is  decom- 
posed by  charcoal  as  in  the  former  process. 

Prop. — When  pure,  transparent  and  almost  colourless.  At  common  tem- 
peratures it  is  a  soft  solid  of  sp.  gr.  1.77;  is  easily  cut  with  a  knife,  and  the 
cut  surface  has  a  waxy  lustre:  at  108°  it  fuses,  and  at  550°  is  converted 
into  vapour,  which  according  to  Dumas  has  a  sp.  gr.  of  4.355.  It  is  soluble 
by  the  aid  of  heat  in  naphtha,  in  fixed  and  volatile  oils,  in  the  chloride  of 
sulphur,  sulphuret  of  carbon,  and  sulphuret  of  phosphorus.  On-  its  cooling 
from  solution  in  the  latter,  Mitscherlich  obtained  it  in  regular  dodecahedral 
crystals.  By  the  fusion  and  slow  cooling  of  a  large  quantity  of  phosphorus, 
M.  Frantween  has  obtained  very  fine  crystals  of  an  octohedral  form,  and  as 
large  as  a  cherry-stone.  Thenard  has  remarked  that  when  phosphorus  is 
fused  at  150°,  and  suddenly  cooled  by  being  plunged  into  cold  water,  it  ap- 
pears black ;  but  by  fusion  and  slow  cooling  it  recovers  its  original  aspect. 

It  is  exceedingly  inflammable.  Exposed  to  the  air  at  common  tempera- 
tures, it  undergoes  slow  combustion,  emits  a  white  vapour  of  a  peculiar 
alliaceous  odour,  appears  distinctly  luminous  in  the  dark,  and  is  gradually 
consumed.  On  this  account,  phosphorus  should  always  be  kept  under  water. 
The  disappearance  of  oxygen  which  accompanies  these  changes  is  shown  by 
putting  a  stick  of  phosphorus  in  a  jar  full  of  air,  inverted  over  water.  The 
volume  of  the  gas  gradually  diminishes;  and  if  the  temperature  of  the  air 
is  at  60°,  the  whole  of  the  oxygen  will  be  withdrawn  in  the  course  of  12  or 
24  hours.  The  residue  is  nitrogen  gas,  containing  about  l-40th  of  its  bulk 
of  the  vapour  of  phosphorus.  It  is  remarkable  that  the  slow  combustion  of 
phosphorus  does  not  take  place  in  pure  oxygen,  unless  its  temperature  be 
about  80°.  But  if  the  oxygen  be  diluted  with  nitrogen,  hydrogen,  or  car- 
bonic acid  gas,  the  oxidation  occurs  at  60° ;  and  it  takes  place  at  tempera- 
tures still  lower  in  a  vessel  of  pure  oxygen,  rarefied  by  diminished  pressure.* 

*  If  a  stick  of  dry  phosphorus  be  dusted  over  with  powdered  resin  or  sul- 
phur, and  then  introduced  under  the  receiver  of  an  air-pump,  it  will  be 
found  that,  as  soon  as  the  exhaustion  commences,  the  phosphorus  will  "be- 
come luminous,  which  appearance  increases  as  the  rarefaction  proceeds, 
until  finally  the  phosphorus  inflames.  Van  Bemmelen,  who  first  attempted 
to  account  for  this  phenomenon,  attributes  it  to  the  combination  of  the  suK 


~.  PHOSPHORUS.  199 

Mr.  Graham  finds  that  the  presence  of  certain  gaseous  substances,  even  in 
minute  quantity,  has  a  remarkable  effect  in  preventing  the  slow  combustion 
of  phosphorus:  thus,  at  66°  it  is  entirely  prevented  by  the  presence,  (Quart. 
Jour,  of  Science,  N.  S.  vi.  83,) 

Volumes  of  air. 

Of  I  volume  of  olefiant  gas  in 450 

1  do.  of  vapour  of  sulphuric  ether  in  .  .  150 
1  do.  of  vapour  of  naphtha  in  ...  .  1820 
1  do.  of  vapour  of  oil  of  turpentine  in  .  .  4444, 

and  by  an  equally  slight  impregnation  of  the  vapour  of  the  other  essential 
oils.  Their  influence  is  not  confined  to  low  temperatures.  Phosphorus  be- 
comes faintly  luminous  in  the  dark,  in  mixtures  of 

1  volume  of  air  and  1  volume  of  olefiant  gas  at     ....  200°  F. 

1  ....  and  1  do.  of  vapour  of  ether  at  .  t  .  215° 

111  .  ...  '.'  and  1  do.  of  vapour  of  naphtha  at  .  .  170° 

156  *  /,  .;  .  and  1  do.  of  vapour  of  turpentine  at  .  186° 

It  may  be  sublimed  at  its  boiling  temperature,  in  air  containing  a  consi- 
derable proportion  of  the  vapour  of  oil  of  turpentine,  without  diminishing 
the  quantity  of  oxygen  present,  provided  the  heat  be  gradually  and  uni- 
formly applied.  Mr.  Graham  has  also  remarked,  that  the  oxidation  of  phos- 
phorus in  the  air  is  promoted  by  the  presence  of  hydrochloric  acid  gas. 
•  A  very  slight  degree  of  heat  is  sufficient  to  inflame  phosphorus  in  the 
open  air.  Gentle  pressure  between  the  fingers,  friction,  or  a  temperature  not 
much  above  its  point  of  fusion,  kindles  it  readily.  It  burns  rapidly  even  in 
the  air,  emitting  a  splendid  white  light,  and  causing  intense  heat.  Its  com- 
bustion is  far  more  rapid  in  oxygen  gas,  and  the  light  proportionally  more 
vivid. 

When  phosphorus  is  kept  for  a  long  time  under  water,  especially  if  ex- 

phur  or  resin  with  the  phosphorus,  the  union  of  which,  accelerated  by  the 
influence  of  the  vacuum,  gives  rise  to  the  evolution  of  so  much  heat,  as  to 
inflame  the  phosphorus,  or  the  new  compound  formed.  Berzelius  rejects 
this  explanation,  as  it  does  not  account  for  an  experiment  by  Van  Bemrnelen, 
in  which  phosphdrus  was  found  to  take  fire  under  an  exhausted  receiver, 
when  merely  enveloped  with  cotton.  Berzelius,  Traite  de  Chimie,  i.  260. 

Professor  A.  D.  Bache,  President  of  Girard  College,  has  repeated  and  ex- 
tended the  experiments  of  Van  Bemmelen,  and  has  had  the  goodness  to 
communicate  to  me  an  abstract  of  his  results.  He  succeeded  in  producing 
the  inflammation  of  the  phosphorus,  under  the  circumstances  above  men- 
tioned, by  means  of  the  following  substances  in  a  finely  divided  state,  in 
addition  to  those  employed  by  Van  Bemmelen : — 

Carbon  in  the  form  of  ivory  black  Lime. 

and  wood  charcoal.  Peroxide  of  manganese. 

Spongy  platinum.  Hydrate  of  potassa. 

Antimony.  Muriate  of  ammonia. 

Arsenic.  Chloride  of  sodium. 

Bisulphuret  of  mercury.  Fluate  of  lime. 

Sulphuret  of  antimony.  Carbonate  of  lime. 
Silica. 

Sulphur  and  charcoal  were  the  substances  which  succeeded  most  readily. 
With  metallic  arsenic  there  was  much  difficulty.  The  temperature  of  the 
room  has  great  influence  on  the  success  of  the  experiments. 

Professor  Bache  is  of  opinion  that  some  of  his  experiments  are  unfavour- 
able to  the  explanation  of  Van  Bemmelen  ;  as,  for  example,  those  with  car- 
bonate of  lime  and  fluor  spar,  which,  though  incombustible  substances,  act 
with  the  same  energy  as  sulphur  or  carbon. — Ed. 


200  PHOSPHORUS. 

posed  to  light,  its  surface  acquires  a  thin  coating  of  white  matter,  which 
some  have  described  as  an  oxide,  and  others  as  a  hydrate  of  phosphorus.  It 
seems  according1  to  Rose  to  be  neither  an  oxide  nor  a  hydrate,  but  phospho. 
rus  in  a  peculiar  mechanical  state,  which  deprives  it  of  its  usual  action  upon 
light  and  renders  it  opaque.  (Pog.  Annalen,  xxvii.  565.) 

Repeated  researches  by  Berzelius  have  shown  that  the  oxygen  in  phospho- 
rous and  phosphoric  acids  is  in  the  ratio  of  3  to  5,  a  result  conformable  to 
experiments  on  the  same  subject  by  Dulong,  and  admitted  by  most  chemists. 
It  is  hence  inferred  that  the  smallest  molecule  of  phosphoric  acid  contains 
five  atoms  of  oxygen.  Also  Berzelius  finds  that  31.4  parts  of  phosphorus  re- 
quire 40  of  oxygen  for  forming  phosphoric  acid  :  if  this  acid  consist  of  one 
atom  of  phosphorus  and  five  atoms  of  oxygen,  31 .4  will  represent  one  atom 
of  phosphorus;  or  if  the  acid  contain  two  atoms  to  five,  the  atom  of  phospho- 
rus will  be  half  31.4  or  15.7.  It  is  doubtful  which  view  is  preferable,  and  I, 
therefore,  contiryie  to  use  the  latter. 

Its  equivalent  is,  therefore,  15.7 ;  eq.  voL=25  ;  symb.  P. 

The  compounds  of  phosphorus  described  in  this  section  are  the  follow- 
ing;— 

Phosphorus.       Oxygen.      Equiv.        FormulsB. 

Oxide  of  phosphorus  47.1  or  3  eq.  -\-  8  or  1  eq.  =  55.1  3P+O  or  PsQ 
Hypophosphorous  acid  31.4  or  2  eq.  -j-  8  or  1  eq.  =  39.4  2P-J-O  or  PsO 
Phosphorous  acid  31.4  or  2  eq.'4-  24  or  3  eq.  =  55.4  2P+3O  or P2O3 

Phosphoric  acid  J 

Pyrophosphoric  acid  >  31.4  or  2  eq.  +  40  or  5  eq.  =  71.4  2P+5Oor  P2O* 
Metaphosphoric  acid  } 


COMPOUNDS  OF  OXYGEN  AND  PHOSPHORUS. 

Oxide. — When  a  jet  of  oxygen  gas  is  thrown  upon  phosphorus  while  in 
fusion  under  hot  water,  combustion  ensues,  phosphoric  acid  is  formed,  and  a 
number  of  red  particles  collect,  which  have  been  examined  by  M.  Pelouzer 
who  has  shown  them  to  be  an  oxide  of  phosphorus.  The  red  matter  left 
when  phosphorus  is  burned,  is  probably  of  the  same  nature. 

This,  the  only  known  oxide  of  phosphorus,  is  of  a  red  colour,  without 
taste  or  odour,  and  is  insoluble  in  water,  ether,  alcohol,  and  oil.  It  is  per- 
manent  in  the  air,  even  at  662°  F.,  but  takes  fire  at.  a  low  red  heat.  Heated 
to  redness  in  a  tube,  phosphorus  is  expelled,  and  ineta phosphoric  acid  re- 
mains. It  takes  fire  in  chlorine  gas,  and  is  rapidly  oxidized  by  nitric  acid. 
It  does  not  appear  to  possess  any  alkaline  character.  (An.  de  Ch.  et  de  Ph. 
1.  83.)  Its  equivalent  is  55.1 ;  symb.  3P-fO,  or  P3O. 

Hypophosphorous  Acid. — This  acid  was  discovered  in  1816  by  Dulong. 
(An.  de  Ch.  et  de  Ph.  ii.)  When  water  acts  upon  the  phosphuret  of  barium 
the  elements  of  both  enter  into  a  new  arrangement,  giving  rise  to  phosphu- 
retted  hydrogen,  phosphoric  acid,  hypophosphorous  acid,  and  baryta.  The 
former  escapes  in  the  form  of  gas,  and  the  two  latter  combine  with  the  ba- 
ryta. Hypophosphite  of  baryta,  being  soluble,  dissolves  in  the  water,  and 
may  consequently  be  separated  by  filtration  from  the  phosphate  of  baryta, 
which  is  insoluble.  On  adding  a  sufficient  quantity  of  sulphuric  acid  for  pre- 
cipitating the  baryta,  hypophosphorous  acid  is  obtained  in  a  free  state,  and  on 
evaporating  the  solution,  a  viscid  liquid  remains,  highly  acid  and  even  crys- 
tallizable,  which  is  a  hydrate  of  hypophosphorous  acid.  When  exposed  to 
heat  in  close  vessels,  it  undergoes  the  same  kind  of  change  as  hydrated 
phosphorous  acid. 

Prop. — It  is  a  powerful  deoxidizing  agent.  It  unites  with  alkaline  bases ; 
and  it  is  remarkable  that  all  its  salts  are  soluble  in  water.  The  hypophos- 
phites  of  potassa,  sodaj  and  ammonia  dissolve  in  every  proportion  in  recti- 
fied alcohol ;  and  hypophosphite  of  potassa  is  even  more  deliquescent  than 
chloride  of  calcium.  They  are  all  decomposed  by  heat,  and  yield  the  same 


PHOSPHORUS.  201 

products  as  the  acid  itself.  They  are  conveniently  prepared  by  precipitating 
hypophosphite  of  baryta,  strontia,  or  lime,  with  the  alkaline  carbonates ;  or 
by  directly  neutralizing-  these  carbonates  with  hypophosphorous  acid.  The 
hypophosphites  of  baryta,  strontia,  and  lime  are  formed  by  boiling  these 
earths  in  the  caustic  state  in  water  together  with  fragments  of  phosphorus. 
The  same  change  occurs  as  during  the  action  of  water  on  phosphuret  of 
barium.  The  composition  of  this  acid,  as  stated  at  page  200,  is  on  the  autho- 
rity of  Rose.  (Poggen.  Annalen  ix.  367.)  Its  eq.  is  39.4;  symb.  2P-{-O,P, 

or  P2O. 

Phosphorous  Acid. — Prep. — When  phosphorus  is  burned  in  air  highly  rare- 
fied, imperfect  oxidation  ensues,  and  metaphosphoric  and  phosphorous  acids  are 
fenerated,  the  latter  being  obtained  in  the  form  of  a  white  volatile  powder, 
t  may  be  procured  more  conveniently  by  subliming  phosphorus  through 
powdered  bichloride  of  mercury  contained  in  a  glass  tube  ;  when  a  limpid 
liquid  comes  over,  which  is  a  compound  of  chlorine  and  phosphorus.  (Davy's 
Elements,  p.  288.)  This  substance  and  water  mutually  decompose  each 
other :  the  hydrogen  of  water  unites  with  the  chlorine,  /and  forms  hydro- 
chloric acid  ;  while  the  oxygen  attaches  itself  to  the  phosphorus,  and  thus 
phosphorous  acid  is  produced.  The  solution  is  then  evaporated  to  the  con- 
sistence of  syrup  to  expel  the  hydrochloric  acid;  and  the  residue,  which  is 
hydrate  of  phosphorous  acid,  becomes  a  crystalline  solid  on  cooling.  It  is 
also  generated  during  the  slow  oxidation  of  phosphorus  in  atmospheric  air. 
The  product  attracts  moisture  from  the  air,  and  forms  an  oil-like  liquid. 
Dulong  thinks  that  a  distinct  acid  is  produced  in  this  case,  which  he  calls 
phosphatic  acid;  but  the  opinion  of  Davy,  that  it  is  merely  a  mixture  of  phos- 
phoric and  phosphorous  acids,  is  in  my  opinion  perfectly  correct. 

Prop. — When  obtained  by  the  first  process,  it  is  anhydrous.  Heated  in  the 
open  air,  it  takes  fire,  and  forms  metaphosphoric  acid  ;  but  in  close  vessels, 
it  is  resolved  into  metaphosphoric  acid  and  phosphorus.  The  action  of  the 
hydrate  under  the  latter  circumstances  is  different,  owing  to  the  reaction  of 
the  elements  of  the  water -and  acid,  by  which  metaphosphoric  acid  and  a 
gaseous  compound  of  phosphorus  and  hydrogen  are  produced.  The  nature 
of  this  gas  will  be  more  particularly  noticed  in  the  section  on  phosphuretted 
hydrogen.  It  dissolves  readily  in  water,  has  a  sour  taste,  and  smells  some- 
what like  garlic.  It  unites  with  alkalies,  and  forms  salts  which  are  termed 
phosphites.  The  solution  of  phosphorous  acid  absorbs  oxygen  slowly  from 
air,  and  is  converted  into  phosphoric  acid.  From  its  tendency  to  unite 
with  an  additional  quantity  of  oxygen,  it  is  a  powerful  deoxidizing  agent ; 
and  hence,  like  sulphurous  acid,  precipitates  mercury,  silver,  platinum,  and 
gold  from  their  saline  combinations  in  the  metallic  form.  Nitric  acid  con- 
verts it  into  phosphoric  acid. 

Its  eq.  is  554 ;  symb.  2P-f3O,  P,  or  P2O3. 

Phosphoric  Acid.— Hist.— It  wa~s~  shown  in  the  year  1827  by  Dr.  Clarke, 
now  Professor  of  Chemistry  in  Aberdeen,  that  under  the  term  phosphoric  acid 
had  previously  been  confounded  two  distinct  acids,  one  of  which  he  propos- 
ed to  distinguish  by  the  name  of  pyrophosphoric  acid  (from  nvg  fire],  to  indi- 
cate that  it  is  phosphoric  acid  modified  by  heat;  and  very  lately  Mr.  Gra- 
ham has  described  another  modification  of  phosphoric  acid,  to  which  he  has 
given  the  provisional  name  of  metaphosphoric  (from  yxgTa  together  witti),  im- 
plying phosphoric  acid  and  something  besides;  but  this  name  is  rather  un- 
fortunate, since  it  is  applied  to  the  only  one  of  the  three  modifications  which 
can  be  obtained  free  from  water.  Perhaps  paraphosphoric  (from  vctgx.  near 
to}  would  be  more  appropriate.  These  three  acids  contain  phosphorus  and 
oxygen  in  the  same  ratio,  and  have  the  same  equivalent,  so  that  they  may 
be  considered  as  isomeric  bodies  (page  152);  but  that  difference  in  the  ar- 
rangement of  their  elements  on  which  their  peculiarities  may  be  presumed 
to  depend,  is  very  slight ;  since  they  are  easily  convertible  into  each  other. 
Mr.  Graham,  indeed,  supposes  the  difference  to  arise  solely  from  a  disposi* 


202 


PHOSPHORUS. 


tion  to  unite  in  different  proportions  with  water  and  alkaline  bases;  but 
this  view  scarcely  suffices  as  an  explanation,  because  it  does  not  account  for 
the  peculiar  disposition  which  causes  their  distinctive  characters.  (Phil. 
Trans.  1833,  Part  ii.,  and  Phil.  Mag.  3d  Series,  iv.  401.) 

Prep. — Phosphoric  acid  has  hitherto  been  obtained  only  in  "combination 
with  water  or  some  alkaline  base.  One  of  the  best  modes  for  procuring  it,  is  to 
oxidize  phosphorus  by  strong  nitric  acid;  but  in  this  process  care  is  neces- 
sary, as  the  action  is  sometimes  very  violent,  and  the  escape  of  binoxide  of 
nitrogen  gas  ungovernably  rapid.  It  is  safely  conducted  by  adding  frag- 
ments of  phosphorus,  or  the  so-called  phosphatic  acid,  to  strong  nitric  acid 
contained  in  a  platinum  crucible  partially  closed  by  its  cover.  Gentle  heat  is 
applied  so  as  to  commence,  and,  when  necessary,  to  maintain  moderate  ef- 
fervescence ;  and  when  one  portion  of  phosphorus  disappears,  another  is 
added,  till  the  whole  of  the  nitric  acid  is  exhausted.  The  solution  is  then 
evaporated  to  dryness,  and  exposed  to  a  red  heat  to  expel  the  last  traces  of 
nitric  acid.  This  should  always  be  done  in  vessels  of  platinum  ;  since  phos- 
phoric acid  acts  chemically  upon  those  of  glass  or  porcelain;  and  is  thereby 
rendered  impure.  In  this  case,  as  in  some  other  instances  of  the  oxidation 
of  combustibles  by  nitric  acid,  water  is  decomposed;  and  while  its  oxygen 
unites  with  phosphorus,  its  hydrogen  combines  with  the  nitrogen  of  the  nitric 
acid.  A  portion  of  ammonia,  thus  generated,  is  expelled  by  heat  in  the  last 
part  of  the  process. 

Phosphoric  acid  may  be  prepared  at  a  much  cheaper  rate  from  bones. 
For  this  purpose,  superphosphate  of  lime,  obtained  in  the  way  already  de- 
scribed, should  be  boiled  for  a  few  minutes  with  excess  of  carbonate  of  am- 
monia. The  lime  is  thus  precipitated  as  a  phosphate,  and  the  solution  con- 
tains phosphate,  together  with  a  little  sulphate  of  ammonia.  The  liquid,  after 
filtration,  is  evaporated  to  dryness,  and  then  ignited  in  a  platinum  crucible, 
by  which  means  the  ammonia  and  sulphuric  acid  are  expelled. 

In  both  the  foregoing  processes  phosphoric  acid  exists  only  in  solution ; 
for  on  heating  to  redness  in  order  to  expel  ammonia  in  the  one  case  and 
nitric  acid  in  the  other,  metaphosphoric  acid  is  generated.  To  reproduce  the 
phosphoric  acid,  the  residue  in  the  crucible  requires  to  be  dissolved  in  water 
and  boiled  for  a  few  minutes. 

Prop, — Phosphoric  acid  is  colourless,  intensely  sour  to  the  taste,  reddens  lit- 
mus strongly,  and  neutralizes  alkalies ;  but  it  does  not  destroy  the  texture  of 
the  skin  like  sulphuric  and  nitric  acids.  Its  solution  may  be  evaporated  at  a 
temperature  of  300°  without  decomposition,  and  when  thus  concentrated  it 
assumes  a  dark  colour,  is  as  thick  as  treacle  when  cold,  and  consists  of  71.4 
parts  or  one  equivalent  of  phosphoric  acid,  and  27  parts  or  three  equivalents 
of  water.  Mr.  Graham  obtained  this  hydrate  in  thin  crystalline  plates, 
which  were  extremely  deliquescent,  by  keeping  it  for  seven  days  in  vacua 
along  with  sulphuric  acid.  On  heating  this  hydrate  for  several  days  to  415°, 
it  lost  nearly  two-thirds  of  an  equivalent  of  water,  and  then  principally  con- 
sisted of  pyrophosphoric  acid  with  two  equivalents  of  water.  At  a  still  higher 
temperature  metaphosphoric  acid  began  to  be  formed ;  and  at  a  red  heat  the 
conversion  was  complete.  But  after  ignition  it  still  contains  water,  amount- 
ing, according  to  Rose,  to  9.44  per  cent.,  which  is  rather  more  than  an  equi- 
valent of  water  to  one  of  metaphosphoric  acid. 

Phosphoric  acid  is  remarkable  for  its  tendency  to  unite  with  alkaline 
bases,  in  such  proportions  that  the  oxygen  of  the  base  and  of  the  acid  is  as 
3  to  5 ;  or,  in  other  words,  it  is  prone  to  form  subsalts,  in  which  one  equiva- 
lent of  acid  is  combined  with  three  equivalents  of  base.  It  manifests  the 
same  character  in  regard  to  water,  and  ceases  to  be  phosphoric  acid  unless 
three  equivalents  of  water  to  one  of  acid  are  present :  it  even  appears  that 
the  water  acts  the  part  of  a  base,  hence  called  basic  water,  and  that  the 
aqueous  solution  is  not  a  mere  solution  of  phosphoric  acid,  but  of  triphos- 
phate  of  water,  a  sort  of  salt  composed  of  one  equivalent  of  acid  and  three 
equivalents  of  water.  Part  of  this  basic  water  enters  along  with  soda  into 
the  constitution  of  two  of  the  phosphates  of  soda,  the  water  and  soda  toge- 


PHOSPHORUS. 


203 


ther  forming  the  three  equivalents  of  base  required  by  one  equivalent  of  the 
acid.  This  point  will  be  more  fully  described  in  the  history  of  the  phos- 
phates. 

When  phosphoric  acid  is  neutralized  by  ammonia,  and  mixed  with  nitrate 
of  oxide  of  silver,  the  yellow  phosphate  of  that  oxide  subsides,  a  character  by 
which  it  is  distinguished  from  pyrophosphoric  and  metaphosphoric  acids,  as 
well  as  from  all  other  acids  except  the  arsenious.  A  certain  test  between 
phosphoric  and  arsenious  acids  is,  that  the  former  is  neither  changed  in  co- 
lour nor  precipitated  when  a  stream  of  hydrosulphuric  acid  gas  is  transmit- 
ted through  it ;  while  the  latter,  with  the  required  precautions,  first  acquires 
a  yellow  tint,  and  then  yields  a  yellow  precipitate. 

Its  eq.  is  714;  symb.2P-f.5O,  P,  or  PO  :  but  as  it  cannot  exist  un- 
combined,  it  is  best  denoted  by  X3  PO5,  where  X  represents  an  equivalent 
of  water  or  any  base. 

Pyrophosphoric  Acid. — This  acid  is  formed  by  exposing  concentrated 
phosphoric  acid  for  some  time  to  a  heat  of  415°.  Its  general  characters  re- 
semble phosphoric  acid;  but  when  neutralized  by  ammonia  and  mixed  with 
nitrate  of  oxide  of  silver,  it  yields  a  snow-white  granular  precipitate,  pyro- 
phosphate  of  that  oxide,  by  which  it  is  distinguished  from  phosphoric  and 
metaphosphoric  acids.  In  solution  with  cold  water,  pyrophosphoric  acid 
passes  gradually,  and  at  a  boiling  temperature  rapidly,  into  phosphoric  acid. 
Its  salts,  while  neutral,  are  very  permanent;  but  when  boiled  with  either  of 
the  stronger  acids  in  water,  they  are  quickly  converted  more  or  less  com- 
pletely into  phosphates. 

Pyrophosphoric  acid  is  remarkable  for  its  tendency  to  unite  with  two 
equivalents  of  a  base.  Its  aqueous  solution  probably  contains  a  dipyrophos- 
phate  of  water,  that  is,  one  equivalent  of  the  acid  with  two  eq.  of  water,  ex- 
pressed by  2HCH-PsO0,  or  2HO.  Ps(X  This  basic  water  is  readily  displaced 
by  two  equivalents  of  stronger  bases,  such  as  soda ;  or  if  one  equivalent  only 
of  soda  be  added,  then  the  soda  and  water  together  makeup  the  two  equiva- 
lents of  base,  the  formula  of  the  salt  being  NaO,  HO.  P^Qs.  The  readiest 
mode  of  obtaining  a  pyrophosphate  is  to  heat  phosphoric  acid  with  any  fixed 
base  in  the  ratio  of  one  to  two  of  their  equivalents.  This  was  done  by  Dr. 
Clarke  in  the  experiments  by  which  he  established  the  existence  of  pyro- 
phosphoric acid.  (Brewster's  Journal,  vii.  298.)  Phosphate  of  soda  is  a 
compound  of  one  eq.  phosphoric  acid,  two  eq.  soda,  one  eq.  basic  water, 
and  twenty-four  eq.  water  of  crystallization,  its  formula  being  2NaO,  HO. 
PsO5-f-24HO :  on  drying  this  salt,  its  water  of  crystallization  is  expelled, 
and  there  remains  2NaO,  HO.  PsO^,  which  is  still  a  phosphate  ;  but  on  heat- 
ing to  redness,  the  basic  water  is  expelled,  and  2NaO.  P2Os,  pyrophosphate 
of  soda,  remains.  By  being  forced  to  unite  with  two  equivalents  of  base, 
the  acid  acquires  a  disposition  to  do  so  on  all  occasions. 

Its  eq.  is  71-4  ;  symb.  X2.  P  Os,  X  being  used  as  above. 

Metaphosphoric  Acid. — This  acid  is  obtained  by  burning  phosphorus  in 
dry  air  or  oxygen  gas,  or  heating  to  redness  a  concentrated  solution  of  phos- 
phoric or  pyrophosphoric  acids.  By  the  former  method,  the  acid  is  a  white 
solid,  and  anhydrous ;  in  the  latter  it  is  a  hydrate,  or  probably  a  mctaphos- 
phate  of  water,  composed  of  one  eq.  acid  and  one  eq.  of  water,  its  formula  being 
HO.  P~O».  The  water  in  this  compound  cannot  be  expelled  by  fire ;  since 
on  attempting  to  do  so  by  a  violent  heat,  the  whole  is  sublimed.  In  an 
open  crucible,  it  volatilizes  at  a  temperature  by  no  means  high. 

The  peculiarity  of  this  acid  is  to  combine  with  one  equivalent  of  a  base. 
On  exposing  the  anhydrous  acid  to  the  air  it  rapidly  deliquesces,  and  at  the 
same  time  acquires  its  basic  water,  which  can  only  be  replaced  by  an  equi- 
valent quantity  of  soda  or  some  other  alkaline  base.  The  water  is  also 
driven  off  by  fusion  with  siliceous  or  aluminous  substances,  with  which  the 
acid  unites  and  forms  very  fusible  compounds.  The  pure  hydrated  acid  is 
of  itself  very  fusible,  and  on  cooling-  concretes  into  a  transparent  brittle  solid, 
being  known  under  the  name  of  glacial  phosphoric  acid,  which  is  highly  de- 


204  BORON. 

liquescent,  and  can  hence  only  be  preserved  in  its  glassy  state  in  bottles 
carefully  closed. 

The  metaphosphoric  resembles  pyrophosphoric  acid  in  the  facility  with 
which  its  aqueous  solution  passes  into  phosphoric  acid.  On  the  contrary, 
both  of  the  other  acids  are  converted  into  uneta phosphates,  when  heated  to 
redness  in  contact  with  no  more  than  one  equivalent  of  certain  fixed  bases, 
such  as  potassa  and  soda.  This  acid,  when  free,  occasions  precipitates  in  so- 
lutions of  the  salts  of  baryta,  and  most  of  the  earths  and  metallic  oxides,  and 
forms  an  insoluble  compound  with  albumen.  The  metaphosphates  of  baryta 
and  oxide  of  silver  both  fall  in  gelatinous  flakes  of  a  gray  colour.  Its  eq.  is 
71-4  ;  symb,  P^O ,  or  X.  P*O*. 


SECTION    IX. 

BORON. 

Hist,  and  Prep. — SIR  H.  DAVY  discovered  the  existence  of  boron  in  1807 
by  exposing  boracic  acid  to  the  action  of  a  powerful  galvanic  battery ;  but  he 
did  not  obtain  a  sufficient  supply  of  it  for  determining  its  properties.  Gay- 
Lussac  andThenard*  procured  it  in  greater  quantity  in  1808,  by  heating  bo- 
racic acid  with  potassium.  The  boracic  acid  is  by  this  means  deprived  of 
its  oxygen,  and  boron  is  set  free.  The  easiest  and  most  economical  method 
of  preparing  this  substance,  according  to  Berzelius,  is  to  decompose  borofluo- 
ride  of  potassium  or  sodium  by  means  of  potassium.  (Annals  of  Philosophy, 
xxvi.  128.) 

Prop. — It  is  a  dark  olive-coloured  substance,  which  has  neither  taste  nor 
smell,  and  is  a  non-conductor  of  electricity.  It  is  insoluble  in  water,  alco- 
hol, ether,  and  oils.  It  does  not  decompose  water  whether  hot  or  cold.  It  bears 
intense  heat  in  close  vessels,  without  fusing  or  undergoing  any  other  change 
except  a  slight  increase  of  density.  Its  sp.  gr.  is  about  twice  as  great  as  that 
of  water.  It  may  be  exposed  to  the  atmosphere  at  common  temperatures 
without  change ;  but  if  heated  to  600°,  it  suddenly  takes  fire,  oxygen  gas 
disappears,  and  boracic  acid  is  generated.  It  is  very  difficult  to  oxidize  all 
the  boron  by  burning  ;  because  the  boracic  acid  fuses  at  the  moment  of  being 
formed,  and  by  glazing  the  surface  of  the  unburned  boron  protects  it  from 
oxidation.  It  also  passes  into  boracic  acid  when  heated  with  nitric  acid,  or 
with  any  substance  that  yields  oxygen  with  facility. 

According  to  the  experiments  of  Davy  and  Berzelius,  boron  in  burning 
unites  with  200  per  cent,  of  oxygen  :  and  the  latter,  from  the  composition  of 
borax,  estimates  the  oxygen  in  boracic  acid  at  68-8  per  cent.  In  this,  as  hi 
some  other  cases,  where  a  combustible  unites  with  oxygen  in  one  proportion 
only,  it  is  difficult  with  any  certainty  to  assign  the  true  atomic  constitution 
of  the  compound,  Boracic  acid  may  be  a  compound  of  boron  and  oxygen  in 
the  ratio  of  one  atom  to  one  atom,  in  that  of  one  to  two  as  supposed  by 
Thomson,  or  of  one  to  three.  When  dry  boracic  acid  is  heated  with  charcoal 
in  chlorine  gas,  it  is  decomposed,  and  two  volumes  of  terchloride  of  boron 
and  three  of  carbonic  oxide  gas  are  produced.  The  latter  contains  one  and  a 
half  volumes  of  oxygen,  and  the  former  has  been  proved  by  Dumas  to  be 
composed  of  three  volumes  of  chlorine  united  with  one  volume  of  the  vapour 
of  boron,  the  density  of  which  is  estimated  at  -751,  its  eq.  vol.  being  100. 


Recherches  Physico-Chimiques,  vol  i. 


SILICON.  205 

From  this  it  may  be  deduced  that  the  constitution  of  boracic  acid  is  BO3, 
which  has  also  been  recently  adopted  by  Berzelius  (Pog.  Ann.  xxiv.  561). 
Hence  its  eq.  is  10-9  ;  eq.  vol.  =  100;  symb.  B. 

Boracic  Acid. — Hist,  and  Prep. — This  is  the  only  known  compound  of 
boron  and  oxygen.  As  a  natural  product  it  is  found  in  the  hot  springs  of 
Lipari,  and  in  those  of  Sasso  in  the  Florentine  territory.  It  is  a  constituent 
of  several  minerals,  among  which  the  datolite  and  boracite  may  in  particular 
be  mentioned.  It  occurs  much  more  abundantly  under  the  form  of  borax,  a 
native  compound  of  boracic  acid  and  soda.  It  is  prepared  for  chemical  pur- 
poses by  adding  sulphuric  acid  to  a  solution  of  purified  borax  in  about  four 
titnes  its  weight  of  boiling  water,  till  the  liquid  acquires  a  distinct  acid  reac- 
tion. The  sulphuric  acid  unites  with  the  soda ;  and  the  boracic  acid  is  de- 
posited, when  the  solution  cools,  in  a  confused  group  of  shining  scaly  crys- 
tals. It  is  then  thrown  on  a  filter,  washed  with  cold  water  to  separate  the 
adhering  sulphate  of  soda  and  sulphuric  acid,  and  still  further  purified  by  so- 
lution in  boiling  water  and  re-crystallization.  But  even  after  this  treatment 
it  is  apt  to  retain  a  little  sulphuric  acid ;  on  this  account,  when  required  to 
be  absolutely  pure,  it  should  be  fused  in  a  platinum  crucible,  and  once  more 
dissolved  in  hot  water  and  crystallized. 

Prop. — In  the  crystallized  state  it  is  a  hydrate,  which  contains  43-62  per 
cent,  of  water,  being  a  ratio  of  34-9  parts  or  one  eq.  of  the  anhydrous  acid  to 
27  parts  or  three  eq.  of  water.  This  hydrate  dissolves  in  25-7  times  its  weight 
of  water  at  60°  and  in  3  times  at  212°.  Boiling  alcohol  dissolves  it  freely, 
and  the  solution,  when  set  on  fire,  burns  with  a  beautiful  green  flame,  a  test 
which  affords  the  surest  indication  of  the  presence  of  boracic  acid.  Its  sp. 
gr.  is  1-479.  It  has  no  odour,  and  its  taste  is  rather  bitter  than  acid.  It  red- 
dens litmus  paper  feebly,  and  effervesces  with  alkaline  carbonates.  Faraday 
has  noticed  that  it  renders  turmeric  paper  brown  like  the  alkalies.  From  the 
weakness  of  the  acid  properties  of  boracic  acid,  all  the  borates,  when  in  so- 
lution, are  decomposed  by  the  stronger  acids ;  and  the  neutral  borates  of 
potassa  and  soda  are  deprived  of  half  their  base  by  carbonic  acid,  at  common 
temperatures. 

When  hydrous  boracic  acid  is  exposed  to  a  gradually  increasing  heat  in  a 
platinum  crucible,  its  water  of  crystallization  is  wholly  expelled,  and  a  fused 
mass  remains  which  bears  a  white  heat  without  being  sublimed.  On  cooling 
it  forms  a  hard,  colourless,  transparent  glass,  which  is  anhydrous  boracic 
acid.  If  the  water  of  crystallization  be  driven  off  by  the  sudden  application 
of  a  strong  heat,  a  large  quantity  of  boracic  acid  is  carried  away  during  the 
rapid  escape  of  watery  vapour.  The  same  happens,  though  in  a"  less  degree, 
when  a  solution  of  boracic  acid  in  water  is  boiled  briskly.  Vitrified  boracic 
acid  should  be  preserved  in  well-stopped  vessels  ;  for  if  exposed  to  the  air,  it 
absorbs  water,  and  gradually  loses  its  transparency.  Its  sp.  gravity  is  1-803. 
It  is  exceedingly  fusible,  and  communicates  this  property  to  the  substances 
with  which  it, unites.  For  this  reason  borax  is  often  used  as  a  ftux. 

k  Its  eq.  is  34-9 ;  syrab.  B-J-3O,  B,  or  BO3, 


SECTION  X. 

SILICON. 

Hist. — THAT  silicic  acid  or  silica  is  composed  of  a  combustible  body  united 
with  oxygen,  was  demonstrated  by  Davy ;  for  on  bringing  the  vapour  of  pot- 
assium in  contact  with  pure  silicic  acid  heated  to  whiteness,  a  silicate  of 
potassa  resulted,  through  which  was  diffused  the  inflammable  base  of  silicic 

18 


206  SILICON, 

acid  in  the  form  of  black  particles  like  plumbago.  To  this  substance,  on 
the  supposition  of  its  being  a  metal,  the  term  silicium  was  applied.  But 
though  this  view  has  been  adopted  by  most  chemists,  so  little  was  known 
with  certainty  concerning  the  real  nature  of  the  base  of  silica,  that  Thomson 
inclined  to  the  opinion  of  its  being  a  non-metallic  body,  and  accordingly  as- 
sociated it  in  his  system  of  chemistry  with  carbon  and  boron  under  the 
name  of  silicon.  The  recent  researches  of  Berzelius  appear  almost  decisive 
of  this  question.  A  substance  which  wants  the  metallic  lustre,  and  is  a  non- 
conductor of  electricity,  cannot  be  regarded  as  a  metal. 

Prep. — Pure  silicon  was  first  procured  by  Berzelius  in  the  year  1824  by 
the  action  of  potassium  on  fluosilicic  acid  gas ;  but  it  is  more  conveniently 
prepared  from  the  double  fluoride  of  silicon  and  potassium  or  sodium,  pre- 
viously dried  by  a  temperature  near  that  of  redness.  When  this  compound 
is  heated  in  a  glass  tube  with  potassium,  the  latter  unites  with  fluorine,  and 
silicon  is  separated.  The  heat  of  a  spirit-lamp  is  sufficient  for  the  purpose, 
and  the  decomposition  takes  place,  accompanied  with  feeble  detonation,  be- 
fore the  mixture  becomes  red-hot.  When  the  mass  is  cold,  the  soluble  parts 
are  removed  by  the  action  of  water;  the  first  portions  of  which  produce  dis- 
engagement of  hydrogen  gas,  owing  to  the  presence  of  some  silicuret  of  pot- 
assium. The  silicon  thus  procured  is  chemically  united  with  a  little  hydro- 
gen, and  at  a  red  heat  burns  vividly  in  oxygen  gas.  In  order  to  render  it  quite 
pure,  it  should  be  first  heated  to  redness,  and  then  digested  in  dilute  hydro- 
fluoric acid  to  dissolve  adherent  particles  of  silicic  acid.  (Ann.  of  Phil.  xxvL 
116.) 

Prop. — Silicon  obtained  in  this  manner  has  a  dark  nut-brown  colour, 
without  the  least  trace  of  metallic  lustre.  It  is  a  non-conductor  of  electricity. 
It  is  incombustible  in  air  and  in  oxygen  gas ;  and  may  be  exposed  to  the 
flame  of  the  blowpipe  without  fusing  or  undergoing  any  other  change.  It 
is  neither  dissolved  nor  oxidized  by  the  sulphuric,  nitric,  hydrochloric,  or 
hydrofluoric  acid ;  but  a  mixture  of  the  nitric  and  hydrofluoric  acids  dis- 
solves it  readily  even  in  the  cold.* 

It  is  not  changed  by  ignition  with  chlorate  of  potassa.  In  nitre  it  does 
not  deflagrate  until  the  temperature  is  raised  so  high  that  the  acid  is  decom- 
posed ;  and  then  the  oxidation  is  effected  by  the  affinity  of  the  disengaged 
alkali  for  silicic  acid,  co-operating  with  the  attraction  of  oxygen  for  silicon. 
For  a  similar  reason  it  burns  vividly  when  brought  into  contact  with  carbo- 

*  Dr.  Turner  has  not,  perhaps,  described  with  sufficient  distinctness,  the 
two  states  under  which  silicon  appears.  Its  characters  are  so  much  altered 
by  exposure  to  a  high  temperature,  that  Berzelius  has  deemed  it  expedient 
to  give  a  separate  description  of  its  properties,  as  it  appears  before  and  after 
ignition. 

Silicon  before  ignition  is  neither  oxidized  nor  dissolved  by  sulphuric,  nitric, 
or  nitro-muriatic  acid,  even  at  the  boiling  temperature ;  but  it  is  soluble  in 
liquid  hydrofluoric  acid  at  common  temperatures,  and  in  a  heated  concen- 
trated solution  of  caustic  potassa.  It  burns  readily  and  vividly  in  air,  and 
still  more  vividly  in  oxygen  gas.  A  part  of  it  only  undergoes  combustion, 
the  remainder  being  protected  by  the  coating  of  silicic  acid  which  becomes 
formed.  In  this  state  silicon  contains  a  little  hydrogen. 

If  a  portion  of  silicon  which  has  undergone  combustion  on  its  surface, 
be  subjected  to  the  action  of  hydrofluoric  acid,  the  silica  is  removed,  and  a 
nucleus  of  silicon  is  obtained  in  that  state  in  which  it  exists,  after  having 
been  condensed  and  altered  in  its  properties  by  heat.  It  is  now  perfectly 
incombustible,  and  is  no  longer  soluble  in  hydrofluoric  acid  or  in  a  solution  of 
caustic  potassa. 

Berzelius  does  not  appear  to  attribute  the  difference  in  properties  between 
the  two  forms  of  silicon  to  the  presence  of  hydrogen  in  one  of  them ;  but 
rather  to  a  difference  in  the  aggregation  of  the  particles.  Berzelius^  Traiti 
dc  CAimie,  i.  370.-— Ed. 


SILICON.  207 

nate  of  potassa  or  soda,  and  the  combustion  ensues  at  a  temperature  consi- 
derably below  that  of  redness.  It  explodes  in  consequence  of  a  copious 
evolution  of  hydrogen  gas,  when  it  is  dropped  upon  the  fused  hydrate  of 
potassa,  soda,  or  baryta. 

Berzelius  ascertained,  by  oxidizing  a  known  weight  of  silicon,  that  100 
parts  of  silicic  acid  are  composed  of  48'4  of  silicon  and  51-6  of  oxygen. 
Now,  if  silicic  acid,  as  Thomson  supposes,  be  composed  of  single  atoms  of  its 
elements,  then  the  equivalent  of  silicon  will  be  7*5 ;  but  if,  as  Berzelius 
believes,  the  smallest  molecule  of  that  acid  contain  three  atoms  of  oxygen 
united  with  one  atom  of  silicon,  the  equivalent  of  silicon  would  be  22-5.  The 
latter  view  is  supported  by  very  strong  analogies.  Its  equivalent  is  there- 
fore 22-5 ;  symb,  SL 

Silicic  Acid. — Hist,  and  Prep. — This  compound,  known  also  by  the  names 
of  silica  and  siliceous  earth,  exists  abundantly  in  nature.  It  enters  into  the 
composition  of  most  of  the  earthy  minerals;  and,  under  the  name  of  quartz 
rock,  forms  independent  mountainous  masses.  It  is  the  chief  ingredient  of 
sandstones,  flint,  calcedony,  rock  crystal,  and  other  analogous  substances. 
It  may  indeed  be  procured,  of  sufficient  purity  for  most  purposes,  by  igniting 
transparent  specimens  of  rock  crystal,  throwing  them  while  red-hot  into 
water,  and  then  reducing  them  to  powder. 

Prop. — Pure  silicic  acid,  in  this  state,  is  a  light  white  powder,  which  feels 
rough  and  dry  when  rubbed*  between  the  fingers ;  is  both  insipid  and  in- 
odorous ;  the  sp.  gr.  is  2.69.  It  is  fixed  in  the  fire,  and  very  infusible ;  but 
fuses  before  the  oxy-hydrogen  blowpipe  with  greater  facility  than  lime  or 
magnesia.  It  is  quite  insoluble  in  water ;  but  Berzelius  has  shown  that, 
if  presented  to  water  while  in  the  nascent  state,  it  is  dissolved  in  large 
quantity.  On  evaporating  the  solution  gently,  a  bulky  gelatinous  hydrate 
separates,  which  is  partially  decomposed  by  a  very  moderate  temperature, 
but  does  not  part  with  all  its  water  except  at  a  red  heat. 

Silicic  acid  has  no  action  on  test  paper ;  but  in  all  its  chemical  relations 
it  manifests  the  properties  of  an  acid,  and  displaces  carbonic  acid  by  the 
aid  of  heat  from  the  alkalies.  Its  combinations  with  the  fixed  alkalies  are 
effected  by  mixing  pure  sand  with  carbonate  of  potassa  or  soda,  and  heating 
the  mixture  to  redness.  During  the  process,  carbonic  acid  is  expelled,  and 
a  silicate  of  the  alkali  is  generated.  The  nature  of  the  product  depends  upon 
the  proportions  which  are  employed.  On  igniting  one  part  of  silicic  acid 
with  three  of  carbonate  of  potassa,  a  vitreous  mass  is  formed,  which  is  de- 
liquescent, and  may  be  dissolved  completely  in  water.  This  solution,  which 
was  formerly  called  liquor  silicum,  has  an  alkaline  reaction,  and  absorbs 
carbonic  acid  on  exposure  to  the  atmosphere,  by  which  it  is  partially  decom- 
posed. Concentrated  acids  precipitate  the  silicic  acid  as  a  gelatinous  hydrate ; 
but  if  a  considerable  quantity  of  water  is  present,  and  the  acid  is  added  gra- 
dually, the  alkali  may  be  perfectly  neutralized  without  any  separation  of 
silicic  acid.  When  a  solution  of  this  kind  is  evaporated  to  dryness,  the 
silicic  acid  is  rendered  quite  insoluble,  and  may  thus  be  obtained  in  a  pure 
form. 

But  if  the  proportion  of  silicic  acid  and  alkali  be  reversed,  a  transparent 
brittle  compound  results,  which  is  insoluble  in  water,  is  attacked  by  none  of 
the  acids  excepting  the  hydrofluoric,  and  possesses  the  well-known  properties 
of  glass.  Every  kind  of  ordinary  glass  is  a  silicate,  and  all  its  varieties  are 
owing  to  differences  in  the  proportion  of  the  constituents,  to  the  nature  of 
the  alkali,  or  to  the  presence  of  foreign  matters.  Thus,  green  bottle  glass 
is  made  of  impure  materials,  such  as  river  sand,  which  contains  iron,  and 
the  most  common  kind  of  kelp  or  pearl-ashes.  Crown  glass  for  windows  is 
made  of  a  purer  alkali,  and  sand  which  is  free  from  iron.  Plate  glass,  for 
looking-glasses,  is  composed  of  sand  and  alkali  in  their  purest  state ;  and  in 
the  formation  of  flint-glass,  besides  these  pure  ingredients,  a  considerable 
quantity  of  litharge  or  red  lead  is  employed.  A  small  portion  of  peroxide 
of  manganese  is  also  used,  in  order  to  oxidize  carbonaceous  matters  con- 
tained in  the  materials  of  the  glass ;  and  nitre  is  sometimes  added  with  the 


208  SELENIUM. 

same  intention.  Ordinary  flint-glass,  according  to  Faraday,  contains  51*93 
per  cent,  of  silicic  acid,  33-28  of  oxide  of  lead,  and  13-77  of  potassa;  propor- 
tions which  correspond  to  one  eq.  of  potassa,  one  eq.  of  oxide  of  lead,  and 
nearly  four  eq.  of  silicic  acid.  Flint-glass,  accordingly,  is  a  double  salt,  con- 
sisting  chiefly  of  bisilicate  of  potassa  and  bisilicate  of  oxide  of  lead. 

Its  eq.  is  46'5;  symb.  Si+3O,  Si,  or  SiQ3. 


SECTION  XL 

SELENIUM. 

Hist,  and  Prep. — This  substance  was  discovered  in  1818  by  Berzeliusv 
who  called  it  selenium,  from  2exviv»,  the  moo/7,  suggested  by  its  having  at 
first  been  mistaken  for  the  metal  tellurium.  (An.  de  Ch.  et  de  Ph.  ix.  160, 
and  An.  of  Phil.  xiii.  401.)  It  has  hitherto  been  obtained  in  very  small 
quantity,  and  occurs  for  the  most  part  in  combination  with  some  varieties  of 
iron  pyrites.  Stromeyer  has  also  detected  it,  as  a  sulphuret  of  selenium, 
among  the  volcanic  products  of  the  Lipari  isles.  It  is  found  likewise  at 
Clausthal  in  the  Hartz,  combined,  according  to  Stromeyer  and  Rose,  with 
several  metals,  such  as  lead,  cobalt,  silver,  mercury,  and  copper.  Berzelius 
found  it  in  the  sulphur  obtained  by  sublimation  from  the  iron  pyrites  of 
Fahlun.  In  a  manufactory  of  sulphuric  acid,  at  which  this  sulphur  was  em- 
ployed, it  was  observed  that  a  reddish-coloured  matter  always  collected  at 
the  bottom  of  the  leaden  chamber;  and  on  burning  this  substance,  Berzelius 
perceived  a  strong  and  peculiar  odour,  similar  to  that  of  decayed  horse- 
radish, which  induced  him  to  submit  it  to  a  careful  examination,  and  thus 
led  to  the  discovery  of  selenium.  For  the  extraction  of  selenium  from  the 
native  sulphuret,  Magnus  proposes  to  mix  it  with  eight  times  its  weight  of 
peroxide  of  manganese,  and  to  expose  the  mixture  to  a  low  red  heat  in  a 
glass  retort,  the  beak  of  which  dips  into  water.  The  sulphur,  oxidized  at 
the  expense  of  the  manganese,  escapes  in  the  form  of  sulphurous  acid ;  while 
the  selenium  either  sublimes  as  such  or  in  the  state  of  selenious  acid.  Should 
any  of  the  latter  be  carried  over  into  the  water,  it  would  there  be  reduced 
by  the  sulphurous  acid. 

Prop. — Selenium,  at  common  temperatures,  is  a  brittle  opaque  solid  body, 
without  taste  or  odour.  It  has  a  metallic  lustre  and  the  aspect  of  lead  when 
in  mass;  but  it  is  of  a  deep  red  colour  when  reduced  to  powder.  Its  sp.  gr. 
is  between  4'3  and  4-32.  At  212°  it  softens,  and  is  then  so  tenacious  that  it 
may  be  drawn  out  into  fine  threads  which  are  transparent,  and  appear  red 
by  transmitted  light.  It  becomes  quite  fluid  at  a  temperature  somewhat 
above  that  of  boiling  water.  It  boils  at  about  650°,  forming  a  vapour  which 
has  a  deep  yellow  colour,  but  is  free  from  odour.  It  may  be  sublimed  in 
close  vessels  without  change,  and  condenses  again  into  dark  globules  of  a 
metallic  lustre,  or  as  a  cinnabar-red  powder,  according  as  the  space  in  which 
it  collects  is  small  or  large.  Berzelius  at  first  regarded  it  as  a  metal ;  but, 
since  it  is  an  imperfect  conductor  of  heat  and  electricity,  it  more  properly  be- 
longs to  the  class  of  the  simple  non-metallic  bodies. 

Selenium  is  insoluble  in  water.  It  suffers  no  change  from  mere  exposure 
to  the  atmosphere ;  but  if  heated  in  the  open  air,  it  combines  readily  with 
oxygen,  and  two  compounds,  oxide  of  selenium  and  selenious  acid,  are  gene- 
rated. If  exposed  to  the  oxidizing  part  of  the  blow-pipe  flame,  it  tinges  the 
flame  with  a  light  blue  colour,  and  exhales  so  strong  an  odour  of  decayed 
horse-radish,  that  l-50th  of  a  grain  is  said  to  be  sufficient  to  scent  the  air  of 
a  large  apartment.  By  this  character  the  presence  of  selenium,  whether 
alone  or  in  combination,  may  always  be  detected. 


SELENIUM.  209 

Berzelius  has  shown  that  selenic  acid  is  composed  of  24  parts  of  oxygen 
and  39-6  of  selenium.  This  substance,  also,  has  three  grades  of  oxidation,  the 
oxygen  in  the  two  last  of  which  is  in  the  ratio  of  2  to  3  ;  and  the  highest 
grade,  selenic  acid,  has  in  all  its  chemical  relations  a  singularly  close  analogy 
to  sulphuric  acid.  From  these  facts  it  is  inferred  that  selenic  acid  is  com- 
posed of  one  atom  of  selenium  and  three  atoms  of  oxygen.  Its  eq.  is  39-6 ; 
symb.  Se. 

The  compounds  of  selenium  described  in  this  section  are  the  following: — 

Selenium.  Oxygen.      Equiv.  Formulae. 

Oxide  of  selenium  (probably)    39-6  or  1  eq.-f  8  or  1  eq.  =  47-6  Se-f-O. 
Selenious  acid  -         -         39-6  -j- 16  or  2  eq.  =  55-6  Se  .f  2O. 

Selenic  acid      -        -         -         39-6  -J-24  or  3  eq.  =  63.6  Se-j-3O. 

Oxide  of  Selenium — This  compound  is  formed  in  greatest  abundance  by 
heating  selenium  in  a  limited  quantity  of  atmospheric  air,  and  by  washing 
the  product  to  separate  selenious  acid,  which  is  generated  at  the  same  time. 
It  is  a  colourless  gas,  which  is  very  sparingly  soluble  in  water,  and  does  not 
possess  any  acid  properties.  It  is  the  cause  of  the  peculiar  odour  which  is 
emitted  during  the  oxidation  of  selenium. 

Selenious  Acid. — This  acid  is  most  conveniently  prepared  by  digesting  se- 
lenium in  nitric  or  nitro-hydrochloric  acid  till  it  is  completely  dissolved.  On 
evaporating  the  solution  to  dryness,  a  white  residue  is  left,  which  is  selenious 
acid.  By  increase  of  temperature,  the  acid  itself  sublimes,  and  condenses 
again  unchanged  into  long  four-sided  needles.  It  attracts  moisture  from  the 
air,  whereby  it  suffers  imperfect  liquefaction.  It  dissolves  in  alcohol  and 
water.  It  has  distinct  acid  properties,  and  its  salts  are  called  selenites, 

Selenious  acid  is  readily  decomposed  by  all  substances  which  have  a 
strong  affinity  for  oxygen,  such  as  sulphurous  and  phosphorous  acids.  When 
sulphurous  acid,  or  an  alkaline  sulphite,  is  added  to  a  solution  of  selenious 
acid,  a  red-coloured  powder,  pure  selenium,  is  thrown  down,  and  the  sul- 
phurous is  converted  into  sulphuric  acid.  Hydrosulphuric  acid  also  decom- 
poses it ;  and  an  orange-yellow  precjpitate  subsides,  which  is  a  sulphuret  of 
selenium. 

Selenic  Acid. — Hist. — The  preceding  compound,  discovered  by  Berzelius, 
was  till  lately  the  only  known  acid  of  selenium,  and  has  been  described  in 
elementary  works  under  the  name  of  selenic  acid ;  but  the  recent  discovery 
of  another  acid  of  selenium  containing  more  oxygen  than  the  other,  has  ren- 
dered necessary  a  change  of  nomenclature.  The  existence  of  selenic  acid  was 
first  noticed  by  M.  Nitzsch,  assistant  of  Mitscherlich,  and  its  properties  have 
been  examined  and  described  by  the  Professor  himself.  (Edin.  Journal  of 
Science,  viii.  294.) 

Prep. — This  acid  is  prepared  by  fusing  nitrate  of  potassa  or  soda  with  se- 
lenium, a  metallic  seleniuret,  or  with  selenious  acid  or  any  of  its  salts.  Se- 
leniurct  of  lead,  as  the  most  common  ore  of  selenium,  will  generally  be  em- 
ployed ;  but  it  is  very  difficult  to  obtain  pure  selenic  acid  by  its  means,  be- 
cause it  is  commonly  associated  with  metallic  sulphurets.  The  ore  is  first 
treated  with  hydrochloric  acid  to  remove  any  carbonate  that  may  be  pre- 
sent; and  the  insoluble  part,  which  is  about  a  third  of  the  mass,  is  mixed 
with  its  own  weight  of  nitrate  of  soda,  and  thrown  by  successive  portions 
into  a  red-hot  crucible.  The  lead  is  thus  oxidized,  and  the  selenium  con- 
verted into  selenic  acid,  which  unites  with  the  soda.  The  fused  mass  is  then 
acted  on  by  hot  water,  which  dissolves  only  seleniate  of  soda,  together  with 
nitrate  and  nitrite  of  soda;  while  the  insoluble  matter,  when  well  washed,  is 
quite  free  from  selenium.  The  solution  is  next  made  to  boil  briskly,  when 
anhydrous  seleniate  of  soda  is  deposited  ;  while,  on  cooling,  nitrate  of  soda 
crystallizes.  On  renewing  the  ebullition  and  subsequent  cooling,  fresh  por- 
tions of  seleniate  and  nitrate  are  procured  ;  and  these  successive  operations 
are  repeated,  until  the  former  salt  is  entirely  separated.  This  process  is 
founded  on  the  fact,  that  seleniate  of  soda,  like  the  sulphate  of  the  same  base, 
is  more  soluble  in  water  of  about  90°  than  at  higher  or  lower  temperatures. 

18* 


210  SELENIUM. 

The  nitrite  of  soda,  formed  during  the  fusion,  is  purposely  reconverted  into 
nitrate  by  digestion  with  nitric  acid. 

Trie  seleniate  of  soda  thus  procured  always  contains  a  little  sulphuric  acid, 
derived  from  the  metallic  sulphurets  of  the  ore  ;  and  it  is  not  possible  to  sepa- 
rate this  acid  by  crystallization.  All  attempts  to  separate  it  by  means  of 
baryta  were  likewise  fruitless;  and  the  only  method  of  effecting  this  object 
is  by  reducing  the  selenic  acid  into  selenium.  This  is  done  by  heating  a 
mixture  of  seleniate  of  soda  with  hydrochlorate  of  ammonia,  when  the  sodium 
unites  with  chlorine,  all  the  hydrogen  with  oxygen,  and  selenium  and  nitro- 
gen are  set  free.  This  change  will  be  more  readily  followed  when  stated  in 
symbols ; — thus 

Na-f-O,  Se-f  3O,N-f  3H,and  H  +  C1,  yield  N,  Se,  4(H-fO),and  Na-fCL 

The  selenium  which  sublimes  is  quite  free  from  sulphur.  It  is  then  convert- 
ed by  nitric  acid  into  selenious  acid,  which  should  be  neutralized  with  soda, 
and  fused  with  nitre  or  nitrate  of  soda.  The  pure  seleniate  of  soda,  sepa- 
rated from  the  nitrate  according  to  the  foregoing  process,  is  subsequently  dis- 
solved in  water,  and  obtained  in  crystals  by  spontaneous  evaporation. 

To  procure  the  acid  in  a  free  state,  seleniate  of  soda  is  decomposed  by  ni- 
trate of  oxide  of  lead.  The  seleniate  of  that  oxide,  which  is  as  insoluble  as 
the  sulphate,  after  being  well  washed,  is  exposed  to  a  current  of  hydrosul- 
phuric  acid  gas,  which  precipitates  all  the  lead  as  a  sulphuret,  but  does  not 
decompose  the  selenic  acid.  The  excess  of  the  gas  is  driven  off  by  heat, 
and  pure  selenic  acid  remains  diluted  with  water.  The  absence  of  fixed  sub- 
stances may  be  proved  by  its  being  volatilized  by  heat  without  residue ;  and 
if  free  from  sulphuric  acid,  it  gives  no  precipitate  with  chloride  of  barium 
after  being  boiled  with  hydrochloric  acid.*  Any  nitric  acid  which  may  be 
present  is  expelled  by  concentrating  the  solution  by  means  of  heat. 

Prop. — It  is  a  colourless  liquid,  which  may  be  heated  to  536°,  without 
appreciable  decomposition ;  but  above  that  point  decomposition  commences, 
and  it  becomes  rapid  at  554°,  giving  rise  to  disengagement  of  oxygen  and 
selenious  acid.  When  concentrated  by  a  temperature  of  329°,  its  sp.  gr.  is 
2-524  ;  at  512°  it  is  2-60,  and  at  545°  it  is  2-625,  but  a  little  selenious  acid  is 
then  present.  When  procured  by  the  process  above  described,  selenic  acid 
always  contains  water,  but  it  is  very  difficult  to  ascertain  its  precise  propor- 
tion. Some  acid,  which  had  been  heated  higher  than  536°,  contained,  sub- 
tracting the  quantity  of  selenious  acid  present,  15-75  per  cent,  of  water,  which 
approximates  to  the  ratio  of  one  equivalent  of  water  and  one  of  the  acid.  It 
is  certain  that  selenic  acid  is  decomposed  by  heat  before  parting  with  all  the 
water  which  it  contains. 

Selenic  acid  has  a  powerful  affinity  for  water,  and  emits  as  much  heat  in 
uniting  with  it  as  sulphuric  acid  does.  Like  this  acid  it  is  not  decomposed 
by  hydrosulphuric  acid,  and  hence  this  gas  may  be  employed  for  decomposing 
seleniate  of  the  oxides  of  lead  or  copper.  With  hydrochloric  acid  the  change 
is  peculiar ;  for  on  boiling  the  mixture  mutual  decomposition  ensues,  water 
and  selenious  acid  are  formed,  and  chlorine  is  set  free  ;  so  that  the  solution, 
like  aqua  regia,  is  capable  of  dissolving  gold  and  platinum.  Selenic  acid 
dissolves  zinc  and  iron  with  disengagement  of  hydrogen  gas,  and  copper  with 
formation  of  selenious  acid.  It  dissolves  gold  also,  but  not  platinum.  Sul- 
phurous acid  has  no  action  on  selenic  acid,  whereas  selenious  acid  is  easily 
reduced  by  it.  Consequently,  when  it  is  wished  to  precipitate  selenium  from 
selenic  acid,  it  must  be  boiled  with  hydrochloric  acid  before  sulphurous  acid 
is  added. 

Mitscherlich  has  observed,  that  selenic  and  sulphuric  acids  are  not  only 


*  The  necessity  for  this  previous  boiling  with  hydrochloric  acid  is  to  con- 
vert the  selenic  into  selenious  acid,  without  which  change  the  chloride  of 
barium  would  produce  a  precipitate  of  seleniate  of  baryta.  The  rationale  of 
the  action  of  hydrochloric  acid  is  explained  further  on, — Ed. 


CHLORINE.  211 


analogous  in  composition  and  in  many  of  their  properties,  but  that  the  simi- 
larity runs  through  their  compounds  with  alkaline  substances ;  their  salts 
resembling  each  other  in  chemical  properties,  constitution,  and  forai. 


SECTION  XII. 

CHLORINE. 

Hist. — THE  discovery  of  chlorine  was  made  in  the  year  1774  by  Scheele, 
while  investigating  the  nature  of  manganese,  and  he  described  it  under  the 
name  of  dephlogisticated  marine  acid.  The  French  chemists  call  it  oxygen- 
ized muriatic  acid,  a  term  which  was  afterwards  contracted  to  oxy '-muriatic 
acid,  from  an  opinion  proposed  by  Berthollet  that  it  is  a  compound  of  muria- 
tic acid  and  oxygen.  In  1809  Gay-Lussac  and  Thenard  published  an  abstract 
of  some  experiments  upon  this  substance,  which  subsequently  appeared  at 
length  in  their  Recherches  Physico-Chimiques,  wherein  they  stated  that  oxy. 
muriatic  acid  might  be  regarded  as  a  simple  body,  though  they  gave  the 
preference  to  the  doctrine  advanced  by  Berthollet.  Davy  engaged  in  the  in- 
quiry  about  the  same  time;  and  after  having  exposed  oxy-muriatic  acid  to 
the  most  powerful  decomposing  agents  which  chemists  possess,  without  being 
able  to  effect  its  decomposition,  he  communicated  to  the  Royal  Society  an 
essay,  in  which  he  denied  its  compound  nature  ;  and  he  maintained  that,  ac- 
cording to  the  true  logic  of  chemistry,  it  is  entitled  to  rank  with  simple 
bodies.  This  view,  which  is  commonly  termed  the  new  theory  of  chlorine, 
though  strongly  objected  to  at  the  time  it  was  first  proposed,  is  now  univer- 
sally received  by  chemists.  The  grounds  of  preference  will  hereafter  be 
briefly  stated. 

Prep. — Chlorine  gas  is  obtained  by  the  action  of  hydrochloric  acid  on 
peroxide  of  manganese.  The  most  convenient  method  of  preparing  it  is  by 
mixing  concentrated  hydrochloric  acid,  contained  in  a  glass  flask,  with  half 
its  weight  of  finely  powdered  peroxide  of  manganese.  Effervescence,  owing 
to  the  escape  of  chlorine,  takes  place  even  in  the  cold ;  but  the  gas  is  evolved 
much  more  freely  by  the  application  of  a  moderate  heat.  It  should  be 
collected  in  inverted  glass  bottles  filled  with  warm  water ;  and  when  the 
water  is  wholly  displaced  by  the  gas,  the  bottles  should  be  closed  with  a 
well-ground  glass  stopper.  As  some  hydrochloric  acid  gas  commonly  passes 
over  with  it,  the  chlorine  should  not  be  considered  quite  pure,  till  after  being 
transmitted  through  water. 

The  theory  of  this  process  will  be  readily  understood  by  first  viewing  the 
elements  which  act  on  each  other,  namely, — 

Manganese        27-7orleq.  Mn  Chlorine  70-84  or  2  eq.  2C1 

Oxygen  16         2eq.  2O  Hydrogen  2       or  2  eq.  2H 

Perox.  of  mang.  43-7  or  1  eq.  Mn  -f  2O.  Hydrochl.  acid  72-84  or  2  eq.2(H-f-Cl); 
and  then  inspecting  the  products  derived  from  them,  namely, 

Manganese  .  .  27-7  Hydrogen  2  „, ,    .      oc  An       -, 

Chlorine       .  .  3542 Oxygen     16  Chlorme  35'42  or  l  e* 

Chloride  of  mang.         63-12  Water       18. 

In  symbols, 

Mn-f  2O,  and  2(H-fCl),  yield  Mn-fCJ,2(H-f  O),and  Cl. 

The  affinities  which  determine  these  changes  are  the  mutual  attraction  of 
oxygen  and  hydrogen,  and  of  chlorine  and  manganese. 

When  it  is  an  object  to  prepare  chlorine  at  the  cheapest  rate,  as  for  the 


212  CHLORINE. 

purposes  of  manufacture,  the  preceding  process  is  modified  in  the  following 
manner.  Three  parts  of  sea-salt  are  intimately  mixed  with  one  of  peroxide 
of  manganese,  and  to  this  mixture  two  parts  of  sulphuric  acid,  diluted  with 
an  equal  weight  of  water,  are  added.  By  the  action  of  sulphuric  acid  on 
sea-salt,  hydrochloric  acid  is  disengaged,  which  reacts,  as  in  the  former 
case,  upon  the  peroxide  of  manganese  ;  so  that,  instead  of  adding  hydro- 
chloric acid  directly  to  the  manganese,  the  materials  for  forming  it  are  em- 
ployed. In  this  process,  however,  the  sulphates  of  soda  and  protoxide  of 
manganese  are  generated,  instead  of  chloride  of  manganese.  Thus  the  ma- 
terials which  act  on  each  other  are  MnO?,  Nad,  and  2SO3;  and  the  pro- 
ducts MnO,  SQ3.  NaO,  SO*,  and  Cl. 

Prop. — Chlorine  (from  ;^Aa>go?,  green)  is  a  yellowish-green  coloured  gas, 
which  has  an  astringent  taste,  and  a  disagreeable  odour.  It  is  one  of  the 
most  suffocating  of  the  gases,  exciting  spasm  and  great  irritation  of  the 
glottis,  even  when  considerably  diluted  with  air.  When  strongly  and  sud- 
denly compressed,  it  emits  both  heat  and  light,  the  latter  being  solely  due,  as 
in  the  case  of  air  and  oxygen,  to  the  chlorine  acting  chemically  on  the  oil 
with  which  the  compressing  apparatus  is  lubricated.  (An.  de  Ch.  et  de  Ph. 
xliv.  181).  According  to  Davy  100  cubic  inches  of  dry  chlorine,  at  30  Bar. 
and  60°F.  weigh  between  76  and  77  grains.  Gay-Lussac  and  Thenard 
found  the  density  of  pure  and  dry  chlorine  to  be  2-47,  which  gives  76-5988 
grains  as  the  weight  of  100  cubic  inches  at  60°  F.  and  30  Bar.  Under  the 
pressure  of  about  four  atmospheres  it  is  a  limpid  liquid  of  a  bright  yellow 
colour,  which  does  not  freeze  at  the  temperature  of  zero,  and  which  assumes 
the  gaseous  form  witli  the  appearance  of  ebullition  when  the  pressure  is  re- 
moved. Kemp  finds  that  this  liquid  is  a  non-conductor  of  electricity. 

Cold  recently  boiled  water,  at  the  common  pressure,  absorbs  twice  its  vo- 
lume of  chlorine,  and  yields  it  again  when  heated.  The  solution,  which  is 
made  by  transmitting  a  current  of  chlorine  gas  through  cold  water,  has  the 
colour,  taste,  and  most  of  the  other  properties  of  the  gas  itself.  When  moist 
chlorine  gas  is  exposed  to  a  cold  of  32°,  yellow  crystals  are  formed,  which 
consist  of  water  and  chlorine  in  definite  proportions.  They  are  composed, 
according  to  Faraday,  of  35-42  parts  or  one  eq.  of  chlorine,  and  90  parts  or 
ten  eq.  of  water.  It  experiences  no  chemical  change  from  the  action  of  the 
imponderables.  Thus  it  is  not  affected  chemically  by  intense  heat,  by  strong 
shocks  of  electricity,  or  by  a  powerful  galvanic  battery.  Davy  exposed  it 
also  to  the  action  of  charcoal  heated  to  whiteness  by  galvanic  electricity, 
without  separating  oxygen  from  it,  or  in  any  way  affecting  its  nature.  Light 
does  not  act  on  dry  chlorine ;  but  if  water  be  present,  the  chlorine  decom- 
poses that  liquid,  unites  with  the  hydrogen  to  form  hydrochloric  acid,  and 
oxygen  gas  is  set  at  liberty.  This  change  takes  place  quickly  in  sunshine, 
more  slowly  in  diffused  daylight,  and  not  at  all  when  light  is  wholly  ex- 
cluded. Hence  the  necessity  of  keeping  moist  chlorine  gas,  or  its  solution, 
in  a  dark  place. 

Chlorine  unites  with  some  substances  with  evolution  of  heat  and  light, 
and  is  hence  termed  a  supporter  of  combustion.  On  plunging  a  lighted 
taper  into  chlorine  gas,  it  burns  for  a  short  time  with  a  small  red  flame,  and 
emits  a  large  quantity  of  smoke.  Phosphorus  takes  fire  in  it  spontaneous- 
ly, and  burns  with  a  pale  white  light.  Several  of  the  metals,  such  as  tin, 
copper,  arsenic,  antimony,  and  zinc,  when  introduced  into  chlorine  in  the 
state  of  powder  or  in  fine  leaves,  are  suddenly  inflamed.  In  all  these  cases 
the  combustible  substances  unite  with  chlorine. 

Chlorine  has  a  very  powerful  attraction  for  hydrogen,  and  many  of  the 
chemical  phenomena,  to  which  it  gives  rise,  are  owing  to  this  property.  A 
striking  example  is  its  power  of  decomposing  water  by  the  action  of  light, 
or  at  a  red  heat;  and  the  same  effect  is  produced  on  most  compound  sub- 
stances, of  which  hydrogen  is  an  element.  For  the  same  reason,  when 
chlorine,  water,  and  some  other  body  which  has  a  strong  affinity  for  oxy- 
gen, are  presented  to  one  another,  water  is  usually  resolved  into  its  elements, 
its  hydrogen  attaching  itself  to  the  chlorine,  and  its  oxygen  to  the  other 


CHLORINE.  213 

body.  Thus  chlorine  is,  indirectly,  one  of  the  most  powerful  oxidizing- 
agents  which  we  possess. 

When  any  compound  of  chlorine  and  an  inflammable  is  exposed  to  the 
influence  of  galvanism,  the  inflammable  body  goes  over  to  the  negative,  and 
chlorine  to  the  positive  jSole  of  the  battery.  This  establishes  a  close  analogy 
between  oxygen  and  chlorine,  both  of  them  being  supporters  of  combustion, 
and  both  negative  electrics. 

Though  formerly  called  an  acid,  it  possesses  no  acid  properties.  It  has 
not  a  sour  taste,  does  not  redden  the  blue  colour  of  plants,  and  shows  com- 
paratively little  disposition  to  unite  with  alkalies.  Its  strong  affinity  for  the 
metals  is  sufficient  to  prove  that  it  is  not  an  acid ;  for  chemists  are  not  ac- 
quainted with  any  instance  of  an  acid  combining  directly  in  definite  pro- 
portion with  a  metal.  Its  action  on  the  pure  alkalies  leads  to  complicated 
changes,  which  will  be  considered  while  speaking  of  the  oxides  of  chlorine. 

One  of  the  most  important  properties  of  chlorine  is  its  bleaching  power. 
All  animal  and  vegetable  colours  are  speedily  removed  by  chlorine;  and 
when  the  colour  is  once  discharged,  it  can  never  be  restored.  Davy  proved 
that  chlorine  cannot  bleach  unless  water  is  present.  Thus  dry  litmus  paper 
suffers  no  change  in  dry  chlorine;  but  when  water  is  admitted,  the  colour 
speedily  disappears.  It  is  well  known  also  that  hydrochloric  acid  is  always 
generated  when  chlorine  bleaches.  From  these  facts  it  is  inferred  that  water 
is  decomposed  during  the  process ;  that  its  hydrogen  unites  with  chlorine, 
and  that  decomposition  of  the  colouring  matter  is  occasioned  by  the  oxygen 
which  is  liberated.  The  bleaching  property  of  binoxide  of  hydrogen,  and 
of  chromic  and  permanganic  acids,  of  which  oxygen  is  certainly  the  de- 
colorizing principle,  leaves  little  doubt  of  the  accuracy  of  the  foregoing  ex- 
planation. 

Chlorine  is  useful,  likewise,  for  the  purposes  of  fumigation.  The  expe- 
rience of  Guyton-Morveau  is  sufficient  evidence  of  its  power  in  destroying 
the  volatile  principles  given  off  by  putrefying  animal  matter ;  it  probably 
acts  in  a  similar  way  on  contagious  effluvia.  A  peculiar  compound,  formed 
by  the  action  of  chlorine  on  soda,  has  been  lately  introduced  for  this  pur- 
pose by  Labarraque. 

Chlorine  is  in  general  easily  recognized  by  its  colour  and  odour.  Chemi- 
cally it  may  be  detected  by  its  bleaching  property,  added  to  the  circum- 
stance that  a  solution  of  nitrate  of  oxide  of  silver  occasions  in  it  a  dense 
white  precipitate  (a  compound  of  chlorine  and  metallic  silver),  which  be- 
comes dark  on  exposure  to  light,  is  insoluble  in  acids,  and  dissolves  com- 
pletely in  pure  ammonia.  The  whole  of  the  chlorine,  however,  is  not  thrown 
down  ;  for  the  oxygen  of  the  oxide  of  silver  unites  with  a  portion  of  chlo- 
rine, and  converts  it  into  chloric  acid. 

Those  compounds  of  chlorine,  which  are  not  acid,  are  termed  chlorides  or 
chlorurets.  The  former  expression,  from  the  analogy  between  chlorine  and 
oxygen,  is  perhaps  the  more  appropriate. 

Berzelius  inferred  the  equivalent  of  chlorine  from  the  oxygen  lost  by  chlo- 
rate of  potassa  when  decomposed  by  heat,  and  the  quantity  of  chlorine 
found  in  the  residual  chloride  of  potassium.  I  investigated  the  same  sub- 
ject by  examining  into  the  composition  of  the  nitrate  of  the  oxide  and  chlo- 
ride of  silver,  of  the  protoxide  and  chloride  of  lead,  and  of  the  peroxide  and 
chlorides  of  mercury.  These  researches  concur  in  showing  36,  the  eq.  of 
chlorine  commonly  adopted  in  this  country,  to  be  erroneous. 

Its  eq.  is  35-42  ;  eq.  vol.  =  100  ;  symb.  Cl. 

The  composition  of  the  compounds  described  in  this  section  is  as  fol- 
lows : — 

Chlorine.  Equiv.  Formulas. 

Hydrochloric  acid  35-42  1  eq.-f  Hydrogen  1  1  eq.  =  36-42  H-f-Cl 
Hypochlorous  acid  35-42  1  eq.  4.  Oxygen  8  1  eq.  =  43-42  C1-J.O 
Chlorous  acid  35-42  1  eq.-f  Ditto  32  4  eq.  =  67-42  C1  +  4O 


214 

CHLORINE. 

Chlorine. 

Equiv.  Formulae. 

Chloric  acid 

35-42 

1 

eq. 

-f-  Oxygen 

40 

5  eq. 

—    75-42    Cl-f  5O 

Perchloric  acid* 

35-42 

1 

eq. 

4.  Ditto 

56 

7eq. 

=    91-42    C1  +  7O 

Quadrochloride 
of  nitrogen 

i 

141-68 

4  eq. 

-}-  Nitrogen 

14-151  eq. 

=  155-83    N4-4C1 

Protochloride  of 
carbon 

35-42 

1 

eq. 

4.  Carbon 

6-12 

leq. 

=    41-54     C4-C1 

Dichloride    of 
carbon     .     . 

j 

35-42 

1 

eq. 

-f  Ditto 

12-24 

2eq. 

=    47-66  2C4-C1 

Perchloride  of 
carbon  . 

f 

106-26 

3 

cq. 

4-  Ditto 

12-24 

2eq. 

=  118-5    2C4-3C1 

Dichloride   of 
sulphur  .    . 

J 

35-42 

1 

eq. 

4.  Sulphur 

32-2 

2eq. 

=    67-62  2S-f-Cl 

Protochloride  of 
sulphur   .     . 

j 

35-42 

1 

eq. 

4.  Ditto 

16-1 

1  eq. 

=     51-52  S4-C1 

Sesquichloride  of 
phosphorus 

j 

106-26 

3 

eq. 

-|-Phosph. 

31-4 

2eq. 

=  137-66  2P  4-  3C1 

Perchloride  of 
phosphorus 

| 

177-1 

5  eq. 

4-  Ditto 

31-4 

2eq 

.=  20852P4-5C1 

Chlorocarbonic 
acid  gas  .     . 

\ 

35-42 

1 

eq. 

-|-Carb.  ox. 

14-12 

leq 

,=  49-54  CO  4-  Cl 

Terchloride  of 
boron  .     .     . 

\ 

106-26 

3 

eq.-{-  Boron 

10-9 

leq 

.—  117-16  B  +  3C1 

Terchloride  of 
silicon    .      . 

j 

106-26 

3 

eq.  -J-  Silicon 

22-5 

1  eq 

,=  128-76  Si  4-  3C1 

Hydrochloric  Acid. — Hist,  and  Prep. — A  concentrated  aqueous  solution 
of  this  acid  has  been  long  known  under  the  names  of  spirit  of  salt,  and  of 
marine  or  muriatic  acid  ;  but  in  its  purer  form  of  gas  it  was  discovered  in 
1772  by  Priestley.  It  may  be  conveniently  prepared  by  putting  an  ounce  of 
strong  hydrochloric  acid  solution  into  a  glass  flask,  and  heating  it  by  means 
of  a  lamp  till  the  liquid  boils,  when  the  gas  is  freely  evolved,  and  may  be 
collected  over  mercury.  Another  method  of  preparing  it  is  by  the  action 
of  concentrated  sulphuric  acid  on  an  equal  weight  of  sea-salt.  Brisk  effer- 
vescence ensues  at  the  moment  of  making  the  mixture,  and  on  the  applica- 
tion of  heat  a  large  quantity  of  hydrochloric  acid  gas  is  disengaged.  In  the 
former  process,  hydrochloric  acid  previously  dissolved  in  water  is  simply 
expelled  from  the  solution  by  heat.  The  explanation  of  the  latter  process  is 
more  complicated.  Sea-salt  was  formerly  supposed  to  be  a  compound  of 
hydrochloric  acid  and  soda ;  and,  on  this  supposition,  the  soda  was  believed 
merely  to  quit  the  hydrochloric  and  unite  with  sulphuric  acid.  But  the  re- 
searches of  Gay-Lussac,  Thenard,  and  Davy  proved  that  it  consists  of  chlo- 
rine and  sodium  combined  in  the  ratio  of  their  equivalents.  The  nature  of 
its  action  with  sulphuric  acid  will  be  understood  by  comparing  the  elements 
concerned  in  the  change  before  and  after  it  has  occurred : — 

Hydrous  Sulp'ric  Acid.    Chloride  of  Sodium.         Sulph.  of  Soda.    Hydrochloric  Acidi 
Real  acid  40-1         Chlorine     35-42      Acid  40-1  Chlorine     35-42 


?°'   g  Sodium      23-3 

or  in  symbols, 
(S-f  3O)-f  (H4-O),  and  Na4-Cl,  yield  (Na -f- O)  4.  (S  4. 3O),  and  H4-C1. 


*  Oxychloric  would  be  a  more  appropriate  appellation  for  this  acid,  as  its 
adoption  would  prevent  all  ambiguity  in  naming  its  salts.  This  name  I  pro- 
posed for  it  in  1819,  in  my  System  of  Chemistry  for  Students  of  Medicine  ; 
and  it  may  be  inferred  that  it  has  the  sanction  of  Berzelius,  as  he  employs 
it  in  his  Traite  de  Chimie. — Ed, 


CHLORINE.  215 

Thus  it  appears  that  single  equivalents  of  water,  sulphuric  acid,  and  chlo- 
ride of  sodium,  yield  sulphate  of  soda  and  hydrochloric  acid.  The  water  of 
the  sulphuric  acid  is  essential;  so  much  so,  indeed,  that  chloride  of  sodium 
is  not  decomposed  at  all  by  anhydrous  sulphuric  acid. 

Hydrochloric  acid  may  be  generated  by  the  direct  union  of  its  elements. 
When  equal  measures  of  chlorine  and  hydrogen  are  mixed  together,  and  an 
electric  spark  is  passed  through  the  mixture,  instantaneous  combination 
takes  place,  heat  and  light  are  emitted,  and  hydrochloric  acid  is  generated. 
A  similar  effect  is  produced  by  flame,  by  a  red-hot  body,  and  by  spongy  pla- 
tinum. Light  also  causes  them  to  unite.  A  mixture  of  the  two  gases  may 
be  preserved  without  change  in  a  dark  place ;  but  if  exposed  to  the  diffused 
light  of  day,  gradual  combination  ensues,  which  is  completed  in  the  course 
of  24  hours.  The  direct  solar  rays  produce,  like  flame  and  electricity,  sud- 
den inflammation  of  the  whole  mixture,  accompanied  with  explosion  ;  and, 
according  to  Brande,  the  vivid  light  emitted  by  charcoal  intensely  heated  by 
galvanic  electricity  acts  in  a  similar  manner. 

This  acid  is  most  commonly  used  in  the  form  of  a  concentrated  aqueous 
solution,  which  is  made  by  transmitting  a  current  of  the  gas  into  water  as 
long  as  any  of  it  is  absorbed.  All  the  Pharmacopoeias  give  directions  for 
conducting  the  process.  That  adopted  by  the  Edinburgh  College  is  prac- 
tically good.  The  proportions  they  recommend  are  equal  weights  of  sea- 
salt,  water,  and  sulphuric  acid  ;  more  acid  being  purposely  employed  than  is 
sufficient  to  form  a  neutral  sulphate  with  the  soda,  so  that  the  more  perfect 
decomposition  of  the  sea-salt  may  be  insured.  The  acid,  to  prevent  too  vio- 
lent effervescence  at  first,  is  mixed  with  one-third  of  the  water  ;  and  when 
the  mixture  has  cooled,  it  is  poured  upon  the  salt  previously  introduced  into 
a  glass  retort.  The  distillation  is  continued  to  dryness  ;  and  the  gas,  as  it 
escapes,  is  conducted  into  the  remainder  of  the  water.  The  theory  of  the 
process  has  been  already  explained.  The  residue  is  a  mixture  of  sulphate 
and  bisulphate  of  soda.  The  sp.  gr.  of  the  acid  solution  obtained  by  this 
process  is  1'17. 

Prop. — It  is  a  colourless  gas,  has  a  pungent  odour  and  an  acid  taste. 
Under  a  pressure  of  40  atmospheres,  and  at  ih&  temperature  of  50°,  it  is 
liquid.  Sp.  gr.  1-2694.  It  is  quite  irrespirable,  exciting  violent  spasm  of 
the  glottis ;  but  when  diluted  with  air,  it  is  far  less  irritating  than  chlorine. 
All  burning  bodies  are  extinguished  by  it,  nor  is  the  gas  itself  inflammable. 

It  is  not  chemically  changed  by  mere  heat.  It  is  readily  decomposed  by 
galvanism,  hydrogen  appearing  at  the  negative,  and  chlorine  at  the  positive 
pole.  It  is  also  decomposed  by  ordinary  electricity.  The  decomposition, 
however,  is  incomplete ;  for  though  one  electric  spark  resolves  a  portion  of 
the  gas  into  its  elements,  the  next  shock  in  a  great  measure  effects  their  re- 
union. It  is  not  affected  by  oxygen  under  common  circumstances;  but  if  a 
mixture  of  oxygen  and  hydrochloric  acid  gases  is  electrified,  the  oxygen 
unites  with  the  hydrogen  of  the  acid  to  form  water,  and  chlorine  is  set  at 
liberty.  For  this  and  the  preceding  fact  we  are  indebted  to  the  researches 
of  Henry. 

One  of  the  most  striking  properties  of  hydrochloric  acid  gas  is  its  pow- 
erful attraction  for  water.  A  dense  white  cloud  appears  whenever  it  escapes 
into  the  air,  owing  to  its  combining  with  the  aqueous  vapour  of  the  atmos- 
phere. A  piece  of  ice  put  into  a  jar  full  of  the  gas  confined  over  mercury 
liquefies  on  the  instant,  and  the  whole  of  the  gas  disappears  in  the  course  of 
a  few  seconds.  On  opening  a  long  wide  jar  of  hydrochloric  acid  gas  under 
water,  the  absorption  of  the  gas  takes  place  so  instantaneously,  that  the 
water  is  forced  up  into  the  jar  with  the  same  violence  as  into  a  vacuum. 
Considerable  increase  of  temperature  takes  place  during  the  absorption,  and 
therefore  the  apparatus  should  be  kept  cool  by  ice.  Davy  states  (Elements, 
p.  252)  that  water  at  the  temperature  of  40°  absorbs  480  times  its  volume  of 
the  gas,  and  that  the  solution  has  a  sp.gr.  of  1-2109.  Thomson  finds  that 
one  cubic  inch  of  water  at  69°  absorbs  418  cubic  inches  of  gas,  and  occu- 
pies the  space  of  1-34  cubic  inch.  The  solution  has  a  sp.  gr.  of  M958,  and 


216 


one  cubic  inch  of  it  contains  311-04  cubic  inches  of  hydrochloric  acid  gas, 
The  quantity  of  real  acid  contained  in  solutions  of  different  densities  may 
be  determined  by  ascertaining  the  quantity  of  pure  marble  dissolved  by  a 
given  weight  of  each.  Every  50-6  grains  of  marble  correspond  to  36-42  of 
real  acid.  The  following  table  from  Thomson's  "Principles  of  Chemistry," 
is  constructed  according  to  this  rule.  The  first  and  second  columns  show  the 
atomic  constitution  of  each  acid. 

Table  exhibiting  the  Specific  Gravity  of  Muriatic  Acid  of  determinate 
Strengths. 


Atoms  of 
Acid. 

Atoms  of 
Water. 

Real  Acidin 
100  of  the 
liquid. 

Specific 
Gravity. 

Atoms 
ofAcid. 

Atoms  of 
Water. 

Real  acid  in 
100  of  the 
liquid. 

Specific. 
Gravity. 

1 

6 

40-659 

1-203 

1 

14 

22-700 

1-1060 

1 

7 

37-000 

•179 

1 

15 

21-512 

1-1008 

1 

8 

33-945 

1-162 

1 

16 

20-442 

1-0960 

1 

9 

31-346 

•149 

1 

17 

19-474 

1-0902 

1 

10 

2.9134 

•139 

1 

18 

18-590 

1-0860 

1 

11 

27-206 

•1285 

1 

19 

.    17-790 

1-0820 

1 

12 

25-517 

1-1197 

1 

20 

17-051 

1-0780 

1 

13 

24-026 

1-1127 

Hydrochloric  acid  of  commerce  has  a  yellow  colour,  and  is  always  impure. 
Its  usual  impurities  are  nitric  acid,  sulphuric  acid,  and  oxide  of  iron.  The 
presence  of  nitric  acid  may  be  inferred  if  the  hydrochloric  acid  has  the  pro- 
perty of  dissolving  gold  leaf.  Iron  may  be  detected  by  ferrocyanuret  of 
potassium,  and  sulphuric  acid  by  chloride  of  barium,  the  suspected  hydro- 
chloric acid  being  previously  diluted  with  three  or  four  parts  of  water.  The 
presence  of  nitric  acid  is  provided  against  by  igniting  the  sea-salt,  as  recom- 
mended by  the  Edinburgh  College,  in  order  to  decompose  any  nitre  which  it 
may  contain.  The  other  impurities  may  be  avoided  by  employing  VVoulfe's 
Apparatus.  A  few  drachms  of  water  are  put  into  the  first  bottle  to  retain 
the  chloride  of  iron  and  sulphuric  acid  which  pass  over,  and  the  hydro- 
chloric acid  gas  is  condensed  in  the  second. 

A  strong  solution  of  pure  hydrochloric  acid  is  a  colourless  liquid,  which 
emits  white  vapours  when  exposed  to  the  air,  is  intensely  sour,  reddens 
litmus  paper  strongly,  and  neutralizes  alkalies.  It  combines  with  water  in 
every  proportion,  and  causes  increase  of  temperature  when  mixed  with  it, 
though  in  a  much  less  degree  than  sulphuric  acid.  It  freezes  at  60°  F.;  and 
boils  at  110°,  or  a  little  higher,  giving  off  pure  hydrochloric  acid  gas  in 
large  quantity. 

Hydrochloric  acid  is  decomposed  by  substances  which  yield  oxygen 
readily.  Thus  several  peroxides,  such  as  those  of  manganese,  cobalt,  and 
lead,  effect  its  decomposition.  Chloric,  iodic,  bromic,  nitric,  and  selenic 
acids  act  on  the  same  principle.  A  mixture  of  nitric  and  hydrochloric  acids, 
in  the  ratio  of  one  measure  of  the  former  to  two  of  the  latter,  has  long  been 
known  under  the  name  of  aqua  regia,  as  a  solvent  for  gold  and  platinum. 
When  these  acids  are  mixed  together,  the  solution  instantly  becomes  yellow  ; 
and  on  heating  the  mixture,  pure  chlorine  is  evolved,  and  the  colour  of  the 
solution  deepens.  On  continuing  the  heat,  chlorine  and  nitrous  acid  vapours 
are  disengaged.  At  length  the  evolution  of  chlorine  ceases,  and  the  residual 
liquid  is  found  to  be  a  solution  of  hydrochloric  and  nitrous  acids,  which  is 
incapable  of  dissolving  gold.  The  explanation  of  these  facts  is,  that  nitric 
and  hydrochloric  acids  decompose  one  another,  giving  rise  to  the  production 
of  water  and  nitrous  acid,  and  the  separation  of  chlorine;  while  hydro- 
chloric and  nitrous  acids  may  be  heated  together  without  mutual  decompo- 
sition. It  is  hence  inferred  that  the  power  of  nitro-hydrochloric  acid  in 


CtiLORINE.  217 

dissolving  gold  is  owing  to  the  chlorine  which  is  liberated.     (Davy  in  the 
Quarterly  Journal,  vol.  i.) 

Hydrochloric  acid  is  distinguished  by  its  odour,  volatility,  and  strong  acid 
properties.  With  nitrate  of  oxide  of  silver  it  yields  the  same  precipitate  as 
chlorine  ;  but  no  chloric  acid  is  generated,  because  the  oxygen  of  the  oxide 
of  silver  unites  with  the  hydrogen  of  the  hydrochloric  acid,  and  the  chlorine 
in  consequence  is  entirely  precipitated.  Notwithstanding  that  nitrate  of  oxide 
of  silver  yields  the  same  precipitate  with  chlorine  and  hydrochloric  acid, 
there  is  no  difficulty  in  distinguishing  between  them ;  for  the  bleaching  pro- 
perty of  the  former  is  a  sure  ground  of  distinction. 

The  composition  of  hydrochloric  acid  has  been  determined  by  Davy,  and 
Gay-Lussac  and  Thenard.  Their  experiments  concur  in  proving  that  chlorine 
and  hydrogen  unite  in  equal  volumes,  and  that  the  hydrochloric  acid,  which 
is  the  sole  and  constant  product,  occupies  the  same  space  as  the  gases  from 
which  it  is  formed.  From  these  facts  the  composition  of  hydrochloric  acid 
is  easily  inferred.  For,  as 

Grains. 

50     cubic  inches  of  chlorine  weigh         '.    - •'-".,;'  "  ••  , /„    .        38-2994 
50       "  "  hydrogen          .        > ."     ,  •'"'...*"•'.'*";•      1-0683 

100     cubic  inches  of  hydrochloric  acid  gas  must  weigh    .        39-3677 

These  numbers  are  in  the  ratio  of  1  to  35-42,  being  that  of  single  eq.  of 
hydrogen  and  chlorine.  Hence  its  eq.  is  36*42 ;  eq.  vol.  =  200 ;  symb. 
H+C1,  or  HC1. 

COMPOUNDS  OF  CHLORINE  AND  OXYGEN. 

The  leading  character  of  these  compounds  is  derived  from  the  circum- 
stance that  chlorine  and  oxygen,  the  attraction  of  which  for  most  element- 
ary substances  i$  so  energetic,  have  but  a  feeble  affinity  for  each  other. 
These  principles,  consequently,  are  never  met  with  in  nature  in  a  state  of 
combination.  Indeed,  they  cannot  be  made  to  combine  directly  ;  and  when 
they  do  unite,  very  slight  causes  effect  their  separation.  Chemists  have  long1 
been  doubtful  as  to  the  exact  number  of  the  compounds  of  chlorine  and 
oxygen.  The  recent  labours  of  Balard  and  Martens  have  established  the 
existence  of  four,  all  of  which  they  have  shown  to  possess  acid  properties. 
Their  names  and  constitutions  are  given  in  the  subjoined  table. 

By  weight.  By  volume. 

Chi.  Oxy.  Chi.  Oxy. 

Hypochlorous  acid        .       35-42  .  .       8  .  2  .  .       1 

Chlorous  acid       .         .       35-42  .  .  32  .  2  .  .      4 

Chloric  acid         .        .       35-42  .  .  40  .  2  .  .      5 

Perchloric  acid     .        .      35-42  .  .  56  .  2  .  .       7 

According  to  the  practice  of  most  British  chemists,  two  volumes  of  chlo- 
rine,  as  also  two  volumes  of  hydrogen  and  of  nitrogen,  are  considered  as 
respectively  corresponding  to  one  equivalent  or  one  atom ;  whereas  one 
volume  of  oxygen  corresponds  to  one  equivalent.  Berzelius,  with  many  Con- 
tinental  chemists,  considering  the  atoms  of  all  elements  to  possess  the  same 
volume,  regards  the  four  preceding  compounds  as  composed  of  two  atoms  or 
two  eq.  of  chlorine,  combined  with  one,  four,  five,  and  seven  atoms  or  eq.  of 
oxygen. 

Hypochlorous  Acid. — Hist,  and  Prep. — Davy  in  1811  discovered  a  gaseous 
compound,  which  was  described  by  him  in  the  Philosophical  Transactions  of 
the  same  year  under  the  name  of  euchlorine.  This  gas,  which  until  recently 
has  been  considered  to  be  the  protoxide  of  chlorine,  is  made  by  the  action  of 
hydrochloric  acid  on  the  chlorate  of  potassa;  and  its  production  is  explicable 
by  the  fact,  that  hydrochloric  and  chloric  acids  mutually  decompose  each 

19 


218  CHLORINE. 

other.  When  hydrochloric  acid  and  chlorate  of  potassa  are  mixed  together^ 
more  or  less  of  the  potassa  is  separated  by  the  hydrochloric  from  the  chloric 
acid,  and  the  latter  being  set  at  liberty,  reacts  on  free  hydrochloric  acid.  The 
result  depends  upon  the  relative  quantities  of  the  materials.  If  hydrochloric 
acid  be  in  excess,  the  chloric  acid  undergoes  complete  decomposition.  For 
each  eq.  of  chloric  acid,  five  eq,  of  hydrochloric  acid  are  decomposed :  the 
five  eq.  of  oxygen,  contained  in  the  former,  unite  with  the  hydrogen  of  the 
latter,  producing  five  eq.  of  water ;  while  the  chlorine  of  both  acids  is  dis- 
engaged. If,  on  the  contrary,  chlorate  of  potassa  be  in  excess,  the  chloric 
acid  is  deprived  of  part  of  its  oxygen  only ;  the  products  are  water  and  the 
euchlorine  of  Davy.  The  chloric  and  hydrochloric  acids  react  on  each  other 
in  the  ratio  of  one  eq.  to  two,  or,  what  is  the  same  thing,  in  that  of  four  eq. 
to  eight  eq. ;  thus 

4  (Cl+50)  8  (H+0) 

and  8  (H+C1)  12  (Cl+O) 

The  gas  thus  obtained,  though  containing  chlorine  and  oxygen  in  the  ratio 
of  atom  to  atom,  is  not,  as  was  supposed  by  Davy,  a  distinct  compound,  but  is 
a  mixture  of  chlorine  and  chlorous  acid.  For  this  fact,  which  has  long  been 
suspected,  we  are  indebted  to  the  researches  of  Soubeiran.  On  transmitting 
a  stream  of  euchlorine  through  a  tube  nearly  full  of  calomel,  the  free  chlo- 
rine is  readily  absorbed;  on  subsequently  exploding  the  purified  gas,  he 
obtained  one  volume  of  chlorine  to  two  volumes  of  oxygen,  being  the  exact 
composition  of  chlorous  acid.  The  product  of  the  last  decomposition  is, 
therefore,  3  (01+40)  and  9  Cl,  and  not  12  (Cl-fO).  The  experiments  of 
Soubeiran  have  been  confirmed  by  the  discoveries  of  Balard. 

If  a  stream  of  chlorine  gas  be  passed  into  a  solution  of  the  pure  alkalies, 
or  be  allowed  to  act  upon  the  alkaline  earths  in  the  form  of  hydrates,  a 
bleaching  substance  is  procured  which  has  been  commonly  viewed  as  a 
direct  compound  of  chlorine  and  an  alkaline  base.  It  consists,  however, 
according  to  Balard,  of  a  mixture  of  a  metallic  chloride,  and  the  hypochlo- 
rite  of  the  alkali  employed.  (An.  de  Ch.  et  de  Ph.  Ivii.  225).  The  process 
recommended  for  obtaining  the  pure  acid  is  to  pour  into  bottles  filled  with 
chlorine  gas,  peroxide  of  mercury  in  fine  powder,  and  mixed  with  twice  its 
weight  of  distilled  water :  by  brisk  agitation  the  chlorine  is  rapidly  and 
completely  absorbed,  if  a  slight  excess  of  the  peroxide  be  used.  By  this  pro- 
cess one  portion  of  the  peroxide  of  mercury,  HgO2,  is  decomposed,  both  its 
constituents  combining  with  chlorine  ;  the  mercury  forming  corrosive  subli- 
mate, HgCl2,  and  the  oxygen  hypochlorous  acid.  The  latter  remains  in 
solution  in  the  water  ;  while  the  former,  by  combining  with  undecomposed 
peroxide  of  mercury,  forms  the  sparingly  soluble  oxychloride  of  mercury, 
which  is  separated  by  filtration.  The  hypochlorous  acid  being  volatile,  is 
obtained  in  a  pure  but  diluted  state  by  distillation.  The  temperature  which 
is  used  for  this  purpose  should  be  kept  considerably  below  212°  ;  as  the 
hypochlorous  acid  decomposes  rapidly  at  that  heat.  The  process  is,  there- 
fore, best  performed  under  reduced  pressure.  A  more  concentrated  solution 
of  the  acid  is  obtained  by  submitting  the  first  products  to  a  second  distil- 
lation. 

Prop. — As  thus  obtained,  hypochlorous  acid  is  a  transparent  liquid  of  a 
slightly  yellow  colour  when  concentrated.  Its  odour  is  strong  and  penetra- 
ting, and  different  though  somewhat  similar  to  that  of  chlorine.  Its  action  on 
the  skin  is  exceedingly  active,  the  effect  being  similar  to  but  greater  than 
that  produced  by  nitric  acid.  It  is  a  highly  bleaching  compound.  In  a 
concentrated  state  it  is  very  unstable,  a  slow  decomposition  taking  place  at 
common  temperatures,  by  which  chlorine  is  evolved  and  chloric  acid  pro- 
duced. This  change  is  promoted  by  light,  and  is  effected  almost  instantly 
by  exposure  for  a  few  moments  to  the  direct  rays  of  the  sun.  It  is  also 
decomposed  by  agitation  with  angular  bodies ;  and  on  throwing  into  the 
acid  a  portion  of  pounded  glass,  a  brisk  effervescence  is  observed  from  the 
escape  of  chlorine. 


CHLORINE.  219 

It  is  one  of  the  most  powerful  oxidizing  agents.  Its  action  in  this  re- 
spect, however,  is  various,  and  is  principally  observed  in  relation  to  the 
simple  non-metallic  elements.  Thus  sulphur  and  phosphorus  are  readily 
brought  to  their  highest  state  of  oxidation,  and  even  selenium  is  converted 
into  selenic  acid,  an  effect  which  nitric  acid  cannot  accomplish.  Iodine  and 
bromine  are  also  instantly  changed  into  iodic  and  bromic  acids.  Its  action 
on  the  more  perfect  metals,  on  the  contrary,  is  slight:  iron  and  silver,  how- 
ever, are  remarkable  exceptions  to  this  rule;  for  when  either  of  them  is 
brought,  in  a  finely  divided  state,  in  contact  with  hypochlorous  acid,  the 
latter  suffers  instantaneous  decomposition.  When  irafe  is  used,  it  is  oxidized 
at  the  expense  of  the  acid,  and  chlorine  is  evolved  ;  with  silver  the  oxygen 
escapes,  and  the  chlorine  unites  exclusively  with  the  metal.  The  decompo- 
sition of  hypochlorous  acid  may  also  be  produced  by  metallic  mercury,  but 
the  decomposition  is  unattended  by  the  evolution  of  eithef  gas.  Both  the 
chloride  and  oxide  of  mercury  are  produced,  and  instantly  unite  to  form  the 
oxychloride. 

Balard  has  also  succeeded  in  obtaining  hypochlorous  acid  in  the  gaseous 
form.  A  small  quantity  of  a  concentrated  solution  is  introduced  into  a  bell 
jar  over  mercury,  and  fragments  of  dry  nitrate  of  lime  are  successively  added. 
The  nitrate  of  lime  being  highly  deliquescent,  unites  with  the  water,  and  the 
acid  gas  escapes  with  effervescence :  the  presence  of  the  saline  solution  is 
essential,  as  it  prevents  the  decomposition  of  the  gas  by  the  mercury.  The 
gas  is  of  a  yellowish-green  colour,  and  is  very  similar  to  chlorine  in  appear- 
ance. It  unites  rapidly  with  water,  which  absorbs  at  least  100  times  its  own 
volume  of  the  gas.  It  detonates  by  a  slight  increase  of  temperature ;  and 
though  less  explosive  than  the  chlorous  acid,  there  is  a  probability  of  an  ac- 
cident in  transferring  it  from  one  vessel  to  another.  The  results  of  explosion 
are  oxygen  and  chlorine  ;  and  Balard  found  that  100  measures  produced  100 
of  chlorine  and  50  of  oxygen.  From  these  data  its  sp.  gr.  is  3*0212;  its  eq. 
4342 ;  eq,  vol.  =  100 ;  symb.  Cl+O,  Cl,  or  CIO. 

Chlorous  Acid. — Hist,  and  Prep. — This  compound  was  discovered  by 
Davy  in  1815  (Phil.  Trans.),  and  soon  after  by  Count  Stadion  of  Vienna.  It 
is  formed  by  the  action  of  sulphuric  acid  on  chlorate  of  potassa.  A  quantity 
of  this  salt  not  exceeding  50  or  60  grains  is  reduced  to  powder,  and  made 
into  a  paste  by  the  addition  of  strong  sulphuric  acid.  The  mixture,  which 
acquires  a  deep  yellow  cologr,  is  placed  in  a  glass  retort,  and  heated  by  warm 
water,  the  temperature  of  which  is  kept  under  212°.  A  bright  yellowish- 
green  gas  of  a  richer  colour  than  chlorine  is  disengaged,  which  has  an  aro- 
matic odour  without  any  smell  of  chlorine,  is  absorbed  rapidly  by  water,  to 
which  it  communicates  its  tint.  This  gas,  which  has  long  been  described  as 
the  peroxide  of  chlorine,  must  now  be  called  chlorous  acid,  as  it  has  been 
shown  to  possess  acid  properties,  and  to  form  definite  compounds  with  the 
alkaline  bases. 

The  chemical  changes  which  take  place  in  the  process  are  explained  in 
the  following  manner.  The  sulphuric  acid  decomposes  some  of  the  chlorate 
of  potassa,  and  sets  chloric  acid  at  liberty.  The  chloric  acid,  at  the  moment 
of  separation,  resolves  itself  into  chlorous  acid  and  oxygen  ;  the  last  of  which, 
instead  of  escaping  as  free  oxygen  gas,  goes  over  to  the  acid  of  some  unde- 
eomposed  chlorate  of  potassa,  and  converts  it  into  perchloric  acid.  The  pro- 
ducts are  bisulphate  and  perchlorate  of  potassa,  and  chlorous  acid.  It  is  most 
probable,  from  the  data  contained  in  the  preceding  table',  that  every  three  eq. 
of  chloric  acid  yield  one  eq.  of  perchloric  acid  and  two  eq.  of  chlorous  acid. 

Prop. — Chlorous  acid  unites  readily  with  the  alkalies  and  alkaline  earths, 
forming  salts  which  are  more  stable  than  those  of  the  hypochlorous  acid. 
They  are  produced  by  transmitting  the  gas  into  the  alkaline  solutions,  which 
may  thus  be  rendered  perfectly  neutral.  (Martens,  An.  de  Ch.  et  de  Ph.  Ixi. 
293).  All  the  salts  hitherto  examined  are  soluble  in  water,  and  are  possessed, 
like  the  acid  itself,  of  bleaching  properties.  The  neutral  salts  pass  readily  into 
a  metallic  chloride,  and  chlorate  of  the  base,  particularly  such  as  the  chlorite 


220  CHLORINE, 

of  potassa,  which  forms  a  sparingly  soluble  chlorate.  This  change  does  not 
so  readily  ensue  when  the  alkali  is  in  excess.  The  proportion  in  which  the 
chloride  and  chlorate  are  produced  indicate  that  six  cq.  of  chlorite  are  decom- 
posed, by  which  one  eq.  of  metallic  chloride  and  five  eq.  of  chlorate  are  pro- 
duced :  thus  6(KO,  CIO*)  yield  KC1  and  5(KO,  CK>).  The  solution  of  the 
pure  acid  gradually  yields  chloric  acid  and  chlorine.  It  is  a  powerful  oxi- 
dizing agent,  and  in  this  respect  is  very  similar  to  the  hypochlorous  acid.  It 
causes  a  precipitate  with  nitrate  of  silver  ;  but  it  is  best  recognized  by  the 
evolution  of  chlorous  acid  gas  on  the  addition  of  an  acid  to  its  salts. 

Phosphorus  takes  fire  when  introduced  into  the  gas,  and  occasions  an  ex- 
plosion. It  explodes  violently  when  heated  to  a  temperature  of  212°,  emits 
a  strong  light,  and  undergoes  a  greater  expansion  than  hypochlorous  acid. 
According  to  Davy,  whose  result  is  confirmed  by  Gay-Lussac,  40  measures 
of  the  gas  occupy  after  explosion  the  space  of  60  measures;  and  of  these,  20 
are  chlorine  and  40  oxygen.  Chlorous  acid  is,  therefore,  composed  of  35-42 
parts,  or  one  eq.  of  chlorine,  united  with  32  or  four  eq.  of  oxygen ;  and  its 
sp.  gr.  must  be  2-3374. 

Its  eq.  is  67-42  ;  eq.  vol.  =  200  ;   symb.  C1-J-4O,  Cl,  or  CKK 

Chloric  Acid. — Prep. — If  a  current  of  chlorine  gas  be  transmitted  into  a 
strong  solution  of  pure  potassa,  a  portion  of  the  alkali  is  decomposed,  and 
chloride  of  potassium  and  hypochlorite  of  potassa  are  generated.  On  bring- 
ing the  solution  to  the  boiling  point,  the  latter  salt  is  decomposed.  The 
changes  which  occur  are  complicated,  and  give  rise  to  the  evolution  of  oxy- 
gen, and  the  formation  of  chlorate  of  potassa  and  chloride  of  potassium.  Ac- 
cording to  the  experiments  of  Morin  and  Soubeiran,  which  accord  entirely 
with  the  observations  of  Balard,  nine  eq.  of  hypochlorite  of  potassa  produce 
one  eq.  of  chlorate  of  potassa,  eight  eq.  of  chloride  of  potassium,  and  twelve 
eq.  of  oxygen:  or  thus, 

9(KO-|-C1O)  yield  (KO  +  CIO*),  8KC1,  and  12O. 
Hence  for  every  eq.  of  chlorate,  eight  eq.  of  chloride  are  formed. 

When  to  a  dilute  solution  of  chlorate  of  baryta,  a  quantity  of  weak  sul- 
phuric acid,  exactly  sufficient  for  combining  with  the  baryta,  is  added,  the 
insoluble  sulphate  of  baryta  subsides,  and  pure  chloric  acid  remains  in  the 
liquid.  This  acid,  the  existence  of  which  was  originally  observed  by  Mr. 
Chenevix,  was  first  obtained  in  a  separate  state  by  Gay-Lussac. 

Prop. — Chloric  acid  reddens  vegetable  blue  colours,  has  a  sour  taste,  and 
forms  neutral  salts,  called  chlvrates>  (formerly  hy per  oxy  muriates},  with  alka- 
line bases.  It  possesses  no  bleaching  properties,  a  circumstance  by  which 
it  is  distinguished  from  chlorine,  hypochlorous,  and  chlorous  acids.  It  gives 
no  precipitate  in  solution  of  nitrate  of  oxide  of  silver,  and  hence  cannot  be 
mistaken  for  hydrochloric  acid.  Its  solution  may  be  concentrated  by  gentle 
heat  till  it  acquires  an  oily  consistence  without  decomposition  :  in  this  state 
of  highest  concentration  it  acquires  a  yellowish  tint,  emits  an  odour  of  nitric 
acid,  sets  fire  to  paper  and  other  dry  organic  matter,  and  converts  alcohol  into 
acetic  acid.  When  sharply  heated  in  a  retort,  part  of  the  acid  is  resolved 
into  chlorine  and  oxygen  ;  but  another  portion,  acquiring  oxygen  from  that 
which  is  decomposed,  is  converted  into  perchloric  acid,  and  then  passes  over 
into  the  receiver  in  the  form  of  a  dense  colourless  liquid.  (Serullas).  Chloric 
acid  is  easily  decomposed  by  deoxidizing  agents.  Sulphurous  acid,  for  in- 
stance, deprives  it  of  oxygen,  with  formation  of  sulphuric  acid  and  evolution 
of  chlorine.  By  the  action  of  hydrosulphuric  acid,  water  is  generated,  while 
sulphur  and  chlorine  are  set  free.  The  power  of  hydrochloric  acid  in  effect- 
ing its  decomposition  has  already  been  explained. 

Chloric  acid  is  readily  known  by  forming  a  salt  with  potassa,  which 
crystallizes  in  tables  and  has  a  pearly  lustre,  deflagrates  like  nitre  when 
flung  on  burning  charcoal,  and  yields  chlorous  acid  by  the  action  of  con- 
centrated sulphuric  acid.  Chlorate  of  potassa,  like  most  of  the  chlorates, 
gives  off  pure  oxygen  when  heated  to  redness,  and  leaves  a  residue  of  chloride 


CHLORINE.  291 

of  potassium.     By  this  mode  Gay-Lussac  ascertained  the  composition  of 
chloric  acid,  as  stated  in  the  preceding  table.     (An.  de  Chimie,  xci.) 


Its  eq.  is  75-42  ;  symb.  C1  +  5O,  Cl,  or 

Perchloric  Acid.  —  The  saline  matter  which  remains  in  the  retort  after 
forming-  chlorous  acid,  is  a  mixture  of  perchlorate  and  hisulphate  of  potass^  : 
and  by  washing-  it  with  cold  water,  the  bisulphate  is  dissolved,  and  the  per- 
chlorate is  left.  Perchloric  acid  may  be  prepared  from  this  salt  by  mixing 
it  in  a  retort  with  half  its  weight  of  sulphuric  acid,  diluted  with  one-third  of 
water,  and  applying  heat  to  the  mixture.  At  the  temperature  of  about  284° 
white  vapours  rise,  which  condense  as  a  colourless  liquid  in  the  receiver. 
This  is  a  solution  of  perchloric  acid. 

The  existence  of  perchloric  acid  was  first  ascertained  by  Count  Stadion, 
who  found  it  to  be  a  compound  of  one  eq.  of  chlorine  and  seven  of  oxygen; 
and  this  view  of  its  constitution  has  been  confirmed  by  Gay-Lussac,  Serullas, 
and  Mitscherlich.  (An.  de  Ch.  et  de  Ph.  viii.  ix.  xlvi.  297,  and  xlix.  113.) 
According  to  Serullas,  it  is  a  very  stable  compound  :  it  may  be  heated  with 
hydrochloric  or  sulphuric  acid  without  change,  does  not  set  fire  to  organic 
substances,  and  is  not  decomposed  by  alcohol.  When  concentrated  it  has  a 
density  of  1x65,  in  which  state  it  emits  vapour  when  exposed  to  the  air,  ab- 
sorbs hygrometric  moisture  powerfully,  and  boils  at  392°.  By  admixture 
with  strong  sulphuric  acid  and  distilling,  Serullas  obtained  it  in  the  solid 
form,  both  massive  and  in  elongated  prisms.  It  hisses  when  thrown  into 
water,  like  red-hot  iron  when  quenched. 

Of  all  the  salts  of  perchloric  acid,  that  with  potassa  is  the  most  insoluble, 
requiring  65  times  its  weight  of  water  at  60°  for  solution.  This  salt  is 
readily  and  safely  formed  by  adding  chlorate  of  potassa,  well  dried  and  in 
fine  powder,  in  small  portions  at  a  time,  to  an  equal  weight  of  concentrated 
sulphuric  acid,  gently  warmed  in  an  open  vessel.  The  chlorous  acid  gas 
escapes  without  danger,  and  the  chlorate  is  entirely  converted  into  perchlo- 
rate and  bisulphate  of  potassa,  the  latter  of  which,  being  very  soluble,  is 
easily  removed  by  cold  water.  Serullus  finds  that  chlorate  of  potassa,  when 
decomposed  by  a  low  heat,  is  converted  into  chloride  of  potassium  and  per- 
chlorate of  potassa;  but  the  temperature  must  be  carefully  managed,  other- 
wise the  perchlorate  itself  would  be  resolved  into  oxygen  and  chloride  of 
potassium.  The  perchlorate  thus  procured  is  purified  by  solution  in  hot 
water  and  crystallization.  It  is  distinguished  from  chlorate  of  potassa  by 
not  acquiring  a  yellow  tint  on  the  addition  of  hydrochloric  acid.  The  pri- 
mary form  of  its  crystals,  according  to  Mitscherlich,  is  a  right  rhomboidal 
prism,  isomorphous  with  permanganate  of  potassa* 

Its  eq.  is  91-42;  symb.  Cl-f  7O,  ci,'or  C1O7. 

Quadrochloride  of  Nitrogen.  —  Hist,  ajyi  Prep.  —  This  compound  was  dis- 
covered by  Dulong  in  1811.  Its  elements  have  a  feeble  mutual  affinity,  and 
do  not  unite  when  presented  to  each  other  in  their  gaseous  form.  The  con- 
dition which  leads  to  their  union  is  the  decomposition  of  ammonia  by  chlo- 
rine, during  which  hydrochloric  acid  is  generated  by  chlorine  combining- 
with  the  hydrogen  of  ammonia;  while  the  nitrogen  of  that  alkali,  in  its 
nascent  state,  enters  into  combination  with  another  portion  of  chlorine.  A 
convenient  mode  of  preparing  the  quadrochloride  of  nitrogen  is  the  follow- 
ing :  —  An  ounce  of  hydrochlorate  of  ammonia  is  dissolved  in  12  or  16  ounce* 
of  hot  water  ;  and  when  the  solution  has  cooled  to  the  temperature  of  90°,. 
a  glass  bottle  with  a  wide  mouth,  full  of  chlorine,  is  inverted  in  it.  The  so- 
lution gradually  absorbs  the  chlorine,  and  acquires  a  yellow  colour  ;  and  in 
about  20  minutes,,  globules  of  a  yellow  fluid  are  seen  floating  like  oil  upon 
its  surface,  which,  after  acquiring  the  size  of  a  small  pea,  sink  to  the  bottom 
of  the  liquid^  The  drops  of  the  chloride,  as  they  descend,  should  be  col- 
lected in  a  small  saueer  of  lead,  placed  for  that  purpose  under  the  mouth  of 
the  bottle.  It  is  also  readily  obtained  by  suspending  a  fragment  of  sal  am* 
moniac  in  a  solution  of  hypochlorons  acid. 

19  * 


222  CHLORINE. 

Prop. — It  is  one  of  the  most  explosive  compounds  yet  known,  having 
been  the  cause  of  serious  accidents  both  to  its  discoverer  and  to  Davy. 
(Phil.  Trans.  1813 ;  An.  de  Ch.  Ixxxvi.)  Its  specific  gravity  is  1-653.  It 
does  not  congeal  in  the  intense  cold  produced  by  a  mixture  of  snow  and 
salt.  It  may  be  distilled  at  160°  ;  but  at  a  temperature  between  200°  and 
212°  it  explodes.  It  appears  from  the  investigation  of  Messrs.  Porrett, 
Wilson,  and  Kirk,  that  its  mere  contact  with  some  substances  of  a  combus- 
tible nature  causes  detonation  even  at  common  temperatures.  This  result 
ensues  particularly  with  oils,  both  volatile  and  fixed.  I  have  never  known 
olive  oil  fail  in  producing  the  effect.  The  products  of  the  explosion  are 
chlorine  and  nitrogen.  (Nicholson's  Journal,  xxxiv.) 

Sir  H.  Davy  analyzed  chloride  of  nitrogen  by  means  of  mercury,  which 
unites  with  chlorine,  and  liberates  the  nitrogen.  He  inferred  from  his  ana- 
lysis that  its  elements  are  united  in  the  proportion  of  four  measures  of  chlo- 
rine to  one  of  nitrogen ;  and  it  hence  follows  that,  by  weight,  it  consists  of 
four  eq.  of  chlorine  and  one  eq.  of  nitrogen.* 

Perchloride  of  Carbon. — Hist,  and  Prep. — The  discovery  of  this  com- 
pound is  due  to  Mr.  Faraday.  When  olefiant  gas  (a  compound  of  carbon 
and  hydrogen)  is  mixed  with  chlorine,  combination  takes  place  between 
them,  and  an  oil-like  liquid  is  generated,  which  consists  of  chlorine,  carbon, 
and  hydrogen.  On  exposing  this  liquid  in  a  vessel  full  of  chlorine  gas  to 
the  direct  solar  rays,  the  chlorine  acts  upon  and  decomposes  the  liquid,  hy- 
drochloric acid  is  set  free,  and  the  carbon,  at  the  moment  of  separation, 
unites  with  the  chlorine.  (Phil.  Trans,  1821.) 

Prop* — -Perchloride  of  carbon  is  solid  at  common  temperatures,  has  an 
aromatic  odour  approaching  to  that  of  camphor,  is  a  non-conductor  of  elec- 
tricity, and  refracts  light  very  powerfully.  Its  sp.  gr.  is  exactly  double  that 
of  water.  It  fuses  at  320°,  and  after  fusion  it  is  colourless  and  very  trans- 
parent. It  boils  at  360°,  and  may  be  distilled  without  change,  assuming  a 
crystalline  arrangement  as  it  condenses.  It  is  sparingly  soluble  in  water, 
but  dissolves  in  alcohol  and  ether,  especially  by  the  aid  of  heat.  It  is  soluble 
also  in  fixed  and  volatile  oils. 

It  burns  with  a  red  light  when  held  in  the  flame  of  a  spirit-lamp,  giving 
out  acid  vapours  and  smoke ;  but  the  combustion  ceases  as  soon  as  it  is 
withdrawn.  It  burns  vividly  in  oxygen  gas.  Alkalies  do  not  act  upon  it ; 
nor  is  it  changed  by  the  stronger  acids,  such  as  the  hydrochloric,  nitric,  or 
sulphuric  acid,  even  with  the  aid  of  heat.  When  its  vapour,  mixed  with 
hydrogen,  is  transmitted  through  a  red-hot  tube,  charcoal  is  separated,  and 
hydrochloric  acid  gas  evolved.  On  passing  its  vapour  over  the  peroxides  of 
metals,  such  as  those  of  mercury  and  copper,  heated  to  redness,  a  chloride  of 
the  metal  and  carbonic  acid  are  generated.  Protoxides,  under  the  same  treat- 
ment, yield  carbonic  oxide  gas  and  metallic  chlorides.  Most  of  the  metals 
decompose  it  also  at  the  temperature  of  ignition,  uniting  with  its  chlorine, 
and  causing  deposition  of  charcoal. 

The  composition  of  the  perchloride  of  carbon  was  inferred  by  Faraday 
from  the  proportions  of  chlorine  and  olefiant  gas  employed  in  its  production, 
and  from  the  quantity  of  chloride  of  eopper  and  carbonic  acid  generated, 
when  its  vapour  was  transmitted  over  oxide  of  copper  at  a  red  heat. 

Its  eq.  is  118-5;  symb.  2C-f-3Cl,  orC2  Cl«. 

Protochloride  of  Carbon. — When  the  vapour  of  the  perchloride  is  passed 
through  a  red-hot  glass  or  porcelain  tube,  filled  with  fragments  of  rock 
crystal  to  increase  the  quantity  of  heated  surface,  partial  decomposition 
occurs,  chlorine  gas  escapes,  and  a  vapour  which,  analyzed  by  Faraday  by 
means  of  oxide  of  copper,  proved  to  be  protochloride  of  carbon.  At  coni- 

*  Berzelius  states  the  composition  of  this  compound  to  be  three  volumes 
of  chlorine  to  one  of  nitrogen,  corresponding  to  three  equivalents  of  the  for- 
mer to  one  of  the  latter.  These  proportions,  if  found  to  be  correct,  will  ren- 
der the  chloride  and  iodide  of  nitrogen  analogous  in  composition.— £^ 


CHLORINE.  223 

mon  temperatures,  it  is  a  limpid  colourless  liquid,  which  has  a  density  of 
1-5526,  does  not  congeal  at  0°,  and  at  160°  or  170°  is  converted  into  vapour. 
It  may  be  distilled  repeatedly  without  change  ;  but  when  exposed  to  a  red 
heat,  some  of  it  is  resolved  into  its  elements.  In  its  chemical  relations  it  is 
very  analogous  to  perchloride  of  carbon. 

Its  eq.  is  41-54 ;  symb.  C-j-CJ,  or  CC1. 

Dichloride  of  Carbon.— 'The  only  sample  of  this  substance  yet  obtained 
was  brought  from  Sweden  by  M.  Julin,  and  is  said  to  have  been  formed 
during  the  distillation  of  nitric  acid  from  crude  nitre  and  sulphate  of  iron. 
It  occurs  in  small,  soft,  adhesive  fibres  of  a  white  colour,  which  have  a  pecu- 
liar odour,  somewhat  resembling  spermaceti.  It  fuses  on  the  application 
of  heat,  and  boils  at  a  temperature  between  350°  and  450°.  At  250°  it 
sublimes  slowly,  and  condenses  again  in  the  form  of  long  needles.  It  is  in- 
soluble in  water,  acids,  arid  alkalies  ;  but  is  dissolved  by  hot  oil  of  turpen- 
tine or  by  alcohol,  and  forms  acicular  crystals  as  the  solution  cools.  It 
burns  with  a  red  flame,  emitting  much  smoke  and  fumes  of  hydrochloric 
acid  gas. 

The  nature  of  this  substance  is  shown  by  the  following  circumstances. 
When  its  vapour  is  exposed  to  a  red  heat,  evolution  of  chlorine  gas  ensuest 
and  charcoal  is  deposited.  A  similar  deposition  of  charcoal  is  produced  by 
heating  it  with  phosphorus,  iron,  or  tin ;  and  a  chloride  is  formed  at  the 
same  time.  Potassium  burns  vividly  in  its  vapour  with  formation  of  chlo- 
ride of  potassium  and  separation  of  charcoal.  On  detonating  a  mixture  of 
its  vapour  with  oxygen  gas  over  mercury,  a  chloride  of  that  metal  and  car- 
bonic acid  are  generated.  By  these  means  Phillips  and  Faraday  ascertained 
its  composition  (An.  of  Phil,  xviii.  150). 

Its  eq.  is  47-66;  symb.  2C  +  C1,  or  C2  Cl. 

Dichloride  of  Sulphur. — This  compound  was  discovered  in  the  year  1804 
by  Thomson,*  and  was  afterwards  examined  by  Berthollet.f  It  is  most  con- 
veniently prepared  by  passing  a  current  of  chlorine  gas  over  flowers  of  sul- 
phur gently  heated,  until  nearly  all  the  sulphur  disappears.  Direct  com- 
bination ensues,  and  the  product,  distilled  off  from  uncombined  sulphur,  is 
obtained  under  the  form  of  a  liquid  which  appears  red  by  reflected,  and 
yellowish-green  by  transmitted  light.  Its  density  is  1*687.  It  is  volatile 
below  200°,  boils  at  280°,  yielding  vapour  which  has  a  density  of  4-70,  and 
condenses  again  without  change  in  cooling.  When  exposed  to  the  air  it 
emits  acrid  fumes,  which  irritate  the  eyes  powerfully,  and  have  an  odour 
somewhat  resembling  sea-weed,  but  much  stronger.  Dry  litmus  paper  is 
not  reddened  by  it,  nor  does  it  unite  with  alkalies.  It  acts  with  energy  on 
water : — mutual  decomposition  ensue?,  with  formation  of  hydrochloric  and 
hyposulphurous  acids,  and  deposite  of  sulphur,  by  which  the  water  is  ren- 
dered cloudy.  From  a  recent  analysis  by  Rose  it  consists  of  35.42  parts  or 
one  eq.  of  chlorine,  and  32-2  parts  or  two  eq.  of  sulphur  (Pog.  Ann.xxi.  431). 

Its  eq.  is  67-62  ;  symb.  2S  +  C1,  or  S2  Cl. 

Rose  maintains  that  the  preceding  is  the  only  chloride  of  sulphur,  arguing 
that  the  chloride  analyzed  by  Davy  was  merely  dichloride  of  sulphur  hold- 
ing chlorine  in  solution.  Dumas,  on  the  other  hand,  contends,  that  when 
sulphur  is  acted  on  by  excess  of  chlorine,  a  chloride  of  sulphur  is  really  ob- 
tained, which  is  apt  to  retain  traces  of  the  dichloride,  and  can  only  be  puri- 
fied by  repeated  distillation  at  about  140°  F.  This  chloride  is  a  liquid  of  a 
deep  reddish-brown  tint,  and  has  a  density  of  1-62.  It  boils  at  147°,  and  the 
density  of  its  vapour  is  between  3-67  and  3*70.  By  decomposition  in  water 
it  should  yield  hydrochloric  and  hyposulphurous  acids.  (An.  de  Ch.  et  de 
Ph.xlix.205.) 

Perchloride  of  Phosphorus. — There  are  two  definite  compounds  of  chlorine 
and  phosphorus,  the  nature  of  which  was  first  satisfactorily  explained  by 
Davy.  (Elements,  p.  290).  When  phosphorus  is  introduced  into  a  jar  of  dry 

*  Nicholson's  Journal,  vol.  vi,  t  Memoires  d'Arcueil»  voL  i* 


224  CHLORINE. 

chlorine,  it  inflames,  and  on  the  inside  of  the  vessel  a  white  matter  collects, 
which  is  pcrrhloride  of  phosphorus.  It  is  very  volatile,  a  temperature  much 
below  212°  being-  sufficient  to  convert  it  into  vapour.  Under  pressure  it 
may  be  fused,  and  it  yields  transparent  prismatic  crystals  in  cooling. 

Water  and  perchloride  of  phosphorus  mutually  decompose  each  other; 
.and  the  sole  products  are  hydrochloric  and  phosphoric  acids.  Now  in  order 
that  these  products  should  be  formed,  consistently  with  the  constitution  of 
phosphoric  acid,  as  stated  at  page  202,  the  perchloride  must  consist  of  31.4 
parts  or  two  eq.  of  phosphorus,  and  177*1  parts  or  five  eq.  of  chlorine.  One 
equivalent  of  the  chloride  and  five  eq.  of  water  will  then  mutually  decompose 
each  other  without  any  element  being  in  excess,  and  yield  one  eq.  of  phos- 
phoric, and  five  eq.  of  hydrochloric  acid.  This  proportion  is  not  far  from 
the  truth ;  for  according  to  Davy,  one  grain  of  phosphorus  is  united  in  the 
perchloride  with  six  of  chlorine. 

Its  eq.  is  208-5  ;  symb.  2P-|-5C1,  or  P2  Cl*. 

Sesquichloride  of  Phosphorus  may  be  made  either  by  heating  the  perchlo- 
ride with  phosphorus,  or  by  passing  the  vapour  of  phosphorus  over  corrosive 
sublimate  contained  in  a  glass  tube.  It  is  a  clear  liquid  like  water,  of  sp. 
gr.  1*45  ;  emits  acid  fumes  when  exposed  to  the  air,  owing  to  the  decompo^ 
sition  of  watery  vapour;  but  when  pure  it  does  not  redden  dry  litmus  paper. 
On  mixing  it  with  water,  mutual  decomposition  ensues,  heat  is  evolved,  and 
a  solution  of  hydrochloric  and  phosphorous  acids  is  obtained.  It  hence 
appears  to  consist  of  31-4  parts  or  two  eq.  of  phosphorus,  and  106-26  parts 
or  three  eq.  of  chlorine.  Its  eq.  is  137-66;  symb.  2P-f  3C1,  or  P2  C13. 

When  hydrosulphuric  acid  gas  is  transmitted  through  a  vessel  containing 
perchloride  of  phosphorus,  hydrochloric  acid  is  disengaged,  and  a  liquid 
produced  which,  according  to  Serullas,  is  a  compound  of  three  equivalents 
of  chlorine,  one  of  phosphorus,  and  one  of  sulphur.  An.  de  Ch.  et  de  Ph. 
xlii.  25.) 

Chlorocarbonic  Acid  Gas. — Hist,  and  Prep. — This  compound  was  disco- 
vered in  1812  by  Dr.  Davy,  who  described  it  in  the  Philosophical  Trans- 
actions for  that  year,  under  the  name  of  phosgene  gas.  (From  quc  light, 
and  7/«vp£/v  to  produce.)  It  is  made  by  exposing  a  mixture  of  equal  measures 
of  dry  chlorine  and  carbonic  oxide  gases  to  sunshine,  when  rapid  but  silent 
combination  ensues,  and  they  contract  to  one  half  their  volume.  Diffused 
daylight  also  effects  their  union  slowly ;  but  they  do  not  combine  at  all 
when  the  mixture  is  wholly  excluded  from  light. 

Prop. — It  is  a  colourless  gas,  has  a  strong  odour,  and  reddens  dry  litmus 
paper.  It  combines  with  four  times  its  volume  of  ammoniacal  gas,  forming  a 
white  solid  salt;  so  that  it  possesses  the  characteristic  property  of  acids.  It 
is  decomposed  by  contact  with  water.  One  equivalent  of  each  compound 
undergoes  decomposition ;  and  as  the  hydrogen  of  the  water  unites  with 
chlorine,  and  its  oxygen  with  carbonic  oxide,  the  products  are  carbonic  and 
hydrochloric  acids.  When  tin  is  heated  in  this  gas,  chloride  of  tin  is  gene- 
rated, and  carbonic  oxide  gas  set  free,  which  occupies  exactly  the  same  space 
as  the  chlorocarbonic  acid  which  was  employed.  A  similar  change  occurs 
when  it  is  heated  in  contact  with  antimony,  zinc,  or  arsenic. 

As  chlorocarbonic  acid  gas  contains  its  own  volume  of  each  of  its  consti- 
tuents, it  follows  that  100  cubic  inches  of  that  gas  at  tl>e  standard  tempera- 
ture and  pressure  must  weigh  106-7638  grains,'  namely,  76*5988  of  chlorine 
added  to  30-1650  of  carbonic  oxide.  Its  sp.  gr.  is,  therefore,  3*4427,  and  it 
consists  of  35*42  parts  or  one  eq.  of  chlorine,  and  14*12,  parts  or  one  eq.  of 
carbonic  oxide. 

Its  eq.  is  49*54 ;  symb.  CO-f-Cl,  or  CO,  Cl. 

Terchloride  of  Boron. — Davy  noticed  that  recently  prepared  boron  takes 
fire  spontaneously  in  an  atmosphere  of  chlorine,  and  emits  a  vivid  light;  but 
he  did  not  examine  the  product.  Berzelius  remarked,  that  if  the  boron  haa 
been  previously  heated',  whereby  it  is  rendered  more  compact,  the  combus- 
tion does  not  take  place  till  heat  is  applied.  This  observation  led  him  ta 
expose  boroQ,  thus  rendered  dense,,  in  a  glass  tube  to  a  current  of  dry  chlo- 


CHLORINE.  225 

rine;  and  to  heat  it  gently  as  soon  as  the  atmospheric  air  was  completely 
expelled,  in  order  to  commence  the  combustion.  The  resulting  compound 
proved  to  be  a  colourless  gas ;  and  on  collecting  it  over  mercury,  which  ab- 
sorbed free  chlorine,  he  procured  the  chloride  of  boron  in  a  state  of  purity. 
This  gas  is  rapidly  absorbed  by  water  ;  but  double  decomposition  takes  place 
at  the  same  instant,  giving  rise  to  hydrochloric  and  boracic  acids  as  the  sole 
products:  from  this  fact  is  inferred  the  composition  of  the  chloride;  for  one 
eq.  of  terchloride  of  boron  or  B-J-3C1,  and  three  eq.  of  water  or  3  (H  +  O,) 
correspond  to  one  eq.  of  boracic  acid  or  B  +  3O,  and  three  eq.  of  hydrochloric 
acid  or  3(H-j-Cl).  The  watery  vapour  of  the  atmosphere  occasions  a  simi- 
lar change;  so  that  when  the  gas  is  mixed  with  air  containing  hygrometric 
moisture,  a  dense  white  cloud  is  produced.  The  sp.  gr.  of  the  gas,  according 
to  Dumas,  is  3-942.  It  is  soluble  in  alcohol,  and  communicates  to  it  an 
ethereal  odour,  apparently  by  the  action  of  hydrochloric  acid.  It  unites 
with  amrnoniacal  gas,  forming  a  fluid  volatile  substance,  the  nature  of  which 
is  unknown. — (Annals  of  Phil.  xxvi.  129.) 

Dumas  finds  that  terchloride  of  boron  may  be  generated  by  the  action  of 
dry  chlorine  on  a  mixture  of  charcoal  and  boracic  acid,  heated  to  redness  in 
a  porcelain  tube.  Although  neither  charcoal  nor  chlorine  can,  when  acting 
alone,  decompose  boracic  acid,  they  do  so  readily  by  their  united  effect. 
According  to  Dumas,  two  volumes  of  terchloride  of  boron,  and  three  of  car- 
bonic oxide"  gas  are  formed.  From  these  data  terchloride  of  boron  may  be 
considered  as  composed  of  three  vol.  of  chlorine  and  one  vol.  of  the  vapour 
of  boron,  condensed  into  two  volumes.  Its  calculated  sp.  gr.  is  4*0805. 

Despretz  also  appears  to  have  invented  a  similar  process.  (Philos.  Maga- 
zine and  Annals,  i.  469.) 

Itseq.  is  U 7-1 6;  eq.  vol.  =  200;  symb.  B  +  3C1,  or  BC13. 

Terchloride  of  Silicon. — When  silicon  is  heated  in  a  current  of  chlorine 
gas,  it  takes  fire,  and  is  rapidly  volatilized.  The  product  of  the  combustion 
condenses  into  a  liquid,  which  appears  to  be  naturally  colourless,  but  to 
which  an  excess  of  chlorine  communicates  a  yellow  tint.  This  fluid  is  very 
limpid  and  volatile,  and  evaporates  almost  instantaneously  in  open  vessels,  in 
the  form  of  a  white  vapour.  It  boils  at  124°,  and  bears  a  cold  of  zero  with- 
out becoming  solid.  It  has  a  suffocating  odour  not  unlike  that  of  cyanogen, 
and  when  put  into  water  is  converted  into  hydrochloric  and  silicic  acids, 
the  latter  being  easily  obtained  in  a  gelatinous  form.  (Berzelius). 

It  may  also  be  prepared  by  the  method  proposed  by  Oersted,  which  has 
been  so  successfully  applied  in  the  formation  of  other  chlorides.  It  consists 
in  mixing  about  equal  parts  of  hydrated  silicic  acid  and  starch  into  a  paste 
with  oil,  heating  the  mass  in  a  covered  crucible  so  as  to  char  the  starch,  in- 
troducing the  mixture  in  fragments  into  a  porcelain  tube,  and  then  transmit, 
ting  through  it  a  current  of  dry  chlorine  gas,  while  the  tube  is  kept  at  a  red 
heat.  The  chlorine  unites  with  silicon,  while  the  charcoal  and  oxygen  com* 
bine.  The  volatile  chloride  is  then  agitated  with  mercury  to  separate  the 
free  chlorine,  and  purified  by  distillation. 

Its  eq.  is  128-76;  symb.  Si-fSCl,  or  SiCl*. 

Chloro-nitrous  Gas. — When  fused  chloride  of  sodium,  potassium,  or  cal- 
cium,  in  powder,  is  treated  with  as  much  strong  nitric  acid  as  is  sufficient 
to  wet  it,  mutual  decomposition  ensues,  and  a  new  gas,  composed  of  chlorine 
and  binoxide  of  nitrogen,  is  generated.  Its  discoverer,  Mr.  E.  Davy,  de, 
scribes  it  as  a  gas  of  a  pale  reddish-yellow  colour,  of  an  odour  similar  to  that 
of  chlorine,  though  less  pungent,  and  possessed  of  bleaching  properties.  It 
fumes  on  exposure  to  the  air,  and  is  freely  absorbed  by  water.  It  is  decom, 
posed  by  sulphur,  phosphorus,  mercury,  and  most  metals,  and  by  substances 
in  general  which  have  an  affinity  for  chlorine.  It  consists,  according  to 
Davy,  of  equal  volumes  of  chlorine  and  binoxide  of  nitrogen,  united  without 
any  condensation. 

In  the  mutual  decomposition  of  chloride  of  sodium  and  nitric  acid,  the 
products  appear  to  be  chloro-nitrous  and  chlorine  gases,  and  nitrate  of  soda. 
Their  formation  must  obviously  depend  on  sodium  beu\g  oxidized  at  the 


226  CHLORINE. 

expense  of  nitric  acid,  while  part  of  the  chlorine  unites,  at  the  moment  of 
separation  from  the  sodium,  with  binoxide  of  nitrogen.  (Phil.  Mag.  ix. 
355.)  Theoretically,  it  should  he  mixed  with  twice  its  volume  of  chlorine, 
the  presence  of  which  must  materially  obscure  the  properties  of  the  new  gas. 

NATURE  OF  CHLORINE. 

The  change  of  opinion  which  has  gradually  taken  place  among  chemists 
concerning  the  nature  of  chlorine,  is  a  remarkable  fact  in  the  history  of  the 
science.  The  hypothesis  of  Berthollet,  unfounded  as  it  is,  prevailed  at  one 
time  universally.  It  explained  phenomena  so  satisfactorily,  and  in  a  manner 
so  consistent  with  the  received  chemical  doctrine,  that  for  some  years  no 
one  thought  of  calling  its  correctness  into  question.  A  singular  reverse, 
however,  has  taken  place  ;  and  this  hypothesis,  though  it  has  not  hitherto 
been  rigidly  demonstrated  to  be  erroneous,  has  within  a  short  period  been 
generally  abandoned,  even  by  persons  who,  from  having  adopted  it  in  early 
life,  were  prejudiced  in  its  favour.  The  reason  of  this  will  readily  appear 
on  comparing  it  with  the  opposite  theory,  and  examining  the  evidence  in 
favour  of  each. 

Chlorine,  according  to  the  new  theory,  is  maintained  to  be  a  simple  body, 
because,  like  oxygen,  hydrogen,  and  other  analogous  substances,  it  cannot 
be  resolved  into  more  simple  parts.  It  does  not  indeed  follow  that  a  body 
is  simple  because  it  has  not  hitherto  been  decomposed  ;  but  as  chemists  have 
no  other  mode  of  estimating  the  elementary  nature  of  bodies,  they  must 
necessarily  adopt  this  one,  or  have  none  at  all.  Hydrochloric  acid,  by  the 
same  rule,  is  considered  to  be  a  compound  of  chlorine  and  hydrogen.  For 
when  exposed  to  the  agency  of  galvanism,  it  is  resolved  into  these  sub- 
stances ;  and  by  mixing  the  two  gases  in  due  proportion,  and  passing  an 
electric  spark  through  the  mixture,  hydrochloric  acid  gas  is  the  product. 
Chemists  have  no  other  kind  of  proof  of  the 'composition  of  water,  of  potassa, 
or  of  any  other  compound. 

Very  different  is  the  evidence  in  support  of  the  theory  of  Berthollet.  Ac- 
cording to  that  view,  hydrochloric  acid  gas  is  composed  of  absolute  muriatic 
acid  and  water  or  its  elements;  chlorine  consists  of  absolute  muriatic  acid 
and  oxygen  ;  and  absolute  muriatic  acid  is  a  compound  of  a  certain  unknown 
base  and  oxygen  gas.  Now  all  these  propositions  are  gratuitous.  For,  in 
the  first  place,  hydrochloric  acid  gas  has  not  been  proved  to  contain  water. 
Secondly,  the  assertion  that  chlorine  contains  oxygen  is  opposed  to  direct 
experiment,  the  most  powerful  deoxidizing  agents  having  been  unable  to  eli- 
cit from  that  gas  a  particle  of  oxygen.  Thirdly,  the  existence  of  such  a  sub- 
stance as  absolute  muriatic  acid  is  wholly  without  proof,  and,  therefore,  its 
supposed  base  is  also  imaginary. 

But  this  is  not  the  only  weak  point  of  the  doctrine.  Since  chlorine  is  ad- 
mitted by  this  theory  to  contain  oxygen,  it  was  necessary  to  explain  how  it 
happened  that  no  oxygen  can  be  separated  from  it.  For  instance,  on  ex- 
posing the  chlorine  to  a  powerful  galvanic  battery,  oxygen  gas  does  not  ap- 
pear at  the  positive  pole,  as  occurs  when  other  oxidized  bodies  are  subjected 
to  its  action  ;  nor  is  carbonic  acid  or  carbonic  oxide  evolved,  when  chlorine  is 
conducted  over  ignited  charcoal.  To  account  for  the  oxygen  not  appearing 
under  these  circumstances,  it  was  assumed  that  absolute  muriatic  acid  is  un- 
able to  exist  in  an  uncombined  state,  and  therefore  cannot  be  separated  from 
one  substance  except  by  uniting  with  another.  This  supposition  was  thought 
to  be  supported  by  the  analogy  of  certain  compounds,  such  as  nitric  and 
oxalic  acids,  which  appear  to  be  incapable  of  existing,  except  when  com- 
bined with  water  or  some  other  substance.  The  analogy,  however,  is  in- 
complete; for  the  decomposition  of  such  compounds,  when  an  attempt  is 
made  to  procure  them  in  an  insulated  state,  is  manifestly  owing  to  the  ten- 
dency of  their  elements  to  enter  into  new  combinations. 

Admitting  the  various  assumptions  which  have  been  stated,  most  of  the 
phenomena  receive  as  consistent  an  explanation  by  the  old  as  by  the  new 


IODINE.  227 

theory.  Thus,  when  hydrochloric  acid  gas  is  resolved  by  galvanism  into 
chlorine  and  hydrogen,  it  may  be  supposed  that  absolute  muriatic  acid 
attaches  itself  to  the  oxygen  of  the  water,  and  forms  chlorine  ;  while  the 
hydrogen  of  the  water  goes  to  the  opposite  pole  of  the  battery.  When  chlo- 
rine and  hydrogen  enter  into  combination,  the  oxygen  of  the  former  may  be 
said  to  unite  with  the  latter ;  and  that  hydrochloric  acid  gas  is  generated  by 
the  water  so  formed  combining  with  the  absolute  muriatic  acid  of  the  chlo- 
rine. The  evolution  of  chlorine,  which  ensues  on  mixing  hydrochloric 
acid  and  peroxide  of  manganese,  is  explained  on  the  supposition  that  abso- 
lute muriatic  acid  unites  directly  with  the  oxygen  of  the  black  oxide  of 
manganese. 

It  will  not  be  difficult,  after  these  observations,  to  account  for  the  pre- 
ference shown  to  the  new  theory.  In  an  exact  science,  such  as  chemistry, 
every  step  of  which  is  required  to  be  matter  of  demonstration,  there  is  no 
room  to  hesitate  between  two  modes  of  reasoning,  one  of  which  is  hypo- 
thetical, and  the  other  founded  on  experiment.  Nor  is  there,  in  the  present 
instance,  temptation  to  deviate  from  the  strict  logic  of  the  science;  for  there 
is  not  a  single  phenomenon  which  may  not  be  fully  explained  on  the  new 
theory,  in  a  manner  quite  consistent  with  the  laws  of  chemical  action  in 
general. 

It  was  supposed,  indeed,  at  one  time,  that  the  sudden  decomposition  of 
water,  occasioned  by  the  action  of  that  liquid  on  the  compounds  of  chlorine 
with  some  simple  substances,  constitutes  a  real  objection  to  the  doctrine ; 
but  it  will  afterwards  appear,  that  the  acquisition  of  new  facts  has  deprived 
this  argument  of  all  its  force.  While  nothing,  therefore,  can  be  gained, 
much  may  be  lost  by  adopting  the  doctrine  of  Berthollet.  If  chlorine  is  re- 
garded as  a  compound  body,  the  same  opinion,  though  in  direct  opposition 
to  the  result  of  observation,  ought  to  be  extended  to  iodine  and  bromine ; 
and  as  other  analogous  substances  may  hereafter  be  discovered,  in  regard 
to  which  a  similar  hypothesis  will  apply,  it  is  obvious  that  this  view,  if  pro- 
per in  one  case,  may  legitimately  be  extended  to  others.  One  encroachment 
on  the  method  of  strict  induction  would  consequently  open  the  way  to  an- 
other, and  thus  the  genius  of  the  science  would  eventually  be  destroyed. 

An  able  attempt  was  made  some  years  ago  by  the  late  Dr.  Murray,  to 
demonstrate  the  presence  of  water  or  its  elements  as  a  constituent  part  of 
hydrochloric  acid  gas,  and  thus  to  establish  the  old  theory  to  the  subversion 
of  the  new.  The  arguments  which  he  used,  though  plausible  and  ingenious, 
were  successfully  combated  by  Sir  H.  and  Dr.  Davy.  The  only  experiment 
which  strictly  bears  upon  the  question — that,  namely,  where  hydrochloric 
acid  and  ammoniacal  gases  were  mixed  together,  goes  far  to  demonstrate 
the  absence  of  combined  water  in  hydrochloric  acid  gas,  and  thereby  to 
establish  the  views  of  Davy.* 


SECTION    XIII. 

IODINE. 

Hist. — IODINE  was  discovered  in  the  year  1812  by  M.  Courtois,  a  manu- 
facturer of  saltpetre  at  Paris.  In  preparing  carbonate  of  soda  from  the 
ashes  of  sea-weeds,  he  observed  that  the  residual  liquor  corroded  metallic 
vessels  powerfully ;  and  on  investigating  the  cause  of  the  corrosion,  he  no- 


*  In  Nicholson's  Journal,  vols.  xxxi.  xxxii.  and  xxxiv.     Edinburgh  Philos. 
Trans,  vol.  viii.  and  Philos.  Trans,  for  1818. 


228  IODINE. 

ticed  that  sulphuric  acid  threw  down  a  dark-coloured  matter,  which  was 
converted  by  the  application  of  heat  into  a  beautiful  violet  vapour.  Struck 
with  its  appearance,  he  gave  some  of  the  substance  to  M.  Clement,  who  re- 
cognized it  as  a  new  body,  and  in  1813  described  some  of  its  leading-  pro- 
perties in  the  Royal  Institute  of  France.  Its  real  nature  was  soon  after 
determined  by  Gay-Lussac  and  Davy,  each  of  whom  proved  that  it  is  a  sim- 
ple non-metallic  substance,  exceedingly  analogous  to  chlorine.* 

Iodine  is  frequently  met  with  in  nature  in  combination  with  potassium  or 
sodium.  Under  this  form  it  occurs  in  many  salt  and  other  mineral  springs, 
both  in  England  and  on  the  Continent.  It  has  been  detected  in  the  water  of 
the  Mediterranean,  in  the  oyster  and  some  other  marine  molluscous  animals, 
in  sponges,  and  in  most  kinds  of  sea-weed.  In  some  of  these  productions, 
such  -as  the  Fucus  serratus  and  Fucus  digilatus^  it  exists  ready  formed,  and 
according  to  Fyfe  (Edin.  Philos.  Journal,  i.  254)  may  be  separated  by  the  ac- 
tion of  water ;  but  in  others  it  can  be  detected  only  after  incineration.  Ma- 
rine animals  and  plants  doubtless  derive  from  the  sea  the  iodine  which  they 
contain.  Vauquelin  found  it  also  in  the  mineral  kingdom,  in  combination 
with  silver.  (An.  de.  Ch.  et  de  Ph.  xxix.) 

Prep. — The  iodine  of  commerce  is  procured  from  the  impure  carbonate 
of  soda,  called  kelp,  which  is  prepared  in  large  quantity  on  the  northern 
shores  of  Scotland,  by  incinerating  sea-weeds.  The  kelp  is  employed  by 
soap-makers,  for  the  preparation  of  carbonate  of  soda ;  and  the  dark  residual 
liquor  remaining  after  that  salt  has  crystallized,  contains  a  considerable 
quantity  of  iodine,  combined  with  sodium  or  potassium.  By  adding  a  suffi- 
cient quantity  of  sulphuric  acid,  hydriodic  acid  is  first  generated,  and  ther 
decomposed.  The  iodine  sublimes  when  the  solution  is  boiled,  and  may  be 
collected  in  cool  glass  receivers.  A  more  convenient  process  is  to  emploj 
a  moderate  excess  of  sulphuric  acid,  and  then  add  to  the  mixture  some  per 
oxide  of  manganese,  which  acts  on  hydriodic  in  the  same  way  as  on  hydro- 
chloric  acid;(page  211),  (Phil.  Mag.  L.  Ure).  Another  method  proposed  b} 
Soubeiran,  is  by  adding  to  the  ley  from  kelp,  a  solution  made  with  the  sul- 
phates  of  protoxides  of  copper  and  iron  in  the  ratio  of  1  of  the  former  to  2^ 
of  the  latter,  as  long  as  a  white  precipitate  appears.  The  diniodide  of  cop- 
per is  thus  thrown  down;  and  it  may  be  decomposed  either  by  peroxide  ol 
manganese  alone,  or  by  manganese  and  sulphuric  acid.  By  means  of  the 
former,  the  iodine  passes  over  quite  dry ;  but  a  strong  heat  is  requisite. 

Prop. — Iodine,  at  common  temperatures,  is  a  soft  friable  opaque  solid  of  a 
bluish-black  colour,  and  metallic  lustre.  It  occurs  usually  in  crystalline 
scales,  having  the  appearance  of  micaceous  iron  ore ;  but  it  sometimes  cry- 
stallizes in  large  rhomboidal  plates,  the  primitive  form  of  which  is  a  rhombic 
octohedron.  The  crystals  are  best  prepared  by  exposing  to  the  air  a  solu- 
tion of  iodine  in  hydriodic  acid.  Its  sp.  gr.  according  to  Gay-Lussac,  is 
4-948;  but  Thomson  found  it  only  3-0844.  At  225°  it  is  fused,  and  enters 
into  ebullition  at  347° ;  but  when  moisture  is  present,  it  is  sublimed  rapidly 
even  below  the  degree  of  boiling  water,  and  suffers  a  gradual  dissipation  at 
low  temperatures.  Its  vapour  is  of  an  exceedingly  rich  violet  colour,  a  cha- 
racter to  which  it  owes  the  name  of  iodine.  (From  ?/^f«?,  violet-coloured.) 
This  vapour  is  remarkably  dense,  its  sp.  gr.  by  calculation,  page  146,  being 
8-7020,  or  8-716  as  directly  observed  by  Dumas.  Hence  100  cubic  inches,  at 
the  standard  temperature  and  pressure,  must  weigh  269-8638  grains. 

It  is  a  non-conductor  of  electricity,  and,  like  oxygen  and  chlorine,  is  a 
negative  electric.  It  has  a  very  acrid  taste,  and  its  odour  is  almost  exactly 
similar  to  that  of  chlorine,  when  much  diluted  with  air.  It  acts  energetic- 
ally on  the  animal  system  as  an  irritant  poison,  but  is  employed  medicinally 
in  very  small  doses  with  advantage. 

It  is  very  sparingly  soluble  in  water,  requiring  about  7000  times  its  weight 

*  The  original  papers  on  this  subject  are  in  the  Annales  de  Chimie,  vols. 
Ixxxviii.  xc.  and  xci. ;  and  in  the  Philos.  Trans,  for  1814  and  1815. 


IODINE.  229 

of  that  liquid  for  solution.  It  communicates,  however,  even  in  this  minute 
quantity,  a  brown  tint  to  the  menstruum.  Alcohol  and  ether  dissolve  it 
freely,  and  the  solution  has  a  deep  reddish-brown  colour. 

Iodine  possesses  an  extensive  range  of  affinity.  It  destroys  vegetable  co- 
lours, though  in  a  much  less  degree  than  chlorine.  It  manifests  little  dis- 
position to  combine  with  metallic  oxides ;  but  it  has  a  strong  attraction  for 
the  pure  metals,  and  for  most  of  the  simple  non-metallic  substances,  producing 
compounds  which  are  termed  iodides  or  iodurets.  It  is  not  inflammable ; 
but  under  favourable  circumstances  may,  like  chlorine,  be  made  to  unite 
with  oxygen.  A  solution  of  the  pure  alkalies  acts  upon  it  and  gives  rise  to 
decomposition  of  water ;  whether  an  hypo-iodite  and  iodide  are  first  produced, 
as  in  the  case  of  chlorine,  has  not  yat  been  determined,  but  on  the  applica- 
tion of  heat  an  iodate  and  iodide  are  formed. 

Pure  iodine  is  not  influenced  chemically  by  the  imponderables.  Exposure 
to  the  direct  solar  rays,  or  to  strong  shocks  of  electricity,  does  not  change  its 
nature.  It  may  be  passed  through  red-hot  tubes,  or  over  intensely  ignited 
charcoal,  without  any  appearance  of  decomposition ;  nor  is  it  affected  by  the 
agency  of  galvanism.  Chemists,  indeed,  are  unable  to  resolve  it  into  more 
simple  parts,  and  consequently  it  is  regarded  as  an  elementary  principle. 

The  violet  hue  of  the  vapour  of  iodine  is  for  many  purposes  a  sufficiently 
sure  indication  of  its  presence.  '  A  far  more  delicate  test,  however,  was  dis- 
covered by  Colin  and  Gaultier  de  Claubry.  They  found  that  iodine  has  the 
property  of  uniting  with  starch,  and  of  forming  with  it  a  compound  insolu- 
ble in  cold  water,  which  is  recognized  with  certainty  by  its  deep  blue  colour. 
This  test,  according  to  Stromeyer,  is  so  delicate,  that  a  liquid,  containing  1- 
450,000th  of  its  weight  of  iodine  receives  a  blue  tinge  from  a  solution  of 
starch.  Two  precautions  should  be  observed  to  ensure  success.  In  the  first 
place,  the  iodine  must  be  in  a  free  state;  for  it  is  the  iodine  itself  only,  and 
not  its  compounds,  which  unites  with  starch.  Secondly,  the  solution  should 
be  quite  cold  at  the  time  of  adding  the  starch ;  for  hot  water  dissolves  the 
blue  compound,  and  forms  a  colourless  solution. 

Berzelius  determined  the  equivalent  of  iodine  by  exposing  fused  iodide  of 
silver  to  a  current  of  chlorine  gas,  whereby  the  iodine  was  expelled  and 
chloride  of  silver  generated.  Through  the  known  composition  of  chloride 
of  silver  he  inferred  that  of  the  iodide,  and  thence  found  the  eq.  of  iodine. 
It  is  126-3;  eq.  vol.  =100;  symb.  I. 

The  composition  of  the  compounds  of  iodine  described  in  this  section  is 
as  follows : — 

Iodine.  Equiv.    Formulae. 

Hydriodic  acid  12fr3  1  eq.  -f  1  1  eq.  hydr.=  127-3  H  -f  I  or  HI. 

Oxide  of  iodine    /  -,  .A.  , 

lodous  acid          (          Composition  unknown. 

lodicacid  ]26-3  1  eq.-f  40        5  eq.  oxyg.=  166-3    I_f-5O. 

Periodic  acid  126-3  1  eq.-f  56        7  eq.    do.    =182-3    I-J-7O. 

Protochloride  of  iodine  126-3  1  e^.-f  35-42    1  eq.  chlor.=  161-72  I-Lci. 
Terchloride        do.       126-3  1  eq.-f  106-26  3 eq.   do.    =232-56  1 4-301. 
Perchloride         do.       Composition  doubtful. 

Teriodide  of  nitrogen  378-9  3  eq.-f  14-15    1  eq.  nitr.  =393-05  N-f  31. 
Protiodide  of  phos.        126-3  1  eq,_f  15-7     1  eq.  phos.=  142       P-f.1. 
Sesquiodide     do.  378-9  3  eq.-f  31-4     2  eq.    do.  =410-3   2P-f  31. 

Periodide        do.  631-5  5  eq.-f  31-4     2  eq.   do.  =662-9   2P-f-5I. 

Iodide  of  sulphur      J 

Periodide  of  carbon  >   Composition  unknown. 
Protiodide  of  carbon  } 

Hydriodic  Acid — Prep. — This  compound  is  formed  by  the  direct  union 
of  its  elements,  when  a  mixture  of  hydrogen  gas  and  iodine  vapour  are  trans- 
mitted through  a  porcelain  tube  at  a  red  heat.  A  more  convenient  process, 
and  by  which  it  is  obtained  in  a  pure  state,  is  by  the  action  of  water  on  the 
periodide  of  phosphorus.  Any  convenient  quantity  of  the  iodide  is  put  into 

20 


230  IODINE. 

a  small  glass  retort,  together  with  a  little  water,  and  a  gentle  heat  is  applied. 
Mutual  decomposition  ensues;  the  oxygen  of  the  water  unites  with  phos- 
phorus, and  its  hydrogen  with  iodine,  giving  rise  to  the  formation  of  phos- 
phoric and  hydriodic  acids,  the  latter  of  which  passes  over  in  the  form  of  a 
colourless  gas.  The  preparation  of  the  iodide  requires  care;  since  phospho- 
rus and  iodine  act  so  energetically  on  each  other  by  mere  contact,  that  the 
phosphorus  is  generally  inflamed,  and  a  great 'part  of  the  iodine  expelled  in 
the  form  of  vapour.  This  inconvenience  is  avoided  by  putting  the  phosphorus 
into  a  tube  sealed  at  one  end,  about  twelve  inches  long,  displacing  the  air 
by  a  current  of  dry  carbonic  acid  gas,  then  gradually  adding  the  iodine,  and 
promoting  the  action  towards  the  close  by  a  gentle  heat.  The  materials 
should  be  well  dried  with  bibulous  paper,  and  the  iodide  preserved  in  a  well- 
stopped  dry  vessel;  for  even  atmospheric  humidity  gives  rise  to  copious 
white  fumes  of  hydriodic  acid.  The  proportions  usually  employed  are  one 
part  of  phosphorus  to  about  twelve  of  iodine.  Another  process  has  been 
recommended  by  F.  d'Arcet,  which  consists  in  evaporating  hypophosphorous 
acid  until  it  begins  to  yield  phosphjiretted  hydrogen,  mixing  it  with  an 
equal  weight  of  iodine,  and  applying  a  gentle  heat.  Hydriodic  acid  gas  of 
great  purity  is  then  rapidly  disengaged;  its  production  depending,  as  in  the 
former  process,  on  the  decomposition  of  water. 

Prop. — Hydriodic  acid  gas  has  a  very  sour  taste,  reddens  vegetable  blue 
colours  without  destroying  them,  produces  dense  white  fumes  when  mixed 
with  atmospheric  air,  and  has  an  odour  similar  to  that  of  hydrochloric  acid 
gas.  The  salts  which  it  forms  with  alkalies  are  called  hydriodates.  Like 
hydrochloric  acid  gas,  it  cannot  be  collected  over  water ;  for  that  liquid  dis- 
solves it  in  large  quantity. 

It  is  decomposed  by  several  substances  which  have  a  strong  affinity  for 
either  of  its  elements.  Thus  oxygen  gas,  when  heated  with  it,  unites  with 
its  hydrogen,  and  liberates  the  iodine.  Chlorine  effects  the  decomposition 
instantly;  hydrochloric  acid  gas  is  produced,  and  the  iodine  appears  in  the 
form  of  vapour.  With  strong  nitrous  acid  it  takes  fire,  and  the  vapour  of 
iodine  is  set  free.  It  is  also  decomposed  by  mercury.  The  decomposition 
begins  as  soon  as  hydriodic  acid  gas  comes  in  contact  with  mercury,  and 
proceeds  steadily  and  even  quickly  if  the  gas  is  agitated,  till  nothing  but  hy- 
drogen remains.  Gay-Lussac  ascertained  by  this  method  that  100  measures 
of  hydriodic  acid  gas  contain  precisely  half  their  volume  of  hydrogen.  As- 
suming it  to  consist  of  equal  volumes  of  hydrogen  gas  and  iodine  vapour, 
-united  without  any  condensation,  then,  since 

Grains. 

50  cubic  inches  of  the  vapour  of  iodine  weigh  ;  ^    -        134-9319 

50         do.  hydrogen  gas  -  1-0683 

100  cubic  inches  of  hydriodic  acid  gas  should  weigh  -       136-0002 

These  numbers  are  obviously  in  the  ratio  of  1  to  126-3,  the  eq.  of  iodine 
and  hydrogen.  On  the  same  principles  the  density  of  the  gas  should  be 
4'3854.  which  is  probably  more  correct  than  4-443,  a  number  found  experi- 
mentally by  Gay-Lussac  (An.  de  Ch.  xci.  16).  From  these  coincidences 
there  is  no  doubt  that  100  measures  of  hydriodic  acid  gas  contain  50  mea- 
sures of  hydrogen  gas  and  50  of  the  vapour  of  iodine. 

When  the  gas  is  conducted  into  water  till  that  liquid  is  fully  charged  with 
it,  a  colourless  acid  solution  is  obtained,  which  emits  white  fumes  on  exposure 
to  the  air,  and  has  a  sp.  gr.  of  1-7.  It  may  be  prepared  also  by  transmitting 
a  current  of  hydrosulphuric  acid  gas  through  water  in  which  iodine  in  fine 
powder  is  suspended.  The  iodine,  from  having  a  greater  affinity  than  sul- 
phur for  hydrogen,  decomposes  the  hydrosulphuric  acid ;  and  hence  sulphur 
is  set  free,  and  hydriodic  acid  produced.  As  soon  as  the  iodine  has  dis- 
appeared and  the  solution  become  colourless,  it  is  heated  for  a  short  time  to 
expel  the  excess  of  hydrosulphuric  acid,  and  subsequently  filtered  to  separate 
free  sulphur. 


IODINE.  231 

The  solution  is  readily  decomposed.  On  exposure  during1  a  few  hours  to 
the  atmosphere,  the  oxygen  of  the  air  forms  water  with  the  hydrogen  of  the 
acid,  and  sets  iodine  free.  The  solution  is  found  to  have  acquired  a  yellow 
tint  from  the  presence  of  uncombined  iodine,  and  a  blue  colour  is  occasioned 
by  the  addition  of  starch.  Nitric  and  sulphuric  acid  likewise  decompose  it 
by  yielding  oxygen,  the  former  being  at  the  game  time  converted  into  nitrous, 
and  the  latter  into  sulphurous  acid.  Chlorine  unites  directly  with  the  hy- 
drogen of  the  hydriodic  acid,  and  hydrochloric  acid  is  formed.  The  separa- 
tion of  iodine  in  all  these  cases  may  be  proved  in  the  way  just  mentioned. 
These  circumstances  afford  a  sure  test  of  the  presence  of  hydriodic  acid, 
whether  free  or  in  combination  with  alkalies.  All  that  is  necessary,  is  to 
mix  a  cold  solution  of  starch  with  the  liquid,  previously  concentrated  by  eva- 
poration if  necessary,  and  then  add  a  few  drops  of  strong  sulphuric  acid. 
A  blue  colour  will  make  its  appearance  if  hydriodic  acid  is  present. 
Its  eq.  is  127-3;  eq.  vol.  =  200 ;  symb.  H  +  I,  or  HI. 
Oxide  of  Iodine  and  lodous  Acid. — On  mixing  the  vapour  of  iodine  and 
oxygen  gas  considerably  heated,  the  violet  tint  of  the  former  disappears, 
and  a  yellow  matter  of  the  consistence  of  solid  oil  is  generated,  which  Semen- 
tini  regards  as  oxide  of  iodine ;  and  if  the  supply  of  oxygen  be  kept  up  after 
its  formation,  it  is  converted  into  a  yellow  liquid,  which  he  supposes  to  be 
iodous  acid.  From  the  mode  in  which  the  process  is  described,  there  can 
scarcely  be  a  doubt  that  some  compound  of  iodine  and  oxygen  is  thus  formed  ; 
but  its  composition  and  properties  have  not  been  satisfactorily  made  out. 
(Quarterly  Journ.  of  Science,  N.  S.  i.  478.)  On  dissolving  iodine  in  a  rather 
dilute  solution  of  soda,  until  the  solution  begins  to  acquire  a  red  tint,  perma- 
nent crystals  are  obtained  by  spontaneous  evaporation,  in  six-sided  prisms, 
which  dissolve  in  cold  water  without  change,  but  by  the  action  of  water 
moderately  heated,  or  by  alcohol,  are  converted  into  iodate  of  soda  and  iodide 
of  sodium.  On  the  addition  of  an  acid,  iodine  and  iodic  acid  are  set  at 
liberty.  From  these  facts  Mitscherlich  infers  the  crystals  to  be  iodite  of 
soda.  (An.  de  Ch.  et  de  Ph.  xxx.  84.)  They  are  more  probably  the  hypo- 
iodite. 

Jodie  Acid. — Hist,  and  Prep. — This  acid  was  discovered  at  about  the  same 
time  by  Gay-Lussac  and  Davy;  but  the  latter  first  succeeded  in  obtaining  it 
in  a  state  of  perfect  purity.  When  iodine  is  brought  into  contact  with  the 
euchlorine  of  Davy,  immediate  action  ensues  ;  the  chlorine  unites  with  one 
portion  of  iodine,  and  the  oxygen  with  another,  forming  two  compounds,  a 
volatile  orange-coloured  matter,  chloride  of  iodine,  and  a  white  solid  sub- 
stance, which  is  iodic  acid.  On  applying  heat,  the  former  passes  off  in  va- 
pour, and  the  latter  remains  (Phil.  Trans,  for  1815.)  Serullas  has  obtained 
it,  in  the  form  of  hexagonal  lamin?e,  by  evaporating,  in  a  warm  place,  its 
solution  either  in  water,  or  in  sulphuric  or  nitric  acid.  The  method  which 
he  found  most  convenient  is  by  forming  a  solution  of  iodate  of  soda  in  a  con- 
siderable excess  of  sulphuric  acid,  keeping  it  at  a  boiling  temperature  for 
twelve  or  fifteen  minutes,  and  then  setting  it  aside  to  crystallize  (Ann.  deCh. 
et  de  Ph.  xliii.  216.)  Iodic  acid  may  also  be  formed  by  dissolving  perchloride 
of  iodine  in  water,  and  gradually  adding  a  large  quantity  of  strong  sulphuric 
acid,  a  rise  of  temperature  being  at  the  same  time  prevented  by  the  applica- 
tion of  cold.  Iodic  acid  will  then  be  precipitated.  The  action  of  strong  al- 
cohol on  moist  perchloride  produces  the  same  result :  water  and  the  perchlo- 
ride are  decomposed,  and  hydrochloric  and  iodic  acids  formed.  The  latter 
is  left  undissolved  by  the  alcohol.  Another  process,  suggested  by  Mr.  Con- 
nell  of  Edinburgh,  is  by  boiling  iodine  in  nitric  acid.  For  this  purpose  a 
pure  acid  of  density  1-5  should  be  introduced  with  about  a  fifth  of  its  weight 
of  iodine  into  a  tube  sealed  at  one  end,  about  an  inch  wide  and  15  inches 
long,  and  these  materials  be  kept  at  a  boiling  temperature  for  at  least  twelve 
hours.  As  the  iodine  rises  and  condenses  on  the  sides  of  the  tube,  it  should 
be  restored  to  the  liquid,  either  by  agitation  or  by  help  of  a  glass  rod.  As 
soon  as  the  iodine  disappears,  the  nitric  acid  is  dissipated  by  cautious  evapo- 
ration. It  is  also  obtained,  as  remarked  by  Balard,  by  the  oxidizing  effect 


232  IODINE. 

of  hypochlorous  acid  on  iodine;  the  latter  unites  with  the  oxygen  of  the  acid, 
and  the  chlorine  escapes  in  the  gaseous  state. 

Prop. — This  compound,  which  was  termed  oxiodine  by  Davy,  is  anhydrous 
iodic  acid.  It  is  a  white  semitransparent  solid,  which  has  a  strong  astrin- 
gent sour  taste,  but  no  odour.  Its  sp.  gr.  is  considerable,  as  it  sinks  rapidly 
in  sulphuric  acid.  When  heated  to  the  temperature  of  about  500°  F.  it  is 
fused,  and  at  the  same  time  resolved  into  oxygen  and  iodine.  In  a  dry  air 
it  is  unchanged;  hut  in  a  moist  atmosphere  it  absorbs  humidity,  forming  the 
hydrated  acid,  and  eventually  deliquesces.  In  water  it  is  very  soluble,  and 
the  solution  has  a  distinct  acid  reaction :  the  bleaching  power  ascribed  to  it 
by  Davy  is  said  by  Hiley  not  to  be  a  property  of  pure  iodic  acid.  (Lancet  for 
July  1833.)  On  evaporating  the  solution,  a  thick  mass  of  the  consistence  of 
paste  is  left,  which  is  hydrous  iodic  acid ;  and  which,  by  the  cautious  applica- 
tion of  heat,  may  be  rendered  anhydrous.  It  acts  powerfully  on  inflamma- 
ble substances.  With  charcoal,  sulphur,  sugar,  and  similar  combustibles,  it 
forms  mixtures  which  detonate  when  heated.  It  enters  into  combination 
with  metallic  oxides,  and  the  resulting  salts  are  called  iodates.  These  com- 
pounds, like  the  chlorates,  yield  pure  oxygen  by  heat,  and  deflagrate  when 
thrown  on  burning  charcoal. 

Iodic  acid  forms,  with  the  pure  alkalies,  salts  which  are  soluble  in  water; 
but  with  lime,  baryta,  strontia,  and  the  oxides  of  lead  and  silver,  it  yields 
compounds  of  very  sparing  solubility.  It  is  readily  detected  by  the  facility 
with  which  it  is  deoxidized,  an  effect  readily  produced  by  the  sulphurous, 
phosphorous,  hydriodic,  and  hydrosulphuric  acids.  Iodine  in  each  case  is 
set  at  liberty,  and  may  be  detected  as  usual  by  starch.  Hydrochloric  and 
iodic  acids  decompose  each  other,  water  and  chloride  of  iodine  being  gene- 
rated. 

Davy  ascertained  the  composition  of  iodic  acid  by  determining  the  quan- 
tity of  oxygen  which  the  acid  loses  when  decomposed  by  heat;  Gay-Lussac 
arrived  at  the  same  result  by  heating  iodate  of  potassa,  when  pure  oxygen 
was  given  off,  and  iodide  of  potassium  remained.  Its  eq.  is  166-3;  symb. 

I_j_5O,'i,'orlOs. 

Periodic  Acid. — Hist,  and  Prep. — This  compound  has  been  lately  disco- 
vered by  Ammermuller  and  Magnus.  (Pogg.  Annalen,  xxviii.  514.)  When 
pure  soda  is  mixed  with  a  solution  of  iodate  of  soda,  and  chlorine  gas  is 
transmitted  into  it  to  saturation,  a  sparingly  soluble  white  pulverulent  salt  is 
generated,  which  subsides  after  heating,  and,  if  necessary,  concentrating,  the 
solution.  This  salt  is  a  periodate  of  soda,  the  production  of  which  appears 
to  depend  on  the  formation  of  chloride  of  sodium,  and  the  union  of  the 
oxygen  of  the  soda  with  the  iodine  of  the  iodic  acid.  For  each  equivalent 
of  periodic  acid,  two  eq.  of  chloride  of  sodium  should  be  generated ;  since 
the  materials  I +  5O,  2(Na -f  O),  2C1,  just  suffice  for  yielding  I +  7O,  and 
2(Na-j-Cl).  On  dissolving  the  periodate  of  soda  in  dilute  nitric  acid,  and 
adding  nitrate  of  oxide  of  silver,  the  periodate  of  this  oxide  of  a  greenish- 
yellow  colour  subsides,  which  should  be  washed  with  water  acidulated  with 
nitric  acid.  This  yellow  salt  is  soluble  in  hot  dilute  nitric  acid,  and  sepa- 
rates again  on  cooling  in  small  shining  straw-yellow  crystals,  which  by  di- 
gestion with  warm  water  acquire,  without  dissolving,  a  reddish-brown 
almost  black  colour.  If  the  nitric  acid  solution  of  the  yellow  salt  is  so  far 
concentrated  by  evaporation  that  it  crystallizes  while  still  warm,  orange- 
coloured  crystals  subside.  These  three  salts  are  readily  analyzed  by  expo- 
sure to  a  red  heat  in  a  glass  tube,  when  iodine  and  metallic  silver  remain  in 
the  tube,  and  oxygen  gas,  along  with  water  when  water  is  present,  is  ex- 
pelled. Their  composition  is  as  follows : — 

Oxide  of  Silver.  Periodic  Acid.  Water.  Form  nice. 

Yellow  salt    232  2  eq.  182-3     1  eq.  27    3  eq.  (AgO)2IO7  +3Aq. 

Red  salt  232  2  eq.  182-3     1  eq.  18    2  eq.  (AgO)2lO7  _f..2Aq. 

Orange  salt     116  1  eq,  182-3     1  eq. AgO,    IO? 


IODINE.  233 

The  two  former  are,  therefore,  hydrated  subperiodates  of  oxide  of  silver, 
and  the  latter  is  a  neutral  periodate.  This  neutral  salt  has  the  peculiarity, 
that  by  pure  cold  water  it  is  converted  into  the  yellow  sub-salt,  while  the 
water  takes  up  exactly  half  of  its  acid  without  a  trace  of  silver.  By  this 
means  a  pure  solution  of  periodic  acid  may  be  obtained. 

Prop. — Periodic  acid  is  analogous  in  composition  to  perchloric  acid,  and 
has  decided  acid  properties.  Its'  solution  may  be  boiled  without  decomposi- 
tion, and  on  evaporation  the  acid  yields  crystals,  which  do  not  change  by 
exposure  to  the  air.  By  hydrochloric  acid  it  is  reduced  to  iodic  acid  with 
disengagement  of  chlorine,  and  the  same  change  will  of  course  be  produced 
by  substances  which  decompose  iodic  acid.  When  the  heat  is  increased 
beyond  232°,  (the  precise  point  is  riot  stated,)  periodic  acid  loses  oxygen,  and 
iodic  acid  remains.  Thus  is  periodic  more  easy  of  decomposition  than  iodic 

acid.     Its  eq.  is  182-3  ;  symb.   I-J-7O,  I,  or  K)7 

Chlorides  of  Iodine. — Chlorine  is  absorbed  at  common  temperatures  by 
dry  iodine  with  evolution  of  heat,  and  a  solid  compound  of  iodine  and  chlo- 
rine results,  which  was  discovered  both  by  Davy  and  Gay-Lussac.  The 
colour  of  the  product  is  orange-yellow  when  the  iodine  is  fully  saturated 
with  chlorine,  but  is  of  a  reddish-orange  if  iodine  is  in  excess.  It  is  con- 
verted by  heat  into  an  orange-coloured  liquid,  which  yields  a  vapour  of  the 
same  tint  on  increase  of  temperature.  It  deliquesces  in  the  open  air,  and 
dissolves  freely  in  water.  Its  solution  is  colourless,  very  sour  to  the  taste, 
and  reddens  vegetable  blue  colours,  but  afterwards  destroys  them.  From  its 
acid  properties  Davy  gave  it  the  name  of  chloriodic  acid.  Gay-Lussac,  on 
the  contrary,  calls  it  chloride  of  iodine,  conceiving  that  the  acidity  of  its 
solution  arises  from  the  presence  of  hydrochloric  and  iodic  acids,  which  he 
supposes  to  be  generated  by  decomposition  of  water.  From  the  observations 
of  Serullas  and  Dumas,  it  appears  that  there  exist  two  compounds  of  chlorine 
and  iodine,  by  the  different  action  of  which  on  water,  the  discordant  opinions 
of  Davy  and  Gay-Lussac  may  be  explained. 

This  subject  has  lately  been  examined  by  Soubciran.  He  has  distin- 
guished a  compound  of  three  eq.  of  chlorine  and  one  eq.  of  iodine,  but 
doubts  the  existence  of  the  perchloride  of  iodine  of  Davy  and  Gay-Lussac 
(Journal  de  Pharmacie,  Feb.  1837.)  This  compound  and  a  protochloride 
appear,  however,  to  have  been  previously  described  by  Kane  (Phil.  Mag.  x. 
430.)  The  protocloride  was  obtained  by  passing  a  current  of  chlorine  gas 
into  water,  in  which  iodine  was  diffused.  A  deep  reddish-yellow  solution  is 
formed,  which  gives  off  fumes  irritating  to  the  eyes  and  nose,  has  a  peculiar 
smell  of  both  its  constituents,  and  first  reddens  and  then  bleaches  litmus 
paper.  The  terchloride  was  obtained  by  repeatedly  distilling  the  protochlo- 
ride; it  may  also  be  procured  by  adding  to  the. protochloride  a  strong  solu- 
tion of  corrosive  sublimate,  which  throws  down  iodine.  The  perchloride  is 
supposed  to  contain  five  eq.  of  chlorine  and  one  eq.  of  iodine,  from  giving- 
rise,  when  decomposed  by  water,  to  hydrochloric  and  iodic  acids. 

Teriodide  of  Nitrogen, — From  the  weak  affinity  that  exists  between  iodine 
and  nitrogen,  these  substances  cannot  be  made  to  unite  directly.  Bat  when 
iodine  is  put  into  a  solution  of  ammonia,  and  the  alkali  is  decomposed ;  its 
elements  unite  with  different  portions  of  iodine,  and  thus  cause  the  forma- 
tion of  hydriodic  acid  and  iodide  of  nitrogen.  The  latter  subsides  in  the 
form  of  a  dark  powder,  which  is  characterized,  like  quadrochloride  of  nitro^ 
gen,  by  its  explosive  property.  It  detonates  violently  as  soon  as  it  is  dried ; 
and  slight  pressure,  while  moist,  produces  a  similar  effect.  Heat  and  light 
are  emitted  during  the  explosion,  arid  iodine  and  nitrogen  are  set  free,  Ac- 
cording  to  the  experiments  of  M.  Colin,  iodide  of  nitrogen  consists  of  one  eq. 
of  nitrogen  and  three  of  iodine. 

It  is  conveniently  made,  according  to  Serullas,  by  saturating  alcohol  of  0'852 
with  iodine,  adding  a  large  quantity  of  pure  ammonia,  and  agitating  the 
mixture.  On  diluting  with  water,  teriodide  of  nitrogen  subsides,  which 
should  be  washed  by  repeated  affusion  of  water  and  decantation.  As  thus 

20* 


234  BROMINE. 

prepared  it  is  very  finely  divided,  and  may  be  pressed  under  water  without 
detonating ;  but  if,  subsequently  to  its  formation,  it  is  put  in  contact  with 
pure  ammonia,  it  will  afterwards  detonate  with  the  same  facility  as  that  pre- 
pared in  the  usual  manner.  Water  and  teriodide  of  nitrogen  mutually  de- 
compose each  other,  giving  rise  to  the  formation  of  hydriodic  and  iodic  acids 
and  ammonia.  The  change  takes  place  slowly  in  cold  water  ;  but  it  is  com- 
pleted in  a  few  minutes,  and  with  scarcely  any  disengagement  of  nitrogen, 
when  gentle  heat  is  applied.  When  a  little  nitric  or  sulphuric  acid  is  used, 
ammonia  and  iodic  acid  are  alone  produced.  (An.  de  Ch.  et  de  Ph.  xlii.  201.) 

Its  eq.  393-05;  symb.  N-f  31,  or  NR 

Iodides  of  Phosphorus. — Iodine  and  phosphorus  combine  readily  in  the 
cold,  evolving  so  much  heat  as  to  kindle  the  phosphorus,  if  the  experiment 
is  made  in  the  open  air;  but  inclose  vessels  no  light  appears.  One  of  these 
compounds,  apparently  a  protiodide,  is  formed  of  1  part  of  phosphorus  and  7 
or  8  parts  of  iodine.  It  has  an  orange  colour,  fuses  at  212°,  sublimes  un- 
changed by  heat,  and  is  decomposed  by  water,  with  the  elements  of  which  it 
gives  rise  to  hydriodic  and  phosphorous  acids,  while  phosphorus  is  set  free. 
Its  eq.  is  142;  symb.  P-f  I,  or  PI. 

The  sesquiodide  is  formed  by  the  action  of  1  part  of  phosphorus  and  12  of 
iodine.  It  appears  as  a  dark  gray  crystalline  mass,  fusible  at  84°,  and  yields 
with  water  hydriodic  and  phosphorous  acids,  from  which  circumstance  its 
elements  are  supposed  to  be  in  the  ratio  of  two  eq.  of  phosphorus  to  three 
eq.  of  iodine. 

Its  eq.  is  410-3;  8ymb.2P-f3I,  or  Psls. 

The  periodide  is  prepared  with  1  part  of  phosphorus  and  20  of  iodine,  and 
is  a  black  compound,  fusible  at  114°.  As  by  the  action  of  water  it  yields 
hydriodic  and  phosphoric  acids  only,  it  is  inferred  to  contain  phosphorus  and 
iodine  in  the  ratio  of  two  eq.  to  five  eq.  Thus 

1  eq.  periodide  phos.  &  5  eq.  water    2     J  eq.  phos'ic  acid  &  5  eq.  hydriodic  acid. 
2P+5I  5(H-|-0)     -S     2P+5O  5(H+1). 

Itseq.  is  662-9  ;  symb.  2P-f  51,  or  P^p. 

Iodide  of  Sulphur.— This  compound  is  formed  by  heating  gently  4  parts 
of  iodine  with  1  of  sulphur.  The  product  has  a  dark  colour  and  radiated  ap- 
pearance like  antimony.  Its  elements  are  easily  disunited  by  heat. 

Periodide  of  Carbon.— *~W  hen  a  solution  of  pure  potassa  in  alcohol  is  mixed 
with  an  alcoholic  solution  of  iodine,  a  portion  of  alcohol  is  decomposed;  and 
its  hydrogen  and  carbon,  uniting  separately  with  iodine,  give  rise  to  perio- 
dide of  carbon  and  hydriodic  acid.  The  latter  combines  with  the  potassa, 
and  remains  in  solution.  The  former  has  a  yellow  colour  like  sulphur,  and 
forms  scaly  crystals  of  a  pearly  lustre ;  its  taste  is  very  sweet,  and  it  has  a 
strong  aromatic  odour  resembling  saffron.  It  was  discovered  by  Serullas, 
and  described  by  him  as  a  hydrocarburet  of  iodine  ;  but  its  real  nature  was 
pointed  out  by  Mitscherlich.  (An.  de  Ch.  et  de  Ph.  xxxvii.  86,) 

The  protiodide  is  formed  by  distilling  a  mixture  of  the  preceding  com- 
pound  with  corrosive  sublimate,  Jt  is  a  liquid  of  a  sweet  taste,  and  has  a  pe- 
netrating ethereal  odour. 


SECTION    XIV. 

BROMINE. 

BROMINE  was  discovered  in  1826  by  Balard  of  Montpellier.  The  name 
originally  applied  to  it  was  muride,  but  the  term  brome  or  bromine,  from 
£go>,uof  graveolentia,  signifying  a  strong  or  rank  odour,  has  since  been  sub- 
stituted. (An,  of  Phil,  xviii.  381.) 


BROMINE.  235 

Bromine  in  its  chemical  relations  bears  a  close  analogy  to  chlorine  and 
iodine,  and  has  hitherto  been  always  found  in  nature  associated  with  the 
former,  and  sometimes  also  with  the  latter.  It  exists  in  sea-water  in  the 
form  of  bromide  of  sodium  or  magnesium.  Its  relative  quantity,  however, 
is  very  minute  ;  and  even  the  uncrystullizable  residue  called  bittern,  left  after 
chloride  of  sodium  has  been  separated  from  sea- water  by  crystallization, 
contains  it  in  small  proportion.  It  may  apparently  be  regarded  as  an  essen- 
tial ingredient  of  the  saline  matter  of  the  ocean  ;  for  it  has  been  detected  in 
the  waters  of  the  Mediterranean,  Baltic,  North  Sea,  arid  Frith  of  Forth.  It 
has  also  been  found  in  the  water  of  the  Dead  Sea,  and  in  a  variety  of  salt 
springs  in  Germany.*  Daubeny  has  detected  it  in  several  mineral  springs 
in  England,  and  states  that  it  is  rarely  wanting  in  those  springs  which  con- 
tain  much  common  salt,  except  that  of  Droitwich  in  Worcestershire.  Balard 
found  that  it  exists  in  marine  plants  growing  on  the  shores  of  the  Mediter- 
ranean, and  has  procured  it  in  appreciable  quantity  from  the  ashes  of  sea- 
weeds  that  furnish  iodine.  He  has  likewise  detected  its  presence  in  the 
ashes  of  some  animals,  especially  in  those  of  the  Janthina  violacea,  one  of 
the  testaceous  mollusca. 

Prep. — Bromine  is  usually  extracted  from  bittern,  and  its  mode  of  prepa- 
ration is  founded  on  the  property  which  chlorine  possesses  of  decomposing 
hydrobromic  acid,  uniting  with  its  hydrogen,  and  setting  bromine  at  liberty. 
Accordingly,  on  adding  chlorine  to  bittern,  the  free  bromine  immediately 
communicates  an  orange-yellow  tint  to  the  liquid  ;  and  on  heating  the  solu- 
tion to  its  boiling  point,  the  red  vapours  of  bromine  are  expelled,  and  may 
be  condensed  by  being  conducted  into  a  tube  surrounded  with  ice.  It  was 
this  change  of  colour  produced  by  chlorine  that  led  to  the  discovery  of  bro- 
mine. The  method  recommended  by  Balard  for  procuring  this  substance, 
as  well  as  for  detecting  the  presence  of  hydrobromic  acid,  is  to  transmit  a 
current  of  chlorine  gas  through  bittern,  and  then  to  agitate  a  portion  of  sul- 
phuric ether  with  the  liquid.  The  ether  dissolves  the  whole  of  the  bromine, 
from  which  it  receives  a  beautiful  hyacinth-red  tint,  and  on  standing  it  rises 
to  the  surface,  When  the  ethereal  solution  is  agitated  with  caustic  potassa, 
its  colour  entirely  disappears,  owing  to  the  formation  of  bromide  of  potas- 
sium and  bromate  of  potassa,  the  former  of  which  is  obtained  in  cubic  crys- 
tals by  evaporation.  The  bromine  may  then  be  set  free  by  means  of  chlo- 
rine, or  still  better  by  sulphuric  acid  and  the  peroxide  of  manganese.  The 
process  should  be  conducted  in  a  retort,  the  beak  dipping  into  cold  water, 
which  collects  the  bromine  driven  over  by  heat.  Balard  has  subsequently 
improved  the  process  so  much,  that  it  is  now  produced  in  considerable  quan- 
tity, and  sold  in  Paris  as  an  article  of  commerce. 

Prop. — At  common  temperatures  bromine  is  a  liquid,  the  colour  of  which 
is  blackish-red  when  viewed  in  mass  and  by  reflected  light,  but  appears  hya- 
cinth-red when  a  thin  stratum  is  interposed  between  the  light  and  the  ob- 
server. Its  odour,  which  somewhat  resembles  that  of  chlorine,  is  very  dis- 
agreeable, and  its  taste  powerful.  Its  sp.  gr.  is  about  3.  By  a  temperature 
between  zero  and — 4°  it  is  congealed,  and  in  that  state  is  brittle.  Its  vola- 
tility is  considerable;  for  at  common  temperatures  it  emits  red-coloured  va- 
pours, which  are  very  similar  in  appearance  to  those  of  nitrous  acid ;  and  at 
]16'5°  it  enters  into  ebullition.  The  sp.  gr.  of  its  vapour  was  found  by 
Mitseherlieh  to  be  5-54,  and  the  number  calculated  (p.  146)  from  its  equiva- 
lent is  5-4017 :  100  cubic  inches  at  60°  and  30  inches  Bar.  should  weigh 
167-5158  grains.  It  is  a  non-conductor  of  electricity,  and  undergoes  no  che- 
mical change  whatever  from  the  agency  of  the  imponderables.  It  may  be 
transmitted  through  a  red-hot  glass  tube,  and  be  exposed  to  the  agency  of 

*  Some  of  the  salt  springs  of  Germany  furnish  a  good  deal  of  bromine. 
The  saline  at  Theodorshalle,  near  Kreuznach,  contains  a  sufficient  quantity 
to  make  its  extraction  profitable.  A  quintal  (100  Ibs.)  of  the  mother-waters 
of  this  spring  yields  two  ounces  and  one  drachm  of  bromine. — Bcrzelius, 
Traitt  de  Chimie,  i.  293.— J3d. 


236  BROMINE. 

galvanism,  without  evincing  the  least  trace  of  decomposition.  Like  oxygen, 
chlorine,  and  iodine,  it  is  a  negative  electric.  It  is  soluhle  in  water,  alcohol, 
and  ether,  the  latter  being  its  best  solvent.  It  does  not  redden  litmus  paper, 
but  bleaches  it  rapidly  like  chlorine;  and  it  likewise  discharges  the  blue  co- 
lour from  a  solution  of  indigo.  Its  vapour  extinguishes  a  lighted  taper;  but 
before  going  out,  it  burns  for  a  few  seconds  with  a  flame  which  is  green  at 
its  base  and  red  at  its  upper  part.  Some  inflammable  substances  take  tire 
by  contact  with  bromine,  in  the  same  manner  as  when  introduced  into  an 
atmosphere  of  chlorine.  It  acts  with  energy  on  organic  matters,  such  as 
wood  or  cork,  and  corrodes  the  animal  texture  ;  but  if  applied  to  the  skin  for 
a  short  time  only,  it  communicates  a  yellow  stain,  which  is  less  intense  than 
that  produced  by  iodine,  and  soon  disappears.  To  animal  life  it  is  highly 
destructive,  one  drop  of  it  placed  on  the  beak  of  a  bird  having  proved  fatal. 

From  the  close  resemblance  observable  between  chlorine  and  bromine,  Ba- 
lard  was  of  course  led  to  examine  its  relations  with  hydrogen,  and  found 
that  these  substances  may  readily  be  made  to  unite;  the  product  of  the  com- 
bination being  a  gas  very  similar  to  hydrochloric  and  hydriodic  acid  gases, 
whence  it  has  received  the  name  of  hydrobromic  acid  gas.  In  its  action  on 
metals,  also,  bromine  presents  the  closest  similarity  to  that  which  chlorine 
exerts  on  the  same  substances.  Antimony  and  tin  take  fire  by  contact  with 
bromine  ;  arid  its  union  with  potassium  is  attended  with  such  intense  heat 
as  to  cause  a  vivid  flash  of  light,  and  often  to  burst  the  vessel  in  which  the 
experiment  is  performed.  Its  affinity  for  metallic  oxides  is  feeble.  By  the 
action  of  alkalies  it  is  resolved  into  hydrobromic  and  bromic  acids,  suffering 
the  same  kind  of  change  as  chlorine  or  iodine  when  similarly  treated. 

According  to  all  the  experiments  hitherto  made,  bromine  appears  to  be  an 
element.  It  is  so  very  similar  in  most  aspects  to  chlorine  and  iodine,  and 
in  the  order  of  its  chemical  relations  is  so  constantly  intermediate  between 
them,  that  Balard  at  first  supposed  it  to  be  some  unknown  compound  of 
these  substances.  There  seems,  however,  to  be  no  good  ground  for  the  sup- 
position ;  but,  on  the  contrary,  an  experiment  performed  by  De  la  Rive  af- 
fords a  very  strong  argument  against  it.  He  finds  that  when  a  compound 
of  bromine  and  iodine  is  mixed  with  starch,  and  exposed  to  the  influence  of 
galvanism,  bromine  appears  at  the  positive  and  iodine  at  the  negative  wire, 
where  the  starch  acquires  a  blue  tint.  On  making  the  experiment  with  bro- 
mine containing  a  little  bromide  of  iodine,  the  same  appearance  ensues;  but 
if  iodine  is  not  previously  added,  the  starch  does  not  receive  a  tint  of  blue. 

Bromine  is  in  most  cases  easily  detected  by  means  of  chlorine;  for  this 
substance  displaces  bromine  from  its  combination  with  hydrogen,  metals,  and 
most  other  bodies.  The  appearance  of  its  vapour  or  the  colour  of  its  solution 
in  ether  will  then  render  its  presence  obvious.  Like  chlorine,  it  forms  a 
crystalline  hydrate  when  exposed  to  32°  F.  in  contact  with  water.  The 
crystals  are  octohedral,  of  a  beautiful  red  tint,  and  suffer  decomposition  at 
54°.  (Lowig.) 

Berzelius  determined  the  equivalent  of  bromine  in  the  same  way  as  that 
of  iodine,  namely,  by  heating  a  known  weight  of  bromide  of  silver  in  a 
current  of  chlorine  gas,  so  as  to  displace  the  bromine  and  obtain  chloride  of 
silver. 

Its  eq.  is  784;  eq.  vol.=  100  ;  syrnb.  Br. 

The  compounds  of  bromine  described  in  this  section  are  as  follows  : — 

Bromine.  Equiv.     Formulae. 

Hydrobromic  acid  78-4  1  eq  +  Hydrogen    1  1  eq.=   794.       H-f-Br. 

Bromic  acid  78-4  1  eq. -{-Oxygen      40  5  eq.=  1184       Bf -J-5O. 

Chloride  of  bromine    ) 

Bromides  of  iodine      >  Composition  uncertain. 
Bromide  of  sulphur    ) 

Protobromide  ofphos.     784  1  eq.  +  Phos.      15-7  1  eq.=  94-1.         P  +  Br. 
Perbromideofphos.     392      5  eq.+     do.       314  2  eq.=4234. 
Bromide  of  carbon          Composition  uncertain. 
Terbromide  of  silicon  235-2  3  eq.  +  Silicon  22-5  1  eq.= 257-7. 


BROMINE.  237 

Hydrobromic  Acid. — Prep. — No  chemical  action  takes  place  between  the 
vapour  of  bromine  and  hydrogen  gas  at  common  temperatures,  not  even  by 
the  agency  of  the  direct  solar  rays;  but  on  introducing  a  lighted  candle,  or 
a  piece  of  red-hot  iron,  into  the  mixture,  combination  ensues  in  the  vicinity 
of  the  heated  body,  though  without  extending  to  the  whole  mixture,  and 
without  explosion.  The  combination  is  readily  effected  by  the  action  of  bro- 
mine on  some  of  the  gaseous  compounds  of  hydrogen.  Thus,  on  mixing  the 
vapour  of  bromine  with  hydriodic  acid,  hydrosulpburicacid,  or  phosphuretted 
hydrogen  gas,  decomposition  ensues,  and  hydrobromic  acid  gas  is  gene- 
rated. It  may  be  conveniently  made  for  experimental  purposes  by  a  process 
similar  to  that  for  forming  hydriodic  acid.  A  mixture  of  bromine  arid  phos- 
phorus, slightly  moistened,  yields,  by  the  aid  of  gentle  heat,  a  large  quantity 
of  pure  hydrobromic  acid  gas,  which  should  be  collected  either  in  dry  glass 
bottles,  or  over  mercury. 

Prop. — It  is  a  colourless  gas,  has  an  acid  taste,  and  pungent  odour.  It  ir- 
ritates the  glottis  powerfully,  so  as  to  excite  cough,  and  when  mixed  with 
moist  air,  yields  white  vapours,  which  are  denser  than  those  occasioned  un- 
der the  same  circumstances  by  hydrochloric  acid  gas.  It  undergoes  no  de- 
composition when  transmitted  through  a  red-hot  tube,  either  alone,  or  mixed 
with  oxygen.  It  is  not  affected  by  iodine;  but  chlorine  decomposes  it  in- 
stantly, with  production  of  hydrochloric  acid  gas,  and  deposition  of  bromine. 
It  may  be  preserved  without  change  over  mercury ;  but  potassium  and  tin 
decompose  it  with  facility,  the  former  at  common  temperatures,  and  the  lat- 
ter by  the  aid  of  heat.  It  is  very  soluble  in  water.  The  aqueous  solution 
may  be  made  by  treating  bromine  with  hydrosulphuric  acid  dissolved  in  wa- 
ter, or,  still  better,  by  transmitting  a  current  of  hydrobromic  acid  gas  into 
pure  water.  The  liquid  becomes  hot  during  the  condensation,  acquires  great 
density,  increases  in  volume,  and  emits  white  fumes  when  exposed  to  the  air. 
This  acid  solution  is  colourless  when  pure,  but  possesses  the  property  of  dis- 
solving a  large  quantity  of  bromine,  and  then  receives  the  tint  of  that  sub- 
stance. 

Chlorine  decomposes  the  solution  of  hydrobromic  acid  in  an  instant. 
Nitric  acid  likewise  acts  upon  it,  though  less  suddenly,  occasioning  the  dis- 
engagement of  bromine,  and  probably  the  formation  of  water  and  nitrous 
acid.  Nitro-hydrobromic  acid  is  analogous  to  aqua  regia,  and  possesses  the 
property  of  dissolving  gold.  The  elements  of  sulphuric  and  hydrobromic 
acids  react  on  each  other  in  a  slight  degree ;  and  hence,  on  decomposing 
bromide  of  potassium  by  sulphuric  acid,  the  hydrobromic  is  generally  mixed 
with  a  little  sulphurous  acid  gas. 

The  composition  of  hydrobromic  acid  gas  is  easily  inferred  from  the  two 
following  facts.  1.  On  decomposing  hydrobromic  acid  gas  by  potassium,  a 
quantity  of  hydrogen  remains,  precisely  equal  to  half  the  volume  of  the  gas 
employed ;  and,  2,  when  hydriodic  acid  gas  is  decomposed  by  bromine,  the 
resulting  hydrobromic  acid  occupies  the  very  same  space  as  the  gas  which 
is  decomposed.  Hence  hydrobromic  is  analogous  to  hydriodic  and  hydro- 
chloric acid  gases,  in  containing  equal  measures  of  bromine  vapour  and 
hydrogen  gas,  united  without  any  change  of  volume ;  and  since 

Grains. 

50  cubic  inches  of  bromine  vapour  weigh    .     .    ,    .     .     83-7579 
50         do.  hydrogen  gas 1-0683 


100         do.  hydrobromic  acid  must  weigh      .     .     84-8262 

These  numbers  are  in  the  ratio  of  1  to  78-4,  which  is  the  composition  of  the 
gas  by  weight.     Its  sp.  gr.  is  2-7353. 

Since  bromine  decomposes  hydriodic,  and  chlorine  hydrobromic  acid,  bro- 
mine, in  relation  to  hydrogen,  is  intermediate  between  chlorine  and  iodine; 
for  it  has  a  stronger  affinity  for  hydrogen  than  iodine,  and  a  weaker  than 
chlorine.  The  affinity  of  bromine  and  oxygen  for  hydrogen  appears  nearly 


238  BROMINE. 

similar ;  for  while  oxygen  cannot  detach  hydrogen  from  bromine,  bromine 
does  not  decompose  watery  vapour. 

The  salts  of  hydrobromic  acid  are  termed  Jtydrobromates.  Like  the  free 
acid,  they  are  decomposed,  and  the  presence  of  bromine  is  detected  by 
means  of  chlorine.  On  mixing  a  soluble  bromide  with  the  nitrates  of  the 
protoxides  of  lead,  silver,  and  mercury,  white  precipitates  are  obtained, 
which  are  very  similar  in  appearance  to  the  chlorides  of  those  metals,  but 
which  are  metallic  bromides.  On  the  addition  of  chlorine,  the  vapour  of 
bromine  is  evolved. 

Its  eq.  is  794;  eq.  vol.  =  200;  symb.  H+Br,  or  HBr. 

Bromic  Acid. — Prep. — The  only  compound  yet  known  of  bromine  and 
oxygen  is  that  formed  by  the  action  of  bromine  on  potassa,  when  a  change 
exactly  similar  to  that  produced  by  chlorine  (page  220)  ensues,  whereby 
bromide  of  potassium  and  bromate  of  potassa  are  generated;  and  the  latter, 
being  much  less  soluble  than  the  former,  is  readily  separated  by  evaporation. 
The  bromate  of  the  other  alkalies  and  alkaline  earths  may  be  prepared  in  a 
similar  manner. 

The  acid  may  be  procured  in  a  separate  state  by  decomposing  a  dilute 
solution  of  bromate  of  baryta  with  sulphuric  acid,  so  as  to  precipitate  the 
whole  of  the  baryta.  The  resulting  solution  of  bromic  acid  may  be  concen- 
trated by  slow  evaporation  until  it  acquire  the  consistence  of  syrup ;  but  on 
raising  the  temperature,  in  order  to  expel  all  the  water,  one  part  of  the  acid 
is  volatilized,  and  the  other  resolved  into  oxygen  and  bromine.  A  similar 
result  took  place  when  the  evaporation  was  conducted  in  vacua  with  sul- 
phuric acid ;  and  accordingly  all  attempts  to  procure  anhydrous  bromic  acid 
have  hitherto  failed. 

Prop. — Bromic  acid  has  scarcely  any  odour,  but  its  taste  is  very  acid, 
though  not  at  all  corrosive.  It  reddens  litmus  paper  powerfully  at  first,  and 
soon  after  destroys  its  colour.  It  is  not  affected  by  nitric  or  sulphuric  acid, 
except  when  the  latter  is  highly  concentrated,  in  which  case  bromine  is  set 
free,  and  effervescence,  probably  owing  to  the  escape  of  oxygen  gas,  ensues. 
From  the  analysis  of  bromate  of  potassa,  bromic  acid  is  obviously  similar  in 
constitution  to  iodic,  chloric,  and  nitric  acids  ;  that  is,  it  consists  of  one  equi- 
valent of  bromine  united  with  five  of  oxygen.  Its  salts  are  analogous  to  the 
chlorates  and  iodates.  Thus  bromate  of  potassa  is  converted  by  heat  into 
bromide  of  potassium,  with  disengagement  of  pure  oxygen  gas,  deflagrates 
like  nitre  when  thrown  on  burning  charcoal,  and  forms  with  sulphur  a  mix- 
ture which  detonates  by  percussion.  The  acid  of  the  bromates  is  decom- 
posed by  deoxidizing  agents,  such  as  sulphurous  and  hydrosulphuric  acids, 
in  the  same  manner  as  the  acid  wf  the  iodates.  The  bromates  likewise  suffer 
decomposition  from  the  action  of  hydrobromic  and  hydrochloric  acids. 

Bromate  of  potassa  is  said  not  to  precipitate  the  salts  of  lead,  but  to  occa- 
sion a  white  precipitate  with  nitrate  of  silver,  and  a  yellowish-white  with 
protonitrate  of  mercury  ;  characters  which,  if  true,  serve  as  a  good  test  to 
distinguish  bromate  from  iodate  and  chlorate  of  potassa. 

The  eq.  of  bromic  acid  is  118-4  ;  symb.  Br-f  5O,  Br,  or  BrO5. 

Chloride  of  Bromine. — This  compound  may  be  formed  at  common  tem- 
peratures by  transmitting  a  current  of  chlorine  through  bromine,  and  con- 
densing the  disengaged  vapours  by  means  of  a  freezing  mixture.  The  re- 
sulting chloride  is  a  volatile  fluid  of  a  reddish-yellow  colour,  much  less 
intense  than  that  of  bromine;  its  odour  is  penetrating,  and  causes  a  dis- 
charge of  tears  from  the  eyes  ;  and  its  taste  very  disagreeable.  Its  vapour 
is  a  deep  yellow,  like  chlorous  acid,  and  it  enables  metals  to  burn  as  in  an 
atmosphere  of  chlorine,  doubtless  giving  rise  to  the  formation  of  metallic 
chlorides  and  bromides. 

Chloride  of  bromine  is  soluble  in  water  without  decomposition ;  for  the 
solution  possesses  the  colour,  odour,  and  bleaching  properties  of  the  com- 
pound, and  discharges  the  colour  of  litmus  paper  without  previously  redden- 


BROMINE.  239 

ing  it.     By  the  action  of  the  alkalies  it  is  decomposed,  being  converted,  by 
means  of  the  elements  of  water,  into  hydrochloric  and  bromic  acids. 

Bromide  of  Iodine. — These  substances  act  readily^on  each  other,  and  ap- 
pear capable  of  uniting  in  two  proportions.  The  protobromide  is  a  solid, 
convertible  by  heat  into  a  reddish-brown  vapour,  which,  in  cooling,  con- 
denses into  crystals  of  the  same  colour,  and  of  a  form  resembling  that  of 
fern  leaves.  An  additional  quantity  of  bromine  converts  these  crystals  into 
a  fluid,  which  in  appearance  is  like  a  strong  solution  of  iodine  in  hydriodic 
acid.  This  compound  dissolves  without  decomposition  in  water,  but  with 
the  alkalies  yields  hydrobromic  and  iodic  acids.  The  existence  of  two  bro- 
mides of  iodine  can  scarcely  be  regarded  as  satisfactorily  established. 

Bromide  of  Sulphur. — On  pouring  bromine  on  sublimed  sulphur,  combi- 
nation ensues,  and-a  fluid  of  an  oily  appearance  and  reddish  tint  is  generated. 
In  odour  it  somewhat  resembles  chloride  of  sulphur,  and  like  that  compound 
emits  white  vapours  when  exposed  to  the  air;  but  its  colour  is  deeper.  It 
reddens  litmus  paper  faintly  when  dry,  but  strongly  if  water  is  added.  Cold 
water  acts  slowly  upon  bromide  of  sulphur;  but  at  a  boiling  temperature, 
the  action  is  so  violent  that  a  slight  detonation  occurs,  and  three  com- 
pounds, hydrobromic,  hydrosulphuric,  and  sulphuric  acids  are  formed.  The 
formation  of  these  substances  is  of  course  attributable  to  decomposition  of 
water,  and  the  union  of  its  elements  with  bromine  and  sulphur.  Bromide 
of  sulphur  is  likewise  decomposed  by  chlorine,  which  unites  with  sulphur, 
and  displaces  bromine. 

The  composition  of  bromide  of  sulphur  is  unknown.  It  dissolves  an  ex- 
cess both  of  chlorine  and  sulphur,  and  its  elements  separate  from  each 
other  so  readily,  that  it  has  hitherto  been  impracticable  to  procure  a  definite 
compound. 

Bromides  of  Phosphorus. — When  bromine  and  phosphorus  are  brought 
into  contact  in  a  flask  filled  with  carbonic  acid  gas,  they  act  suddenly  on 
each  other  with  evolution  of  heat  and  light,  and  two  compounds  are  gene- 
rated :  one,  a  crystalline  solid,  which  is  sublimed  and  collects  in  the  upper 
part  of  the  flask;  and  the  other,  a  fluid,  which  remains  at  the  bottom.  The 
former  contains  the  most  bromine,  and  the  latter  is  supposed  by  Balard  to 
consist  of  single  equivalents  of  its  elements. 

The  protobromide  retains  its  liquid  form  even  at  52°  F.  It  is  readily 
converted  into  vapour  by  heat,  and  on  exposure  to  the  air  emits  penetrating 
fumes.  It  reddens  litmus  paper  faintly,  an  effect  which  is  probably  owing 
to  the  presence  of  moisture.  With  water  it  acts  energetically  and  with  free 
disengagement  of  heat,  hydrobromic  acid  gas  being  evolved  when  only  a 
few  drops  of  water  are  employed;  but  if  a  large  quantity  is  used,  the  gas  is 
dissolved,  and  the  acid  solution  leaves  by  evaporation  a  residuum,  which 
burns  slightly  when  dried,  and  is  converted  into  phosphoric  acid. 

The  perbromide  is  yellow  in  its  solid  state;  but  with  gentle  heat  it  becomes 
a  red-coloured  liquid,  which  by  increase  of  temperature  is  converted  into  a 
vapour  of  the  same  tint.  On  cooling,  after  fusion,  it  yields  rhombic  crystals ; 
but  when  its  vapour  is  condensed,  the  crystals  are  acicular.  It  is  decom- 
posed by  metal?,  probably  with  the  formation  of  metallic  bromides  and  phos- 
phurets.  It  emits  dense  penetrating  fumes  on  exposure  to  the  air,  and  with 
water  gives  rise  to  the  production  of  hydrobromfc  and  phosphoric  acids. 
Hence  its  elements  should  be  in  the  ratio  of  two  eq.  of  phosphorus  to  five  eq. 
of  bromine. 

Chlorine  has  a  greater  affinity  for  phosphorus  than  bromine,  and  decom- 
poses both  the  bromides  with  evolution  of  the  vapour  of  bromine.  These 
compounds  are  not  decomposed  by  iodine;  but,  on  the  contrary,  bromine 
decomposes  iodide  of  phosphorus. 

Bromide  of  Carbon. — This  compound  is  formed  by  the  action  of  bromine 
on  half  its  weight  of  periodide  of  carbon,  when  bromide  of  carbon  and  a 
sub-bromide  of  iodine  are  formed,  the  latter  of  which  is  removed  by  a  solu- 
tion of  caustic^ potassa.  At  common  temperatures  it  is  liquid,  but  crystal- 
lizes at  32°  F.  Its  taste  is  sweet,  and  it  has  a  penetrating  ethereal  odour. 


240  FLUORINE. 

It  resembles  protiodide  of  "carbon  in  many  respects,  but  is  distinguished 
from  it  by  the  vapour  which  it  emits  on  exposure  to  heat  (Serullas,  An.  de 
Ch.  et  de  Ph.  xxxix.  225.) 

Terbromide  of  Silicon. — This  compound  was  made  by  Serullas  in  precise- 
ly the  same  mode  as  that  described  for  forming  the  terchloride.  When  pu- 
rified from  free  bromine  by  mercury,  and  redistilled,  it  is  a  colourless  liquid, 
which  emits  dense  vapours  in  an  open  vessel,  being  decomposed  by  the 
moisture  of  the  air,  and  is  denser  than  strong  sulphuric  acid.  At  302°  it 
enters  into  ebullition,  and  freezes  at  10°.  Potassium,  when  gently  heated, 
acts  on  it  with  such  energy  that  detonation  ensues.  By  water  it  is  resolved 
into  hydrobromic  arid  silicic  acids.  (Phil.  Mag.  and  Annals,  xi.  295.)  Its 
eq.  is  257-7 ;  symb.  Si+SBr,  or  SiBrs. 


SECTION   XV. 

FLUORINE. 

THE  substance  to  which  this  name  is  applied,  though  long  known  to  exist 
in  various  compounds,  has  only  recently  been  obtained  in  an  insulated  form, 
and,  therefore,  the  properties  peculiar  to  it  in  that  state  are  but  imperfectly 
known.  It  was  first  procured  by  Baudrimorit  by  passing  fluoride  of  boron 
over  minium  heated  to  redness,  and  receiving  the  gas  in  a  dry  vessel.  As  it 
is  mixed  with  a  large  quantity  of  oxygen,  his  present  method  is  to  treat  a 
mixture  of  fluoride  of  calcium  and  peroxide  of  manganese  with  strong  sul- 
phuric acid.  This  process,  however,  does  not  give  a  pure  gas,  as  hydro- 
fluoric and  fluosilicic  acid  gases  are  at  the  same  time  evolved.  The  presence 
of  the  latter  does  not  prevent  the  observation  of  some  of  the  properties  of  fluo- 
rine. It  is  a  gas  of  a  yellowish-brown  colour ;  its  odour  resembles  chlorine 
and  burnt  sugar;  it  bleaches.  It  does  not  act  on  glass,  but  combines  directly 
with  gold  (Phil.  Mag.  x.  149.)  The  latter  fact  is  confirmed  by  the  observa- 
tions of  Messrs.  Knox,  who  have  succeeded  so  far  in  the  preparation  of  fluo- 
rine as  to  leave  no  doubt  of  its  existence  as  a  coloured  gas  (Phil.  Mag.  x.  107.) 
Its  sp.  gr.  is  1-289.  From  the  nature  of  its  compounds,  it  appears  to  belong 
to  the  class  of  negative  electrics,  and,  like  oxygen  and  chlorine,  to  have  a 
powerful  affinity  for  hydrogen  and  metallic  substances.  Berzelius  deter- 
mined its  eq.  by  finding  that  100  parts  of  pure  fluoride  of  calcium  yield  with 
sulphuric  acid  175  parts  of  sulphate  of  lime.  Its  eq.  is  18-68;  eq.  vol.  =100; 
symb.  F. 

The  compounds  of  fluorine  described  in  this  section  are  the  following  : — 

Fluorine.  Equiv.  Formulae. 

Hydrofluoric  acid     18-68  1  eq.  4-  Hydrogen     1      1  eq.=  19-68.  H-fF. 
Fluoboric  acid  56-04  3  eq.  + Boron          10-9  1  eq.=  66-94.  B  -f  3F. 

Fluosilicic  acid        56-04  3  eq.-f  Silicon        22-5  1  eq.=  78-54.  Si-j-3F. 

Hydrofluoric  Acid. — Hist,  and  Prep. — This  acid  was  first  procured  in  its 
pure  state  in  the  year  1810  by  Gay-Lussac  and  Thenard,  and  described  in  the 
second  volume  of  their  Recherches  Phijsico-Chimiques.  It  is  prepared  by  act- 
ing on  the  mineral  called  fluor-spar,  which  is  a  fluoride  of  calcium,  carefully 
separated  from  siliceous  earth  and  reduced  to  fine  powder,  with  twice  its  weight 
of  concentrated  sulphuric  acid.  The  mixture  is  made  in  a  leaden  retort; 
and  on  applying  heat,  an  acid  and  highly  corrosive  vapour  distils  over, 
which  must  be  collected  in  a  receiver  of  the  same  metal  surrounded  with 
ice.  As  the  materials  swell  up  considerably  during  the  process,  owing  to  a 
quantity  of  vapour  forcing  its  way  through  a  viscid  mass,  the  retort  should 


FLUORINE.  241 

be  capacious.  At  the  close  of  the  operation  pure  hydrofluoric  acid  is  found 
in  the  receiver,  and  the  retort  contains  dry  sulphate  of  lime.  The  chemical 
changes  are  precisely  the  same  as  in  the  formation  of  hydrochloric  acid  gas, 
at  page  214,  fluorine  being  substituted  for  chlorine,  and  calcium  for  sodium. 
If  the  oil  of  vitriol  is  of  sufficient  strength,  all  its  water  is  decomposed,  and 
the  resulting  hydrofluoric  acid  is  anhydrous. 

Prop. — It  is  at  32°  a  colourless  liquid,  and  remains  in  that  state  at  59°  if 
preserved  in  well-stopped  bottles ;  but  when  exposed  to  the  air,  it  flies  off  in 
dense  white  fumes,  which  consist  of  the  acid  vapour  combined  with  the 
moisture  of  the  atmosphere.  Its  sp.  gr.  is  1-0609 ;  but  its  density  may  be 
increased  to  1'25  by  gradual  additions  of  water.  Its  affinity  for  this  liquid 
far  exceeds  that  of  the  strongest  sulphuric  acid,  and  the  combination  is  ac- 
companied with  a  hissing  noise,  as  when  red-hot  iron  is  quenched  by  im- 
mersion in  water. 

Its  vapour  is  much  more  pungent  than  chlorine  or  any  of  the  irritating 
gases.  Of  all  known  substances,  it  is  the  most  destructive  to  animal  matter. 
When  a  drop  of  the  concentrated  acid  of  the  size  of  a  pin's  head  comes  in 
contact  with  the  skin,  instantaneous  disorganization  ensues,  and  deep  ulcera- 
tion  of  a  malignant  character  is  produced.  On  this  account  the  greatest 
care  is  requisite  in  its  preparation.  It  acts  energetically  on  glass.  The 
transparency  of  the  glass  is  instantly  destroyed,  heat  is  evolved,  and  the  acid 
boils,  and  in  a  short  time  entirely  disappears.  A  colourless  gas,  commonly 
known  by  the  name  of  fluosilicic  acid  gas,  is  the  sole  product.  This  com- 
pound is  always  formed  when  hydrofluoric  acid  comes  in  contact  with  a  sili- 
ceous substance.  For  this  reason  it  cannot  be  preserved  in  glass  ;  but  must 
be  prepared  and  kept  in  metallic  vessels.  Those  of  lead,  from  their  cheap- 
ness, are  often  used;  but  vessels  of  silver  or  platinum  are  preferable.  In 
consequence  of  its  powerful  affinity  for  siliceous  matter,  hydrofluoric  acid 
may  be  employed  for  etching  on  glass;  and  when  used  with  this  intention, 
it  should  be  diluted  with  three  or  four  times  its  weight  of  water. 

Hydrofluoric  acid  has  all  the  usual  characters  of  a  powerful  acid.  It  has 
a  strong  sour  taste,  reddens  litmus  paper,  and  neutralizes  alkalies,  either 
forming  salts  termed  hydrofluates,  or  most  generally  giving  rise  to  metallic 
fluorides.  All  these  compounds  are  decomposed  by  strong  sulphuric  acid 
with  the  aid  of  heat,  and  the  hydrofluoric  acid  while  escaping  may  be  de- 
tected by  its  action  on  glass. 

On  some  of  the  metals  it  acts  violently,  especially  on  the  bases  of  the  al- 
kalies. Thus  when  potassium  is  brought  in  contact  with  the  concentrated 
acid,  an  explosion  attended  with  heat  and  light  ensues  ;  hydrogen  gas  is  dis- 
engaged, and  a  white  compound,  fluoride  of  potassium,  is  generated.  It  is 
a  solvent  for  some  elementary  principles  which  resist  the  action  even  of 
nitro-hydrochloric  acid.  Thus  it  dissolves  silicon,  zirconium,  and  colum- 
bium,  with  evolution  of  hydrogen  gas ;  and  when  mixed  with  nitric  acid,  it 
proves  a  solvent  for  silicon  which  has  been  condensed  by  heat,  and  for  tita- 
nium. Nitro-hydrofluoric  acid,  however,  is  incapable  of  dissolving  gold  and 
platinum.  Several  oxidized  bodies,  which  are  not  attacked  bj-  sulphuric, 
nitric,  or  hydrochloric  acid,  arc  readily  dissolved  by  hydrofluoric  acid.  As 
examples  of  this  fact,  several  of  the  weaker  acids,  such  as  silica  or  silicic 
acid,  titanic,  columbic,  molybdic,  and  tungstic  acids  may  be  enumerated. 
(Berzelius.) 

A  different  view  of  the  compounds  of  fluorine  was  originally  taken  by 
Gay-Lussac  and  Thenard,  and  is  still  held  by  some  chemists.  They  adopt- 
ed the  opinion  that  hydrofluoric  acid  is  a  com  pound  of  a  certain  inflammable 
principle  and  oxygen,  and  applied  to  it  the  name  of  fluoric  acid,  previously 
introduced  by  Scheele.  Fluor-spar  on  this  view  is  a  fluate  of  lime,  and  when 
this  salt  is  decomposed  by  oil  of  vitriol,  the  fluoric  is  merely  displaced  by 
the  sulphuric  acid,  and  the  former  passes  off  combined  with  the  water  of  the 
latter.  What  I  have  described  as  anhydrous  hydrofluoric  acid  is,  according" 
to  this  hypothesis,  hydrated  fluoric  acid ;  and  when  acted  upon  by  potassium, 
this  metal  is  oxidized  at  the  expense  of  the  water,  and  potassa  thus  generat 

21 


242  FLUORINE. 

ed  unites  with  fluoric  acid,  forming,  not  fluoride  of  potassium,  but  fluate  of 
potassa.  The  equivalent  of  fluoric  acid,  as  inferred  from  the  analysis  of 
Berzelius,  is  10-68 ;  for  39*18  parts  or  one  equivalent  of  fluor-spar  is  suppos- 
ed to  contain  28-5  parts  of  lime  (20-5  calcium  and  8  oxygen),  thus  leaving 
10'68  as  the  equivalent  of  the  acid. 

The  theory,  according  to  which  fluor-spar  is  a  compound  of  fluorine  and 
calcium,  originated  as  a  suggestion  with  M.  Ampere  of  Paris,  and  was  af- 
terwards supported  experimentally  by  Davy*  It  was  found  that  pure  hydro- 
fluoric acid  evinces  no  sign  of  containing  either  oxygen  or  water.  Charcoal 
may  be  intensely  heated  in  the  vapour  of  the  acid  without  the  production  of 
carbonic  acid.  When  hydrofluoric  acid  was  neutralized  with  dry  ammoni- 
acal  gas,  a  white  salt  resulted,  from  which  no  water  could  be  separated;  and  on 
treating  this  salt  with  potassium,  no  evidence  could  be  obtained  of  the  pre- 
sence of  oxygen.  On  exposing  the  acid  to  the  agency  of  galvanism,  there  was 
a  disengagement  at  the  negative  pole  of  a  small  quantity  of  gas,  which  from 
its  combustibility  was  inferred  to  be  hydrogen ;  while  the  platinum  wire  of  the 
positive  side  of  the  battery  was  rapidly  corroded,  and  became  covered  with  a 
chocolate-coloured  powder.  Davy  explained  these  phenomena  by  supposing 
that  hydrofluoric  acid  was  resolved  into  its  elements ;  and  that  fluorine,  at 
the  moment  of  arriving  at  the  positive  side  of  the  battery,  entered  into  com- 
bination with  the  platinum  wire  which  was  employed  as  a  conductor.  Un- 
fortunately, however,  he  did  not  succeed  in  obtaining  fluorine  in  an  insulated 
state.  Indeed,  from  the  noxious  vapours  that  arose  during  the  experiment, 
it  was  impossible  to  watch  its  progress,  and  examine  the  different  products 
with  that  precision  which  is  essential  to  the  success  of  minute  chemical  in- 
quiries, and  which  Davy  has  so  frequently  displayed  on  other  occasions. 

Though  these  researches  led  to  no  conclusive  result,  they  afforded  so 
strong  a  presumption  in  favour  of  the  opinion  of  Ampdre  and  Davy,  that  it 
was  adopted  by  several  other  chemists.  This  view  has  received  strong  ad- 
ditional support  from  the  experiments  of  M.  Kuhlman.  (Quarterlv  Journal 
of  Science  for  July  1827,  p.  205.)  It  was  found  by  this  chemist  that  fluor- 
spar is  not  in  the  slightest  degree  decomposed  by  the  action  of  anhydrous 
sulphuric  acid,  whether  at  common  temperatures  or  at  a  red  heat.  The  ex- 
periment  was  made  both  by  transmitting  the  vapour  of  anhydrous  sulphuric 
acid  over  fluor-spar  heated  to  redness  in  a  tube  of  platinum,  and  by  putting 
the  mineral  into  the  liquid  acid.  In  neither  case  did  decomposition  ensue  ; 
but  when  the  former  experiment  was  repeated  with  the  difference  of  employ- 
ing concentrated  hydrous  instead  of  anhydrous  sulphuric  acid,  evolution 
of  hydrofluoric  acid  was  produced.  M.  Kuhlman  also  transmitted  hydro- 
chloric acid  gas  over  fluor-spar  at  a  red  heat,  when  hydrofluoric  acid  was 
disengaged,  without  any  evolution  of  hydrogen,  and  chloride  of  calcium  re- 
mained. I  am  aware  of  no  satisfactory  explanation  of  these  facts,  except 
by  regarding  fluor-spar  as  a  compound  of  fluorine  and  calcium,  and  hydro- 
fluoric acid  as  a  compound  of  fluorine  and  hydrogen.  I  shall  accordingly 
adopt  this  view  in  the  subsequent  pages,  and  never  employ  the  term  fluoric 
acid,  except  when  explaining  phenomena  according  to  the  theory  of  Gay- 
Lussac. 

Its  eq.  is  19-68 ;  symb.  H-{-  F,  or  HF. 

Fluoboric  Acid. — Prep. — The  chief  difficulty  in  determining  the  nature 
of  hydrofluoric  acid  arises  from  the  water  of  the  sulphuric  acid  which  is 
employed  in  its  preparation.  To  avoid  this  source  of  uncertainty,  Gay- 
Lussac  and  Thenard  made  a  mixture  of  vitrified  boracic  acid  and  fluor-spar, 
and  exposed  it  in  a  leaden  retort  to  heat,  under  the  expectation  that  as  no 
water  was  present,  anhydrous  fluoric  acid  would  be  obtained.  In  this,  how- 
ever, they  were  disappointed  ;  but  a  new  gas  carne  over,  to  which  they  ap- 
plied the  term  offluoboric  acid  gas.  A  similar  train  of  reasoning  led  Davy 
about  the  same  time  to  the  same  discovery ;  though  the  French  chemists 
had  the  advantage  in  priority  of  publication.  Another  process,  given  by 
Dr.  Davy,  is  to  mix  1  part  of  vitrified  boracic  acid  and  2  of  fluor-spar  with 
12  parts  of  strong  sulphuric  acid,  heating  the  mixture  gently  in  a  glass  flask 
(Phil.  Trans.  1812) ;  but  the  gas  thus  developed  contains  a  considerable 


FLUORINE.  243 

quantity  of  fluosilicic  acid.  Fluoboric  acid  gas  may  also  be  formed  by  heat- 
ing- a  strong-  solution  of  hydrofluoric  and  boracic  acids  in  a  metallic  retort. 

In  the  decomposition  of  fluor-spar  by  vitrified  boracic  acid,  the  former 
and  part  of  the  latter  undergo  an  interchange  of  elements.  The  fluorine 
uniting  with  boron  gives  rise  to  fluoboric  acid  gas;  and  by  the  union  of 
calcium  and  oxygen,  Ikne  is  generated,  which  combines  with  boracic  acid, 
and  is  left  in  the  retort  as  borate  of  lime.  Fluoboric  acid  gas,  therefore,  is 
composed  of  boron  and  fluorine.  Those  who  adopt  the  theory  of  Gay-Lussac 
give  a  different  explanation,  and  regard  this  gas  as  a  compound  of  fluoric 
and  boracic  acids.  The  lime  of  fluor-spar  is  supposed  to  unite  with  one 
portion  of  boracic  acid,  and  fluoric  acid  at  the  moment  of  separation  with 
another,  yielding  borate  of  lime  and  fluoboric  acid  gas.  , 

Prop. — It  is  a  colourless  gas,  has  a  penetrating  pungent  odour,  and  extin- 

fuishes  flame  on  the  instant.  Its  sp.  gr.,  according  to  Thomson,  is  2-3622. 
t  reddens  litmus  paper  as  powerfully  as  sulphuric  acid,  and  forms  salts 
with  alkalies  which  are  called  fluoborates.  It  has  a  singularly  great  affinity 
for  water.  When  mixed  with  air  or  any  gas  which  contains  watery  vapour, 
a  dense  white  cloud,  a  combination  of  water  and  fluoboric  acid,  appears, 
thus  affording  an  extremely  delicate  test  of  the  presence  of  moisture  in  gases. 
Water  acts  powerfully  on  this  gas,  absorbing,  according  to  Dr.  Davy,  700 
times  its  volume,  during  which  the  water  increases  in  temperature  and 
volume.  The  solution  is  limpid,  fuming,  and  very  caustic.  On  the  applica- 
tion of  heat,  part  of  the  gas  is  disengaged ;  but  afterwards  the  whole  solution 
is  distilled. 

Gay-Lussac  and  Thenard,  and  Dr.  Davy  were  of  opinion  that  fluoboric 
acid  gas  is  dissolved  by  water  without  decomposition ;  but  Berzelius  denies 
the  accuracy  of  their  observation.  On  transmitting  the  gas  into  water  until 
the  liquid  acquires  a  sharply  sour  taste,  but  is  far  from  being  saturated,  a 
white  powder  begins  to  subside;  and,  on  cooling,  a  considerable  quantity  of 
boracic  acid  is  deposited  in  crystals.  It  appears  that  in  a  certain  state  of 
dilution,  part  of  the  fluoboric  acid  and  water  mutually  decompose  each  other, 
with  formation  of  boracic  and  hydrofluoric  acids.  The  latter  unites,  accord- 
ing- to  Berzelius,  with  undecomposed  fluoboric  acid,  forming  what  he  has 
called  boro-hydrqfluoric  acid.  On  concentrating  the  liquid  by  evaporation, 
the  boracic  and  hydrofluoric  acids  decompose  each  other,  and  the  original 
compound  is  reproduced. 

Fiuoboric  acid  gas  does  not  act  on  glass,  but  attacks  animal  and  vegetable 
matters  with  energy,  converting  them,  like  sulphuric  acid,  into  a  carbona- 
ceous substance.  This  action  is  most  probably  owing  to  its  affinity  for 
water. 

When  potassium  is  heated  in  fluoboric  acid  gas,  the  metal  takes  fire,  and 
a  chocolate-coloured  solid,  wholly  devoid  of  metallic  lustre,  is  formed.  This 
substance  is  a  mixture  of  boron  and  fluoride  of  potassium,  from  which  the 
latter  is  dissolved  by  water,  and  the  boron  is  left  in  a  solid  state. 

The  composition  of  fluoboric  acid  gas  has  not  hitherto  been  determined  by 
direct  experiment.  Dr.  Davy  ascertained  that  it  unites  with  an  equal 
measure  of  ammoniacal  gas,  forming  a  solid  salt;  and  that  it  also  combines 
with  twice  and  three  times  its  volume  of  ammonia,  yielding  liquid  com- 
pounds. In  the  former  salt  the  relative  weights  of  the  constituent  gases  are 
in  the  ratio  of  their  specific  gravities;  and  if  the  compound  consists  of  one 
equivalent  of  each,  it  will  be  constituted  of, 

Fluoboric  acid  gas        .        .        2-3622        .        68-69  one  eq. 
Ammoniacal  gas  .         .         0-5897         .         17-15  one  eq. 

so  that  the  equivalent  of  the  acid,  thus  deduced,  is  68-69.  But  supposing  it 
to  be  formed  of  three  eq.  of  fluorine  and  one  of  boron,  its  eq.  would  be  66-94, 
a  number  which  approximates  to  the  preceding.  This  view  is  consistent 
with  the  composition  of  boracic  acid,  as  given  at  page  205,  and  with  the  con- 
version of  fluoboric  acid  by  water  into  hydrofluoric  and  boracic  acids, 


244  FLUORINE. 

Its  symb.  is  B-f-3F,  or  BF*. 

Fluosilicic  Acid. — Prep. — This  gas  is  formed  whenever  hydrofluoric  and 
silicic  acids  come  in  contact ;  and  hence  pure  hydrofluoric  acid  can  be  pre- 
pared in  metallic  vessels  only,  and  with  fluor-spar  that  is  free  from  rock 
crystal.  The  most  convenient  method  of  procuring  it,  is  to  mix  in  a  retort 
one  part  of  pulverized  fluor-spar  with  its  own  weight  of  sand  or  pounded 
glass,  and  two  parts  of  strong  sulphuric  acid.  On  applying  a  gentle  heat, 
fluosilicic  acid  gas  is  disengaged  with  effervescence,  and  may  be  collected 
over  mercury. 

The  chemical  changes  attending  this  process  are  differently  explained, 
according  to  the  view  which  is  taken  concerning  the  nature  of  the  product. 
In  regarding  fluor-spar  as  a  compound  of  fluoric  acid  and  lime,  the  former 
at  the  moment  of  being  set  free  is  thought  to  unite  directly  with  silicic  acid, 
thereby  giving  rise  to  a  compound  of  silicic  and  fluoric  acids.  But  for 
reasons  already  stated  (page  242,)  fluor-spar  is  not  considered  as  fluate  of 
lime;  and,  therefore,  this  view  cannot  be  admitted.  It  is  inferred,  on  the 
contrary,  that  when,  by  the  action  of  sulphuric  acid  on  fluoride  of  calcium, 
hydrofluoric  acid  is  generated,  the  elements  of  this  acid  react  on  those  of 
silicic  acid,  and  give  rise  to  the  production  of  water  and  fluosilicic  acid  gas. 
This  gas  is,  therefore,  a  fluoride  of  silicon.  It  may  occur  to  some  whether 
hydrofluoric  acid  does  not  unite  directly  with  silicic  acid;  but  this  idea  is 
inconsistent  with  the  proportion  in  which  the  elements  of  the  gas  are  found 
to  be  united. 

Prop. — It  is  a  colourless  gas  which  extinguishes  flame,  destroys  animals 
that  are  emersed  in  it,  and  irritates  the  respiratory  organs  powerfully.  It 
does  not  corrode  glass  vessels  provided  they  are  quite  dry.  When  mixed 
with  atmospheric  air  it  forms  a  white  cloud,  owing  to  the  presence  of  watery 
vapour.  Its  sp.  gr.,  according  to  Thomson,  is  3-6111 ;  and  300  cubic  inches 
of  it  at  60°,  and  when  the  barometer  stands  at  30  inches,  weigh  111-985 
grains. 

Water  acts  powerfully  on  fluosilicic  acid  gas,  of  which  it  condenses,  ac- 
cording to  Dr.  Davy,  365  times  its  volume  (Phil.  Trans,  for  1812.)  The  gas 
suffers  decomposition  at  the  moment  of  contact  with  water,  silicic  acid  in 
the  form  of  a  gelatinous  hydrate  being  deposited,  which  when  well  washed 
is  quite  pure.  The  liquid,  which  has  a  sour  taste  and  reddens  litmus  paper, 
contains  the  whole  of  the  hydrofluoric  acid,  together  with  two-thirds  of  the 
silicic  acid  which  was  originally  present  in  the  gas.  (Berzelius.)  By  con- 
ducting fluosilicic  acid  gas  into  a  solution  of  ammonia,  complete  decomposi- 
tion ensues: — hydrofluoric  acid  unites  with  the  alkali,  forming  hydrofluate 
of  ammonia,  and  all  the  silicic  acid  is  deposited.  On  this  fact  is  founded 
the  mode  of  analyzing  fluosilicic  acid  gas,  adopted  by  Dr.  Davy  and  Thomson. 

The  solution  which  is  formed  by  fully  saturating  water  with  fluosilicic 
acid  gas  is  powerfully  acid,  and  emits  fumes  on  exposure  to  the  air.  It  is 
commonly  known  by  the  name  of  silicated  fluoric  acid  ;  but  a  more  appro- 
priate term  is  silico-hydrofluoric  acid.  According  to  the  experiments  of 
Berzelius,  it  appears  to  be  a  definite  compound  of  hydrofluoric  and  silicic 
acids  in  the  ratio  of  three  eq.  of  the  former  to  two  of  the  latter.  If  evapo- 
rated before  separation  from  the  silicic  acid  deposited  by  the  action  of  water 
on  fluosilicic  acid  gas,  this  compound  is  reproduced.  But  if  the  solution  is 
poured  off  from  the  silicic  acid  thus  deposited,  and  then  evaporated,  fluo- 
silicic acid  gas  is  at  first  evolved,  and  subsequently  hydrofluoric  acid  and 
water  are  expelled.  The  evaporation  of  silico-hydrofluoric  acid  in  vacua  is 
attended  by  a  similar  change,  so  that  this  acid  cannot  be  obtained  free  from 
water.  It  does  not  corrode  glass;  but  when  evaporated  in  glass  vessels,  the 
production  of  free  hydrofluoric  acid  of  course  gives  rise  to  corrosion. 

On  neutralizing  silico-hydrofluoric  acid  with  ammonia,  and  gently  evapo- 
rating to  dryness,  all  the  silicic  acid  is  rendered  insoluble.  By  exactly  neu- 
tralizing with  carbonate  of  potassa,  a  sparingly  soluble  double  fluoride  of 
silicon  and  potassium  subsides;  the  precipitation  is  still  more  complete  with 
chloride  of  barium,  when  the  insoluble  fluoride  of  silicon  and  barium  is  gs- 


HYDROGEN  AND  NITROGEN. — AMMONIACAL  GAS.  245 

nerated.     A  variety  of  similar  compounds  may  be  obtained  either  by  double 
decomposition,  or  by  the  action  of  silico-hydrofluoric  acid  on  metallic  oxides 
Its  eq.  is  78-54 ;  symb.  Si+3F,  or  SiF*. 


ON  THE  COMPOUNDS  OF  THE  SIMPLE  NON-METALLIC 
ACIDIFIABLE  COMBUSTIBLES  WITH  EACH  OTHER. 


SECTION    I. 
HYDROGEN  AND  NITROGEN.— AMMONIACAL  GAS. 

Hist,  and  Prep. — THE  aqueous  solution  of  ammonia,  under  the  name  of 
spirit  of  hartshorn,  has  been  long  known  to  chemists ;  but  its  existence  as  a 
gas  was  first  noticed  by  Priestley,  who  described  it  in  his  works  under  the 
title  of  alkaline  air.  It  is  often  called  the  volatile  alkali;  but  the  terms  am- 
monia and  ammoniacal  gas  are  now  usually  employed. 

An  abundant  supply  of  ammoniacal  gas  may  be  obtained  from  any  salt  of 
ammonia  by  the  action  of  a  pure  alkali  or  alkaline  earth;  but  hydrochlorate 
of  ammonia  and  lime,  from  economical  considerations,  are  always  employed. 
The  proportions  to  which  I  give  the  preference  are  equal  parts  of  hydro- 
chlorate  of  ammonia  and  well-burned  quicklime,  considerable  excess  of  lime 
being  taken,  in  order  to  decompose  the  hydrochlorate  more  expeditiously  and 
completely.  The  lime  is  slaked  by  the  addition  of  water;  and  as  soon  as  it 
has  fallen  into  powder,  it  should  be  placed  in  an  earthen  pan  and  be  covered 
till  it  is  quite  cold,  in  order  to  protect  it  from  the  carbonic  acid  of  the  air. 
It  is  then  mixed  in  a  mortar  with  the  hydpochlorate  of  ammonia,  previously 
reduced  to  a -fine  powder;  and  the  mixture  is  put  into  a  retort  or  other  con- 
venient glass  vessel.  Heat  is  then  applied,  and  the  temperature  gradually 
increased  as  long  as  free  evolution  of  gas  continues.  The  ammonia  should 
be  conducted  by  means  of  a  safety  tube  of  Welter  into  a  quantity  of  distilled 
water  equal  to  the  weight  of  the  salt  employed.  The  residue  consists  of 
chloride  of  calcium  and  lime. 

The  gas,  thus  liberated,  must  be  collected  over  mercury,  as  it  is  most 
rapidly  absorbed  by  water.  Advantage  is  taken  of  this  property  to  prepare 
what  is  commonly  though  incorrectly  termed  liquid  ammonia.  For  this 
purpose  a  current  of  gas  is  transmitted  into  distilled  water,  which  is  kept 
eool  by  means  of  ice  or  moist  cloths,  and  the  process  is  continued  as  long  as 
any  gas  is  absorbed.  A  highly  concentrated  solution  of  ammonia  is  thus 
obtained.  The  most  convenient  method  of  preparing  ammoniacal  gas  for 
purposes  of  experiment  is  by  applying  a  gentle  heat  to  the  concentrated  so- 
lution, contained  in  a  glass  vessel.  It  soon  enters  into  ebullition,  and  a 
large  quantity  of  pure  ammonia  is  disengaged. 

Prop. — Ammonia  is  a  colourless  gas,  which  has  a  strong  pungent  odour, 
and  acts  powerfully  on  the  eyes  and  nose.  It  is  quite  irrespirable  in  its  pure 
form,  but  when  diluted  with  air,  it  may  be  taken  into  the  lungs  with  safety. 
Burning  bodies  are  extinguished  by  it,  nor  is  the  gas  inflamed  by  their  ap- 
proach. Ammonia,  however,  is  inflammable  in  a  low  degree;  for  when  a 
lighted  candle  is  immersed  in  it,  the  flame  is  somewhat  enlarged,  and  tinged 
of  a  pale  yellow  colour  at  the  moment,  of  being  extinguished  ;  and  a  small 
jet  of  the  gas  will  burn  in  an  atmosphere  of  oxygen.  A  mixture  of  ammo- 
niacal and  oxygen  gases  detonates  by  the  electric  spark ;  water  being  forrn- 

21* 


246  HYDROGEN  AND  NITROGEN. — AMMONIACAL  GAS, 

ed,  and  nitrogen  set  free.  A  little  nitric  acid  is  generated  at  the  same  time, 
except  when  a  smaller  quantity  of  oxygen  is  employed  than  is  sufficient  for 
combining  with  all  the  hydrogen  of  the  ammonia.  (Henry,  Phil.  Trans.  1809.) 

Ammoniacal  gas  at  the  temperature  of  50°  and  under  a  pressure  equal  to 
6'5  atmospheres,  becomes  a  transparent  colourless  liquid.  I,t  is  also  liquefied, 
according  to  Guyton-Morveau,  under  the  common  pressure,  by  a  cold  of 
— 70°  ;  but  there  is  no  doubt  that  the  liquid  which  he  obtained  was  a  solu- 
tion of  ammonia  in  water. 

It  has  all  the  properties  of  an  alkali  in  a  very  marked  manner.  Thus  it 
has  an  acrid  taste,  and  gives  a  brown  stain  to  turmeric  paper  ;  though  the 
yellow  colour  soon  reappears  on  exposure  to  the  air,  owing  to  the  volatility 
of  the  alkali.  It  combines  also  with  acids,  and  neutralizes  their  properties 
completely.  All  these  salts  suffer  decomposition  by  being  heated  with  the 
fixed  alkalies  or  alkaline  earths,  such  as  potassa  or  lime,  the  union  of  which 
with  the  acid  of  the  salt  causes  the  separation  of  its  ammonia.  None  of 
the  ammoniacal  salts  can  sustain  a  red  heat  without  being  dissipated  in  va- 
pour or  decomposed,  a  character  which  manifestly  arises  from  the  volatile 
nature  of  the  alkali.  If  combined  with  a  volatile  acid,  such  as  the  hydro- 
chloric, the  compound  itself  sublimes  unchanged  by  heat;  but  when  united 
with  an  acid,  which  is  fixed  at  a  low  red  heat,  such  as  the  phosphoric,  the 
ammonia  alone  is  expelled.  It  is  here  considered  that  the  salts  of  ammonia 
are  formed  by  its  direct  union  with  acids.  Another,  and  a  very  scientific 
view,  has  been  adopted  by  JBerzelius.  When  an  electric  current  is  passed 
through  a  weak  solution  of  ammonia,  it  is  decomposed  by  the  secondary 
action,  hydrogen  from  decomposed  water  being  evolved  at  the  negative  elec- 
trode, and  nitrogen  at  the  positive  (Faraday,  Phil.  Trans.  1834.)  But  if  a 
portion  of  mercury  form  the  negative  electrode,  no  hydrogen  is  evolved,  and 
the  mercury  is  rapidly  converted  into  a  light  porous  substance,  which  has 
the  lustre  and  all  the  characters  of  an  amalgam.  As  soon  as  it  is  removed 
from  the  influence  of  the  electric  current,  rapid  decomposition  ensues,  mer- 
cury is  reproduced,  and  hydrogen  and  ammoniacal  gases  are  evolved  in  the 
ratio  of  one  measure  of  the  former  to  two  of  the  latter,  according  to  the 
observations  of  Gay-Lussac  and  Theriard.  The  production  of  this  com- 
pound is  explained  by  Berzelius  on  the  supposition  that  ammonia  by  uniting 
with  an  additional  eq.  of  hydrogen  forms  a  compound,  which  has  all  the 
properties  of  a  metal;  he,  therefore,  calls  it  ammonium.  The  oxide  of  am- 
monium, the  composition  of  which  is  represented  by  the  formula  NH^-f-O, 
he  considers  to  be  the  base  of  the  ammoniacal  salts.  This  view  is  supported 
by  several  facts,  which  will  be  considered  when  treating  of  the  salts. 

Hydrogen  and  nitrogen  gases  do  not  unite  directly,  and,  therefore,  che- 
mists have  no  synthetic  proof  of  the  constitution  of  ammonia.  Its  compo- 
sition, however,  has  been  determined  analytically  with  great  exactness. 
When  a  succession  of  electric  sparks  is  passed  through  ammoniacal  gas,  it  is 
resolved  into  its  elements;  and  the  same  effect  is  produced  by  conducting  it 
through  porcelain  tubes  heated  to  redness.  A.  Berthollet  analyzed  ammonia 
in  both  ways,  and  ascertained  that  200  measures  of  that  gas,  on  being  de- 
composed, occupy  the  space  of  400  measures,  300  of  which  are  hydrogen, 
and  100  nitrogen.  Henry  has  made  an  analysis  of  ammonia  by  means  of 
electricity,  and  his  experiment  proves  beyond  a  doubt  that  the  proportions 
above  given  are  rigidly  exact.  (Annals  of  Philosophy,  xxiv.  346.) 

Grains. 

Now  since  150  cubic  inches  of  hydrogen  weigh   -        -        3-2050 
and  50  of  nitrogen  -  15-0825 

100  cubic  inches  of  ammonia  must  weigh    -        -        -      18-2875 
and  it  is  composed  by  weight  of 

Hydrogen    -        -        3-2050  3        -        or  three  equivalents. 

Nitrogen      -        -       15-0825        -      14-15    -        or  one  equivalent. 


COMPOUNDS  OF  HYDROGEN  AND  CARBON. 


247 


The  sp,  gr.  of  ammonia,  according  to  this  calculation,  is  0-5897,  a  number 
which  agrees  closely  with  those  ascertained  directly  by  Davy  and  Thom- 
son. 

Ammoniacal  gas  has  a  powerful  affinity  for  water.  Owing  to  this  attrac- 
tion, a  piece  of  ice,  when  introduced  into  a  jar  full  of  ammonia,  is  instantly 
liquefied,  and  the  gas  disappears  in  the  course  of  a  few  seconds.  Davy,  in 
his  Elements,  stated  that  water  at  50°,  and  when  the  barometer  stands  at 
29-8  inches,  absorbs  670  times  its  volume  of  ammonia,  and  that  the  solution 
has  a  sp.  gr.  of  0*875.  According1  to  Thomson,  water  at  the  common  tem- 
perature and  pressure  takes  up  780  times  its  bulk.  By  strong  compression, 
water  absorbs  the  gas  in  still  greater  quantity.  Heat  is  evolved  during  its 
absorption;  and  a  considerable  expansion,  independently  of  the  increased 
temperature,  occurs  at  the  same  time. 

The  concentrated  solution  of  ammonia  is  a  clear  colourless  liquid,  of  sp. 
gr.  0-936.  It  possesses  the  peculiar  pungent  odour,  taste,  alkalinity,  and 
other  properties  of  the  gas  itself.  On  account  of  its  great  volatility  it  should 
be  preserved  in  well-stopped  bottles,  a  measure  which  is  also  required  to  pre- 
vent the  absorption  of  carbonic  acid.  At  a  temperature  of  130°  it  enters 
into  ebullition,  owing  to  the  rapid  escape  of  pure  ammonia ;  but  the  whole 
of  the  gas  cannot  be  expelled  by  this  means,  as  at  last  the  solution  itself 
evaporates.  It  freezes  at  about  the  same  temperature  as  mercury. 

The  following  table,  from  Davy's  Elements  of  Chemical  Philosophy, 
shows  the  quantity  of  real  ammonia  contained  in  100  parts  of  solutions  of 
different  sp.  gravities  at  59°  F.  arid  when  the  barometer  stands  at  30  inches. 
The  sp.  gr.  of  water  is  supposed  to  be  10,000 : — 

Table  of  the  Quantity  of  real  Ammonia  in  Solutions  of  different  Densities. 


100  parts  of 

Of  real 

100  parts  of 

Of  real 

sp.  gravity. 

Ammonia. 

sp.  gravity. 

Ammonia. 

8750 

32-5 

9435 

14-53 

8875 

29-25 

9476 

13-46 

9000 

M 

26-00 

9513 

a 

12-40 

9054 

1 

2537 

9545 

| 

11-56 

9166 

8 

22-07 

9573 

0 

10-82 

9255 

19-54 

9597 

10-17 

9326 

17-5-2 

9619 

9-60 

9385 

15-88 

9692 

9-50 

The  presence  of  free  ammoniacal  gas  may  always  be  detected  by  its  odour 
by  its  temporary  action  on  yellow  turmeric  paper,  and  by  its  forming  dense 
white  fumes— hydrochlorate  of  ammonia—when  a  glass  rod  moistened  with 
hydrocloric  acid  is  brought  near  it- 
Its  eq.  is  17-15 ;  eq.  vol.=200 ;  symb.  N-f3H, 


SECTION    II. 

*'•"••*.  *'v 

COMPOUNDS  OF  HYDROGEN  AND  CARBON. 

CHEMISTS  have  for  several  years  been  acquainted  with  two  distinct  com- 
pounds of  carbon  and  hydrogen,  viz.  carburetted  hydrogen  and  olefiant  ffases  • 
but  late  researches  have  enriched  the  science  with  several  other  compounds 
of  a  similar  nature,  to  which  much  interest  is  attached.  They  are  remark- 


248  COMPOUNDS  OF  HYDROGEN  AND  CARBON. 

able  for  their  number,  for  supplying  some  instructive  instances  of  isomerism, 
and  for  their  tendency  to  unite  with  and  even  neutralize  powerful  acids, 
without,  in  their  uncombined  state,  manifesting  any  ordinary  signs  of  alka- 
linity. Several  of  them  are  particularly  distinguished  by  their  chemical  affi- 
nities ;  for  although  compound,  they  exhibit,  in  their  combinations  with 
other  substances,  the  characteristics  of  an  element.  They  have  hence  been 
called  compound  radicals.  These  compound  radicals  are  closely  associated 
both  with  organic  and  inorganic  chemistry.  In  the  latter  they  must 
hold  a  place,  as  being  compounds  formed  by  the  direct  union  of  two  ele- 
ments ;  and  in  the  former  they  are  the  roots  or  radicals  of  the  various  organic 
products.  The  following  tabular  view  represents  the  composition  of  those 
which  have  as  yet  been  studied. 

Hydrogen.     Carbon.         Equiv.   Formulae. 
Light  carburetted  hydrogen    2    2  eq.-f-  6-12     1  eq.=  8-12 
Olefiantgas       ...       2     2  eq.-|-12-24     2  eq.= 14-24 
Etherine  .'•        .        .4    4  eq.-f- 24-48    4  eq.=28-48 

Paraffine       ."•     "  •"       •/ 

Eupione        '    .    '    .        .  f  Same  ratio  of  elements  as  in  etherine,  but  eq. 


Rose-oil-stearine        .        .{ 

f        is  unknown. 

Wax-oil    .        .    ,  :;;.;•'    . 

S 

Benzin,  or  bicarburet   of' 
hydrogen      .  .,  «'  »\     . 

/ 

(33  eq.4-36-72     6  eq.=39-72 

Naphtha  .       '.         .-•';.. 

5    5eq.+36-72    6  eq.=41-72 

Oil  of  turpentine 

Citrine     ... 

Camphine         ',         .         .* 

Oil  of  copaiva  .        .        .  f 

Juniper  oil   ;    .        .         .  / 

"8    8eq.+  61-2     10  eq.==69-2 

Lemon  oil        .        .        A 

Savin-tree  oil  .         .         . 

) 

Black  pepper  oil      .         .  s 

Naphthaline     .         ,         '<\ 
Paranaphthaline       .         .  < 

>  4    4  eq.-f-61-2     10  eq.=  65-2 

Idrialine          .         .         . 

1  7     7  eq.4-122-4  20  eq.=  129-4 

H:Cso 

Light  Carburetted  Hydrogen. — Hist. — This  gas  is  sometimes  called  heavy 
inflammable  air,  the  inflammable  air  of  marshes,  and  hydrocarburet.  Agree- 
ably to  the  principles  of  chemical  nomenclature,  taking  carbon  as  the  electro- 
negative element,  it  is  a  dicarburet  of  hydrogen  ;  but  it  is  generally  termed 
light  carburetted  hydrogen.  It  is  formed  abundantly  in  stagnant  pools  dur- 
ing the  spontaneous  decomposition  of  dead  vegetable  matter ;  and  it  may 
readily  be  procured  by  stirring  the  mud  at  the  bottom  of  them,  and  collect- 
ing the  gas,  as  it  escapes,  in  an  inverted  glass  vessel.  In  this  state  it  is 
found  to  contain  l-20th  of  carbonic  acid  gas,  which  may  be  removed  by 
means  of  lime-water  or  a  solution  of  pure  potassa,  and  l-15th  or  l-20th  of 
nitrogen.  This  is  the  only  convenient  method  of  obtaining  it. 

Prop. — Colourless,  tasteless,  near  inodorous;  always  gaseous  when  uncom- 
bined ;  does  not  change  the  colour  of  litmus  or  turmeric  paper.  Water, 
according  to  Henry,  absorbs  about  l-60th  of  its  volume.  It  extinguishes  all 
burning  bodies,  and  is  unable  to  support  the  respiration  of  animals.  It  is 
highly  inflammable ;  and  when  a  jet  of  it  is  set  on  fire,  it  burns  with  a  yellow 
flame,  and  with  a  much  stronger  light  than  is  occasioned  by  hydrogen  gas. 
With  a  due  proportion  of  atmospheric  air  or  oxygen  gas,  it  forms  a  mixture 
which  detonates  powerfully  with  the  electric  spark,  or  by  the  contact  of 
flame.  The  sole  products  of  the  explosion  are  water  and  carbonic  acid. 

Dalton  first  ascertained  the  real  nature  of  light  carburetted  hydrogen;  and 
it  has  since  been  particularly  examined  by  Thomson,  Davy,  and  Henry. 
When  100  meususes  are  detonated  with  rather  more  than  twice  their  volume 


COMPOUNDS  OF  HYDROGEN  AND  CARBON.  249 

of  oxygen  gas,  the  whole  of  the  inflammable  gas  and  precisely  200  measures 
of  the  oxygen  disappear,  water  is  condensed,  and  100  measures  of  carbonic 
acid  are  produced.  Now  100  measures  of  carbonic  acid  gas  contain  (page  187) 
100  of  carbon  vapour  and  100  of  oxygen  gas,  just  half  the  oxygen  which  had 
been  employed;  and  the  remaining  oxygen  requires  200  measures  of  hydro- 
gen to  form  water.  Hence  as,  at  60°  F.  and  30  inches  Bar., 

Grains. 

100  cubic  inches  of  carbon  vapour  weigh     .         .-    '.         13-0714 
200  do.  hydrogen  gas         .         .       V    'V         4-2734 


100  do.  light  carburetted  hydrogen  must  weigh  17-3448 

These  weights  are  obviously  in  the  ratio  of  2  to  6-12,  as  already  assigned; 
and  the  sp.  gr.  of  such  a  gas  ought  to  be  0-5593,  which  is  nearly  the  quantity 
found  experimentally  by  Thomson  and  Henry. 

Light  carburetted  hydrogen  is  not  decomposed  by  electricity,  nor  by  being 
passed  through  red-hot  tubes,  unless  the  temperature  is  very  intense,  in 
which  case  some  of  the  gas  does  suffer  decomposition,  each  volume  yielding 
two  volumes  of  pure  hydrogen  gas  and  a  deposite  of  charcoal.  Mixed  with 
chlorine,  no  action  takes  place  at  common  temperatures,  when  quite  dry,  even 
if  exposed  to  the  direct  solar  rays.  If  moist,  and  the  mixture  is  kept  in  a 
dark  place,  still  no  action  ensues ;  but  if  light  be  admitted,  particularly  sun- 
shine, decomposition  follows.  The  nature  of  the  products  depends  upon  the 
proportion  of  the  gases.  If  four  measures  of  chlorine  and  one  of  light  car- 
buretted hydrogen  are  present,  carbonic  and  hydrochloric  acid  gases  will  be 
produced :  two  volumes  of  chlorine  combine  with  two  volumes  of  hydrogen 
contained  in  the  carburetted  hydrogen,  and  the  other  two  volumes  of  chlorine 
decompose  so  much  water  as  will  likewise  give  two  volumes  of  hydrogen, 
forming  hydrochloric  acid ;  while  the  oxygen  of  the  water  unites  with  the 
carbon,  and  converts  it  into  carbonic  acid.  If  there  are  three  instead  of  four 
volumes  of  chlorine,  carbonic  oxide  will  be  generated  instead  of  carbonic 
acid,  because  one-half  less  water  will  be  decomposed  (Henry).  If  a  mixture 
of  chlorine  and  light  carburetted  hydrogen  is  electrified  or  exposed  to  a  red- 
heat,  hydrochloric  acid  is  formed  and  charcoal  deposited. 

Its  eq.  is  8-12;  eq.  vol.  =  100;  symb.  H2C. 

It  was  first  ascertained  by  Henry  (Nicholson's  Journal,  vol.  xix.) ;  and  his 
conclusions  have  been  fully  confirmed  by  the  subsequent  researches  of  Davy, 
that  the  jive-damp  of  coal-mines  consists  almost  solely  of  light  carburetted 
hydrogen.  This  gas  often  issues  in  large  quantity  from  between  beds  of  coal, 
and  by  collecting  in  mines,  owing  to  deficient  ventilation,  gradually  mingles 
with  atmospheric  air,  and  forms  an  explosive  mixture.  The  first  unprotected 
light  which  then  approaches,  sets  fire  to  the  whole  mass,  and  an  explosion 
ensues.  These  accidents,  which  were  formerly  so  frequent  and  so  fatal,  are 
now  comparatively  rare,  owing  to  the  employment  of  the  safety-lamp.  For 
this  invention  we  are  indebted  to  Davy,  who  established  the  principles  of  its 
construction  by  a  train  of  elaborate  experiment  and  close  reasoning,  which 
may  be  regarded  as  one  of  the  happiest  efforts  of  his  genius,  (Essay  on 
Flame). 

Davy  commenced  the  inquiry  by  determining  the  best  proportion  of  air 
and  light  carburetted  hydrogen  for  forming  an  explosive  mixture. '  When 
the  inflammable  gas  is  mixed  with  3  or  4  times  its  volume  of  air,  it  does  not 
explode  at  all.  It  detonates  feebly  when  mixed  with  5  or  6  times  its  bulk  of 
air,  and  powerfully  when  1  to  7  or  8  is  the  proportion.  With  14  times  its 
volume,  it  still  forms  a  mixture  which  is  explosive ;  but  if  a  larger  quantity 
of  air  be  admitted,  a  taper  burns  in  it  only  with  an  enlarged  flame. 

The  temperature  required  for  causing  an  explosion  was  next  ascertained. 
It  was  found  that  the  strongest  explosive  mixture  may  come  in  contact  with 
iron  or  other  solid  bodies  heated  to  redness,  or  even  to  whiteness,  without 
detonating,  provided  they  are  not  in  a  state  of  actual  combustion  ;  whereas 
the  smallest  point  of  flame,  owing  to  its  higher  temperature,  instantly 
causes  an  explosion. 


250  COMPOUNDS  OF  HYDROGEN  AND  CARBON. 

The  last  important  step  in  the  inquiry  was  the  observation  that  flame  can- 
not pass  through  a  narrow  tube.  This  led  to  the  discovery,  that  the  power  of 
tubes  in  preventing  the  transmission  of  flame  is  not  necessarily  connected 
with  any  particular  length;  and  that  a  very  short  one  will  have  the  effect, 
provided  its  diameter  is  proportionally  reduced.  Thus,  a  piece  of  fine  wire 
gauze,  which  may  be  regarded  as  an  assemblage  of  short  narrow  tubes,  is 
quite  impermeable  to  flame;  and  consequently,  if  a  common  oil  lamp  be 
completely  surrounded  with  a  cage  of  such  gauze,  it  may  be  introduced  into 
an  explosive  atmosphere  of  fire-damp  and  air,  without  kindling-  the  mixture. 
This  simple  contrivance,  which  is  appropriately  termed  the  safety-lamp,  not 
only  prevents  explosion,  but  indicates  the  precise  moment  of  danger.  When 
the  lamp  is  carried  into  an  atmosphere  charged  with  fire-damp,  the  flame 
begins  to  enlarge ;  and  the  mixture,  if  highly  explosive,  takes  fire  as  soon  as 
it  has  passed  through  the  gauze,  and  burns  on  its  inner  surface,  while  the 
light  in  the  centre  of  the  lamp  is  extinguished.  Whenever  this  appearance 
is  observed,  the  miner  must  instantly  withdraw;  for  though  the  flame  should 
not  be  able  to  communicate  with  the  explosive  mixture  on  the  outside  of  the 
lamp,  as  long  as  the  texture  of  the  gauze  remains  entire,  yet  the  heat  emit- 
ted during  the  combustion  is  so  great,  thai  the  wire,  if  exposed  to  it  for  a 
few  minutes,  would  suffer  oxidation,  and  fall  to  pieces. 

The  peculiar  operation  of  small  tubes  in  obstructing  the  passage  of  flame 
admits  of  a  very  simple  explanation.  Flame  is  gaseous  matter  heated  so  in- 
tensely as  to  be  luminous  ;  and  Davy  has  shown  that  the  temperature  ne- 
cessary for  producing  this  effect  is  far  higher  than  the  white  heat  of  solid 
bodies.  Now,  when  flame  comes  in  contact  with  the  sides  of  very  minute 
apertures,  as  when  wire  gauze  is  laid  upon  a  burning  jet  of  coal  gas,  it  is 
deprived  of  so  much  heat  that  its  temperature  instantly  falls  below  the  de- 
gree at  which  gaseous  matter  is  luminous ;  and  consequently,  though  the 
gas  itself  passes  freely  through  the  interstices,  and  is  still  very  hot,  it  is  no 
longer  incandescent.  Nor  does  this  take  place  when  the  wire  is  cold  only; 
— the  effect  is  equally  certain  at  any  degree  of  heat  which  the  flame  can 
communicate  to  it.  For  since  the  gauze  has  a  large  extent  of  surface,  and 
from  its  metallic  nature  is  a  good  conductor  of  heat,  it  loses  heat  with  great 
rapidity.  Its  temperature,  therefore,  though  it  may  be  heated  to  whiteness, 
is  always  so  far  below  that  of  flame,  as  to  exert  a  cooling  influence  over  the 
burning  gas,  and  reduce  its  heat  below  the  point  at  which  it  is  incandescent. 

These  principles  suggest  the  conditions  under  which  Davy's  lamp  would 
cease  to  be  safe.  If  a  lamp  with  its  gauze  red-hot  be  exposed  to  a  current 
of  explosive  mixture,  the  flame  may  possibly  pass  so  rapidly  as  not  to  be  cooled 
below  the  point  of  ignition,  and  in  that  case  an  accident  might  occur  with  a 
lamp  which  would  be  quite  safe  in  a  calm  atmosphere.  It  has  been  lately 
shown  by  Messrs.  Upton  and  Roberts,  lamp  manufacturers  of  London,  that 
flame  may  in  this  way  be  made  to  pass  through  the  safety-lamp  as  commonly 
constructed  ;  and  I  am  satisfied,  from  having  witnessed  some  of  their  experi- 
ments, that  the  observation  is  correct.  This  then  may  account  for  accidents 
in  coal-mines,  where  the  safety-lamp  is  constantly  employed.  An  obvious 
mode  of  avoiding  such  an  evil  is  to  diminish  the  apertures  of  the  gauze  ; 
but  this  remedy  is  nearly  impracticable  from  the  obstacle  which  very  fine 
gauze  causes  to  the  diffusion  of  light.  A  better  method  is  to  surround  the 
common  safety-lamp  with  a  glass  cylinder,  allowing  air  to  enter  solely  at 
the  bottom  of  the  lamp  through  wire  gauze  of  extreme  fineness,  placed  ho- 
rizontally, and  to  escape  at  top  by  a  similar  contrivance.  Upton  and  Roberts 
have  constructed  a  lamp  of  this  kind,  through  which  I  have  in  vain  tried  to 
cause  the  communication  of  flame,  and  which  appears  to  me  perfectly  se- 
cure :  should  an  accident  break  the  glass,  their  lamp  would  be  reduced  to  a 
safety-lamp  of  the  common  construction.  Davy's  lamp  thus  modified  gives 
a  much  better  light  than  without  the  glass,  just  as  all  lamps  burn  better 
with  a  shade  than  without  one. 

defiant   Gas. — Hist. — Discovered   in   1796   by    some   associated    Dutch 
chemists,  who  gave  it  the  name  of  olefiant  gas,  from  its  property  of  forming 


"  .       COMPOUNDS  OF  HYDROGEN  AND  CARBON.  251 

an  oil-like  liquid  with  chlorine.  It  is  sometimes,  but  very  improperly,  called 
bicarburetted  or  percarburetted  hydrogen.  The  ratio  of  its  elements  being 
as  one  eq.  to  one  eq.  suggests  the  term  carburet  of  hydrogen  ;  but  this  does 
not  indicate  that  two  eq.  of  carbon  are  combined  with  two  eq.  of  hydrogen 
to  form  one  eq.  of  the  gas.  Perhaps  the  expression  -'_.  carburet  of  hydrogen 
will  adequately  express  this,— a  principle  of  nomenclature  already  adopted 
by  some  of  the  German  chemists. 

Prep. — By  mixing  in  a  capacious  retort  one  part  by  weight  of  absolute 
alcohol  with  four  of  concentrated  sulphuric  acid,  and  heating  the  mixture  as 
soon  as  it  is  made.  The  acid  soon  acts  upon  the  alcohol,  effervescence  ensues, 
and  olefiant  gas  passes  over.  The  chemical  changes  which  take  place  are 
of  a  complicated  nature,  and  the  products  numerous.  At  the  commencement 
of  the  process,  the  olefiant  gas  is  mixed  only  with  a  little  ether ;  but  in  a 
short  time  the  solution  becomes  dark,  the  formation  of  ether  declines,  and 
the  odour  of  sulphurous  acid  begins  to  be  perceptible:  towards  the  close  of 
the  operation,  though  olefiant  gas  is  still  the  chief  product,  sulphurous  acid 
is  freely  disengaged,  some  carbonic  acid  is  formed,  and  charcoal  in  large 
quantity  deposited.  The  olefiant  gas  may  be  collected  either  over  water  or 
mercury.  The  greater  part  of  the  ether  condenses  spontaneously  ;  and  the 
sulphurous  and  carbonic  acids  may  be  separated  by  washing  the  gas  with 
lime-water,  or  a  solution  of  pure  potassa.  The  olefiant  gas  in  this  process 
is  derived  solely  from  the  alcohol ;  the  theory  of  its  formation,  as  well  as 
that  of  the  accompanying  products,  will  be  given  under  the  head,  Alcohol. 

Prop. — Colourless,  tasteless,  inodorous;  hitherto  only  known  in  a  gaseous 
state.  Water  absorbs  about  one-eighth  of  its  volume.  Like  the  preceding- 
compound,  it  extinguishes  flame,  is  unable  to  support  the  respiration  of  ani- 
mals, and  is  set  on  fire  when  a  lighted  candle  is  presented  to  it,  burning 
slowly  with  the  emission  of  a  dense  white  light.  With  a  proper  quantity  of 
oxygen  gas,  it  forms  a  mixture  which  may  be  kindled  by  flame  or  the  elec- 
tric spark,  and  which  explodes  with  great  violence.  To  burn  it  completely, 
it  should  be  detonated  with  four  or  five  limes  its  volume  of  oxygen.  On 
conducting  this  experiment  with  the  requisite  care,  Henry  finds  that  for 
each  measure  of  olefiant  gas,  precisely  three  of  oxygen  disappear,  deposition 
of  water  takes  place,  and  two  measures  of  carbonic  acid  are  produced. 
From  these  data  the  proportion  of  its  constituents  may  easily  be  deduced  in 
the  following  manner  : — Two  measures  of  carbonic  acid  contain  two  mea- 
sures of  the  vapour  of  carbon,  which  must  have  been  present  in  the  olefiant 
gas,  and  two  measures  of  oxygen.  Two-thirds  of  the  oxygen  which  disap- 
peared are  thus  accounted  for ;  and  the  other  third  must  have  combined 
with  hydrogen.  But  one  measure  of  oxygen  requires  for  forming  water  pre- 
cisely two  measures  of  hydrogen,  which  must  likewise  have  been  contained 
in  the  olefiant  gas.  Hence,  as 

Grains. 

200  cubic  inches  of  the  vapour  of  carbon,  weigh         -         26'1428 
200         do  hydrogen  gas,  weigh         -  -  4*2734 

100  cubic  inches  of  olefiant  gas  must  weigh   -        ?'•<:      30-4162 

These  weights  are  in  the  ratio  12-24  or  two  equivalents  of  carbon  to  2  or 
two  eq.  of  hydrogen,  as  in  the  table.  The  sp.  gr.  of  a  gas  so  constituted 
(page  146)  should  be  0.9808;  whereas  the  density  found  experimentally  by 
Saussure  is  0-9852,  by  Henry  0-967,  and  by  Thomson  0-97. 

By  a  succession  of  electric  sparks  it  is  resolved  into  charcoal  and  hydro- 
gen ;  and  the  latter  of  course  occupies  twice  as  much  space  as  the  gas  from 
which  it  was  derived.  It  is  also  decomposed  by  transmission  through  red- 
hot  tubes  of  porcelain.  The  nature  of  the  products  varies  with  the  tem- 
perature. By  employing  a  very  low  degree  of  heat,  it  may  probably  be 
converted  solely  into  carbon  and  light  carburetted  hydrogen;  and  in  this 
case  no  increase  of  volume  can  occur,  because  these  two  gases,  for  equal 
bulks,  contain  the  same  quantity  of  hydrogen.  But  if  the  temperature  is 


252  COMPOUNDS  OF  HYDROGEN  AND  SULPHUR. 

high,  then  a  great  increase  of  volume  takes  place ;  a  circumstance  which 
indicates  the  evolution  of  free  hydrogen,  and  consequently  the  total  decora* 
position  of  some  of  the  olefiant  gas. 

Its  eq.  is  14-24;  eq.  vol.=100;  symb.  2H  +  2C,  or  HXX 
Chlorine  acts  powerfully  on  olefiant  gas.  When  these  gases  are  mixed 
together  in  the  ratio  of  two  measures  of  the  former  to  one  of  the  latter, 
they  form  a  mixture  which  takes  fire  on  the  approach  of  flame,  and  which 
burns  rapidly  with  formation  of  hydrochloric  acid  gas,  and  deposition  of  a 
large  quantity  of  charcoal.  But  if  the  gases  are  allowed  to  remain  at  rest 
after  being  mixed  together,  a  very  different  action  ensues.  The  chlorine, 
instead  of  decomposing  the  olefiant  gas,  enters  into  direct  combination  with 
it,  and  a  yellow  liquid  like  oil  is  generated.  Wohler  has  remarked  its  pro- 
duction by  the  contact  of  olefiant  gas  with  certain  metallic  chlorides,  espe- 
cially the  perchloride  of  antimony. 

The  other  compounds,  the  composition  of  which  is  given  at  page  248,  are 
described  under  Organic  Chemistry.  They  belong  to  this  department  not 
only  as  being  products  of  the  organic  kingdom,  but  also  on  account  of  their 
atomic  constitution  ;  for  whenever  they  are  acted  on  by  chlorine  or  any  other 
dehydrodizing  agents,  one  part  of  the  hydrogen,  which  enters  into  their 
composition,  is  shown  to  be  in  a  state  of  combination  different  from  the  rest. 
Thus  evidence  is  obtained  that  these  compounds,  although  composed  of 
nothing  but  hydrogen  and  carbon,  are  not  formed  by  the  direct  union  of 
these  elements,  but  that  a  portion  of  the  hydrogen  with  the  carbon  forms  a 
compound  radical,  which  acts  the  part  of  an  element,  and  combines  as  such 
with  the  remainder  of  the  hydrogen. 


SECTION  III. 


COMPOUNDS  OF  HYDROGEN  AND  SULPHUR. 

SULPHUR  unites  with  hydrogen  in  at  least  two  proportions,  and  the  result- 
ing compounds  are  thus  constituted:  — 

Hydrogen.     Sulphur.     Equiv.      Formulae. 

Hydrosulphuric  acid  1     1  eq.+16-l     1  eq.=  17-l  HS. 

Persulphuret  of  hydrogen  1     1  eq.-j-32  2     2  eq.=33-2  HSa. 

Hydrosulphuric  Acid.  —  Hist,  and  Prep.  —  Commonly  known  under  the 
name  of  sulphuretted  hydrogen.  It  is  best  prepared  by  heating  sesquisul- 
phuret  of  antimony  in  a  retort,  or  other  convenient  glass  vessel,  with  four  or 
five  times  its  weight  of  strong  hydrochloric  acid;  when,  by  an  interchange 
of  elements,  sesquichloride  of  antimony  and  hydrosulphuric  acid  are  ge- 
nerated, the  latter  of  which  escapes  with  effervescence.  The  elements  con- 
cerned before  and  after  the  change,  are 

1  eq.  sesquisulphuret  of  antimoriv,  and  3  eq.  hydrochloric  acid 


which  yield 

3  eq.  hydrosulphuric  acid,  and  1  eq.  sesquichloride  of  antimony. 
3(H-fS)  2Sb-f3Cl. 

It  may  also  be  formed  by  the  action  of  sulphuric  acid,  diluted  with  3  or  4 
parts  of  water,  on  protosulphuret  of  iron:  this  sulphuret  and  water  inter- 
change elements,  hydrosulphuric  acid  and  protoxide  of  iron  are  generated, 
and  the  latter  unites  with  sulphuric  acid,  while  the  former  in  a  state  of  gas 


.  COMPOUNDS  OP  HYDROGEN  AND  SULPHUR.  .  253 

is  rapidly  disengaged.  Hydrochloric  acid  may  be  substituted  for  the  sul- 
phuric. A  sulphuret  of  iron  may  be  procured  for  the  purpose/either  by  igniting 
common  iron  pyrites,  by  which  means  nearly  half  of  its  sulphur  is  expelled, 
or  by  exposing  to  a  low  red  heat,  a  mixture  of  two  parts  of  iron  filings  and 
rather  more  than  one  part  of  sulphur.  The  materials  should  be  placed  in  a 
common  earthen  or  cast-iron  crucible,  and  be  protected  as  much  as  possible 
from  the  air  during  the  process.  The  sulphuret  procured  from  iron  filings 
and  sulphur  always  contains  some  uncombined  iron,  and,  therefore,  the  gas 
obtained  from  it  is  never  quite  pure,  being  mixed  with  a  little  free  hydrogen. 
This,  however,  for  many  purposes,  is  immaterial. 

Prop. — Colourless  gas,  which  reddens  moist  litmus  paper  feebly,  and  is 
distinguished  from  all  other  gaseous  substances  by  its  offensive  taste  and 
odour,  which  is  similar  to  that  of  putrefying  eggs,  or  the  water  of  sulphurous 
springs.  Under  a  pressure  of  17  atmospheres,  at  50°,  it  is  compressed  into 
a  limpid  liquid,  which  resumes  the  gaseous  state  as  soon  as  the  pressure  is 
removed.  To  animal  life  it  is  very  injurious.  According  to  Dupuytren  and 
Thenard,  the  presence  of  l-1500th  of  this  gas  in  the  air  is  instantly  fatal  to 
a  small  bird ;  1-lOOOt.h  killed  a  middle-sized  dog;  and  a  horse  died  in  an  at- 
mosphere which  contained  l-250th  of  its  volume. 

It  extinguishes  all  burning  bodies ;  but  the  gas  takes  fire  when  a  lighted 
candle  is  immersed  in  it,  and  burns  with  a  pale  blue  flame.  Water  and  sul- 
phurous acid  are  the  products  of  its  combustion,  and  sulphur  is  deposited. 
With  oxygen  gas  it  forms  a  mixture  which  detonates  by  the  application  of 
flame  or  the  electric  spark  :  if  100  measures  of  it  are  exploded  with  150  of 
oxygen,  the  former  is  completely  consumed,  the  oxygen  disappears,  water  is 
deposited,  and  100  measures  of  sulphurous  acid  gas  remain  (Thomson). 
From  the  result  of  this  experiment,  the  composition  of  hydrosulphuric  acid 
gas  may  be  inferred;  for  it  is  clear,  from  the  composition  of  sulphurous  acid 
(page  192),  that  two-thirds  of  the  oxygen  must  have  combined  with  sulphur; 
and,  therefore,  that  the  remaining  one-third  contributed  to  the  formation  of 
water.  Consequently,  hydrosulphuric  acid  contains  its  own  volume  of  hy- 
di;ogen  gas,  and  16-66  of  the  vapour  of  sulphur;  and  since 

Grains. 

16-66  cubic  inches  of  the  vapour  of  sulphur  weigh   .  .~    34-4012 

100  do.  hydrogen  gas  weigh  .  .  2-1367 

100  do.  hydrosulphuric  acid  gas  must  weigh         36'5379 

The  sp.  gr.  of  a  gas  so  constituted  should  be  1-1782,  which  agrees  with  ob- 
servations; and  its  elements  are  in  the  ratio  of  1  to  16-1,  as  already  men- 
tioned. 

The  accuracy  of  this  view  is  confirmed  by  several  circumstances.  Thus, 
according  to  Gay-Lussac  and  Thenard,  the  weight  of  100  cubic  inches  of 
hydrosulphuric  acid  gas  is  36-33  grains.  When  sulphur  is  heated  in  hydro- 
gen gas,  hydrosulphuric  acid  is  generated  without  any  change  of  volume. 
On  igniting  platinum  wires  in  it  by  means  of  the  voltaic  apparatus,  sulphur 
is  deposited,  and  an  equal  volume  of  pure  hydrogen  remains;  and  a  simi- 
lar effect  is  produced,  though  more  slowly,  by  a  succession  of  electric  sparks 
(Elements  of  Davy,  p.  282).  Gay-Lussac  and  Thenard  found  that  on  heat- 
ing tin  in  hydrosulphuric  acid  gas,  sulphuret  of  tin  is  formed;  and  when 
potassium  is  heated  in  it,  vivid  combustion  ensues,  with  formation  of  sul- 
phuret of  potassium.  In  both  cases,  pure  hydrogen  is  left,  which  occupies 
precisely  the  same  space  as  the  gas  from  which  it  was  derived  (Recherches 
Physico-Chimiques,  vol.  i.) 

The  salts  of  hydrosulphuric  acid  are  called  hydrosulphales,  and  sometimes 
hydrosulphurets.  This  acid,  however,  rarely  unites  directly  with  metallic 
oxides;  but  in  most  cases  its  hydrogen  combines  with  the  oxygen  of  the 
oxide,  and  its  sulphur  with  the  metal.  All  the  hydrosulphates  which  do 
exist  are  decomposed  by  sulphuric  or  hydrochloric  acid,  and  hydrosulphuric 
acid  gas  is  disengaged  with  e  fFervescence. 

22 


254  COMPOUNDS  OF  HYDROGEN  AND  SULPHUR. 

Recently  boiled  water  absorbs  its  own  volume  of  hydrosulphuric  acid,  be- 
comes thereby  feebly  acid,  and  acquires  the  peculiar  odour  and  taste  of  sul- 
phurous springs.  The  gas  is  expelled  without  change  by  boiling  the  water. 

The  elements  of  hydrosulphuric  acid  may  easily  be  separated  from  one 
another.  A  solution  of  the  gas  cannot  be  preserved  in  an  open  vessel,  be- 
cause its  hydrogen  unites  with  the  oxygen  of  the  atmosphere,  and  sulphur 
is  deposited.  When  mixed  with  sulphurous  acid,  both  compounds  are  de- 
composed, water  is  generated  and  sulphur  set  free.  On  pouring  into  a  bottle 
of  the  gas  a  little  fuming  nitric  acid,  mutual  decomposition  ensues,  a  bluish- 
white  flame  frequently  appears,  sulphur  and  nitrous  acid  fumes  come  into 
view,  and  water  is  generated.  Chlorine,  iodine,  and  bromine  decompose  it, 
with  separation  of  sulphur,  and  formation  of  hydrochloric,  hydriodic,  and 
hydrobromic  acids.  An  atmosphere  charged  with  hydrosulphuric  acid  gas 
may  be  purified  by  means  of  chlorine  in  the  space  of  a  few  minutes. 

Hydrosulphuric  acid  gas  is  readily  distinguished  from  other  gases  by  its 
odour,  by  tarnishing  silver  with  which  it  forms  a  sulphuret,  and  by  the  cha- 
racter of  the  precipitate  which  it  produces  \$fth  solutions  of  arsenious  acid, 
tartar  emetic,  and  salts  of  lead.  The  most  delicate  test  of  its  presence, 
when  diffused  in  the  air,  is  moist  carbonate  of  oxide  of  lead  spread  on  white 
paper. 

Its  eq.  is  17-1;  eq.  vol.— 100;  symb.  HS. 

Persulphuret  of  Hydrogen. — Hist,  and  Prep. — Discovered  by  Scheele,  but 
first  specially  described  by  Berthollet  (An.  de  Chimie,  xxv.)  When  proto- 
sulphuret  of  potassium  (or  of  any  metal  of  the  alkalies  and  alkaline  earths) 
is  mixed  in  solution  with  sulphuYic  acid,  the  oxygen  of  water  unites  with 
potassium  and  its  hydrogen  with  sulphur,  just  as  when  protosulphuret  of 
iron  is  employed,  hydrosulphuric  acid  and  sulphate  of  potassa  being  genera- 
ted: the  elements  K-f-S  and  H+O  mutually  interchange,  and  yield  K+O 
and  H-|-S.  If  the  potassium  be  combined  with  two  or  more  equivalents  of 
sulphur,  as  in  the  so  called  liver  of  sulphur,  made  by  fusing  carbonate  of 
potassa  with  half  its  weight  of  sulphur,  then  one  of  two  events  will  happen : 
the  hydrogen  of  the  decomposed  water  will  either  unite  with  one  eq.  of  sul- 
phur and  form  hydrosulphuric  acid,  the  superfluous  sulphur  subsiding  in  the 
form  of  a  gray  hydrate,  or  with  two  eq,  of  sulphur,  and  give  rise  to  persul- 
phuret  of  hydrogen.  Now,  the  former  of  these  changes  always  occurs  when 
the  acid  is  added  to  the  persulphuret  of  potassium ;  and  the  latter  takes 
place  when  a  concentrated  solution  of  that  sulphuret  is  added  by  little  and 
little  to  the  acid,  provided  the  acid  is  in  considerable  excess,  and  the  mixture 
well  stirred  after  each  addition.  The  same  phenomena  ensue  when  hydro- 
chloric instead  of  sulphuric  acid  is  employed;  but  then  there  are  two  sources 
from  which  hydrogen  may  be  supplied.  It  may  be  derived,  as  above,  from 
decomposed  water,  hydrochlorate  of  potassa  being  generated;  or  hydrochloric 
acid  itself  may  be  decomposed,  its  hydrogen  uniting  with  sulphur  and  its 
chlorine  with  potassium.  On  all  such  occasions  I  adopt  the  latter  view, 
and  give  reasons  for  doing  so  in  the  section  introductory  to  the  study  of 
the  metals. 

Such  are  the  principles  to  be  attended  to  in  preparing  persulphuret  of 
hydrogen.  In  practice  it  is  conveniently  made  by  boiling  equal  parts  of 
recently  slaked  lime  and  flowers  of  sulphur  with  5  or  6  parts  of  water  for 
half  an  hour,  when  a  deep  orange-yellow  solution  is  formed,  which  contains 
persulphuret  of  calcium.  Let  this  liquid  be  filtered,  and  gradually  added 
cold  to  an  excess  of  hydrochloric  acid  diluted  with  about  twice  its  weight  of 
water,  briskly  stirring.  A  copious  deposite  of  sulphur  falls  (the  Sulphur 
Prcecipitatum  of  the  London  Pharmacopeia),  and  persulphuret  of  hydrogen 
gradually  subsides  in  the  form  of  a  yellowish  semi-fluid  matter  like  oil.  The 
change  which  ensues  in  the  formation  of  the  yellow  solution  may  be  theo- 
retically represented  thus : — 

2  eq.  lime  &  6  eq.  sulphur  2    leq.  hyposulphurous  acid  &  2  eq.  bisulphuret  of  calcium. 
6S        .2          2S-f2O  2(Ca+2S). 


HYDROGEN  AND  SELENIUM. — HYDROSELENIC  ACID.  255 

The  hyposulphurous  acid  exists  in  solution  united  with  lime,  and  is  decom- 
posed when  hydrochloric  acid  is  added,  resolving-  itself  into  sulphurous  acid 
and  sulphur  (page  196) ;  a  change  not  essentially  connected  with  the  pro- 
duction of  persulphuret  of  hydrogen,  but  resulting  from  the  mode  of  prepar- 
ing the  persulphuret  of  calcium.  It  is  probable  that  the  calcium  is  combined 
with  more  than  two  eq.  of  sulphur,  and  that  the  deposited  sulphur  is  derived 
from  that  source  as  well  as  from  decomposed  hyposulphurous  acid. 

Prop. — From  the  facility  with  which  this  substance  resolves  itself  into 
sulphur  and  hydrosulphuric  acid,  its  history  is  imperfect:  we  are  indebted 
to  an  essay  by  Thenard  for  the  principal  facts  which  are  known  (An.  de  Ch. 
et  de  Ph.  xlviii.  79).  At  common  temperatures  it  is  a  viscid  liquid,  of  a 
yellow  colour,  with  a  density  of  about  1'769,  and  a  consistence  varying  be- 
tween that  of  a  volatile  and  fixed  oil.  It  has  the  peculiar  odour  and  taste 
of  hydrosulphuric  acid,  though  in  a  less  degree.  Its  elements  are  so  feebly 
united,  that  in  the  cold  it  gradually  resolves  itself  into  sulphur  and  hydro- 
sulphuric  acid,  and  suffers  the  same  change  instantly  by  a  heat  considerably 
short  of  212°  F.  Decomposition  is  also  produced  by  the  contact  of  most 
substances,  especially  of  metnls,  metallic  oxides,  even  the  alkalies,  and  me- 
tallic sulphurets.  Thus  effervescence  from  the  escape  of  hydrosulphuric 
acid  gas  is  produced  by  peroxide  of  manganese,  silica,  the  alkaline  earths  in 
powder,  and  solutions  of  potassa  or  soda;  and  the  oxides  of  gold  and  silver 
are  reduced  by  it  with  such  energy,  that  they  are  rendered  incandescent.  It 
is  remarkable  that  the  substance  which  causes  the  decomposition  often  under- 
goes no  chemical  change  whatever.  In  these  respects  persulphuret  of  hy- 
drogen bears  a  close  analogy  to  peroxide  of  hydrogen  ;  and  Thenard  has 
traced  other  points  of  resemblance.  They  are  both,  for  instance,  rendered 
more  stable  by  the  presence  of  acids;  they  both  whiten  the  tongue  and  skin 
when  applied  to  them,  and  they  are  both  possessed  of  bleaching-  properties. 

The  composition  of  persulphuret  of  hydrogen  has  been  variously  stated. 
According  to  Dalton  it  is  a  bisulphuret,  consisting  of  two  equivalents  of  sul- 
phur and  one  of  hydrogen:  and  this  view  of  its  composition  is  corroborated 
by  Sir  John  Herschel's  analysis  of  persulphuret  of  calcium  (Edin.  Phil. 
Journal,  i.  13.)  But  Thenard  found  its  constituents  to  vary;  whence  it  is 
probable  that  hydrogen  is  capable  of  uniting  with  sulphur  in  several  pro- 
portions. 

Persulphuret  of  hydrogen  is  sometimes  regarded  as  an  acid  ;  and  on  this 
supposition  it  may  be  termed  hydroper sulphuric  acid,  and  its  salts  hydroper- 
sulphates.  This  view  is  founded  on  the  hypothesis,  that  the  solution  formed 
by  boiling  lime  with  sulphur  contains  hyposulphite  and  hydropersulphate  of 
lime,  the  hydrogen  in  the  one  acid  and  oxygen  in  the  other  being-  attributed 
to  decomposed  water,  and  not  hyposulphite  of  lime  and  persulphuret  of  cal- 
cium, as  I  have  supposed.  The  latter  view  is  more  consistent  with  the  fact 
that  persulphuret  of  hydrogen  in  its  free  state  has  no  acidity,  and  exhibits 
no  tendency  to  unite  with  alkalies. 

Its  eq.  is  =  33-2;  symb.  HS2. 


SECTION   IV. 

HYDROGEN  AND  SELENIUM.— HYDROSELENIC  ACID. 

SELENIUM,  like  sulphur,  forms  a  gaseous  compound  with  hydrogen,  which 
has  distinct  acid  properties,  and  is  termed  seleniuretted  hydrogen,  or  hydro- 
selenic  acid.  It  is  disengaged  by  the  action  of  dilute  sulphuric  or  hydro- 
chloric acid  on  a  protoseleniuret  of  any  of  the  more  oxidable  metals,  such  as 
potassium,  calcium,  manganese,  or  iron,  the  explanation  being  the  same  as 
in  the  formation  of  hydrosulphuric  acid  from  protosulphuret  of  iron. 


256  COMPOUNDS  OF  HYDROGEN  AND  PHOSPHORUS. 

Hydroselenic  acid  gas  is  colourless.  Its  odour  is  at  first  similar  to  that  of 
hydrosulphuric  acid  ;  but  it  afterwards  irritates  the  lining  membrane  of  the 
nose  powerfully,  excites  catarrhal  symptoms,  and  destroys  for  some  hours  the 
sense  of  smelling.  It  is  absorbed  freely  by  water,  forming  a  colourless  solu- 
tion, which  reddens  litmus  paper,  and  gives  a  brown  stain  to  the  skin.  The 
acid  is  soon  decomposed  by  exposure  to  the  atmosphere  ;  for  the  oxygen  of 
the  air  unites  with  the  hydrogen  of  the  hydroselenic  acid,  and  selenium,  in 
the  form  of  a  red  powder,  subsides.  It  is  decomposed  by  nitric  acid  and 
chlorine  in  the  same  manner  as  hydrosulphuric  acid  ;  and,  like  that  gas,  it 
decomposes  many  metallic  salts,  the  hydrogen  of  the  acid  combining  with 
the  oxygen  of  the  oxide,  while  an  insoluble  seleniuret  of  the  metal  is  gene- 
rated. 

According  to  the  analysis  of  Berzelius,  hydroselenic  acid  consists  of  39*6 
parts  or  one  eq.  of  selenium,  and  1  part  or  one  eq.  of  hydrogen  :  so  that  its 
eq.  is  40-6;  its  symb.  HSe. 


SECTION   V. 

COMPOUNDS  OF  HYDROGEN  AND  PHOSPHORUS. 

THE  existence  of  two  compounds. of  phosphorus  and  hydrogen,  the  phos- 
phuretted  arid  perphosphuretted  hydrogen,  have,  until  lately,  been  generally 
admitted  by  chemists.  Their  composition  and  properties  have  been  closely 
studied  by  Dumas,  Buff,  Rose,  and  Graham  (An.  de  Ch.  et  de  Ph.  xxxi.  113, 
xli.  220,  and  xli.  5.  Phil.  Mag.  v.  401.)  The  investigations  of  these  chemists 
concurred  in  proving  that  phosphuretted  hydrogen  consists  of  31'4  parts  or 
two  eq.  of  phosphorus,  and  3  parts  or  three  eq.  of  hvdrogen  ;  while  the  dis- 
cordancy in  their  analyses  of  perphosphuretted  hydrogen  caused  great  un- 
certainty respecting  its  constitution.  Thus,  although  Dumas  and  Rose  agree 
that  100  measures  of  perphosphuretted  hydrogen  contain  150  measures  of 
hydrogen,  the  former  states  that  1  part  of  hydrogen  is  united  with  15-9  of 
phosphorus,  the  latter  with  10-52,  while  Thomson  estimates  the  quantity 
at  12.  The  result  of  Rose  would  indicate  that  the  two  compounds  of 
phosphorus  and  hydrogen  are  isomeric,  being  identical  in  composition, 
and  differing  in  "character  only  by  the  one  being  spontaneously  inflam- 
mable, and  the  other  not  so.  The  accuracy  of  the  analytical  results  of 
Rose  has  been  recently  established  by  the  discoveries  of  Leverrier  (An.  de 
Ch.  et  de  Ph.  Ix.  174,)  who  has  proved  that  perphosphuretted  hydrogen  is  a 
mixture  of  phosphuretted  hydrogen  with  about  -jV  of  its  volume  of  a  sponta- 
neously inflammable  compound,  which  he  considers  to  be  composed  of  3V4 
parts  or  two  eq.  of  phosphorus,  and  2  parts  or  two  eq.  of  hydrogen.  In  the 
same  paper  he  establishes  the  existence  of  a  solid  compound,  formed  of  31-4 
parts  or  two  eq.  of  phosphorus,  and  1  part  or  one  eq.  of  hydrogen.  The 
compounds  of  phosphorus  and  hydrogen  are,  therefore, 

Phos.  Hyd.          Eq.  Formulas. 

Solid  phosphuretted  hydrogen     .     31-4  2  eq.-f     11  eq.=32-4 

Spon.  inflarn.  ditto  .     31-4  2  eq.-f-  2  2  eq.=  33-4 

Gaseous  ditto  .    31-4  2  eq.-f-  3  3  eq.=  34-4 

Solid  Phosphurelted  Hydrogen. — When  phosphuretted  hydrogen  gas,  re- 
cently prepared  by  the  action  of  quick-lime  and  phosphorus,  is  exposed  in 
the  moist  state  to  a  strong  diffused  light,  or  to  the  direct  rays  of  the  sun,  the 
solid  phosphuretted  hydrogen  is  deposited  on  the  sides  of  the  glass  vessel. 
It  is  also  left  as  an  insoluble  powder,  when  phosphuret  of  potassium  is  dis- 
solved in  water.  As  obtained  by  the  former  process,  it  is  a  canary-yellow 
flocculent  matter,  is  insoluble  in  water  and  alcohol;  but  with  the  former,  a 
Blow  oxidation  takes  place,  and  hydrogen  is  evolved.  It  is  not  altered  by  a 


COMPOUNDS  OF  HYDROGEN  AND  PHOSPHORUS.  257 

temperature  of  234°,  but  heated  beyond  that  point  it  is  decomposed.  When 
brought  into  contact  with  chlorine  and  nitric  acid,  it  suffers  instantaneous 
decomposition.  According  to  the  analysis  of  Leverrier,  it  is  composed  of  1 
part  or  one  eq.  of  hydrogen,  and  31-4  parts  or  two  eq.  of  phosphorus. 
Hence  its  eq.  is  32-4;  symb.  HP^. 

PHOSPHURETTED  HYDROGEN. 

Hist,  and  Prep. — Discovered  by  Davy  in  1812.  It  may  be  prepared  by 
several  methods.  Davy  prepared  it  by  heating  hydrated  phosphorous  acid 
in  a  retort  (page  201) ;  and  it  is  evolved  from  hydrous  hypophosphorous  acid 
by  similar  treatment,  and  by  the  action  of  strong  hydrochloric  acid  on  phos- 
phuret  of  calcium,  according  to  Dumas.  It  may  also  be  obtained,  but  in  an 
impure  state,  by  boiling  phosphorus  with  a  solution  of  potassa,  or  milk  of 
lime.  Its  production  is  in  these  cases  dependent  on  the  decomposition  of 
water,  the  oxygen  and  hydrogen  of  which  unite  with  different  portions  of 
phosphorus,  and  phosphoric  acid,  hypophosphorous  acid,  and  phosphuretted 
hydrogen  are  generated. 

Prop. — A  transparent  colourless  gas,  of  an  exceedingly  offensive  odour 
and  bitter  taste.  It  has  no  action  on  test  paper.  It  is  absorbed  in  small 
quantity  by  water,  but  freely  by  solutions  of  chloride  of  calcium  or  sulphate 
of  the  oxide  of  copper,  by  which  means  its  purity  may  be  ascertained.  Like 
sulphuretted  hydrogen,  it  frequently  decomposes  metallic  salts,  giving  rise 
to  the  formation  of  water  and  a  phosphuret  of  the  metal.  But  if  the  metal 
have  a  feeble  affinity  for  oxygen,  it  is  thrown  down  in  the  metallic  state,  and 
water  and  phosphoric  acid  are  generated.  This  is  the  case,  according  to 
Rose,  with  solutions  of  gold  and  silver. 

It  is  a  non-supporter  of  combustion,  and  is  very  destructive  to  animal  life. 
When  pure,  it  may  be  mixed  with  air  or  oxygen  gas  at  common  tempera- 
tures without  danger ;  but  the  mixture  detonates  with  the  electric  spark,  or 
at  a  temperature  of  3UO°.  Even  diminished  pressure  causes  an  explosion  ; 
an  effect  which,  in  operating  with  a  mercurial  trough,  is  produced  simply  by 
raising  the  tube,  so  that  the  level  of  the  mercury  within  may  be  a  few  inches 
higher  than  at  the  outside.  Such  is  the  property  of  the  pure  gas,  as  obtained 
from  the  hydrated  phosphorous  or  hypophosphorous  acids ;  but  if  it  be  pro- 
cured from  the  action  of  phosphorus  on  potassa  or  hydrate  of  lime,  it  is  re- 
markable for  being  spontaneously  inflammable  when  mixed  with  air  or  oxy- 
gen gas.  If  the  beak  of  the  retort  from  which  it  issues  is  plunged  under 
water,  so  that  successive  bubbles  of  the  gas  may  arise  through  the  liquid,  a 
very  beautiful  appearance  takes  place.  Each  bubble,  on  reaching  the  surface 
of  the  water,  bursts  into  flame,  and  forms  a  ring  of  dense  white  smoke, 
which  enlarges  as  it  ascends,  and  retains  its  shape,  if  the  air  is  tranquil,  until 
it  disappears.  The  wreath  is  formed  by  the  products  of  the  combustion — 
metaphosphoric  acid  and  water.  If  received  in  a  vessel  of  oxygen  gas,  the 
entrance  of  each  bubble  is  instantly  followed  by  a  strong  concussion,  and  a 
flash  of  white  light  of  extreme  intensity.  It  is  remarkable  that  whatever 
may  be  the  excess  of  oxygen,  traces  of  phosphorus  always  escape  combus- 
tion ;  but  that  if  the  gas  be  previously  mixed  with  three  times  its  volume  of 
carbonic  acid,  and  be  then  mixed  with  oxygen,  the  combustion  is  perfect. 
Dalton  observed  that  it  may  be  mixed  with  pure  oxygen  in  a  tube  three- 
tenths  of  an  inch  in  diameter  without  taking  fire;  but  that  the  mixture  deto- 
nates when  an  electric  spark  is  transmitted  through  it. 

In  consequence  of  the  combustibility  of  phosphuretted  hydrogen,  it  would 
be  hazardous  to  mix  it  in  any  quantity  with  air  or  oxygen  gas  in  close  vessels. 
For  the  same  reason  care  is  necessary  in  the  formation  of  this  gas,  lest,  in 
mixing  with  the  air  of  the  apparatus,  an  explosion  ensue,  and  the  vessel 
burst.  The  risk  of  such  an  accident  is  avoided,  when  phosphuret  of  calcium 
is  used,  by  filling  the  flask  or  retort  entirely  with  dilute  acid;  and  in  either 
of  the  other  processes,  by  causing  the  phosphuretted  hydrogen  to  be  formed 
slowly  at  first,  in  order  that  the  oxygen  gas  within  the  apparatus  may  be 

22  * 


258  COMPOUNDS  OF  HYDROGEN  AND  PHOSPHORUS. 

gradually  consumed.  A  very  simple  method  of  averting  all  danger  has  been 
mentioned  by  Graham.  It  consists  in  moistening  the  interior  of  the  retort 
with  one  or  two  drops  of  ether,  the  vapour  of  which,  when  mixed  with 
atmospheric  air  even  in  small  proportion,  effectually  prevents  the  combus- 
tion of  phosphuretted  hydrogen.  The  same  effect  may  be  produced  by  the 
addition  of  several  other  bodies.  He  also  finds  that  a  gas,  which  is  not 
spontaneously  inflammable,  acquires  this  property  on  being  mixed  with 
from  TuVo  to  ~nT5"o"o  °f  *ts  volume  of  nitrous  acid.  According  to  Leverrier, 
it  is  very  probable  that  there  exists  a  compound  of  phosphorus  and  hydrogen 
composed  of  two  eq.  of  each  of  its  elements,  and  that  this  compound,  being 
spontaneously  inflammable,  communicates  that  property  to  phosphuretted 
hydrogen  gas.  This  opinion  is  grounded  on  the  fact  that  when  spontaneously 
inflammable  phosphuretted  hydrogen  is  kept  for  any  length  of  time  in  a 
dark  place  it  suffers  no  change,  but  if  brought  into  a  strong  light,  solid  phos- 
phuretted hydrogen  is  deposited,  and  the  residual  gas  is  no  longer  spontane- 
ously inflammable.  Thus  it  appears  that  by  the  action  of  light  P^H2  is  de- 
composed, and  PaH  and  P^H3  are  formed.  The  result  of  his  analysis  sup- 
ports this  view. 

Dumas  ascertained  the  composition  of  phosphuretted  hydrogen  by  intro- 
ducing into  a  tube,  containing  the  gas,  a  fragment  of  bichloride  of  mercury, 
and  applying  heat  so  as  to  convert  it  into  vapour.  Mutual  decomposition 
instantly  took  place;  phosphuret  of  mercury  and  hydrochloric  acid  were 
generated  ;  and  100  measures  of  gas,  thus  decomposed,  yielded  300  measures 
of  hydrochloric  acid  gas,  corresponding  to  150  of  hydrogen.  The  quantity 
of  hydrogen  contained  in  any  given  volume  of  phosphuretted  hydrogen  is 
thus  found ;  and  the  weight  of  the  former  deducted  from  that  of  the  latter 
gives  the  quantity  of  combined  phosphorus.  This  inference  is  conformable 
to  the  quantity  of  oxygen  required  for  the  combustion  of  phosphuretted  hy- 
drogen. Thomson  affirms  that  when  this  gas  is  detonated  with  1-5  of  its 
volume  of  oxygen  gas,  the  only  products  are  waler  and  phosphorous  acid ; 
but  that  when  the  oxygen  is  in  considerable  excess,  two  volumes  disappear  for 
one  of  the  compound,  and  water  and  phosphoric  acid  are  generated.  Now 
the  hydrogen  contained  in  one  volume  of  phosphuretted  hydrogen  is  equal 
to  1-5,  and  it  unites  with  0-75  of  oxygen.  Hence  if  0-75,  or  £,  be  deducted 
from  1-5  and  from  2,  the  remainders,  j*.  and  j^  represent  the  relative  quantity 
of  oxygen  which  is  required  to  convert  the  same  weight  of  phosphorus  into 
phosphorous  and  phosphoric  acid.  These  numbers  are  obviously  in  the 
ratio  of  3  to  5,  as  already  stated  on  the  authority  of  Berzelius  (page  200.) 
The  elements  of  the  calculation  have  been  confirmed  both  by  Dumas  and 
Buff. 

Agreeably  to  these  views,  and  to  the  combining  volume  of  phosphorus 
(page  146,)  100  measures  of  phosphuretted  hydrogen  gas  contain  150  of 
hydrogen  gas,  and  25  of  the  vapour  of  phosphorus ;  and  hence,  as 

Grains. 

150  cubic  inches  of  hydrogen  gas  weigh     -         -         -         -         3-2050 
25         do.  phosphorus  vapour  weigh     ...       33-5461 

100         do.  phosphuretted  hydrogen  gas  should  weigh    36-7511 

The  calculated  density  of  a  gas  so  constituted  should  be  1-1850  which  is 
nearly  a  mean  of  the  observations  of  Dumas  and  Rose. 

If 'the  equivalent  of  phosphorus  were  31-4  instead  of  15-7,  as  is  very  far 
from  improbable,  then  the  combining  volume  of  phosphorus  vapour  would  be 
50  instead  of  25  (page  146;)  and  phosphuretted  hydrogen  would  consist  of 
50  measures  of  phosphorus  vapour  and  150  of  hydrogen  gas,  condensed  into 
100  measures,  thus  agreeing  in  composition  with  ammoniacal  gas.* 

*  This  statement  is  inaccurate.  On  the  supposition  made  by  Dr.  Turner, 
phosphuretted  hydrogen  would  consist  jof  50  measures  of  phosphorus  vapour 
and  300  of  hydrogen  gas,  condensed  into  200  measures.  Consequently,  it 
would  not  agree  in  composition  with  ammoniacal  gas. — Ed. 


COMPOUNDS  OF  NITROGEN  AND  CARBON.  259 

Phosphuretted  hydrogen  has  neither  an  acid  nor  alkaline  reaction ;  but  in 
its  chemical  relations  it  inclines  to  alkalinity.  Thus  it  unites  with  hydro- 
bromic  and  hydriodic  acids,  forming  definite  compounds  which  crystallize  in 
cubes ;  and  Rose  finds  that  it  unites  with  metallic  chlorides,  forming  com- 
pounds analogous  to  those  which  ammonia  forms  with  metallic  chlorides. 

Its  eq.  is  34-4;  eq.  vol.=200  ;  symb.  2P  +  3H,  or  PaRs. 


SECTION   VI. 

COMPOUNDS  OF  NITROGEN  AND  CARBON. 

BICARBURET  OF  NITROGEN,  OR  CYANOGEN  GAS. 

Hist,  and  Prep. — Discovered  in  1815  by  Gay-Lussac  (An.  de  Ch.  xcv.)  It 
is  prepared  by  heating  carefully  dried  bicyanuret  of  mercury  in  a  small 
glass  retort  by  means  of  a  spirit  lamp.  This  cyanuret,  which  was  formerly 
considered  a  compound  of  oxide  of  mercury  and  prussic  acid,  and  was  then 
called  prussiate  of  mercury,  is  composed  of  metallic  mercury  and  cyanogen. 
On  exposure  to  a  low  red  heat  it  is  resolved  into  its  elements  ;  the  cyanogen 
passes  over  in  the  form  of  gas,  and  the  metallic  mercury  is  sublimed.  The 
retort,  at  the  close  of  the  process,  contains  a  small  residue  of  a  dark  brown 
matter  like  charcoal,  but  which  Johnson  has  shown  to  consist  of  the  same 
ingredients  as  the  gas  itself. 

Prop. — A  colourless  gas  possessing  a  strong  pungent  and  very  peculiar 
odour.  At  the  temperature  of  45°  and  under  a  pressure  of  3-6  atmospheres, 
it  is  a  limpid  liquid,  which  Kemp  finds  to  be  a  non-conductor  of  electricity, 
and  which  resumes  the  gaseous  form  when  the  pressure  is  removed.  It  ex- 
tinguishes burning  bodies;  but  it  is  inflammable,  and  burns  with  a  beautiful 
and  characteristic  purple  flame.  It  can  support  a  strong  heat  without  de- 
composition. Water  at  the  temperature  of  60°  absorbs  4-5  times,  and  alco- 
hol 23  times  its  volume  of  the  gas.  The  aqueous  solution  reddens  litmus 
paper  ;  but  this  effect  is  not  to  be  ascribed  to  the  gas  itself,  but  to  the  pre- 
sence of  acids  which  are  generated  by  the  mutual  decomposition  of  cyano- 
gen and  water.  It  appears  from  the  observations  of  Wohler  that  two  of  the 
products  are  cyanic  acid  and  ammonia  ;  which,  uniting  together,  generate 
urea  (An.  de  Ch.  et  de  Ph.  xliii.  73). 

The  composition  of  cyanogen  may  be  determined  by  mixing  that  gas  with 
a  due  proportion  of  oxygen,  and  inflaming  the  mixture  by  electricity.  Gay- 
Lussac  ascertained  in  this  way  that  100  measures  of  cyanogen  require  200 
of  oxygen  for  complete  combustion,  that  no  water  is  formed,  and  that  the 
products  are  200  measures  of  carbonic  acid  gas  and  100  of  nitrogen.  Hence 
it  follows  that  cyanogen  contains  its  own  bulk  of  nitrogen,  and  twice  its 
volume  of  the  vapour  of  carbon.  Consequently,  since 

Grains. 

100  cubic  inches  of  nitrogen  gas  weigh      .         .        .         .         •        30-1650 
200         do.  the  vapour  of  carbon  weigh         .        *m        .         26-1428 

100  cubic  inches  of  cyanogen  gas  must  weigh  .        •        •         56-3078 

The  ratio  of  its  elements  by  weight  is, 

Nitrogen      .      30-1650        •        0-9727        .      -V*       14-15    1  eq. 
Carbon         .      261428        •        0-8430(2  +  0-4215)      12-24    2  eq. 


260  COMPOUND  OF  PHOSPHORUS  AND  NITROGEN. 

The  sp.  gr.  of  a  gas  so  constituted  is  0-9727 +  0-843  =1-8157,  vvhicli  is  near 
]'8064,  the  number  found  experimentally  by  Gay-Lussac. 

Cyanogen  is  a  bicarburet  of  nitrogen,  the  formula  of  which  is  N-f-2C,  or 
NC^ ;  but  its  most  convenient  name  is  cyanogen,  proposed  by  its  discoverer,* 
which  may  be  expressed  shortly  by  Cy.  Its  eq.  is  26'39. 

Paracyanogen. — An  examination  of  the  brown  matter,  left  in  the  retort 
after  the  preparation  of  cyanogen  gas,  has  been  made  by  Johnston,  who,  by 
burning  it  with  chlorate  of  potassa,  found  it  to  contain  carbon  and  nitrogen, 
united  in  the  same  ratio  as  in  cyanogen  gas.  It  is,  in  fact,  a  solid  bicarburet 
of  nitrogen,  isomeric  with  cyanogen,  but  differing  from  it  essentially  in  its 
physical  and  chemical  relations.  On  heating  this  solid  bicarburet  in  the 
open  air,  several  definite  compounds  of  carbon  and  nitrogen  may  be  suc- 
cessively obtained.  After  considerable  heating,  the  ratio  of  carbon  to  nitro- 
gen in  equivalents  is  as  3  to  2 ;  again  heated,  the  proportion  becomes  as  7 
to  6  ;  and  finally,  after  a  still  longer  heat,  the  ratio  of  the  equivalents  is  as 
1  to  1.  Thus  the  carbon  is  gradually  burned  away,  leaving  the  nitrogen 
fixed,  until  a  protocarburet  of  nitrogen  is  formed.  On  continuing  the  heat 
after  this  period,  both  elements  fly  off  together,  and  the  whole  is  dissipated. 
The  solid  bicarburet  of  cyanogen  is  also  generated,  when  a  saturated  solu- 
tion of  cyanogen  in  alcohol  is  kept  in  contact  with  mercury ;  and  Johnston 
suggests  that  the  carbonaceous  residue,  after  the  charring  of  animal  substances 
by  heat,  is  probably  in  many  cases  a  carburet  of  nitrogen,  and  not  pure 
charcoal  as  is  commonly  thought.  (Brcwster's  Journ.  N,  S.  i.  75.)  Para- 
cyanogen  is  soluble  in  sulphuric  and  nitric  acids,  and  forms  a  compound 
with  oxygen  in  which  one  eq.  of  oxygen  is  combined  with  four  eq.  of  nitro- 
gen and  eight  eq.  of  carbon.  Hence  the  eq.  of  paracyanogen  is  probably 
105-56,  and  its  symb.  NO. 

Mellon. — Is  obtained  when  sulphuret  of  cyanogen,  melams,  rnelamins, 
ammelins,  or  ammelids,  is  exposed  to  a  red  heat.  It  is  a  lemon-yellow 
*  powder,  is  insoluble  in  water  and  alcohol,  but  is  dissolved  and  decomposed 
by  acids  and  alkalies.  Exposed  to  a  strong  red  heat,  it  is  decomposed  and 
forms  one  vol.  of  nitrogen  and  three  vols.  of  cyanogen  gas.  It  is  one  of  the 
compound  radicals.  Its  eq.  is  93-32  ;  symb.  N4(X  (Lieb.  Ann.  ix.  5.) 

Cyanogen,  though  a  compound  body,  has  a  remarkable  tendency  to  com- 
bine with  elementary  substances.  Thus  it  is  capable  of  uniting  with  the 
simple  non-na-etallic  bodies,  and  evinces  a  strong  attraction  for  metals.  When 
potassium,  for  instance,  is  heated  in  cyanogen  gas,  such  energetic  action  en- 
sues, that  the  metal  becomes  incandescent,  and  cyanuret  of  potassium  is 
generated.  The  affinity  of  cyanogen  for  metallic  oxides,  on  the  contrary,  is 
comparatively  feeble.  It  enters  into  direct  combination  with  a  few  alkaline 
bases  only,  and  these  compounds  are  by  no  means  permanent.  From  these 
remarks  it  is  apparent  that  cyanogen  has  no  claim  to  be  regarded  as  an  acid. 
It  is,  in  fact,  a  compound  radical  of  organic  chemistry,  and,  therefore,  its  va- 
rious combinations  will  be  described  in  that  part  of  the  work. 


SECTION  VII. 

COMPOUND  OF  PHOSPHORUS  AND  NITROGEN. 

Phosphuret  of  Nitrogen. — First  described  by  Rose  (Pogg.  Ann.  xxviii. 
529.)  On  saturating  either  of  the  chlorides  of  phosphorus  with  dry  ammo- 
niacal  gas,  a  white  solid  mass  is  obtained,  which,  on  exposure  to  a  strong 
red  heat,  gives  rise  to  the  formation  of  phosphuret  of  nitrogen,  hydrochloric 

*  From  xfavos  blue,  and  yevvda  I  generate  ;  because  it  is  an  essential  in- 
gredient of  Prussian  blue. 


COMPOUNDS  OF  SULPHUR  WITH  CARBON,  ETC.  261 

acid  gas  being  at  the  same  time  evolved.  It  is  also  formed  when  the  vapour 
of  either  of  the  chlorides  of  phosphorus  is  brought  into  contact  with  sal  am- 
moniac heated  nearly  to  its  point  of  sublimation, 

It  is  a  light  snow-white  powder ;  is  insoluble  in  water,  and  in  dilute  acid 
or  alkaline  solutions.  It  is  not  changed  by  a  red  heat  in  close  vessels,  or  in 
an  atmosphere  of  chlorine,  or  of  the  vapour  of  sulphur  ;  but  in  hydrogen  it  is 
decomposed  with  the  formation  of  ammoniacal  gas.  It  is  composed  of  31'4 
parts  or  two  eq.  of  phosphorus,  and  14-15  parts  or  one  eq.  of  nitrogen. 

Its  eq.  is  45-55;  syinb.  N-f2P,  or  NP2. 


SECTION  VIIl. 

COMPOUNDS  OF  SULPHUR  WITH  CARBON,  ETC. 

The  compounds  described  in  this  section  are  thus  constituted : 

Equiv.        Formulae. 

Bisulph.  of  carbon      Carbon     6-12  -J-  Sulphur  32'2=38-32    C+2S  or  CS2. 
Sulph.  of  phosphorus.    Composition  uncertain. 
Bisulph.  of  selenium  Selenium  39-6  +  Sulphur  32-2=71-8    Se-|-2S  or  SeS2. 

—tain. 

Bisulphuret  of  Carbon. — Hist. — This  substance  was  discovered  accident- 
ally in  the  year  1796  by  Professor  Lampadius,  who  regarded  it  as  a  com- 
pound of  sulphur  and  hydrogen,  and  termed  it  alcohol  of  sulphur.  Clement 
and  Desormes  first  declared  it  to  be  a  sulphuret  of  carbon,  and  their  state- 
ment was  fully  confirmed  by  the  joint  researches  of  Berzelius  and  the  late 
Dr.  Marcet  (Phil.  Trans.  1813.) 

Prep. — Bisulphuret  of  carbon  may  be  obtained  by  heating  in  close  vessels 
native  bisulphuret  of  iron  (iron  pyrites)  with  one-fifth  of  its  weight  of  well- 
dried  charcoal ;  or  by  transmitting  the  vapour  of  sulphur  over  fragments  of 
charcoal  heated  to  redness  in  a  tube  of  porcelain.  The  compound,  as  it  is 
formed,  should  be  conducted  by  means  of  a  glass  tube  into  cold  water,  at  the 
bottom  of  which  it  is  collected.  To  free  it  from  moisture  and  adhering  sul- 
phur, it  should  be  distilled  at  a  low  temperature  in  contact  with  chloride  of 
calcium. 

Prop. — It  is  a  transparent  colourless  liquid,  which  is  remarkable  for  its 
high  refractive  power.  Its  sp.  gr.  is  1-272 ;  of  its  vapour,  2-668.  It  has  an 
acid,  pungent,  and  somewhat  aromatic  taste,  and  a  very  fetid  odour.  It  is 
exceedingly  volatile  ;  its  vapour  at  63-5°  supports  a  column  of  mercury  7-36 
inches  long  ;  and  at  110°  it  enters  into  brisk  ebullition.  From  its  great  vo- 
latility it  may  be  employed  for  producing  intense  cold.  It  is  very  inflam- 
mable, and  kindles  in  the  open  air  at  a  temperature  scarcely  exceeding  that 
at  which  mercury  boils.  It  burns  with  a  pale  blue  flame.  Admitted  into  a 
vessel  of  oxygen  gas,  so  much  vapour  rises  as  to  form  an  explosive  mixture; 
and  when  mixed  in  like  manner  with  binoxide  of  nitrogen,  it  forms  a  com- 
bustible mixture,  which  is  kindled  on  the  approach  of  a  lighted  taper,  and 
burns  rapidly,  with  a  large  greenish-white  flame  of  dazzling  brilliancy.  It 
dissolves  readily  in  alcohol  and  ether,  and  is  precipitated  from  the  solution 
by  water.  It  dissolves  sulphur,  phosphorus,  and  iodine,  and  the  solution  of 
the  latter  has  a  beautiful  pink  colour.  Chlorine  decomposes  it,  with  forma- 
tion of  chloride  of  sulphur.  The  pure  acids  have  little  action  upon  it.  By 
nitro-hydrochloric  acid  it  is  changed  into  a  white  crystalline  substance  like 
camphor,  which  Berzelius  regards  as  a  compound  of  the  hydrochloric,  car- 
bonic, and  sulphurous  acids. 


262  COMPOUNDS  OF  SULPHUR  WITH  CARBON,  ETC. 

Bisulphuret  of  carbon  is  a  sulphur-acid,  that  is,  unites  with  sulphur-bases 
to  constitute  compounds  analogous  to  ordinary  salts,  and  hence  called  sul- 
phur-salts. Thus  bisulphuret  of  carbon  unites  with  sulphuret  of  potassium, 
forming  a  sulphur-salt,  in  which  the  former  acts  as  an  acid  and  the  latter  as 
a  base.  The  same  compound  is  formed  by  the  action  of  bisulphuret  of  car- 
bon on  a  solution  of  pure  potassa  :  but  in  this  case  sulphuret  of  potassium  is 
first  generated  by  an  interchange  of  elements  with  a  portion  of  bisulphuret 
of  carbon,  carbonic  acid  being  produced  at  the  same  time.  Thus 

2  eq.  potassa  &.  1  eq.  bisulph.  carbon  2    2eq.  sulphuret  potassium  &  1  eq.  carb.  acid. 
2(K-fO)          C  +  2S  .2^        2(K  +  S)  C  +  2O. 

If  the  bisulphuret  of  carbon  is  in  sufficient  quantity,  carbonic  acid  gas  is 
disengaged,  and  a  neutral  compound  results.  Such  is  inferred  to  be  the 
nature  of  the  change,  agreeably  to  the  researches  of  Berzelius  on  the  sul- 
phur-salts. 

Its  eq.  is  38-32;  eq.  vol.=  100  ;  symb.  CSa. 

Sulphuret  of  Phosphorus. — When  sulphur  and  fused  phosphorus  are  brought 
into  contact  they  unite  readily,  but  in  proportions  which  have  not  been  pre- 
cisely determined ;  and  they  frequently  react  on  each  other  with  such  violence 
as  to  cause  an  explosion.  For  this  reason  the  experiment  should  be  made 
with  a  quantity  of  phosphorus  not  exceeding  30  or  40  grains.  The  phos- 
phorus is  placed  in  a  glass  tube,  5  or  6  inches  long,  and  about  half  an  inch 
wide ;  and  when  by  a  gentle  heat  it  is  liquefied,  the  sulphur  is  added  in  suc- 
cessive small  portions.  Heat  is  evolved  at  the  moment  of  combination,  and 
hydrosulphuric  and  phosphoric  acids,  owing  to  the  presence  of  moisture,  are 
generated.  This  compound  may  also  be  made  by  agitating  flowers  of  sulphur 
with  fused  phosphorus  under  water.  The  temperature  should  not  exceed 
160°;  for  otherwise  hydrosulphuric  and  phosphoric  acids  would  be  evolved 
so  freely  as  to  prove  dangerous,  or  at  least  to  interfere  with  the  success  of 
the  process. 

Sulphuret  of  phosphorus,  from  the  nature  of  its  elements,  is  highly  com- 
bustible. It  is  much  more  fusible  than  phosphorus.  A  compound  made  by 
Faraday  with  about  5  parts  of  sulphur  and  7  of  phosphorus,  was  quite  fluid 
at  32°,  and  did  not  solidify  at  20°  (Quarterly  Journal,  iv.). 

Bisulphuret  of  Selenium. — Sulphur  and  selenium  rnix  together  in  all  pro- 
portions by  fusion,  and,  therefore,  by  such  means  it  is  difficult  to  procure  a 
definite  compound ;  but  the  bisulphuret,  of  an  orange  colour,  was  formed  by 
Berzelius  by  precipitating  a  solution  of  selenious  acid  with  hydrosulphuric 
acid.  Tiie  sulphuret  found  by  Stromeyer  among  the  volcanic  products  of 
the  Lipari  isles  is  probably  similar  in  composition.  Bisulphuret  of  selenium 
fuses  at  a  heat  a  little  above  212°,  and  at  a  higher  temperature  may  be  sub- 
limed without  change.  In  the  open  air  it  takes  fire  when  heated,  and  sul- 
phurous, selenious,  and  selenic  acids  are  the  products  of  its  combustion. 
The  alkalies  and  soluble  metallic  sulphurets  dissolve  it.  Nitric  acid  acts 
upon  it  with  difficulty ;  but  the  nitro-hydrochloric  converts  it  into  sulphuric 
and  selenious  acids  (An.  of  Phil,  xiv.) 

Seleniuret  of  Phosphorus. — This  compound  may  be  prepared  in  the  same 
manner  as  the  sulphuret  of  phosphorus;  but  as  selenium  is  capable  of  unit- 
ing with  phosphorus  in  several  proportions,  the  compound  formed  by  fusing 
them  together  can  hardly  be  supposed  to  be  of  a  definite  nature.  This  sele- 
niuret  is  very  fusible,  sublimes  without  change  in  close  vessels,  and  is  inflam- 
mable. It  decomposes  water  gradually  when  digested  in  it,  giving  rise  to 
seleniuretted  hydrogen,  and  one  of  the  acids  of  phosphorus. 

Sulphuret  of  Nitrogen. — This  compound  was  formed  by  Gregory  by  the 
reaction  of  chloride  of  sulphur  on  a  solution  of  ammonia.  It  is  a  colourless 
powder,  insoluble  in  water,  but  dissolves  in  alcohol,  and  may  thus  be  obtain- 
ed in  small  crystals.  It  is  characterized  by  its  alcoholic  solution  forming 
with  potassa  a  fine  purple  colour,  which  disappears  shortly  after,  when  the 
solution  is  found  to  contain  hyposulphurous  acid  and  ammonia.  It  contains 
from  92  to  93  per  cent,  of  sulphur,  and  7  to  8  of  nitrogen. 


263 


METALS. 


GENERAL  PROPERTIES  OF  METALS. 

METALS  are  distinguished  from  other  substances  by  the  following  pro- 
perties.  They  are  all  conductors  of  electricity  and  heat.  When  the  com- 
pounds  which  they  form  with  oxygen,  chlorine,  iodine,  sulphur,  and  similar 
substances,  are  submitted  to  tne  action  of  galvanism,  the  metals  always 
appear  at  the  negative  side  of  the  battery,  and  are  hence  said  to  be  positive 
electrics.  They  are  quite  opaque,  refusing  a  passage  to  light,  though  re- 
duced to  very  thin  leaves.  They  are  in  general  good  reflectors  of  light,  and 
possess  a  peculiar  lustre,  which  is  termed  the  metallic  lustre. — Every  substance 
in  which  these  characters  reside  may  be  regarded  as  a  metal. 

The  number  of  metals,  the  existence  of  which  is  admitted  by  chemists, 
amounts  to  forty- one.  The  following  table  contains  the  names  of  those  that 
have  been  procured  in  a  state  of  purity,  together  with  the  date  at  which 
they  were  discovered,  and  the  names  of  the  chemists  by  whom  the  discovery 
was  made. 

Table  of  the  Discovery  of  Metals. 


Names  of  Metals. 

Authors  of  the  Discovery. 

Dates  of  the 
Discovery. 

Gold     .        .     1 

Silver   . 

Iron     .        .  ::fi 

Copper          .      \ 

Known  to  the  Ancients.      -  ^    ' 

Mercury       .      | 

Lead    . 

Tin      .         .    J 

Antimony    . 

Described  by  Basil  Valentine 

1490 

Bismuth 

Described  by  Agricola 

1530 

Zinc     . 

First  mentioned  by  Paracelsus 

16th  century 

Arsenic        .      ) 

Brandt          .         .         .-       V"      * 

1733 

Cobalt  .        .      \ 

Platinum 

Wood,  assay-master,  Jamaica 

1741 

Nickel  .       . 

Cronstcdt      .         .         .       "/'£ 

1751 

Manganese  .    "  '  .' 

Gahn  and  Scheele       .  .'•'•*  *' 

1774 

Tungsten     .;   ,.  .; 

D'Elhuyart  .        f  *     Sm    t''  s  ^ 

1781 

Tellurium    .        .; 

Mailer          .       7       .:     &      - 

1782 

Molybdenum 

Hielm           .         .         .     r  '/*>_ 

1782 

Uranium      »^,  *' 

Klaproth      .         .__    »*,  ..»..* 

1789 

rji'i        • 

1791 

Chromium  .'  '     »' 

Vauquelin    .         .         ... 

1797 

Columbium. 

Hatchett       .        .        ;    v    -:      «; 

1802 

Palladium    .      ) 
Rhodium      .      ^ 

Wollaston    .         .       ^       v,  „  < 

1803 

Iridium 

Descotils  and  Smithson  Tennant 

1803 

Osmium 

Smithson  Tennant 

1803 

Cerium 

Kissinger  and  Berzelius 

1804 

Potassium    .     ^j 

Sodium 

Barium        .      **• 

1807 

Strontium    . 

Calcium       .     J 

7'^    :   • 

264  GENERAL   PROPERTIES   OF   METALS. 

Table  of  the  Discovery  of  Metals — (continued.} 


Names  of  Metals. 

Authors  of  the  Discovery. 

Dates  of  the 
Discovery. 

Cadmium     . 
Lithium       .         . 

Stromeyer    .         .         .         .         ,^ 

1818 
1818 

Zirconium    . 
Aluminium  .      J 
Glucinium          > 

Berzelius      ..... 

Wohler         .     *   .    *  -V 

1824 

1828 

Vttrium      .       ) 
Thorium      .         * 

1829 

Magnesium. 
Vanadium   . 

Bussy  .         .         .         .  -  .    .*-  ;    V~: 
Sefstrttm       .        •     ,    •        «(   .,r;  v 

1829 
1830 

Most  of  the  metals  are  remarkable  for  their  great  sp.  gravity;  some  of 
them,  such  as  gold  and  platinum,  which  are  the  densest  bodies  known  in 
nature,  being  more  than  nineteen  times  as  heavy  as  an  equal  bulk  of  water. 
Great  density  was  once  supposed  to  be  an  essential  characteristic  of  metals  ; 
but  the  discovery  of  potassium  and  sodium,  which  are  so  light  as  to  float  on 
the  surface  of  water,  has  shown  that  this  supposition  is  erroneous.  Some 
metals  experience  an  increase  of  density  to  a  certain  extent  when  hammered, 
their  particles  being  permanently  approximated  by  the  operation.  On  this 
account,  the  density  of  some  of  the  metals,  contained  in  the  following  table, 
is  represented  as  varying  between  two  extremes. 

Fahr.  compared  to  Water  as 

Brisson. 

Do. 

Children. 

D'Elhuyart. 

Brisson. 

Wollaston. 

Brisson. 

Do. 

Do. 

Buchholz. 

Hatchett. 

Buchholz. 

Stromeyer. 

Kichter. 

John. 

Turner. 

Brisson. 

Do. 

Do. 

Do. 

Klaproth. 

Turner. 

Wollaston. 

Thomson. 

SGay-Lussac  and 
Thenard. 

Some  metals  possess  the  property  of  malleability,  that  is,  admit  of  being 
beaten  into  thin  plates  or  leaves  by  hammering.  The  malleable  metals  are 
gold,  silver,  copper,  tin,  platinum,  palladium,  cadmium,  lead,  zinc,  iron,  nickel, 


Table  of  the  Specific 

Gravity  of  Metals  at  60° 

Unity. 

Platinum 

';•'•    '..'         20-98 

Gold 

,.       .         19-257 

Iridium 

..,'•...     is-68    .•••;•-• 

Tungsten 

17-6 

Mercury 

13-568 

Palladium 

.    >    .         11-3  to  11-8 

Lead 

11-352   •     /'•' 

Silver 

10-474        . 

Bismuth 

9-822 

Uranium 

9-000        .    . 

Copper 

Y-'    V-^      8-895    ;  '.  t;; 

Molybdenum 

„•      *•.       8-615  to  8-636 

Cadmium 

*••",•**.-        8-604        . 

Nickel 

8-279 

Manganese 
Cobalt 

.-•   *  •-.'         8-013 
'•&££$&      7-834 

Iron 

7-788 

Tin 

7-291 

Zinc 

v     ••„•  :v,      6-861  to  7-1 

Antimony 

*     /,;     6-702 

Tellurium 

i>-       „  I      6-115 

Arsenic 

,'./-,  w.r  :      5-8843      . 

Titanium 

5-3            .; 

Chromium 

^       v    ,     5+         • 

Sodium 

'-  »•    ^mi    0-972  >    . 

Potassium 

'•-V^?"  •*--•      0-865^      . 

GENERAL   PROPERTIES   OF   METALS.  265 

potassium,  sodium,  and  frozen  mercury.  The  other  metals  are  either  malleable 
in  a  very  small  degree  only,  or,  like  antimony,  arsenic,  and  bismuth,  are 
actually  brittle.  Gold  surpasses  all  metals  in  malleability  :  one  grain  of  it 
may  be  extended  so  as  to  cover  about  52  square  inches  of  surface,  and  to  have 
a  thickness  not  exceeding  -.--^-.^th  of  an  inch. 

Nearly  all  malleable  metals  may  be  drawn  out  into  wires,  a  property  which 
is  expressed  by  the  term  ductility.  The  only  metals  which  are  remarkable 
in  this  respect  are  gold,  silver,  platinum,  iron,  and  copper.  Wollaston  devised 
a  method  by  which  gold  wire  may  be  obtained  so  fine  that  its  diameter  shall 

be  only  . ? th  of  an  inch,  and  that  550  feet  of  it  are  required  to  weigh  one 

grain.  He  obtained  a  platinum  wire  so  small,  that  its  diameter  did  not  exceed 
T_£__th  of  an  inch  (Phil.  Trans.  1813).  It  is  singular  that  the  ductility 
and  malleability  of  the  same  metal  are  not  always  in  proportion  to  each 
other.  Iron,  for  example,  cannot  be  made  into  fine  leaves,  but  it  may  be 
drawn  into  very  small  wires. 

The  tenacity  of  metals  is  measured  by  ascertaining  the  greatest  weight 
which  a  wire  of  a  certain  thickness  can  support  without  breaking.  Ac- 
cording to  the  experiments  of  Guyton-Morveau,  whose  results  are  comprised 
in  the  following  table,  iron,  in  point  of  tenacity,  surpasses  all  other  metals. 

The  diameter  of  each  wire  was  0-787th  of  a  line. 

Pounds. 

Iron  wire  supports         * '/    Wi*-.     ..    ,;.        ~  .  549-25 

Copper        .        -'«'  V'        ;-       rfpl      -*  '          .      302-278 
Platinum       $*Lf|    V  ;        '    ;/~     jSfgj    ''.''••         274-32 
Silver        .  .  '*  /  ''        ,,?'       '  J       187-137 

Gold   .  .„.         .  ;'"•£    :  v  '      i    .  .  150-753 

Zinc          .  V  .-       $3fiS   i§l        109'54 

Tin     .         Li       ,.  ^  *        ;-tv    ,  «*|        *  i         .     34-63 
Lead    '^V    ';•'.;•;.    f1^  -~;y';:    -'%-'        27-621 

According  to  some  recent  observations  of  Baudrimont,  the  process  of 
annealing  destroys  the  tenacity  of  metals  to  a  considerable  extent.  Thus  he 
found  that  a  wire  of  soft  iron  which  supported  a  weight  of  26  Ibs.,  on  being 
annealed  could  only  bear  12  Ibs.;  and  a  copper  wire  which  could  support 
22  Ibs.  was  broken,  when  annealed,  by  9  Ibs.  Numerous  experiments  with 
different  specimens  of  brass  wire  confirm  the  generality  of  the  result  (An. 
de  Ch.  et  de  Ph.  Ix.  78). 

Metals  differ  also  in  hardness ;  but  I  am  not  aware  that  their  exact  relation 
to  each  other,  under  this  point  of  view,  has  been  determined  by  experiment. 
In  the  list  of  hard  metals  may  be  placed  titanium,  manganese,  iron,  nickel, 
copper,  zinc,  and  palladium.  Gold,  silver,  and  platinum  are  softer  than 
these ;  lead  is  softer  still,  and  potassium  and  sodium  yield  to  the  pressure  of 
the  fingers.  The  properties  of  elasticity  and  sonorousness  are  allied  to  that 
of  hardness.  Iron  and  copper  are  in  these  respects  the  most  conspicuous. 

Many  of  the  metals  have  a  distinctly  crystalline  texture.  Iron,  for  example, 
is  fibrous ;  and  zinc,  bismuth,  and  antimony  are  lamellated.  Metals  are 
sometimes  obtained  also  in  crystals;  and  most  of  them  in  crystallizing 
assume  the  figure  of  a  cube,  the  regular  octohedron,  or  some  form  allied  to 
it.  Gold,  silver,  and  copper  occur  naturally  in  crystals  ;  while  others  crys- 
tallize when  they  pass  gradually  from  the  liquid  to  the  solid  condition. 
Crystals  are  most  readilly  procured  from  those  metals  which  fuse  at  a  low 
temperature;  and  bismuth,  from  conducting  heat  less  perfectly  than  other 
metals,  and,  therefore,  cooling  more  slowly,  is  best  fitted  for  the  purpose. 
The  process  should  be  conducted  in  the  way  already  described  for  forming 
crystals  of  sulphur.  (Page*  191.) 

Metals,  with  the  exception  of  mercury,  are  solid  at  common  temperatures; 
but  they  may  all  be  liquefied  by  heat.  The  degree  at  which  they  fuse,  or 
their  point,  of  fusion,  is  very  different  for  different  metals,  as  appears  from 
the  following  table. 

23 


266 


GENERAL  PROPERTIES  OP  METALS. 


Fusible   below 
red  heat. 


Table  of  the  Fusibility  of  different  Metals. 


Fahr. 

Mercury    -        -    —39°  Different  chemists. 

Potasaium  -         -       1367  /-,      •, 

Sodium       -        -       190  5  Gay-L«ssac  and  Thenard. 

Cadmium    -    about  442      Stromeyer. 
Tin             .        -      442) 
Bismuth     -        -      497  >  Crichton. 
Lead        -^       S      612$ 
Tellurium rather 

less  fusible   than 

lead         -         -  Klaproth. 


Arsenic undeter- 
mined. 

Zinc  .         .       773 

Antimony — a   little 
below  a  red  heat. 


Daniell. 


Infusible  below  a 
red  heat. 


ilver       '  ... '   l 
opper        » 
Gold 

ron,  cast    - 
ron,  malleable    - 
langanese 
obalt — rather   less 
fusible  than  iron, 
fickel — nearly  the  same  as  cobalt, 
^lladium. 

Almost  infusible,  and  not 
to  be  procured  in  but- 
tons by  the  heat  of  a 
smith's  forge. 


[olybdenum 

ranium 
Tungsten 

hromium 

'itanium 

Cerium 

)smium 

ridium 

hodium 
Matinum 

olumbium 


1873^ 
^K  Daniell. 

2786  ) 

{Requiring  the  highest  heat  of  a 
smith's  forge. 


Fusible    be- 
fore the  oxy- 
hydrogen 
blowpipe. 


Infusible  in  the  heat  of  a  smith's  forge, 
but  fusible  before  the  oxy-hydrogen 
blowpipe. 


Metals  differ  also  in  volatility.  Some  are  readily  volatilized  by  heat, 
while  others  are  of  so  fixed  a  nature  that  they  may  be  exposed  to  the  most 
intense  heat  of  a  wind  furnace  without  being  dissipated  in  vapour.  There 
are  seven  metals,  the  volatility  of  which  has  been  ascertained  with  certainty ; 
namely,  cadmium,  mercury,  arsenic,  tellurium,  potassium,  sodium,  and 
zinc. 

Metals  cannot  be  resolved  into  more  simple  parts;  and,  therefore,  in  the 
present  state  of  chemistry,  they  must  be  regarded  as  elementary  bodies.  It 
was  formerly  conceived  that  they  might  be  converted  into  each  other;  and 
this  notion  led  to  the  vain  attempts  of  the  alchemists  to  convert  the  baser 
metals  into  gold.  The  chemist  has  now  learned  that  his  art  solely  consists 
in  resolving  compound  bodies  into  their  elements,  and  causing  substances  to 
unite  which  were  previously  uncombiried.  One  elementary  principle  cannot 
assume  the  properties  peculiar  to  another. 

Metals  have  an  extensive  range  of  affinity,  and  on  this  account  few  of 
them  are  found  in  the  earth  native,  that  is,  in  an  uncombined  form.  They 
commonly  occur  in  combination  with  other  bodies,  especially  with  oxygen 
and  sulphur,  in  which  state  they  are  said  to  be  mineralized.  It  is  a  singular 
fact  in  the  chemical  history  of  the  metals,  that  they  are  little  disposed  to 
combine  in  the  metallic  state  with  compound  bodies,  such  as  an  oxide  or  an 


GENERAL  PROPERTIES  OP  METALS.  267 

acid.  They  unite  readily,  on  the  contrary,  with  elementary  substances. 
Thus  they  often  combine  with  each  other,  yielding  compounds  termed  alloys, 
which  possess  all  the  characteristic  physical  properties  of  pure  metals.  They 
unite  likewise  with  the  simple  non-metallic  substances,  such  as  oxygen, 
chlorine,  and  sulphur,  giving  rise  to  new  bodies  in  which  the  metallic  cha- 
racter is  wholly  wanting.  In  all  these  combinations  the  same  tendency  to 
unite  in  a  few  definite  proportions  is  equally  conspicuous  as  in  that  depart- 
ment of  the  science  of  which  I  have  just  completed  the  description.  The 
chemical  changes  are  regulated  by  the  same  general  laws,  and  in  describing 
them  the  same  nomenclature  is  applicable. 

The  order  which  it  is  proposed  to  follow  in  describing  the  metals  has 
already  been  explained  in  the  introduction ;  but  before  treating  of  each  se- 
parately, some  general  observations  may  be  premised,  by  which  the  study 
of  this  subject  will  be  much  facilitated. 

Metals  are  of  a  combustible  nature,  that  is,  they  are  not  only  susceptible 
of  slow  oxidation,  but,  under  favourable  circumstances,  they  unite  rapidly 
with  oxygen,  giving  rise  to  all  the  phenomena  of  real  combustion.  Zinc 
burns  with  a  brilliant  flame  when  heated  to  full  redness  in  the  open  air;  iron 
emits  vivid  scintillations  on  being  inflamed  in  an  atmosphere  of  oxygen  gas; 
and  the  least  oxidizable  metals,  such  as  gold  and  platinum,  scintillate  in  a 
similar  manner  when  heated  by  the  oxy-hydrogen  blowpipe. 

The  product  either  of  the  slow  or  rapid  oxidation  of  a  metal,  when  heated 
in  the  air,  has  an  earthy  aspect,  and  was  called  a  calx  by  the  older  chemists, 
the  process  of  forming  it  being  expressed  by  the  term  calcination.  Another 
method  of  oxidizing  metals  is  by  deflagration;  that  is,  by  mixing  them  with 
nitrate  or  chlorate  of  potassa,  and  projecting  the  mixture  into  a  red-hot  cru- 
cible. Most  metals  may  be  oxidized  by  digestion  in  nitric  acid ;  and  nitro- 
hydrochloric  acid  is  an  oxidizing  agent  of  still  greater  power. 

Some  metals  unite  with  oxygen  in  one  proportion  only,  but  most  of  them 
have  two  or  three  degrees  of  oxidation.  Metals  differ  remarkably  in  their 
relative  forces  of  attraction  for  oxygen.  Potassium  and  sodium,  for  example, 
are  oxidized  by  mere  exposure  to  the  air;  and  they  decompose  water  at  all 
temperatures,  the  instant  they  come  in  contact  with  it.  Iron  and  copper 
may  be  preserved  in  dry  air  without  change,  nor  can  they  decompose  water 
at  common  temperatures;  but  they  are  both  slowly  oxidized  by  exposure  to 
a  moist  atmosphere,  and  combine  rapidly  with  oxygen  when  heated  to  red- 
ness in  the  open  air.  Iron  has  a  stronger  affinity  for  oxygen  than  copper ; 
for  the  former  decomposes  water  at  a  red-heat,  whereas  the  latter  cannot 
produce  that  effect.  Mercury  is  less  inclined  than  copper  to  unite  with 
oxygen.  Thus  it  may  be  exposed  without  change  to  the  influence  of  a  moist 
atmosphere.  At  the  temperature  of  650°  or  700°  it  is  oxidized  ;  but  at  a 
red  heat  it  is  reduced  to  the  metallic  state,  while  oxide  of  copper  can  sustain 
the  strongest  heat  of  a  blast  furnace  without,  losing  its  oxygen.  The  affinity 
of  gold  for  oxygen  is  still  weaker  than  that  of  mercury;  for  it  will  bear  the 
most  intense  heat  of  our  furnaces  without  oxidation. 

Metallic  oxides  suffer  reduction,  or  may  be  reduced  to  the  metallic  state 
in  several  ways : 

1.  By  heat  alone.     By  this  method  the  oxides  of  gold,  silver,  mercury,  and 
platinum  may  be  decomposed. 

2.  By  the  united  agency  of  heat  and  combustible  matter.    Thus,  by  trans- 
mitting a  current  of  hydrogen  gas  over  the  oxides  of  copper  or  iron  heated 
to  redness  in  a  tube  of  porcelain,  water  is  generated,  and  the  metals  are  ob- 
tained in  a  pure  form.     Carbonaceous  matters  are  likewise  used  for  the  pur- 
pose with  great  success.     Potassa  and  soda,  for  example,  may  be  decomposed 
by  exposing  them  to  a  white  heat,  after  being  intimately  mixed  with  charcoal 
in  fine  powder.     A  similar  process  is  employed  in  metallurgy  for  extracting 
metals  from  their  ores,  the  inflammable  materials  being  wood,  charcoal,  coke, 
or  coal.     In  the  more  delicate  operations  of  the   laboratory,  charcoal  and 
black  flux  are  preferred. 

3.  By  the  galvanic  battery.    This  is  a  still  more  powerful  agent  than  the 


268  GENERAL  PROPERTIES  OF  METALS. 

preceding-;  since  some  oxides,  such  as  baryta  and  strontia,  which  resist  the 
united  influence  of  heat  and  charcoal,  are  reduced  by  the  agency  of  gal- 
vanism. 

4.  By  the  action  of  deoxidizing  agents  on  metallic  solutions.  Phosphorous 
acid,  for  example,  when  added  to  a  liquid  containing  oxide  of  mercury,  de- 
prives the  oxide  of  its  oxygen,  metallic  mercury  subsides,  and  phosphoric 
acid  is  generated.  In  like  manner,  one  metal  may  be  precipitated  by  another, 
provided  the  affinity  of  the  latter  for  oxygen  exceeds  that  of  the  former. 
Thus,  when  mercury  is  added  to  a  solution  of  nitrate  of  the  oxide  of  silver, 
metallic  silver  is  thrown  down,  and  oxide  of  mercury  is  dissolved  by  the 
nitric  acid.  On  placing  metallic  copper  in  the  liquid,  pure  mercury  sub- 
sides, and  a  nitrate  of  the  oxide  of  copper  is  formed ;  and  from  this  solution 
metallic  copper  may  be  precipitated  by  means  of  iron. 

Metals,  like  the  simple  non-metallic  bodies,  may  give  rise  to  oxides  or 
acids  by  combining  with  oxygen.  The  former  are  the  most  frequent  pro- 
ducts. Many  metals  which  are  not  acidified  by  oxygen  may  be  formed  into 
oxides ;  whereas  one  metal  only,  arsenic,  is  capable  of  forming  an  acid  and 
not  an  oxide.  All  the  other  metals  which  are  convertible  into  acids  by  oxy- 
gen, such  as  chromium,  tungsten,  and  molybdenum,  are  also  susceptible  of 
yielding  one  or  more  oxides.  In  these  instances,  the  acids  always  contain  a 
larger  quantity  of  oxygen  than  the  oxides  of  the  same  metal. 

Many  of  the  metallic  oxides  have  the  property  of  combining  with  acids, 
In  some  instances  all  the  oxides  of  a  metal  are  capable  of  forming  salts  with 
acids,  as  is  exemplified  by  the  oxides  of  iron ;  but,  generally,  the  protoxide 
is  the  sole  alkaline  or  salijiable  base.  Most  of  the  metallic  oxides  are  inso- 
luble in  water ;  but  all  those  that  are  soluble  have  the  property  of  giving  a 
brown  stain  to  yellow  turmeric  paper,  and  of  restoring  the  blue  colour  of 
reddened  litmus. 

Oxides  sometimes  unite  with  each  other,  and  form  definite  compounds. 
The  most  abundant  ore  of  chromium,  commonly  called  chromate  of  iron,  is 
an  instance  of  this  kind  ;  and  the  red  oxide  of  manganese,  and  the  red  oxide 
of  lead  appear  to  belong  to  the  same  class  of  bodies. 

Chlorine  has  a  powerful  affinity  for  metallic  substances.  It  combines 
readily  with  most  metals  at  common  temperatures,  and  the  action  is  in  many 
instances  so  violent  as  to  be  accompanied  with  the  evolution  of  light.  For 
example,  when  powdered  zinc,  arsenic,  or  antimony  is  thrown  into  a  jar  of 
chlorine  gas,  the  metal  is  instantly  inflamed.  The  attraction  of  chlorine  for 
metals  even  surpasses  that  of  oxygen.  Thus,  when  chlorine  is  brought  into 
contact  at  a  red  heat  with  pure  lime,  magnesia,  baryta,  strontia,  potassa,  or 
soda,  oxygen  is  emitted,  and  a  chloride  of  the  metal  is  generated,  the  ele- 
ments of  which  are  so  strongly  united  that  no  temperature  hitherto  tried  can 
separate  them.  All  other  metallic  oxides  are,  with  few  exceptions,  acted  on 
in  the  same  manner  by  chlorine,  and  in  some  cases  the  change  takes  place 
below  the  temperature  of  ignition. 

Most  of  the  metallic  chlorides  are  solid  at  common  temperatures.  They 
are  fusible  by  heat,  assume  a  crystalline  texture  in  cooling,  and  under  fa- 
vourable circumstances  crystallize  with  regularity.  Several  of  them,  such  as 
the  chlorides  of  tin,  arsenic,  antimony,  and  mercury,  are  volatile,  and  may 
be  sublimed  without  change.  They  are  for  the  most  part  colourless,  do  not 
possess  the  metallic  lustre,  and  have  the  aspect  of  a  salt.  Two  of  the  chlo- 
rides are  insoluble  in  water,  namely,  chloride  of  silver  and  protochloride  of 
mercury  ;  several,  such  as  the  chlorides  of  antimony,  arsenic,  and  titanium, 
are  decomposed  by  that  liquid ;  but  most  of  them  are  more  or  less  soluble. 

Some  of  the  metallic  chlorides,  those  especially  of  gold  and  platinum,  are 
decomposable  by  heat.  All  the  chlorides  of  the  common  metals  are  decom- 
posed at  a  red  heat  by  hydrogen  gas,  hydrochloric  acid  being  disengaged, 
while  the  metal  is  set  free.  Pure  charcoal  does  not  effect  their  decomposi- 
tion; but  if  moisture  be  present  at  the  same  time,  hydrochloric  and  carbonic 
acid  gases  are  formed,  and  the  metal  remains.  They  resist  the  action  of  an- 
hydrous sulphuric  acid ;  but  all  the  chlorides,  excepting  those  of  silver  and 


GENERAL  PROPERTIES  OF  METALS.  269 

mercury,  are  readily  decomposed  by  hydrated  sulphuric  acid,  with  disen- 
gagement of  hydrochloric  acid  gas.  The  change  is  accompanied  with  de- 
composition of  water,  the  hydrogen  of  which  combines  with  chlorine,  and  its 
oxygen  with  the  metal.  When  in  solution,  they  may  be  recognized  by  yield- 
ing with  nitrate  of  oxide  of  silver  a  white  precipitate,  which  is  chloride  of 
silver. 

Metallic  chlorides  may  in  most  cases  be  formed  by  direct  action  of  chlo- 
rine on  the  pure  rnetals.  They  are  also  frequently  procured  by  dissolving 
metallic  oxides  in  hydrochloric  acid,  evaporating  to  dryness,  and  applying 
heat  so  long  as  any  water  is  expelled.  Metallic  chlorides  are  often  deposited 
from  sucli  solutions  by  crystallization. 

Iodine  has  a  strong  attraction  for  metals;  and  most  of  the  compounds 
which  it  forms  with  them  sustain  a  red  heat  in  close  vessels  without  decom- 
position. But  iu  the  degree  of  its  affinity  for  metallic  substances  it  is  infe- 
rior to  chlorine  and  oxygen.  We  have  seen  that  chlorine  has  a  stronger  af- 
finity than  oxygen  for  metals,  since  it  decomposes  nearly  all  oxides  at  high 
temperatures  ;  and  it  separates  iodine  also  from  metals  under  the  same  cir- 
cumstances. If  the  vapour  of  iodine  is  brought  into  contact  with  potassa, 
soda,  protoxide  of  lead,  or  oxide  of  bismuth,  heated  to  redness,  oxygen  gas  is 
evolved,  and  the  metals  of  those  oxides  will  unite  with  iodine.  But  iodine, 
so  far  as  is  known,  cannot  separate  oxygen  from  any  other  metal;  nay,  all 
the  iodides,  except  those  just  mentioned,  are  decomposed  by  exposure  to  oxy- 
gen gas  at  the  temperature  of  ignition.  All  the  iodides  are  decomposed  by 
chlorine,  bromine,  and  concentrated  sulphuric  and  nitric  acids;  and  the  io- 
dine which  is  set  free  may  be  recognized  either  by  the  colour  of  its  vapour, 
or  by  its  action  on  starch  (page  229.)  The  metallic  iodides  are  generated 
under  circumstances  analogous  to  those  above  mentioned  for  procuring  the 
chlorides. 

The  action  of  iodine  on  metallic  oxides,  when  dissolved  or  suspended  in 
water,  is  precisely  analogous  to  that  of  chlorine.  On  adding  iodine  to  a  so- 
lution of  the  pure  alkalies  or  alkaline  earths,  an  iodide  and  iodate  are  gene- 
rated. 

Bromine,  in  its  affinity  for  metallic  substances,  is  intermediate  between 
chlorine  and  iodine;  for  while  chlorine  disengages  bromine  from  its  combi- 
nation witli  metals,  metallic  iodides  are  decomposed  by  bromine.  The  same 
phenomena  attend  the  union  of  bromine  with  metals,  as  accompany  the  for- 
mation of  metallic  chlorides.  Thus,  antimony  and  tin  take  fire  by  contact 
with  bromine,  and  its  action  with  potassium  is  attended  with  a  flash  of  light 
and  intense  heat.  These  compounds  have  as  yet  been  but  partially  examined. 
They  may  be  formed  by  the  action  of  bromine  on  the  pure  metals,  and  often 
by  dissolving  metallic  oxides  in  hydrobromic  acid,  and  evaporating  the  solu- 
tion to  dryness.  Bromine  unites  with  potassa,  soda,  and  some  other  oxides, 
constituting  bleaching  compounds.  Bromide  of  lirne  is  obtained  by  the  action 
of  bromine  on  milk  of  lime,  a  yellowish  solution  being  formed  with  water, 
which  bleaches  powerfully. 

As  fluorine  has  only  recently  been  obtained  in  a  separate  state,  the  nature 
of  its  action  on  the  metals  is  imperfectly  known.  The  chief  difficulty  of  pro- 
curing it  in  an  insulated  form  arose  from  its  extremely  powerful  affinity 
for  metallic  substances,  in  consequence  of  which,  at  the  moment  of  becoming 
free,  it  attacks  the  vessels  and  instruments  employed  in  its  preparation.  The 
best  mode  of  preparing  the  soluble  fluorides,  such  of  those  of  potassium  and 
sodium,  is  by  dissolving  the  carbonates  of  potassa  and  soda  in  hydrofluoric 
acid,  and  evaporating  the  solution  to  perfect  dryness.  The  insoluble  fluorides 
are  easily  formed  by  precipitation  from  the  soluble  fluorides.  They  are 
without  exception  decomposed  by  concentrated  sulphuric  acid  with  the  aid 
of  heat;  and  the  hydrofluoric  acid,  in  escaping,  may  easily  be  detected  by 
its  action  on  glass.  » 

Sulphur,  like  the  preceding  elementary  substances,  has  a  strong  tendency 
to  unite  with  metals,  and  the  combination  may  be  effected  in  several  ways  : 

1.  By  heating  the  metal  directly  with  sulphur.  The  metal,  in  the  form  of 
23* 


270  •  GENERAL  PROPERTIES  OF  METALS. 

powder  or  filings,  is  mixed  with  a  due  proportion  of  sulphur,  and  the  mixture 
heated  in  an  earthen  crucible,  which  is  covered  to  prevent  the  access  of  air ; 
or  if  the  metal  can  sustain  a  red  heat  without  fusing1,  the  vapour  of  sulphur 
may  be  passed  over  it  while  heated  to  redness  in  a  tube  of  porcelain.  The 
act  of  combination,  which  frequently  ensues  below  the  temperature  of  igni- 
tion, is  attended  by  free  disengagement  of  heat,  which  in  several  instances  is 
so  great,  that  the  whole  mass  becomes  luminous,  and  shines  with  a  vivid 
light.  This  appearance  of  combustion,  which  occurs  quite  independently  of 
the  presence  of  oxygen,  is  exemplified  by  the  sulphurets  of  potassium,  so- 
dium, copper,  iron,  lead,  and  bismuth. 

2.  By  igniting  a  mixture  of  a  metallic  oxide  and  sulphur. 

3.  By  depriving  the  sulphate  of  an  oxide  of  its  oxygen  by  means  of  heat 
and  combustible  matter.     Charcoal  or  hydrogen  gas  may  be  employed  for 
the  purpose,  as  will  be  described  immediately. 

4.  By  hydrosulphuric  acid,  or  a  soluble  metallic  sulphuret.     Nearly  all 
the  salts  of  the  second   class  of  metals   are  decomposed  when  a  current  of 
hydrosulphuric  acid   gas   is  conducted   into  their   solutions.     The  salts  of 
uranium,  iron,  manganese,  cobalt,  and  nickel  are  exceptions  ;  but  these  are 
precipitated  by  sulphuret  of  potassium. 

The  sulphurets  are  opaque  brittle  solids,  many  of  which,  such  as  the  sul- 
phurets of  lead,  antimony,  and  iron,  have  a  metallic  lustre.  They  are  all 
fusible  by  heat,  and  commonly  assume  a  crystalline  texture  in  cooling. 
Most  of  them  are  fixed  in  the  fire ;  but  the  sulphurets  of  mercury  and 
arsenic  are  remarkable  for  their  volatility.  All  the  sulphurets,  excepting 
those  of  the  first  class  of  metals,  are  insoluble  in  water. 

Most  of  the  protosulphurets  support  an  intense  heat  without  decomposi- 
tion ;  but,  in  general,  those  which  contain  more  than  one  equivalent  of 
sulphur,  lose  part  of  it  when  strongly  heated.  They  are  all  decomposed 
without  exception  by  exposure  to  the  combined  agency  of  air  or  oxygen  gas 
and  heat ;  and  the  products  depend  entirely  on  the  degree  of  heat  and  the 
nature  of  the  metal.  The  sulphuret  is  more  or  less  converted  into  the  sul- 
phate of  an  oxide,  provided  the  sulphate  is  able  to  support  the  temperature 
employed  in  the  operation.  If  this  is  not  the  case,  the  sulphur  is  evolved 
under  the  form  of  sulphurous  acid,  and  a  metallic  oxide  is  left  ;  or  if  the 
oxide  itself  is  decomposed  by  heat,  the  pure  metal  remains.  The  action  of 
heat  and  air  in  decomposing  metallic  sulphurets  is  the  basis  of  several 
metallurgic  processes.  A  few  sulphurets  are  decomposed  by  the  action  of 
hydrogen  gas  at  a  red  heat,  the  pure  metal  being  set  free  and  hydrosulphuric 
acid  evolved.  Rose  finds  that  the  only  sulphurets  which  admit  of  being 
easily  reduced  to  the  metallic  state  in  this  way  are  those  of  antimony, 
bismuth,  and  silver.  The  sulphuret  of  tin  is  decomposed  with  difficulty, 
and  requires  a  very  high  temperature.  All  the  other  sulphurets  which  he 
subjected  to  this  treatment  were  either  deprived  of  a  part  only  of  their 
sulphur,  such  as  bisulphuret  of  iron ;  or  w7ere  not  attacked  at  all,  as  hap- 
pened with  the  sulphurets  of  zinc,  lead,  and  copper.  (Poggendorff's  An- 
nalen,  iv.  109.) 

Many  of  the  metallic  sulphurets  were  formerly  thought  to  be  compounds 
of  sulphur  and  a  metallic  oxide  ;  an  error  first  pointed  out  by  Proust,  who 
demonstrated  that  protosulphuret  of  iron,  as  well  as  the  bisulphuret  are 
compounds  of  sulphur  and  metallic  iron  without  any  oxygen.  (Journal  de 
Physique  liii.)  He  proved  the  same  of  the  sulphurets  of  other  metals,  such 
as  mercury  and  copper.  He  was  of  opinion,  however,  that  in  some  instances 
sulphur  does  unite  with  a  metallic  oxide.  Thus,  when  sulphur  and  perox- 
ide of  tin  are  heated  together,  sulphurous  acid  is  disengaged,  and  the  residue, 
according  to  Proust,  is  a  sulphuret  of  the  protoxide  ;  but  in  this  he  was  in 
error. 

In  1817  Vauquelin  extended  these  views  to  the  compounds  formed  by 
heating  an  alkali  or  alkaline  earth  with  sulphur,  which  were  previously  re- 
garded as  sulphurets  of  a  metallic  oxide.  He  explained  that  the  elements  of 
the  alkali  unite  with  separate  portions  of  sulphur,  forming  a  metallic  sul- 


f  GENERAL  PROPERTIES  OF  METALS.  271 

phuret  and  sulphuric  acid,  the  latter  of  which  unites  with  undecomposed 
alkali.  Thus,  in  preparing  the  so-called  liver  of  sulphur ,  made  by  fusing 
carbonate  of  potassa  with  sulphur,  one  portion  of  the  alkali  is  completely 
decomposed  ;  its  elements  unite  separately  with  sulphur,  giving  rise  to  sui- 
phuret  of  potassium  and  sulphuric  acid,  the  latter  of  which  combines  with 
undecomposed  potassa.  These  views  were  at  the  same  time  supported  by 
Gay-Lussac.  (An.  de  Ch.  et  de  Ph.  vi.) 

One  of  the  chief  arguments  adduced  by  Vauquelin  in  support  of  his 
opinion  was  drawn  from  the  action  of  charcoal  on  sulphate  of  potassa. 
When  a  mixture  of  this  salt  with  powdered  charcoal  is  ignited  without  ex- 
posure to  the  air,  carbonic  oxide  and  carbonic  acid  gases  are  formed,  and  a 
sulphuret  is  left,  analogous  both  in  appearance  and  properties  to  that  which 
may  be  made  by  igniting  carbonate  of  potassa  directly  with  sulphur.  They 
are  both  essentially  the  same  substance,  and  Vauquelin  conceived  from  the 
strong  attraction  of  carbon  for  oxygen,  that  both  the  sulphuric  acid  and 
potassa  would  be  decomposed  by  charcoal  at  a  high  temperature;  and  that, 
consequently,  the  product  must  be  a  sulphuret  of  potassium. 

Berthier  has  proved  that  these  changes  do  actually  occur.  (An.  de  Ch.  et 
de  Ph.  xxii.)  He  put  a  known  weight  of  sulphate  of  baryta  into  a  crucible 
lined  with  a  mixture  of  clay  and  charcoal,  defended  it  from  contact  with  the 
air,  and  exposed  it  to  a  white  heat  for  the  space  of  two  hours.  By  this  treat- 
ment it  suffered  complete  decomposition,  and  it  was  found  that  in  passing 
into  a  sulphuret,  it  had  suffered  a  loss  in  weight  precisely  equal  to  the  quan- 
tity of  oxygen  originally  contained  in  the  acid  and  earth.  This  circumstance, 
coupled  with  the  fact  that  there  had  been  no  loss  of  sulphur,  is  decisive  evi- 
dence  that  the  baryta  as  well  as  the  acid  had  lost  its  oxygen,  and  that  a  sul- 
phuret of  barium  had  been  formed.  He  obtained  the  same  results  also  with 
the  sulphates  of  strontia,lime,  potassa,  and  soda  ;  but  from  the  light  fusibility 
of  the  sulphurets  of  potassium  and  sodium,  their  loss  of  weight  could  not  be 
determined  with  such  precision  as  in  the  other  instances. 

The  experiments  of  Berzelius,  performed  about  the  same  time,  are  exceed- 
ingly elegant,  and  still  more  satisfactory  than  the  foregoing.  (An.  de  Ch.  et 
de  Ph.  xx.)  He  transmitted  a  current  of  dry  hydrogen  gas  over  a  known 
quantity  of  sulphate  of  potassa,  heated  to  redness.  It  was  expected  from  the 
strong  affinity  of  hydrogen  for  oxygen,  that  the  sulphate  would  be  decom- 
posed ;  and,  accordingly,  a  considerable  quantity  of  water  was  formed,  which 
was  carefully  collected  and  weighed.  The  loss  of  weight  which  the  salt  had 
experienced  was  precisely  equivalent  to  the  oxygen  of  the  acid  and  alkali ; 
and  the  oxygen  of  the  water  was  exactly  equal  to  the  loss  in  weight.  A  si- 
milar result  was  obtained  with  the  sulphates  of  soda,  baryta,  strontia,  and 
lime. 

It  is  demonstrated,  therefore,  that  the  metallic  bases  of  the  alkalies  and  al- 
kaline earths  agree  with  the  common  metals  in  their  disposition  to  unite 
with  sulphur.  It  is  now  certain  that,  whether  a  sulphate  be  decomposed  by 
hydrogen  or  charcoal,  or  sulphur  ignited  with  an  alkali  or  an  alkaline  earth, 
a  metallic  sulphuret  is  always  the  product.  Direct  combination  between  sul- 
phur and  a  metallic  oxide  is  a  very  rare  occurrence,  nor  has  the  existence  of 
such  a  compound  been  clearly  established.  Gay-Lussac  indeed  states  that, 
when  an  alkali  or  an  alkaline  earth  is  heated  with  sulphur  in  such  a  manner 
that  the  temperature  is  never  so  high  as  a  low  red  heat,  the  product  is  really 
the  sulphuret  of  an  oxide.  But  the  facts  adduced  in  favour  of  this  opinion 
are  not  altogether  satisfactory ;  so  that  the  real  nature  of  the  product  must 
be  decided  by  future  observation. 

Several  of  the  metallic  sulphurets  occur  abundantly  in  nature.  Those  that 
are  most  frequently  met  with  are  the  sulphurets  of  lead,  antimony,  copper, 
iron,  zinc,  molybdenum,  and  silver. 

The  metallic  seleniurets  have  so  close  a  resemblance  in  their  chemical 
relations  to  the  sulphurets,  that  it  is  unnecessary  to  give  a  separate  descrip- 
tion of  them.  They  may  be  prepared  either  by  bringing  selenium  in  con. 


272  GENERAL  PROPERTIES  OF  METALS. 

tact  with  the  metals  at  a  high  temperature,  or  by  the  action  of  hydroselenic 
acid  on  metallic  solutions. 

Respecting  the  preceding  compounds  there  remains  one  subject,  the  con- 
sideration of  which,  as  applying  equally  to  all,  has  been  purposely  delayed. 
The  non-metallic  ingredient  of  each  is  the  radical  of  a  hydracid  ;  that  is, 
has  the  property  of  forming  with  hydrogen  an  acid,  which,  like  other  acids, 
is  unable  to  unite  with  metals,  but  appears  to  combine  readily  with  many 
metallic  oxides.  Owing  to  this  circumstance,  a  difficulty  arises  in  explaining 
the  action  of  such  substances  on  water.  Thus,  when  chloride  of  potassium 
is  put  into  water,  it  may  dissolve  without  suffering  any  other  chemical 
change,  and  the  liquid  accordingly  contain  chloride  of  potassium  in  solution. 
But  it  is  also  possible  that  the  elements  of  this  compound  may  react  on  those 
of  water,  its  potassium  uniting  with  oxygen,  and  its  chlorine  with  hydrogen  ; 
and  as  the  resulting  potassa  and  hydrochloric  acid  have  a  sjtrong  affinity  for 
each  other,  the  solution  would  of  course  contain  hydrochlorate  of  potassa. 
A  similar  uncertainty  attends  the  action  of  water  on  other  metallic  chlorides, 
and  on  the  compounds  of  metals  with  i»dine,  sulphur,  cyanogen,  and  similar 
substances ;  so  that  when  iodide,  sulphuret,  and  cyanuret  of  potassium  are 
put  into  water,  it  may  be  doubted  whether  they  dissolve  as  such,  or  whether 
they  may  not  be  converted,  by  decomposition  of  water,  into  hydriodate,  hy- 
drosulphate,  and  hydrocyanate  of  potassa.  This  question  would  at  once  be 
decided,  could  it  be  ascertained  whether  water  is  or  is  not  decomposed  dur- 
ing the  process  of  solution  ;  but  this  is  the  precise  point  of  difficulty,  since, 
from  the  operation  of  the  laws  of  chemical  union,  no  disengagement  of  gas 
does  or  can  take  place  by  which  the  occurrence  of  such  a  change  may  be  in- 
dicated. Chemists,  accordingly,  being  guided  by  probabilities,  are  divided 
in  opinion,  and  I  shall,  therefore,  give  a  brief  statement  of  both  views,  with 
the  arguments  in  favour  of  each. 

According  to  one  view,  then,  chloride  of  potassium  and  all  similar  com- 
pounds dissolve  in  water  without  undergoing  any  other  change,  and  are 
deposited  in  their  original  state  by  crystallization.  When  any  hydracid, 
such  as  hydrochloric  or  hydriodic  acid,  is  mixed  with  potassa  or  any  similar 
metallic  oxide,  the  acid  and  salifiable  base  do  not  unite ;  but  the  oxygen  of 
the  oxide  combines  with  the  hydrogen  of  the  acid,  and  the  metal  itself  with 
the  radical  of  the  hydracid.  This  kind  of  double  decomposition  unquestion- 
ably takes  place  in  some  instances,  as  when  hydrosulphuric  acid  acts  upon 
acetate  of  oxide  of  lead,  the  insoluble  sulphuret  of  lead  being  actually  preci- 
pitated ;  but  it  is  also  thought  to  occur  even  when  the  transparency  of  the 
solution  is  undisturbed.  It  is  argued,  accordingly,  that  hydrochlorate  of 
potassa,  and  the  salts  of  the  hydracids  in  general,  have  no  existence.  Thus, 
when  nitrate  of  the  oxide  of  silver  is  added  to  a  solution  of  chloride  of  potas- 
sium, metallic  silver  is  said  to  unite  with  chlorine,  while  the  oxygen  of  the 
oxide  of  silver  combines  with  potassium;  so  that  nitrate  of  potassa  and  chlo- 
ride of  silver  are  genel-ated.  On  adding  sulphuric  acid  to  a  solution  of  chlo- 
ride of  potassium,  hydrochloric  acid  and  potassa,  not  previously  existing,  are 
instantly  formed  in  consequence  of  the  decomposition  of  water,  which  yields 
its  hydrogen  to  chlorine,  and  its  oxygen  to  potassium;  exactly  as  happens 
when  concentrated  sulphuric  acid  is  brought  into  contact  with  solid  chloride 
of  potassium.  It  is  further  believed  that  the  crystallized  hydrochlorate  of 
lime,  baryta,  and  strontia,  which  contain  water  or  its  elements,  are  metallic 
chlorides  combined  with  water  of  crystallization ;  and  the  same  view  is 
applied  to  all  analogous  compounds.  >  ^: 

According  to  the  other  doctrine,  chloride  of  potassium  is  converted  into 
hydrochlorate  of  potassa  in  the  act  of  dissolving  ;  and  when  the  solution  is 
evaporated,  the  elements  existing  in  the  salt  reunite  at  the  moment  of  crys- 
tallization, and  crystals  of  chloride  of  potassium  are  deposited.  The  same 
explanation  applies  in  all  cases,  when  the  salt  of  a  hydracid  crystallizes  with- 
out retaining  the  elements  of  water.  Of  those  compounds  which  in  crystal' 
lizing  retain  water  or  its  elements  in  combination,  two  opinions  may  be 
formed,  Thus  crystallized  hydrochlorate  of  baryta,  which  consists  of  one 


GJENERAL   PROPERTIES   OF   METALS.  273 

equivalent  of  chlorine,  one  of  barium,  two  of  oxygen,  and  two  of  hydrogen, 
may  be  regarded  as  a  compound  either  of  hydrochlorate  of  baryta  with  one 
equivalent  of  water  of  crystallization,  or  of  chloride  of  barium  with  two  equi- 
valents of  water.  When  exposed  to  heat,  two  equivalents  of  water  are  ex- 
pelled, and  chloride  of  barium  is  left.  When  nitrate  of  the  oxide  of  silver  is 
mixed  in  solution  with  hydrochlorate  of  potassa,  the  oxygen  of  the  oxide  of 
silver  unites  with  the  hydrogen  of  the  hydrochloric  acid,  chloride  of  silver  is 
precipitated,  and  nitrate  of  potassa  remains  in  the  liquid.  On  adding  sul- 
phuric acid  to  a  hydrochlorate,  hydrochloric  acid  is  simply  displaced ;  just 
as  when  carbonic  acid  in  marble  is  separated  from  lime  by  the  action  of 
nitric  acid. 

On  comparing  these  opinions  it  is  manifest  that  both  are  consistent  with 
well-known  affinities.  When  a  metallic  chloride  is  dissolved  in  water,  the 
attraction  of  chlorine  for  the  metal,  and  that  of  oxygen  for  hydrogen,  tend 
to  prevent  chemical  change;  but  the  affinities  of  the  metal  for  oxygen,  of 
chlorine  for  hydrogen,  and  of  hydrochloric  acid  for  metallic  oxides,  co-operate 
in  determining  the  decomposition  of  water,  and  the  production  of  a  hydro- 
chlorate.  In  favour  of  the  latter  view,  the  following  considerations  may  be 
adduced: — 1.  The  solutions  of  some  compounds,  such  as  sulphuret  of  potas- 
sium, actually  emit  an  odour  of  bydrosulphuric  acid.  2.  Other  compounds, 
such  as  the  chlorides  of  copper,  cobalt,  and  nickel,  instantly  acquire,  when 
put  into  water,  the  colour  peculiar  to  the  salts  of  the  oxides  of  those  metals. 
3  The  solution  of  protochloride  of  iron,  like  the  protosulphate,  absorbs  oxy- 
gen from  the  atmosphere ;  an  effect  which  seems  to  indicate  the  presence  of 
the  protoxide  of  iron  in  the  liquid.  4.  In  some  instances  there  is  direct 
proof  of  decomposition  of  water.  Thus  when  sulphuret  of  aluminium  is  put 
into  that  fluid,  alumina  is  generated,  and  hydrosulphuric  acid  gas  disengaged 
with  effervescence.  In  like  manner  chloride  and  sulphuret  of  silicon  are 
converted  by  water  into  silica,  and  hydrochloric  and  hydrosulphuric  acid. 
In  these  cases  the  want  of  affinity  between  the  new  compounds  causes  their 
separation,  and  thus  affords  direct  proof  that  water  is  decomposed.  But  the 
affinities  which  produce  this  change  do  not  appear  so. likely  to  be  effective, 
as  those  which  are  in  operation  when  chloride  of  potassium  is  put  into  water; 
especially  when  it  is  considered  that  the  attraction  of  chlorine  for  hydrogen, 
and  potassium  for  oxygen,  is  aided  by  that  of  the  resulting  acid  and  oxide 
for  each  other. 

These  arguments  may  be  successively  answered  in  the  following  man- 
ner : — 1.  That  the  solution  of  sulphuret  of  potassium  smells  of  hydro- 
sulphuric  acid,  because  the  carbonic  acid  of  the  atmosphere  gradually 
decomposes  it.  2.  That  metals  may  yield  with  chlorine  compounds  of 
the  same  colour  as  the  oxides  of  the  same  metals.  Thus  the  terchlo- 
ride  and  terfluoride  of  chromium  have  a  red  colour  closely  resembling 
that  of  chromic  acid.  3.  Protochloride  of  iron  may  attract  oxygen  from 
the  air  because  of  its  known  tendency  to  pass  into  the  state  of  a  ses- 
quichloride,  a  portion  of  iron  being  at  the  same  time  converted  into  per- 
oxide. 4.  That  while  certain  chlorides  do  really  decompose  water,  it  must 
be  conceded  that  others  dissolve  directly  without  change.  The  bichloride 
of  platinum  and  terchloride  of  gold  are  soluble  in  ether,  forming  solutions 
which  must  be  regarded  as  chlorides  and  not  hydrochlorates,  since  pure 
ether  is  anhydrous;  and  when  aqueous  solutions  of  these  chlorides  are  agi- 
tated with  ether,  ethereal  solutions  of  platinum  and  gold  are  formed,  exactly 
similar  to  those  made  with  ether  alone.  It  can  scarcely  be  doubted,  then, 
that  these  chlorides  exist  as  such  in  water.  In  favour  of  the  same  view  it 
may  with  truth  be  alleged,  that  the  chlorides  of  potassium  and  sodium  dis- 
solve in  and  crystallize  out  of  water,  without  evincing  the  least  sign  of  any 
other  change  than  mere  solution  and  mere  crystallization.  Again,  crystals 
of  the  so-called  hydrochlorate  of  baryta  become  chloride  of  barium  with  loss 
of  water  by  mere  exposure  to  a  dry  air;  a  cause  apparently  inadequate  to 
determine  the  hydrogen  of  the  acid  to  unite  with  the  oxygen  of  the  oxide, 
but  sufficient  to  explain  the  phenomena,  if  the  crystals  were  chloride  of  ba- 
rium .with  water  of  crystallization. 


274  GENERAL   PROPERTIES   OF   METALS. 

.  •'.  -  •~x'*... 

On  weighing-  these  and  other  considerations  of  a  like  kind,  it  appears  un- 
deniable that  some  metallic  chlorides,  iodides,  and  similar  compounds,  dissolve 
as  such  in  water :  that  all  do  so,  is  a  position  which  cannot,  I  think,  be 
maintained;  and,  therefore,  the  existence  of  such  compounds  as  hydracids 
united  with  metallic  oxides  can  scarcely  be  denied.  At  the  same  time  it  is 
necessary,  to  avoid  a  perpetually  recurring  two-fold  explanation,  to  adhere 
consistently  to  one  view ;  and  the  reader  may  have  observed  that  I  have,  in 
this  edition,  uniformly  gone  on  the  supposition  that  chlorides,  and  the  same 
class  of  bodies,  dissolve  as  such  in  water.  The  considerations  which  have 
led  to  this  preference  are  principally  drawn  from  the  history  of  the  sulphur- 
salts. 

Chemists  are  acquainted  with  several  metallic  phosphurets ;  and  it  is  pro- 
bable that  phosphorus,  like  sulphur,  is  capable  of  uniting  with  all  the  metals. 
Little  attention,  however,  has  hitherto  been  devoted  to  these  compounds;  and 
for  the  greater  part  of  our  knowledge  concerning  them  we  are  indebted  to 
the  researches  of  Pelletier  and  Rose.  (An.  de  Ch.  i.  and  xiii. ;  and  Pog.  An. 
vi.  205.) 

The  metallic  phosphurets  may  be  prepared  in  several  ways.  The  most 
direct  method  is  by  bringing  phosphorus  in  contact  with  metals  at  a  high 
temperature,  or  by  igniting  metals  in  contact  with  phosphoric  acid  and  char- 
coal. Several  of  the  phosphurets  may  be  formed  by  transmitting  a  current 
of  phosphuretied  hydrogen  gas  over  metallic  oxides  heated  to  redness  in  a 
porcelain  tube,  when  water  is  generated,  and  a  phosphuret  of  the  metal  re- 
mains. By  similar  treatment  the  chlorides  and  sulphurets  of  many  metals 
may  be  decomposed,  and  phosphurets  formed,  provided  the  metal  is  capable 
of  retaining  phosphorus  at  a  red  heat.  According  to  Rose,  the  phosphurets 
of  copper,  nickel,  cobalt,  and  iron,  are  the  only  ones  which  admit  of  being 
advantageously  prepared  by  this  method.  When  chlorides  are  employed, 
hydrochloric  acid,  and  when  sulphurets,  hydrosulphuric  acid  gas,  is  of  course 
generated. 

Phosphorus  is  said  to  unite  with  metallic  oxides.  For  example,  phosphu- 
ret of  lime  is  said  to  be  formed  by  conducting  the  vapour  of  phosphorus  over 
that  earth  at  a  low  red  heat;  but  it  is  probable  that  in  this  instance,  as  with 
a  mixture  of  sulphur  and  an  alkali,  part  of  the  metallic  oxide  is  decomposed, 
and  that  the  product  contains  phosphuret  of  calcium  and  phosphate  of  lime. 

The  only  metallic  carburets  of  importance  are  those  of  iron,  which  will  be 
described  in  the  section  on  that  metal. 

Hydrogen  unites  with  few  metals.  The  only  metallic  hydrogurets,  or  hy- 
durets,  known  are  those  of  zinc,  potassium,  arsenic,  antimony,  and  tellurium. 
No  definite  compound  of  nitrogen  and  :i  metal  has  hitherto  been  discovered. 

The  discoveries  of  modern  chemistry  have  materially  added  to  the  number 
of  the  metals,  especially  by  associating  with  them  a  class  of  bodies  which 
was  formerly  believed  to  be  of  a  nature  entirely  different.  The  metallic 
bases  of  the  alkalies  and  earths,  previous  to  the  year  1807,  were  altogether 
unknown ;  and  before  that  date  the  list  of  metals,  with  few  exceptions,  in- 
cluded those  only  which  are  commonly  employed  in  the  arts,  and  which  are 
hence  often  called  the  common  metals.  In  consequence  of  this  increase  in 
number,  it  is  found  convenient,  for  the  purpose  of  description,  to  arrange 
them  in  separate  groups;  and  as  the  alkalies  and  earths  differ  in  several 
respects  from  the  other  metallic  oxides,  it  will  be  convenient  to  describe  their 
metallic  bases  separately.  I  have  accordingly  divided  the  metals  into  the 
two  following  classes  : — 

CLASS  I.  Metals  which  by  oxidation  yield  alkalies  or  earths. 

CLASS  II.  Metals,  the  oxides  of  which  are  neither  alkalies  nor  earths. 

CLASS  I.  This  class  includes  twelve  metals,  which  may  properly  be  ar- 
ranged in  three  orders. 

Order  I.  Metallic  bases  of  the  alkalies.  They  are  three  in  number  ; 
namely, 

Potassium,  Sodium,  Lithium. 


GENERAL   PROPERTIES   CF   METALS.  275 

These  metals  have  such  a  powerful  attraction  for  oxygen,  that  they  de- 
compose cold  water  and  even  ice  at  the  moment  of  contact,  and  are  oxydized 
with  disengagement  of  hydrogen  gas.  The  resulting  oxides  are  distinguished 
by  their  causticity  and  solubility  in  water,  and  by  possessing  alkaline  pro- 
perties in  an  eminent  degree.  They  are  called  alkalies,  and  their  metallic 
bases  are  sometimes  termed,  aZ&aZirze  or  alkaligenovs  metals. 

Order  2.  Metallic  bases  of  the  alkaline  earths.     These  are  four  in  number 
namely, 

Barium,  Strontium,  Calcium,  Magnesium. 

These  metals,  excepting-  magnesium,  also  decompose  water  rapidly  at 
common  temperatures.  The  resulting  oxides  are  called  alkaline  earths; 
because,  while  in  their  appearance  they  resemble  the  earths,  they  are  similar 
to  the  alkalies  in  having  a  strong  alkaline  reaction  with  test  paper,  and  in 
neutralizing  acids.  The  first  three  are  strongly  caustic,  and  baryta  and 
strontia  are  soluble  in  water  to  a  considerable  extent. 

Order  3.  Metallic  bases  of  the  earths.     These  are  five  in  number ;  namely, 

Aluminium,  Yttrium,  Zirconium. 

Glucinium,  Thorium, 

The  oxides  of  these  metals  are  well  known  as  the  pure  earths.  They  are 
white  and  of  an  earthy  appearance,  in  their  ordinary  state  are  quite  insoluble 
in  water,  and  do  not  affect  the  colour  of  turneric  or  litimus  paper.  As  salifi- 
able  bases  they  are  inferior  to  the  alkaline  earths. 

CLASS  II.  The  number  of  the  metals  included  in  this  class  amounts  to 
twenty-nine.  They  are  all  capable  of  uniting  with  oxygen,  and  generally 
in  more  than  one  proportion.  Their  protoxides  have  an  earthy  appearance, 
but  with  few  exceptions  are  coloured.  They  are  insoluble  in  water,  and  in 
general  do  not  affect  the  colour  of  test  paper.  Most  of  them  act  as  salifiable 
bases  in  uniting  with  acids,  and  forming  salts;  but  in  this  respect  they  are 
much  inferior  to  the  alkalies  and  alkaline  earths,  by  which  they  may  be 
separated  from  their  combinations.  Several  of  these  metals  are  capable  of 
forming  with  oxygen  compounds,  which  possess  the  characters  of  acids. 
The  metals  in  which  this  property  has  been  noticed  are  manganese,  arsenic, 
chromium,  vanadium,  molybdenum,  tungsten,  columbium,  antimony,  tita- 
nium, tellurium,  gold,  and  osmium. 

The  metals  belonging  to  the  second  class  may  be  conveniently  arranged 
in  the  three  following  order§  : — 

Order  1.  Metals  which  decompose  water  at  a  red  heat.  They  are  seven 
in  number ;  namely, 

Manganese,  Cadmium,  Cobalt, 

Iron,  Tin,  Nickel. 

Zinc, 

Order  2.  Metals  which  do  not  decompose  water  at  any  temperature,  and 
the  ©xides  of  which  are  not  reduced  to  the  metallic  state  by  the  sole  action 
of  heat.  Of  these  there  are  fourteen  in  number  ;  namely, 

Arsenic,  Columbium,  Titanium, 

Chromium,  Antimony,  Tellurium, 

Vanadium,  Uranium,  Copper, 

Molybdenum,  Cerium,  Lead. 

Tungsten,  Bismuth, 

Order  3.  Metals,  the  oxides  of  which  are  reduced  to  the  metallic  state  by 
a  red  heat.  These  are, 

Mercury,  Platinum,  Osmium, 

Silver,  Palladium,  Iridium. 

Gold,  Rhodium, 


276 


CLASS  I. 

METALS  WHICH   BY  OXIDATION  YIELD  ALKALIES 
OR  EARTHS. 

ORDER  I. 

METALLIC  BASES  OF  THE  ALKALIES. 


SECTION    I. 
POTASSIUM. 

Hist,  and  Prep. — Discovered  in  the  year  1807  by  Davy,  and  the  circum- 
stances which  led  to  the  discovery  have  already  been  described.  Hydrate  of 
potassa,  slightly  moistened  for  the  purpose  of  increasing  its  conducting 
power,  was  made  to  communicate  with  the  opposite  poles  of  a  galvanic  bat- 
tery of  200  double  plates ;  when  the  oxygen  both  of  the  water  and  the  pot- 
assa passed  over  to  the  positive  pole,  while  the  hydrogen  of  the  former,  and 
the  potassium  of  the  latter,  made  their  appearance  at  the  negative  pole.  By 
this  process  potassium  is  obtained  in  small  quantity  only;  but  Gay-Lussac 
and  Thenard  invented  a  method  by  which  a  more  abundant  supply  may  be 
procured.  (Recherches  Physico-Chimiques,  vol.  i.)  Their  process  consists 
in  bringing  fused  hydrate  of  potassa  in  contact  with  turnings  of  iron  heated 
to  whiteness  in  a  gun-barrel.  The  iron,  under  these  circumstances,  deprives 
the  water  and  potassa  of  oxygen,  hydrogen  gas  combined  with  a  little  potas- 
sium is  evolved,  and  pure  potassium  sublimes,  and  may  be  collected  in  a  cool 
part  of  the  apparatus. 

Potassium  may  also  be  prepared,  as  first  noticed  by  Curaudau,  by  mixing 
dry  carbonate  of  potassa  with  half  its  weight  of  powdered  charcoal,  and  ex- 
posing the  mixture,  contained  in  a  gun-barrel  or  spheroidal  iron  bottle,  to  a 
strong  heat.  An  improvement  on  both  processes  has  been  made  by  Brun- 
ner,  who  decomposes  potassa  by  means  of  iron  and  charcoal.  From  eight 
ounces  of  fused  carbonate  of  potassa,  six  ounces  of  iron  filings,  and  two 
ounces  of  charcoal,  mixed  intimately  and  heated  in  an  iron  bottle,  he  ob- 
tained 140  grains  of  potassium.  (Quarterly  Journal,  xv.  379.)  Berzelius  has 
observed  that  the  potassium  thus  made,  though  fit  for  all  the  usual  purposes 
to  which  it  is  applied,  contains  a  minute  quantity  of  carbon  ;  and,  therefore, 
if  required  to  be  quite  pure,  must  be  rendered  so  by  distillation  in  a  retort 
of  iron  or  green  glass.  A  modification  of  this  process  has  been  since  des- 
cribed by  WcJhler,  who  effects  the  decomposition  of  the  potassa  solely  by 
means  of  charcoal.  The  material  employed  for  the  purpose  is  carbonate  of 
potassa,  prepared  by  heating  cream  of  tartar  to  redness  in  a  covered  cruci- 
ble. (Poggendorff's  Annalen,  iv.  23.)  According  to  Liebig,  two  eq.  of  char- 
coal and  one  eq.  of  carbonate  of  potassa  react  on  each  other,  and  form  one 
eq.  of  potassium  and  three  eq.  of  carbonic  oxide;  or 

and  2C  yield  K  and  3CO. 


POTASSIUM.  277 

The  whole  of  the  potassium  thus  liberated  is  not,  however,  obtained  in  the 
metallic  form;  for  two  out  of  every  three  eq.  combine  with  seven  out  of  the 
nine  eq.  of  carbonic  oxide  gas  at  the  same  time  produced.  The  resulting 
compound  has  a  dark  gray  colour,  and  is  recognized  by  burning  on  water 
with  a  violet  flame,  and  the  production  of  croconate  and  oxalate  of  potassa. 
This  compound  is  sometimes  almost  the  sole  product  of  the  process.  (Geiger's 
Pharmacie,  348.) 

Prop. — Solid  at  the  ordinary  temperature  of  the  atmosphere.  At  70°  it  is 
somewhat  fluid,  though  its  fluidity  is  not  perfect  till  it  is  heated  to  150°. 
At  50°  it  is  soft  and  malleable,  and  yields  like  wax  to  the  pressure  of  the 
fingers ;  but  it  becomes  brittle  when  cooled  to  32°.  It  sublimes  at  a  low  red 
heat  without  undergoing  any  change,  provided  atmospheric  air  be  completely 
excluded.  Its  texture  is  crystalline,  as  may  be  seen  by  breaking  it  across 
while  brittle,  and  cubic  crystals  have  been  obtained  by  Pleischl  (Pog.  An. 
xxxi.  431).  In  colour  and  liistre  it  is  precisely  similar  to  mercury.  At  60° 
its  density  is  0-865,  so  that  it  is  considerably  lighter  than  water.  It  is  quite 
opaque,  and  is  a  good  conductor  of  heat  and  electricity. 

The  most  prominent  chemical  property  of  potassium  is  its  affinity  for  ox- 
ygen gas.  It  oxidizes  rapidly  in  the  air,  or  by  contact  with  fluids  which 
contain  oxygen.  On  this  account  it  must  be  preserved  either  in  glass  tubes 
hermetically  sealed,  or  under  the  surface  of  liquids,  such  as  naphtha,  of 
which  oxygen  is  not  an  element.*  If  heated  in  the  open  air,  it  takes  fire, 
and  burns  with  a  purple  flame  and  great  evolution  of  heat.  It  decomposes 
water  on  the  instant  of  touching  it;  and  so  much  heat  is  disengaged,  that 
the  potassium  is  inflamed,  and  burns  vividly  while  swimming  upon  its  sur- 
face. The  hydrogen  unites  with  a  little  potassium  at  the  moment  of  separa- 
tion ;  and  this  compound  takes  fire  as  it  escapes,  and  thus  augments  the 
brilliancy  of  the  combustion.  When  potassium  is  plunged  under  water, 
violent  reaction  ensues,  but  without  light,  and  pure  hydrogen  gas  is  evolved. 

The  combining  weight  or  equivalent  of  potassium  is  easily  deducible  from 
the  composition  of  potassa  and  chloride  of  potassium,  which  are  admitted  to 
consist  of  single  equivalents  of  their  elements.  Gay-Lussac  and  Thenard, 
and  Davy  inferred  the  composition  of  potassa  from  the  hydrogen  gas  evolved 
when  a  known  weight  of  potassium  is  oxidized  under  water,  the  volume  of 
the  oxygen  which  unites  with  the  metal  being  equal  to  half  the  volume  of 
the  hydrogen.  Berzelius  analyzed  chloride  of  potassium  by  means  of  nitrate 
of  oxide  of  silver,  and  inferred  that  39-15  is  the  eq.  of  potassium.  Its  symb. 
is  K. 

Potassium.  Equiv.         Formulae. 

Protoxide         39-15  1  eq.-f-Oxygen       8         1  eq.=  47-15  K-fO  or  KO. 
Teroxide          39-15  1  eq.-{-     do.         24         3  eq.r=  63-15  K+SO  or  K(X 
Chloride          39-15  1  eq.+Chlorine     35-42  1  eq.=  74-57  K+ClorKCl. 
Iodide  39-15  1  eq.-f-Iodine       126'3     1  eq.=165-45  K+I  or  KI. 

Bromide          39-15  1  eq.+ Bromine     78-4     1  eq.=l  17-55  K+Br.  or  KBr. 
Fluoride          39-15  1  eq.-f  Fluorine     18-68  1  eq.=  57-83  K+F  or  KF. 
Hydurets      7  ^ 
Carburet       ]  Composition  uncertain. 

Protosulph't    39-15  1  eq.+  Sulphur       16-1      1  eq.=  55-25  K+S  or  KS. 
Bisulphuret     39-15  1  eq.-f-    do.  32-2      2  eq.=  71-35  K+2S  or  KS*. 

Tersulphuret  39-15  1  eq.-f-     do.  48-3      3  eq.=   87-45  K-J-3S  or  KSs. 

'151  eq.-f    do.  64-4     4eq.=103-55  K+4S  or  KS«. 

39<15leq.+    do.  80-5      5eq.  =  119-65  K  +  5S  or  KS». 

Phosphurets  ?  ^ 

Seleniurets    (  ^omPosltlon  anc*  number  uncertain. 

*  Mr.  Durand,  pharmaceutist  of  Philadelphia,  has  ascertained  that  the  es- 
sential oil  of  copaiba  is  a  good  liquid  for  the  preservation  of  potassium. 

24 


278  POTASSIUM. 

Protoxide  of  Potassium.— Hist,  and  Prep. — This  compound,  commonly 
called  potash  or  potassa,  and  by  the  Germans  kali  (an  Arabic  word),  is  al- 
ways formed  when  potassium  is  put  into  water,  or  when  it  is  exposed  at  com- 
mon temperatures  to  dry  air  or  oxygen  gas.  By  the  former  method  the  pro- 
toxide is  obtained  in  combination  with  water;  and  in  the  latter  it  is  anhydrous. 
In  performing  the  last-mentioned  process,  the  potassium  should  be  cut  into 
very  thin  slices ;  for  otherwise  the  oxidation  is  incomplete.  The  product, 
when  partially  oxidized,  is  regarded  by  Berzelius  as  a  distinct  oxide ;  but 
most  chemists  admit  it  to  be  a  mere  mixture  of  potassa  and  potassium. 

Prop. — Anhydrous  potassa  is  a  white  solid  substance,  highly  caustic, 
which  fuses  at  a  temperature  somewhat  above  that  of  redness,  and  bears  the 
strongest  heat  of  a  wind  furnace  without  being  decomposed  or  volatilized. 
It  has  a  powerful  affinity  for  water,  and  intense  heat  is  disengaged  during 
the  act  of  combination.  Three  compounds  are  known ;  they  are  composed 
of  47-15,  or  one  eq.  of  potassa,  united  with  9,  27,  and  45  parts,  or  one,  three, 
and  five  eq.  of  water  respectively.  In  the  last  compound,  a  portion  of  the 
water  probably  exists  as  water  of  crystallization. 

The  protohydrate  of  potassa  is  solid  at  common  temperatures.  It  fuses 
at  a  heat  rather  below  redness,  and  assumes  a  somewhat  crystalline  texture 
in  cooling.  It  is  not  decomposed  by  any  degree  of  heat  to  which  it  has  been 
exposed,  and  hence  was  long  considered  to  be  pure  potassa.  Its  sp.  gr.  is 
T706.  It  is  highly  deliquescent,  and  requires  about  half  its  weight  of  water 
for  solution.  It  is  soluble,  likewise,  in  alcohol.  It  destroys  all  animal  tex- 
tures, and  on  this  account  is  employed  in  surgery  as  a  caustic.  It  was  for- 
merly called  lapis  causticus,  but  it  is  now  termed  Potassa  and  Potassa  Fusa 
by  the  Colleges  of  Edinburgh  and  London.  This  preparation  is  made  by 
evaporating  the  aqueous  solution  of  potassa  in  a  silver  or  clean  iron  capsule 
to  the  consistence  of  oil,  and  then  pouring  it  into  moulds.  In  this  state  it  is 
impure,  containing  oxide  of  iron,  together  with  chloride  of  potassium,  and 
carbonate  and  sulphate  of  potassa.  It  is  purified  from  these  substances  by 
solution  in  alcohol,  and  evaporation  to  the  same  extent  as  before  in  a  silver 
vessel.  The  operation  should  be  performed  expeditiously,  in  order  to  pre- 
vent, as  far  as  possible,  the  absorption  of  carbonic  acid.  When  common 
caustic  potassa  of  the  druggists  is  dissolved  in  water,  a  number  of  small  bub- 
bles of  gas  is  disengaged,  which  is  pure  oxygen.  Graham  finds  its  quantity 
to  be  variable  in  different  specimens,  and  to  depend  apparently  on  the  impu- 
rity of  the  specimen. 

If  the  protohydrate  be  exposed  to  the  air,  it  rapidly  becomes  moist ;  but 
after  absorbing  a  certain  portion  of  water,  a  perfectly  dry  substance  is  again 
obtained,  which  is  the  terhydrate  of  potassa.  It  is  very  similar  in  all  its 
characters  to  the  protohydrate,  but  is  much  whiter  and  more  crystalline  in 
its  texture.  The  quintohydrate  is  obtained  by  exposing  a  very  concentrated 
solution  of  potassa  to  an  intense  cold.  It  is  then  deposited  in  four-sided 
prisms  terminated  by  a  four-sided  pyramid,  and  sometimes  in  four-sided 
tables  and  octohedrons. 

The  aqueous  solution  of  potassa,  Aqua  Potassa  of  the  Pharmacopoeia,  is 
prepared  bv  decomposing  carbonate  of  potassa  by  lime.  To  effect  this  ob- 
ject completely,  it  is  advisable  to  employ  equal  parts  of  quicklime  and  car- 
bonate of  polassa.  The  lime,  as  soon  as  it  is  slaked,  is  added  to  the  carbo- 
nate, dissolved  in  six  or  ten  times  its  weight  of  hot  water,  and  the  mixture 
is  boiled  briskly  in  a  clean  iron  vessel  for  about  ten  minutes.  The  liquid, 
after  subsiding,  is  filtered  through  a  funnel,  the  throat  of  which  is  obstructed 
by  a  piece  of  clean  linen.  This  process  is  founded  on  the  fact  that  lime  de- 


I  have  used  it  myself  for  this  purpose,  and  am  satisfied  that  it  is  superior  to 
the  ordinary  naphtha.  The  brightness  of  the  metal  is  but  slightly  impaired, 
while  in  common  naphtha  it  becomes  covered  with  a  blackish  film.  Several 
chemists  have  used  this  oil  on  the  recommendation  of  Mr,  Durand,  and  with 
satisfactory  results. — Ed. 


279 


prives  carbonate  of  potassa  of  its  acid,  forming  an  insoluble  carbonate  of 
lime,  and  setting-  the  pure  alkali  at  liberty.  If  the  decomposition  is  com- 
plete, the  filtered  solution  should  not  effervesce  when  neutralized  with  an 
acid.  Liebig  finds  that  a  strong  solution  of  caustic  potassa  actually  deprives 
carbonate  of  lime  of  its  acid,  and  that,  from  this  circumstance,  carbonate  of 
potassa  cannot  be  rendered  quite  caustic  by  lime,  unless  diluted  with  about 
ten  times  its  weight  of  water. 


ing  apparatus  devised  by  Donovan.  It  consists  of  two  vessels  A  and  D,  of 
equal  capacity,  and  connected  with  each  other  as 
represented  in  the  annexed  wood-cut.  The  neck  b 
of  the  upper  vessel  contains  a  tight  cork,  perforated 
to  admit  one  end  of  the  glass  tube  c ;  and  the  lower 
extremity  of  the  same  vessel  terminates  in  a  funnel 
pipe,  which  fits  into  one  of  the  necks  of  the  under 
vessel  D  by  grinding,  luting,  or  a  tight  cork.  The 
vessel  D  is  furnished  with  another  neck  e,  which  re- 
ceives the  lower  end  of  the  tube  c,  the  junction  being 
secured  by  means  of  a  perforated  cork,  or  luting. 
The  throat  of  the  funnel  pipe  is  obstructed  by  a  piece  - 
of  coarse  linen  loosely  rolled  up,  and  not  pressed 
down  into  the  pipe  itself.  The  solution  is  then 
poured  in  through  the  mouth  at  6,  the  cork  and  tube 
having  been  removed ;  and  the  first  droppings, 
which  are  turbid,  are  not  received  in  the  lower  ves- 
sel. The  parts  of  the  apparatus  are  next  joined  to- 
gether, and  the  filtration  may  proceed  at  the  slowest 
rate,  without  exposure  to  more  air  than  was  con- 
tained in  the  vessels  at  the  beginning  of  the  process. 
This  apparatus  should  be  made  of  green  in  prefer- 
ence to  white  glass ;  as  the  pure  alkalies  act  on  the 
former  much  less  than  on  the  latter.  (Annals  of  D 
Philosophy,  xxvi.  115.) 

The  mode  by  which  this  apparatus  acts  scarcely 
needs  explanation.  In  order  that  the  liquid  should- 
descend  freely,  two  conditions  are  required : — first,  that  the  air  above  the 
liquid  should  have  the  same  elastic  force,  and  therefore  exert  the  same  pres- 
sure, as  that  below ;  and  secondly,  as  one  means  of  securing  the  first  condi- 
tion, that  the  air  should  have  free  egress  from  the  lower  vessel.  Both  objects, 
it  is  manifest,  are  accomplished  in  the  filtering  apparatus  of  Donovan  ;  since 
for  every  drop  of  liquid  which  descends  from  the  upper  to  the  lower  vessel, 
a  corresponding  portion  of  air  passes  along  the  tube  c,  from  the  lower  vessel 
to  the  upper. 

Solution  of  potassa  is  highly  caustic,  and  its  taste  intensely  acrid.  It  pos- 
sesses alkaline  properties  in  an  eminent  degree,  converting  the  vegetable 
blue  colours  to  green,  and  neutralizing  the  strongest  acids.  It  absorbs  car- 
bonic acid  gas  rapidly,  and  is  consequently  employed  for  withdrawing  that 
substance  from  gaseous  mixtures.  For  the  same  reason  it  should  be  pre. 
served  in  well-closed  bottles,  that  it  may  not  absorb  carbonic  acid  from  the 
atmosphere. 

Potassa  is  employed  as  a  reagent  in  detecting  j.he  presence  of  bodies, 
and  in  separating  them  from  each  other.  The  solid  hydrate,  owing  to  its 
strong  affinity  for  water,  is  used  for  depriving  gases  of  hygrometric  mois- 
ture, and  is  admirably  fitted  for  forming  frigorific  mixtures  (page  39). 

Potassa  may  be  distinguished  from  all  other  substances  by  the  following 
characters — 1.  If  tartaric  acid  be  added  in  excess  to  a  salt  of  potassa  dis- 
solved in  cold  water,  and  the  solution  be  stirred  with  a  glass  rod,  a  white 
precipitate,  bitartrate  of  potassa,  soon  appears,  which  forms  peculiar  white 


280  POTASSIUM. 

streaks  upon  the  glass  by  the  pressure  of  the  rod  in  stirring-.  2.  It  is  pre- 
cipitated by  perchloric  acid  in  the  cold,  the  perchlorate  of  potassa  having 
nearly  the  same  degree  of  solubility  as  the  bitartrate.  3.  A  solution  of 
chloride  of  platinum  causes  a  yellow  precipitate,  the  double  chloride  of  pla- 
tinum and  potassium.  A  drop  or  two  of  hydrochloric  acid  should  be  added 
at  the  same  time  as  the  test,  the  mixture  be  evaporated  to  dryness  at  212°, 
and  a  little  cold  water  be  afterwards  added,  when  the  double  chloride  is  left 
*  in  the  form  of  small  shining  yellow  crystals.  Chloride  of  platinum  dissolved 
in  alcohol  often  gives  an  immediate  precipitate,  which  falls  of  a  pale  yellow 
colour.  4.  The  alcoholic  solution  of  carbazotic  acid  throws  down  potassa 
in  yellow  crystals  of  carbazotate  of  potassa,  which  is  very  sparingly  soluble. 
5.  It  yields  a  light  gelatinous  precipitate,  the  double  fluoride  of  potassium 
and  silicon  with  silicated  hydrofluoric  acid.  Of  these  tests  carbuzotic  acid 
is  the  most  delicate  in  a  solution  of  pure  potassa  ;  but  when  the  alkali  is 
combined  with  a  strong  acid,  the  chloride  of  platinum  is  preferable. 

The  following  test  has  been  recommended  by  Harkort  for  distinguishing 
between  potassa  and  soda  in  minerals  :  —  Oxide  of  nickel,  when  fused  by  the 
blowpipe  flame  with  borax,  gives  a  brown  glass  ;  and  this  glass,  if  melted 
with  a  mineral  containing  potassa,  becomes  blue,  an  effect  which  is  not  pro- 
duced by  the  presence  of  soda. 

Its  eq.  is  47-15  ;  symb.  K-j-O,  K,  or  KO. 

Teroxide.  —  When  potassium  burns  in  the  open  air  or  in  oxygen  gas,  it  is 
converted  into  an  orange-coloured  substance,  which  is  teroxide  of  potassium. 
It  may  likewise  be  formed  by  conducting  oxygen  gas  over  potassa  at  a  red 
heat  ;  and  it  is  produced  in  small  quantity  when  potassa  is  heated  in  the 
open  air.  It  is  the  residue  of  the  decomposition  of  nitre  by  heat  in  metallic 
vessels,  provided  the  temperature  be  kept  up  for  a  sufficient  time.*  When 
the  teroxide  is  put  into  water,  it  is  resolved  into  oxygen  and  potassa,  the  for- 
mer of  which  escapes  with  effervescence,  and  the  latter  is  dissolved. 


Its  eq.  is  63-15  ;  symb.  K-J-3O,  K,  or 

Chloride  of  Potassium.  —  Potassium  takes  fire  spontaneously  in  an  atmos- 
phere of  chlorine,  and  burns  with  greater  brilliancy  than  in  oxygen  gas. 
This  chloride  is  generated  with  evolution  of  hydrogen  when  potassium  is 
heated  in  hydrochloric  acid  gas;  and  it  is  the  residue  after  the  decomposi- 
tion of  chlorate  of  potassa  by  heat.  It  is  formed  when  potassa  is  dissolved 
in  a  solution  of  hydrochloric  acid,  and  is  deposited  by  slow  evaporation  in 
anhydrous  colourless  cubic  crystals.  It  has  a  saline  and  rather  bitter  taste, 
is  insoluble  in  alcohol,  and  requires  for  solution  3  parts  of  water  at  60°,  and 
still  less  of  hot  water.  Its  eq.  is  74-57  ;  symb.  K  +  C1.  or  KC1. 

Iodide  of  Potassium.  —  Prep.  —  This  compound  is  formed  with  evolution  of 
heat  and  light,  when  potassium  is  heated  in  contact  with  iodine  :  it  is  the 
sole  residue  after  decomposing  iodate  of  potassa  by  heat  ;  and  by  neutralizing 
potassa  with  hydriodic  acid  it  is  obtained  in  solution.  The  simplest  process 
for  preparing  it  in  quantity  is  to  add  iodine  to  a  hot  solution  of  pure  potassa 

*  This  fact  was  ascertained  by  Dr.  Bridges  of  Philadelphia,  in  the  spring 
of  1827,  while  investigating  the  nature  of  the  gas  given  off,  on  the  addition 
of  water,  from  the  residue  of  nitre,  after  exposure  in  an  iron  bottle  to  a  red 
heat.  This  gas  proved  to  consist  of  oxygen  nearly  pure,  and  the  residue 
was  converted  into  a  solution  of  hydrate  of  potassa.  These  results  evident- 
ly prove,  that  the  residue  in  question  consists  of  teroxide  of  potassium.  Dr. 
Bridges  suggests  that  the  employment  of  this  residue  might  prove  conve- 
nient to  the  chemist  for  obtaining  oxygen  extemporaneously  ;  as  it  would  be 
necessary  only  to  add  water  in  order  to  obtain  the  gas.  —  North  American 
Medical  and  Surgical  Journal,  v.  241. 

About  the  same  time  that  Dr  Bridges  made  the  above  observations, 
similar  ones  were  made  by  Mr.  Phillips  in  London.  —  Annals  of  Philosophy, 
April  1827.—  Ed. 


POTASSIUM.  281 

until  the  alkali  is  neutralized,  when  iodide  of  potassium  and  iodate  of  potassa 
are  generated  ;  evaporate  to  dryness,  and  expose  the  dry  mass  in  a  platinum 
crucible  to  a  gentle  red  heat,  in  order  to  decompose  the  iodate.  The  fused 
mass  is  then  dissolved  out  by  water  and  crystallized.  Another  process  is  to 
digest  iodine  with  zinc  or  iron  filings  in  water,  and  then  decompose  the  re- 
sulting iodide  of  zinc  or  iron  by  a  quantity  of  potassa  just  sufficient  to  pre- 
cipitate the  oxide. 

Prop. — Iodide  of  potassium  fuses  readily  when  heated,  and  rises  in  vapour 
at  a  heat  below  full  redness,  especially  in  an  open  vessel.  It  is  very  soluble 
in  water,  requiring  only  two-thirds  of  its  weight  at  60°  for  solution,  and  in 
a  moist  atmosphere  deliquesces.  It  dissolves  also  in  strong  alcohol,  even  in 
the  cold  ;  and  the  solution,  when  evaporated,  yields  colourless  cubic  crystals 
of  iodide  of  potassium. 

The  commercial  iodide  is  frequently  impure,  often  containing  chloride  of 
potassium  or  sodium,  and  sulphate  or  carbonate  of  potassa,  the  last  some- 
times in  very  large  quantity.  It  is  well  to  purchase  it  in  crystals,  which 
ought  not  to  deliquesce  in  a  moderately  dry  air,  but  when  in  powder  are 
completely  soluble  in  the  strongest  alcohol. 

Iodine  is  freely  soluble  in  water  which  contains  iodide  of  potassium,  a 
brown  solution  resulting,  which  has  been  thought  to  arise  from  potassium 
uniting  with  two  or  more  equivalents  of  iodine.  No  solid  compound  of  the 
kind,  however,  has  been  obtained. 

Its  eq.  is  16545  ;  symb.  K  +  I,  or  KI. 

Bromide  of  Potassium. — This  compound  is  formed  by  processes  similar  to 
those  for  preparing  the  iodide,  and  is  analogous  to  it  in  most  of  its  proper- 
ties. It  is  very  soluble  in  water,  and  crystallizes  by  evaporation  in  anhy- 
drous cubic  crystals,  which  fuse  readily,  and  decrepitate  when  heated  like 
sea-salt.  It  is  but  slightly  soluble  in  alcohol. 

Its.  eq.  is  117-55  ;  symb.  K+Br,  or  KBr. 

Fluoride  of  Potassium. — This  compound  is  best  formed  by  nearly  saturat- 
ing hydrofluoric  acid  with  carbonate  of  potassa,  evaporating  to  dryness  in 
platinum,  and  igniting  to  expel  any  excess  of  acid.  The  resulting  fluoride 
has  a  sharp  saline  taste,  is  alkaline  to  test  paper,  deliquesces  in  the  air,  and 
dissolves  freely  in  water.  On  evaporating  its  solution  at  a  temperature  of  100° 
it  may  be  obtairfed  in  cubes  or  rectangular  four-sided  prisms,  which  deli- 
quesce rapidly.  The  solution  acts  on  glass  in  which  it  is  kept  or  evaporated. 
Heated  with  silicic  acid  it  forms  a  fusible  limpid  glass,  which  when  cold  is 
opaque  and  deliquescent.  Water  dissolves  fluoride  of  potassium,  and  the 
silicic  acid  is  left. 

Its  eq.  is  57-83 ;  symb.  K-f-F,  or  KF. 

Hydrogen  and  Potassium. — These  substances  unite  in  two  proportions, 
forming  in  one  case  a  solid,  and  in  the  other  a  gaseous  compound.  The  lat- 
ter is  produced  when  hydrate  of  potassa  is  decomposed  by  iron  at  a  white 
heat,  and  it  appears  also  to  be  generated  when  potassium  burns  on  the  sur- 
face of  water.  It  inflames  spontaneously  in  air  or  oxygen  gas ;  but  on  stand- 
ing for  some  hours  over  mercury,  the  greater  part,  if  not  the  whole  of  the 
potassium,  is  deposited. 

The  solid  hyduret  of  potassium  was  made  by  Gay-Lussac  and  Thenard, 
by  heating  potassium  in  hydrogen  gas.  It  is  a  gray  solid  substance,  which 
is  readily  decomposed  by  heat  or  contact  with  water.  It  does  not  inflame 
spontaneously  in  oxygen  gas. 

Carburet  of  Potassium. — This  compound  has  not  been  obtained  in  a  pure 
state;  but  it  is  thought  to  form  part  of  the  residue  in  the  preparation  of  potas- 
sium from  charcoal  (page  276) ;  for  on  pouring  that  matter  into  water,  effer- 
vescence ensues  owing  to  the  escape  of  carburetted  hydrogen  gas,  and  carbo- 
nate of  potassa  is  found  in  solution. 

Sulphurets  of  Potassium. — Potassium  unites  readily  with  sulphur  by  the 
aid  of  gentle  heat,  emitting  so  much  heat  that  the  mass  becomes  incandes- 
cent. The  nature  of  the  product  depends  on  the  proportions  which  are  em- 
ployed. The  protosulphuret  is  readily  prepared  by  decomposing  sulphate  of 

24* 


282  POTASSIUM. 

potassa  by  charcoal  or  hydrogen  gas  at  a  red  heat  (page  270).  It  may  be 
prepared  in  the  moist  way  by  a  process  which  will  be  mentioned  in  describ- 
ing the  sulphur-salts. 

The  protosulphuret  of  potassium  fuses  below  a  red  heat,  and  acquires  on 
cooling  a  crystalline  texture.  It  has  a  red  colour,  its  taste  is  at  first  strongly 
alkaline  and  then  sulphurous,  has  an  alkaline  reaction  with  test  paper,  deli- 
quesces on  exposure  to  the  air,  and  is  soluble  in  water  and  alcohol.  Most  of 
the  acids  decompose  it  with  evolution  of  hydrosulphuric  acid  gas,  and  with- 
out any  deposite  of  sulphur.  It  takes  fire  when  heated  before  the  blowpipe, 
and  quickly  acquires  a  coating  of  sulphate  of  potassa,  which  stops  the  com- 
bustion ;  but  when  mixed  in  fine  division  with  charcoal,  it  kindles  spontane- 
ously, forming  a  good  pyrophorus. 

Its  eq.  is  55-25 ;  symb.  K+S,  or  KS. 

The  bisulphuret  is  formed  by  exposing  a  saturated  solution  in  alcohol  of 
hydrosulphate  of  sulphuret  of  potassium  (KS-f-HS),  until  a  pellicle  begins  to 
form  upon  its  surface,  and  then  evaporating  to  dryness  without  further  ex- 
posure. The  first  change  consists  in  oxygen  of  the  air  uniting  with  hydro- 
gen of  hydrosulphuric  acid,  the  sulphur  of  which  unites  with  potassium. 
Then  the  formation  of  hyposulphurous  acid  begins ;  and  as  the  hyposulphite 
of  potassa  is  insoluble  in  alcohol,  it  gives  a  pellicle  on  its  surface.  It  may 
ulso  be  obtained  from  an  aqueous  solution  of  the  protosulphuret.  This  com- 
pound, when  pure,  dissolves  in  water  without  colour ;  but  exposed  to  the  air, 
oxygen  is  rapidly  absorbed,  and  the  solution  becomes  yellow.  The  change 
is  effected  by  one-half  of  the  potassium  combining  with  oxygen  and  yielding 
its  sulphur  to  the  remainder,  by  which  the  bisulphuret  of  potassium  and 
potassa  are  formed.  Thus  2KS  yield  KS9,  and  KO.  If  the  solution  conti- 
nues to  be  exposed,  it  again  becomes  colourless,  owing  to  the  conversion  of 
the  bisulphuret  into  hyposulphite  of  potassa. 

Its  eq.  is  71-35  ;  symb.  K+2S,  or  KS2. 

The  tersulphuret  is  prepared  pure  by  transmitting  the  vapour  of  bisulphu- 
ret of  carbon  over  carbonate  of  potassa  at  a  red  heat,  as  long  as  carbonic  acid 
or  carbonic  oxide  gases  are  disengaged.  It  is  also  formed  when  carbonate 
of  potassa  is  heated  to  low  redness  with  half  its  weight  of  sulphur,  until  the 
mass  appears  in  tranquil  fusion:  the  oxygen  of  3-4ths  of  the  potassa  unites 
with  sulphur  to  form  sulphuric  acid,  which  exactly  suffices  to  neutralize 
l-4th  of  the  alkali,  and  all  the  carbonic  acid  is  evolved  as  gas. — Thus- 

4  eq.  potassa  and  10  eq.  sulphur^  3  eq.  tersulphuret  and  1  eq.  sulphate. 
4(K+O)  10S         -^    3(K+3S)  (K+O)-{-(S-r-3O). 

This  is  known  under  the  name  of  liver  of  sulphur  (p.  271.) 

Its  eq.  is  8745 :  symb.  K+3S,  or  KSs. 

The  quadrosulphuret  is  prepared  by  transmitting  the  vapour  of  bisulphuret 
of  carbon  over  sulphate  of  potassa  at  a  red  heat,  until  carbonic  acid  gas 
ceases  to  be  disengaged ;  or  by  conducting  the  same  process  with  the  tersul- 
phuret prepared  by  the  second  method,  until  its  sulphuric  acid  arid  potassa 
are  decomposed. 

Its  eq.  is  103-55;  symb.  K  +  4S,  or  KS*. 

The  quinlosulphuret  is  formed  by  fusing  carbonate  of  potassa  with  its  own 
weight  of  sulphur,  the  residue  containing  sulphate  of  potassa  as  in  preparing 
the  tersulphuret.  Each  equivalent  of  potassium  is  united  with  five  of  sul- 
phur, being  the  highest  degree  of  sulphuration  which  can  be  formed  by 
fusion. 

Its  eq.  is  119-65  ;  symb.  K-f-5S,  or  KS^. 

These  four  last  sulphurets  are  deliquescent  in  the  air,  have  a  sulphurous 
odour,  and  are  soluble  in  water;  and  those  who  consider  them  to  decompose 
water  in  dissolving,  suppose  the  formation  of  corresponding  compounds  of 
hydrogen  and  sulphur.  On  decomposing  the  solutions  with  hydrochloric  or 
sulphuric  acid,  the  changes  ensue  which  have  already  been  explained  (page 
254).  As  the  solution  of  the  quintosulphuret  dissolves  sulphur,  a  still  higher 
degree  of  sulphuration  must  probably  exist. 


SODIUM.  283 

Two  other  compounds  of  sulfchur  and  potassium,  the  composition  of  which 
are  K2S7,  and  KaS9,  have  been  described.  The  first  of  these  is  produced 
when  sulphate  of  potassa  is  heated  in  a  stream  of  sulphuretted  hydrogen; 
and  the  latter,  when  the  quadrosulphuret  of  potassium  is  heated  in  a  similar 
manner.  The  definite  nature  of  these  compounds  may  be  considered  doubtful. 

Phosphurets  of  Potassium. — When  potassium  is  heated  in  phosphuretted 
hydrogen  gas,  it  takes  fire,  phosphuret  of  potassium  is  formed,  and  hydrogen 
set  free;  and  combination  is  also  effected  by  gently  heating  phosphorus 
with  potassium.  The  number  and  proportion  of  these  compounds  have  not 
yet  been  determined.  They  decompose  water  with  formation  of  phosphuret- 
ted hydrogen,  potassa,  and  some  acid  of  phosphorus. 

Seleniurets  of  Potassium. — These  elements  unite  when  fused  together, 
sometimes  with  explosive  violence,  forming  a  crystalline  fusible  compound 
of  an  iron-gray  colour  and  metallic  lustre.  It  dissolves  completely  in  water, 
yielding  a  deep  red  solution,  very  similar  in  taste  and  odour  to  solutions  of 
sulphuret  of  potassium.  On  adding  an  acid,  hydroselenic  acid  gas  is  evolved, 
and  selenium  deposited.  Solution  of  potassa  dissolves  selenium,  and  gives 
rise  to  a  seleniuret  of  potassium  and  selenite  of  potassa ;  and  the  same  com- 
pounds are  formed  when  selenium  is  heated  with  carbonate  of  potassa. 


SECTION    II. 

SODIUM. 

Hist,  and  Prep. — The  natrium  of  the  Germans,  was  discovered  in  1807,  a 
few  days  after  the  discovery  of  potassium.  The  first  portions  of  it  were  ob- 
tained by  means  of  galvanism  ;  but  it  may  be  procured  in  much  larger  quan- 
tity by  chemical  processes,  precisely  similar  to  those  described  in  the  last 
section. 

Prop. — It  has  a  strong  metallic  lustre,  and  in  colour  is  very  analogous  to 
silver.  It  is  so  soft  at  common  temperatures,  that  it  may  be  formed  into 
leaves  by  the  pressure  of  the  fingers.  It  fuses  at  200°,  and  rises  in  vapour  at 
a  red  heat.  Its  sp.  gr.  is  0-972.  It  soon  tarnishes  on  exposure  to  the  air, 
though  less  rapidly  than  potassium.  Like  that  metal,  it  is  instantly  oxidized 
by  water,  hydrogen  gas  in  temporary  union  with  a  little  sodium  being  disen- 
gaged. When  thrown  on  cold  water,  it  swims  on  its  surface,  and  is  rapidly 
oxidized,  though  in  general  without  inflaming  ;  but  with  hot  water  it  scintil- 
lates, or  even  takes  fire.  Ducatel  finds  that  the  heat  rises  high  enough  for 
inflammation  with  cold  water,  if  the  sodium  be  confined  to  one  spot,  and  the 
water  rest  on  a  non-conducting  substance,  such  as  charcoal.  (Silliman's 
Journal,  xxv.  90.)  In  each  case,  soda  is  generated,  and  the  water  acquires 
an  alkaline  reaction. 

The  composition  of  soda  was  determined  by  the  same  methods  as  that  of 
potassa,  and  agreeably  to  the  observations  of  JBerzelius,  23-3  may  be  taken  as 
the  eq.  of  sodium.  Its  symb.  is  Na.  The  composition  of  the  compounds  of 
sodium  described  in  this  section  is  as  follows : — 

Sodium.  Equiv.          Formulae. 

Protoxide      23-3  1  eq.  4  Oxygen        8        1  eq.==  31-3       Na-fO  or  Na. 
Sesquioxide  46-6  2  eq.+do.  24       3  eq.=  70-6    2Na-f  3O  or  Na. 

Chloride        23-3  1  eq.-f  Chlorine    35-42  1  eq.=  58-72  Na-f  Cl  or  NaCl. 

Iodide    .   .  23-3  1  eq. 4- Iodine      126-3    1  eq.- 149-6  Na-florNal. 

Bromide     .  23-3  1  eq.-j- Bromine    78-4     1  eq,=  101-7  Na  +  BrorNaBr. 

Fluoride     .  23-3  1  eq.-f  Fluorine     18-68  1  eq.=  41-98  Na-fForNaF. 

Protosulph't  23-3  1  eq.-f  Sulphur     16-1     1  eq.=  39-4  Na+S  or  NaS. 


284  SODIUM. 

Soda.  —  Prep.  —  The  protoxide  of  sodium,  commonly  called  soda,  and  by 
the  Germans  natron,  is  formed  by  the  oxidation  of  sodium  in  air  or  water,  as 
potassa  is  from  potassium.  In  its  anhydrous  state  it  is  a  gray  solid,  difficult 
of  fusion,  and  very  similar  in  all  its  characters  to  potassa.  With  water  it 
forms  a  solid  hydrate,  easily  fusible  by  heat,  which  is  very  caustic,  soluble  in 
water  and  alcohol,  has  powerful  alkaline  properties,  and  in  all  its  chemical 
relations  is  exceedingly  analogous  to  potassa.  It  is  prepared  from  the  solu- 
tion of  pure  soda,  exactly  in  the  same  manner  as  the  corresponding  prepara- 
tion of  potassa.  The  solid  hydrate  is  composed  of  31.3  parts  or  one  eq.  of 
soda,  and  9  parts  or  one  eq.  of  water. 

Prop.  —  Soda  is  readily  distinguished  from  other  alkaline  bases  by  the  fol- 
lowing characters.  1.  It  yields  with  sulphuric  acid  a  salt,  which  by  its  taste 
and  form  is  easily  recognized  as  Glauber's  salt,  or  sulphate  of  soda.  2.  All 
its  salts  are  soluble  in  water,  and  are  not  precipitated  by  any  reagent.  3.  On 
exposing  its  salts  by  means  of  platinum  wire  to  the  blowpipe  flame,  they 
communicate  to  it  a  rich  yellow  colour. 

Its  eq.  is  31-3  ;  symb.  Na-fO,  Na,  or  NaO. 

Sesquiozide  of  Sodium.  —  This  compound  is  formed  when  sodium  is  heated 
to  redness  in  an  excess  of  oxygen  gas.  It  has  an  orange  colour,  has  neither 
acid  nor  alkaline  properties,  and  is  resolved  by  water  into  soda  and  oxygen. 


Its  eq.  is  70-6;  symb.  2Na-f3O,  Na,  or 

Chloride  of  Sodium.  —  Hist,  and  Prep.  —  This  compound  may  be  formed 
directly  by  burning  sodium  in  chlorine,  by  heating  sodium  in  hydrochloric 
acid  gas,  and  by  neutralizing  soda  with  hydrochloric  acid.  It  exists  as  a 
mineral  under  the  name  of  rock  salt,  is  the  chief  ingredient  of  sea-water, 
and  is  contained  in  many  saline  springs.  From  these  sources  are  derived 
the  different  varieties  of  common  salt,  such  as  rock,  bay,  fishery,  and  stoved 
salt,  which  differ  from  each  other  only  in  degress  of  purity  and  mode  of 
preparation.  The  rock  and  bay  salt  are  the  purest,  but  always  contain 
small  quantities  of  sulphate  of  magnesia  and  lime,  arid  chloride  of  magne- 
sium. These  earths  may  be  precipitated  as  carbonates  by  boiling  a  solution 
of  salt  for  a  few  minutes  with  a  slight  excess  of  carbonate  of  soda,  filtering 
the  liquid,  and  neutralizing  with  hydrochloric  acid.  On  evaporating  this 
solution  rapidly,  chloride  of  sodium  crystallizes  in  hollow  four-sided  pyra- 
mids ;  but  it  occurs  in  regular  cubic  crystals  when  the  solution  is  allowed 
to  evaporate  spontaneously.  These  crystals  contain  no  water  of  crystalliza- 
tion, but  decrepitate  remarkably  when  heated,  owing  to  the  expansion  of 
water  mechanically  confined  within  them. 

Prop.  —  Pure  chloride  of  sodium  has  an  agreeably  saline  taste.  It  fuses 
at  a  red  heat,  and  becomes  a  transparent  brittle  mass  on  cooling.  It  deli- 
quesces slightly  in  a  moist  atmosphere,  but  undergoes  no  change  when  the 
air  is  dry.  In  pure  alcohol  it  is  insoluble.  It  requires  twice  and  a  half  its 
weight  of  water  at  60°  for  solution,  and  its  solubility  is  not  increased  by 
heat.  Hydrous  sulphuric  acid  decomposes  it  with  evolution  of  hydrochloric 
acid  gas,  and  formation  of  sulphate  of  soda. 

The  uses  of  chloride  of  sodium  are  well  known.  Besides  its  employment 
in  seasoning  food,  and  in  preserving  meat  from  putrefaction,  a  property 
which  when  pure  it  possesses  in  a  high  degree,  it  is  used  for  various  pur- 
poses in  the  arts,  especially  in  the  formation  of  hydrochloric  acid  and  hypo- 
chlorite  of  lime. 

Its  eq.  is  58-72;  symb.  Na  +  Cl,  or  NaCI. 

Iodide  of  Sodium.  —  It  is  obtained  pure  by  processes  similar  to  those  for 
preparing  iodide  of  potassium  ;  but  it  is$|ontained  in  sea-water,  in  many  salt 
springs,  and  in  the  residual  liquor  from  kelp  (page  228).  It  is  a  neutral 
compound,  deliquescent  in  the  air,  soluble  in  water  and  alcohol,  fuses  rea- 
dily by  heat,  and  is  volatile,  though  in  a  less  degree  than  iodide  of  potassium. 
Evaporated  at  123°  it  crystallizes  from  its  aqueous  solution  in  cubes,  which 
Berzelius  found  to  contain  20-23  per  cent,  of  water. 


LITHIUM.  285 

Its  eq.  is  149-6  ;  symb.  Na+I,  or  Nal. 

Bromide  of  Sodium. — This  compound  is  very  analogous  to  sea-salt,  and  is 
associated  with  it  in  sea-water  and  most  salt  springs.  At  86°  it  crystallizes 
from  its  aqueous  solution  in  anhydrous  cubes ;  but  at  lower  temperatures  it 
separates  in  hexagonal  tables,  which  Mitscherlich  found  to  contain  26-37  per 
cent  of  water,  or  four  eq.  to  one  eq.  of  the  bromide. 

Its  eq.  is  101-7  ;  symb.  Na-fr-Br,  or  NaBr. 

Fluoride  of  Sodium. — This  compound  is  formed  by  neutralizing  hydro- 
fluoric acid  by  soda,  and  by  igniting  the  double  fluoride  of  sodium  and  sili- 
con, when  the  fluoride  of  silicon  is  expelled.  When  obtained  by  the  second 
process,  it  crystallizes  from  its  aqueous  solution  in  rhomboidal  crystals,  but 
is  obtained  in  cubes,  its  proper  form,  by  a  second  crystallization :  when  car- 
bonate of  soda  is  present,  it  crystallizes  in  octohedrons. 

Fluoride  of  sodium  in  crystals  is  anhydrous,  is  almost  insoluble  in  alcohol, 
and  requires  25  times  its  weight  both  of  hot  and  cold  water  for  solution.  It 
attacks  glass  vessels  when  evaporated  in  them,  and  by  fusion  unites  with 
silicic  acid,  forming  a  glass  which  is  more  fusible  than  the  pure  fluoride; 
but  water  dissolves  out  the  fluoride,  and  leaves  the  silicic  acid. 

Its  eq.  is  41-98 ;  symb.  Na  +  F,  or  NaF. 

Sulphurets  of  Sodium. — The  protosulphuret  is  obtained  by  processes  simi- 
lar to  those  for  protosulphuret  of  potassium,  to  which  in  its  taste  and  chemi- 
cal relations  it*is  very  similar.  A  concentrated  solution  of  it  yields  hydrated, 
square,  four-sided  prisms,  which,  when  heated,  fuse  in  their  water  of  crystal- 
lization, and  then  leave  a  white  anhydrous  mass.  It  deliquesces  in  the  air, 
is  very  soluble  in  water,  and  is  also  dissolved,  though  in  a  smaller  degree, 
by  alcohol.  In  solution  it  absorbs  oxygen  very  rapidly  from  the  air,  and 
passes  into  hyposulphate  of  soda. 

Its  eq.  is  39-4;  symb.  Na-{-S,  or  NaS. 

Sodium  unites  with  sulphur  in  other  proportions ;  but  the  resulting  com- 
pounds  have  not  been  studied. 

According  to  Gmelin  of  Tubingen,  sulphuret  of  sodium  is  the  colouring 
principle  of  lapis  lazuli,  to  which  the  colour  of  ultra-marine  is  owing ;  and 
he  has  succeeded  in  preparing  artificial  ultra-marine  by  heating  sulphuret  of 
sodium  with  a  mixture  of  silicic  acid  and  alumina.  (An.  de  Ch.  et  de  Ph. 
xxxvii.  409.) 


SECTION    III. 

LITHIUM. 

DAVY  succeeded  by  means  of  galvanism  in  obtaining  from  lithia  a  white- 
coloured  metal  like  sodium ;  but  it  was  oxidized,  and  thus  reconverted  into 
lithia,  with  such  rapidity  that  its  properties  could  not  be  farther  examined. 
Its  eq.,  inferred  from  the  composition  of  sulphate  of  lithia  by  Stromeyer  and 
Thomson,  is  10;  but  the  accuracy  of  this  estimate  is  rendered  doubtful  by 
the  experiments  of  M.  Herrman,  according  to  which  6  is  a  nearer  estimate. 
The  number  given  by  Berzelius  is  6-44,  which  is  here  adopted.  Its  symb. 
is  L.  The  compounds  of  lithium  described  in  this  section  are  thus  consti- 
tuted :— 


Lithium.                               * 

Equiv. 

Formulae. 

Lithia 
Chloride 
Fluoride 

6-44 
6-44 
6-44 

1  eq.-}-  Oxygen 
1  eq.-|-  Chlorine 
1  eq.  -J-  Fluorine 

8 
35-42 

18-68 

1  eq.  =14-44 
1  eq.=41-86 
1  eq.=25-12 

L-LOor  LO. 
L-f-CLor  LCI. 
L-t-F  or  LF. 

286  LITHIUM. 

Lithia. — Hist. — This,  the  only  known  oxide  of  lithium,  was  discovered  in 
1818  by  M.  Arfwedson  (An.  de  Ch.  et  de  Ph.  x.)  in  a  mineral  called  petalite ; 
and  its  presence  has  since  been  detected  in  spodumene,  lepidolite,  and  in 
several  varieties  of  mica.  Bcrzelius  has  found  it  also  in  the  waters  of  Carls- 
bad in  Bohemia.  From  the  circumstance  of  its  having-  been  first  obtained 
from  an  earthy  mineral,  Arfwedson  gave  it  the  name  cfltihion,  (from  x/9g*o?, 
lapideus,}  a  term  since  changed  in  this  country  to  lithia.  It  has  hitherto 
been  procured  in  small  quantity  only,  because  spodumene  and  petalite  are 
rare,  and  do  not  contain  more  than  6  or  8  per  cent,  of  the  alkali.  It  is  com- 
bined in  these  two  minerals  with  silicic  acid  and  alumina;  whereas  potassa 
is  likewise  present  in  lepidolite  and  lithion-mica,  and,  therefore,  lithia  should 
be  prepared  solely  from  the  former. 

Prep. — The  best  process  for  preparing  lithia  is  that  which  was  suggested 
by  Berzelius.  One  part  of  petalite  or  spodumene,  in  fine  powder,  is  mixed 
intimately  with  two  parts  of  flour-spar,  and  the  mixture  is  heated  with  three 
or  four  times  its  weight  of  sulphuric  acid,  as  long  as  any  acid  vapours  are 
disengaged.  The  silicic  acid  of  the  mineral  is  attacked  by  hydrofluoric  acid, 
and  dissipated  in  the  form  of  fluosilicic  acid  gas,  while  the  alumina  and  lithia 
unite  with  sulphuric  acid.  After  dissolving  these  salts  in  water,  the  solution 
is  boiled  with  pure  ammonia  to  precipitate  the  alumina:  it  is  then  filtered 
and  evaporated  to  dryness,  and  the  dry  mass  heated  to  redness  to  expel  the 
sulphate  of  ammonia.  The  residue  is  pure  sulphate  of  lithia.* 

Prop. — jCithia,  in  its  alkalinity,  in  forming  a  hydrate  with  water,  and  in 
its  chemical  relations,  is  closely  allied  to  potassa  and  soda.  It  is  distinguished 
from  them  by  its  greater  neutralizing  power,  by  forming  sparingly  soluble 
compounds  with  carbonic  and  phosphoric  acids,  and  by  its  salts,  when  heated 
on  platinum  wire  before  the  blowpipe,  tinging  the  flame  of  a  red  colour. 
Also,  when  fused  on  platinum  foil,  it  attacks  that  metal  and  leaves  a  dull 
yellow  trace  round  the  spot  w%ere  it  lay.  It  is  distinguished  from  baryta, 
strontia,  and  lime,  by  forming  soluble  salts  with  sulphuric  and  oxalic  acids, 
and  from  magnesia  by  its  carbonate,  though  sparingly  soluble  in  water, 
forming  with  it  a  solution  which  has  an  alkaline  reaction.  Its  eq.  is  14-44; 
symb.  L-f-O,  L,  or  LO. 

Chloride  of  Lithium. — It  is  readily  obtained  by  dissolving  lithia  or  its  car- 
bonate in  hydrochloric  acid.  Like  the  chlorides  of  sodium  and  potassium, 
it  yields  by  evaporation  in  a  warm  place  colourless,  anhydrous,  cubic  crys- 
tals, which  differ  from  those  chlorides  in  being  very  delinquescent,  dissolving 
freely  in  alcohol  as  well  as  water,  and  in  its  alcoholic  solution  burning  with  a 
red  flame. 

Its  eq.  is  41-86;  symb.  L-J-C1,  or  LCI. 

The  iodide  and  bromide  of  lithium  have  not  been  examined. 

Fluoride  of  Lithium. — This  is  a  fusible  compound,  prepared  by  dissolving 
lithia  in  hydrofluoric  acid,  and  possesses  about  the  same  solubility  in  water 
as  the  carbonate. 


*  The  sulphate  of  lithia  may  be  decomposed  by  acetate  of  baryta,  and  the 
acetate  of  lithia  thus  obtained,  by  exposure  to  a  red  heat,  is  converted  into 
the  carbonate.  The  carbonate  may  then  be  brought  to  the  state  of  a  caustic 
hydrate  by  the  action  of  lime  in  the  usual  manner, — Ed, 


287 


CLASS   I. 
ORDER  II. 

METALLIC  BASES  OF  THE  ALKALINE  EARTHS. 

SECTION    IV. 
BARIUM. 

Hist,  and  Prep. — DAVY  discovered  barium,  the  metallic  base  of  baryta,  in 
the  year  1808,  by  a  process  suggested  by  Berzelius  and  Pontin.  It  consists 
in  forming  carbonate  of  baryta  into  a  paste  with  water,  placing  a  globule  of 
mercury  in  a  little  hollow  made  in  its  surface,  and  laying  the  paste  on  a 
platinum  tray  which  communicated  with  the  positive  pole  of  a  galvanic  bat- 
tery of  100  double  plates,  while  the  negative  wire  was  in  contact  with  the 
mercury.  The  baryta  was  decomposed,  and  its  barium  combined  with  mer- 
cury. This  amalgam  was  then  heated  in  a  vessel  free  from  air,  by  which 
means  the  mercury  was  expelled,  and  barium  obtained  in  a  pure  form. 

Prop. — A  dark  gray-coloured  metal,  with  a  lustre  inferior  to  that  of  cast 
iron.  It  is  far  denser  than  water,  for  it  sinks  rapidly  in  strong  sulphuric 
acid.  It  attracts  oxygen  with  avidity  from  the  air,  and  in  doing  so  yields  a 
white  -powder,  which  is  baryta.  It  effervesces  strongly  from  the  escape  of 
hydrogen  gas  when  thrown  into  water,  and  a  solution  of  baryta  is  produced. 
It  has  hitherto  been  obtained  in  very  minute  quantities,  and  consequently  its 
properties  have  not  been  determined  with  precision. 

The  eq.  of  barium,  deduced  from  an  anylysis  of  the  chloride  by  Berzelius 
and  myself,  is  68*7.  Its  symb.  is  Ba.  The  composition  of  its  compounds 
described  in  this  section  is  as  follows : — 

Barium.  Equiv.       Formulse. 

Protoxide      68-7   1  eq.-{- Oxygen  8  1  eq.=   76-7     Ba-f-OorBaO. 

Peroxide       68-7  1  eq.  +  do.  16  2  eq.=  84-7     Ba  -f  2O  or  BaO*. 

Chloride        68-7  1  eq. 4- Chlorine  35-42  1  eq.=  104-12   Ba-fClorBaCl. 

Iodide  68-7   1  eq.  + Iodine      126-3  1  eq.=  195        Ba+I  or  Bal. 

Bromide        68-7   1  eq.-j-  Bromine    78-4  1  eq.=147-l     Ba  -f  Br  or  BaBr. 

Fluoride        68-7   1  eq.  4.  Fluorine  18-68  1  eq.=  87-38  Ba  4.  F  or  BaF. 

Protosulph't  68-7  1  eq.  + Sulphur  16-1  1  eq.=  84-8    Ba-f-S  or  BaS. 

Protoxide  of  Barium. — Hist,  and  Prep. — Barytes,  or  Baryta,  so  called  from 
the  great  density  of  its  compounds,  (from  $*gyc,  heavy,)  was  discovered  in 
the  year  1774  by  Scheele.  It  is  the  sole  product  of  the  oxidation  of  barium 
in  air  or  water.  It  may  be  prepared  by  decomposing  nitrate  of  baryta  at  a 
red  heat ;  or  by  exposing  carbonate  of  baryta,  contained  in  a  black-lead  cru- 
cible, to  an  intense  white  heat,  a  process  which  succeeds  much  better  when 
the  carbonate  is  intimately  mixed  with  charcoal. 

Prop. — A  gray  powder,  the  specific  gravity  of  which  is  about  4.  It  re- 
quires  a  very  high  temperature  for  fusion  ;  has  a  sharp  caustic  alkaline 
taste,  converts  vegetable  blue  colours  to  green,  and  neutralizes  the  strongest 
acids.  Its  alkalinity,  therefore,  is  equally  distinct  as  that  of  potassa  or  soda ; 


288  BARIUM. 

but  it  is  much  less  caustic  and  less  soluble  in  water  than  those  alkalies.  In 
pure  alcohol  it  is  insoluble.  It  has  an  exceedingly  strong-  affinity  for  water. 
When  mixed  with  that  liquid  it  slakes  in  the  same  manner  as  quicklime, 
but  with  the  evolution  of  a  more  intense  heat,  which,  according  to  Dobe- 
reiner,  sometimes  amounts  to  incandescence.  The  result  is  a  white  bulky 
hydrate,  fusible  at  a  red  heat,  and  which  bears  the  highest  temperature  of  a 
smith's  forge  without  parting  with  its  water.  It  is  composed  of  76-7  parts 
or  one  eq.  of  baryta,  and  9  parts  or  one  eq.  of  water. 

Hydrate  of  baryta  dissolves  in  three  times  its  weight  of  boiling  water,  and 
in  twenty  parts  of  water  at  the  temperature  of  60°  F.  (Davy.)  A  saturated 
solution  of  baryta  in  boiling  water  deposiles,  in  cooling,  transparent,  flatten- 
ed prismatic  crystals,  which  are  composed,  according  to  Phillips,  of  76'7 
parts  or  one  eq.  of  baryta,  and  90  parts  or  ten  eq.  of  water.  Smith  states, 
however,  that  the  quantity  of  water  amounts  only  to  81  parts  or  nine  eq. 
He  has  also  pointed  out  the  existence  of  a  hydrate  containing  only  two  eq. 
of  water ;  it  is  a  white  powder  which  is  formed  by  exposing  the  crystallized 
hydrate  to  the  temperature  of  a  sand  bath.  (Phil.  Mag.  and  Annals,  vi.  53. 
and  ix.  87.) 

The  aqueous  solution  of  baryta  is  an  excellent  test  of  the  presence  of  car- 
bonic acid  in  the  atmosphere  or  in  other  gaseous  mixtures.  The  carbonic 
acid  unites  with  the  baryta,  and  a  white  insoluble  precipitate,  carbonate  of 
baryta,  subsides. 

Baryta  is  distinguished  from  all  other  substances  by  the  following  charac- 
ters. 1.  By  dissolving  in  water  and  forming  an  alkaline  solution.  2.  By  all 
its  soluble  salts  being  precipitated  as  white  carbonate  of  baryta  by  alkaline 
carbonates,  and  as  sulphate  of  baryta,  which  is  insoluble  both  in  acid  and 
alkaline  solutions,  by  sulphuric  acid  or  any  soluble  sulphate.  3.  By  the 
characters  of  chloride  of  barium,  formed  by  the  action  of  hydrochloric  acid 
on  baryta. 

The  readiest  method  of  preparing  the  soluble  salts  of  baryta  is  by  dissolv- 
ing the  carbonate  in  dilute  acid.  All  of  its  soluble  salts  are  poisonous;  and 
the  carbonate,  from  being  dissolved  by  the  juices  of  the  stomach,  likewise 
acts  as  a  poison.  The  sulphate,  from  its  insolubility,  is  inert. 

Its  eq.  is  76-7 ;  symb.  Ba-f-O,  Ba,  or  BaO. 

Peroxide  of  Eariuih. — This  oxide,  which  is  used  by  Thenard  in  preparing 
peroxide  of  hydrogen,  may  be  formed  by  conducting  dry  oxygen  gas  over 
pure  baryta  at  a  low  red  heat.  A  still  easier  process,  lately  given  by  Wohler 
and  Liebig,  is  to  heat  pure  baryta  to  low  redness  in  a  platinum  crucible,  and 
then  gradually  to  add  chlorate  of  potassa  in  the  ratio  of  about  one  part  of 
the  latter  to  four  of  the  former.  The  oxygen  of  the  chlorate  goes  over  to 
the  baryta,  and  chloride  of  potassium  is  generated.  Cold  water  afterwards 
removes  the  chloride,  and  the  peroxide  of  barium  is  left  as  a  hydrate  with  six 
eq.  of  water,  its  formula  being  BaO3-f-6Aq. 

Chloride  of  Barium. — It  is  generated  when  chlorine  gas  is  conducted  over 
baryta  at  a  red  heat,  oxygen  gas  being  disengaged ;  but  it  is  most  con- 
veniently prepared  by  dissolving  carbonate  of  baryta  in  hydrochloric  acid 
diluted  with  about  three  times  its  weight  of  water,  or  by  decomposing  a 
solution  of  sulphuret  of  barium  with  hydrochloric  acid.  On  concentrating 
its  solution,  the  chloride  crystallizes  on  cooling  in  flat  four-sided  tables  bevel- 
led at  the  edges,  very  like  crystals  of  heavy  spar.  These  crystals  consist  of 
104-12  parts  of  one  eq.  of  chloride  of  barium,  and  18  parts  or  two  eq.  of 
water,  its  formula  being  BaCl-J-2Aq.  They  do  not  change  in  ordinary 
states  of  the  air ;  but  in  a  very  dry  atmosphere  at  60°  they  lose  all  their 
water,  and  recover  it  again  in  a  moist  air.  They  are  still  more  rapidly  ren- 
dered anhydrous  at  212°,  and  fusion  ensues  at  a  full  red  heat.  They  are 
insoluble  in  strong  alcohol:  100  parts  of  water  dissolve  43-5  at  60°,  and  78 
at  222°,  which  is  the  boiling  point  of  the  solution. 

Its  eq.  is  104-12;  symb.  Ba  +  Cl,  or  Bad. 

Iodide  of  Barium. — This  compound  may  be  formed  in  the  same  way  as 
iodide  of  potassium.  It  is  very  soluble  in  water,  and  crystallizes  in  small 


STRONTIUM.  289 

colourless  needles,  which  deliquesce  slightly.  On  exposure  to  the  air,  a  por- 
tion of  carbonate  of  baryta  is  formed  and  iodine  set  free,  which  probably 
forms  a  periodide  of  barium. 

Its  eq.  is  195;  symb.  Ba-J-I,  or  Bal. 

Bromide  of  Barium. — It  was  prepared  by  M.  Henry,  jun.,  who  has  exa- 
mined it,  by  boiling  protobromide  of  iron  with  moist  carbonate  of  baryta  in 
excess,  evaporating  the  filtered  solution,  and  heating  the  residue  to  redness. 
The  product  crystallizes  by  careful  evaporation  in  white  rhombic  prisms, 
which  have  a  bitter  taste,  are  slightly  deliquescent,  and  are  soluble  in  water 
and  alcohol. 

Its  eq.  is  147-1 ;  symb.  Ba-j-Br,  or  BaBr. 

Fluoride  of  Barium. — On  digesting  recently  precipitated  and  moist  carbo- 
nate of  baryta  in  hydrofluoric  acid,  carbonic  acid  is  expelled,  and  fluoride  of 
barium  collects  in  the  form  of  a  white  powder,  which  bears  a  red  heat  with- 
out decomposition.  It  is  sparingly  soluble  in  water,  and  by  evaporation 
separates  in  crystalline  grains.  It  is  soluble  in  nitric  and  hydrochloric 
acids. 

Its  eq.  is  87-38;  symb.  Ba+F,  or  BaF. 

Protosulphuret  of  Barium. — Prep. — This  compound  may  be  formed  by 
transmitting  dry  hydrosulphuric  acid  gas  over  pure  baryta  at  a  red  heat; 
and  by  the  action  of  hydrogen  gas  or  charcoal  on  sulphate  of  baryta  (page 
271).  The  easiest  process  is  to  mix  sulphate  of  baryta  in  fine  powder  into 
a  paste  with  an  equal  volume  of  flour,  place  it  in  a  Hessian  crucible  on 
which  a  cover  is  luted,  and  expose  it  to  a  white  heat  for  an  hour  or  two, 
raising  the  temperature  slowly.  On  pouring  hot  water  on  the  ignited  mass, 
the  sulphuret  of  barium  is  dissolved,  and  may  be  separated  from  undecomposed 
sulphate  and  excess  of  charcoal  by  filtration. 

Protosulphuret  of  barium  is  very  soluble  in  hot  water,  and  the  solution,  if 
saturated,  deposites  colourless  crystals  on  cooling,  which  are  sulphuret  of 
barium  with  water  of  crystallization.  The  solution  has  a  sulphurous  odour, 
and  absorbs  oxygen  and  carbonic  acid  from  the  air,  yielding  carbonate  and 
hyposulphite  of  baryta.  Boiled  with  sulphur,  it  yields  a  yellow  solution,  and 
contains  a  persulphuret  of  barium. 

Protosulphuret  of  barium  supplies  a  ready  mode  of  obtaining  pure  baryta 
and  its  salts,  when  the  carbonate  cannot  be  obtained.  Thus  its  solution, 
boiled  with  black  oxide  of  copper  until  it  ceases  to  precipitate  a  salt  of  lead 
black,  yields  pure  baryta,  which  should  be  filtered  while  hot  to  separate  the 
sulphuret  of  copper :  it  is  apt  to  retain  traces  of  oxide  of  copper.  With  a 
solution  of  carbonate  of  potassa,  carbonate  of  baryta  falls,  and  sulphuret  of 
potassium  remains  in  solution;  and  with  hydrochloric  acid  it  interchanges 
elements,  by  which  hydrosulphuric  acid  and  chloride  of  barium  are  formed. 

Its  eq.  is  84-8;  symb.  Ba-f.S,  or  BaS. 


SECTION   V. 

STRONTIUM. 


DAVY  discovered  the  metallic  base  of  strontia,  called  strontium,  by  a  pro- 
cess analogous  to  that  described  in  the  last  section.  All  that  is  known  re- 
specting its  properties  is,  that  it  is  a  heavy  metal,  similar  in  appearance  to 
barium,  that  it  decomposes  water  with  evolution  of  hydrogen  gas,  and  ox- 
idizes quickly  in  the  air,  being  converted  in  both  cases  into  strontia,  which 
is  the  protoxide  of  the  metal. 

25 


290 


STRONTIUM. 


The  eq.  of  strontium,  deduced  from  the  experiments  of  Stromeyer,  is 
43-8;  its  symb.  Sr.  The  composition  of  its  several  compounds  described  in 
this  section  is  as  follows  : — 

Strontium.  Equiv.       Formulae. 

Protoxide         43-8  1  eq.-j-Oxygen       8  1  eq.=  51-8    Sr-f-OorSrO. 

Peroxide          43-8  1  eq.  4.     do.        16  2  eq.=  59-8    Sr-f2O  or  SrO 

Chloride  43-8  1  eq.+Chlorine  35-42  1  eq.=  79-22  Sr-fCl  or  SrCl. 

Iodide  43-8  1  eq.-f  Iodine   126-3  1  eq.=170-l     SrJ-I  or  Sri. 

Fluoride  43-8  1  eq.-f  Fluorine  18-68  1  eq.=  62-48  Sr-j-For  SrF. 

Protosulphuret43-8  1  eq.-f-Sulphur  16-1  1  eq.=  59-9     Sr-j-S  or  SrS. 

Protoxide  of  Strontium. — Hist. — From  the  close  resemblance  between 
baryta  and  strontia,  these  substances  were  once  supposed  to  be  identical. 
Crawford,  however,  and  Sulzer  noticed  a  difference  between  them ;  but  the 
existence  of  strontia  was  first  established  with  certainty  in  the  year  1792  by 
Hope,*  and  the  discovery  was  made  about  the  same  time  by  Klaproth.f  It 
was  originally  extracted  from  strontianite,  native  carbonate  of  strontia,  a 
mineral  found  at  Strontian  in  Scotland ;  and  hence  the  origin  of  the  term 
strontites,  or  strontia^  by  which  the  earth  itself  is  designated. 

Prep,  and  Prop. — Pure  strontia  may  be  prepared  from  nitrate  and  carbo- 
nate of  strontia,  in  the  same  manner  as  baryta.  It  resembles  this  earth  in 
appearance,  in  infusibility,  and  in  possessing  distinct  alkaline  properties.  It 
slakes  when  mixed  with  water,  causing  intense  heat,  and  forming  a  white 
solid  hydrate,  which  consists  of  51-8  parts  or  one  eq.  of  strontia,  and  9  parts 
or  one  eq.  of  water.  Hydrate  of  strontia  fuses  readily  at  a  red  heat.  It  is 
insoluble  in  alcohol.  Boiling  water  dissolves  it  freely,  and  a  hot  saturated 
solution,  on  cooling,  deposites  transparent  crystals  in  the  form  of  thin  quad- 
rangular tables,  which  consists  of  one  eq.  of  strontia  and  ten  eq.  of  water 
according  to  Phillips.  Smith  gives  its  composition  to  be  SrO -f-9HO.  He 
also  states  that  dried  at  212°,  it  becomes  SrO  -{-  HO,  and  is  anhydrous  on 
exposure  to  a  red  heat.  It  requires  50  times  its  weight  of  water  at  60°  for 
solution,  and  twice  its  weight  at  212°  F.  (Dalton.) 

The  solution  of  strontia  has  a  caustic  taste  and  alkaline  reaction.  Like 
the  solution  of  baryta,  it  is  a  delicate  test  of  the  presence  of  carbonic  acid  in 
air  or  other  gaseous  mixtures,  forming  with  it  the  insoluble  carbonate  of 
strontia. 

The  salts  of  strontia  are  best  prepared  from  the  native  carbonate.  Like 
those  of  baryta,  they  are  precipitated  by  alkaline  carbonates,  and  by  sulphuric 
acid  or  soluble  sulphates.  But  sulphate  of  strontia  is  less  insoluble  than 
sulphate  of  baryta  :  on  adding  sulphate  of  soda  in  excess  to  a  barytic  solu- 
tion, baryta  cannot  afterwards  be  found  in  the  liquid  by  any  precipitant ;  but 
when  strontia  is  thus  treated,  so  much  sulphate  of  strontia  remains  in  solu- 
tion, that  the  filtered  liquid  yields  a  white  precipitate  with  carbonate  of  soda. 
The  salts  of  strontia  are  not  poisonous ;  and  most  of  them,  when  heated  on 
platinum  wire  before  the  blowpipe,  communicate  to  the  flame  a  red  tint. 

Its  eq.  is  51-8  ;  symb.  Sr  +  O,  Sr,  or  SrO. 

Peroxide  of  Strontium  is  prepared  in  the  same  way  as  peroxide  of  barium, 
and,  like  it,  is  resolved  by  dilute  acids  into  slrontia  and  oxygen,  the  latter  of 
which  forms  peroxide  of  hydrogen  with  the  water. 

Chloride  of  Strontium. — This  compound  is  formed  by  processes  similar 
to  those  for  preparing  chloride  of  barium,  and  crystallizes  from  its  solution 
in  colourless  prismatic  crystals,  which  deliquesce  in  a  moist  atmosphere,  re- 
quire only  twice  their  weight  of  water  at  60°  for  solution,  and  still  less 
of  boiling  water,  and  are  soluble  in  alcohol.  The  alcoholic  solution,  when 
set  on  fire,  burns  with  a  red  flame.  These  characters  afford  a  certain  mode 

*  Edin.  Philos.  Trans,  iv.  3.  f  Klaproth's  Contributions,  i. 


CALCIUM.  291 

of  distinguishing1  slrontia  from  baryta.  The  crystals  consist  of  79-22  parts 
or  one  eq.  of  chloride  of  strontium,  and  81  parts  or  nine  eq.  of  water,  which 
are  expelled  by  heat.  The  anhydrous  chloride  fuses  at  a  red  heat,  and  yields 
a  white  crystalline  brittle  mass  on  cooling. 

Its  eq.  is  79-22;  symb.  Sr-f-Cl,  or  SrCl. 

Iodide  of  Strontium  may  be  prepared  in  the  same  manner  as  that  of 
barium.  It  is  very  soluble  in  water,  and  fuses  without  decomposition  in  close 
vessels ;  but  when  heated  to  redness  in  the  open  air,  iodine  escapes,  and 
strontia  is  generated. 

Fluoride  of  Strontium  is  obtained  in  the  same  way  as  fluoride  of  barium, 
and  is  a  white  powder  of  sparing  solubility. 

Protosulphuret  of  Strontium  is  similar  in  its  properties  and  mode  of  pre- 
paration to  protosulphuret  of  barium,  and  may  be  applied  to  similar  uses. 
Strontium  also  combines  with  more  than  one  equivalent  of  sulphur ;  but 
these  compounds  have  not  been  examined. 


SECTION   VI. 

CALCIUM. 

THE  existence  of  calcium,  the  metallic  base  of  lime,  was  demonstrated 
by  Davy  by  a  process  similar  to  that  described  in  the  section  on  barium.  It 
is  of  a  whiter  colour  than  barium  or  strontium,  and  is  converted  into  lime 
by  being  oxidized.  Its  other  properties  are  unknown. 

According  to  the  analysis  of  chloride  of  calcium  by  Berzelius,  the  eq.  of 
calcium  is  20-5 ;  its  symb.  is  Ca.  Its  compounds  described  in  this  section 
are  composed  as  follows : — 

Calcium.  Equiv.         Formulae. 

Protoxide   .       .20-5  1  eq.  -f  Oxygen      8       1  eq.=  28-5    Ca-fOorCaO. 

Peroxide     .       .20-5  1  eq.-f-do.  16      2  eq.=  36-5    Ca-f-2QorCaO2. 

Chloride     .       .  20-5  1  eq.J- Chlorine  35-42  1  eq.=  55-92  Ca-f  Cl  or  CaCl. 

Iodide         .       .  20-5  1  eq.+Iodine    126-3    1  eq.=:146-8    Ca+I  or  Cal. 

Bromide     .       .20-5  1  eq.-f-Bromine  78-4    leq.=  989    Ca-j-BrorCaBr. 

Fluoride     •       .  20-5  1  eq.-j-  Fluorine  18-68  1  eq.=  39-18  Ca-f-.F  or  CaF. 

Protosulphuret    20-5  1  eq.  -f-  Sulphur  16-1     1  eq.=  36-6    Ca-f-S  or  CaS. 

Bisulphuret       .20-5  1  eq.-]-do.          32-2     2  eq.=  52-7    Ca-f2S  or  CaS?. 

Quintosulphuret20-5  1  eq.+clo.  80-5      5  eq.=101       Ca-f-5S  or  CaS*. 

Phosphuret         20-5  1  eq-f-Phospb.  15-7     1  eq.=  36'2     Ca-fPorCaP. 

Protoxide  of  Calcium. — Prep. — This  compound,  commonly  known  by  the 
name  of  lime  and  quicklime,  is  obtained  by  exposing  carbonate  of  lime  to  a 
strong  red  heat,  so  as  to  expel  its  carbonic  acid.  If  lime  of  great  purity  is 
required,  it  should  be  prepared  from  pure  carbonate  of  lime,  such  as  Iceland 
spar  or  Carrara  marble;  but  in  burning  lime  in  lime-kilns  for  making  mor- 
tar, common  limestone  is  employed.  The  expulsion  of  carbonic  acid  is 
facilitated  by  mixing  the  carbonate  with  combustible  substances,  in  which 
ease  carbonic  oxide  is  generated  (page  190). 

Prop. — It  is  a  brittle  white  earthy  solid,  the  sp.  gr.  of  which  is  about  2-3. 
It  phosphoresces  powerfully  when  heated  to  full  redness,  a  property  which  it 
possesses  in  common  with  strontia  and  baryta.  It  is  one  of  the  most  infu- 
sible bodies  known,  fusing  with  difficulty,  even  by  the  heat  of  the  oxy- 
hydrogen  blowpipe.  It  has  a  powerful  affinity  for  water,  and  the  combi- 
nation is  attended  with  great  increase  of  temperature,  and  formation  of  a 
white  bulky  hydrate,  which  is  composed  of  28-5  parts  or  one  eq.  of  lime,  and 
9  parts  or  oneeq,  of  water.  The  process  of  slaking  lime  consists  in  forming- 


292  CALCIUM. 

this  hydrate,  and  the  hydrate  itself  is  called  slaked  lime.  It  differs  from  the 
hydrate  of  baryta  in  parting  with  its  water  at  a  red  heat. 

Hydrate  of  lime  is  dissolved  very  sparingly  by  water,  and  it  is  a  singular 
fact,  first  noticed,  I  believe,  by  Dalton,  that  it  is  more  soluble  in  cold  than  in 
hot  water.  Thus  he  found  that  one  grain  of  lime  requires  for  solution 

778  grains  of  water        .  .          •  . .         at     60°  F. 

972          .  .  .  .  .  .  130 

1270         .  .  -,'"   ."*!:"V    ;".'T        .  212 

And,  consequently,  on  heating  lime-water,  which  has  been  prepared  in  the 
cold,  deposition  of  lime  ensues.  This  fact  was  determined  experimentally 
by  Phillips,  who  has  likewise  observed  that  water  at  32°  is  capable  of  dis- 
solving twice  as  much  lime  as  at  212°  F.  Owing  to  this  circumstance, 
pure  lime  cannot  be  made  to  crystallize  in  the  same  manner  as  baryta  or 
strontia;  but  Gay-Lussac  succeeded  in  obtaining  crystals  of  lirne  by  evapo- 
rating lime-water  under  the  exhausted  receiver  of  an  air  pump  by  means  of 
sulphuric  acid.  Small  transparent  crystals,  in  the  form  of  regular  hexa- 
hedrons, were  deposited,  which  consist  of  water  and  lime  in  the  same  pro- 
portion as  in  the  hydrate  above  mentioned. 

Lime-water  is  prepared  by  mixing  hydrate  of  lime  with  water,  agitating 
the  mixture  repeatedly,  and  then  setting  it  aside  in  a  well-stopped  bottle  until 
the  undissolved  parts  shall  have  subsided.  The  substance  called  milk  or 
cream  of  lime  is  made  by  mixing  hydrate  of  lime  with  a  sufficient  quantity 
of  water  to  give  it  the  liquid  form  ; — it  is  merely  lime-water,  in  which  hydrate 
of  lime  is  mechanically  suspended. 

Lime-water  has  a  harsh  acrid  taste,  and  converts  vegetable  blue  colours  to 
green.  It  agrees,  therefore,  with  baryta  and  strontia  in  possessing  distinct 
alkaline  properties.  Like  the  solutions  of  these  earths,  it  has  a  strong 
affinity  for  carbonic  acid,  and  forms  with  it  an  insoluble  carbonate.  On 
this  account  lime-water  should  be  carefully  protected  from  the  air.  For  the 
same  reason,  lime-water  is  rendered  turbid  by  a  solution  of  carbonic  acid ; 
but  on  adding  a  large  quantity  of  the  acid,  the  transparency  of  the  solution 
is  completely  restored,  because  carbonate  of  lime  is  soluble  in  an  excess  of 
carbonic  acid.  The  action  of  this  acid  on  the  solutions  of  baryta  and  strontia 
is  precisely  similar. 

The  salts  of  lime,  which  are  easily  prepared  by  the  action  of  acids  on  pure 
marble,  are  in  many  respects  similarly  affected  by  reagents,  as  those  of  baryta 
and  strontia.  They  are  precipitated,  for  example,  by  alkaline  carbonates. 
Sulphuric  acid  and  soluble  sulphates  likewise  precipitate  lime  from  a  mode- 
rately strong  solution.  But  sulphate  of  lime  has  a  considerable  degree  of 
solubility.  Thus,  a  dilute  solution  of  a  salt  of  lime  is  not  precipitated  at  all 
by  sulphuric  acid ;  and  when  the  sulphate  of  lime  is  separated,  it  may  be 
redissolved  by  the  addition  of  nitric  acid. 

The  most  delicate  test  of  the  presence  of  lime  is  oxalate  of  ammonia  or 
potassa;  for  of  all  the  salts  of  lime,  the  oxalate  is  the  most  insoluble  in  water. 
This  serves  to  distinguish  lime  from  most  substances,  though  not  from  baryta 
and  strontia ;  because  the  oxalates  of  baryta  and  strontia,  especially  the  latter, 
are  likewise  sparingly  soluble.  All  these  oxalates  dissolve  readily  in  water, 
acidulated  with  nitric  or  hydrochloric  acid.  It  is  distinguished  from  baryta 
and  strontia  by  the  fact,  that  nitrate  of  lime  yields  prismatic  crystals  by 
evaporation,  is  deliquescent  in  a  high  degree,  and  very  soluble  in  alcohol; 
while  the  nitrates  of  baryta  and  strontia  crystallize  in  regular  oetohedrons 
or  segments  of  the  octohedron,  undergo  no  change  on  exposure  to  the  air, 
except  when  it  is  very  moist,  and  do  not  dissolve  in  pure  alcohol. 

The  salts  of  lime,  when  heated  before  the  blowpipe,  or  when  their  solutions 
in  alcohol  are  set  on  fire,  communicate  to  the  flame  a  dull  brownish-red 
colour. 

Its  eq.  is  28-5 ;  symb.  Ca  -fO,  Ca,  or  CaO. 

Peroxide  of  Calcium. — This  oxide  is  prepared  in  the  same  way  as  per- 
oxide of  barium,  and  is  similar  to  it  in  its  properties. 


CALCIUM.  293 

Chloride  of  Calcium. — This  compound  exists  in  sea-water  and  in  many 
saline  springs,  is  the  residue  of  the  process  for  preparing  ammonia,  and  is 
readily  formed  by  dissolving  marble  or  chalk  in  hydrochloric  acid.  On  eva- 
porating its  solution  to  the  consistence  of  a  syrup,  the  chloride  crystallizes 
on  cooling  in  irregular,  colourless  prismatic  crystals,  which  consist  of  55*92 
parts  or  one  eq.  of  chloride  of  calcium,  and  54  parts  or  six  eq.  of  water.  By 
heat  it  loses  its  water,  and  at  a  gentle  red  heat  fuses ;  but  on  exposure  to 
the  air  it  rapidly  recovers  its  water  of  crystallization  and  then  deliquesces. 
Owing  to  its  strong  affinity  for  water,  it  is  much  used  for  frigorific  mixtures 
with  snow ;  but  for  this  purpose  the  hydrous  chloride  is  preferable,  as  pre- 
pared by  evaporating  its  solution  so  far  that  the  whole  becomes  a  solid  mass 
on  removal  from  the  fire,  reducing  it  when  cold  quickly  to  powder,  and  pre- 
serving it  in  bottles  closed  with  great  care.  Chloride  of  calcium  is  very 
soluble  in  alcohol,  and  forms  with  it  a  definite  compound. 

Its  eq.  is  55-92 ;  symb.  Ca+Cl,  or  CaCl. 

Iodide  of  Calcium. — This  compound  may  be  prepared  by  digesting  hydrate 
of  lime  with  protiodide  of  iron.  It  is  deliquescent  and  very  soluble  in  water, 
sustains  a  red  heat  unchanged  in  close  vessels,  but  when  heated  in  the  open 
air,  its  iodine  is  replaced  by  oxygen,  and  lime  remains.  The  solution  of 
iodide  of  calcium  dissolves  a  large  quantity  of  iodine,  and  on  evaporating  the 
brown  solution  in  vacuo  above  a  vessel  with  dry  carbonate  of  potassa,  a  per- 
iodide  of  calcium  crystallizes  in  large  black  prisms  of  a  metallic  lustre. 

Its  eq.  is  146-8;  symb.  Ca-fl,  or€al. 

Bromide  of  Calcium. — It  was  prepared  by  Henry  by  digesting  hydrate  of 
lime  with  a  solution  of  protobromide  of  iron,  and  crystallizes  in  acicular 
crystals  which  are  very  deliquescent,  and  extremely  soluble  in  alcohol  and 
water.  It  is  very  analogous  in  taste  and  properties  to  chloride  of  calcium, 
fuses  by  heat,  but  in  open  vessels  suffers  partial  decomposition. 

Its  eq.  is  98-9;  symb.  Ca-f-Br,  or  CaBr. 

Fluoride  of  Calcium. — Hist,  and  Prep. — This  is  a  natural  product,  which 
frequently  accompanies  metallic  ores,  especially  those  of  lead  and  tin,  often 
occurs  in  cubic  crystals,  and  is  well  known  under  the  name  offluor  or  Der- 
byshire spar.  The  crystals  found  in  the  lead  mines  of  Derbyshire  are  re- 
markable for  the  largeness  of  their  size,  the  regularity  of  their  iform,  and  the 
variety  and  beauty  of  their  colours.  It  may  be  prepared  artificially  by  di- 
gesting moist,  recently  precipitated,  carbonate  of  lime  in  an  excess  of  hydro- 
fluoric acid ;  or  by  mixing  a  solution  of  chloride  of  calcium  with  fluoride  of 
potassium  or  sodium.  As  prepared  in  the  latter  mode,  it  is  a  bulky  gelati- 
nous mass,  which  it  is  very  difficult  to  wash  ;  whereas  the  former  method 
gives  it  in  the  state  of  a  granular  white  powder,  which  may  be  washed  with 
ease. 

Prop. — Fluoride  of  calcium  fuses  at  a  red  heat  without  farther  change.  It 
is  insoluble  in  water,  slightly  soluble  in  hot  diluted  hydrochloric  acid,  and  is 
decomposed  by  sulphuric  acid  aided  by  gentle  heat  (page  240.)  It  is  in  a 
small  degree  decomposed  by  boiling  nitric  acid.  Fused  with  carbonate  of 
potassa,  carbonate  of  lime  and  fluoride  of  potassium  are  generated. 

Fluor-spar  is  much  used  in  forming  vases,  as  a  flux  in  metallurgic  pro- 
cesses, and  in  the  preparation  of  hydrofluoric  acid. 

Its  eq.  is  39-18;  symb.  Ca-f  F,  or  CaF. 

Prolosulphuret  of  Calcium. — Prep. — By  reduction  from  the  sulphate  of 
lime  by  hydrogen  or  charcoal,  and  when  pure  is  white  with  a  reddish  tint, 
and  is  very  sparingly  soluble  in  water.  It  has  the  property,  in  common  with 
sulphuret  of  barium,  of  being  phosphorescent  after  exposure  to  light,  and 
appears  to  be  the  essential  ingredient  of  Canton's  phosphorus  (page  69.) 

When  3  parts  of  slaked  lime,  1  of  sulphur,  and  20  of  water  are  boiled  to- 
gether for  an  hour,  and  the  solution,  without  separation  from  the  sediment, 
is  set  aside  in  a  corked  flask  for  a  few  days,  orange-coloured  crystals  are  co- 
piously deposited,  which,  when  slowly  formed,  are  flat  quadrilateral  prisms. 
These,  from  the  analysis  of  Herschel,  appear  to  be  lisulphuret  of  calcium 

*25 


294  MAGNESIUM. 

with  three  eq.  of  water.  They  are  decomposed  by  exposure  to  the  air,  and 
are  of  sparing  solubility  in  water. 

When  either  of  the  foregoing  sulphurets  is  boiled  in  water  along  with  sul- 
phur, a  yellow  solution  is  formed  containing  calcium  combined  with  5  eq. 
of  sulphur. 

Phosphuret  of  Calcium. — It  is  formed  by  passing  the  vapour  of  phos- 
phorus over  fragments  of  quicklime  at  a  low  red  heat,  when  a  brown  matter 
is  formed  consisting  of  phosphate  of  lime  and  phosphuret  of  calcium.  When 
put  into  water,  mutual  decomposition  ensues,  and  phosphuretted  hydrogen, 
hypophosphorous  acid,  and  phosphoric  acid  are  generated. 


SECTION   VII. 

MAGNESIUM. 


Hist,  and  Prep.— THE  galvanic  researches  of  Davy  demonstrated  the  ex- 
istence  of  magnesium,  though  he  obtained  it  in  a  quantity  too  minute  for 
determining  its  properties.  It  was  prepared,  by  Bussy,  in  the  year  1830,  by 
the  action  of  potassium  on  chloride  of  magnesium.  For  this  purpose  five  or 
six  pieces  of  potassium,  of  the  size  of  peas,  were  introduced  into  a  glass 
tube,  the  sealed  extremity  of  which  was  bent  into  the  form  of  a  retort,  and 
upon  the  potassium  were  laid  fragments  of  chloride  of  magnesium.  The 
latter  being  then  heated  to  near  its  point  of  fusion,  a  lamp  was  applied  to  the 
potassium,  and  its  vapour  transmitted  through  the  mass  of  heated  chloride. 
Vivid  incandescence  immediately  took  place,  and  on  putting  the  mass,  after 
cooling,  into  water,  the  chloride  of  potassium  with  undecomposed  chloride  of 
magnesium  was  dissolved,  and  metallic  magnesium  subsided.  These  results 
have  been  since  confirmed  by  Liebig.  (An.  de  Ch.  et  de  Ph.  xlvi.  435.) 

Prop.-~ Magnesium  has  a  brilliant  metallic  lustre,  and  a  white  colour  like 
silver,  is  very  malleable,  and  fuses  at  a  red  heat.  Moist  air  oxidizes  it  super- 
ficially ;  but  it  undergoes  no  change  in  a  dry  air,  and  may  be  boiled  in  wa- 
ter without  oxidation.  Heated  to  redness  in  air  or  oxygen  gas,  it  burns  with 
brilliancy,  yielding  magnesia;  and  it  inflames  spontaneously  in  chlorine 
gas.  It  is  readily  dissolved  by  dilute  acids  with  disengagement  of  hydrogen, 
and  the  solution  is  found  to  contain  a  pure  salt  of  magnesia. 

The  eq.  of  magnesium,  inferred  by  Berzelius  from  the  quantity  of  sul- 
phate obtained  from  a  known  weight  of  pure  magnesia,  is  12-7;  its  symb.  is 
Mg.  Its  compounds  described  in  this  section  are  composed  as  follows :•— 

Magnesium.  Equiv.     Formulae. 

Protoxide      12-7     1  eq.-f  Oxygen      8  1  eq.=  20-7     Mg-fO  or  MgO. 

Chloride        12-7     1  eq.  -f  Chlorine  35-42  1  eq.=  48-12  Mg-f-Cl  or  MgCl. 

Iodide  12-7     1  eq.  -f  Iodine    126-3  1  eq.=139       Mg  +  I  or  Mgl. 

Bromide        12-7     1  eq.-j- Bromine  78.4  1  eq.=  91 1     Mg-fBr  or  MgBr. 

Fluoride.      12-7     1  eq.-j- Fluorine  18-68  1  eq.=  31-38  Mg4-F  or  MgF. 

Protoxide  of  Magnesium. — Prep. — This,  the  only  known  oxide  of  magne- 
sium, commonly  known  by  the  name  of  magnesia,  is  best  obtained  by  ex- 
posing carbonate  of  magnesia  to  a  very  strong  red  heat,  by  which  its'  carbonic 
acid  is  expelled.  It  is  a  white  friable  powder,  of  an  earthy  appearance  ; 
and  when  pure,  it  has  neither  taste  nor  odour.  Its  sp,  gr.  is  about  2-3,  and 
it  is  exceedingly  infusible.  It  has  a  weaker  affinity  than  lime  for  water ;  for 


MAGNESIUM.  295 

though  it  forms  a  hydrate  when  moistened,  the  combination  is  effected  with 
hardly  any  disengagement  of  heat,  and  the  product  is  readily  decomposed  by 
a  red  heat.  According  to  the  analysis  of  Stromeyer,  the  native  hydrate  con- 
tains one  eq.  of  each  of  its  constituents;  and  the  results  of  the  analyses  of 
Berzelius  and  Fyfe  accord  very  nearly  with  this  proportion.  It  has  generally 
been  thought  that  magnesia  formed  several  hydrates ;  but  the  recent  obser- 
vations of  Rees  indicate  that  the  artificial  hydrates  have  the  same  composi- 
tion as  the  native.  (Phil.  Mag.  and  Annals,  x.  454.) 

Prop. — Very  sparingly  soluble  in  water.  According  to  Fyfe,  it  requires 
5142  times  "its  weight  of  water  at  60°,  and  36,000  of  boiling  water  for 
solution.  The  resulting  liquid  does  not  change  the  colour  of  violets ;  but 
when  pure  magnesia  is  put  upon  moistened  turmeric  paper,  it  causes  a 
brown  stain.  From  this  there  is  no  doubt  that  the  inaction  of  magnesia  with 
respect  to  vegetable  colours,  when  tried  in  the  ordinary  mode,  is  owing  to  its 
insolubility.  It  possesses  the  still  more  essential  character  of  alkalinity, 
that,  namely,  of  forming  neutral  salts  with  acids,  in  an  eminent  degree.  It 
absorbs  both  water  and  carbonic  acid  when  exposed  to  the  atmosphere,  and, 
therefore,  should  be  kept  in  well-closed  phials. 

Magnesia  is  characterized  by  the  following  properties.  With  nitric  and 
hydrochloric  acids  it  forms  salts  which  are  soluble  in  alcohol,  and  exceedingly 
deliquescent.  The  sulphate  of  magnesia  is  very  soluble  in  water,  a  circum- 
stance by  which  it  is  distinguished  from  the  other  alkaline  earths.  Mag- 
nesia is  precipitated  from  its  salts  as  a  bulky  hydrate  by  the  pure  alkalies. 
It  is  precipitated  as  carbonate  of  magnesia  by  the  carbonates  of  potassa  and 
soda ;  but  the  bicarbonates  and  the  common  carbonate  of  ammonia  do  not 
precipitate  it  in  the  cold.  If  moderately  diluted,  the  salts  of  magnesia  are 
not  precipitated  by  oxalate  of  ammonia.  By  means  of  this  reagent  magnesia 
may  be  both  distinguished  and  separated  from  lime. 

Its  eq.  is  20-7;  symb.  Mg-fO,  itfg,  or  MgO. 

Chloride. — This  compound  may  be  prepared  by  transmitting  dry  chlorine 
gas  over  a  mixture  of  magnesia  and  charcoal  at  a  red  heat;  but  Liebig  has 
given  an  easier  process,  which  consists  in  dissolving  magnesia  in  hydrochloric 
acid,  evaporating  to  dryness,  mixing  the  residue  with  its  own  weight  of  hy- 
drochlorate  of  ammonia,  and  projecting  the  mixture  in  successive  portions 
into  a  platinum  crucible  at  a  red  heat.  As  soon  as  the  ammoniacal  salt  is 
wholly  expelled,  the  fused  chloride  of  magnesium  is  left  in  a  stale  of  tranquil 
fusion,  and  on  cooling  becomes  a  transparent  colourless  mass,  which  is 
highly  deliquescent,  and  very  soluble  in  alcohol  and  water. 

Its  eq.  is  48-12 ;  symb.  MgCl. 

Iodide  of  Magnesium  is  obtained  by  dissolving  magnesia  in  hydriodic  acid, 
is  very  soluble  in  water,  and  is  only  known  in  solution. 

Bromide  of  Magnesium,  obtained  by  dissolving  magnesia  in  hydrobromic 
acid,  crystallizes  in  small  acicular  prisms,  which  have  a  sharp  taste,  are  deli- 
quescent, and  very  soluble  in  water  and  alcohol.  It  is  decomposed  by  a 
strong  heat. 

Fluoride  of  Magnesium  is  prepared  by  digesting  magnesia  in  hydrofluoric 
acid  in  excess.  It  is  insoluble  in  water  arid  in  excess  of  hydrofluoric  acid, 
and  bears  a  red  heat  without  decomposition. 


296 

CLASS  i/;"^ 

ORDER  III. 

METALLIC  BASES  OF  THE  EARTHS. 


SECTION  VIII. 

ALUMINIUM. 


Hist. — THAT  alumina  is  an  oxidized  body  was  proved  by  Davy,  who  found 
that  potassa  is  generated  when  the  vapour  of  potassium  is  brought  into  con- 
tact with  pure  alumina  heated  to  whiteness ;  and  it  was  inferred,  chiefly  by 
analogical  reasoning,  to  be  a  metallic  oxide.  The  propriety  of  this  inference 
has  been  demonstrated  by  Wohler,  who  has  procured  aluminium,  the  me- 
tallic base  of  alumina,  in  a  pure  state.  (Edinburgh  Journal  of  Science,  No. 
xvii.  178). 

Prep. — Depends  on  the  property  which  potassium  possesses  of  decompos- 
ing the  chloride  of  aluminium.  Decomposition  is  effected  by  aid  of  a  mo- 
derate increase  of  temperature ;  but  the  action  is  so  violent,  and  accompa- 
nied with  such  intense  heat,  that  the  process  cannot  be  safely  conducted  in 
glass  vessels.  Wtfhler  succeeded  with  a  platinum  crucible,  retaining  the 
cover  in  its  place  by  a  piece  of  wire.  The  heat  developed  during  the  action 
was  so  great,  that  the  crucible,  though  but  gently  heated  externally,  suddenly 
became  red-hot.  The  platinum  is  scarcely  attacked  during  the  process ;  but  to 
prevent  the  possibility  of  error  from  this  source,  the  decomposition  was  also 
effected  in  a  crucible  of  porcelain.  The  potassium  employed  for  the  purpose 
should  be  quite  free  from  carbon,  and  the  quantity  operated  on  at  one  time 
not  exceed  the  size  of  ten  peas.  The  heat  was  applied  by  means  of  a  spirit 
lamp,  and  continued  until  the  action  was  completed.  The  proportion  of  the 
materials  requires  to  be  carefully  adjusted ;  for  the  potassium  should  be  in 
such  quantity  as  to  prevent  any  chloride  of  aluminium  from  subliming  during 
the  process,  but  not  so  much  as  to  yield  an  alkaline  solution  when  the  pro- 
duct is  put  into  water.  The  matter,  contained  in  the  crucible  at  the  close  of 
the  operation,  is  in  general  completely  fused,  and  of  a  dark  gray  colour.  When 
quite  cold,  the  crucible  is  put  into  a  large  glass  full  of  water,  in  which  the 
saline  matter  is  dissolved,  with  slight  disengagement  of  hydrogen  of  an  of- 
fensive odour,  and  a  gray  powder  separates,  which,  on  close  inspection,  espe- 
cially in  sunshine,  is  found  to  consist  solely  of  minute  scales  of  metal.  These 
scales,  after  being  well  washed  with  cold  water,  are  pure  aluminium.  The 
saline  matter  removed  by  water  is  chloride  of  potassium,  and  a  considerable 
quantity  of  chloride  of  aluminium. 

Prop. — As  thus  formed,  it  is  a  gray  powder,  very  similar  to  that  of  platinum. 
It  is  generally  in  small  scales  or  spangles  of  a  metallic  lustre ;  and  some- 
times small,  slightly  coherent,  spongy  masses  are  observed,  which  in  some 


ALUMINIUM.  297 

places  have  the  lustre  and  white  colour  of  tin.  The  same  appearance  is 
rendered  perfectly  distinct  by  pressure  on  steel,  or  in  an  agate  mortar ;  so  that 
the  lustre  of  aluminium  is  decidedly  metallic.  In  its  fused  state  it  is  a  con- 
ductor of  electricity,  though  it  does  not  possess  this  property  when  in  the 
form  of  powder.  This  remark,  of  a  metal  conducting  the  electric  fluid  in 
one  state  and  not  in  another,  is  very  instructive ;  and  Wtfhler  observed  an  in- 
stance of  the  same  kind  in  iron,  which  in  the  state  of  fine  powder  is  a  non- 
conductor of  electricity. 

Aluminium  requires  for  fusion  a  temperature  higher  than  that  at  which 
cast  iron  is  liquefied.  When  heated  to  redness  in  the  open  air,  it  takes  fire 
and  burns  with  vivid  light,  yielding  aluminous  earth  of  a  white  colour,  and 
of  considerable  hardness.  Sprinkled  in  powder  in  the  flame  of  a  candle, 
brilliant  sparks  are  emitted,  like  those  given  off  during  the  combustion  of 
iron  in  oxygen  gas.  When  heated  to  redness  in  a  vessel  of  pure  oxygen  gas, 
it  burns  with  an  exceedingly  vivid  light,  and  emission  of  intense  heat.  The 
resulting  alumina  is  partially  vitrified,  of  a  yellowish  colour,  and  equal  in 
hardness  to  the  native  crystallized  aluminous  earth,  corundum.  Pleated  to 
near  redness  in  an  atmosphere  of  chlorine,  it  takes  fire,  and  chloride  of  alumi- 
nium is  sublimed. 

Aluminium  is  not  oxidized  by  water  at  common  temperatures,  nor  is  its 
lustre  tarnished  by  lying  in  water  during  its  evaporation.  On  heating  the 
water  to  near  its  boiling  point,  oxidation  of  the  metal  commences,  with  fee- 
ble disengagement  of  hydrogen  gas,  the  evolution  of  which  continues  even 
long  after  cooling,  but  at  length  wholly  ceases.  The  oxidation,  however,  is 
very  slight;  and  even  after  continued  ebullition,  the  smallest  particles  of 
aluminium  appear  to  have  suffered  scarcely  any  change. 

It  is  not  attacked  by  concentrated  sulphuric  or  nitric  acid  at  common 
temperatures.  In  the  former,  with  the  aid  of  heat,  it  is  rapidly  dissolved 
with  disengagement  of  sulphurous  acid  gas.  In  dilute  hydrochloric  and 
sulphuric  acid,  and  also  in  a  dilute  solution  of  potassa,  it  dissolves  with  evo- 
lution of  hydrogen  gas.  Ammonia  produces  a  similar  effect,  and  dissolves 
a  large  quantity  of  alumina.  The  hydrogen  gas  which  makes  its  appearance 
is  of  course  derived  from  water,  the  oxygen  of  which  combines  with  the 
metal  so  as  to  constitute  alumina. 

From  the  composition  of  the  sulphates  of  alumina,  ascertained  by  Berze- 
lius,  Stromeyer,  and  Phillips,  the  equivalent  of  alumina  may  be  estimated 
either  at  25-7,  or  at  51 '4,  twice  that  number.  Now  chemists  have  no  direct 
means  of  discovering  the  atomic  constitution  of  alumina,  inasmuch  as  alumi- 
nium combines  with  oxygen  and  most  other  elements  in  one  proportion  only. 
Thomson  assumes  alumina  to  consist  of  single  atoms  of  its  elements ;  but 
most  chemists,  seeing  that  alumina  has  little  analogy  to  protoxides  in  its 
modes  of  combining,  but  that  in  its  form  and  all  its  chemical  relations  it 
closely  resembles  sesquioxide  of  iron,  have  inferred  that  the  simplest  mole- 
cule of  alumina  contains  two  atoms  of  aluminium  and  three  atoms  of  oxygen. 
On  this  supposition  51-4  must  be  the  eq.  of  alumina,'and  13-7  that  of  alumi- 
nium; its  symb.  Al.  The  composition  of  its  compounds  described  in  this 
section  is  the  following : — 

2  eq. 

Aluminium.  Equiv.        Formulae. 

Sesquioxide  27-4+Oxygen    24       3  eq.==  51-4    2A1+3O  or  ATOs 

Sesquichloride      27-4+Chlorine  106-26  3  eq.  =133-66  2A1+3C1  or  AlsCla 
Sesquisulphuret    27-4-}-Sulphur     48-3    3  eq.==  75-7     2A1-J-3S  or  AlaSs 
Sesquiphosphuret27-4-HPhosph.     47-1    3  eq.=  74-5     2A1+3P  or  Al^Ps 
Sesquiseleniuret  27-44-Seleniumll8-8    3  eq.  =146-2    2Al-|-3Se  or  Al^Ses 
The  composition  of  the  last  four  compounds  is  matter  of  inference  from  the 
change«which  they  respectively  undergo  by  the  action  of  water. 

Sesquioxide  af  Aluminium. — Hist,  and  Prep. — The  only  known  oxide  of 
this  metal,  and  is  commonly  called  alumina  or  aluminous  earth.  It  is  one 
of  the  most  abundant  productions  of  nature.  It  is  found  in  every  region  of 


298  ALUMINIUM. 

the  globe,  and  in  rocks  of  all  ages,  being  a  constituent  of  the  oldest  primary 
mountains,  of  the  secondary  strata,  and  of  the  most  recent  alluvial  deposi- 
tions. The  different  kinds  of  clay  of  which  bricks,  pipes,  and  earthenware 
are  made,  consist  of  hydrate  of  alumina  in  a  greater  or  less  degree  of  purity. 
Though  this  earth  commonly  appears  in  rude  amorphous  masses,  it  is  some- 
times found  beautifully  crystallized.  The  ruby  and  the  sapphire,  two  of  the 
most  beautiful  gems  with  which  we  are  acquainted,  are  composed  almost 
solely  of  alumina. 

Pure  alumina  is  prepared  from  alum,  the  sulphate  of  alumina  and  potassa. 
This  salt,  as  purchased  in  the  shops,  is  frequently  contaminated  with  scsqui- 
oxide  of  iron,  and  consequently  unfit  for  many  chemical  purposes;  but  it  may 
be  separated  from  this  impurity  by  repeated  crystallization.  Its  absence  is 
proved  by  the  alum  being  soluble  without  residue  in  a  solution  of  pure 
potassa;  whereas  when  sesquioxide  of  iron  .is  present,  it  is  either  left  undis- 
solved  in  the  first  instance,  or  deposited  after  a  few  hours  in  yellowish- 
brown  flocks.  Any  quantity  of  purified  alum  is  dissolved  in  four  or  five 
times  its  weight  of  boiling  water,  a  slight  excess  of  carbonate  of  potassa 
added,  and  after  digesting  for  a  few  minutes,  the  bulky  hydrate  of  alumina 
is  collected  on  a  filter,  and  well  washed  with  hot  water.  It  is  necessary  in 
this  operation  to  digest  and  employ  an  excess  of  alkali ;  since  otherwise  the 
precipitate  would  retain  some  sulphuric  acid  in  the  form  of  a  subsulphate. 
But  the  alumina,  as  thus  prepared,  is  not  yet  quite  pure;  for  it  retains  some 
of  the  alkali  with  such  force,  that  it  cannot  be  separated  by  the  action  of 
water.  For  this  reason  the  precipitate  must  be  re-dissolved  in  dilute  hydro- 
chloric acid,  and  thrown  down  by  means  of  pure  ammonia  or  its  carbonate. 
This  precipitate,  after  being  well  washed  and  exposed  to  a  white  heat,  yields 
pure  anhydrous  alumina.  Ammonia  cannot  be  employed  for  precipitating 
aluminous  earth  directly  from  alum,  because  sulphate  of  alumina  is  not  com- 
pletely decomposed  by  this  alkali.  (Berzelius.)  An  easier  process,  proposed 
by  Gay-Lussac,  is  to  expose  sulphate  of  alumina  and  ammonia  to  a  strong 
heat,  so  as  to  expel  the  ammonia  and  sulphuric  acid. 

Prop. — Alumina  has  neither  taste  nor  smell,  and  is  quite  insoluble  in 
water.  It  is  very  infusible,  though  less  so  than  lime  or  magnesia.  It  has  a 
powerful  affinity  for  water,  attracting  moisture  from  the  atmosphere  with 
avidity;  and  for  a  like  reason,  it  adheres  tenaciously  to  the  tongue  when 
applied  to  it.  Mixed  with  a  due  proportion  of  water,  it  yields  a  soft  cohesive 
mass,  susceptible  of  being  moulded  into  regular  forms,  a  property  upon 
which  depends  its  employment  in  the  art  of  pottery.  When  once  moistened, 
it  cannot  be  rendered  anhydrous,  except  by  exposure  to  a  full  white  heat; 
and  in  proportion  as  it  parts  with  water,  its  volume  diminishes  (page  27). 
Owing  to  its  insolubility,  it  does  not  affect  the  blue  colour  of  plants.  It  ap- 
pears to  possess  the  properties  both  of  an  acid  and  of  an  alkali : — of  an  acid, 
by  uniting  with  alkaline  bases,  such  as  potassa,  lime,  and  baryta; — and  of  an 
alkali,  by  forming  salts  with  acids.  In  neither  case,  however,  are  its  soluble 
compounds  neutral  with  respect  to  test  paper. 

Alumina  most  probably  forms  several  different  hydrates  with  water,  and 
two  have  been  described  by  Thomson.  One  of  these,  apparently  composed 
of  six  eq.  of  water  to  one  of  alumina,  so  that  its  formula  is  AbOs-j-G  Aq., 
was  procured  by  exposing  precipitated  alumina  for  the  space  of  two  months 
to  a  dry  air,  the  temperature  of  which  did  not  exceed  50°.  The  other  is  a 
terhydrate  prepared  by  drying  the  preceding  at  a  heat  of  about  100°,  and 
its  formula  is,  therefore,  Al3O3-r-3Aq.  The  mineral  called  Gibbsite  has  a 
similar  composition. 

Alumina  is  easily  recognized  by  the  following  characters.  1.  It  is  sepa- 
rated from  acids,  as  a  hydrate,  by  all  the  alkaline  carbonates  and  by  pure 
ammonia.  2.  It  is  precipitated  by  pure  potassa  or  soda,  but  th&  precipitate 
is  completely  redissolved  by  an  excess  of  the  alkali. 

Its  eq.  is  51-4;  syrnb.  2A1  +  3O,  Al,  or 


ALUMINIUM.  299 

Sesquichloride  of  Aluminium. — Hist. — Oersted  discovered  this  compound 
by  transmitting  dry  chlorine  gas  over  a  mixture  of  alumina  and  charcoal 
heated  to  redness.  By  acting  on  this  substance  with  an  amalgam  of  potas- 
sium and  expelling  the  mercury  by  heat,  he  obtained  metallic  matter,  which 
he  believed  to  be  aluminium ;  but  not  having  leisure  to  pursue  the  inquiry 
himself,  he  requested  Wohler  to  investigate  the  subject.  Wohler  did  not 
arrive  at  any  satisfactory  conclusion  by  the  method  suggested  by  Oersted  ; 
but  met  with  complete  success  by  means  of  pure  potassium,  as  already  de- 
scribed. 

Prep. — To  procure  sesquichloride  of  aluminium,  Wohler  precipitated 
aluminous  earth  from  a  hot  solution  of  alum  by  means  of  potassa,  and  mixed 
the  hydrate,  when  dry,  with  pulverized  charcoal,  sugar,  and  oil,  so  as  to 
form  a  thick  paste,  which  was  heated  in  a  covered  crucible  until  all  the 
organic  matter  was  destroyed.  By  this  means  the  alumina  was  brought  into 
a  state  of  intimate  mixture  with  finely  divided  charcoal,  and  while  yet  hot, 
was  introduced  into  a  tube  of  porcelain,  fixed  in  a  convenient  furnace.  After 
expelling  atmospheric  air  from  the  interior  of  the  apparatus  by  a  current  of 
dry  chlorine  gas,  the  tube  was  brought  to  a  red  heat.  The  formation  of 
sesquichloride  of  aluminium  then  commenced,  and  continued,  with  disen- 
gagement of  carbonic  oxide  gas,  during  an  hour  and  a  half,  when  the  tube 
became  impervious  from  sublimed  sesquichloride  collected  within  it.  The 
process  was  then  necessarily  discontinued. 

Prop. — -As  thus  formed,  sesquichloride  of  aluminium  is  of  a  pale  greenish- 
yellow  colour,  partially  translucent,  and  of  a  highly  crystalline  lamellated 
texture,  somewhat  like  talc,  but  without  regular  crystals.  On  exposure  to 
the  air,  it  fumes  slightly,  emits  an  odour  of  hydrochloric  acid  gas,  and,  deli- 
quescing, yields  a  clear  liquid.  When  thrown  into  water,  it  is  speedily  dis- 
solved with  a  hissing  noise;  and  so  much  heat  is  evolved,  that  the  water,  if 
in  small  quantity,  is  brought  into  a  state  of  brisk  ebullition.  The  solution 
is  probably  a  true  hydrochlorate  of  alumina,  formed  by  decomposition  of 
water.  According  to  Oersted  it  is  volatile  at  a  temperature  a  little  higher 
than  212°,  and  fuses  nearly  at  the  same  degree. 

Sesquisulphuret  of  Aluminium. — Sulphur  may  be  distilled  from  aluminium 
without  combining  with  it;  but  if  a  piece  of  sulphur  is  dropped  on  alumi- 
nium when  strongly  incandescent,  so  that  it  may  be  enveloped  in  an  atmos- 
phere of  the  vapour  of  sulphur,  the  union  is  effected  with  vivid  emission  of 
light.  The  resulting  sulphuret  is  a  partially  vitrified,  semi-metallic  mass, 
which  acquires  an  iron-black  metallic  lustre  when  burnished.  Applied  to 
the  tongue,  it  excites  a  pricking  warm  taste  of  hydrosulphuric  acid.  When 
put  into  pure  water,  or  on  exposure  to  the  air,  it  is  resolved,  by  an  inter- 
change of  elements,  into  alumina  and  hydrosulphuric  acid,  the  latter  es- 
caping as  gas.  It  is  to  be  presumed  that 

1  eq.  sesquisulphuret  and  3  eq.  water 
2A1+3S  3(H  +  O) 

yield 
1  eq.  alumina  and  3  eq.  hydrosulph.  acid. 

2A1-J-3O  3(H  +  S). 

Wohler  finds  that  sesquisulphuret  of  aluminium  cannot  be  generated  by 
the  action  of  hydrogen  gas  on  sulphate  of  alumina  at  a  red  heat ;  for  in  that 
case  all  the  acid  is  expelled,  without  the  aluminous  earth  being  reduced. 

Sesquiphosphuret  of  Aluminium. — When  aluminium  is  heated  to  redness 
in  contact  with  the  vapour  of  phosphorus,  it  takes  fire,  and  emits  a  brilliant 
light.  The  product  is  described  by  Wohler  as  a  blackish-gray  pulverulent 
mass,  which  by  friction  acquires  a  dark-gray  metallic  lustre,  and  in  the  air 
smells  instantly  of  phosphuretted  hydrogen.  By  the  action  of  water,  alumina 
and  phosphuretted  hydrogen  gas  are  generated,  but  the  latter  is  not  spon- 
taneously inflammable.  The  effervescence  is  less  rapid  than  with  the  sesqui- 
sulphuret, but  is  increased  by  heat. 

Sesquiseleniuret  of  Aluminium. — This  compound  is  formed,  with  disen- 


300  GLUCINIUM. 

gagement  of  heat  and  light,  by  heating  to  redness  a  mixture  of  selenium 
and  aluminium.  The  product  is  black  and  pulverulent,  and  assumes  a  dark 
metallic  lustre  when  rubbed.  In  the  air  it  emits  a  strong  odour  of  hydrose- 
lenic  acid ;  and  this  gas  is  rapidly  disengaged  by  the  action  of  water,  which 
is  speedily  reddened  by  the  separation  of  selenium. 


SECTION   IX. 

GLUCINIUM,  YTTRIUM,  THORIUM,  AND  ZIRCONIUM. 

GLUCINIUM. 

Glucina,  which  was  discovered  by  Vauquelin  in  the  year  1798,  has  hi- 
therto been  found  only  in  three  rare  minerals,  the  euclase,  beryl,  and  eme- 
rald. It  is  the  only  oxide  of  a  metal  which  Wohler  succeeded  in  preparing 
in  the  year  1828  by  a  process  exactly  similar  to  that  described  in  the  last 
section.  Chloride  of  glucinium  is  readily  attacked  by  potassium  when  heated 
with  the  flame  of  a  spirit-lamp,  and  the  decomposition  is  attended  with  in- 
tense heat.  After  removing  the  resulting  chloride  of  potassium  by  cold  wa- 
ter, the  glucinium  appears  in  the  form  of  a  grayish-black  powder,  which 
acquires  a  dark  metallic  lustre  by  burnishing.  It  may  be  exposed  to  air  and 
moisture,  or  be  even  boiled  in  water,  without  oxidation.  When  heated  in  the 
open  air,  it  takes  fire  and  burns  with  a  most  vivid  light ;  and  in  oxygen  gas 
the  combustion  is  attended  with  extraordinary  splendour.  The  product  in 
both  cases  is  glucina,  which  is  not  at  all  fused  by  the  intense  heat  that  ac- 
companied its  formation.  The  metal  is  readily  oxidized  and  dissolved  in 
sulphuric,  nitric,  or  hydrochloric  acid  with  the  aid  of  heat ;  and  the  same 
ensues,  with  disengagement  of  hydrogen  gas,  in  solution  of  potassa.  It  is 
not  attacked,  however,  by  pure  ammonia.  When  moderately  heated  in 
chlorine  gas,  it  burns  with  great  splendour,  and  a  crystallized  chloride  sub- 
limes. Similar  phenomena  ensue  in  the  vapour  of  bromine  and  iodine;  and 
it  unites  readily  with  sulphur,  selenium,  phosphorus,  and  arsenic.  (Phil. 
Mag.  and  Annals,  v.  392.) 

According  to  the  experiments  of  Berzelius,  glucina  contains  31*154  per 
cent,  of  oxygen,  and  consequently  the  eq.  of  glucinium  is  26'5,  on  the  suppo- 
sition that  the  constitution  of  glucina  is  similar  to  that  of  alumina,  with 
which  it  is  closely  associated  both  in  nature  and  in  many  of  its  properties. 
Its  syrnb.  is  G. 

Sesquioxide  of  Glucinium  or  Glucina. — Prep. — This  oxide  is  commonly 
prepared  from  beryl,  in  which  it  exists  to  the  extent  of  about  14  per.  cent., 
combined  with  silicic  acid  and  alumina.  In  order  to  procure  it  in  a  separate 
state,  the  mineral  is  reduced  to  an  exceedingly  fine  powder,  mixed  with 
three  times  its  weight  of  carbonate  of  potassa,  and  exposed  to  a  strong 
red  heat  for  half  an  hour,  so  that  the  mixture  may  be  fused.  The  mass  is 
then  dissolved  in  dilute  hydrochloric  acid,  and  the  solution  evaporated  to  per- 
fect dryness ;  by  which  means  the  silicic  acid  is  rendered  quite  insoluble. 
The  alumina  and  glucina  are  then  redissolved  in  water  acidulated  with  hy- 
drochloric acid,  and  thrown  down  together  by  pure  ammonia.  The  preci- 
pitate, after  being  well  washed,  is  macerated  with  a  large  excess  of  carbonate 
of  ammonia,  by  which  glucina  is  dissolved;  and  on  boiling  the  filtered  liquid, 
carbonate  of  glucina  subsides.  By  means  of  a  red  heat  its  carbonic  acid  is 
entirely  expelled. 

Another  process  has  been  recommended  by  Berthier,  who  directs  the  beryl 
to  be  mixed  in  fine  powder  with  its  own  weight  of  marble,  and  the  mixture 


YTTRIUM — THORIUM.  3G1 

to  be  exposed  in  a  crucible  to  a  strong1  heat.  In  this  manner  a  glass  is  ob- 
tained, which  when  in  fine  powder  is  attacked  freely  by  hydrochloric  or 
sulphuric  acid.  From  this  solution  the  glucma  may  be  obtained  as  before. 

Prop. — Glucina  is  a  white  powder,  which  has  neither  taste  nor  odour,  and 
is  quite  insoluble  in  water.  Its  sp.  gr.  is  3.  Vegetable  colours  are  not  af- 
fected by  it.  The  salts  which  it  forms  with  acids  have  a  sweetish  taste,  a 
circumstance  which  distinguishes  glucina  from  other  earths,  and  from 
which  its  name  is  derived  (from  yxvKvs-,  sweet.) 

Glucina  may  be  known  chemically  by  the  following  characters.  1.  Pure 
potassa  or  soda  precipitates  glucina  from  its  salts,  but  an  excess  of  the 
alkali  redissolves  it.  2.  It  is  precipitated  permanently  by  pure  ammonia  as  a 
hydrate,  and  by  fixed  alkaline  carbonates  as  a  carbonate  of  glucina.  3.  It  is 
dissolved  completely  by  a  cold  solution  of  carbonate  of  ammonia,  and  is 
precipitated  from  it  by  boiling.  By  means  of  this  property,  glucina  may  be 
both  distinguished  and  separated  from  alumina. 

Its  eq.  is  77 ;  symb.  2G  4. 3O,  G^  or  0*0*. 

YTTRIUM. 

Yttrium  is  the  metallic  base  of  an  earth  which  was  discovered  in  the  year 
1794  by  Professor  Gadolin,  in  a  mineral  found  at  Ytterby  in  Sweden,  from 
which  it  received  the  name  of  yttria.  The  metal  itself  was  prepared  by 
Wohler  in  1828  by  a  process  similar  to  that  above  described.  Its  texture, 
by  which  it  is  distinguished  from  glucinium  and  aluminium,  is  scaly,  its  co- 
lour grayish-black,  and  its  lustre  perfectly  metallic.  In  colour  and  lustre  it 
is  inferior  to  aluminium,  bearing  in  these  respects  nearly  the  same  relation 
to  that  metal,  that  iron  does  to  tin.  It  is  a  brittle  metal,  while  aluminium  is 
ductile.  It  is  not  oxidized  either  in  air  or  water ;  but  when  heated  to  red- 
ness, it  burns  with  splendour  even  in  atmospheric  air,  and  with  far  greater 
brilliancy  in  oxygen  gas.  The  product  yttria,  is  white,  and  shows  unequi- 
vocal marks  of  fusion.  It  dissolves  in  sulphuric  acid,  and  also,  though  less 
readily,  in  solution  of  potassa;  but  it  is  not  attacked  by  ammonia.  It  com- 
bines with  sulphur,  selenium,  and  phosphorus.  (Phil.  Mag1,  and  Annals,  v. 
393.) 

The  salts  of  yttria  have  in  general  a  sweet  taste,  and  the  sulphate  and  sev- 
eral others  have  an  amethyst  colour.  It  is  precipitated  as  a  hydrate  by  the 
pure  alkalies,  and  is  not  redissolved  by  an  excess  of  the  precipitant;  but  al- 
kaline carbonates,  especially  that  of  ammonia,  dissolve  it  in  the  cold,  though 
less  freely  than  glucina,  and  carbonate  of  yttria  is  precipitated  by  boiling. 
Of  all  the  earths  it  bears  the  closest  resemblance  to  glucina ;  but  it  is  readily 
distinguished  from  it  by  the  colour  of  its  sulphate,  by  its  insolubility  in  pure 
potassa,  and  by  yielding  a  precipitate  with  ferrocyanuret  of  potassium. 
(Berzelius.)  The  eq.  of  yttrium,  as  deduced  by  Berzelius,  is  32-2;  and  that 
of  yttria,  which  is  probably  a  protoxide,  is  40-2. 

The  symb.  of  the  metal  is  Y;  of  its  oxide  Y-f.0,  Y,  or  YO, 

THORIUM. 

The  earthy  substance  formerly  called  thorina  was  found  by  Berzelius  to 
be  phosphate  of  yttria ;  but  in  1828  he  discovered  a  new  earth,  so  similar 
in  some  respects  to  what  was  formerly  called  thorina,  that  he  applied  this 
term  ,to  the  new  substance.  The  metallic  base  of  thorina  (thorium)  was 
procured  by  the  action  of  potassium  on  chloride  of  thorium,  the  decomposi- 
tion being  accompanied  with  a  slight  detonation.  On  washing  the  mass, 
thorium  is  left  in  the  form  of  a  heavy  metallic  powder,  of  a  deep  leaden- 
gray  colour;  and  when  pressed  in  an  agate  mortar,  it  acquires  metallic 
lustre  and  an  iron-gray  tint.  Thorium  is  not  oxidized  either  by  hot  or  cold 
water ;  but  when  gently  heated  in  the  open  air,  it  burns  with  great  bril- 
liancy, comparable  to  that  of  phosphorus  burning  in  oxygen.  The  resulting 
thorina  is  as  white  as  snow,  and  does  not  exhibit  the  least  trace  of  fusion, 

26 


302  ZIRCONIUM. 

It  is  not  attacked  by  caustic  alkalies  at  a  boiling  heat ;  is  scarcely  at  all 
acted  on  by  nitric  acid,  and  very  slowly  by  the  sulphuric ;  but  it  is  readily 
dissolved,  with  disengagement  of  hydrogen  gas,  by  hydrochloric  acid.  The 
eq,  of  thorium  is  59'6,  on  the  supposition  that  thorina  is  a  protoxide.  Its 
symb.  is  Th. 

Thorina. — Hist,  and  Prep. — Procured  from  a  rare  Norwegian  mineral, 
now  called  thorite,  wl^ich  was  sent  to  Berzelius  by  Esmarck.  It  constitutes 
57'91  per  cent  of  the  mineral,  and  occurs  in  the  form  of  a  hydrated  silicate 
of  thorina.  In  order  to  prepare  thorina,  the  mineral  is  reduced  to  powder, 
and  digested  in  hydrochloric  acid  ;  when  a  gelatinous  mass  is  formed,  from 
which  silicic  acid  is  separated  by  evaporating  to  dryness,  and  dissolving  the 
soluble  parts  in  dilute  acid.  The  solution  is  then  freed  from  lead  and  tin, 
which  koccur  in  thorite  along  with  several  impurities,  by  hydrosulphuric 
acid,  and  the  earths  are  thrown  down  by  pure  ammonia.  The  precipitate, 
after  being  well  washed,  is  dissolved  in  dilute  sulphuric  acid,  and  the  solu- 
tion evaporated  at  a  high  temperature  till  only  a  small  quantity  of  fluid  re- 
mains. During  the  evaporation  the  greater  part  of  the  thorina  is  deposited 
as  a  sulphate;  and  on  decanting  the  remaining  fluid,  washing  the  residue, 
and  heating  it  to  redness,  pure  thorina  remains.  (An.  de  Ch.  et  de  Ph. 
xliii.  5.) 

Prop. — Thorina,  when  formed  by  the  oxidation  of  thorium,  or  after  being 
strongly  heated,  is  a  white  earthy  substance,  of  sp.  gr.  9'402,  and  insoluble 
in  all  the  acids  except  the  sulphuric;  and  it  dissolves  even  in  that  with 
difficulty.  It  is  precipitated  from  its  solutions  by  the  caustic  alkalies  as  a 
hydrate,  and  in  this  state  absorbs  carbonic  acid  from  the  atmosphere,  and 
dissolves  readily  in  acids.  All  the  alkaline  carbonates  dissolve  the  hydrate, 
carbonate,  and  sub-salts  of  thorina.  Its  exact  composition  is  not  known  ; 
but  its  eq.  is  about  67'6. 

Thorina  is  distinguished  from  alumina  and  glucina  by  its  insolubility  in 
pure  potassa;  from  yttria  by  forming  with  sulphate  of  potassa  a  doable  salt 
which  is  quite  insoluble  in  a  cold  saturated  solution  of  sulphate  of  potassa  ; 
and  from  zirconia  by  the  circumstance  that  this  earth,  after  being  precipi- 
tated from  a  hot  solution  of  sulphate  of  potassa,  is  almost  insoluble  in  water 
and  the  acids.  Thorina  is  precipitated,  also,  by  ferrocyanuret  of  potassium, 
which  does  not  separate  zirconia  from  its  solutions.  Berzelius  has  remarked 
that  sulphate  of  thorina  is  much  more  soluble  in  cold  than  in  hot  water  ;  so 
that  a  cold  saturated  solution  becomes  turbid  when  heated,  and  in  cooling 
recovers  its  transparency. 

Chloride  of  thorium  is  readily  prepared  by  carbonizing  an  intimate  mix- 
ture of  thorina  and  sugar  in  a  covered  platinum  crucible,  and  then  exposing 
the  residue  at  a  red  heat  in  a  porcelain  tube  to  a  current  of  dry  chlorine. 
The  chloride,  possessing  but  little  volatility,  collects  in  the  tube  just  beyond 
the  ignited  part  in  the  form  of  a  partially  fused,  crystalline,  white  mass. 
It  is  soluble  in  water  with  considerable  rise  of  temperature. 

When  thorium  is  heated  in  the  vapour  of  sulphur,  the  phenomena  of 
combustion  ensue  with  the  same  brilliancy  as  in  air,  and  a  sulphuret  results. 
A  phosphuret  may  be  formed  by  a  similar  process. 

ZIRCONIUM. 

Hist,  and  Prep. — The  experiments  of  Davy  proved  zirconia  to  be  an  oxi- 
dized body,  and  afforded  a  presumption  that  its  base,  zirconium,  is  of  a  me- 
tallic nature;  but  Berzelius  first  obtained  the  metal  in  1824  by  heating  with 
a  spirit-lamp,  a  mixture  of  potassium  and  the  double  fluoride  of  zirconium 
and  potassium,  carefully  dried,  in  a  tube  of  glass,  or  iron.  The  reduction 
takes  place  at  a  temperature  below  redness,  without  emission  of  light ;  and 
the  mass  is  washed  with  boiling  water,  and  afterwards  digested  for  some 
time  in  dilute  hydrochloric  acid.  The  residue  is  pure  zirconium. 

Prop. — Zirconium,  thus  obtained,  is  in  the  form  of  a  black  powder,  which 
may  be  boiled  in  water  without  being  oxidized,  and  is  attacked  with  diffi- 
culty by  sulphuric,  hydrochloric,  or  nitro-hydrochloric  acid ;  but  it  is  dis- 


ZIRCONIUM.  303 

solved  readily,  and  with  disengagement  of  hydrogen  gas,  by  hydrofluoric 
acid.  Heated  in  the  open  air,  it  takes  fire  at  a  temperature  far  below  in- 
candescence, burns  brightly,  and  is  converted  into  zirconia.  Its  metallic 
nature  seems  somewhat  questionable.  It  may  indeed  be  pressed  out  into 
thin  shining  scales  of  a  dark  gray  colour,  and  of  a  lustre  which  may  be 
called  metallic  ;  but  its  particles  cohere  together  very  feebly,  and  it  has  not 
been  procured  in  a  state  capable  of  conducting  electricity.  These  points, 
however,  require  farther  investigation  before  a  decisive  opinion  on  the 
subject  can  be  adopted.  (Pog.  Annalen,  iv.) 

Sesquioxide  of  Zirconium  or  Zirconia  was  discovered  in  the  year  1789  by 
Klaproth  in  the  jargon  or  zircon  of  Ceylon,  and  has  since  been  found  in  the 
hyacinth  from  Expailly  in  France.  Berthier  prepares  it  by  fusing  zircon 
in  fine  powder  with  litharge  in  the  ratio  of  17  to  21,  when  a  glass  is  ob- 
tained which  is  soluble  in  acids.  It  is  an  earthy  substance,  resembling 
alumina  in  appearance,  of  sp.  gr.  4-3,  having  neither  taste  nor  odour,  and 
quite  insoluble  in  water.  It  is  so  hard  that  it  will  scratch  glass.  Its 
colour,  when  pure,  is  white ;  but  it  has  frequently  a  tinge  of  yellow,  owing 
to  the  presence  of  iron,  from  which  it  is  separated  with  great  difficulty.  It 
phosphoresces  vividly  when  heated  strongly  before  the  blowpipe.  Its  salts 
are  distinguished  from  those  of  alumina  or  glucina  by  being  precipitated  by 
all  the  pure  alkalies,  in  an  excess  of  which  it  is  insoluble.  The  alkaline 
carbonates  precipitate  it  as  carbonate  of  zirconia,  and  a  small  portion  of  it 
is  redissolved  by  an  excess  of  the  precipitant,  especially  when  a  bicarbonate 
is  employed.  It  differs  from  all  the  earths,  except  thorina,  in  being  preci- 
pitated when  any  of  its  neutral  salts  are  boiled  with  a  saturated  solution  of 
sulphate  of  potassa,  the  zirconia  subsiding  as  a  subsalt,  and  the  potassa  re- 
maining in  solution  as  a  bisulphate.  Zirconia  is  precipitated  from  its  salts 
by  pure  ammonia  as  a  bulky  hydrate,  which  is  readily  soluble  in  acids ;  but 
if  this  hydrate  is  ignited,  dried,  or  even  washed  with  boiling  water,  it  after- 
wards resists  the  action  of  the  acids,  and  is  dissolved  by  them  with  great 
difficulty.  Strong  sulphuric  acid  is  then  its  best  solvent  (Berzelius).  When 
hydrated  zirconia  is  heated  to  commencing  redness,  it  parts  with  its  water, 
and  soon  after  emits  a  very  vivid  glow  for  a  short  time.  This  phenomenon 
appears  to  depend  upon  the  particles  of  the  zirconia  suddenly  approaching 
each  other,  the  earth  thus  acquiring  much  greater  density  than  it  previously 
possessed.  Sesquioxide  of  chromium,  titanic  acid,  and  several  other  com- 
pounds afford  instances  of  the  same  appearance;  and  whenever  it  takes 
place,  the  susceptibility  of  the  substance  to  be  attacked  by  fluid  reagents  is 
greatly  diminished.  (Berzelius). 

The  composition  of  zirconia  has  not  yet  been  satisfactorily  determined. 
From  some  analyses  by  Berzelius,  described  in  the  Essay  above  referred  to, 
it  is  probable  that  the  eq.  of  Zirconium  is  about  33-7.  The  symb.  of  the 

earth  is  2Zr-f  3O,  Zr,  or  ZrsOs.     Its  eq.  91*4. 

Sulphuret  of  Zirconium. — This  compound  may  be  prepared,  according  to 
Berzelius,  by  heating  zirconium  with  sulphur  in  an  atmosphere  of  hydro-' 
gen  gas ;  and  the  union  is  effected  with  feeble  emission  of  light.  The  pro- 
duct is  pulverulent,  a  non-conductor  of  electricity,  of  a  dark  chestnut-brown 
colour,  and  without  lustre.  It  is  insoluble  in  sulphuric,  nitric,  and  hydro- 
chloric acid ;  and  it  is  slowly  attacked  by  nitro-hydrochloric  acid,  even  with 
the  aid  of  heat.  It  is  readily  dissolved  by  hydrofluoric  acid,  with  disengage- 
ment of  hydrogen  gas. 


304 


CLASS   II. 

METALS,  THE  OXIDES  OF  WHICH  ARE  NEITHER 
ALKALIES  NOR  EARTHS. 

ORDER  I. 

METALS  WHICH  DECOMPOSE  WATER  AT  A  RED  HEAT. 
SECTION    X. 


MANGANESE. 

Hist,  and  Prep. — THE  black  oxide  of  manganese  was  described  in  the 
year  1774  by  Scheele  as  a  peculiar  earth,  and  Gahn  subsequently  showed 
that  it  contains  a  new  metal,  to  which  he  gave  the  name  of  magnesium  ; 
a  term  since  applied  to  the  metallic  base  of  magnesia,  and  for  which  the 
words  manganesium  and  manganium  have  been  substituted.  This  rnetal, 
owing  doubtless  to  its  strong  affinity  for  oxygen,  has  never  been  found  in  an 
uncombined  state  in  the  earth ;  but  its  oxides  are  very  abundant.  The 
metal  may  be  obtained  by  forming  finely  powdered  oxide  of  manganese  into 
a  paste  with  oil,  laying  the  mass  in  a  Hessian  crucible  lined  with  charcoal, 
luting  down  a  cover  carefully,  and  exposing  it  during  an  hour  and  a  half,  or 
two  hours,  to  the  strongest  heat  of  a  smith's  forge. 

Prop. — A  hard  brittle  metal,  of  a  grayish-white  colour,  and  granular  tex- 
ture. Its  sp.  gr.  according  to  John,  is  8-013.  When  pure  it  is  not  attracted 
by  the  magnet,  but  Berthier  has  lately  stated  that  it  possesses  this  property 
at  very  low  temperatures.  It  is  exceedingly  infusible,  requiring  the  highest 
heat  of  a  wind  furnace  for  fusion.  It  soon  tarnishes  on  exposure  to  the  air, 
and  absorbs  oxygen  with  rapidity  when  heated  to  redness  in  open  vessels.  It 
slowly  decomposes  water  at  common  temperatures  with  disengagement  of 
hydrogen  gas ;  but  at  a  red  heat  decomposition  is  rapid,  and  protoxide  of 
manganese  is  generated.  Decomposition  of  water  is  likewise  occasioned  by 
dilute  sulphuric  acid,  and  sulphate  of  protoxide  of  manganese  is  the  product. 

Berzelius,  from  an  analysis  of  chloride  of  manganese,  found  27-7  as  the 
eq.  of  manganese,  a  number  which  agrees  closely  with  my  own  experiments 
on  the  same  chloride.  Its  symb.  is  Mn.  The  composition  of  the  compounds 
of  manganese  described  in  this  section  is  as  follows  : — 

Manganese.  Equiv.    Formula. 

Protoxide            27-7  1  eq.-f  Oxygen  8  1  eq.=  35-7     Mn+O. 

Sesquioxide         55-4  2  eq.-j-do.  24  3  eq.=5  79-4    2Mn-f3O. 

Peroxide              27-7  1  eq.-fdo.  16  2  eq.=  43-7     Mn-f-2O. 

Red  oxide             83-1  3  eq.-fdo.  32  4  eq.=115-l     3Mn-f-4O. 

Varvicite            110-8  4  eq.-f  do.  56  7  eq.=166-8    4Mn-f7O. 

Manganic  acid    27-7  leq.-J-do.  24  3  eq.=  51-7     Mn.-f3O. 

Permang.  acid    55-4  2  eq.-fdo.  56  7  eq.=lll-4    2Mn-f?O. 

Protochloride      27-7  1  eq.-f  Chlorine  35-42  1  eq.=  63-12  Mn-fCL 

Perchloride         55-4  2  eq.-f  do.  247-94  7  eq.=  303-34  2Mn-f7Cl. 

Perfluoride          55-4  2  eq.-f  Fluorine  130-76  7  eq.=:186-16  2Mn-f  7F. 


Protosulphuret    27-7    1  eq.+Sulphur      16-1      1  eq.=  43-8 


MANGANESE,  305 

OXIDES  OF  MANGANESE. 

In  studying  metallic  oxides,  it  is  necessary  to  distinguish  oxides  formed 
by  the  direct  union  of  oxygen  and  a  metal,  from  those  that  consist  of  two 
other  oxides  united  with  each  other,  and  which,  therefore,  in  composition, 
partake  of  the  nature  of  a  salt  rather  than  of  an  oxide.  An  instance  of  this 
kind  of  combination  is  supplied  by  the  black  oxide  of  iron ;  and  it  is  proba- 
ble that  two  of  the  five  compounds  enumerated  as  oxides  of  manganese  have 
a  similar  constitution.  Their  composition  has  been  particularly  investigated 
by  Berzelius,  Thomson  (First  Principles,  i.),  Arfwedson,*  Berthier,t  and 
inyself.t 

Protoxide. — Prep. — By  this  term  is  meant  that  oxide  of  manganese  which 
is  a  strong  salifiable  base,  is  contained  in  all  the  ordinary  salts  of  this  metal, 
and  which  appears  to  be  its  lowest  degree  of  oxidation.  This  oxide  may  be 
formed  by  exposing  the  peroxide,  sesquioxide,  or  red  oxide  of  manganese  to 
the  combined  agency  of  charcoal  and  a  white  heat;  or  by  exposing  either  of 
the  oxides  of  manganese  contained  in  a  tube  of  glass,  porcelain,  or  iron,  to  a 
current  of  hydrogen  gas  at  an  elevated  temperature.  The  best  material  for 
this  purpose  is  the  red  oxide,  prepared  from  nitrate  of  oxide  of  manganese ; 
since  the  native  oxides,  especially  the  peroxide,  are  fully  reduced  to  the  state 
of  protoxide  by  hydrogen  with  difficulty*  The  reduction  commences  at  a 
low  red  heat;  but  to  decompose  all  the  red  oxide,  a  full  red  heat  is  required. 
The  same  compound  is  formed  by  the  action  of  hydrogen  gas  at  an  intense 
white  heat.  Wohler  and  Liebig  have  shown  that  the  protoxide  is  also  ob- 
tained by  fusing  chloride  of  manganese  in  a  platinum  crucible  with  about 
twice  its  weight  of  carbonate  of  soda,  and  afterwards  dissolving  the  chloride 
of  sodium  by  water. 

Prop. — Protoxide  of  manganese,  when  pure,  is  of  a  light  green  colour, 
very  near  the  mountain  green.  According  to  Forchammer  it  attracts  oxygen 
rapidly  from  the  air ;  but  in  my  experiments  it  was  very  permanent,  under- 
going  no  change  either  in  weight  or  appearance  during  the  space  of  nineteen 
days.  At  600°  it  is  oxidized  with  considerable  rapidity,  and  at  a  low  red  heat 
is  converted  in  an  instant  into  red  oxide.  It  sometimes  takes  fire  when  thus 
heated,  especially  when  the  mass  is  considerable.  It  unites  readily  with 
acids  without  effervescence,  producing  the  same  salts  as  when  the  same  acids 
act  on  carbonate  of  oxide  of  manganese.  When  it  comes  in  contact  with 
concentrated  sulphuric  acid,  intense  heat  is  instantly  evolved ;  and  the  same 
phenomenon  is  produced,  though  in  a  less  degree,  by  strong  hydrochloric 
acid.  The  resulting  salt  is  the  same  as  when  these  acids  are  heated  with 
either  of  the  other  oxides  of  manganese.  If  quite  pure,  the  protoxide  should 
readily  and  completely  dissolve  in  cold  dilute  sulphuric  acid,  and  yield  a 
colourless  solution. 

In  order  to  prepare  a  pure  salt  of  manganese  from  the  common  peroxide 
of  commerce,  either  of  the  following  processes  may  be  employed,  The  im- 
pure sesquioxide  left  in  the  process  for  procuring  oxygen  gas  from  the  per- 
oxide by  heat,  is  mixed  with  a  sixth  of  its  weight  of  charcoal  in  powder, 
and  exposed  to  a  white  heat  for  half  an  hour  in  a  covered  crucible.  The 
protoxide  thus  formed  is  to  be  dissolved  in  hydrochloric  acid,  the  solution 
evaporated  to  dryness,  and  the  residue  kept  for  a-quarter  of  an  hour  in  per- 
fect fusion  ;  being  protected  as  much  as  possible  from  the  air.  By  this  means 
the  chlorides  of  iron,  calcium,  and  other  metals  are  decomposed.  The  fused 
chloride  of  manganese  is  then  poured  out  on  a  clean  sandstone,  dissolved  in 
water,  and  the  solution  separated  from  insoluble  matters  by  filtration.  If  free 
from  iron,  it  will  give  a  white  precipitate  with  ferrocyanuret  of  potassium, 
without  any  appearance  of  green  or  blue,  and  a  flesh-coloured  precipitate 
with  hydrosulphate  of  ammonia.  The  protoxide  is  thrown  down  as  a  white 

*  Letter  from  Berzelius  in  the  An.  de  Ch.  et  de  Ph.  vi.  t  Ibid,  xx, 

t  Philos.  Trans,  of  Edin,  for  1828 ;  or  Phil.  Mag.  and  Annals,  iv. 


306  MANGANESE. 

carbonate  by  bicarbonate  of  potassa  or  soda ;  and  from  this  salt,  after  being 
well  washed,  all  the  other  salts  of  manganese  may  be  prepared.  The  other 
method  of  forming  a  pure  chloride  was  suggested  by  Faraday,  and  consists  in 
heating  to  redness  a  mixture  of  peroxide  of  manganese  with  half  its  weight 
of  hydrx>chlorate  of  ammonia.  Owing  to  the  volatility  of  the  sal  ammoniac, 
it  is  necessary  to  apply  the  required  heat  as  rapidly  as  possible ;  and  this  is 
best  done  by  projecting  the  mixture  in  small  portions  at  a  time  into  a  cruci- 
ble kept  red-hot.  In  this  process  the  chlorine  of  the  hydrochloric  acid  unites 
with  the  metal  of  the  oxide  to  the  exclusion  of  every  other  substance,  provided 
an  excess  of  manganese  be  present.  The  resulting  chloride  is  then  dissolved 
in  water,  and  the  insoluble  matters  separated  by  filtration.  (Faraday  in  Quart. 
Journal,  vi.)  One  of  the  most  common  impurities  is  iron:  Everitt  has 
shown  that  this  may  be  removed,  if  present  in  the  form  of  perchloride,  by 
boiling  the  solution  with  a  little  carbonate  of  manganese.  (Phil.  Mag.  and 
Annals,  vi.  193.) 

In  preparing  manganese  of  great  purity,  the  operator  should  bear  in  mind 
that  the  precipitated  carbonate  sometimes  contains  hydrochloric  acid.  It  may 
likewise  contain  traces  of  lime;  for  oxalate  of  lime,  insoluble  as  it  is  in  pure 
water,  does  not  completely  subside  from  a  strong  solution  of  chloride  of 
manganese,  and,  therefore,  a  small  quantity  of  that  earth  may  be  present, 
although  not  indicated  by  oxalate  of  ammonia. 

The  salts  of  manganese  are  in  general  colourless  if  quite  pure  ;  but  more 
frequently  they  have  a  shade  of  pink,  owing  to  the  presence  of  a  little  red 
oxide  or  permanganic  acid.  The  protoxide  is  precipitated  from  its  solutions 
as  a  white  hydrate  by  ammonia,  or  the  pure  fixed  alkalies;  as  white  carbo- 
nate of  protoxide  of  manganese  by  alkaline  carbonates  and  bicarbonates ; 
.and  as  white  ferrocyanuret  of  manganese  by  ferrocyanuret  of  potassium,  a 
character  by  which  the  absence  of  iron  may  be  demonstrated.  These  white 
precipitates,  with  the  exception  of  that  obtained  by  means  of  a  bicarbonate, 
very  soon  become  brown  from  the  absorption  of  oxygen,  None  of  the  salts 
of  manganese  which  contain  a  strong  acid,  such  as  the  nitric  or  sulphuric, 
are  precipitated  by  hydrosulphuric  acid.  With  an  alkaline  hydrosulphate, 
on  the  contrary,  a  flesh-coloured  precipitate  is  formed,  which  is  a  hyd rated 
protosulphuret  of  manganese:  when  heated  in  close  vessels,  it  yields  a  dark, 
coloured  sulphuret,  and  water  is  evolved. 

Its  eq,  is  35-7;  symb.  Mn-fO,  Mn,  or  MnO. 

Sesquioxide. — Hist,  and  Prep. — This  oxide  occurs  nearly  pure  in  nature, 
and  as  a  hydrate  it  is  found  abundantly,  often  in  large  prismatic  crystals,  at 
Jhlefeld  in  the  Hartz.  It  may  be  formed  artificially  by  exposing  peroxide 
of  manganese  for  a  considerable  time  to  a  moderate  red  heat,  and,  therefore, 
is  the  chief  residue  of  the  usual  process  for  procuring  a  supply  of  oxygen 
gas;  but  it  is  difficult  so  to  regulate  the  degree  and  duration  of  the  heat,  that 
the  resulting  oxide  shall  be  quite  pure. 

Prop. The  colour  of  the  sesquioxide  of  manganese  varies  with  the 

source  from  which  it  is  derived,  That  which  is  procured  by  means  of  heat 
from  the  native  peroxide  or  hydrated  sesquioxide,  has  a  brown  tint;  but 
when  prepared  from  nitrate  of  protoxide  of  manganese,  it  is  nearly  as  black  as 
the  peroxide,  and  the  native  sesquioxide  is  of  the  same  colour.  With  sul- 
phuric and  hydrochloric  acids  it  gives  rise  to  the  same  phenomenon  as  the 
peroxide,  but  of  course  yields  a  smaller  proportional  quantity  of  oxygen  and 
chlorine  gases,  It  is  more  easily  attacked  than  the  peroxide  by  cold  sul- 
phuric acid.  With  strong  nitric  acid  it  yields  a  soluble  protonitrate  and  the 
peroxide,  and  when  boiled  with  dilute  sulphuric  acid,  it  undergoes  a  similar 
change.  From  the  proportion  of  oxygen  and  manganese  in  this  oxide,  it  has 
sometimes  been  regarded  as  a  compound  of  43-7  parts  of  one  eq.  of  peroxide, 
and  35-7  parts  or  one  eq.  of  protoxide  of  manganese.  In  that  case  the  ses- 
quioxide  would  be  constituted  like  a  salt,  and  should  have  the  properties  of 
that  class  of  compounds ;  but  Mitscherlich  has  succeeded  in  combining  it 
with  sulphuric  acid,  and  has  obtained  with  it  an  alum  similar  in  form  and 


MANGANESE.  307 

constitution  to  those  of  sesquioxide  of  iron  and  alumina.  It  must  therefore  be 
considered  as  a  direct  compound  of  two  eq.  of  manganese  and  three  eq.  of 
oxygen, 

Its  eq.  is  79-4 ;  symb.  2Mn-f  3O,  Mn,  or  Mn2  (X 

Peroxide. — Hist,  and  Prep. — The  well-known  ore  commonly  called,  from 
its  colour,  black  oxide  of  manganese.  It  generally  occurs  massive,  of  an 
earthy  appearance,  and  mixed  with  other  substances,  such  as  siliceous  and 
aluminous  earths,  oxide  of  iron,  and  carbonate  of  lime.  It  is  sometimes 
foun.d,  on  the  contrary,  in  the  form  of  minute  prisms  grouped  together,  and 
radiating  from  a  common  centre.  In  these  states  it  is  anhydrous ;  but  the 
essential  ingredient  of  one  variety  of  the  earthy  mineral  called  wad  is 
hydrated  peroxide  of  manganese,  consisting  of  one  eq.  of  water  and  two  of 
the  oxide.  The  peroxide  may  be  made  artificially  by  exposing  nitrate  of 
protoxide  of  manganese  to  a  commencing  red  heat,  until  the  whole  of  the 
nitric  acid  is  expelled  ;  but  I  have  never  succeeded  in  procuring  it  quite  pure 
by  this  process,  because  the  heat  required  to  drive  off  the  last  traces  of  acid 
likewise  expels  some  oxygen  from  the  peroxide.  The  hydrated  peroxide,  con- 
taining one  eq.  of  water  and  one  of  oxide,  is  formed  by  precipitating  the 
protochloride  of  manganese  by  chloride  of  lime ;  and  the  same  compound 
results  from  the  decomposition  of  the  acids  of  manganese,  either  in  water  or 
by  dilute  acid. 

Prop. — Not  changed  by  exposure  to  the  air,  is  insoluble  in  water,  and 
does  not  unite  either  with  acids  or  alkalies.  When  boiled  with  sulphuric 
acid,  it  yields  oxygen  gas,  and  a  sulphate  of  the  protoxide  is  formed  (page 
153).  With  hydrochloric  acid,  chloride  of  manganese  is  generated,  and 
chlorine  is  evolved  (page  i211).  The  solution  in  both  cases  is  of  a  deep-red 
colour,  provided  undissolved  oxide  is  present;  but  if  separated  from  the  un- 
dissolved  portions,  it  is  readily  rendered  colourless  by  heat.  The  colour  is 
commonly  attributed  to  a  small  quantity  of  the  sesquioxide  or  red  oxide  of 
manganese,  dissolved  by  the  free  acid  ;  but  Mr.  Pearsall  of  Hull  has  gone  far 
to  prove  that  it  is  owing  to  the  presence  of  permanganic  acid.  (R.  Inst. 
Journal,  N.  S.  No.  iv.  49.)  The  action  of  sulphuric  acid  in  the  cold  is  ex- 
ceedingly tardy  and  feeble,  a  minute  quantity  of  oxygen  gas  is  slowly  disen- 
gaged, and  the  acid  acquires  an  amethyst-red  tint.  On  exposure  to  a  red 
heat,  it  is  converted,  with  evolution  of  oxygen  gas,  into  the  sesquioxide  of 
manganese.  (Page  153  ) 

Peroxide  of  manganese  is  employed  in  the  arts,  in  the  manufacture  of 
glass,  and  in  preparing  chlorine  for  bleaching.  In  the  laboratory  it  is  used 
for  procuring  chlorine  and  oxygen  gases,  and  in  the  preparation  of  the  salts 
of  manganese. 

Red  Oxide. — The  substance  called  red  oxide  of  manganese,  oxidum  man- 
ganoso-manganicum  of  Arfwedson,  occurs  as  a  natural  production,  and  may 
be  formed  artificially  by  exposing  the  peroxide  or  sesquioxide  to  a  white  heat 
either  in  close  or  open  vessels.  It  is  also  produced  by  absorption  of  oxygen 
from  the  atmosphere,  when  the  protoxide  is  precipitated  from  its  salts  by  pure 
alkalies,  or  when  the  anhydrous  protoxide  or  carbonate  is  heated  to  redness. 
It  is  very  permanent  in  the  air,  not  passing  to  a  higher  stage  of  oxidation  at 
any  temperature.  Its  colour  when  rubbed  to  the  same  degree  of  fineness  is 
brownish-red  when  cold,  and  nearly  black  while  warm.  Fused  with  borax 
or  glass  it  communicates  a  beautiful  violet  tint,  a  character  by  which  man- 
ganese may  be  easily  detected  before  the  blowpipe;  and  it  is  the  cause  of  the 
rich  colour  of  the  amethyst.  It  is  acted  on  by  strong  sulphuric  and  hydro- 
chloric acids,  with  the  aid  of  heat,  in  the  same  manner  as  the  peroxide  and 
sesquioxide,  but  of  course  yields  proportionally  a  smaller  quantity  of  oxygen 
and  chlorine  gases.  By  cold  concentrated  sulphuric  acid  it  is  dissolved  in 
small  quantity,  without  appreciable  disengagement  of  oxygen  gas,  and  the 
solution  is  promoted  by  a  slight  increase  of  temperature.  The  liquid  has  an 
amethyst  tint,  which  disappears  when  heat  is  applied,  or  by  the  action  of 
deoxidizing  substances,  such  as  protochloride  of  tin,  or  sulphurous  and  phos- 


308  MANGANESE. 

phorous  acids,  sulphate  of  protoxide  of  manganese  being  generated.  By 
strong  nitric  acid,  or  when  boiled  with  dilute  sulphuric  acid,  it  undergoes  the 
same  kind  of  change  as  the  sesquioxide. 

It  may  be  doubted  whether  the  red  oxide  is  not  rather  a  kind  of  salt  com- 
posed  of  two  other  oxides,  than  a  direct  compound  of  manganese  and  oxy- 
gen. From  the  ratio  of  its  elements  it  may  consist  either  of 

Sesquioxide      79-4  or  one  equiv.  >       \  Peroxide          43-7  or  one  equiv. 
Protoxide         35-7  or  one  equiv.  $       f  Protoxide        71-4  or  two  equiv. 

115-1  11^1 

It  contains  27-586  per  cent,  of  oxygen,  and  loses  6-896  per  cent,  when  con- 
verted  into  the  green  or  protoxide.  Its  eq.  is  115*1  :  its  symb.  either 
MnO-f  MnsO,  or  2MnO+ MnO>. 

Varvicite. — This  compound  is  known  only  as  a  natural  production,  having 
been  first  noticed  a  few  years  ago  by  Mr.  Phillips  among  some  ores  of  man- 
ganese found  at  Hartshill,  in  Warwickshire.  The  locality  of  the  mineral 
suggested  its  name ;  but  1  have  also  detected  it  as  the  constituent  of  an  ore 
of  manganese  from  Jhlefeld,  sent  me  by  Professor  Stromeyer.  Varvicite 
was  at  first  mistaken  for  peroxide  of  manganese,  to  which  in  the  colour  of 
its  powder  it  bears  considerable  resemblance;  but  it  is  readily  distinguished 
from  that  ore  by  its  stronger  lustre,  greater  hardness,  more  lamellated  tex- 
ture, which  is  very  similar  to  that  of  manganite,  and  by  yielding  water 
freely  when  heated  to  redness.  Its  sp.  gr.  is  4-531.  It  has  not  been  found 
regularly  crystallized;  but  my  specimen  from  Jhlefeld  is  in  pseudo-crystals, 
possessing  the  form  of  the  six-sided  pyramid  of  calcareous  spar.  When 
strongly  heated  it  is  converted  into  red  oxide,  losing  5-725  per  cent  of  water, 
and  7-385  of  oxygen.  It  is  probably,  like  the  red  oxide,  a  compound  of  two 
other  oxides;  and  the  proportions  just  stated  justify  the  supposition  that  it 
consists  of  two  eq.  of  peroxide  and  one  of  sesquioxide  of  manganese,  united 
in  the  mineral  with  one  eq.  of  water.  (Phil.  Mag.  and  Annals,  v.  209,  vi. 
281,  and  vii.  284.) 

It  has  been  inferred  from  some  experiments  of  Berzelius  and  John,  that 
there  are  two  other  oxides  of  manganese,  which  contain  less  oxygen  than 
the  green  or  protoxide.  We  have  no  proof,  however,  of  the  existence  of  such 
compounds. 

Its  eq.  is  166-8;  symb.  probably  Mn?O34-2MnO3. 

Manganic  Acid. — Hist,  and  Prep. — Manganese  is  one  of  those  metals 
which  is  capable  of  forming  an  acid  with  oxygen.  Manganate  of  potassa  is 
generated  when  hydrate  or  carbonate  of  potassa  is  heated  to  redness  with 
peroxide  of  manganese ;  and  nitre  may  be  used  successfully,  provided  the 
heat  be  high  enough  to  decompose  the  nitrate  of  potassa.  The  materials 
absorb  oxygen  from  the  air  when  fused  in  open  vessels ;  but  manganate  of 
potassa  is  equally  well  formed  in  close  vessels,  one  portion  of  oxide  of  man- 
ganese then  supplying  oxygen  to  another.  The  product  has  been  long  known 
under  the  name  of  mineral  chameleon,  from  the  property  of  its  solution  to 
pass  rapidly  through  several  shades  of  colour:  on  the  first  addition  of  cold 
water  a  green  solution  is  formed,  which  soon  becomes  blue,  purple,  and  red; 
and  ultimately  a  brown  flocculcnt  matter,  hydrated  peroxide  of  manganese, 
subsides,  and  the  liquid  becomes  colourless.  These  changes,  which  are  more 
rapid  by  dilution  with  hot  water,  have  been  successively  elucidated  by  Che, 
villot  and  Edwards,  Forchammer,  and  Mitscherlich.  (An.  de  Ch.  et  de  Ph. 
viii.,  and  xlix.  113  ;  and  Ann.  of  Phil,  xvi.) 

Prop. — The  phenomena  above  mentioned  are  owing  to  the  formation  of 
manganate  of  potassa  of  a  green  colour,  and  to  its  ready  conversion  into  the 
red  permanganate  of  potassa.  the  blue  and  purple  tints  being  due  to  a  mix- 
ture of  these  compounds.  Manganic  acid  itself  cannot  be  obtained  in  an 
uncombined  state,  because  it  is  then  resolved  into  the  hydrated  peroxide  and 
oxygen,  a  property  which  Mitscherlich  availed  himself  of  in  analysing  this 


~.      ,  MANGANESE.  303 

acid  ;  but  Mitscherlich  has  proved  that  it  is  analogous  in  composition  to  sul- 
phuric acid,  and  its  salts  are  isomorphous  with  the  sulphates.  Manganate  of 
potassa  is  obtained  in  crystals  by  for  mi  ng  a  concentrated  solution  of  mineral 
chameleon  in  cold  water,  very  pure  and  free  from  carbonic  acid,  allowing  it 
to  subside  in  a  stoppered  bottle,  and  evaporating  the  clear  green  solution  in 
vacno  with  the  aid  of  sulphuric  acid.  All  contact  of  paper  and  other  organic 
matter  must  be  carefully  avoided,  since  they  deoxidize  the  acid,  and  the  pro- 
cess be  conducted  in  a  cool  apartment.  The  crystals  are  anhydrous,  and 
permanent  in  the  dry  state ;  but  in  solution  the  carbonic  acid  of  the  air  suf- 
fices to  decompose  the  acid,  or  even  simple  dilution  with  cold  water.  Mixed 
with  a  solution  of  potassa,  the  manganate  may  be  crystallized  a  second  time 
in  vacuo  without  change. 

Its  eq.  is  51-7;  symb.  Mn-f-3O,  Mn,  or  MnQs. 

Permanganic  Acid. — Prep. — Permanganate  of  potassa  is  obtained  by 
heating  a  solution  of  mineral  chameleon,  however  prepared.  A  better  pro- 
cess has  been  indicated  by  Wtthler  (Pog.  Ann.  xxvii.  626) :  it  consists  in 
fusing  chlorate  of  potassa  in  a  platinum  crucible,  and  then  adding  peroxide 
of  manganese  in  fine  powder.  An  improvement  on  this  has  been  proposed 
by  Gregory  (Lieb.  Ann.  xv.  237) :  he  recommends  4  parts  of  peroxide  of 
manganese  to  be  mixed  in  fine  powder  with  3£  parts  of  chlorate  of  potassa, 
and  then  added  to  5  parts  of  hydrate  of  potassa  dissolved  in  a  small  quantity 
of  water.  The  whole  is  evaporated  to  perfect  dryness,  powdered,  and  exposed 
in  a  platinum  crucible  to  a  low  red  heat.  The  mass,  which  has  not  been  fused, 
is  again  powdered,  and  added  to  a  large  quantity  of  boiling  water,  which 
when  clear  is  decanted  from  the  sediment  of  peroxide  of  manganese,  rapidly 
concentrated,  and  allowed  to  crystallize.  The  crystals  are  at  first  small  and 
almost  black;  but  by  washing-  with  a  little  cold  water,  and  re-solution  in  the 
smallest  possible  quantity  of  boiling  water,  they  are  obtained  in  very  fine 
crystals.  The  acid  may  be  obtained  by  adding  to  a  solution  of  perman- 
ganate of  baryta,  a  quantity  of  dilute  sulphuric  acid  exactly  sufficient  for  pre- 
cipitating the  baryta. 

Prop. — Has  a  rich  red  colour ;  is  more  stable  than  the  manganic  acid, 
though  still  very  prone  to  decomposition.  Contact  with  paper  or  linen  as  in 
filtering,  particles  of  cork,  organic  particles  floating  in  the  atmosphere,  de- 
compose it  rapidly;  colouring  matters  are  bleached  by  it;  and  in  pure  wa- 
ter its  decomposition  begins  at  86°,  and  is  complete  at  212°.  On  these  oc- 
casions oxygen  gas  is  abstracted  or  given  out,  and  hydrated  peroxide  of 
manganese  subsides.  Its  salts  are  more  permanent  than  the  free  acid,  so 
that  most  of  them  may  be  boiled  in  solution,  especially  if  concentrated. 
When  heated  they  give  out  oxygen  gas,  and  are  reconverted  into  manga- 
nates.  They  deflagrate  like  nitre  with  burning-  charcoal,  and  detonate  pow- 
erfully with  phosphorus.  Their  colour  in  solution  is  a  rich  purple,  and  a 
small  quantity  of  the  salt  imparts  this  colour  to  a  very  large  quantity  of  wa- 
ter. When  mixed  with  dilute  nitric  acid  and  boiled,  oxygen  gas  is  evolved, 
and  hydrated  peroxide  of  manganese  subsides,  from  the  respective  quantities 
of  which  Mitscherlich  ascertained  the  composition  of  the  acid.  In  addition 
to  the  remarkable  analogy  which  its  constitution  bears  to  perchloric  acid, 
Mitscherlich  finds  that  permanganate  and  perchlorate  of  potassa  are  isomor- 
phous, an  observation  confirmed  by  Miller. 

Its  eq.  is  1114;  symb.  2Mn4  7O,  Mn,  or  Mn*Or. 

Protochloride  of  Manganese. — This  compound  is  best  prepared  by  evapo- 
rating a  solution  of  the  chloride  to  dryness  by  a  gentle  heat,  and  heating  the 
residue  to  redness  in  a  glass  tube,  while  a  current  of  hydrochloric  acid  gas 
is  transmitted  through  it.  The  heat  of  a  spirit-lamp  is  sufficient  for  the  pur- 
pose. It  fuses  readily  at  a  red  heat,  and  forms  a  pink-coloured  lamellated 
mass  on  cooling.  It  is  deliquescent,  and  of  course  very  soluble  in  water. 

Its  eq.  is  63-12 ;  symb.  Mn  -j-Cl,  or  MnCl. 


310  MANGANESE. 

PercUoride  of  Manganese. — Hist,  and  Prep. — Dumas  discovered  this 
compound,  which  is  readily  formed  by  putting  a  solution  of  permanganic 
into  strong-  sulphuric  acid,  and  then  adding-  fused  sea-salt.  The  hydrochloric 
and  permanganic  acids  mutually  decompose  each  other;  water  and  percblo- 
ride  of  manganese  are  generated,  and  the  latter  escapes  in  the  form  of  va- 
pour. The  best  mode  of  preparation  is  to  form  the  green  mineral  chameleon, 
and  acidulate  with  sulphuric  acid  :  the  solution,  when  evaporated,  leaves  a 
residue  of  sulphate  and  permanganate  of  potassa.  The  mixture,  treated  by 
strong  sulphuric  acid,  yields  a  solution  of  permanganic  acid,  to  which  are 
added  small  fragments  of  sea-salt,  as  long  as  coloured  vapour  continues  to  be 
evolved.  (Edin.  Journ.  of  Science,  viii.  179.) 

Prop. — The  perchloride,  when  first  formed,  appears  as  a  vapour  of  a  cop- 
per or  greenish  colour ;  but  on  traversing  a  glass  tube  cooled  to  — 4°,  it  is 
condensed  into  a  greenish-brown  coloured  liquid.  When  generated  in  a  ca- 
pacious tube,  its  vapour  gradually  displaces  the  air,  and  soon  fills  the  tube. 
If  it  is  then  poured  into  a  large  flask,  the  sides  of  which  are  moist,  the  colour 
of  the  vapour  changes  instantly  on  coming  into  contact  with  the  moisture,  a 
dense  smoke  of  a  pretty  rose-tint  appears,  and  hydrochloric  and  permanganic 
acids  are  generated.  It  is  hence  analogous  in  composition  to  permanganic 
acid,  its  elements  being  in  such  a  ratio  that 

1  eq.  perchloride   and  7  eq.  water 
2Mn-f7Cl  7(H-fO) 

yield 

1  eq.  permanganic  acid  and  7  eq.  hydrochloric  acid. 
2Mn-f7O  7(H-fCJ). 

Hence  its  eq.  is  303-34;  symb.  2Mn+7Cl,  or  MnsCI7. 

Perjluoride  of  Manganese. — This  gaseous  compound,  discovered  by  Du- 
mas and  Wohler  (Edin.  Journ.  of  Science,  ix.),  is  best  formed  by  mixing 
common  mineral  chameleon  with  half  its  weight  of  fluor  spar,  and  decom- 
posing the  mixture  in  a  platinum  vessel  by  fuming  sulphuric  acid.  The 
fluoride  is  then  disengaged  in  the  form  of  a  greenish-yellow  gas  or  vapour, 
of  a  more  intensely  yellow  tint  than  chlorine.  When  mixed  with  atmospheric 
air,  it  instantly  acquires  a  beautiful  purple-red  colour ;  and  it  is  freely  ab- 
sorbed by  water,  yielding  a  solution  of  the  same  red  tint.  It  acts  instantly  on 
glass,  with  formation  of  fluosilicic  acid  gas,  a  brown  matter  being  at  the  same 
time  deposited,  which  becomes  of  a  deep  purple-red  tint  on  the  addition  of 
water. 

It  may  be  inferred  from  the  experiments  of  Wohler  that  this  yellow  gas  is 
a  fluoride  of  manganese;  that  when  mixed  with  water  both  compounds  are 
decomposed,  and  hydrofluoric  and  permanganic  acids  generated,  which  are 
dissolved;  that  a  similar  formation  of  the  two  acids  ensues  from  the  admix- 
ture of  the  yellow  gas  with  atmospheric  air,  owing  to  the  moisture  contained 
in  the  latter ;  and  that  by  contact  with  glass,  fluosilicic  acid  gas  is  produced, 
and  anhydrous  permanganic  acid  deposited.  In  consequence  of  its  acting  so 
powerfully  on  glass,  its  other  properties  have  not  been  ascertained ;  but  from 
those  above  mentioned,  its  composition  is  obviously  similar  to  that  of  the 
gaseous  chloride  of  manganese. 

Its  eq.  is  186-16;  symb.  2Mn-f  7F,  or  Mn^Fr. 

Prolosulphuret  of  Manganese  may  be  procured  by  igniting  the  sul- 
phate with  one-sixth  of  its  weight  of  charcoal  in  powder.  (Berthier.)  It  ia 
also  formed  by  the  action  of  hydrosulphuric  acid  gas  on  the  protosulphate  at 
a  red  heat.  (Arfwedson  in  Ann.  of  Phil.  vol.  vii.  N.  S.)  It  occurs  native 
in  Cornwall,  and  at  Nagyag  in  Transylvania.  It  dissolves  completely  in 
dilute  sulphuric  or  hydrochloric  acid,  with  disengagement  of  very  pure  hy. 
drosulphuric  acid  gas.  Its  eq.  is  43-8 ;  symb.  Mn-}-S,  or  MnS. 


311 


SECTION  XL 

IRON. 

Hist. — KNOWN  from  the  remotest  antiquity.  The  occurrence  of  native 
iron,  except'that  of  meteoric  origin,  which  always  contains  nickel  and  cobalt, 
is  exceedingly  rare ;  and  few  of  the  specimens  said  to  be  such  have  been  well 
attested.  In  combination,  however,  especially  with  oxygen  and  sulphur,  it 
is  abundant ;  being  contained  in  animals  and  plants,  and  being  diffused  so 
universally  in  the  earth,  that  there  are  few  mineral  substances  in  which  its 
presence  may  not  be  detected.  Minerals  which  contain  iron  in  such  form, 
and  in  such  quantity,  as  to  be  employed  in  the  preparation  of  the  metal,  are 
called  ores  of  iron;  and  of  these  the  principal  are  the  following.  The  red 
oxides  of  iron  included  under  the  name  of  red  haematite ;  the  brown  hse- 
matite  of  mineralogists,  consisting  of  hydrated  sesquioxide  of  iron  ;  the  black 
oxide,  or  magnetic  iron  ore  ;  and  carbonate  of  protoxide  of  iron,  either  pure, 
or  in  the  form  of  clay  iron  ore,  when  it  is  mixed  with  siliceous,  aluminous, 
and  other  foreign  substances.  The  three  former  occur  most  abundantly  in 
primary  districts,  and  supply  the  finest  kinds  of  iron,  as  those  of  Sweden 
and  India;  while  clay-iron  stone,  from  which  most  of  the  English  iron  is 
extracted,  occurs  in  secondary  deposites,  and  chiefly  in  the  coal  formation. 

Prep. — The  extraction  of  iron  from  its  ores  is  effected  by  exposing  the 
ore,  previously  roasted  and  reduced  to  a  coarse  powder,  to  the  action  of  char- 
coal or  coke,  and  lime  at  a  high  temperature.  The  action  of  carbonaceous 
matter  in  depriving  the  ore  of  its  oxygen  is  obvious ;  and  the  lime  plays  a 
part  equally  important.  It  acts  as  a  flux  by  combining  with  all  the  impuri- 
ties of  the  ore,  and  forming  a  fusible  compound  called  a  slag.  The  whole 
mass  being  thus  in  a  fused  state,  the  particles  of  reduced  metal  descend  by 
reason  of  their  greater  density,  and  collect  at  the  bottom  ;  while  the  slag 
forms  a  stratum  above,  protecting  the  melted  metal  from  the  action  of  the 
air.  The  latter,  as  it  collects,  runs  out  at  an  aperture  in  the  side  of  the  fur- 
nace ;  and  the  fused  iron  is  let  off  by  a  hole  in  the  bottom,  which  was  previ- 
ously filled  with  sand.  The  process  is  never  successful  unless  the  flux,  to- 
gether with  the  impurities  of  the  ore,  is  in  such  proportion  as  to  constitute  a 
fusible  compound.  The  mode  of  accomplishing  this  object  is  learned  only 
by  experience ;  and  as  different  ores  commonly  differ  in  the  nature  or  quan- 
tity of  their  impurities,  the  workman  is  obliged  to  vary  his  flux  according 
to  the  composition  of  the  ore  with  which  he  operates.  Thus  if  the  ore  is 
deficient  in  siliceous  matter,  sand  must  be  added;  and  if  it  contain  a  large 
quantity  of  lime,  proportionally  less  of  that  earth  will  be  required.  Much 
is  often  accomplished  by  the  admixture  of  different  ores  with  each  other. 
The  slag  consists  of  a  compound  of  earthy  salts,  similar  to  some  siliceous 
minerals,  in  which  silicic  acid  is  combined  with  lime,  alumina,  magnesia, 
protoxide  of  manganese,  and  sometimes  oxide  of  iron.  The  most  usual  corrf- 
bination,  according  to  Mitscherlich,  is  bisilicate  of  lime  and  magnesia,  some- 
times with  a  little  protoxide  of  iron ;  a  compound  which  he  has  obtained  in 
crystals,  having  the  precise  form  and  composition  of  augite.  Artificial  mi- 
nerals may  in  fact  by  such  processes  be  procured,  similar  in  form  and  com- 
position to  those  which  occur  in  the  earth.  We  are  indebted  to  Mitscher- 
lich for  some  valuable  facts  on  this  subject.  (An.  de  Ch.  et  de  Ph.  xxiv. 
355.) 

The  iron  obtained  by  this  process  is  the  cast  iron  of  commerce,  and  con- 
tains a  considerable  quantity  of  carbon,  unreduced  ore,  and  earthy  sub- 
stances. It  is  converted  into  soft  or  malleable  iron  by  exposure  to  a  strong 
heat  while  a  current  of  air  plays  upon  its  surface.  By  this  means  any  un- 
decomposed  ore  is  reduced,  earthy  impurities  rise  to  the  surface  as  slag,  and 


312  IRON. 

carbonaceous  matter  is  burned.  The  exposed  iron  is  also  more  or  less  oxid- 
ized at  its  surface,  and  the  resulting  oxide,  being  stirred  with  the  fused  metal 
below,  facilitates  the  oxidation  of  the  carbon.  As  the  purity  of  the  iron  in- 
creases, its  fusibility  diminishes,  until  at  length,  though  the  temperature 
continue  the  same,  the  iron  becomes  solid.  It  is  then  subjected,  while  still 
hot,  to  the  operation  of  rolling  or  hammering,  by  which  its  particles  are 
approximated,  arid  its  tenacity  greatly  increased.  It  is  then  the  malleable 
iron  of  commerce.  It  is  not,  however,  absolutely  pure;  for  Berzelius  has 
detected  in  it  about  half  of  one  per  cent,  of  carbon,  and  it  likewise  con- 
tains traces  of  silicon.  The  carbonaceous  matter  may  be  removed  by  mix- 
ing iron  filings  with  a  quarter  of  its  weight  of  black  oxide  of  iron,  and 
fusing  the  mixture,  confined  in  a  covered  Hessian  crucible,  by  means  of  a 
blast  furnace.  A  little  powdered  green  glass  should  be  laid  on  the  mixture, 
in  order  that  the  iron  maybe  completely  protected  from  the  air  by  a  covering 
of  melted  glass,  and  any  unreduced  oxide  dissolved.  But  the  best  and 
readiest  mode  of  procuring  iron  in  a  state  of  perfect  purity,  is  by  transmit- 
ting hydrogen  gas  over  the  pure  oxide  heated  to  redness  in  a  tube  of  porce- 
lain. The  oxygen  of  the  oxide  unites  with  hydrogen,  and  the  metal  is  left 
in  the  form  of  a  porous  spongy  mass. 

Prop. — Iron  has  a  peculiar  gray  colour,  and  strong  metallic  lustre,  which 
is  susceptible  of  being  heightened  by  polishing.  In  ductility  and  malleability 
it  is  inferior  to  several  metals,  but  exceeds  them  all  in  tenacity  (page  265). 
At  common  temperatures  it  is  very  hard  and  unyielding,  and  its  hardness 
may  be  increased  by  being  heated  and  then  suddenly  cooled ;  but  it  is  at  tire 
same  time  rendered  brittle.  When  heated  to  redness  it  is  remarkably  soft 
and  pliable,  so  that  it  may  be  beaten  into  any  form,  or  be  intimately  incor- 
porated or  welded  with  another  piece  of  red-hot  iron  by  hammering.  Its 
texture  is  fibrous.  Its  sp.  gr.  according  to  Brisson,  is  7'788 ;  but  it  varies 
slightly  according  to  the  degree  with  which  it  has  been  rolled,  hammered, 
or  drawn,  and  it  is  increased  by  fusion.  In  its  pure  state  it  is  exceedingly 
infusible,  requiring  for  fusion  the  highest  temperature  of  a  wind  furnace.  It 
is  attracted  by  the  magnet,  and  may  itself  be  rendered  permanently  mag- 
netic by  several  processes; — a  property  of  great  interest  and  importance, 
and  which  is  possessed  by  no  other  metal  excepting  nickel.  It  retains  this 
quality,  however,  only  within  certain  temperatures :  thus  iron  at  an  orange- 
red  heat  ceases  to  be  attracted,  and  a  steel  magnet  loses  its  polarity  at  the 
boiling  point  of  almond  oil — a  loadstone  just  below  visible  ignition.  (Faraday.) 
Iron,  in  its  ordinary  state,  has  a  strong  affinity  for  oxygen.  In  a  perfectly 
dry  atmosphere  it  undergoes  no  change ;  but  when  moisture  is  present,  its 
oxidation,  or  rusting,  is  rapid.  In  the  first  part  of  the  change  carbonate  of 
protoxide  of  iron  is  generated ;  but  the  protoxide  gradually  passes  into  hy- 
drated  sesquioxide,  and  the  carbonic  acid  at  the  same  time  is  evolved.  Rust  of 
iron  always  contains  ammonia,  a  circumstance  which  indicates  that  the  oxi- 
dation is  probably  accompanied  by  decomposition  of  water;  and  Chevallier 
has  observed  that  ammonia  is  also  present  in  the  native  oxides  of  iron. 
Heated  to  redness  in  the  open  air,  iron  absorbs  oxygen  rapidly,  and  is  con- 
verted into  black  scales,  called  the  black  oxide  of  iron  ;  and  in  an  atmosphere 
of  oxygen  gas  it  burns  with  vivid  scintillations.  The  same  effect  was  ob- 
served by  Bierley  on  exposing  a  bar  of  iron  at  a  full  white  heat  to  the  blast 
of  a  powerful  pair  of  bellows.  This  has  been  confirmed  by  D'Arcet,  who 
also  obtained  the  combustion  by  causing  the  heated  iron  to  revolve  rapidly 
through  the  air:  for  this  purpose  he  attached  one  extremity  of  the  bar  by 
means  of  wire  to  a  string,  and  then  whirled  it  rapidly  round.  Magnus  has 
observed  that  the  spongy  mass,  obtained  by  reducing  the  oxide  of  iron  with 
hydrogen,  may  be  obtained  at  a  heat  considerably  below  that  of  redness  ; 
and  that  when  the  iron,  thus  reduced,  is  exposed  to  the  air,  it  takes  fire  spon- 
taneously, and  the  oxide  is  instantly  reproduced.  This  singular  property, 
which  Magnus  has  also  remarked  in  nickel  and  cobalt  prepared  in  a  similar 
manner,  appears  to  depend  on  the  extremely  divided  and  expanded  state  of 
the  metallic  mass;  for  when  the  reduction  is  effected  at  a  red  heat,  which 


313 


enables  the  metal  to  acquire  its  natural  degree  of  compactness,  the  phenome- 
non is  not  observed.  If  the  oxide  be  mixed  with  a  little  alumina,  and  then 
reduced  at  a  red  heat,  the  presence  of  the  earth  prevents  that  contraction 
which  Would  otherwise  ensue :  the  metal  is  in  the  same  mechanical  condi- 
tion as  when  it  is  deoxidized  at  a  low  temperature,  and  its  spontaneous  com- 
bustibility is  preserved. 

Iron  decomposes  the  vapour  of  water,  by  uniting  with  its  oxygen  at  all 
temperatures  from  a  dull  red  to  a  white  heat;  a  singular  fact  when  it  is  con- 
sidered, that,  at  the  very  same  temperatures,  the  oxides  of  iron  are  reduced  to 
the  metallic  state  by  hydrogen  gas.  (Gay-Lussac  in  An.  de  Ch.  et  de  Phy- 
sique, i.  36.)  These  opposite  effects,  various  instances  of  which  are  known 
to  chemists,  are  accounted  for  by  a  mode  of  reasoning  similar  to  that  ex- 
plained on  a  former  occasion  (page  131).  It  is  rapidly  oxidized  by  sulphuric 
and  nitric  acids  :  in  the  former  case  the  oxidation  occurs  at  the  sole  expense 
of  water,  the  hydrogen  of  which  is  at  the  same  time  evolved  (page  158), 
while  in  the  latter  the  nitric  acid  itself  yields  a  part  of  its  oxygen.  The 
action  of  nitric  acid  on  iron  is  attended  by  a  series  of  very  remarkable  phe- 
nomena, which  have  recently  been  observed  by  Professor  Schonbein.  He 
first  observed  that  nitric  acid,  of  sp.  gr.  1-35,  though  capable  of  acting  with 
great  violence  on  ordinary  iron,  was  perfectly  inert  on  a  portion  of  iron  wire, 
one  extremity  of  which  had  been  made  red-hot  previous  to  its  introduction 
into  the  acid.  He  found,  too,  that  this  indifference  to  nitric  acid  may  be 
communicated,  by  mere  contact,  from  one  iron  wire  to  another,  by  submer- 
sion for  a  few  moments  into  strong  nitric  acid,  or  by  making  it  the  positive 
electrode  of  a  galvanic  current,  the  negative  electrode  having  been  previously 
introduced  into  the  acid.  It  is  remarkable  that,  under  these  circumstances, 
the  iron  wire  possesses  the  properties  of  one  of  gold  or  platinum,  and  does 
not  combine  with  the  oxygen  liberated  at  its  surface.  Faraday,  who  has 
examined  this  voltaic  condition  of  iron  with  his  usual  success,  has  remarked 
that  the  same  property  is  communicated  to  iron  by  contact  with  platinum, 
and  that  the  effect  is  not  limited  to  nitric  acid,  but  extends  to  various  saline 
solutions  which  are  usually  acted  on  by  iron.  For  the  particulars  on  this 
interesting  subject  the  reader  may  consult  the  original  papers  of  SchOnbein 
and  Faraday  in  the  Phil.  Mag.  and  Annals,  ix.  53;  x.  133,  172,  175,  267, 
428. 

The  equivalent  of  iron  has  not  yet  been  determined  with  accuracy.  From 
the  analysis  of  its  oxides  by  Berzelius,  Stromeyer,  and  Gay-Lussac,  it  may 
be  estimated  at  27-16,  27-8,  and  28-3.  In  the  uncertainty  as  to  which  of 
these  numbers  is  the  most  accurate,  I  shall  continue  to  use  28,  the  number 
generally  adopted  in  this  country.  Its  symb.  is  Fe.  The  composition  of  the 
compounds  of  iron  described  in  this  section  is  as  follows  : — 

Iron, 

Protox-7    oo     ,         .  ~ 
ide       5    28     ieq-r-Oxyg. 

£    56    2eq.-fdo. 

oxide  \    Sesquioxide  . 

Proto-  i 

chlo.  V    28     leq.-f-Chlor.    35-42  1  eq.    =63-42    Fe-fCl  or  Fed 

ride  ) 

Sesqui-  ) 

chlo-  >   56    2eq.-f.do.        106-26  3  eq.    =162-26    2Fe4-3Cl  or 

ride  ) 


Equiv. 

Formulas. 

8 

leq. 

=  36 

Fe-f-Oor  FeO. 

24 

3  eq. 

=  80 

2Fe-f-3OorFe'O3 

36 
80 

leq. 
leq. 

5=116 

FeO-f  FesOs 

ide°"  \   28    leq-+Iodine   126-3     1  eq.     =154-3      Fe  +  I  or  Fel 

56    2eq-Ho          378-9    3  eq.     =434-9      2Fe+31  or  Fe»Ii 
27 


314 


Iron. 

Equiv. 

Formulas, 

Proto- 

bro- 
mide 

28 

1  eq.-f-Brom. 

78-4 

leq. 

=  106-4 

Fe  +  Br  or  FeBr 

Sesqui- 

bro- 

56 

2  eq.-fdo          235-2 

3eq. 

=291-2 

2Fe+3BrorFe 

aBr 

mide 

Proto- 

fluo- 

28 

1  eq.+Fluor. 

18-68 

1  eq. 

—  46-68 

Fe-f-F  or  FeF 

ride 

Sesqui- 

fluo- 

56 

2eq.-f  Fluor. 

56-04  3  eq. 

=112-04 

2Fe+3F  or  Fe 

sFs 

ride 

Tetra-    ) 

sul-      VI  12 

4  eq.+Sulph. 

16-1 

leq. 

=128-1 

4Fe  +  SorFe4S 

phuret  \ 

Disul-    7    i-R 
phuret  I   56 

2  eq.-fdo. 

16-1 

leq. 

=  72-1 

2Fe-f  Sor  Fes 

S 

Proto-    ) 

sulph->   28 

1  eq.-f.do. 

16-1 

leq. 

=  44-1 

Fe  +  Sor  FeS 

uret     ) 

>Sesqui-  ) 

sulph-  >   56 

2  eq.+do. 

48-3 

3eq. 

=104-3 

2Fe+3S  or  Fe^Ss 

uret     ) 

Bisul-    I    2g 
phuret  5 

1  eq.-}-do. 

32-2 

2eq. 

=  60-2 

Fe  +  2Sor  Fe 

3* 

TVT        *       ^  ^ 

isulph.  of  iron 

60-2 

leq. 

1 

3    i  ** 

rotosulph.  of 

^=280-7 

5FeS+FeSa 

pyrites      ^ 

iron 

220-5 

5  eq. 

} 

Diphos-  )    cc 
phuret  C   56 

2eq.+Phosph. 

15-7 

leq. 

=  71-7 

2Fe-fP  or  FesP 

Per-        ) 

phos-    >   84 

3  eq.+do. 

62-8 

4eq. 

=146-8 

3Fe-f4Por  F 

esP 

phuret  ) 

Carburets.    Constitution  not  determined. 

OXIDES  OF  IRON. 

Protoxide. — This  oxide  is  the  base  of  the  native  carbonate  of  iron,  and  of 
the  green  vitriol  of  commerce.  Its  existence  was  inferred  some  years  ago 
by  Gay-Lussac  (An.  de  Ch.  vol.  Ixxx);  but  it  is  doubtful  if  it  has  ever  been 
obtained  in  an  insulated  form.  Its  salts,  particularly  when  in  solution,  ab- 
sorb oxygen  from  the  atmosphere  with  such  rapidity  that  they  may  even  be 
employed  in  eudiometry.  This  protoxide  is  always  formed  with  evolution 
of  hydrogen  gas,  when  metallic  iron  is  put  into  dilute  sulphuric  acid ;  and  its 
composition  may  be  determined  by  collecting  and  measuring  the  gas  which 
is  disengaged. 

Protoxide  of  iron  is  precipitated  from  its  salts  as  a  white  hydrate  by  pure 
alkalies,  as  a  white  carbonate  by  alkaline  carbonates,  and  as  a  white  ferro- 
cyanuret  by  ferrocyanuret  of  potassium.  The  two  former  precipitates  be- 
come first  green  and  then  red,  and  the  latter  green  and  blue,  by  exposure  to 
the  air.  The  solution  of  gall-nuts  produces  no  change  of  colour.  Hydrosul- 
phuric  acid  does  not  act,  if  the  protoxide  is  united  with  any  of  the  stronger 
acids ;  but  alkaline  hydrosulphates  cause  a  black  precipitate,  protosulphuret 
of  iron. 

Its  eq.  is  36;  symb.  Fe  +  O,  Fe,  or  FeO. 

Sesquioxide. — Hist  and  Prep. — The  red  or  sesquioxide  is  a  natural  product, 
known  to  mineralogists  under  the  name  of  red  h&matite.  It  sometimes  oc- 
curs massive,  at  other  times  fibrous,  and  occasionally  in  the  form  of  beauti- 


IRON.  315 

ful  rhomboidal  crystals.  It  may  be  made  chemically  by  dissolving  iron  in 
nitro-hydrochloric  acid,  and  adding  an  alkali.  The  hydrate  of  the  red  oxide 
of  a  brownish-red  colour  subsides,  which  is  identical  in  composition  with  the 
mineral  called  brown  h&matite,  and  consists  of  80  parts  or  one  eq.  of  the  ses- 
quioxide,  and  18  parts  or  two  eq.  of  water. 

Prop. — Is  not  attracted  by  the  magnet.  Fused  with  vitreous  substances 
it  communicates  to  them  a  red  or  yellow  colour.  It  combines  with  most  of 
the  acids,  forming  salts,  the  greater  number  of  which  are  red.  Its  presence 
may  be  detected  by  very  decisive  tests.  The  pure  alkalies,  fixed  or  volatile, 
precipitate  it  as  the  hydrate.  Alkaline  carbonates  have  a  similar  effect,  ses- 
quioxide  of  iron  not  forming  a  permanent  salt  with  carbonic  acid.  With  fer- 
rocyanuret  of  potassium  it  forms  Prussian  blue.  Sulphocyanuret  of  potas- 
sium causes  a  deep  blood-red,  and  infusion  of  gall-nuts  a  black  colour.  Hy- 
drosulphuric  acid  converts  the  sesquioxide  into  protoxide  of  iron,  with  depo- 
sition of  sulphur.  These  reagents,  and  especially  ferrocyanuret  and  sulpho- 
cyanuret  of  potassium,  afford  an  unerring  test  of  the  presence  of  minute 
quantities  of  sesquioxide  of  iron.  On  this  account  it  is  customary,  in  testing 
for  iron,  to  convert  it  into  the  sesquioxide,  an  object  which  is  easily  accom- 
plished by  boiling  the  solution  with  a  small  quantity  of  nitric  acid. 

Its  eq.  is  80;  symb.  2Fe-f  3O,  Fe,  or  Fe^Qs. 

Black  or  Magnetic  Oxide. — Hist,  and  Prep. — This  substance,  the  oxidum 
ferroso-ferricum  of  Berzelius,  long  supposed  to  be  protoxide  of  iron,  contains 
more  oxygen  than  the  protoxide,  and  less  than  the  red  oxide.  It  cannot  be 
regarded  as  a  definite  compound  of  iron  and  oxygen ;  but  it  is  composed  of 
the  two  real  oxides.  It  occurs  native,  frequently  crystallized  in  the  form  of 
a  regular  octohedron  and  dodecahedron  ;  and  it  is  not  only  attracted  by  the 
magnet,  but  is  itself  sometimes  magnetic.  It  is  always  formed  when  iron  is 
heated  to  redness  in  the  open  air ;  and  is  likewise  generated  by  the  contact 
of  watery  Vapour  with  iron  at  elevated  temperatures.  The  composition  of 
the  product,  however,  varies  with  the  duration  of  the  process  and  the  tempe- 
rature which  is  employed.  Thus,  according  to  Buchholz,  Berzelius,  and 
Thomson,  100  parts  of  iron,  when  oxidized  by  steam,  unite  with  nearly  30  of 
oxygen;  whereas  in  a  similar  experiment  performed  by  Gay-Lussac,  37'8 
parts  of  oxygen  were  absorbed.  The  oxide  of  Gay-Lussac  has  the  composi- 
tion stated  in  the  table;  and  Berzelius  thinks  that  of  magnetic  iron  ore  to  be 
similar.  This  has  been  satisfactorily  confirmed  by  Abich,  by  precipitating 
a  mixture  of  the  two  oxides  from  their  solution  in  sulphuric  acid,  in  which 
they  were  contained  in  their  equivalent  proportions.  The  green  precipitate 
which  falls  he  found  to  be  as  highly  magnetic  as  the  native  magnetic  iron 
ore,  and  to  suffer  no  change  on  exposure  to  the  atmosphere.  But  if  the  prot- 
oxide were  contained  in  the  solution  in  greater  quantity,  its  presence  in  the 
precipitate  as  such  was  indicated  by  the  production  of  the  hydrated  sesqui- 
oxide on  exposure  to  the  air.  An  excess  of  the  sesquioxide  diminished  the 
magnetic  effects.  (An.  de  Ch.  et  de  Ph.  Ix.  369.)  M.  Mosander  states,  that 
on  heating  a  bar  of  iron  in  the  open  air,  the  outer  layer  of  the  scales  contains 
a  greater  quantity  of  sesquioxide  than  the  inner  layer.  The  former  consists 
of  one  eq.  of  sesquioxide  to  four  of  the  protoxide,  and  in  the  latter  are  con- 
tained one  eq.  of  sesquioxide  to  six  eq.  of  protoxide.  The  inner  layer  seems 
uniform  in  composition ;  but  the  outer  is  variable,  its  more  exposed  parts 
being  richer  in  oxygen. 

The  nature  of  the  black  oxide  is  farther  elucidated  by  the  action  of  acids. 
On  digesting  the  black  oxide  in  sulphuric  acid,  an  olive-coloured  solution  is 
formed,  containing  two  salts,  sulphate  of  the  sesquioxide  and  protoxide,  which 
may  be  separated  from  each  other  by  means  of  alcohol.  (Proust  and  Gay- 
Lussac.)  The  solution  of  these  mixed  salts  gives  green  precipitates  with 
alkalies,  and  a  very  deep  blue  ink  with  infusion  of  gall-nuts.  The  black 
oxide  of  iron  is  the  cause  of  the  dull  green  colour  of  bottle  glass, 
Its  eq.  is  116;  symb, 


316  IRON. 

Protochloride  of  Iron. — Prep. — This  compound  is  formed  by  transmitting 
dry  hydrochloric  acid  gas  over  iron  at  a  red  heat,  when  hydrogen  gas  is 
evolved,  and  the  surface  of  the  iron  is  covered  with  a  white  crystalline  pro- 
tochloride, which  at  a  stronger  heat  is  sublimed.  Also,  by  acting  with  hydro- 
chloric acid  on  iron,  which  is  dissolved  with  evolution  of  hydrogen  gas,  eva- 
porating to  dryness,  and  heating  to  redness  in  a  tube  without  exposure  to  the 
air,  a  gray  crystalline  protochloride  is  left;  but  it  contains  some  protoxide 
formed  by  an  interchange  of  elements  between  the  last  portions  of  water  and 
the  chloride,  hydrochloric  acid  being  also  generated. 

Prop. — It  dissolves  freely  in  water,  yielding  a  pale  green  solution,  from 
which  rhomboidal  prisms  of  the  same  colour  are  obtained  by  evaporation. 
The  crystals  contain  several  equivalents  of  water  of  crystallization,  deliquesce 
by  exposure  to  the  air,  owing  to  the  formation  of  sesquichloride,  and  are  so- 
luble in  alcohol  as  well  as  water.  The  aqueous  solution  absorbs  oxygen  from 
the  air,  and  becomes  yellow  from  the  formation  of  sesquichloride  of  iron : 
one  portion  of  iron  takes  oxygen  from  the  air,  and  yields  its  chlorine  to  an- 
other portion  of  iron,  whereby  sesquichloride  and  sesquioxide  of  iron  are  gene- 
rated, and  the  latter  falls  as  an  ochreous  sediment  combined  with  some  of  the 
sesquichloride.  A  solution  of  the  protochloride  of  iron  dissolves  binoxide  of 
nitrogen  with  the  same  phenomena  as  the  protosulphate  (page  178,)  a  cir- 
cumstance favourable  to  the  view  entertained  by  many  that  protochloride  of 
iron  is  converted  by  water  into  hydrochlorate  of  the  protoxide. 

Its  eq.  is  63-42  ;  symb.  Fe-f-Cl,  or  Fed. 

Sesquichloride  of  Iron. — It  is  formed  by  the  combustion  of  iron  wire  in 
dry  chlorine  gas,  and  by  transmitting  that  gas  over  iron  moderately  heated, 
when  it  is  obtained  in  small  iridescent  plates  of  a  red  colour,  which  are 
volatile  at  a  heat  a  little  above  212°,  deliquesce  readily,  and  dissolve  in  water, 
alcohol,  and  ether.  On  agitating  ether  with  a  strong  aqueous  solution  of  the 
sesquichloride,  the  ether  abstracts  a  part  of  it,  and  acquires  a  gold-yellow 
colour.  The  readiest  mode  of  obtaining  a  solution  of  the  sesquichloride  is 
to  dissolve  sesquioxide  of  iron  in  hydrochloric  acid.  On  concentrating  to 
the  consistence  of  syrup  and  cooling,  it  separates  as  red  crystals,  which  by 
distillation  yield  at  first  water  and  hydrochloric  acid,  and  then  anhydrous 
sesquichloride  of  iron,  leaving  a  compound  of  sesquioxide  and  sesquichloride 
of  iron  in  crystalline  laminae.  The  formation  of  sesquioxide  appears  due  to 
an  interchange  of  elements  between  it  and  water.  The  same  kind  of  inter- 
change ensues  between  the  vapours  of  water  and  the  sesquichloride  at  a  high 
temperature  ;  and  this  is  probably  the  source,  as  Mitscherlich  suggests,  of 
the  crvstals  of  sesquioxide  of  iron  found  in  volcanic  products. 

Its  eq.  is  162-26 ;  symb,  2Fe-t-3Cl,  or  Fedl*. 

Protiodide  of  Iron. — It  exists  as  a  pale  green  solution  when  iodine  is 
digested  with  water  and  iron  wire,  the  latter  being  in  excess ;  and  on  eva- 
porating the  solution,  without  exposure  to  the  air,  to  dryness,  and  heating 
moderately,  the  protiodide  is  fused,  and  on  cooling  becomes  an  opaque  crys- 
talline mass  of  an  iron-gray  colour  and  metallic  lustre.  It  is  deliquescent 
and  very  soluble  in  water  and  alcohol.  Its  aqueous  solution  attracts  oxygen 
rapidly  from  the  air,  undergoing  the  same  kind  of  change  as  the  proto- 
chloride :  to  preserve  a  solution  of  protiodide  as  such,  a  long  piece  of  iron 
wire  should  be  kept  permanently  in  the  liquid.  This  compound  has  been 
very  successfully  employed  in  medical  practice  by  my  colleague  Dr.  A.  T. 
Thomson. 

Its  eq.  is  154-3;  symb.  Fe-f  I,  or  Fel. 

The  sesquiodide,  of  a  yellow  or  orange  colour  according  to  the  strength  of 
the  solution,  is  obtained  by  freely  exposing  a  solution  of  the  protiodide  to  the 
air,  or  digesting  iron  wire  with  excess  of  iodine,  gently  evaporating,  and 
subliming  the  sesquiodide.  It  is  a  volatile  red  compound,  deliquescent,  and 
soluble  in  water  and  alcohol.  Its  eq.  is  434-9  ;  symb.  2Fe-f-3I,  or  Fe2Is. 

The  bromides  of  iron  are  formed  under  similar  conditions  to  the  chlorides 
and  iodides,  and  are  very  analogous  to  them  in  their  properties. 

Protofluoride  of  Iron  is  best  prepared  by  dissolving  iron  in  a  solution  of 


IRON.  317 

hydrofluoric  acid,  out  of  which  it  crystallizes  as  the  acid  becomes  saturated- 
in  small  white  square  tables,  which  are  sparingly  soluble  in  water,  and  be, 
come  pale  yellow  by  the  action  of  the  air.  By  heat  they  part  with  their 
water  of  crystallization,  and  afterwards  bear  a  red  heat  without  decomposition. 
(Berzelius.) 

Its  eq.  is  46-68;  symb.  Fe+F,  or  FeF. 

The  sesquifluoride  is  formed  by  dissolving  sesquioxide  of  iron  in  hydro- 
fluoric acid,  and  yields  a  colourless  solution  even  when  saturated.  By 
evaporation  it  is  left  as  a  crystalline  mass  of  a  pale  flesh-colour,  and  of  a 
mild  astringent  taste.  It  is  sparingly  soluble  in  water.  Its  eq.  s  112-04; 
symb.  2Fe-|-3F,  or  Fe2Fs. 

Sulphurets  of  Iron. — These  elements  have  for  each  other  a  remarkably 
strong  affinity,  and  unite  under  various  circumstances  and  in  several  pro- 
portions. The  two  lowest  degrees  of  sulphuration,  the  tetrasulphuret  and 
disulphuret,  were  prepared  by  Arfwedson,  by  transmitting  a  current  of 
hydrogen  gas  at  a  red  heat  over  the  anhydrous  disulphate  of  sesquioxide  of 
iron  to  procure  the  tetrasulphuret,  and  over  anhydrous  sulphate  of  protoxide 
of  iron  for  the  disulphuret.  In  both  cases  sulphurous  acid  and  water  are 
evolved,  and  the  resulting  sulphurets  are  left  as  grayish-black  powders, 
susceptible  of  a  metallic  lustre  by  friction.  They  both  dissolve  in  dilute 
sulphuric  acid  with  evolution  of  hydrogen  and  hydrosulphuric  acid  gases. 

Protosulphuret  of  Iron  is  prepared  by  heating  thin  laminae  of  iron  to  red- 
ness with  sulphur  in  a  covered  Hessian  crucible,  and  continuing  the  heat 
until  any  excess  of  sulphur  is  expelled.  The  iron  is  found  with  a  crust  of 
protosulphuret,  which  is  brittle,  of  a  yellowish-gray  colour  and  metallic 
lustre,  and  is  attracted  by  the  magnet.  When  pure  it  is  completely  dissolved 
by  dilute  sulphuric  acid,  yielding  pure  hydrosulphuric  acid.  The  protosul- 
phuret of  iron  exists  in  nature  as  an  ingredient  in  variegated  copper  pyrites ; 
and  it  falls  on  mixing  hydrosulphate  of  ammonia  with  sulphate  of  protoxide 
of  iron  as  a  black  precipitate,  which  oxidizes  rapidly  by  absorbing  oxygen 
from  the  air,  as  soon  as  the  excess  of  hydrosulphate  of  ammonia  is  removed 
by  washing. 

Its  eq.  is  44-1 ;  symb.  Fe-f-  S,  or  FeS. 

The  sesquisulphuret  is  formed  in  the  moist  way  by  adding  sesquichloride 
of  iron  drop  by  drop  to  hydrosulphate  of  ammonia  or  sulphuret  of  potassium 
in  excess,  and  falls  as  a  black  precipitate,  which  is  oxidized  readily  by  the 
air.  In  the  dry  way  it  is  slowly  produced  by  the  action  of  hydrosulphuric 
acid  gas  on  sesquioxide  of  iron  at  a  heat  not  exceeding  212°,  water  being 
also  formed ;  and  by  the  action  of  the  same  gas  on  the  hydrated  sesquioxide 
at  common  temperatures.  This  sulphuret,  when  anhydrous,  has  a  yellowish- 
gray  colour,  is  not  attracted  by  the  magnet,  and  dissolves  in  dilute  sulphuric 
or  hydrochloric  acid,  yielding  hydrosulphuric  acid  and  a  residue  of  bisul- 
phuret  of  iron.  (Berzelius.) 

Its  eq.  is  104-3;  symb.  2Fe-f-3S,  or  Fe2Ss. 

Bisulphuret  of  Iron,  iron  pyrites  of  mineralogists,  exists  abundantly  in  the 
earth.  It  occurs  in  cubes  or  some  allied  form,  has  a  yellow  colour,  metallic 
lustre,  a  density  of  4-981,  and  is  so  hard  that  it  strikes  fire  with  steel.  Some 
varieties  have  a  white  colour ;  but  these  usually  contain  arsenic.  Others 
occur  in  rounded  nodules,  have  a  radiated  structure  divergent  from  a  com-, 
mon  centre,  are  often  found  in  beds  of  clay,  and  are  much  disposed  by  the 
influence  of  air  and  moisture  to  yield  sulphate  of  protoxide  of  iron  :  these  are 
suspected  by  Berzelius  to  be  com  pounds  of  protosulphuret  and  bisulphuret  of 
iron. 

Bisulphuret  of  iron  is  not  attacked  by  any  of  the  acids  except  the  nitric, 
and  its  best  solvent  is  the  nitro-hydrochloric  acid.  Heated  in  close  vessels  it 
gives  off  nearly  half  its  sulphur,  and  is  converted  into  magnetic  iron  pyrites. 
By  heat  and  air  together  it  yields  sesquioxide  of  iron.  Its  eq.  is  60-2 ;  symb. 
Fe  +  2S,  orFeS*. 

magnetic  Iron  Pyrites. — This  is  a  natural  product,  termed  magnetic  py- 
rites from  being  attracted  by  the  magnet,  and  was  formerly  regarded  as 

27* 


318  IRON. 

protosulphuret  of  iron;  but  Stromeyer  has  shown  that  its  elements  are  m 
such  a  ratio,  that  it  may  be  regarded  as  a  compound  of  bisulphuret  and  proto- 
sulphuret. It  is  formed  by  heating1  the  bisulphuret  to  redness  in  close  ves- 
sels, by  fusing  iron  filings  with  half  their  weight  of  sulphur,  or  by  rubbing 
sulphur  upon  a  rod  of  iron  heated  to  whiteness.  It  is  soluble  in  dilute  sul- 
phuric acid,  yielding  hydrosulphuric  acid  gas  and  a  residue  of  sulphur.  It  is 
much  more  oxidable  by  air  and  moisture  than  the  pure  bisulphuret.  Its  eq. 
is  280-7  ;  symb.  5FeS-f  FeS*. 

Diphosphuret  of  Iron. — It  is  prepared  by  exposing  the  phosphate  of  prot- 
oxide of  iron  to  a  strong  heat  in  a  covered  crucible  lined  with  charcoal,  the 
excess  of  phosphorus  being  dissipated  in  vapour.  It  is  a  fifeed  granular  mass, 
of  the  colour  and  lustre  of  iron,  but  very  brittle,  and  is  not  attacked  by  hy- 
drochloric acid.  It  is  sometimes  contained  in  metallic  iron,  to  the  properties 
of  which  it  is  very  injurious  by  rendering  it  brittle  at  common  temperatures. 
Its  eq,  is  71-7;  symb.  2Fe-{-P,  or  FeaP. 

The  perphosphuret  has  been  obtained  by  Rose  by  the  action  of  phosphu- 
retted  hydrogen  gas  on  sulphuret  of  iron  at  a  moderate  temperature,  and  re- 
sembles the  former  in  its  properties. 

Its  eq.  is  146-8  ;  symb.  3Fe-f-4P,  or  Fe^P*. 

Carburets  Jof  Iron. — Carbon  and  iron  unite  in  very  various  proportions  ; 
but  there  are  three  compounds  very  distinct  from  each  other — namely,  gra- 
phite, cast  or  pig  iron,  and  steel. 

Graphite,  also  known  under  the  names  of  plumbago  and  black  lead,  occurs 
not  unfrequently  as  a  mineral  production,  and  is  found  in  great  purity  at 
Borrowdale  in  Cumberland.  It  may  be  made  artificially  by  exposing  iron 
with  excess  of  charcoal  to  a  violent  and  long -continued  heat;  and  it  is  com- 
monly generated  in  small  quantity  during  the  preparation  of  cast  iron.  Pure 
specimens  contain  about  four  or  five  per  cent,  of  iron,  but  sometimes  its 
quantity  amounts  to  10  per  cent.  Most  chemists  believe  the  iron  to  be  che- 
mically united  with  the  charcoal ;  but  according  to  the  researches  of  Karsten 
of  Berlin,  native  graphite  is  only  a  mechanical  mixture  of  charcoal  and  iron, 
while  artificial  graphite  is  a  real  carburet. 

Graphite  is  exceedingly  unchangeable  in  the  air,  and,  like  charcoal,  is  at- 
tacked with  difficulty  by  chemical  reagents.  It  may  be  heated  to  any  extent 
in  close  vessels  without  change ;  but  if  exposed  at  the  same  time  to  the  air, 
its  carbon  is  entirely  consumed,  and  oxide  of  iron  remains.  It  has  an  iron- 
gray  colour,  metallic  lustre,  and  granular  texture ;  and  it  is  soft  and  unctuous 
to  the  touch.  Its  chief  use  is  in  the  manufacture  of  pen-oils  and  crucibles, 
arid  in  burnishing  iron  to  protect  it  from  rust. 

Cast  iron  is  the  product  of  the  process  for  extracting  iron  from  its  ores, 
and  is  commonly  regarded  as  a  real  compound  of  iron  and  charcoal.  It  al- 
ways contains  impurities,  such  as  charcoal,  undecomposed  ore,  and  earthy 
matters,  which  are  often  visible  by  mere  inspection  ;  and  sometimes  traces 
of  chromium,  manganese,  sulphur,  phosphorus,  and  arsenic  are  present*  It 
fuses  readily  at  2786°  (Daniell),  which  is  a  full  red  heat,  and  in  cooling  it 
acquires  a  crystalline  granular  texture.  The  quality  of  different  specimens 
is  by  no  means  uniform ;  and  two  kinds,  white  and  gray  cast  iron,  are  in 
particular  distinguished  from  each  other.  The  former  is  exceedingly  hard 
and  brittle,  sometimes  breaking  like  glass  from  sudden  change  of  tempera- 
ture ;  while  the  latter  is  softer  and  much  more  tenacious.  This  difference 
appears  owing  to  the  mode  of  combination,  rather  than  to  a  difference  in  the 
proportion  of  carbon  ;  for  the  white  variety  may  be  converted  into  the  gray 
by  exposure  to  a  strong  heat  and  cooling  slowly,  and  the  gray  may  be 
changed  into  the  white  by  being  heated  and  rapidly  cooled.  According  to 
Karsten,  the  carbon  of  the  white  is  combined  with  the  whole  mass  of  iron, 
and  amounts  as  a  maximum  to  5-25  per  cent.;  but  in  some  specimens  its 
proportion  is  considerably  less.  The  gray,  on  the  contrary,  contains  from 
3-15  to  4*65  j>er  cent,  of  carbon,  of  which  about  three-fourths  are  in  the  state 
of  graphite,  and  are  left  as  such  after  the  iron  is  dissolved  by  acids ;  while 
the  remaining  fourth  is  in  combination  with  the  whole  mass  of  metalt  con^ 


* .  ZINC.  319 

stituting  a  carburet  which  is  very  similar  to  steel.  Gray  cast  iron  may 
hence  be  regarded  as  a  kind  of  steel,  in  which  graphite  is  mechanically 
mixed. 

Steel  is  commonly  prepared  in  this  country  by  the  process  of  cementation, 
which  consists  in  filling  a  large  furnace  with  alternate  strata  of  bars  of  the 
purest  malleable  iron  and  powdered  charcoal,  closing  every  aperture  so  as 
perfectly  to  exclude  atmospheric  air,  and  keeping  the  whole  during  several 
days  at  a  red  heat.  By  this  treatment  the  iron  gradually  combines  with 
from  1-3  to  T75  per  cent  of  carbon,  its  texture  is  greatly  changed,  and  its 
surface  is  blistered.  It  is  subsequently  hammered  at  a  red  heat  into  small 
bars,  and  may  be  welded  either  with  other  bars  of  steel  or  with  malleable 
iron.  Mackintosh  of  Glasgow  has  introduced  an  elegant  process  of  forming 
steel  by  exposing  heated  iron  to  a  current  of  coal  gas ;  when  carburetted 
hydrogen  is  decomposed,  its  carbon  enters  into  combination  with  the  iron, 
and  hydrogen  gas  is  evolved. 

In  ductility  and  malleability  it  is  far  inferior  to  iron  ;  but  exceeds  it  greatly, 
in  hardness,  sonorousness,  and  elasticity.  Its  texture  is  also  more  compact, 
and  it  is  susceptible  of  a  higher  polish.  It  sustains  a  full  red  heat  without 
fusing,  and  is,  therefore,  less  fusible  than  cast  iron  ;  but  it  is  much  more  so 
than  malleable  iron.  By  fusion  it  forms  cast  steel,  which  is  more  uniform 
in  composition  and  texture,  and  possesses  a  closer  grain,  than  ordinary  steeL 


SECTION  XII. 

ZINC   AND  CADMIUM. 
ZINC. 

Hist,  and  Prep. — THIS  metal  was  first  mentioned  under  the  term  zinetum 
in  the  sixteenth  century  by  Paracelsus ;  but  it  was  probably  known  at  a 
much  earlier  period.  In  commerce  it  is  often  called  speller,  and  is  obtained 
either  from  calamine,  native  carbonate  of  zinc,  or  from  the  native  sulphuret, 
zinc  blende  of  mineralogists.  It  is  procured  from  the  former  by  heat  and 
carbonaceous  matters ;  and  from  the  latter  by  a  similar  process  after  the  ore 
has  been  previously  oxidized  by  roasting,  that  is,  by  exposure  to  the  air  at  a 
low  red  heat.  Its  preparation  affords  an  instance  of  what  is  called  distilla- 
tion by  descent.  The  furnace  or  crucible  for  reducing  the  ore  is  closed 
above,  and  in  its  bottom  is  fixed  an  iron  tube,  the  upper  aperture  of  which  is 
in  the  interior  of  the  crucible,  and  its  lower  terminates  just  above  a  vessel  of 
water.  The  vapour  of  zinc,  together  with  all  the  gaseous  products,  passes 
through  this  tube,  and  the  zinc  is  condensed.  The  first  portions  are  com- 
monly very  impure,  containing  cadmium  and  arsenic,  the  period  of  their 
disengagement  being  indicated  by  what  the  workmen  call  the  brown  blaze  ; 
but  when  the  blue  blaze  begins,  that  is,  when  the  metallic  vapour  burns  with 
a  bluish-white  flame,  the  zinc  is  collected.  As  thus  obtained,  it  is  never 
quite  pure:  it  frequently  contains  traces  of  charcoal,  sulphur,  cadmium,  arse- 
nic, lead,  and  copper ;  and  iron  is  always  present.  It  may  be  freed  from 
these  impurities  by  distillation, — by  exposing  it  to  a  white  heat  in  an  earthen 
retort,  to  which  a  receiver  full  of  water  is  adapted ;  but  the  first  portions  as 
liable  to  contain  arsenic  and  cadmium,  should  be  rejected. 

Prop. — It  has  a  strong  metallic  lustre,  and  a  bluish-white  colour.  Its 
texture  is  lamellated,  and  its  sp.  gr.  about  7.  It  is  a  hard  metal,  being  acted 
on  by  the  file  with  difficulty.  At  low  or  high  degrees  of  heat  it  is  brittle  ; 
but  at  temperatures  between  210°  and  3000>  it  is  both  malleable  and  ductile,, 


320  ZINC. 

a  property  which  enables  zinc  to  be  rolled  or  hammered  into  sheets  of  con- 
siderable thinness.  Its  malleability  is  considerably  diminished  by  the  impu- 
rities which  the  zinc  of  commerce  contains.  It  fuses  at  773°  (Daniell),  and 
when  slowly  cooled  crystallizes  in  four  or  six-sided  prisms.  Exposed  in 
close  vessels  to  a  white  heat,  it  sublimes  unchanged. 

Zinc  undergoes  little  change  by  the  action  of  air  and  moisture.  When 
fused  in  open  vessels  it  absorbs  oxygen,  and  forms  the  white  oxide,  called 
flowers  of  zinc.  Heated  to  full  redness  in  a  covered  crucible,  it  bursts  into 
flame  as  soon  as  the  cover  is  removed,  and  burns  with  a  brilliant  white 
light.  The  combustion  ensues  with  such  violence,  that  the  oxide  as  it  is 
formed  is  mechanically  carried  up  into  the  air.  The  heat  at  which  it  begins 
to  burn  is  estimated  by  Daniell  at  941°  F.  Zinc  is  readily  oxidized  by  dilute 
sulphuric  or  hydrochloric  acid,  and  the  hydrogen  which  is  evolved  contains 
a  small  quantity  of  metallic  zinc  in  combination. 

Gay-Lussac  and  Berzelius  found  that  the  protoxide  of  zinc  consists  of  100 
parts  of  metallic  zinc  and  24-8  of  oxygen,  being  a  ratio  of  32-3  to  8.  Its 
other  combinations  justify  the  adoption  of  32-3  as  the  eq.  of  zinc;  its  symb. 
is  Zn.  The  composition  of  its  compounds  described  in  this  section  is  as 
follows : 

Zinc.  Equiv.       Formulae. 

Protoxide  32-3  1  eq.-f  Oxygen      8  1  eq.=  40-3    Zn-fOorZnO. 

Peroxide  Composition  uncertain. 

Chloride  32-3  1  eq.  + Chlorine  35-42  1  eq.=  67-72  Zn  +  Cl  or  ZnCL 

Iodide  32-3  1  eq.-j- Iodine    126-3  1  eq.=158-6    Zn-florZnI. 

Bromide  32-3  1  eq.-f  Bromine  78.4  1  eq.=  110-7     Zn-j-Br  or  ZnBr. 

Fluoride.  32-3  1  eq.-j-  Fluorine  18-68  1  eq.==  50-98  Zn-fF  or  ZnF. 

Sulphuret  32-3  1  eq.-f-  Sulphur  16-1  1  eq.=  48-4    Zn-fSorZnS. 

Protoxide  of  Zinc. — This  is  the  only  oxide  of  zinc  which  acts  as  a  salifiable 
base,  and  the  only  one  of  known  composition.  It  is  generated  during  the 
solution  of  zinc  in  dilute  sulphuric  acid,  and  may  be  obtained  in  a  dry  state 
by  collecting  the  flakes  which  rise  during  the  combustion  of  zinc,  or  by 
heating  the  carbonate  to  redness.  At  common  temperatures  it  is  white;  but 
when  heated  to  low  redness,  it  assumes  a  yellow  colour,  which  gradually 
disappears  on  cooling.  It  is  quite  fixed  in  the  fire.  It  is  insoluble  in  water, 
and,  therefore,  does  not  affect  the  blue  colour  of  plants;  but  it  is  a  strong 
salifiable  base,  forming  regular  salts  with  acids,  most  of  which  are  colourless. 
It  combines  also  with  some  of  the  alkalies. 

The  presence  of  zinc  is  easily  recognized  by  the  following  characters. — 
The  protoxide  is  precipitated  from  its  solutions  as  a  white  hydrate  by  pure 
potassa  or  ammonia,  and  as  carbonate  by  carbonate  of  ammonia,  but  is  com- 
pletely redissolved  by  an  excess  of  the  precipitant.  The  fixed  alkalline 
carbonates  precipitate  it  permanently  as  white  carbonate  of  protoxide  of  zinc. 
Hydrosulphate  of  ammonia  causes  a  white  precipitate,  a  hydrated  sulphuret 
of  zinc.  Hydrosulphuric  acid  acts  in  a  similar  manner,  if  the  solution  is 
quite  neutral ;  but  it  has  no  effect  if  an  excess  of  any  strong  acid  is  present. 

Its  eq.  is  40-3  ;  symb.  Zn  +  O,  Zn,  or  ZnO. 

When  metallic  zinc  is  exposed  for  some  time  to  air  and  moisture,  or  is  kept 
under  water,  it  acquires  a  superficial  coating  of  a  gray  matter,  which  Ber- 
zelius describes  as  a  suboxidc.  It  is  probably  a  mixture  of  metallic  zinc 
and  the  protoxide,  into  which  it  is  resolved  by  the  action  of  acids.  The  per- 
oxide is  prepared,  according  to  Thenard,  by  acting  on  hydrated  protoxide 
of  zinc  with  peroxide  of  hydrogen  diluted  with  water.  It  resolves  itself  so 
readily  into  oxygen  and  the  protoxide  already  described,  that  it  cannot  be 
preserved  even  under  the  surface  of  water ;  and  its  composition  is  quite 
unknown. 

Chloride  of  Zinc. — This  compound  is  formed,  with  evolution  of  heat  and 
light,  when  zinc  filings  are  introduced  into  chlorine  gas ;  and  it  is  readily 
prepared  by  dissolving  zinc  in  hydrochloric  acid,  evaporating  to  dryness,  and 


CADMIUM.  321 

heating  the  residue  in  a  tube  through  which  dry  hydrochloric  acid  gas  is 
transmitted.  It  is  colourless,  fusible  at  a  heat  a  little  above  212°,  has  a  soft 
consistence  at  common  temperatures,  hence  called  butter  of  zinc,  sublimes  at 
a  red  heat,  and  deliquesces  in  the  air. 

Its  eq.  is  67-72  ;  symb.  Zn-j-Cl,  or  ZnCl. 

Iodide  of  Zinc  is  prepared  by  digesting  iodine  in  water  with  zinc  filings 
in  excess.  A  colourless  solution  results,  which  by  evaporation  yields  a  de- 
liquescent iodide.  By  heat  in  close  vessels  it  may  be  sublimed,  and  then 
crystallizes  in  brilliant  needles ;  but  if  heated  in  the  open  air,  protoxide  of 
zinc  is  formed,  and  iodine  expelled.  If  zinc  is  digested  in  water  with  an 
excess  of  iodine,  a  brown  solution  results,  which  probably  contains  a  bin- 
iodide. 

Its  eq.>  158-6;  symb.  Zn+I,  or  Znl. 

Bromide  of  Zinc  may  be  formed  by  a  process  similar  to  that  for  the  iodide, 
but  its  properties  have  not  been  studied. 

Its  eq.  is  110-7 ;  symb.  Zn-j-Br,  or  ZnBr. 

Fluoride,  of  Zinc  is  obtained  by  acting  directly  on  protoxide  of  zinc  with 
hydrofluoric  acid,  and  is  a  white  compound  of  sparing  solubility. 

Its  eq.  is  50-98;  symb.  Zn+F,  or  ZnF. 

Sulphuret  of  Zinc. — This  compound  is  well  known  to  mineralogists  under 
the  name  of  zinc  blende,  and  occurs  in  dodecahedral  crystals  or  some  allied 
form.  Its  structure  is  lamellated,  lustre  adamantine,  and  colour  variable, 
being  sometimes  yellow,  red,  brown,  or  black.  It  may  be  formed  artificially 
by  igniting,  in  a  closed  crucible,  a  mixture  of  protoxide  of  zinc  and  sulphur, 
or  sulphate  of  protoxide  of  zinc  and  charcoal,  or  by  drying  the  hydrated  sul- 
phuret of  zinc.  Its  eq.  is  48-4;  symb.  Zn-j-S,  or  ZnS. 

CADMIUM. 

Hist. — Cadmium,  so  called  (from  *a<t/u&iet,  a  term  applied  to  calamine  and 
to  the  volatile  matters  which  rise  from  the  furnace  in  preparing  brass)  be- 
cause it  is  associated  with  zinc,  was  discovered  in  the  year  1817,  by  Stro- 
meyer,  in  an  oxide  of  zinc  which  had  been  prepared  for  medical  use;  and  he 
has  since  found  it  in  several  of  the  ores  of  that  metal,  especially  in  a  radiated 
blende  from  Bohemia,  which  contains  about  five  per  cent,  of  cadmium.  The 
late  Dr.  Clarke  detected  its  existence  in  some  of  the  zinc  ores  of  Derbyshire, 
and  in  the  common  zinc  of  commerce.  Herapath  has  found  it  in  considerable 
quantity  in  the  zinc  works  near  Bristol.  During  the  reduction  of  calamine 
by  coal,  the  cadmium,  which  is  very  volatile,  flies  off  in  vapour  mixed  with 
soot  and  some  oxide  of  zinc,  and  collects  in  the  roof  of  the  vault,  just 
above  the  tube  leading  from  the  crucible.  Some  portions  of  this  substance 
yielded  from  12  to  20  per  cent,  of  cadmium.  (Ann.  of  Phil.  xiv.  and  xvii.) 

Prep. — The  process  by  which  Stromeyer  separates  cadmium  from  zinc  or 
other  metals  is  the  following.  The  ore  of  cadmium  is  dissolved  in  dilute  sul- 
phuric or  hydrochloric  acid,  and  after  adding  a  portion  of  free  acid,  a  cur- 
rent of  hydrosulphuric  acid  gas  is  transmitted  through  the  liquid,  by  which 
means  the  cadmium  is  precipitated  as  sulphuret,  while  the  zinc  continues  in 
solution.  The  sulphuret  of  cadmium  is  then  decomposed  by  nitric  acid,  and 
the  solution  evaporated  to  dryness.  The  dry  nitrate  is  dissolved  in  water, 
and  an  excess  of  carbonate  of  ammonia  added.  The  white  carbonate  of  oxide 
of  cadmium  subsides,  which,  when  heated  to  redness,  yields  a  pure  oxide. 
By  mixing  this  oxide  with  charcoal,  and  exposing  the  mixture  to  a  red  heat, 
metallic  cadmium  is  sublimed. 

A  very  elegant  process  for  separating  zinc  from  cadmium  was  proposed  by 
Wollaston.  The  solution  of  the  mixed  metals  is  put  into  a  platinum  cap- 
sule, and  a  piece  of  metallic  zinc  is  placed  in  it.  If  oadmium  is  present,  it 
is  reduced,  and  adheres  so  tenaciously  to  the  capsule,  that  it  may  be  washed 
with  water  without  danger  of  being  lost.  It  may  then  he  dissolved  either  by 
nitric  or  dilute  hydrochloric  acid. 

Prop. — Cadmium,  in  colour  and  lustre,  has  a  strong  resemblance  to  tin, 


322  TIN. 

but  is  somewhat  harder  and  more  tenacious.  It  is  very  ductile  and  malleable, 
Its  sp.  gr.  is  8-604  before  being  hammered,  and  8-694  afterwards.  It  melts 
at  about  the  same  temperature  as  tin,  and  is  nearly  as  volatile  as  mercury, 
condensing  like  it  into  globules  which  have  a  metallic  lustre.  Its  vapour 
has  no  odour.  When  heated  in  the  open  air,  it  absorbs  oxygen,  and  is  con- 
verted into  an  oxide.  Cadmium  is  readily  oxidized  and  dissolved  by  nitric 
acid,  which  is  its  proper  solvent.  Sulphuric  and  hydrochloric  acids  act  upon 
it  less  easily,  and  the  oxygen  is  then  derived  from  water. 

The  eq.  of  cadmium,  deduced  from  Stromeyer's  analysis  of  its  oxide,  is 
55-8.  Its  symb.  is  Cd.  The  composition  of  its  compounds  described  in  this 
section  is  as  follows  : — 


Cadmium. 

Equiv. 

Formulae. 

Oxide 

55-8 

1 

eq. 

-(-Oxygen 

8 

1 

eq.= 

63-8 

Cd-f-O 

or  CdO. 

Chloride 

55-8 

1 

cq. 

-f.  Chlorine 

35-42 

1 

eq.= 

91-22 

Cd-fCl 

or  CdCl. 

Iodide 

55-8 

1 

Cq. 

-j-  Iodine 

126-3 

1 

eq.= 

182-1 

Cd-florCdI. 

Sulphuret 

55-8 

1 

eq, 

,  4.  Sulphur 

16-1 

1 

eq.= 

71-9 

Cd-fS 

or  CdS. 

Oxide  of  Cadmium. — This,  the  only  known  oxide  of  cadmium,  is  prepared 
by  igniting  its  carbonate,  has  an  orange  colour,  is  fixed  in  the  fire,  and  is 
insoluble  in  water.  It  has  no  action  on  test  paper,  but  is  a  strong  alkaline 
base,  forming  neutral  salts  with  acids.  It  is  precipitated  as  a  white  hydrate 
by  pure  ammonia,  but  is  redissolved  by  excess  of  that  alkali.  It  is  precipi- 
tated permanently  by  pure  potassa  or  soda  as  a  hydrate,  and  by  all  the  alka- 
line carbonates  as  carbonute  of  oxide  of  cadmium. 

Its  eq.  is  63-8 ;  symb.  Cd+O,  Cd,  or  CdO. 

Chloride  of  Cadmium. — By  dissolving  oxide  of  cadmium  in  hydrochloric 
acid  and  concentrating  duly,  the  chloride,  with  water  of  crystallization, 
crystallizes  in  transparent  four-sided  rectangular  prisms,  which  lose  their 
water  by  heat  and  even  in  a  dry  air,  fuse  at  a  heat  short  of  redness,  and 
acquire  a  lamellated  texture  in  cooling.  At  a  high  temperature  it  is  sub- 
limed. 

Its  eq.  is  91-22 ;  symb.  Cd  -fCl,  or  CdCl. 

Iodide  of  Cadmium  may  be  formed  in  the  same  manner  as  iodide  of  zinc, 
i§  soluble  in  water  and  alcohol,  and  crystallizes  by  evaporation  in  large,  co- 
lourless, transparent,  hexagonal  tables,  which  do  not  change  in  the  air,  and 
have  a  pearly  lustre.  By  heat  they  lose  water,  and  then  fuse.  Its  eq.  is 
1821;  symb.  Cd-fl,  orCdl. 

Sulphuret  of  Cadmium  occurs,  in  mixture  or  combination,  in  some  kinds 
of  zinc  blende,  and  is  easily  prepared  by  the  action  of  hydrosulphuricacidon 
a  salt  of  cadmium.  It  has  a  yellowish-orange  colour,  and  is  distinguished 
from  the  sulphurets  of  arsenic  by  being  insoluble  in  pure  potassa,  and  by 
sustaining  a  white  heat  without  subliming.  (Stromeycr,) 

Its  eq.  is  71-9  ;  symb.  Cd+S,  or  CdS. 


SECTION   XIII. 

TIN. 

Hist,  and  Prep. — WAS  known  to  the  ancients,  who  obtained  it  principally, 
if  not  solely,  from  Cornwall.  The  tin  of  commerce  is  distinguished  into -two 
varieties,  called  block  and  grain  tin,  both  of  which  are  procured  from  the  na- 
tive oxide  by  means  of  heat  and  charcoal.  In  Cornwall,  which  has  been 
celebrated  for  its  tin  mines  during  many  centuries,  the  ore  is  both  extracted 


TIN.  323 

from  veins,  and  found  in  the  form  of  rounded  grains  among  beds  of  rolled 
materials,  which  have  been  deposited  by  the  action  of  water.  These  grains, 
commonly  called  stream  tin,  contain  a  very  pure  oxide,  and  yield  the  purest 
kind  of  grain  tin.  An  inferior  sort  is  prepared  by  heating  bars  of  tin,  ex- 
tracted from  the  common  ore,  to  very  near  their  point  of  fusion,  when  the 
more  fusible  parts,  which  are  the  purest,  flow  out;  and  the  less  fusible 
portions  constitute  block  tin.  The  usual  impurities  are  iron,  copper,  and 
arsenic. 

Prop. — It  has  a  white  colour,  and  a  lustre  resembling  that  of  silver.  The 
brilliancy  of  its  surface  is  but  very  slowly  impaired  by  exposure  to  the  atmos- 
phere, nor  is  it  oxidized  even  by  the  combined  agency  of  air  and  moisture. 
Its  malleability  is  very  considerable ;  for  the  thickness  of  common  tin-foil 
does  not  exceed  l-1000th  of  an  inch.  In  ductility  and  tenacity  it  is  inferior 
to  several  metals.  It  is  soft  and  inelastic,  and  when  bent  backwards  and 
forwards  emits  a  peculiar  crackling  noise.  Its  sp.  gr.  is  about  {7-291.  At 
442°  it  fuses,  and,  if  exposed  at  the  same  time  to  the  air,  its  surface  tarnishes, 
and  a  gray  powder  is  formed.  When  heated  to  whiteness,  it  takes  fire  and 
burns  with  a  white  flame,  being  converted  into  binoxide  of  tin. 

The  eq.  of  tin  deduced  by  Berzelius  from  his  analysis  of  its  oxides  is 
58-9 ;  its  symb.  is  Sri.  The  composition  of  the  compounds  of  tin  described 
in  this  section  is  as  follows  : — 

Tin.  Equiv.     Formulae. 

Protoxide          58-9  1  eq.-f  Oxygen     8        1  eq.=  66-9   Sn  +  OorSnO. 
Sesquioxide     117-8  2  eq.-f     do.       24        3  eq.=  141-8   Sn -j- 3O or  Sn2Q8. 
Binoxide  58-9  1  eq. 4.     do.      16        2  eq.=  74-9   Sn-f2O  or  SnO. 

Protochloride    58-9  1  eq.-f Chlorine  35-42    1  eq.=  94-32  Sn-fCl  or  SnCl. 
Bichloride         58-9  1  eq.  -f     do.       70-84  2  eq.  ==129-74  Sn  -f  2C1  or  SnCK 
Protiodide          58-9  1  eq.-j-  Iodine  126-3      1  eq.  =185-2    Sn-florSnI. 
Biniodide          58'9  1  eq.-f     do.    252-6     2  eq.=  319-5   Sn-f2I  or  Snl*. 
Protosulphuret  58-9  1  eq.  4.  Sulphur  16-1      1  eq.==   75      Sn-fSorSnS. 
Sesquisulph't   117-8  2  eq.-f     do.       48-3     3  eq.=  166-l   2Sn-f  3Sor  SnsS3. 
Bisulphuret       58-9  1  eq.-f     do.      32-2     2  eq.=    91-1  Sn-f2SorSnS^ 
Terphosphuret  58-9  1  eq.-f  Phosph.  47-1     3  eq.=106      Sn-f  3P  or  SnP«. 

Protoxide  of  Tin. — Prep. — When  protochloride  of  tin  in  solution  is  mixed 
with  an  alkaline  carbonate,  hydrated  protoxide  of  tin  falls,  which  may  be 
obtained  as  such  in  a  dry  form  by  washing-  with  warm  water,  and  drying  at 
a  heat  not  above  196°,  with  the  least  possible  exposure  to  the  air.  The  best 
mode  of  obtaining  the  anhydrous  protoxide  is  by  heating  the  hydrate  to  red- 
ness in  a  tube  from  which  air  is  [excluded  by  a  current  of  carbonic  acid 
gas.  The  same  oxide  is  formed  when  tin  is  kept  for  some  time  fused  in  an 
open  vessel. 

Prop. — Its  sp.  gr.  is  6'666.  At  common  temperatures  it  is  permanent  in 
the  air;  but  if  touched  by  a  red-hot  body,  it  takes  fire  and  is  converted  into 
the  binoxide.  It  is  dissolved  by  the  sulphuric  and  hydrochloric  acids,  as  also 
by  dilute  nitric  acid  ;  and  the  pure  fixed  alkalies  likewise  dissolve  it.  From 
the  alkaline  solution,  metallic  tin  is  gradually  deposited,  and  binoxide  of  tin 
remains  in  solution.  Its  salts  are  remarkably  prone  to  absorb  oxygen,  both 
from  the  air  and  from  compounds  which  yield  oxygen  readily.  Thus  it  con- 
verts sesquioxide  of  iron  into  protoxide,  and  throws  down  mercury,  silver, 
and  platinum  in  the  metallic  state  from  their  salts.  With  a  solution  of  gold, 
it  causes  a  purple  precipitate,  the  purple  of  Cassius,  which  appears  to  be  a 
compound  of  binoxide  of  tin  and  protoxide  of  gold.  By  this  character  pro- 
toxide of  tin  is  recognized  with  certainty.  It  is  thrown  down  by  hydrosul- 
pliuric  acid  as  black  protosulphuret  of  tin. 

Its  eq.  is  66-9;  symb.  Sn-f  O,  S*n,  or  SnO. 

Sesquioxide  of  Tin. — Fuchs  has  lately  succeeded  in  preparing  this  oxide, 
by  mixing  recently  precipitated  and  moist  hydrated  sesquioxide  of  iron  with 


324  TIN. 

a  solution  of  protochloride  of  tin,  as  free  as  possible  from  hydrochloric  acid  ; 
when  by  an  interchange  of  elements 

1  eq.  sesquioxide  of  iron  and  2  eq.  protochloride  of  tin 

2Fe+3O  2(Sn-fCl)  -% 

yield 

1  eq.  sesquioxide  of  tin  and  2  eq.  protochloride  of  iron. 
2Sn+3O  2(Fe-|-Cl) 

The  sesquioxide  falls  as  a  slimy  gray  matter,  and  in  general  rather  yellow 
from  adhering  oxide  of  iron.  Berzelius  obtained  it  purer  by  using  a  solution 
made  by  saturating  hydrochloric  acid  as  far  as  possible  with  hydrated  ses- 
quioxide of  iron.  The  sesquioxide  of  tin,  while  rnoist,  is  soluble  in  hydro- 
chloric  acid,  and  the  solution  strikes  the  purple  of  Cassius  with  gold ;  and  it 
is  readily  soluble  in  a  solution  of  ammonia,  which  distinguishes  it  from  the 
protoxide  of  tin,  just  as  its  action  on  gold  does  from  thebinoxide.  (Pog.  An- 
nalen,  xxviii.  443.) 

Its  eq.  is  141-8;  symb.  2Sn-j-3O,  Sn,  or  Sn^O. 

Binoxide  of  Tin. — Prep. — Most  conveniently  by  the  action  of  nitric  acid, 
on  metallic  tin.  The  acid,  in  its  most  concentrated  state,  does  not  act  easily 
upon  tin  ;  but  when  a  small  quantity  of  water  is  added,  violent  effervescence 
takes  place,  owing  to  the  evolution  of  nitrous  acid  and  binoxide  of  nitrogen, 
and  a  white  powder,  the  hydrated  binoxide,  is  produced.  On  edulcorating 
this  substance,  and  heating  it  to  redness,  watery  vapour  is  expelled,  and  the 
pure  binoxide,  of  a  straw-yellow  colour,  remains.  In  this  process  ammonia 
is  generated,  a  circumstance  which  proves  water  as  well  as  nitric  acid  to  be 
decomposed.  Binoxide  of  tin  may  likewise  be  obtained  by  precipitation 
from  a  solution  of  bichloride  of  tin,  by  potassa,  ammonia,  or  the  alkaline 
carbonates;  but  in  this  case  it  falls  as  a  very  bulky  hydrate,  different  from 
the  other  hydrate  both  in  appearance  and  in  several  of  its  chemical  proper, 
ties.  Thus  the  latter  dissolves  readily  in  sulphuric,  nitric,  and  hydrochloric 
acid  even  when  diluted;  while  the  former  is  completely  insoluble  in  the  same 
acids,  even  when  concentrated.  It  unites,  indeed,  with  hydrochloric  acid, 
and  the  compound  is  soluble  in  pure  water. 

Prop. — It  has  very  little  disposition  in  any  state  to  unite  with  acids,  and, 
when  dissolved  by  them,  is  very  apt  to  separate  spontaneously  as  a  gelatin- 
ous hydrate.  It  acts  the  part  of  a  feeble  acid  :  it  reddens  litmus  when  its 
hydrate  moistened  is  laid  upon  it,  and  it  unites  with  the  pure  alkalies,  form- 
ing soluble  compounds  which  are  called  stannates. 

Binoxide  of  tin  is  recognized  by  its  insolubility  in  acids  in  its  anhydrous 
state;  by  separating  from  its  solution  by  means  of  hydrochloric  acid  as  a 
bulky  hydrate  by  any  of  the  alkalies  or  alkaline  carbonates,  which  is  easily 
and  completely  dissolved  by  pure  potassa  or  soda  in  excess ;  and  by  yielding 
with  hydrosulphuric  acid  the  yellow  bisulphuret  of  tin,  which  is  also  soluble 
in  pure  potassa.  Binoxide  of  tin,  when  melted  with  glass,  forms  a  white 
enamel. 

Its  eq.  74-9;  symb.  Sn-f-SO,  Sn,  or  SnO. 

Protochloride  of  Tin. — This  compound  is  obtained  by  transmitting  hydro- 
chloric acid  gas,  over  metallic  tin  heated  in  a  glass  tube,  when  hydrogen  gas 
is  evolved  ;  or  by  distilling  a  mixture  either  of  granulated  tin  with  an  equal 
weight  of  bichloride  of  mercury,  or  of  an  amalgam  of  tin  with  calomel,  urg- 
ing the  heat  till  the  mercury  is  expelled.  In  this  state  it  is  a  gray  solid,  of  a 
resinous  lustre,  which  fuses  below  redness,  and  at  a  high  temperature  sub- 
limes. It  is  obtained  by  crystallization  from  a  concentrated  solution  of  the 
chloride  in  crystals,  which  are  sometimes  in  small  white  needles,  and  at  others 
in  large  transparent  prisms,  and  consist  of  94-32  parts  or  one  eq.  of  proto- 
chloride of  tin  and  27  parts  of  three  eq.  of  water.  On  heating  these  crystals, 
they  not  only  lose  water,  but  reaction  ensues  between  the  elements  of  water 


TIN.  325 

and  the  chloride,  hydrochloric  acid  gas  is  evolved,  and  protoxide  of  tin  re- 
mains combined  with  the  chloride.  The  same  kind  of  compound  is  formed 
when  a  large  quantity  of  water  is  poured  upon  the  crystals :  the  solution 
contains  protochloride  of  tin  and  hydrochloric  acid,  and  a  white  powder  sub- 
sides which  consists  of  one  eq.  of  the  protochloride,  one  eq.  of  protoxide,  and 
two  eq.  of  water.  (Berzelius.) 

A  solution  of  protochloride  of  tin  is  obtained  by  heating  granulated  tin  in 
strong  hydrochloric  acid  as  long  as  hydrogen  gas  continues  to  be  evolved. 
This  solution  is  much  employed  as  a  deoxidizing  agent,  being  more  powerful 
than  the  sulphate  or  nitrate  of  the  protoxide;  owing  apparently  to  the  ten- 
dency of  the  protochloride  of  tin  to  resolve  itself  into  bichloride  and  metallic 
tin,  the  latter  taking  oxygen  or  chlorine  from  any  metallic  solutions  which 
yield  them  readily.  Its  eq.  is  94-32;  symb.  Sn-f-Cl,  or  SnCl. 

Bichloride  of  Tin. — When  protochloride  of  tin  is  heated  in  chlorine  gas, 
or  on  distilling  a  mixture  of  8  parts  of  granulated  tin,  with  24  of  bichloride 
of  mercury,  a  very  volatile,  colourless,  liquid  passes  over,  which  is  bichloride 
of  tin.  In  an  open  vessel  it  emits  dense  white  fumes,  caused  by  the  mois- 
ture of  the  air,  and  hence  it  was  formerly  called  the  fuming  liquor  of  Liba- 
vius,  who  discovered  it.  At  248°  it  boils,  and  the  sp.  gr.  of  its  vapour  was 
found  by  Dumas  to  be  9-1997.  With  one-third  of  its  weight  of  water  it 
forms  a  solid  hydrate,  and  in  a  larger  quantity  of  water  dissolves. 

The  solution  of  bichloride  of  tin,  commonly  called  permuriate  of  <in,  is 
much  used  in  dyeing,  and  is  prepared  by  dissolving  tin  in  nitro-hydrochloric 
acid.  The  process  requires  care  ;  for  if  the  action  be  very  rapid,  as  is  sure 
to  happen  if  strong  acid  be  employed  and  much  tin  added  at  once,  the  bin- 
oxide  will  be  spontaneously  deposited  as  a  bulky  hydrate,  and  be  subse- 
quently redissolved  with  great  difficulty.  But  the  operation  will  rarely  fail, 
if  the  acid  is  made  with  two  measures  of  hydrochloric  acid,  one  of  nitric 
acid,  and  one  of  water,  and  if  the  tin  is  gradually  dissolved,  one  portion  dis- 
appearing before  another  is  added.  The  most  certain  mode  of  preparation, 
however,  is  to  prepare  a  solution  of  the  protochloride,  and  convert  it  into 
the  bichloride  either  by  chlorine,  or  by  gentle  heat  and  nitric  acid. 

Its  eq.  is  129-74;  symb.  Sn-f  2C1,  or  SnCls. 

Iodides  of  Tin. — The  protiodide  is  formed  by  heating  granulated  tin  with 
about  2^  times  its  weight  of  iodine,  and  is  a  brownish-red,  translucid  sub- 
stance, very  fusible,  volatile  at  a  high  temperature,  and  soluble  in  water. 

Its  eq.  is  185-2;  symb.  Sn-f  I,  or  SnI. 

The  biniodide  is  prepared  by  dissolving,  in  hydriodic  acid,  the  hydrate  of 
the  binoxide,  precipitated  by  alkalies  from  the  bichloride.  It  crystallizes  in 
yellow  crystals  of  a  silky  lustre,  which  are  resolved  by  boiling  water  into 
hydriodic  acid  and  binoxide  of  tin. 

Its  eq.  is  311-5;  symb.  Sn-f  21,  or  Snla. 

Protosulphuret  of  Tin. — This  compound  is  prepared  by  pouring  melted 
tin  upon  its  own  weight  of  sulphur,  and  stirring  rapidly  with  a  stick  during 
the  action  ;  as  some  tin  usually  escapes  the  sulphur,  from  the  latter  being 
rapidly  expelled,  the  product  should  be  pulverized,  mixed  with  its  weight  of 
sulphur,  and  projected  in  successive  portions  into  a  hot  Hessian  crucible, 
and  then  heated  to  redness.  It  is  a  brittle  compound,  of  a  bluish-gray, 
nearly  black  colour,  and  metallic  lustre,  which  fuses  at  a  red  heat,  and 
acquires  a  lamellated  texture  in  cooling.  It  is  dissolved  by  hydrochloric  acid 
with  evolution  of  hydrosulphuric  acid.  The  same  sulphuret  is  obtained  in  the 
moist  way  by  adding  hydrosulphuric  acid  to  a  solution  of  protochloride  of  tin. 

Its  eq.  is  75  ;  symb.  Sn  -f  S,  or  SnS. 

The  sesquisulphuret  is  formed  by  mixing  the  protosulphuret  in  fine  pow- 
der with  a  third  of  its  weight  of  sulphur,  and  heating  the  mixture  to  low 
redness  until  sulphur  ceases  to  escape.  Its  colour  is  of  a  deep  grayish-yel- 
low. It  is  reconverted  by  a  strong  heat  into  the  protosulphuret,  and  dis- 
solves in  hydrochloric  acid  gas,  yielding  hydrosulphuric  acid  gas,  and  a  resi- 
due of  bisulphuret  of  tin. 

Its  eq.  is  166-1 ;  symb.  2Sn-f  3S,  or  SnaSs. 

28 


326 


Bisulphuret  of  Tin,  formerly  called  mosaic  gold,  is  prepared  by  heating, 
in  a  glass  or  earthen  retort,  a  mixture  of  2  parts  of  binoxide  of  tin,  2  of  sul- 
phur, and  1  part  of  sal  ammoniac,  and  maintaining  a  low  red  heat  until  sul- 
phurous acid  ceases  to  be  evolved.  These  materials  are  sometimes  employed 
without  sal  ammoniac,  but  Berzelius  says  that  the  latter  is  essential  for  ob- 
taining the  bisulphuret.  The  product,  when  successfully  prepared,  is  in 
crystalline  scales,  and  sometimes  even  in  regular  six-sided  tables,  of  a 
golden-yellow  colour  and  metallic  lustre.  It  is  soluble  in  pure  potassa,  and 
in  its  carbonate  by  boiling ;  but  its  only  solvent  among  the  acids  is  the 
mtro-hydrochloric.  The  bisulphuret  is  obtained  as  a  bulky  hydrate  of  a 
dirty  yellow  colour  by  the  action  of  hydrosulphuric  acid  or  hydrosulphate  of 
ammonia  on  bichloride  of  tin  in  solution. 

Its  eq.  is  91-1 ;  symb.  Sn-j-2S,  or  SnS'. 

Terphosphuret  of  Tin.— Rose  formed  this  compound  by  acting  on  a  solu- 
tion of  protochloride  of  tin  by  phosphuretted  hydrogen.  It  is  readily  oxi- 
djzed  by  the  action  of  the  air. 

Its  eq.  is  106;  symb.  Sn-f-3P, 


SECTION  XIV. 

COBALT   AND   NICKEL. 
COBALT. 

Hist. — THIS  metal  is  met  with  in  the  earth  chiefly  in  combination  with 
arsenic,  constituting  an  ore  from  which  all  the  cobalt  of  commerce  is 
derived.  It  is  a  constant  ingredient  of  meteoric  iron,  though  in  very  small 
quantity.  (Stromeyer.)  Its  name  is  derived  from  the  term  Kebold,  an  evil 
spirit,  applied  to  it  by  the  German  miners  at  a  time  when  they  were  igno- 
rant of  its  value,  and  considered  it  unfavourable  to  the  presence  of  valuable 
metals. 

Prep. — When  native  arseniuret  of  cobalt  is  broken  into  small  pieces,  and 
exposed  in  a  reverberatory  furnace  to  the  united  action  of  heat  and  air,  its 
elements  are  oxidized,  most  of  the  arsenious  acid  is  expelled  in  the  form  of 
vapour,  and  an  impure  oxide  of  cobalt,  called  zaffre,  remains.  This  is  dis- 
solved in  hydrochloric  acid,  and  a  current  of  hydrosulphuric  acid  gas  is  trans- 
mitted through  the  solution,  until  the  arsenious  acid  is  completely  separated 
in  the  form  of  orpiment.  The  filtered  liquid  is  then  boiled  with  a  little  nitric 
acid,  in  order  to  convert  the  protoxide  into  sesquioxide  of  iron,  and  an  excess 
of  carbonate  of  potassa  is  added.  The  precipitate,  consisting  of  sesquioxide 
of  iron  and  carbonate  of  protoxide  of  cobalt,  after  being  well  washed  with 
water,  is  digested  in  a  solution  of  oxalic  acid,  which  dissolves  the  oxide  of 
iron,  and  leaves  the  oxide  of  cobalt  in  the  form  of  an  insoluble  oxalate. 
(Laugier.)  On  heating  this  oxalate  in  a  retort  from  which  atmospheric  air 
is  excluded,  a  large  quantity  of  carbonic  acid  is  evolved,  and  a  black  powder, 
metallic  cobalt,  is  left.  (Thomson  in  Annals  of  Philosophy,  N.  S.  i.)  The 
pure  metal  is  easily  procured  also  by  passing  a  current  of  dry  hydrogen  gas 
over  protoxide  of  cobalt  heated  to  redness  in  a  tube  of  porcelain.  In  this 
state  it  is  porous,  and  if  formed  at  a  low  temperature  it  inflames  spontaneously, 
as  stated  in  the  section  on  iron  (page  312). 

Prop. — A  brittle  metal,  of  a  reddish-gray  colour,  and  weak  metallic  lustre. 
Its  density,  according  to  my  observation,  is  7-834.  It  fuses  at  a  heat  rather 
lower  than  iron,  and  when  slowly  cooled  it  crystallizes.  It  has  long  been 
considered  to  be  attracted  by  the  magnet,  but  Faraday  denies  that  it  possesses 


COBALT.  327 

this  property  when  pure.  It  undergoes  little  change  in  the  air,  but  absorbs 
oxygen  when  heated  in  open  vessels.  It  is  attacked  with  difficulty  by  sul- 
phuric or  hydrochloric  acid,  but  is  readily  oxidized  by  means  of  nitric  acid. 
Like  iron  and  the  other  metals  of  this  order,  it  decomposes  water  at  a  red 
heat  with  disengagement  of  hydrogen  gas.  (Despretz.) 

According  to  the  analyses  by  Rothoff  of  the  oxides  of  cobalt,  its  equivalent 
is  inferred  to  be  29-5  (Ann.  of  Phil,  iii,  356.)  Its  symb.  is  Co.  The  com- 
position of  its  compounds  described  in  this  section  is  as  follows  : — 

Cobalt.  Equiv.        Formulae. 

Protoxide       .    29-5  1  eq.-j-Oxygen     8  1  eq.==  37-5     Co-f-O  or  CoO. 

|Oxide          .     8853eq.-fdo.  32  4eq.=  120-5    3Co-j-4O  or  Co3(X 

Sesquioxide   .    59     2eq.+do.  24  3  eq.=  83      2Co-j-3O  or  Co2Os. 

Chloride         .    29-5  1  eq.+Chlorine  35-42  1  eq.=  64-92  Co+Cl  or  CoCl. 

Protosulphuret  29-5  1  eq.+Sulphur  16'1  1  eq.==  45-6     Co-f-S  or  CoS. 

Sesquisulphuret  59     2  eq.-fdo.  48-3  3eq.=  107-3   2Co  -f  3S  or  Go^Ss. 

Bisulphuret    .    29-5  1  eq.4-do.  32-2  2eq.=  61-7     Co-f-2S  or  CoS* 

Subphosphuret  88-5  3  eq.+Phosph.  31-4  2eq.=  119-9    3Co-r-2Por  Co^P3 

Protoxide  of  Cobalt. — Prepared  by  decomposing  carbonate  of  the  protoxide 
by  heat  in  a  vessel  from  which  atmospheric  air  is  excluded.  It  is  of  an 
ash-gray  colour,  and  is  the  basis  of  the  salts  of  cobalt,  most  of  which  are  of 
a  pink  hue.  When  heated  to  redness  in  open  vessels  it  absorbs  oxygen,  and  is 
converted  into  the  sesquioxide.  It  is  easily  recognized  by  giving  a  blue  tint 
to  borax  when  melted  with  it ;  and  is  employed  in  the  arts,  in  the  form  of 
smalt,  for  communicating  a  similar  colour  to  glass,  earthenware,  and  porce- 
lain. It  is  precipitated  from  its  salts  by  pure  potassa  as  a  blue  hydrate, 
which  absorbs  oxygen  from  the  air,  and  gradually  acquires  a  dirty  green  tint. 
Pure  ammonia  likewise  causes  a  blue  precipitate,  which  is  redissolved  by  the 
alkali  if  in  excess.  It  is  thrown  down  as  a  pale  pink  carbonate  by  car- 
bonate of  potassa,  soda,  or  ammonia  ;  but  an  excess  of  the  last  redissolves  it 
with  facility.  Hydrosulphuric  acid  produces  no  change,  unless  the  solution 
is  quite  neutral,  or  the  oxide  is  combined  with  a  weak  acid.  Alkaline  hydro- 
sulphates  always  precipitate  it  as  black  protosulphuret  of  cobalt.  Its  eq.  is 
37-5  ;  symb.  Co+O,  Co,  or  CoO. 

^Oxide  of  Cobalt. — It  is  said  that  when  protoxide  of  cobalt,  or  the  nitrate, 
carbonate,  or  oxalate  of  that  oxide,  is  gently  ignited  in  an  open  fire,  sesqui- 
oxide of  cobalt  results ;  but  M.  Hess  has  lately  shown  that  the  oxide  then 
obtained  is  analogous  in  composition  to  the  red  oxide  of  manganese.  The 
sesquioxide  of  cobalt  is  converted  into  it,  with  loss  of  oxygen,  by  a  full  red 
heat,  whether  exposed  to  the  air  or  not ;  so  that  of  the  oxides  of  cobalt,  it  is 
the  most  stable.  The  same  compound  is  obtained  as  a  dirty  green  hydrate 
by  the  action  of  the  air  on  the  hydrated  protoxide.  It  is  probably  a  compound 
of  protoxide  and  sesquioxide  of  cobalt,  since  3Co-f-4O  obviously  contain  the 
elements  CoO-f  Co2Oa.  This  intermediate  oxide  is  of  a  dark  brown  colour, 
and  does  not  unite  with  acids  or  alkalies  (Pog.  Annalen,  xxvi.  542.) 

Its  eq.  is  120-5  ;  symb.  CoO-K^CX 

Sesquioxide. — Is  obtained  as  a  black  hydrate  containing  two  eq.  of  water, 
Co2O3-|-2HO,  when  chloride  of  cobalt  in  solution  is  decomposed  by  hypo- 
chlorite  of  lime,  or  chlorine  is  transmitted  into  water  in  which  hydrated 
protoxide  of  cobalt  is  suspended.  In  this  case 

3  eq.  protoxide  and  1  eq.  chlorine  2    1  eq.  sesquioxide  and  1  eq.  chloride. 
3(Co-r-0)  Cl  •£  2Co-r-3O  Co-fCl 

This  hydrate  has  a  black  colour  and  yields  the  black  anhydrous  sesqui. 
oxide  by  exposure  to  a  heat  of  600°  or  700°  ;  but  it  is  difficult  to  drive  off  all 
the  water,  without  also  losing  oxygen.  It  combines  with  none  of  the  acids 


328  COBALT. 

and  when  digested  with  hydrochloric  acid  it  emits  chlorine  gas,  and  chloride 
of  cobalt  is  generated. 

Its  eq.  is  83  ;  symb.  2Co-h3O,  Co,  or  Co*O*. 

When  a  salt  of  cobalt  is  treated  with  pure  ammonia  in  close  vessels,  part 
of  the  cobalt  is  dissolved,  and  part  subsides  in  form  of  a  blue  powder.  On 
admitting  atmospheric  air,  this  substance  passes  to  a  higher  state  of  oxida- 
tion, and  is  gradually  dissolved.  If  nitrate  of  cobalt  is  used,  a  double  salt 
may  be  obtained  in  crystals,  which  L.  Gmelin,  to  whom  we  are  indebted  for 
these  remarks,  believes  to  consist  of  nitrate  and  cobaltate  of  ammonia.  Of 
the  existence  of  an  acid  of  cobalt,  however,  Winkelblcch,  who  has  examined 
the  subject,  could  obtain  no  evidence  (Lieb.  Ann.  xiii.  253.) 

Chloride  of  Cobalt.  —  It  is  obtained  in  solution  on  dissolving  metallic  cobalt, 
its  protoxide,  or  either  of  the  other  oxides  in  hydrochloric  acid,  with  evolu- 
tion of  hydrogen  gas  with  the  first  and  of  chlorine  with  the  latter.  It  yields 
a  pink-coloured  solution,  and  by  evaporation  small  crystals  of  the  same 
colour  containing  water  of  crystallization.  When  deprived  of  water  its  colour 
is  blue,  a  character  on  which  is  founded  its  use  as  a  sympathetic  ink  :  when 
letters  are  written  with  a  dilute  solution  of  the  chloride,  the  colour,  is  so  pale 
that  it  is  invisible  in  the  cold  ;  but  on  heating  gently,  the  letters  appear  of  a 
blue  colour,  and  disappear  as  soon  as  the  chloride  has  recovered  its  moisture 
from  the  atmosphere.  When  iron  or  nickel  is  present  the  dry  chloride  of 
cobalt  is  green  instead  of  blue. 

Its  eq.  is  64-92  ;  symb.  Co-|-Cl,  or  CoCl. 

Sulphurets.  —  Cobalt  appears  to  unite  with  sulphur  in  three  proportions  ; 
the  first  being  a  protosulphuret,the  second  a  sesquisulphuret,  and  the  third  a 
bisulphuret.  The  protosulphuret  may  be  formed  in  the  dry  way,  either  by 
throwing  fragments  of  sulphur  on  red-hot  cobalt,  or  by  igniting  protoxide  of 
cobalt  with  sulphur  ;  and  it  is  thrown  down  as  a  black  precipitate  from  the 
salts  of  cobalt  by  alkaline  hydrosulphates,  or  even  by  hydrosulphuric  acid 
gas  if  the  salt  is  quite  neutral,  or  the  oxide  united  with  any  of  the  feebler 
acids.  It  has  a  gray  colour,  a  metallic  lustre,  and  a  crystalline  texture.  Its 
eq.  45-6;  symb.  Co+S,or  CoS. 

Arfwedson  has  observed  that  when  hydrogen  gas  is  transmitted  over  sul- 
phate of  protoxide  of  cobalt  heated  to  redness,  water  and  sulphurous  acid  are 
evolved,  and  a  compound  remains,  called  an  oxy  sulphur  et,  consisting  of  prot- 
oxide of  cobalt  united  with  protosulphuret  of  cobalt.  When  this  substance 
is  exposed  to  hydrosulphuric  acid  gas  at  a  red  heat,  the  oxide  is  decomposed, 
and  the  sesquisulphuret  is  formed.  Its  eq.  is  107*3;  symb.  2Co-[-3S,  or 


The  bisulphuret  is  prepared,  according  to  Settcrberg,  by  heating  2  parts  of 
carbonate  of  protoxide  of  cobalt,  intimately  mixed  with  3  parts  of  sulphur. 
The  process  is  conducted  in  a  glass  retort,  and  the  heat  continued  as  long  as 
sulphur  is  expelled  ;  but  the  temperature  should  not  be  suffered  to  reach  that 
of  redness. 

Its  eq.  61-7  ;  symb.  Co-f  2S,  or  CoSa. 

Subphosphuret  of  Cobalt.  —  Rose  obtained  this  phosphuret  by  the  action  of 
hydrogen  gas  on  subphosphate  of  protoxide  of  cobalt  heated  in  a  tube,  water 
being  also  generated.  In  this  case 

1  eq.  subphosphate  and  8  eq.  hydrogen 
3(Co+O)+(2P+50)  8H 

yield 

1  eq,  subphosphuret  and  8  eq.  of  water. 
3Co+2P  8(H+O) 

This  phosphuret  is  pulverulent  and  of  a  gray  colour,  and  is  also  obtained 
by  the  action  of  phosphuretted  hydrogen  gas  on  chloride  of  cobalt.  Its  eq.  is 
119-9  ;  symb.  3Co+2P,  or 


329 


NICKEL. 

Hist,  and  Prep. — Nickel  is  a  constituent  of  meteoric  iron ;  but  its  princi- 
pal ore  is  the  copper-coloured  mineral  of  Westphalia,  termed  kupfernickel, 
copper-nickel;  nickel  being  an  epithet  of  detraction,  applied  by  the  older 
German  miners,  because  the  mineral  looked  like  an  ore  of  copper,  and  yet 
they  could  extract  none  from  it.  The  combinations  of  nickel  may  be  pre- 
pared either  from  copper-nickel,  which  is  an  arseniuret  of  nickel  containing1 
small  quantities  of  sulphur,  copper,  cobalt,  and  iron,  or  from  the  artificial 
arseniuret  called  speiss,  a  metallurgic  production  obtained  in  forming  smalt 
from  the  roasted  ores  of  cobalt.  Various  processes  have  been  devised  for  pro- 
curing a  pure  salt  of  nickel,  but  the  following  appears  to  me  as  simple  and 
perhaps  as  successful  as  any.  After  reducing  speiss  to  fine  powder,  it  is  di- 
gested in  sulphuric  acid,  to  which  a  fourth  part  of  nitric  acid  is  added  ;  and 
when  the  solution  is  saturated  with  nickel,  it  is  set  aside  for  several  hours 
in  order  that  arsenious  acid  may  separate,  and  is  then  filtered.  The  clear 
liquid  is  subsequently  mixed  with  a  solution  of  sulphate  of  potassa,  and  set 
aside  to  crystallize  spontaneously ;  when  a  double  salt,  sulphate  of  protoxide 
of  nickel  and  potassa,  is  deposited.  Thomson  who  proposed  this  process, 
states  that  the  crystals  thus  obtained  are  quite  free  from  arsenic  and  iron,  and 
contain  no  impurities  except  copper  and  cobalt.  The  former  is  precipitated 
as  sulphuret  by  a  current  of  hydrosulphuric  acid  gas,  a  little  free  sulphuric 
acid  being  previously  added ;  and  at  the  same  time  any  traces  of  arsenic,  if 
present,  would  likewise  subside  as  orpiment.  The  filtered  liquid  is  then  heated 
to  expel  free  hydrosulphuric  acid,  and  the  protoxides  of  nickel  and  cobalt 
precipitated  by  carbonate  of  potassa.  The  separation  of  these  oxides  may 
then  be  effected  by  the  method  suggested  by  Berthier ;  namely,  by  precipitat* 
ing  them  together  by  pure  potassa,  and,  after  washing  the  mixed  hydrates, 
suspending  them  in  water  through  which  chlorine  gas  is  transmitted  to  satu- 
ration. All  the  cobalt  and  generally  some  nickel  is  converted  into  sesquioxide 
and  thus  rendered  insoluble;  while  the  greater  part  of  the  nickel  is  dissolved 
in  the  form  of  chloride,  and  may  be  removed  from  the  insoluble  sesquioxides 
by  filtration.  The  metal  may  be  prepared  either  by  heating  the  oxalate  in 
close  vessels,  or  by  the  combined  action  of  heat  and  charcoal  or  hydrogen 
on  protoxide  of  nickel. 

Prop. — It  is  of  a  white  colour,  intermediate  between  that  of  tin  and  silver. 
It  has  a  strong  metallic  lustre,  and  is  both  ductile  and  malleable.  It  is  at- 
tracted by  the  magnet,  and  like  iron  may  be  rendered  magnetic  at  common 
temperatures,  but  loses  this  power  at  630°  (Faraday.)  Its  sp.  gr.  after  fusion 
is  about  8-279,  and  is  increased  to  near  9  by  hammering. 

Nickel  is  very  infusible,  but  less  so  than  pure  iron,  It  suffers  no  change 
at  common  temperatures  by  exposure  to  air  and  moisture ;  but  it  absorbs 
oxygen  at  a  red  heat,  though  not  rapidly,  and  is  partially  oxidized.  It  de- 
composes water  at  the  same  temperature.  Hydrochloric  and  sulphuric  acids 
act  upon  it  with  difficulty ;  but  by  nitric  acid  it;  is  readily  oxidized,  ana* 
forms  a  nitrate  of  the  protoxide  of  nickel. 

From  the  analyses  of  the  oxides  of  nickel  by  Rothoffand  Tupputi,  the  eq. 
of  nickel  may  be  estimated  at  29<5.  Its  symb.  is  Ni.  The  composition  of 
its  compounds  described  in  this  section  is  as  follows : — 

Nickel.  Equiv.      Formulae. 

Protoxide  29-5  1  eq.-f  Oxygen     8  1  eq.=  37-5   Ni-fOorNiO. 

Sesquioxide       59     2  eq.-f  do.  24  3eq.=  83      2Ni  J-3O  or  Ni*O3, 

Chloride  29-5  1  eq.  4. Chlorine  35-42  1  eq.=  64-92  Ni  4.  Cl  or  NiCl. 

Protosulphuret29.5  1  eq.  -f Sulphur  16-1  1  eq-=  45-6  Ni  J-S  or  NiS. 

Disulphuret      59     2  eq.-f  do.  16-1  1  eq.=  75-1   2Ni-f  S  or  Ni«S, 

Subphosphuret  88-5  3  eq.  -f  Phos,       31-4  2  eq.  =119-9   3Ni  -f  2P  or  NisP*, 

Protoxide  of  Nickel,-~Th\s  oxide  may  be  formed  by  heating  the  carbo* 

28* 


330  NICKEL. 

nate,  oxalate,  or  nitrate  to  redness  in  an  open  vessel,  and  is  then  of  an  ash- 
gray  colour ;  but  after  exposure  to  a  white  heat,  its  colour  is  a  dull  olive- 
green.  It  is  not  reducible  by  heat  unaided  by  combustibles.  It  is  not  at- 
tracted by  the  magnet.  It  is  a  strong  alkaline  base,  and.  nearly  all  its  salts 
have  a  green  tint.  It  is  precipitated  as  a  hydrate  of  a  pale  green  colour  by 
the  pure  alkalies,  but  is  redissolved  by  ammonia  in  excess;  as  a  pale  green 
carbonate  by  alkaline  carbonates,  hut  is  redissolved  by  an  excess  of  carbonate 
of  ammonia  ;  and  as  a  black  sulphuret  by  alkaline  hydrosulphates.  Hydro- 
sulphuric  acid  occasions  no  precipitate,  unless  the  solution  is  quite  neutral, 

or  the  oxide  combined  with  a  weak  acid.  Its  eq.  is  37'5 ;  Symb.  Ni  -f-O,  Ni, 
or  NiO. 

Sesquioxide. — It  is  formed  by  transmitting  chlorine  gas  through  water  in 
which  the  hydrate  of  the  protoxide  is  suspended.  It  has  a  black  colour,  does 
not  unite  with  acids,  is  decomposed  by  a  red  heat,  and  with  hot  hydrochloric 
acid  forms  the  chloride,  with  disengagement  of  chlorine  gas. 

Its  eq.  is  83  ;  symb.  2Ni-f-3O,  Ni,  or  Ni-Qs. 

Thenard  succeeded  in  preparing  an  oxide  by  the  action  of  peroxide  of  hy- 
drogen on  hydrated  protoxide  of  nickel ;  but  it  is  uncertain  whether  the 
composition  of  this  oxide  is  identical  with  that  of  the  sesquioxide  above  de- 
scribed, or  different.  Two  suboxides  have  likewise  been  enumerated ;  but 
their  existence  is  exceedingly  problematical. 

Chloride  of  Nickel. — This  compound  is  formed  by  acting  with  hydrochloric 
acid  on  metallic  nickel,  its  protoxide,  or  sesquioxide,  hydrogen  gas  being 
evolved  with  the  former,  and  chlorine  with  the  latter.  It  forms  an  emerald 
green  solution,  and  by  evaporation  yields  crystals  of  the  same  tint,  which  lose 
water  or  deliquesce  according  as  the  air  is  dry  or  moist.  In  its  anhydrous 
state  it  is  yellow ;  but  a  small  admixture  with  cobalt  causes  a  green  tint.  At 
a  low  red  heat  it  sublimes,  and  condenses  in  brilliant  scales  of  a  gold-yellow 
colour.  Its  eq.  is  64-92;  symb.  Ni-fCl,  or  NiCJ. 

Protosulphuret  of  Nickel  is  formed  by  processes  similar  to  those  described 
for  preparing  protosulphuret  of  cobalt.  The  precipitated  sulphuret  is  dark 
brown  or  nearly  black,  and  is  dissolved  by  hydrochloric  acid  with  evolution 
of  hydrosulphuric  acid ;  while  that  procured  in  the  dry  way  is  of  a  grayish- 
yellow  colour,  and  requires  for  solution  nitric  or  nitro-hydrochloric  acid. 
It  occurs  as  a  natural  production  in  very  delicate  acicular  crystals,  the 
haarkies  of  the  Germans.  Its  eq.  is  45-6  ;  symb.  Ni-f-S  or  NiS. 

Arfwedson  obtained  the  disulphuret  by  transmitting  hydrogen  gas  over 
sulphate  of  protoxide  of  nickel  at  a  red  heat.  It  is  of  a  lighter  yellow  and 
more  fusible  than  the  other. 

Its  eq.  is  75-1;  symb.  2Ni-{-S,  or  Ni9S. 

Subphosphuret  of  Nickel. — Rose  obtained  it  by  the  action  of  hydrogen 
gas  on  subphosphate  of  protoxide  of  nickel,  the  same  change  ensuing  as 
with  cobalt;  and  it  is  generated  by  the  action  of  phosphuretted  hydrogen  gas 
on  chloride  of  nickel.  It  has  a  black  colour,  is  insoluble  in  hydrochloric 
acid,  but  dissolves  in  nitric  acid.  Heated  by  the  blowpipe  it  burns  with 
flame. 

Its  eq.  is  119-9;  symb.  3Ni-f  2P,  or 


331 


CLASS  II. 
ORDER  II. 


METALS  WHICH  DO  NOT  DECOMPOSE  WATER  AT  ANY  TEM- 
PERATURE, AND  THE  OXIDES  OF  WHICH  ARE  NOT  RE- 
DUCED  TO  THE  METALLIC  STATE  BY  THE  SOLE  ACTION 
OF  HEAT. 

SECTION    XV. 

ARSENIC. 

Hist,  and  Prep. — METALLIC  arsenic  sometimes  occurs  native,  but  more 
frequently  it  is  found  in  combination  with  other  metals,  and  especially 
with  cobalt  and  iron.  On  roasting  these  arsenical  ores  in  a  reverberatory  fur- 
nace, the  arsenic,  from  its  volatility,  is  expelled,  combines  with  oxygen  as  it 
rises,  and  condenses  into  thick  cakes  on  the  roof  of  the  chimney.  The  sub- 
limed mass,  after  being  purified  by  a  second  sublimation,  is  the  virulent  poi- 
son known  by  the  name  of  arsenic,  or  white  oxide  of  arsenic.  From  this 
substance  the  metal  itself  is  procured  by  heating  it  with  charcoal.  The  most 
convenient  process  is  to  mix  the  white  oxide  with  about  twice  its  weight  of 
black  flux,  and  expose  the  mixture  to  a  red  heat  in  a  Hessian  crucible,  over 
which  is  luted  an  empty  crucible  for  receiving  the  metal.  The  reduction  is 
easily  effected,  and  metallic  arsenic  collects  in  the  xapper  crucible,  which 
should  be  kept  cool  for  the  purpose  of  condensing  the  vapour. 

Prop. — An  exceedingly  brittle  metal,  of  a  strong  metallic  lustre  and  white 
colour,  running  into  steel-gray.  Its  structure  is  crystalline,  and  when  slowly 
sublimed  it  is  said  to  crystallize  in  rhombohedrons.  Its  sp.  gr.  is  5-8843. 
When  heated  to  356°  it  sublimes  without  previously  liquefying ;  for  its  point 
effusion  is  far  above  that  of  its  sublimation,  and  has  not  hitherto  been  deter- 
mined. Its  vapour  has  a  strong  odour  of  garlic,  a  property  which  affords  a 
distinguishing  character  for  metallic  arsenic ;  as  it  is  not  possessed  by  any 
other  metal,  with  the  exception  perhaps  of  zinc,  which  is  said  to  emit  a  simi- 
lar odour  when  thrown  in  powder  on  burning  charcoal.  In  close  vessels  it 
may  be  sublimed  without  change;  but  if  atmospheric  air  be  admitted,  it  is 
rapidly  converted  into  the  white  oxide.  According  to  Hahneman  it  is  slowly 
oxidized  and  dissolved  by  being  boiled  in  water.  In  general  it  speedily 
tarnishes  by  exposure  to  air  and  moisture,  acquiring  upon  its  surface  a  dark 
film,  which  is  extremely  superficial ;  but  Berzelius  remarks  that  he  has  kept 
some  specimens  in  open  vessels  for  years  without  loss  of  lustre,  while  others 
are  oxidized  through  their  whole  substance,  and  fall  into  powder.  The  pro- 
duct of  this  spontaneous  oxidation,  which  is  known  abroad  under  the  name 
of  fly -powder,  is  supposed  by  Berzelius  to  be  an  oxide ;  but  it  is  more  gene- 
rally regarded  as  a  mixture  of  white  oxide  and  metallic  arsenic. 

The  eq.  of  arsenic,  as  inferred  by  Berzelius  from  the  composition  of  arse- 


332  ARSENIC. 

nious  and  arsenic  acids,  is  37-7.     Its  symb.  is  As.     The  compounds  of  this 
metal  described  in  this  section  are  thus  constituted  : — 

Arsenic.  Equiv.  Formulae. 

Arsenious   f  «t  A  0         .  /-\  o  no  A 

>  75-4  2  eq.  4- Oxygen    24      3  eq.=  99-4 
acid          \  *        j  ° 


>  75-4  2  eq.  +  do.  40      5  eq.=115-4    2As-J-5O  or  AssQ*. 

1  37-7  1  eq.+Chlorine     35-42  1  eq.=  73-12  As-j-Cl  or  AsCl. 
> 

'  |  75.4  2  eq.-f-do.          106-26  3  eq.=181-66  2As+3Clor  As^Cls. 
Periodide       75-4  2  eq.-f  Iodine     631-5    5  eq.=706-9     2As+5Iior  As^Is. 
i.4  2  eq.  4- Bromine  235-2   3  eq.=310-6    2As-|-3Br  or  As  fir* 

['     |  37-7  1  eq.-f. Hydrogen    1  1  eq.=  38-7  As+H  or  AsH. 

Ar^1rur*    J75-4  2  eq.  +  do.              3  3eq.=  78-4  2As-r-3HorAs3H^ 

Pr>huret     £37'7  leq-  +  SulPhur     16<1  1  eq.=  53-8  As-j-S  or  AsS. 

Se8hur8eUtl"  {  75'4  2  e(l--H0-              48'3  3  eq.=!23-7  2As+3S  or  As  S*. 

Persulphu-  )  ?5.4  2  eq  ^  da              go.5  5  eq>=155.9  2  As+SSorAsaS*. 

-Arseniows  .Acid. — Prep. — This  compound,  frequently  called  white  arsenic 
and  white  oxide  of  arsenic,  is  always  generated  when  arsenic  is  heated  in 
open  vessels,  and  may  be  prepared  by  digesting  the  metal  in  dilute  nitric 
acid.  The  white  arsenic  of  commerce  is  derived  from  the  native  arseniurets 
of  cobalt,  being  sublimed  during  the  roasting  of  these  ores  for  the  prepara- 
tion of  zaffre,  and  it  is  purified  by  a  second  sublimation  in  iron  vessels. 

Prop. — It  is  commonly  sold  in  the  state  of  a  fine  white  powder  ;  but  when 
first  sublimed,  it  is  in  the  form  of  brittle  masses,  more  or  less  transparent, 
colourless,  of  a  vitreous  lustre,  and  conchoidal  fracture.  This  glass,  which 
may  also  be  obtained  by  fusion,  gradually  becomes  opaque  without  undergo- 
ing any  apparent  change  of  constitution,  either  with  respect  to  water  or  any 
other  substance ;  but  the  change  is  certainly  promoted  by  exposure  to  the 
atmosphere.  Its  sp.  gr.  is  3-7.  At  380°  it  is  volatilized,  yielding  vapours 
which  do  not  possess  the  odour  of  garlic,  and  which  condense  unchanged  on 
cold  surfaces.  Its  point  effusion  is  rather  higher  than  that  at  which  it  sub- 
limes; and,  therefore,  in  order  to  be  fused,  it  must  either  be  heated  under 
pressure,  or  its  temperature  be  suddenly  raised  above  380°.  Arsenious  acid 
is  dimorphous,  that  is,  susceptible  of  assuming  two  crystalline  forms  belong- 
ing to  different  systems  of  crystallization.  By  slow  sublimation  in  a  glass 
tube,  it  is  always  obtained  in  distinct  octohedral  crystals  of  adamantine 
lustre  and  perfectly  transparent.  Its  unusual  form  is  that  of  six-sided  scales 
derived  from  a  rhombic  prism,  and  was  first  lately  found  by  Wohler  among 
the  products  in  a  manufacture  of  smalt ;  the  conditions  for  enabling  it  to 
assume  this  form  are  unknown,  and  by  subliming  the  crystals,  they  crystal- 
lized in  octohedrons.  (An.  de  Ch.  et  de  Ph.  li.  201.) 

The  taste  of  arsenious  acid  is  stated  differently  by  different  persons.  It  is 
prevalently  thought  to  be  acrid ;  but  I  am  satisfied  from  personal  observa- 
tion that  it  may  be  deliberately  tasted  without  exciting  more  than  a  very 
faint  impression  of  sweetness,  and  perhaps  of  acidity.  The  acrid  taste 
ascribed  to  it  has  probably  been  confounded  with  the  local  inflammation,  by 
which  its  application,  if  of  some  continuance,  is  followed.  (Christison  on 
Poisons.)  It  reddens  vegetable  blue  colours  feebly,  an  effect  which  is  best 
shown  by  placing  the  acid  in  powder  on  moistened  litmus  paper.  It  com- 
bines with  salifiable  bases,  forming  salts  which  are  termed  arsenites. 


ARSENIC.  333 

According  to  the  experiments  of  Klaproth  and  Buchholz,  1000  parts  of 
boiling-  wafer  dissolve  77'75  of  arsenions  acid  ;  ond  the  solution,  after  having 
cooled  to  60°  F.,  contains  only  30  parts.  The  same  quantity  of  water  at  60°, 
when  mixed  with  the  acid  in  powder,  dissolves  only  2-5  parts.  Guibourt  has 
lately  observed  that  the  transparent  and  opaque  varieties  of  arsenic  differ 
in  solubility.  He  found  that  1000  parts  of  temperate  water  dissolve,  during 
36  hours,  9'6  of  the  transparent,  and  12-5  of  the  opaque  variety;  that  the 
same  quantity  of  boiling  water  dissolves  97  parts  of  the  transparent  variety, 
retaining  18  when  cold,  but  takes  up  115  of  the  opaque  variety,  and  retains 
29  on  cooling.  By  the  presence  of  organic  substances,  such  as  milk  or  tea, 
its  solubility  is  materially  impaired.  (Christison  on  Poisons.) 

When  metallic  arsenic  is  sharply  heated  with  hydrate  of  potassa,  pure  hy- 
drogen gas  is  evolved,  and  a  mass  is  left  consisting  of  arseniuret  of  potas- 
sium and  arsenite  of  potassa;  facts  which  prove  that  a  portion  of  arsenic  is 
oxidized,  arid  derives  its  oxygen  partly  from  water  and  partly  from  potassa. 
If  the  heat  is  raised  to  redness,  the  arsenious  acid  is  resolved  into  arsenic 
acid  and  metal,  the  former  remaining  as  an  arseniate,  while  the  latter  is  ex- 
pelled. Similar  phenomena  ensue  with  the  hydrates  of  soda,  baryta,  and 
lime;  except  that  with  the  two  latter  no  arsenic  acid  is  produced.  (Soubeiran 
in  An.  de  Ch.  et  de  Ph.  xliii.  410.) 

Its  eq.  994;  symb.  2As-f  3O,  As,  or  As2(X 

The  frequent  exhibition  of  arsenious  acid  as  a  poison  renders  the  detection 
of  this  compound  an  object  of  great  importance  to  medical  practitioners  as 
well  as  to  the  chemist.  In  this  as  in  all  similar  inquiries,  the  object  to  be 
held  in  view  is  the  discovery  of  a  few  decisive  characters,  by  means  of 
which  the  poison  may  be  distinguished  from  all  other  bodies  ;  and,  when 
present  but  in  small  quantity,  either  in  pure  water,  or  in  any  fluids  likely  to  be 
met  with  in  the  stomach,  may  with  certainty  be  detected.  The  attention 
should  be  fixed  on  one  or  two  tests  of  admitted  value,  and  all  others  be  set 
aside.  With  this  feeling  I  shall  indicate  the  mode  of  applying  the  four  prin- 
cipal tests,  namely,  the  ammoniaco-nitrate  of  silver,  ammoniaco-sulphate  of 
copper,  hydrosulphuric  acid,  and  hydrogen  gas. 

1.  Arsenious  acid  is  not  precipitated  by  nitrate  of  oxide  of  silver,  unless  an 
alkali  is  present  to  neutralize  the  nitric  acid.  Ammonia  is  commonly  em- 
ployed for  the  purpose  ;  but  as  arsenite  of  oxide  of  silver  is  very  soluble  in 
ammonia,  an  excess  of  the  alkali  would  retain  the  arsenite  in  solution.  To 
remedy  this  inconvenience,  Hume,  of  Long  Acre,  proposed  to  employ  the 
arnmoniacal  nitrate  of  silver,  which  is  made  by  dropping  ammonia  into  a 
rather  strong  solution  of  lunar  caustic,  till  the  oxide  of  silver  at  first  thrown 
down  is  nearly  all  dissolved.  The  liquid  thus  prepared  contains  the  precise 
quantity  of  ammonia  which  is  required  ;  and  when  mixed  with  arsenious  acid, 
two  neutral  salts  result,  the  soluble  nitrate  of  ammonia,  and  the  insoluble 
yellow  arsenite  of  oxide  of  silver.  Ammoniacal  nitrate  of  silver  likewise  di- 
minishes the  risk  of  fallacy  that  might  arise  from  the  presence  of  phosphoric 
acid.  Phosphate  of  oxide  of  silver  is  so  very  soluble  in  ammonia,  that  when 
a  neutral  phosphate  is  mixed  with  the  ammoriiacal  nitrate  of  silver,  the  result- 
ing phosphate  is  held  almost  entirely  in  solution  by  the  free  ammonia. 

This  test,  however,  even  in  its  improved  state,  is  still  liable  to  objection. 
For  when  arsenious  acid  in  small  proportion  is  mixed  with  sea  salt,  or  ani- 
mal and  vegetable  infusions,  the  arsenite  of  oxide  of  silver  either  does  not 
subside  at  all,  or  is  precipitated  in  so  impure  a  state  that  its  characteristic 
colour  cannot  be  distinguished.  Several  methods  have  been  proposed  for 
obviating  this  source  of  fallacy ;  but  Christison  has  shown,  that  this  test, 
taken  singly,  cannot  be  relied  on  in  practice. 

2.  Ammoniacal  sulphate  of  copper,  which  is  made  by  adding  ammonia  to  a 
solution  of  sulphate  of  protoxide  of  copper  until  the  precipitate  at  first  thrown 
down  is  nearly  all  redissolved,  occasions  with  arsenious  acid  a  green  pre- 
cipitate, which  has  been  long  used  as  a  pigment  under  the  name  of  Scheele*s 


334  ARSENIC. 

green.  This  test,  though  well  adapted  for  detecting  arsenious  acid  dissolved 
in  pure  water,  is  very  fallacious  when  applied  to  mixed  fluids.  Christison 
has  proved  that  ammoniacal  sulphate  of  copper  produces  in  some  animal 
and  vegetable  infusions,  containing  no  arsenic,  a  greenish  precipitate,  which 
may  be  mistaken  for  Scheele's  green;  whereas  in  other  mixed  fluids,  such 
as  tea  and  porter,  to  which  arsenic  has  been  previously  added,  it  occasions 
none  at  all,  if  the  arsenious  acid  is  in  small  quantity.  In  some  of  these 
liquids,  a  free  vegetable  acid  is  doubtless  the  solvent ;  for  arsenite  of  prot- 
oxide of  copper  is  dissolved  by  tannic  acid,  and  perhaps  by  other  vegetable 
as  well  as  some  animal  principles. 

3.  When  a  current  of  hydrosulphuric  acid  gas  is  conducted  through  a  solu- 
tion of  arsenious  acid,  the  fluid  immediately  acquires  a  yellow  colour,  and 
in  a  short  time  becomes  turbid,  owing  to  the  formation  of  orpiment,  the 
sesquisulphuret  of  arsenic.  The  precipitate  is  at  first  partially  suspended  in 
the  liquid  ;  but  as  soon  as  free  hydrosulphuric  acid  is  expelled  by  heating 
the  solution,  it  subsides  perfectly,  and  may  easily  be  collected  on  a  filter. 
One  condition,  however,  must  be  observed  in  order  to  insure  success, 
namely,  that  the  liquid  does  not  contain  a  free  alkali;  for  sesquisulphuret  of 
arsenic  is  dissolved  with  remarkable  facility  by  pure  potassa  or  ammonia. 
To  avoid  this  fallacy,  it  is  necessary  to  acidulate  the  solution  with  a  little 
acetic  or  hydrochloric  acid.  Hydrosulphuric  acid  likewise  acts  on  arsenic 
in  all  vegetable  and  animal  fluids,  if  previously  boiled,  filtered,  and  acidu- 
lated. 

But  it  does  not  necessarily  follow,  because  hydrosulphuric  acid  causes  a 
yellow  precipitate,  that  arsenic  is  present ;  since  there  are  not  less  than  four 
other  substances,  namely,  selenium,  cadmium,  tin,  and  antimony,  the  sul- 
phurets  of  which,  judging  from  their  colour  alone,  might  possibly  be  mistaken 
for  orpiment.  From  these  and  all  other  substances  whatever,  the  sesquisul- 
phuret of  arsenic  may  be  thus  distinguished. — On  drying  the  sesquisulphu- 
ret, mixing  it  with  black  flux,  and  heating  the  mixture,  contained  in  a  glass 
tube,  to  redness  by  means  of  a  spirit-lamp,  decomposition  ensues,  and 
a  metallic1  crust  of  an  iron-gray  colour  externally,  and  crystalline  on  its 
inner  surface,  is  deposited  on  the  cool  part  of  the  tube.  'This  character 
alone  is  quite  satisfactory  ;  but  it  is  easy  to  procure  additional  evidence,  by 
reconverting  the  metal  into  arsenious  acid,  so  as  to  obtain  it  in  the  form  of 
resplendent  octohedral  crystals.  This  is  done  by  holding  that  part  of  the 
tube  to  which  the  arsenic  adheres  about  three-fourths  of  an  inch  above  a 
very  small  spirit-lamp  flame,  so  that  the  metal  may  be  slowly  sublimed.  As 
it  rises  in  vapour,  it  combines  with  oxygen,  and  is  deposited  in  crystals 
within  the  tube.  The  character  of  these  crystals  with  respect  to  volatility, 
lustre,  transparency,  and  form,  is  so  exceedingly  well  marked,  that  a  prac- 
tised eye  may  safely  identify  them,  though  their  weight  should  not  exceed 
the  100th  part  of  a  grain.  This  experiment  does  not  succeed  unless  the 
tube  be  quite  clean  and  dry. 

The  only  circumstance  which  occasions  a  difficulty  in  the  preceding  pro- 
cess, is  the  presence  of  organic  substances,  which  cause  the  precipitate  to 
subside  imperfectly,  render  filtration  tedious,  and  froth  up  inconveniently 
during  the  reduction.  Hence,  if  so  abundant  as  materially  to  impede  filtra- 
tion and  prevent  the  liquid  from  becoming  clear,  they  should  be  removed 
before  hydrosulphuric  acid  is  employed.  This  is  often  sufficiently  effected 
by  acidulating  with  acetic  acid,  by  which  caseous  and  albuminous  sub- 
stances are  coagulated  ;  but  a  more  complete  separation  is  accomplished  by 
evaporating  the  solution  at  a  moderate  heat  to  dryness,  dissolving  anew  by 
boiling  successive  portions  of  distilled  water  on  the  residue,  and  then  filter- 
ing the  solution  after  it  has  cooled.  Most  of  the  organic  matters  are  thus 
rendered  insoluble.  It  is  of  course  necessary  towards  the  close  of  the  desic- 
cation to  guard  against  too  high  a  temperature;  since  otherwise  the  arsenic 
itself  might  be  expelled.  (Christison  on  Poisons,  2nd  edition,  252.) 

The  black  flux  employed  in  the  processes  for  reducing  arsenic,  is  prepared 
by  deflagrating  a  mixture  of  bitartrate  of  potassa  with  rather  less  than  half 


ARSGNIC.  335 

its  weight  of  nitre.  The  nitric  and  tartaric  acids  undergo  decomposition, 
and  the  solid  product  is  charcoal  derived  from  tartaric  acid,  and  pure  carbo- 
nate of  potassa.  As  it  contains  a  deliquescent  salt,  it  should  be  kept  in  well- 
stopped  bottles.  When  this  substance  is  employed  in  the  reduction  of  arse- 
nious  acid  or  its  salts,  the  charcoal  is  of  course  the  decomposing  agent;  but 
the  alkali  is  of  use  in  retaining  the  arsenious  acid  until  the  temperature  is 
sufficiently  high  for  its  decomposition.  With  sulphuret  of  arsenic,  on  the 
contrary,  the  alkali  is  the  active  principle,  the  potassium  of  which  unites  with 
sulphur  and  liberates  the  arsenic;  but  the  charcoal  operates  usefully  by  faci- 
litating the  decomposition  of  the  alkaline  carbonate,  The  whole  of  the 
arsenic,  however,  is  not  sublimed  ;  but  part  of  it  enters  into  union  with  po- 
tassium, and  remains  with  the  flux. 

4.  For  the  application  of  hydrogen  in  testing  for  arsenic  we  are  indebted 
to  the  ingenuity  of  Marsh.  (Edinburgh  New  Phil.  Journ.  October  1836.)  Its 
employment  is  dependent  on  the  fact,  that  whenever  hydrogen  in  the  nas- 
cent state  is  brought  into  contact  with  any  compound  of  oxygen  and  ar- 
senic, the  latter  is  instantly  decomposed,  and  water  and  a  gaseous  compound 
of  arsenic  and  hydrogen,  the  arseniuretted  hydrogen,  are  generated.  If  the 
gas  be  inflamed  as  it  escapes  into  the  air  through  a  fine  tube,  it  burns 
with  the  production  of  the  vapour  of  water  ;  while  metallic  arsenic  or  ar- 
senious acid  is  deposited,  according  as  the  supply  of  oxygen  be  more  or  less 
abundant.  Plence  if  a  piece  of  cold  window-glass  be  held  in  the  flame,  its 
surface  is  instantly  covered  with  a  thin  coating  of  metallic  arsenic  ;  but  if 
the  flarne  be  made  to  burn  in  the  centre  of  a  glass  tube  open  at  both  ex- 
tremities, the  inner  surface  of  the  latter  is  covered  in  the  course  of  half  a 
minute  with  arsenious  acid.  If  the  tube  be  held  obliquely  against  it,  both 
depositions  take  place,  and  on  bringing  the  tube  while  still  warm  to  the 
nose,  the  peculiar  odour  of  arsenic  is  readily  perceived. 

The  experiment  is  made  in  the  following  manner  : — The  suspected  sub- 
stances, if  in  the  solid  form,  such  as  bread,  must  first  be  boiled  with  a  few 
ounces  of  distilled  water,  and  the  clear  solution,  while  still  hot,  is  to  be  sepa- 
rated from  the  solid  parts  by  filtration.  The  same  process  must  be  adopted 
with  very  thick  soups,  or  the  contents  of  the  stomach ;  while  thin  soups, 
wine,  beer,  coffee,  tea,  and  similar  fluids  require  no  previous  preparation. 
The  liquid  is  then  mixed  with  a  few  ounces  of  dilute  sul- 
phuric acid,  and  introduced  into  the  apparatus  represented 
by  the  accompanying  wood-cut.  This  consists  of  two 
parts,  a  cylindrical  glass  vessel  a,  and  a  capped  bell  jar 
furnished  with  a  stop-cock  and  small  gas  burner ;  to  the 
stop-cock  is  suspended  a  string,  to  which  a  fragment  of 
zinc  c,  reaching  nearly  to  the  bottom  of  the  bell  jar,  is 
attached.  The  stop-cock  b  being  open,  when  the  liquid 
to  be  examined  is  poured  into  a  it  rises  in  the  bell  jar, 
and  so  much  must  be  used  that  the  latter  is  almost  full. 
By  the  action  of  the  dilute  acid  on  the  zinc,  hydrogen  is 
rapidly  evolved,  and,  after  permitting  a  small  quantity 
to  escape  in  order  to  ensure  the  removal  of  atmo- 
spheric air  from  the  vessel,  the  stop-cock  is  turned,  and  the 
gas  allowed  to  accumulate  in  the  bell  jar.  On  burning  it,  the  presence  of 
arsenic  is  readily  recognized  by  the  characters  above  stated,  arid  by  the  light 
blue  tint  it  communicates  to  the  flame.  The  extreme  delicacy  of  this  me- 
thod has  been  recently  amply  attested  by  Liebig  and  Mohr  in  their  valuable 
journal.  (Lieb.  Ann.  xxiii.  217.)  To  avoid  every  source  of  fallacy,  however, 
several  precautions  are  necessary  :  the  most  important  are — to  ensure  the 
perfect  purity  of  the  reagents  used,  as  arsenic  is  commonly  contained  both  in 
the  zinc  and  sulphuric  acid  of  commerce  ;  to  employ  a  fresh  piece  of  zinc 
with  each  experiment,  as  a  portion  of  the  arsenic  in  the  solution  is  deposited 
as  a  metallic  crust  on  the  zinc,  which  is  thus  rendered  impure ;  and  to  prove 
experimentally  the  purity  of  the  apparatus  before  each  experiment.  Liebig 
recommends  that  a  fragment  of  porcelain  be  held  in  the  flame  instead  of  the 


336  ARSENIC. 

window-glass ;  as  a  very  thin  film  of  metallic  arsenic  is  better  seen  on  the 
white  opaque  ground  than  on  the  transparent  glass.  He  observes,  toq,  that 
owing  to  the  rapid  evolution  of  the  gas,  other  metals,  as  for  example  iron, 
which  may  be  contained  in  the  solution,  being  carried  up  by  the  hydrogen 
and  deposited  on  the  porcelain,  may  prove  a  source  of  error  to  the  inexpe- 
rienced. For  this  reason  he  recommends  that  the  gas,  instead  of  being  burnt 
by  the  jet,  be  transmitted  through  a  fine  tube  of  difficultly  fusible  glass  :  on 
bringing  apart  of  the  glass  to  a  red  heat  by  a  spirit-lamp  flame,  the  arseniu- 
retted  hydrogen  is  decomposed  as  it  passes,  and  the  metallic  arsenic  is  de- 
posited just  beyond  the  heated  part  of  the  glass  ;  while  other  metals  are  de- 
posited in  the  hot  parts  themselves. 

It  was  hoped  that  this  test  might  prove  infallible,  even  in  the  hands  of 
inexperienced  chemists;  but,  according  to  a  recent  discovery  of  Mr.  L. 
Thompson,  antimony  combines  with  hydrogen,  forming  with  it  a  gaseous 
compound  which  is  similar  to  arseniu  retted  hydrogen  in  the  mode  of  its 
prod  action,  in  the  colour  of  its  flame  when  burnt,  and  in  the  deposition  of  a 
metallic  crust  on  a  cold  surface.  The  two  gases  may  nevertheless  be  readily 
distinguished  by  decomposing  them  by  means  of  heat  while  passing  through 
a  fine  tube,  as  was  proposed  by  Liebig  for  arseniuretted  hydrogen ;  for  al- 
though the  metallic  crusts  are  very  similar,  yet  by  attention  to  the  directions 
of  page  334,  the  crust  of  arsenic  cannot  be  mistaken  for  that  of  antimony. 
For  by  bringing  the  spirit-lamp  flame  under  the  crust  when  the  stream  of 
hydrogen  has  ceased  to  pass  along  the  tube,  if  it  be  arsenic  it  rapidly  vola- 
tilizes and  condenses  again  on  the  neighbouring  cool  parts  of  the  tube  ;  the 
antimonial  crust,  on  the  contrary,  when  thus  heated,  fuses,  runs  into  small 
globules,  and  assumes  the  appearance  of  mercury.  If  the  tube  be  now  de- 
tached from  the  vessel  in  which  the  hydrogen  is  generated,  and  the  flame  of 
the  spirit-lamp  cautiously  applied  to  the  metal,  the  arsenic  volatilizes  without 
fumes,  and  distinct  octohedral  crystals  of  arsenious  acid  are  formed  on  the 
upper  part  of  the  tube;  with  antimony,  on  the  contrary,  dense  white  fumes 
are  produced  and  an  amorphous  white  powder  is  deposited.  The  different 
characters  of  the  two  substances  may  be  carried  still  further  :  if  the  tube  be 
boiled  in  a  small  quantity  of  pure  water,  the  arsenious  acid  is  dissolved,  and 
the  first  two  tests  may  be  successfully  employed  ;  the  antimony,  on  the  con- 
trary, is  insoluble. 

Arsenic  Acid. — This  compound  is  made  by  dissolving  arsenious  acid  in 
concentrated  nitric,  mixed  with  a  little  hydrochloric  acid,  distilling  in  glass, 
till  it  acquires  the  consistence  of  syrup,  and  then  exposing  it  in  a  platinum 
crucible  for  some  time  to  a  heat  somewhat  short  of  low  redness  to  expel  the 
nitric  acid.  The  acid  thus  prepared  has  a  sour  metallic  taste,  reddens  vege- 
table blue  colours,  and  with  alkalies  forms  neutral  salts,  which  are  termed 
arseniates.  It  is  much  more  soluble  in  water  than  arsenious  acid,  dissolving 
in  five  or  six  times  its  weight  of  cold,  and  in  a  still  smaller  quantity  of  hot 
water.  It  forms  irregular  grains  when  its  solution  is  evaporated,  but  does 
not  crystallize.  If  strongly  heated,  it  fuses  into  a  glass  which  is  deliquescent. 
When  urged  by  a  very  strong  red  heat,  it  is  resolved  into  oxygen  and  arseni- 
ous acid.  It  is  an  active  poison. 

Arsenic  acid  is  decomposed  by  hydrosulpburic  acid  gas,  and  yields  a 
sulphuret  of  arsenic  very  like  orpiment  in  colour,  but  containing  a  greater 
proportional  quantity  of  sulphur.  The  soluble  arseniates,  when  mixed  with 
the  nitrates  of  lead  and  silver,  form  insoluble  arseniates,  the  former  of  which 
has  a  white,  and  the  latter  a  brick-red  colour.  They  dissolve  readily  in  dilute 
nitric  acid,  and  when  heated  with  charcoal  yield  metallic  arsenic. 

Its  eq.  is  1154;  symb.  2As-f-5O,   As,  or  As^O. 

Prolochloride  of  Arsenic. — It  is  prepared,  according  to  Dumas,  by  intro- 
ducing into  a  tubulated  retort  a  mixture  of  arsenious  acid  with  ten  times  its 
weight  of  concentrated  sulphuric  acid ;  and  after  raising  its  temperature  to 
near  212°,  fragments  of  sea-salt  are  thrown  in  by  the  tubulure.  If  the  suit 


ARSENIC.  337 

is  added  in  successive  small  portions,  scarcely  any  hydrochloric  acid  gas  is 
evolved,  and  the  pure  chloride  may  be  collectedjn  cooled  vessels.  Towards  the 
end  of  the  process,  a  little  water  frequently  passes  over  with  the  chloride  ;  but 
this  hydrated  portion  does  not  mix  with  the  anhydrous  chloride,  but  swims 
on  its  surface.  The  hydrate  may  be  decomposed,  and  a  pure  chloride  ob- 
tained, by  distilling  the  mixture  from  a  sufficient  quantity  of  concentrated 
sulphuric  acid.  Dumas  considers  this  compound  a  protochloride  of  arsenic  ; 
so  that  it  is  probably  different  from  that  obtained  by  means  of  corrosive  sub- 
limate. (Quarterly  Journal  of  Science,  N.  S.  i.  235.) 
Its  eq.  is  73-12;  symb.  As  +  CI,  or  AsCl. 

Sesquichloride  of  Arsenic. — When  arsenic  in  powder  is  thrown  into  a  jar 
full  of  dry  chlorine  gas,  it  takes  fire,  and  sesquichloride  of  arsenic  is  ge- 
nerated ;  and  the  same  compound  may  be  formed  by  distilling  a  mixture  of 
six  parts  of  corrosive  sublimate  with  one  of  arsenic.  It  is  a  colourless 
volatile  liquid,  which  fumes  strongly  on  exposure  to  the  air,  (hence  called 
fuming  liquor  of  arsenic),  and  is  resolved  by  water  into  hydrochloric  and 
arsenious  acids.  (Dr.  Davy.) 

Its  eq.  is  181-66;  symb.  2As-f  3C1,  or  AssCls. 

Periodide  of  Arsenic  is  formed  by  bringing  its  elements  into  contact,  and 
promoting  union  by  gentle  heat.  They  form  a  deep  red  compound,  which  is 
resolved  into  arsenic  and  hydriodic  acids  by  the  action  of  water.  (Plisson  in 
An.  de  Ch.  et  de  Ph.  xxxix.  226.) 

Its  eq.  is  706'9  ;  symb.  2 As  -f  51,  or  As2R 

Sesquibromide  of  Arsenic. — The  elements  of  this  compound  unite  at  the 
moment  of  contact,  with  vivid  evolution  of  heat  and  light.  Serullas  prepared 
it  by  adding  dry  arsenic  to  bromine  as  long  as  light  was  emitted,  the  former 
being  added  in  successive  small  quantities,  to  prevent  the  temperature  from 
rising  too  high.  The  bromide  is  then  distilled,  and  collected  in  a  cool  re- 
ceiver. (An.  de  Ch.  et  de  Ph.  xxxviii.  318.) 

This  compound  is  solid  at  or  below  68°,  liquefies  between  68°  and  77°, ,  and 
boils  at  428°.  As  a  liquid  it  is  transparent  and  slightly  yellow,  and  yields 
long  prisms  by  evaporation.  By  water  it  is  resolved  into  arsenious  and 
hydrobromic  acids. 

Its  eq.  is  310-6;  symb.  2As-f  3Br,  or  As2Br*. 

Protohyduret  of  Arsenic. — This  compound,  which  is  solid  and  of  a  brown 
colour,  was  discovered  by  Davy  as  well  as  Gay-Lussac  and  Thenard.  The 
former  prepared  it  by  attaching  a  piece  of  arsenic  to  the  negative  wire 
during  the  decomposition  of  water  by  galvanism  ;  and  the  French  chemists, 
by  the  action  of  water  on  an  alloy  of  potassium  and  arsenic. 
Its  eq.  is  38-7  ;  symb.  As-^H,  or  AsH. 

Arseniuretted  Hydrogen. — This  gas,  which  was  discovered  by  Scheele,  has 
been  studied  by  Proust,  Trommsdorf,  and  others,  but  especially  by  Stromeyer. 
It  is  generally  made  by  digesting  an  alloy  of  tin  and  arsenic  in  hydrochloric 
acid  ;  but  as  thus  prepared  it  is  always  mixed  with  free  hydrogen.  Sou- 
beiran  generated  it  by  fusing  arsenic  with  its  own  weight  of  granulated  zinc, 
and  decomposing  the  alloy  with  strong  hydrochloric  acid.  The  gas,  thus 
developed,  is  quite  free  from  hydrogen,  being  absorbed  without  residue  by  a 
saturated  solution  of  sulphate  of  protoxide  of  copper.  Its  sp.  gravity,  ac- 
cording to  Dumas,  is  2-695.  It  is  colourless,  and  has  a  fetid  odour  like  that 
of  garlic.  It  extinguishes  bodies  in  combustion,  but  is  itself  kindled  by 
them,  and  burns  with  a  blue  flame.  It  instantly  destroys  small  animals  that 
are  immersed  in  it,  and  is  poisonous  to  man  in  a  high  degree,  having  proved 
fatal  to  a  German  philosopher,  the  late  M.  Gehlen.  Water  absorbs  one-fifth 
of  its  volume,  and  acquires  the  odour  of  the  gas.  It  wants  altogether  the 
properties  of  an  acid. 

Arseniuretted  hydrogen  is  decomposed  by  various  agents.  It  suffers 
gradual  decomposition  when  mixed  with  atmospheric  air,  water  being  formed, 
and  metallic  arsenic,  together  with  a  little  oxide,  deposited.  With  nitric 
acid,  water  is  generated,  and  a  deposite  of  metal  takes  place,  which  is  sub- 
sequently oxidized.  Chlorine  decomposes  it  instantly  with  disengagement 

29 


338  ARSENIC. 

of  heat  and  light,  hydrochloric  acid  being  generated,  and  the  metal  set  free. 
With  iodine  it  yields  hydriodic  acid  gas  and  iodide  of  arsenic,  and  sulphur 
and  phosphorus  produce  analogous  changes.  By  its  action  on  salts  of  the 
easily  reducible  metals,  such  as  silver  and  gold,  the  metal  is  revived,  and  its 
oxygen,  uniting  with  the  elements  of  the  gas,  constitutes  arsenious  acid  and 
water.  With  salts  of  copper  the  products  are  water  and  arseniuret  of  copper ; 
and  with  several  other  metallic  salts  its  action  is  similar. 

Soubeiran  observed  that  arseniuretted  hydrogen  in  a  glass  tube  is  com- 
pletely decomposed  by  the  heat  of  a  spirit-lamp,  and  that  its  hydrogen  oc- 
cupies one  and  a  half  as  much  space  as  when  in  combination.  He  has  also 
confirmed  the  observation  of  Dumas,  that,  when  mixed  with  oxygen  and 
detonated  by  the  electric  spark,  each  volume  of  the  gas,  in  forming  water 
and  arsenious  acid,  requires  one  and  a  half  its  volume  of  oxygen  gas.  The 
oxygen,  therefore,  is  equally  divided  between  the  arsenic  and  hydrogen,  and 
arseniuretted  hydrogen  consists  of  two  eq.  of  arsenic  and  three  eq.  of  hydro- 
gen. By  volume,  it  is  composed  of  half  a  volume  of  the  vapour  of  arsenic, 
and  three  volumes  of  hydrogen,  condensed  into  two  volumes.  (An.  de  Ch. 
et  de  Ph.  xliii.  407.) 

Its  eq.  is  78-4 ;  symb.  2As-f-3H,  or  AsSR3. 

Sulphurets  of  Arsenic. — Sulphur  unites  with  arsenic  in  at  least  three  pro- 
portions, forming  compounds,  two  of  which  occur  in  the  mineral  kingdom, 
and  are  well  known  by  the  name  of  realgar  and  orpiment.  Realgar  or  the 
protosulphuret  may  be  formed  artificially  by  heating  arsenious  acid  with 
about  half  its  weight  of  sulphur,  until  the  mixture  is  brought  into  a  state  of 
perfect  fusion.  The  cooled  mass  is  crystalline,  transparent,  and  of  a  ruby- 
red  colour ;  and  may  be  sublimed  in  close  vessels  without  change. i 
Its  eq.  is  53f8;  symb.  As-|-S,  or  AsS. 

Orpiment,  or  sesquisulphuret  of  arsenic  may  be  prepared  by  fusing  toge- 
ther equal  parts  of  arsenious  acid  and  sulphur;  but  the  best  mode  of  obtain- 
ing it  quite  pure  is  by  transmitting  a  current  of  hydrosulphuric  acid  gas 
through  a  solution  of  arsenious  acid.  Orpiment  has  a  rich  yellow  colour, 
fuses  readily  when  heated,  and  becomes  crystalline  on  cooling,  and  in  close 
vessels  may  be  sublimed  without  change.  It  is  dissolved  with  great  facility 
by  the  pure  alkalies,  and  yields  colourless  solutions. 

Orpiment  is  employed  as  a  pigment,  and  is  the  colouring  principle  of  the 
paint  called  King's  yellow.  Braconnot  has  proposed  it  likewise  for  dyeing 
silk,  woollen,  or  cotton  stuffs  of  a  yellow  colour ;  the  cloth  being  soaked  in 
a  solution  of  orpiment  in  ammonia,  and  then  suspended  in  a  warm  apart- 
ment. The  alkali  evaporates,  and  leaves  the  orpiment  permanently  attached 
to  the  cloth.  (An.  de  Ch.  et  de  Ph.  xii.) 
Its  eq.  is  123-7;  symb.  2As+3S,  or  As3S*. 

The  persulphuret  of  arsenic  is  prepared  by  transmitting  hydrosulphuric 
acid  gas  through  a  moderately  strong  solution  of  arsenic  acid ;  or  by  satu- 
rating a  solution  of  arseniate  of  potassa  or  soda  with  the  same  gas,  and 
acidulating  with  hydrochloric  or  acetic  acid.  The  oxygen  of  the  acid  unites 
with  the  hydrogen  of  the  gas,  and  persulphuret  of  arsenic  subsides.  In 
colour  it  is  very  similar  to  orpiment,  is  dissolved  by  pure  alkalies,  fuses  by 
heat,  and  may  be  sublimed  in  close  vessels  without  decomposition. 
Its  eq.  is  155-9;  symb.  2As-f5S,  or  AssS*. 

The  experiments  of  Orfila  have  proved  that  the  sulphurets  of  arsenic  arc 
poisonous,  though  in  a  much  less  degree  than  arsenious  acid.  The  precipitated 
sesquisulphuret  is  more  injurious  than  native  orpiment.  The  antidote  of 
arsenious  acid  is  hydrated  sesquioxide  of  iron.  (Bunson). 


339 


SECTION   XVI. 

CHROMIUM  AND  VANADIUM. 
CHROMIUM. 

Hist. — DISCOVERED  in  the  year  1797  by  Vauquelin  in  a  beautiful  red 
mineral,  the  native  dichromate  of  oxide  of  lead.  (An.  de  Ch.  xxv.  and  Ixx.) 
It  has  since  been  detected  in  the  mineral  called  chromate  of  iron,  a  com- 
pound of  the  sesquioxides  of  chromium  and  iron,  which  occurs  abundantly 
in  several  parts  of  the  Continent,  in  America,  and  at  Unst  in  Shetland. 
(Hibbert.)  It  derives  its  name  from  ^gw^et,  colour,  owing  to  its  remarka- 
ble tendency  to  form  coloured  compounds. 

Prep.— By  exposing  the  sesquioxide  of  chromium  mixed  with  charcoal  to 
the  most  intense  heat  of  a  smith's  forge  ;  but  owing  to  its  strong  affinity  for 
oxygen,  the  reduction  is  extremely  difficult.  A  better  process,  that  of  Vau- 
quelin, is  to  mix  the  dry  chloride  into  a  paste  with  oil,  place  the  mass  in  a 
crucible  lined  with  charcoal,  lute  on  a  cover,  and  to  expose  it  for  an  hour  to 
a  very  strong  heat.  Liebig  has  obtained  the  metal  in  the  form  of  a  black 
powder,  which  acquires  the  metallic  aspect  from  pressure,  by  heating  the 
compound  of  terchloride  of  chromium  and  ammonia  to  redness,  and  trans- 
mitting over  it  dry  ammoniacal  gas ;  the  chlorine  unites  with  the  hydrogen 
of  the  ammonia,  hydrochloric  acid  and  nitrogen  gases  are  evolved,  and  pul- 
verulent chromium  remains.  A  still  more  convenient  process  is  to  decom- 
pose the  sesquichloride  by  heat  and  ammoniacal  gas,  in  which  case  the 
metal  has  a  chocolate-brown  colour.  In  this  finely  divided  state  it  takes  fire 
when  heated  in  the  open  air.  (An.  dc  Ch.  et  de  Ph.  xlviii.  297.) 

Prop. — As  obtained  by  Vauquelin's  process  it  has  a  white  colour  with  a 
shade  of  yellow,  and  a  distinct  metallic  lustre.  It  is  brittle,  very  infusible, 
and  with  difficulty  attacked  by  acids,  even  by  the  nitro-hydrochloric.  Its  sp. 
gr.  has  been  stated  at  5-9 ;  but  Thomson  found  it  a  little  above  5.  When 
fused  with  nitre  it  is  oxidized  and  converted  into  chromic  acid.  With  a 
smaller  quantity  of  oxygen  it  forms  the  green  or  sesquioxide. 

From  the  experiments  of  Berzelius  and  Thomson  the  eq.  of  chromic  acid 
may  be  estimated  at  52]  and  as  the  salts  of  this  acid  are  isomorphous  with 
the  sulphates  and  seleniates,  it  is  inferred  that  chromic  acid  has  the  same 
atomic  constitution  as  sulphuric  and  selenic  acids,  or  consists  of  one  eq.  of 
chromium  and  three  eq.  of  oxygen.  Berzelius  has  moreover  remarked  that 
when  the  acid  is  converted  into  the  sesquioxide  of  chromium,  it  parts  with 
exactly  half  of  its  oxygen.  Hence,  24  deducted  from  52,  leaves  28  as  the 
eq.  of  chromium.  Its  symb.  is  Cr.  The  composition  of  its  compounds 
described  in  this  section  is  as  follows : — 

Chromium.  Equiv.  Formulae. 

Sesquioxide      56  2  eq.-f  Oxygen     24      3  eq.=  80       2Cr  4.  3O  or  Cr^O3. 
Chromic  acid  28  1  eq.-j.do.  24       3  eq.=  52       Cr-f-3O  or  CrOs. 

Sesquichloride 56  2  eq.-f  Chlorine  106-26  3  eq.=162-26  2Cr -f  3C1  or Cr*C\3 
Sesquifluoride  56  2  eq.  .j- Fluorine  56-04  3  eq.=112-04  2Cr  -f  3F  or  Cr*F  *. 
Perfluoride  Composition  unknown. 

Sesquisulph't  56  2  eq.-L  Sulphur  48-3  3  eq.=  104-3  2Cr+3S  or  Cr*Ss. 
Protophosph't  28  1  eq.  +  Phosph.  15-7  1  eq.=  43-7  Cr+P  or  Cr  P. 

104          +CrCls         134-26        =238-26  CrCl3-f-2CrQ3 


340  CHROMIUM. 

Sesquioxide  of  Chromium. — Prep. — This,  the  only  known  oxide  of  chro- 
mium, is  prepared  by  dissolving  chromate  of  potassa  in  water,  and  mixing 
it  with  a  solution  of  nitrate  of  protoxide  of  mercury,  when  an  orange- 
coloured  precipitate,  chromate  of  that  oxide,  subsides.  On  heating  this  salt 
to  redness  in  an  earthen  crucible,  the  mercury  is  dissipated  in  vapour,  and 
the  chromic  acid  is  resolved  into  oxygen  and  sesquioxide  of  chromium.  It 
may  also  be  obtained  in  small  tabular  crystals  by  exposing  the  bichromate 
of  potassa  to  a  strong  red  heat;  one  eq.  of  chromic  acid  loses  oxygen,  while 
the  other  forms  a  neutral  salt  with  the  potassa.  The  latter  is  readily  re- 
moved from  the  insoluble  oxide  by  boiling  water.  Wohler  has  succeeded  in 
in  obtaining  this  oxide  in  fine  crystals  by  conducting  the  vapour  of  the  oxy- 
chloride  of  chromium  (formerly  terchloride  of  chromium)  through  a  red-hot 
glass  tube;  when  it  is  decomposed,  sesquioxide  of  chromium  is  deposited  in 
fine  crystals,  and  a  mixture  of  oxygen  and  chlorine  gases  is  evolved. 

Prop. — As  obtained  by  either  of  the  first  processes,  it  is  a  green  powder; 
but  the  crystals  of  Wohler  are  black  and  possess  a  strong  metallic  lustre, 
and  are  identical  in  form  and  very  similar  in  appearance  to  specular  iron 
ore :  it  is  as  hard  as  corundum,  and  has  a  sp.  gr.  of  5-21  ;  its  powder  has 
the  common  green  colour  of  sesquioxide  of  chromium.  (Pog.  Ann.  xxxiii.  341.) 

It  is  insoluble  in  water,  and  after  being  strongly  heated,  resists  the  action 
of  the  most  powerful  acids.  Deflagrated  with  nitre,  or  fused  with  chlorate 
of  potassa,  it  is  oxidized  to  its  maximum,  and  is  thus  reconverted  into  chro- 
mic acid.  Fused  with  borax  or  vitreous  substances,  it  communicates  to 
them  a  beautiful  green  colour,  a  property  which  affords  an  excellent  test  of 
its  presence,  and  renders  it  exceedingly  useful  in  the  arts.  _  The  emerald^ 
owes  its  colour  to  the  presence  of  this  oxide. 

Sesquioxide  of  chromium  is  a  salifiable  base,  and  its  salts,  which  have  a 
green  colour,  may  be  easily  prepared  in  the  following  manner.  To  a  boil- 
ing solution  of  chromate  of  potassa  in  water,  equal  measures  of  strong  hy- 
drochloric acid  and  alcohol  are  added  in  successive  small  portions,  until  the 
red  tint  of  the  chromic  acid  disappears  entirely,  and  the  liquid  acquires  a 
pure  green  colour.  On  pouring  an  excess  of  pure  ammonia  into  this  solu- 
tion, a  pale  green  bulky  hydrate  subsides,  which  consists  of  one  eq.  of  the 
oxide,  and  twenty-six  eq.  of  water.  (Thomson.)  The  oxide,  in  this  state,  is 
readily  dissolved  by  acids.  On  expelling  the  water  by  heat,  the  sudden  ap- 
proximation of  the  particles,  which  abruptly  occurs  at  a  certain  temperature, 
causes  such  intense  evolution  of  heat  that  the  whole  mass  becomes  vividly 
incandescent. 

The  anhydrous  sesquioxide  is  formed  when  bichromate  of  potassa  is 
briskly  boiled  with  sugar  and  a  little  hydrochloric  acid.  At  first  a  brown 
matter  falls,  consisting  of  the  acid  and  sesquioxide  of  chromium  ;  but  subse- 
quently the  sesquioxide  appears  in  the  form  of  a  finely  divided  powder.  If 
the  bichromate  and  sugar  are  employed  without  hydrochloric  acid,  the 
brown  matter  is  the  only  solid  product,  and  on  boiling  this  compound  with 
a  little  carbonate  of  potassa,  a  greenish-blue  carbonate  of  chromium,  of  a 
very  fine  colour,  is  obtained.  For  this  mode  of  preparation  I  am  indebted  to 
my  late  pupil,  Mr.  Thomas  Thomson,  of  Clitheroe,  near  Manchester. 

Its  eq.  is  80;  symb.  20+30,  Cr,  or  Cr2O\ 

Chromic  Acid. — Prep — This  acid  is  best  prepared  by  transmitting  the 
gaseous  fluoride  of  chromium  into  water  contained  in  a  vessel  of  silver  or 
platinum,  when  by  mutual  decomposition  of  the  gas  and  the  water,  hydro- 
fluoric and  chromic  acids  are  generated  :  the  former  is  then  expelled  by 
evaporating  the  solution  to  dryness,  and  the  latter  in  a  pure  state  remains. 
If  the  gas  is  conducted  into  a  silver  vessel  which  is  only  moistened  with 
water,  and  the  aperture  of  which  is  closed  by  a  piece  of  moist  paper,  the 
chromic  acid  is  obtained  in  the  form  of  acicular  crystals  of  a  cinnabar-red 
colour,  which  are  so  voluminous  and  abundant  as  to  fill  the  interior  of  the 
vessel.  Another  method  of  preparing  chromic  acid  has  been  suggested  by 


CHROMIUM.  341 

Arnold  Maus,  which  consists  in  decomposing  a  hot  concentrated  solution  of 
bichromate  of  potassa  by  silicated  hydrofluoric  acid.  The  chromic  acid, 
after  being  separated  from  the  sparingly  soluble  fluoride  of  silicon  and  po- 
tassium, is  evaporated  to  dryness  in  a  platinum  capsule,  and  then  redissolved 
in  the  smallest  possible  quantity  of  water.  By  this  means  the  last  portions 
of  the  double  salt  are  rendered  insoluble,  and  the  pure  chromic  acid  may  be 
separated  by  decantation.  The  acid  must  not  be  filtered  in  this  concen- 
trated state,  as  it  then  corrodes  paper  like  sulphuric  acid,  and  is  converted 
into  chromate  of  the  sesquioxide  of  chromium.  When  it  is  wished  to  pre- 
pare a  large  quantity  of  chromic  acid  by  this  process,  porcelain  vessels  may 
be  safely  employed  in  the  first  part  of  the  operation,  provided  care  is  taken 
to  add  a  quantity  of  silicated  hydrofluoric  acid  not  quite  sufficient  for 
precipitating  the  whole  of  the  potassa.  (Edinburgh  Journal  of  Science, 
viii.  175.) 

It  was  formerly  prepared  by  digesting  chromate  of  baryta  or  protoxide  of 
lead  in  dilute  sulphuric  acid,  the  quantity  of  the  latter  being  regulated  with 
the  view  of  decomposing  the  chromate  without  being  in  excess.  A  dark 
ruby-red  solution  is  thus  obtained,  which  by  evaporation  yields  irregular 
crystals,  and  was  supposed  to  contain  pure  chromic  acid ;  but  Gay-Lussac 
showed  that  the  acid  when  thus  procured  is  never  pure,  being  intimately 
combined  with  sulphuric  acid.  On  endeavouring  to  expel  the  latter  by  heat, 
the  chromic  acid  itself  yields  oxygen,  and  is  more  or  less  completely  con- 
verted into  sulphate  of  the  sesquioxide. 

Prop. — Pure  dry  chromic  acid  is  black  while  warm,  and  of  a  dark  red 
colour  when  cold.  It  is  very  soluble  in  water,  rendering  it  red  or  yellow 
according  to  the  degree  of  dilution.  When  the  solution  is  concentrated  by 
heat  and  allowed  to  cool,  it  deposites  red  crystals,  which  deliquesce  readily 
in  the  air.  In  alcohol  it  is  also  soluble,  but  the  action  of  heat  or  light  causes 
its  conversion  into  the  sesquioxide.  Its  taste  is  sour,  and  with  alkalies  it  acts 
as  a  strong  acid.  It  is  converted  into  the  sesquioxide,  with  evolution  of 
oxygen,  by  exposure  to  a  strong  heat.  It  yields  a  chloride  when  boiled 
with  hydrochloric  acid  and  alcohol,  and  the  direct  solar  rays  have  a  similar 
effect  when  hydrochloric  acid  is  present :  the  mutual  action  sets  chlorine 
free,  and  hence  the  solution  acquires  the  property  of  dissolving  gold.  With 
sulphurous  acid  it  forms  a  sulphate  of  the  sesquioxide ;  and  it  is  more  or 
less  completely  converted  into  the  oxide  by  being  boiled  with  sugar,  starch, 
or  various  other  organic  principles.  It  destroys  the  colour  of  indigo,  and  of 
most  vegetable  and  animal  colouring  matters;  a  property  advantageously 
employed  in  calico-printing,  and  which  manifestly  depends  on  the  facility 
with  which  it  is  deprived  of  oxygen. 

Chromic  acid  is  characterized  by  its  colour,  and  by  forming  coloured  salts 
with  alkaline  bases.  The  most  important  of  these  salts  is  chromate  of  prot- 
oxide of  lead,  which  is  found  native  in  small  quantity,  and  is  easily  prepared 
by  mixing  chromate  of  potassa  with  a  soluble  salt  of  lead.  It  is  of  a  rich 
yellow  colour,  and  is  employed  in  the  arts  of  painting  and  dyeing  to  great 
extent. 

When  sulphurous  acid  gas  is  transmitted  into  a  solution  of  chromate  or 
bichromate  of  potassa,  a  brown  precipitate  subsides,  which  was  long  regarded 
as  a  distinct  oxide  of  chromium  ;  but  Thomson  has  proved  that  it  is  the 
green  or  sesquioxide  combined  with  a  little  chromic  acid.  The  acid  may  in 
a  great  measure  be  washed  away  by  means  of  water,  and  by  ammonia  it  is 
entirely  removed ;  but  the  best  mode  of  separating  it,  is  to  dissolve  the 
brown  matter  with  hydrochloric  acid,  and  then  precipitate  the  sesquioxide' by 
ammonia.  The  brown  compound  may  be  formed  by  boiling  a  solution  of 
bichromate  of  potassa  with  alcohol ;  and  it  is  also  rapidly  generated,  when 
bichromate  of  potassa  is  gently  boiled  with  sugar  and  a  very  little  hydror 
chloric  acid. 

Its  eq.  is  52  ;  symb.  Cr-J-3O,  Cr,  or  CrO. 

Sesquichloride  of  Chromium. — It  is  prepared  by  transmitting  dry  chlorine 
gas  over  a  mixture  of  sesquioxide  of  chromium'and  charcoal,  heated  to  redness 

29* 


342  CHROMIUM. 

in  a  tube  of  porcelain,  when  the  sesquichloride  gradually  collects  as  a  crys- 
talline sublimate  of  a  peach-purple  colour,  which  in  thin  layers  is  transparent, 
but  in  thicker  masses  is  opaque.  Another  method  is  to  evaporate  the  green 
solution  of  this  chloride  gently  to  dryness  at  a  temperaiure  of  212°,  when  a 
green  powder  remains,  consisting  of  one  eq.  of  the  sesquichloride  and  three 
eq.  of  water  (Cr3Cl3_f-3H),  these  elements  being  exactly  in  the  ratio  to  form 
sesquioxide  of  chromium  and  hydrochloric  acid.  On  raising  the  temperature 
above  212°,  no  water  is  lost  until  it  reaches  400°  :  the  powder  then  begins  to 
swell  up  from  the  escape  of  water,  the  colour  changes  from  green  to  the  red 
of  peach-blossoms,  and  pure  sesquichloride  remains.  This  part  of  the  pro- 
cess should  be  conducted  in  a  tube  from  which  air  is  excluded  by  a  current 
of  dry  carbonic  acid  gas.  These  phenomena  are  quoted  by  Liebig  as  fa- 
vouring the  notion  that  the  green  solution  and  powder  are  a  hydrochlorate  of 
an  oxide,  and  not  a  chloride  with  water. 

The  sesquichloride  of  chromium  dissolves  slowly,  forming  a  deep  green 
solution.  The  same  may  be  prepared  by  directly  dissolving  the  hydrated 
sesquioxide  in  hydrochloric  acid  ;  or  by  digesting  chromate  of  protoxide  of 
lead  in  ^strong  hydrochloric  acid,  adding  a  little  alcohol  from  time  to  time  to 
promote  the  deoxidation  of  the  chromic  acid,  and  then  separating  the  re- 
sulting chloride  of  chromium  from  that  of  lead  by  strong  alcohol,  which, 
together  with  any  excess  of  hydrochloric  acid,  is  ultimately  expelled  by 
evaporating  to  dryness.  Traces  of  lead  which  may  have  been  dissolved  are 
easily  precipitated  by  hydrosulphuric  acid. 

Its  eq.  is  162-2G;  syrnb.  2Cr  +  3Cl,  or  Cr*C\3- 

Sesquifluoride  of  Chromium  is  formed  by  dissolving  the  sesquioxide  in 
hydrofluoric  acid,  and  evaporating  the  solution  to  dryness,  when  the  sesqui- 
fluoride  remains  as  a  green  crystalline  residue,  which  is  soluble  in  water. 
Its  eq.  is  112-04  ;  symb.  2Cr-f  3F,  or  Cr^X 

Perfluoride  of  Chromium. — Discovered  by  Unverdorben  in  1825  (Ed. 
Journ.  of  Science,  iv.  129).  When  a  mixture  of  3  parts  of  fluor  spar  and  4 
of  chromate  of  protoxide  of  lead  is  distilled  with  5  parts  of  fuming  or  even 
common  sulphuric  acid  in  a  leaden  or  silver  retort,  a  red-coloured  gas  is  dis- 
engaged, which  acts  rapidly  upon  glass,  with  deposition  of  chromic  acid  and 
formation  of  fluosilicic  acid  gas.  It  is  decomposed  by  water,  and  the  solu- 
tion is  found  to  contain  a  mixture  of  hydrofluoric  and  chromic  acids.  The 
watery  vapour  of  the  atmosphere  effects  its  decomposition ;  so  that  when 
mixed  with  air,  red  fumes  appear,  owing  to  the  separation  of  minute  crystals 
of  chromic  acid. 

The  red  colour  of  perfluoride  of  chromium  naturally  excites  the  suspicion 
that  the  gas  itself  may  consist,  not  of  fluoride  of  chromium,  but  of  hydroflu- 
oric and  chromic  acids ;  and  its  production  by  means  of  hydrous  sulphuric 
acid  is  consistent  with  this  idea.  But  since  the  gas  may  also  be  formed  from 
fluor  spar,  chromate  of  protoxide  of  lead,  and  anhydrous  sulphuric  acid,  it  is 
clear  that  this  view  is  inadmissible.  It  was  formerly  considered  to  be  com- 
posed of  one  eq.  of  chromium  and  three  eq.  of  fluorine,  and  was  hence  de- 
scribed as  the  terfluoride.  H.  Rose  has  shown,  however,  that  the  equivalents 
of  its  elements  approximate  more  closely  to  the  ratio  of  one  to  five  rather 
than  one  to  three ;  but  its  true  constitution  is  not  yet  satisfactorily  deter- 
mined. It  is  perhaps  CrF*. 

Sesquisulphuret  of  Chromium  may  be  formed  by  transmitting  the  vapour 
of  bisulphuret  of  carbon  over  sesquioxide  of  chromium  at  a  white  heat;  by 
heating  in  close  vessels  an  intimate  mixture  of  sulphur  and  the  hydrated 
sesquioxide  ;  by  fusing  the  sesquioxide  with  a  persulphuret  of  potassium,  and 
dissolving  the  soluble  parts  in  water ;  or  by  transmitting  hydrosulphuric  acid 
gas  aided  by  heat  over  the  sesquichJoride  of  chromium.  It  cannot  be  pre- 
pared in  the  moist  way.  It  is  of  a  dark  gray  colour,  and  acquires  metallic 
lustre  by  friction  in  a  mortar.  It  is  readily  oxidized  when  heated  in  the 
open  air,  and  is  dissolved  by  nitric  or  nitro-hydrochloric  acid» 

Its  eq.  is  104-3  ;  symb.  3Cr+3S, 


VANADIUM.  343 

Proiophosphuret  of  Chromium. — Rose  prepared  this  compound  by  acting 
on  the  sesquichloride  of  chromium  by  phosphuretted  hydrogen  gas  at  a  red 
heat.  By  mutual  interchange  of  elements, 

1  eq.  sesquichloride,  2Cr-f-3Cl,  and  1  eq.  phosph.  hyd.,  3H+2P, 

yield 
2  eq.  phosphuret,  2(Cr+P),  and  3  eq.  hydrochloric  acid,  3(H-f-Cl). 

This  phosphuret  is  black,  insoluble  in  hydrochloric  acid,  feebly  attacked  by 
nitric  and  nitro-hydrochloric  acid,  and  burns  before  the  blowpipe  with  a 
flame  of  phosphorus. 

Its  eq.  is  43-7  ;  syrnb.  Cr+P,  or  CrP. 

Another  phosphuret  of  a  gray  colour  may  be  formed  by  exposing  the 
phosphate  of  sesquioxide  of  chromium  to  a  strong  heat  in  a  covered  crucible 
lined  with  charcoal.  Its  composition  is  unknown. 

Oxychloride  of  Chromium. — Hist. — Discovered  by  Unverdorben  at  the 
same  time  as  the  perfluoride  of  chromium  :  it  was  long  considered  and  de- 
scribed as  the  terchloride,  until  Rose  pointed  out  its  real  constitution.  (Pog. 
An.  xxvii.  565.)  • 

Prep. — By  the  action  of  fuming  sulphuric  acid  on  a  mixture  of  about  equal 
weights  of  chromate  of  protoxide  of  lead  and  chloride  of  sodium.  Wohler 
recommends  the  following  process  :  10  parts  of  chloride  of  sodium  are  fused 
in  a  common  crucible  with  16-9  parts  of  the  neutral  chromate  of  potassa,  the 
fused  salts  are  thrown  upon  a  clean  stone,  and  the  mass  when  cold  is  broken 
into  coarse  fragmentvS.  These  are  to  be  introduced  into  a  capacious  tubulated 
retort,  to  which  a  receiver  kept  cold  by  moistened  paper  is  adapted.  Twelve 
parts  of  fuming  sulphuric  acid  are  then  added  to  the  fused  salts,  when  an 
energetic  action  commences,  and  in  a  few  minutes  the  oxychloride  is  formed, 
and  distilled  over  without  the  application  of  external  heat.  (Pog.  An.  xxxiii. 
343.) 

Prop. — It  is  a  heavy  red  liquid,  exceedingly  volatile,  yielding  abundant 
red  vapours  when  exposed  to  the  air.  By  water  it  is  instantly  decomposed 
into  hydrochloric  and  chromic  acids.  Its  vapour  is  decomposed  by  a  red 
heat  into  sesquioxide  of  chromium,  oxygen,  and  chlorine,  as  observed  by 
Wohler,  who  has  thus  confirmed  the  composition  of  the  oxychloride  as  stated 
by  Rose.  The  latter  chemist  found  it  was  composed  of  two  eq.  of  chromic 
acid  and  one  eq.  of  the  terchloride  j  and  the  former,  that  two  eq.  of  the  oxy- 
chloride produced  three  eq.  of  the  sesquioxide  of  chromium,  three  eq.  of  oxy* 
gen,  and  six  eq.  of  chlorine.  In  symbols, 

C  3Cr»O\ 

2(CrCl»+2CrO»)        yield     J  3O 
<6C1. 
Its  eq.  is  238-26  ;  symb.  CrCls+SCrOs. 

VANADIUM. 

Hist. — Vanadium,  so  called  from  Vanadis,  the  name  of  a  Scandinavian 
deity,  was  discovered  in  the  year  1830  by  SefstrOm,  of  Fahlun,  in  iron  pre- 
pared from  the  iron-ore  of  Taberg  in  Sweden.  The  state  in  which  it  occurs 
in  the  ore  is  unknown  ;  but  SefstrOm  separated  it  from  the  iron  by  dissolving 
the  latter  in  hydrochloric  acid,  when  a  black  powder  came  into  view  con- 
taining a  small  quantity  of  vanadium,  together  with  iron,  copper,  cobalt, 
silica,  alumina,  and  lime.  He  afterwards  found  a  more  abundant  source  in 
the  slag  or  cinder  formed  during  the  conversion  of  the  cast  iron  of  Taberg 
into  malleable  iron.  Soon  after  SefstrOm's  discovery,  the  same  metal  was 
found  by  Johnston,  of  Durham,  in  a  mineral  from  Wanlockhead  in  Scotland, 
where  it  occurs  as  a  vanadiate  of  protoxide  of  lead.  A  similar  mineral, 
found  at  Zimapan  in  Mexico,  was  examined  in  the  year  1801  by  Professor 
del  Rio,  who,  in  the  belief  of  having  discovered  a  new  metal,  gave  it  the  name 
of  erythronium,  apparently  from  the  red  colour  of  its  acid ;  but  as  Collet 


344  VANADIUM. 

Descotils,  on  being-  appealed  to,  declared  the  mineral  to  be  chromate  of  lead, 
del  Rio  abandoned  his  own  opinion  in  deference  to  a  higher  authority.  Thus 
have  three  persons  noticed  the  existence  of  vanadium,  without  the  knowledge 
of  each  other's  labours ;  but  the  merit  of  being-  the  first  discoverer  is  fairly 
due  to  Sefstrttm.* 

Prep. — From  the  slag  above  mentioned  vanadic  acid  may  be  obtained  by 
the  following  process,  contrived  by  SefstrOm  and  improved  by  Bcrzelius : — 
The  slag  in  fine  powder,  mixed  with  its  own  weight  of  nitre  and  twice  its 
weight  of  carbonate  of  potassa,  is  strongly  ignited  for  the  space  of  one  hour. 
The  soluble  parts  are  then  removed  by  boiling  water,  and  the  solution,  after 
being  filtered  and  neutralized  with  colourless  nitric  acid,  is  precipitated  by 
chloride  of  barium  or  acetate  of  lead.  The  precipitate,  which  consists  of 
vanadiate  and  phosphate  of  baryta  or  protoxide  of  lead,  zirconia,  alumina,  and 
silicic  acid,  is  decomposed,  while  still  moist,  by  digestion  with  strong  sul- 
phuric acid  ;  to  the  deep-red  solution,  alcohol  is  then  added,  when  by  con- 
tinued digestion  ether  is  disengaged,  and  all  the  vanadic  acid  converted  into 
the  salifiable  oxide,  the  solutions  of  which  are  blue  ; — a  change  effected  in 
order  the  more  completely  to  remove  the  vanadic  acid  from  the  insoluble 
matters.  The  blue  liquid  is  then  evaporated ;  and  when  it  acquires  a  syrupy 
consistence,  it  is  mixed  in  a  platinum  crucible  with  a  little  hydrofluoric  acid, 
and  sharply  heated  in  an  open  fire.  By  this  means  the  silicic  acid,  which 
can  only  be  got  rid  of  in  this  way,  is  converted  into  the  gaseous  fluoride  of 
silicon,  the  sulphuric  acid  expelled,  and  the  oxide  reconverted  into  the  acid 
of  vanadium. 

The  vanadic  acid  still  contains  phosphoric  acid,  alumina,  and  zirconia. 
For  its  further  purification  it  is  fused  with  nitre  added  in  successive  small 
portions,  until,  on  cooling  a  small  quantity,  the  red  tint  is  found  to  have  dis- 
appeared. In  this  process  the  acid  of  the  nitre  is  displaced  by  the  phosphoric 
and  vanadic  acids,  the  object  being  to  cause  those  acids  to  unite  with  potassa 
without  employing  an  excess  of  nitre.  The  vanadiute  and  phosphate  of  po- 
tassa are  then  taken  up  by  as  small  a  quantity  of  water  as  will  suffice,  and 
into  the  filtered  liquid  a  piece  of  sal  ammoniac,  larger  than  can  be  dissolved 
by  it,  is  introduced  :  as  it  dissolves,  vanadiate  of  ammonia,  insoluble  in  a 
saturated  solution  of  sal  ammoniac,  subsides  as  a  white  powder,  leaving  the 
phosphoric  acid  in  the  liquid.  The  vanadiate  of  ammonia  should  be  first 
washed  with  a  solution  of  sal  ammoniac,  and  then  with  alcohol  of  sp.  ST. 
0-86. 

By  heating  this  salt  in  an  open  platinum  crucible,  vanadic  acid  is  obtained ; 
but  the  temperature  ought  to  be  kept  below  that  of  redness,  and  the  mass  be 
well  stirred  until  it  acquires  a  dark  red  colour.  Heated  in  close  vessels  the 
vanadiate  of  ammonia  is  converted  principally  into  the  salifiable  oxide ; 
though  some  of  the  protoxide  and  acid  are  mixed  with  it.  With  the  zirconia 
and  alumina,  left  by  the  water  after  fusion  with  nitre,  some  vanadium  re- 
mains: it  may  be  extracted  by  fusion  with  sulphur  and  carbonate  of  potassn, 
when  a  double  sulphuret  of  vanadium  and  potassium  is  generated,  which  is 
soluble  in  water.  On  adding  sulphuric  acid  to  the  solution,  sulphuret  of 
vanadium  is  precipitated. 

The  preparation  of  vanadium  from  the  native  vanadiate  of  lead  is  much  less 
complicated  than  the  process  above  described.  It  suffices  to  dissolve  the  ore, 
as  Johnston  advises,  in  nitric  acid,  and  to  precipitate  the  lead  by  hydrosul- 
phuric  acid,  which  also  throws  down  any  arsenic  that  may  be  present.  As 
vanadic  acid  is  deoxidized  by  hydrosulphuric  acid,  a  blue  solution  is  formed  ; 
but  by  evaporating  to  dryness  the  acid  is  reproduced.  The  residue  is  then 
dissolved  by  a  solution  of  ammonia,  and  the  vanadiate  of  ammonia  pre- 
cipitated as  before  by  a  piece  of  sal  ammoniac.  The  vanadic  acid  is  thus 


*  Phil.  Mag.  and  Annals,  x.  321.    An.  de  Ch,  et  de  Ph.  xlvii.  337.    Brews, 
ter's  Journal,  v.  318,  N.  S.    Poggendorff's  Annalen,  xxii.  1. 


VANADIUM.  345 

separated  from  arsenic,  phosphoric,  and  hydrochloric  acids,  with  which,  in 
the  ore  of  Wanlockhead,  it  is  generally  associated. 

The  attempts  of  Berzelius  to  reduce  vanadic  acid  to  the  metallic  state  by 
the  agency  of  hydrogen  or  charcoal  at  high  temperatures  proved  unsuccess- 
ful, as  the"  protoxide  alone  was  obtained.  He  procured  the  metal,  however, 
in  the  form  of  a  heavy  black  powder,  by  placing  fragments  of  fused  vanadic 
acid  and  potassium  of  equal  size,  in  alternate  layers,  in  a  porcelain  crucible, 
the  potassium  being  in  the  largest  proportion  :  a  cover  was  then  luted  on, 
and  heat  applied  by  means  of  a  spirit-lamp.  The  reduction  took  place  sud- 
denly and  with  violence ;  and  when  the  mass  had  cooled,  the  potassa  and  re- 
dundant potassium  were  separated  by  water.  But  Berzelius  succeeded  better 
by  a  process  similar  to  that  of  H.  Rose  for  procuring  metallic  titanium. 
The  liquid  chloride  of  vanadium  is  introduced  into  a  glass  bulb  blown  in  a 
barometer  tube,  and  through  it  is  transmitted  dry  amrnoniacal  gas  until  a 
white  saline  mass  is  produced,  during  the  formation  of  which  the  gas  is  ra- 
pidly absorbed,  and  heat  disengaged.  A  spirit-lamp  flame  is  then  applied, 
which  expelsja  quantity  of  hydrochlorate  of  ammonia,  and  metallic  vanadium 
is  left,  adhering  to  the  interior  of  the  bulb.  The  production  of  hydrochloric 
acid  is  obviously  owing  to  chlorine  leaving  the  vanadium,  and  uniting  with 
the  hydrogen  of  part  of  the  ammonia. 

Prop. — The  pulverulent  vanadium,  produced  by  means  of  potassium,  has 
but  a  little  of  the  tenacity  and  appearance  of  a  metal,  though  under  strong 
pressure  it  assumes  a  lustre  like  that  of  graphite.  Heated  in  the  open  air  to 
commencing  redness  it  takes  fire,  and  is  converted  into  the  black  protoxide. 
It  conducts  electricity,  however,  and  is  strongly  electro-negative  in  relation 
to  zinc.  As  procured  by  Rose's  process,  the  vanadium  has  a  strong  metallic 
lustre  and  a  white  colour  considerably  resembling  silver,  but  still  more  like 
molybdenum.  It  is  so  extremely  brittle  that  it  cannot  be  removed  from  the 
glass  bulb  without  falling  into  powder.  It  is  not  oxidized  either  by  air  or 
water ;  although  by  continued  exposure  to  the  air  its  lustre  gradually  grows 
weaker,  and  it  acquires  a  reddish  tint.  It  is  not  dissolved  by  boiling  sul- 
phuric, hydrochloric,  or  hydrofluoric  acid;  but  by  nitric  and  nitro-hydro- 
chloric  acid  it  is  attacked,  and  the  solution  has  a  beautiful  dark  blue  colour. 
It  is  not  oxidized  by  being  boiled  with  caustic  potassa,  nor  by  carbonated 
alkalies  at  a  red  heat. 

The  eq.  of  vanadium,  according  to  the  analysis  of  its  oxides  by  Berzelius, 
is  68-5 ;  its  symb.  is  V  :  and  its  compounds  described  in  this  section  are  thus 
coustituted  : — 

Vanadium.  Equiv.       Formulae. 

Protoxide         68-5  1  eq.+Oxygen         8       1  eq.=   76-5  V+OorVO. 

Binoxide          68-5  1  eq.+do.  16       2  eq.=  84-5  V+2OorVCP. 

Vanadic  acid  68-5  1  eq.+do.  24       3  eq.=  92.5  V+3O  or  VO. 

Bichloride        68-5  1  eq.-j-Chlorine     70-84  2  eq.=139-34  V+2C1  or  VCla. 

Terchloride     68-5.  1  eq.-j-do.  106-26  3  eq.=174-76  V-J-3C1  or  VCF. 

Bibromide       68-5  1  eq.-f  Bromine  156-8    2  eq.  =225-3  V4-2Br  or  VBr*. 

Bisulphuret     68-5  1  eq.-j- Sulphur     32-2    2  eq.=  100-7  V4-2SorVS3. 

Tersulphuret  68-5  1  eq.+do.  48-3    3  eq.==116-8  V+3S  or  VSs. 

Protoxide. — This  compound  is  readily  formed  from  vanadic  acid  by  the 
combined  agency  of  heat,  and  charcoal  or  hydrogen  gas.  By  means  of  the 
latter  Berzelius  found  that  the  reduction  is  effected  as  perfectly  at  a  tempe- 
rature short  of  ignition,  as  at  the  strongest  heat  of  a  wind  furnace.  When 
prepared  from  fused  vanadic  acid,  the  protoxide  retains  the  crystalline  struc- 
ture of  the  acid,  and  has  a  black  colour  and  a  semi-metallic  lustre;  but  it  is 
easily  broken  down  into  a  fine  black  powder.  When  rendered  coherent  by 
compression,  it  possesses  a  property  very  unusual  in  oxides,  that  of  con- 
ducting electricity,  and,  in  relation  to  zinc,  of  being  as  strongly  electro- 
negative as  silver  or  copper, 

It  is  very  infusible.    When  heated  in  open  vessels  it  takes  fire  and  burns 


346  VANADIUM. 

like  tinder,  being  converted  into  the  binoxide.  On  exposure  to  air  and  mois- 
ture it  is  slowly  oxidized,  a  process  which  is  best  seen  by  putting-  it  into 
water,  when  the  liquor  gradually  acquires  a  green  tint.  In  both  cases  the 
oxygen  is  derived  from  the  atmosphere.  A  similar  change  occurs  in  acid 
and  alkaline  solutions,  which,  with  the  exception  of  nitric  acid,  do  not  dis- 
solve it  even  at  a  boiling  temperature.  Heated  in  nitric  aeid,  oxidation  en- 
sues  with  escape  of  nitric  oxide  gas,  and  a  blue  nitrate  of  the  binoxide  of 
vanadium  is  generated.  The  character  of  an  alkaline  base  seems  wholly 
wanting  in  the  protoxide,  and  hence  Berzelius  considers  it  as  a  suboxide. 
Its  eq.  is  76-5 ;  symb.  V+O,  V,  or  VO. 

Binoxide. — Prep. — Best  prepared,  in  the  dry  way,  by  heating  to  full  red- 
ness an  intimate  mixture  of  10  parts  of  the  protoxide  with  12  of  vanadic  acid 
in  a  vessel  filled  with  carbonic  acid,  or  from  which  combustible  matter  on 
the  one  hand,  and  oxygen  gas  on  the  other,  are  carefully  excluded.  From 
the  salts  of  the  binoxide,  and  especially  the  sulphate,  it  is  precipitated  as  a 
grayish-white  hydrate  by  means  of  a  very  slight  excess  of  carbonate  of  soda. 
The  residual  solution  is  colourless,  when  the  process  has  been  properly  con- 
ducted: it  remains  blue,  from  undecomposed  salt,  if  an  insufficient  quantity 
of  alkali  is  used ;  it  is  brown  when  the  alkaline  carbonate  is  too  freely 
employed,  because  some  of  the  binoxide  is  then  dissolved  by  the  free  alkali; 
and  if  the  solution  contained  vanadic  acid,  its  colour  after  precipitation  is 
green.  The  presence  of  the  latter  is  avoided  by  transmitting  hydrosulphu- 
ric  acid  gas  into  the  solution,  whereby  vanadic  acid  is  effectually  converted 
into  the  binoxide,  but  the  redundant  gas  should  be  expelled  by  gentle  heat 
before  the  binoxide  is  precipitated.  As  the  hydrate,  whilst  moist,  readily  ab- 
sorbs oxygen,  and  hence  acquires  a  tint  of  brown,  it  must  be  washed  and 
dried  without  exposure  to  the  air.  When  thus  prepared  it  retains  its  gray 
tint.  By  exposure  to  heat  in  a  vessel  from  which  the  air  is  excluded,  it  gives 
out  water,  and  acquires  all  the  characters  of  the  binoxide  prepared  in  the  dry 
way. 

Prop. — A  black  pulverulent  substance,  very  infusible,  insoluble  in  water, 
and  Tree  from  any  acid  or  alkaline  reaction.  When  heated  in  the  open  air  it 
is  converted  into  vanadic  acid,  and  when  moist  it  gradually  suffers  the  same 
change  at  ordinary  temperatures.  It  is  dissolved  by  acids  more  readily  as  a 
hydrate  than  after  being  heated  to  redness,  and  forms  salts,  most  of  which 
have  a  blue  colour,  and  are  more  or  less  soluble  in  water.  They  may  all  be 
conveniently  formed  by  the  direct  action  of  acids  on  the  hydrated  oxide.  The 
nitrate  may  be  made  by  acting  on  vanadium,  or  either  of  its  oxides,  by  nitric 
acid ;  the  salt,  when  diluted  with  water,  may  be  boiled  without  change ;  but 
when  evaporated,  even  spontaneously,  the  blue  colour  passes  through  green 
into  red,  owing  to  the  production  of  vanadic  acid.  The  sulphate  is  easily 
prepared  by  dissolving  vanadic  acid  in  warm  sulphuric  acid  diluted  with  an 
equal  weight  of  water,  decomposing  the  vanadic  acid  by  hydrosulphuric  acid, 
concentrating  the  solution  in  order  that  the  salt  may  be  deposited,  and 
washing  away  adhering  sulphuric  acid  by  means  of  alcohol.  The  deoxida- 
tion  of  vanadic  acid  in  the  preceding  process  may  also  be  effected  by  adding 
pure  oxalic  acid  as  long  as  carbonic  acid  gas  is  evolved. 

The  salts  of  the  binoxide  of  vanadium  are  distinguished  by  their  blue 
colour,  by  yielding  with  the  alkalies  or  their  carbonate  in  very  slight  excess 
the  hydrated  binoxide,  which  becomes  red  by  oxidation,  and  by  forming  with 
solution  of  gall-nuts  a  black  compound,  a  tannate  of  the  binoxide,  very  simi- 
lar to  ink. 

The  binoxide  is  disposed  to  act  the  part  of  an  acid  by  uniting  with  alkaline 
bases,  with  which  it  forms  definite  and  in  some  cases  crystalline  compounds. 
On  digesting  the  hydrated  binoxide  in  pure  potassaor  ammonia,  combination 
is  readily  enacted,  and  a  dark  brown  solution  is  formed.  These  compounds, 
though  soluble  in  water,  are  very  sparingly  so  in  strong  and  cold  alkaline 
solutions,  and  may  be  precipitated  by  them.  Most  of  the  other  salts  formed 


VANADIUM.  347 

by  the  binoxide  and  salifiable  bases  are  insoluble  in  water,  and  may  be 
formed  from  the  preceding  by  way  of  double  decomposition, 

Its  eq.  is  84-5 ;  symb.  V+2O,  V,  or  V(K 

Vanadic  Acid — When  vanadiate  of  ammonia,  prepared  as  already  men- 
tioned (page  344),  is  heated  in  close  vessels,  the  acid  is  decomposed  by  the 
hydrogen  of  the  ammonia,  and  binoxide  of  vanadium  is  formed,  mixed  with 
a  little  protoxide  and  undecom posed  acid.  If  the  salt  is  heated  in  an  open 
vessel,  and  well  stirred,  the  whole  mass  acquires  a  dark  red  colour,  and  pure 
vanadic  acid  is  obtained ;  but  a  red  heat  should  be  avoided,  since  fusion 
would  thereby  be  occasioned,  and  free  exposure  of  every  part  to  the  atmos- 
phere prevented.  Its  colour  in  the  state  of  fine  powder  is  a  light  rust-yellow ; 
but  the  fused  acid  is  red  with  a  shade  of  orange,  and  has  a  strong  lustre.  By 
light  transmitted  through  thin  layers  it  appears  yellow.  In  the  fire  it  is  fixed, 
and  is  not  decomposed  by  a  very  strong  heat,  provided  combustible  matters 
are  excluded.  It  fuses  at  a  heat  lower  than  that  of  redness,  and  crystallizes 
readily  as  it  cools.  In  the  act  of  becoming  solid  it  contracts  considerably  in 
volume,  and  emits  so  much  heat  of  fluidity  that  the  acid,  after  ceasing  to  be 
luminous,  is  again  rendered  incandescent,  and  remains  so  until  the  congela- 
tion is  complete. 

It  is  tasteless,  insoluble  in  alcohol,  and  very  slightly  soluble  in  water, 
which  takes  up  rather  less  than  l-100th  of  its  weight,  acquiring  a  yellow 
colour  and  an  acid  reaction.  Heated  with  combustible  matter  it  is  deoxidized, 
being  converted  into  the  protoxide  or  binoxide,  or  mixture  of  these  oxides. 
In  solutions  it  is  deprived  of  oxygen  by  all  deoxidizing  agents,  such  as  alco- 
hol, sugar,  and  most  organic  substances,  including  the  oxalic  and  several 
vegetable  acids,  by  hydrosulphuric  acid  and  most  of  the  other  hydracids,  not 
excepting  the  hydrochloric,  by  sulphurous  and  phosphorous  acids,  and  even 
by  nitrous  acid.  Like  molybdic  and  tungstic  acids  it  is  disposed  to  act  as  a 
base  to  such  of  the  stronger  acids  as  do  not  decompose  it,  and  to  form  with 
them  definite  compounds,  which  are  soluble  in  water.  It  unites  on  this 
principle  with  sulphuric  and  phosphoric  acid;  and  Berzelius  has  remarked  a 
compound  of  the  phosphoric,  silicic,  and  vanadic  acids,  a  sort  of  double  salt, 
in  which  the  latter  acid  is  a  base  to  the  two  former,  and  which  crystallizes 
in  scales  :  it  is  formed  in  Sefstro'm's  process  for  preparing  vanadic  acid  (page 
344,)  and  its  solubility  opposes  a  great  obstacle  to  the  separation  of  vanadic 
from  silicic  acid. 

Vanadic  acid  unites  with  salifiable  bases  often  in  two  or  more  proportions, 
forming  soluble  salts  with  the  alkalies,  and  in  general  sparingly  soluble  salts 
with  the  other  metallic  oxides.  Those  with  excess  of  acid  are  commonly  of 
a  red  or  orange-red  colour.  Most  of  the  neutral  salts  are  yellow ;  but  it  is 
singular  that  the  neutral  vanadiates  of  the  alkalies,  the  alkaline  earths,  and 
the  oxides  of  lead,  zinc,  and  cadmium  may  be  yellow  at  one  time  and  co- 
lourless at  another,  without  suffering  any  appreciable  change  in  composition. 
Thus,  on  neutralizing  vanadic  acid  with  ammonia,  a  yellow  salt  is  obtained, 
the  solution  of  which  gradually  becomes  colourless  if  kept  for  some  hours, 
and  suffers  the  same  change  rapidly  when  heated.  The  solution,  as  it  is 
coloured  or  colourless,  gives  a  yellow  or  white  residue  by  evaporation,  and 
a  yellow  or  white  precipitate  with  a  salt  of  baryta  or  protoxide  of  lead. 
These  changes  appear  to  be  of  the  same  kind  as  those  already  noticed  in  the 
description  of  phosphoric  acid. 

Vanadic  acid  unites  in  different  proportions  with  binoxide  of  vanadium, 
and  forms  compounds  which  are  soluble  in  pure  water,  but  sparingly  so  in 
saline  solutions,  and  which  are  purple,  green,  yellow,  or  ocange,  according  as 
the  acid  is  in  a  smaller  or  larger  proportion.  They  are  best  formed  by  ex- 
posing the  hydrated  binoxide  to  the  atmosphere,  when  these  different  colours 
successively  appear,  as  a  gradually  increasing  quantity  of  the  acid  is  gene- 
rated. 

Vanadic  acid  is  distinguished  from  all  other  acids  except  the  chromic  by  its 


348  VANADIUM. 

colour,  and  from  this  acid  by  the  action  of  deoxidizing  substances,  which 
give  a  blue  solution  with  the  former  and  a  green  with  the  latter  (page  340.) 
When  heated  with  borax  in  the  reducing  flame  of  the  blowpipe,  both  of  the 
acids  yield  a  green  glass ;  but  in  the  oxidizing  flame  the  bead  becomes  yel- 
low if  vanadium  is  present,  while  the  green  colour  produced  by  chromium  is 
permanent. 

Its  eq.  is  92-5;  symb.  V-J-3O,  V,  or  VO. 

Chlorides. — The  bichloride  is  prepared  by  digesting  a  mixture  of  vanadic 
and  hydrochloric  acids,  deoxidizing  any  undecomposed  vanadic  acid  by  hy- 
drosulphuric  acid,  and  evaporating  the  solution  to  dryness.  A  brown  residue 
is  obtained,  which  yields  a  blue  solution  with  water,  part  being  left  as  an 
insoluble  subsalt.  It  may  also  be  generated  by  acting  directly  on  the  ignited 
binoxide  with  strong  hydrochloric  acid.  As  thus  obtained  its  solution  is 
brown  instead  of  blue,  though  in  composition  it  seems  identical  with  the 
preceding  Its  eq.  is  139-34 ;  symb.  V-f  2C1,  or  VCl*. 

The  terchloride  may  be  formed  by  transmitting  a  current  of  dry  chlorine 
gas  over  a  mixture  of  protoxide  of  vanadium  and  charcoal  heated  to  low  red- 
ness, when  the  terchloride  passes  over  in  vapour,  and  condenses  in  the  form 
of  a  yellow  liquid,  from  which  free  chlorine  may  be  removed  by  a  current  of 
dry  air.  It  is  converted  by  water  into  hydrochloric  and  vanadic  acid,  and 
atmospheric  humidity  produces  the  same  change,  which  is  indicated  by  the 
escape  of  red  fumes.  Its  eq.  is  174-76  ;  symb.  V-f  3C1,  or  VCR 

A  bibromide  of  vanadium  may  be  formed  in  the  same  manner  as  the 
bichloride,  substituting  the  hydrobromic  for  hydrochloric  acid.  Similar 
compounds  may  be  procured  with  iodine,  fluorine,  arid  cyanogen  by  dissolving 
binoxide  of  vanadium  in  hydriodic,  hydrofluoric,  and  hydrocyanic  acid. 

Sulphurets. — When  the  binoxide  of  vanadium  is  heated  to  redness  in  a 
current  of  hydrosulphuric  acid  gas,  it  is  converted  into  protoxide,  and  both 
water  and  sulphur  are  obtained  :  on  continuing  the  process,  the  protoxide  is 
decomposed,  hydrogen  gas  and  water  pass  over,  and  bisulphurel  of  vanadium 
is  generated.  This  compound  may  also  be  procured  by  mixing  hydrosul- 
phate  of  ammonia  with  a  salt  of  the  binoxide  of  vanadium  until  the  precipi- 
tate at  first  formed  is  redissolved,  and  then  decomposing  the  deep  purple- 
coloured  solution  by  sulphuric  or  hydrochloric  acid.  The  bisulphuret  of  a 
brown  colour  subsides,  which  becomes  black  when  it  is  dried.  It  is  un- 
changed at  common  temperatures  by  exposure  to  the  air,  but  takes  fire 
when  heated.  In  the  hydrated  state  it  is  dissolved  by  alkalies  and  alkaline 
sujphurets;  but  it  is  insoluble  in  acids,  with  the  exception  of  the  nitric  and 
nitre-hydrochloric,  by  which  it  is  converted  into  sulphate  of  the  binoxide. 

Its  eq.  is  100-7;  symb.  V-f-2S,  or  VS2. 

When  hydrosulphuric  acid  gas  is  transmitted  through  an  aqueous  solution 
of  vanadic  acid,  a  grayish-brown  precipitate  is  formed^  consisting  of  hy- 
drated binoxide  of  vanadium  mixed  mechanically  with  sulphur.  But  if  a 
solution  of  vanadic  acid  in  hydrosulphate  of  ammonia  is  acidulated  by  hy- 
drochloric or  sulphuric  acid,  the  hydrated  tersulphuret  of  vanadium  sub- 
sides. Its  colour  is  of  a  much  lighter  brown  than  the  bisulphuret,  becomes 
almost  black  in  drying,  and  is  resolved  by  a  red  heat  in  close  vessels  into 
the  bisulphuret  with  loss  of  water  and  sulphur.  It  is  soluble  in  alkalies  and 
alkaline  sulphurets,  and  is  oxidized  by  nitric  acid. 

Its  eq.  is  116-8 ;  syrnb.  V+3S,  or  VS». 

The  phosphuret  of  vanadium,  of  a  leaden-gray  colour,  may  be  formed  by 
exposing  to  a  white  heat  phosphate  of  the  binoxide  of  vanadium  mixed  with 
a  small  quantity  of  sugar. 


MOLYBDENUM.  349 


SECTION  XVII. 

MOLYBDENUM,  TUNGSTEN  AND  COLUMBIUM. 
MOLYBDENUM. 

Hist,  and  Prep. — THE  principal  ore  of  molybdenum  is  the  sulphuret, 
which  was  long  mistaken  for  graphite,  and  was  first  distinguished  from  it 
in  1778  by  Scheele  ;  but  the  metal  was  obtained  in  a  separate  state  by  Hjelm. 
When  this  ore,  in  fine  powder,  is  digested  in  nitro-hydrochloric  acid  until  it 
is  completely  decomposed,  and  the  residue  is  briskly  heated  in  order  to  ex- 
pel sulphuric  acid,  molybdic  acid  remains  in  the  form  of  a  white  heavy  pow- 
der. From  this  acid  metallic  molybdenum  may  obtained  by  exposing  it  with 
charcoal  to  the  strongest  heat  of  a  smith's  forge ;  or  by  conducting  over  it 
a  current  of  hydrogen  gas  while  strongly  heated  in  a  tube  of  porcelain. 
(Berzelius.)  Molybdenum  likewise  occurs  in  nature  in  the  form  of  molyb- 
date  of  protoxide  of  lead. 

Prop. — It  is  a  brittle  metal,  of  a  white  colour,  and  so  very  infusible,  that 
hitherto  it  has  only  been  obtained  in  a  state  of  semi-fusion,  In  this  form  it 
has  a  sp.  gr.  varying  between  8-615  and  8*636.  When  heated  in  open  ves- 
sels it  absorbs  oxygen,  and  is  converted  into  molybdic  acid ;  and  the  same 
compound  is  generated  by  the  action  of  chlorine  or  nitro-hydrochloric  acid. 
It  has  three  degrees  of  oxidation,  forming  two  oxides  and  one  acid,  from  the 
composition  of  which  Berzelius  estimates  the  eq.  of  molybdenum  at  47*7. 
Its  symb.  is  Mo.  The  composition  of  its  compounds  described  in  this  sec- 
tion is  as  follows  : — 

Molybdenum.  Equiv.         Formulae, 

Protoxide         47-7  1  eq.-}-Oxygen     8       1  eq.=   55-7     Mo+O  or  MoO. 

Binoxide          47-7  1  eq.+  do.  16       2  eq.=   63-7    Mo+2O  or  MoO'2 

Molybdic  acid  47-7  1  eq.+do  24       3  eq.=   71-7    Mo+3O  or  MoO3 

Protochloride  47-7  1  eq.+Chlorine  35-42  1  eq.=   83.12  Mo+Cl  or  MoCl. 

Bichloride        47-7  1  eq.+do.  70-84  2  eq.=l  18-54  Mo+2Cl  or  MoCl2 

Bisulphuret     47-7  1  eq.+Sulphur  32-2    2  eq.=  79-9    Mo+2S  or  MoS2 

Tersulphuret  47-7  1  eq.+do.  48-3    3  eq.=  96        Mo+3S  or  MoS3 

Persulphuret  47-7  1  eq.+do.  64-4    4eq.=  112-l     Mo+4S  or  MoS4 

+MoC13    153-96         =297-36   2MoO3+MoC13 

Protoxide  of  Molybdenum. — On  dissolving  molybdate  of  potassa  or  soda  in 
a  small  quantity  of  water,  adding  hydrochloric  acid  until  the  molybdic  acid 
at  first  thrown  down  is  redispolved,  and  digesting  with  a  piece  of  pure  me- 
tallic zinc,  the  latter  deoxidizes  the  molybdic  acid,  the  liquid  changes  to 
blue,  red,  and  black,  and  then  contains  chloride  of  zinc  and  protochloride  of 
molybdenum.  From  the  black  solution  pure  potassa  throws  down  the  pro- 
toxide of  molybdenum  as  a  black  hydrate,  an  excess  of  the  alkali  being  used 
in  order  to  hold  the  zinc  in  solution.  The  hydrate  is  washed  with  the  least 
possible  exposure  to  the  air,  and  dried  in  vacuo  by  sulphuric  acid.  When 
heated  to  low  redness  in  the  open  air  it  takes  fire  and  is  converted  into  the 
binoxide  ;  but  if  not  exposed  to  the  air  it  becomes  incandescent  at  the  mo- 
ment of  losing  its  water,  like  hydrated  sesquioxide  of  chromium.  The  an- 
hydrous oxide  is  black  and  insoluble  in  acids ;  but  in  the  state  of  hydrate 
acids  dissolve  it.  The  recently  precipitated  hydrate  is  soluble  in  the  cold  by 
carbonate  of  ammonia,  but  in  none  of  the  other  alkalies. 

Its  eq,  is  55-7 ;  symb.  Mo+O,  Mo,  or  MoO. 

30 


350  MOLYBDENUM. 

Binoxide  of  Molybdenum. — Prep. — Obtained  as  a  deep  brown  anhydrous 
powder  by  mixing-  molybdate  of  soda  with  half  its  weight  of  sal  ammoniac  in 
fine  powder,  projecting  the  mixture  into  a  red-hot  crucible  which  is  to  be  in- 
stantly covered,  and  the  heat  continued  until  vapours  of  sal  ammoniac  cease  to 
appear.  In  this  process  chloride  of  sodium  is  generated,  and  molybdic  acid  is 
reduced  by  the  ammonia  to  the  state  of  binoxide  :  by  adding  water  to  the 
mass  when  cold,  chloride  of  sodium  is  dissolved,  and  the  dark  brown,  nearly 
black,  binoxide  left.  The  hydrate,  of  a  rust-brown  colour,  may  be  formed  by 
digesting  molybdenum  in  powder  with  molybdic  acid  dissolved  in  hydro- 
chloric acid,  until  the  liquid  acquires  a  deep  red  colour,  and  then  adding  am- 
monia ;  or  by  adding  ammonia  to  a  solution  of  the  bichloride;  or  digesting 
with  metallic  copper  a  solution  of  molybdic  in  hydrochloric  acid,  until  a 
deep  red  solution  is  formed,  and  employing  an  excess  of  ammonia  in  order 
to  keep  protoxide  of  copper  in  solution. 

Prop. — The  anhydrous  binoxide  is  insoluble  in  acids  and  is  changed  into 
molybdic  acid  by  strong  nitric  acid.  The  hydrate  is  very  like  hydrated 
sesquioxide  of  iron,  reddens  litmus  paper  when  placed  on  it,  is  dissolved  by 
acids  with  which  it  forms  red  salts,  is  insoluble  in  the  alkalies,  but  dissolves 
in  alkaline  carbonates.  It  is  soluble,  though  sparingly,  in  pure  water,  so 
that  it  should  be  washed  after  precipitation  by  a  solution  of  sal  ammoniac, 
which  salt  is  afterwards  removed  by  alcohol.  On  exposure  to  the  air,  the 
hydrate  absorbs  oxygen  and  becomes  blue  at  its  surface:  this  blue  compound 
is  more  soluble  in  water  than  the  hydrate,  and  was  supposed  by  Buchholz  to 
be  a  distinct  acid,  which  he  termed  molybdous  acid;  but  Berzclius  has 
shown  that  it  is  a  bimolybdate  of  the  binoxide.  (Berzelius.) 

Its  eq.Js  63-7 ;  symb.  Mo-|-2O,  Mo,  or  MoO*. 

Molybdic  Acid. — Prep. — When  sulphuret  of  molybdenum  is  roasted  in  an 
open  crucible  kept  at  a  low  red  heat,  and  constantly  stirred  until  sulphurous 
acid  ceases  to  escape,  a  dirty  yellow  powder  is  left,  which  contains  impure 
molybdic  acid.  The  acid  is  taken  up  by  ammonia  and  the  filtered  solution 
evaporated  to  dryness;  it  is  again  taken  up  by  a  little  dilute  ammonia  and 
filtered  ;  it  is  then  purified  by  crystallization.  On  heating  gently  in  an  open 
platinum  crucible,  taking  care  to  prevent  fusion,  the  ammonia  is  expelled, 
and  pure  acid  remains.  It  is  also  obtained  by  oxidizing  the  binoxide  with 
nitric  acid. 

Prop. — As  thus  formed,  it  is  a  white  powder,  of  sp.  gr.  3-49,  fusible  by  a 
red  heat  into  a  yellow  liquid,  which  bears  a  strong  red  heat  in  close  vessels 
without  subliming,  but,  in  an  open  crucible,  rises  with  the  current  of  air, 
and  collects  on  cold  surfaces  in  colourless  crystalline  scales.  It  requires  570 
times  its  weight  of  water  for  solution,  which  nevertheless  has  an  acid  reac- 
tion. It  is  soluble  in  the  alkalies,  forming  colourless  molybdales,  from  which 
molybdic  acid  is  precipitated  by  the  stronger  acids,  though  an  excess  of  the 
acids  dissolves  it ;  but  after  exposure  to  a  red  heat  it  is  insoluble  in  acids. 

Chlorides. — Berzelius  has  described  three  chlorides  of  molybdenum  which 
he  considered  analogous  in  composition  to  the  oxides;  but  his  terchloride  has 
recently  been  shown  by  Rose  to  be  an  oxychloride  which  has  the  same  con- 
stitution as  the  oxychloride  of  chromium.  (Pog.  An.  xl.  395.) 

The  protochloride  is  formed  by  dissolving  the  hydrated  protoxide  in  liy 
drochloric  acid,  when  it  forms  a  deep  nearly  black  coloured  solution,  which 
leaves  a  black  viscid  mass  by  evaporation. 

Its  eq.  is  83-12;  symb.  Mo-fCl,  or  Mod. 

The  bichloride  is  obtained  as  above  mentioned,  and  yields  a  red  solution. 
It  is  obtained  in  the  anhydrous  state  by  gently  heating  molybdenum  in  pow- 
der in  dry  chlorine  gas,  atmospheric  air  being  excluded.  The  metal  takes 
fire  at  its  surface,  but  it  is  soon  extinguished,  after  which  the  chlorine  is  re- 
placed by  a  red  vapour  of  such  intensity  that  it  is  completely  opaque  in  a 
vessel  |ths  of  an  inch  in  diameter:  this  vapour  condenses  in  the  cooler  parts 
of  the  apparatus  in  brilliant  black  crystals  just  like  those  of  iodine,  which 
are  very  fusible,  and  sublime  at  a  gentle  heat.  Exposed  to  dry  oxygen  gas 


TUNGSTEN.  351 

it  is  transformed  gradually  into  oxychloride  of  molybdenum  and  molybdic 
acid.  With  water  the  bichloride  acts  violently  from  the  intense  heat  evolved, 
and  the  whole  is  dissolved. 

Its  eq.  is  118-54;  symb.  Mo+2Cl,  or  MoCK 

Sulphurets. — Molybdenum  combines  with  sulphur  in  three  proportions. 
The  lowest  grade  is  the  bisulphuret,  which  is  the  most  common  ore  of  mo- 
lybdenum and  is  usually  associated  with  ores  of  tin,  has  a  lead-gray  colour 
and  metallic  lustre  resembling  graphite,  for  which  it  was  formerly  mistaken. 
Its  density  varies  from  4-138  to  4-569.  It  bears  a  strong  heat  in  close  vessels 
without  change  or  fusion  ;  but  it  is  oxidized  by  nitric  acid  or  by  the  joint 
action  of  heat  and  air.  Its  eq.  is  79-9  ;  symb.  Mo^-2S,  or  MoS3. 

The  tersulphuret  is  obtained  by  saturating  molybdate  of  potassa,  soda,  or 
ammonia  with  hydrosulphuric  acid  gas,  and  adding  hydrochloric  acid,  when 
the  tersulphuret  falls  of  a  deep  brown  colour,  and  becomes  black,  on  drying. 
It  is  partially  oxidized  when  dried  in  the  air.  By  heat  in  close  vessels  it  is 
changed  into  the  bisulphuret  with  loss  of  sulphur. 

Its  eq.  is  96;  symb.  Mo  +  3S,  or  MoSa. 

The  persulphuret  is  made  by  boiling  the  sulphur-salt  formed  of  tersul- 
phuret of  molybdenum  and  sulphuret  of  potassium  for  a  long  time  with  the 
bisulphuret  of  molybdenum,  when  a  precipitate  collects  which  is  to  be  well 
washed  with  cold  water.  It  is  a  sulphur-salt  composed  of  persulphuret  of 
molybdenum  and  sulphuret  of  potassium,  which  forms  with  boiling  water 
a  deep  red  solution,  from  which  on  the  addition  of  hydrochloric  acid  the 
persulphuret  subsides. 

Its  eq.  is  112-1 ;  symb.  Mo+4S,  or  MoS*. 

Oxychloride  of  Molybdenum. — Formerly  described  as  a  terchloride.  It  is 
obtained  by  heating  the  binoxide  in  a  current  of  dry  chlorine.  It  is  white 
with  a  shade  of  yellow,  sublimes  at  a  heat  short  of  redness,  and  condenses 
into  crystalline  scales.  It  dissolves  in  water,  but  the  solution  is  slightly 
milky  from  the  separation  of  molybdic  acid.  From  its  composition,  which 
has  been  recently  determined  by  Rose,  it  would  appear  that 

3  eq.  of  binoxide  and  3  eq.  of  chlorine  )    .  , ,  $  1  ecl'  of  oxychloride. 
3(Mo+20)  3C1  £  y*ld  £     MoCl3+2MoCK 

Its  eq.  is  297-36;  symb.  MoCls+2MoO3, 

TUNGSTEN. 

It  derives  its  name  from  the  Swedish  words  tung  &ten,  heavy  stone,  from 
the  density  of  its  ores ;  and  it  is  called  wolfram  from  the  mineral  of  that 
name,  which  is  a  tungstate  of  the  oxides  of  iron  and  manganese.  This  metal 
may  be  procured  in  the  metallic  state  by  exposing  tungstic  acid  to  the  action 
of  charcoal  or  dry  hydrogen  gas  at  a  red  heat ;  but  though  the  reduction  is 
easily  effected,  an  exceedingly  intense  temperature  is  required  for  fusing  the 
metal.  Tungsten  has  a  grayish-white  colour,  and  considerable  lustre.  It  is 
brittle,  nearly  as  hard  as  steel,  and  less  fusible  than  manganese.  Its  sp.  gr. 
is  near  17'6.  When  heated  to  redness  in  the  open  air  it  takes  fire,  and  is 
converted  into  tungstic  acid ;  and  it  undergoes  the  same  change  by  the 
action  of  nitric  acid.  Digested  with  a  concentrated  solution  of  pure  polassa, 
it  is  dissolved  with  disengagement  of  hydrogen  gas,  and  tungstate  of  potassa 
is  generated. 

Chemists  are  acquainted  with  two  compounds  of  this  metal  and  oxygen ; 
namely,  the  dark  brown  oxide,  and  the  yellow  acid  of  tungsten ;  and  according 
to  the  analysis  of  Berzelius,  (An.  de  Ch.  et  de  Ph.  xvii.)  the  oxygen  of  the 
former  is  to  that  of  the  latter  in  the  ratio  of  two  to  three.  From  the  com- 
position of  the  latter,  and  assuming  that  it  contains  three  atoms  of  oxygen, 
the  eq.  of  tungsten  is  94-8.  Its  symb.  is  W.  Its  compounds  described  in  this 
section  are  thus  constituted  : — 


352  TUNGSTEN. 

Tungsten.  Equiv.          Formula, 

Binoxide  94-8  1  eq.-f  Oxygen  16        2eq.=110-8    W  -f2O  or  WO ". 

Tungstic  acid      94-8  1  eq.-j-do.  24      k3eq.=  118-8   W^-SOor  WOs. 

Blue  oxide         189-6  2  eq.-f-do.          40        5eq.=229-6  2W-f-5Oor  W^O. 
Bichloride  94-8  1  eq.-j-Chlorine70-84   2eq.=165-64  W-f-2Clor  WCls. 

Bisulphuret         94-8  I  eq.  4. Sulphur  32-2      2eq,=127       W-f2S  or  WSs. 
Tersulphuret       94'8  I  eq.-j-do.  48-3      3cq.=  143-l    W-J-3S  or  WS-. 

Oxychl.  2WO3  237-6          -J-WC13    201-06          =438-66  WC13  4. 2WOs. 

Binoxide. — Prep. — By  the  action  of  hydrogen  gas  on  tungstic  acid  at  a 
low  red'heat ;  but  the  besfmode  of  procuring  it,  both  pure  and  in  quantity,  is 
that  recommended  by  Wohler.  (QuarterlyFJournal  of  Science,  xx.  177.)  This 
process  consists  in  mixing  wolfram  in  fine  powder  with  twice  its  weight  of 
carbonate  of  potassa,  and  fusing  the  mixture  in  a  platinum  crucible.  The 
resulting  tungstatc  of  potassa  is  dissolved  in  hot  water,  mixed  with  about 
half  its  weight  of  hydrochlorate  of  ammonia  in  solution,  evaporated  to  dry- 
ness,  and  exposed  in  a  Hessian  crucible  to  a  red  heat.  The  mass  is  well 
washed  with  boiling  water,  and  the  insoluble  matter  digested  in  dilute  po- 
tassa to  remove  any  tungstic  acid.  The  residue  is  binoxide  of  tungsten.  It 
appears  that  in  this  process  the  tungstate  of  potassa  and  hydrochlorate  of 
ammonia  mutually  decompose  each  other,  so  that  the  dry  mass  consists  of 
chloride  of  potassium  and  tungstate  of  ammonia.  The  elements  of  the  latter 
react  on  each  other  at  a  red  heat,  giving  rise  to  water,  nitrogen  gas,  and 
binoxide  of  tungsten  ;  and  this  compound  is  protected  from  oxidation  by  the 
fused  chloride  of  potassium  with  which  it  is  enveloped.  This  oxide  is  also 
formed  by  putting  tungstic  acid  in  contact  with  zinc  in  dilute  hydrochloric 
acid.  The  tungstic  acid  first  becomes  blue,  and  then  assumes  a  copper  co- 
lour ;  but  the  binoxide  in  this  state  can  with  difficulty  be  preserved ;  as  by 
exposure  to  the  air,  and  even  under  the  surface  of  water,  it  absorbs  oxygen, 
and  is  reconverted  into  tungstic  acid. 

Prop. — When  prepared  by  means  of  hydrogen  gas,  it  has  a  brown  colour, 
and  when  polished  acquires  the  colour  of  copper ;  but  when  procured  by 
Wohler's  process,  it  is  nearly  black.  It  does  not  unite,  so  far  as  is  known, 
with  acids  ;  and  when  heated  to  near  redness,  it  takes  fire  and  yields  tungstic 
acid. 

Its  eq.  is  110-8 ;  symb.  W  -f  2O,  W,  or  WO2. 

Tungstic  Acid — Prep. — Conveniently  by  digesting  native  tungstate  of 
lime,  very  finely  levigated,  in  nitric  acid;  by  which  means  nitrate  of  lime  is 
formed,  and  tungstic  acid  separated  in  the  form  of  a  yellow  powder.  Long 
digestion  is  required  before  all  the  lime  is  removed ;  but  the  process  is  fa- 
cilitated by  acting  upon  the  mineral  alternately  by  nitric  acid  and  ammonia. 
The  tungstic  acid  is  dissolved  readily  by  that  alkali,  and  may  be  obtained  in 
a  separate  state  by  heating  the  tungstate  of  ammonia  to  redness.  Tungstic 
acid  may  also  be  prepared  by  the  action  of  hydrochloric  acid  on  wolfram,. 
It  is  also  obtained  by  heating  the  binoxide  to  redness  in  open  vessels. 

Prop. — Tungstic  acid  is  of  a  yellow  colour,  is  insoluble  in  water,  and  has 
no  action  on  litmus  paper.  With  alkaline  bases  it  forms  salts  called  tung- 
states,  which  are  decomposed  by  the  stronger  acids,  the  tungstic  acid  in  ge- 
neral falling  combined  with  the  acid  by  which  it  is  precipitated.  When 
strongly  heated  in  open  vessels  it  acquires  a  green  colour,  and  becomes  blue 
when  exposed  to  the  action  of  hydrogen  gas  at  a  temperature  of  500°  or  600° 
F.  The  blue  oxide,  thus  formed,  is,  according  to  Berzelius,  a  tungstate  of 
the  binoxide  of  tungsten ;  and  the  green  colour  is  probably  produced  by  an 
admixture  of  this  compound  with  the  yellow  acid. 

Its  eq.  is  118-8;  symb.  W-f  3O,  W,  or  WO. 

Malaguti  finds  that  the  blue  oxide,  formed  in  the  manner  stated  above,  is 
never  constant  in  its  composition  ;  but  he  obtained  a  definite  compound  by 
heating  tungstic  acid  by  the  flame  of  a  spirit-lamp  in  a  current  of  dry  hy- 


COLUMBIUM.  353 

drogen.  According  to  his  analysis  it  contains  17'72  per  cent,  of  oxygen  ; 
and  he  considers  it  a  distinct  acid,  the  constitution  of  which  is  represented 
by  the  symb.  2W  -f  5O,  or  W^O5.  (An.  de  Oh.  et  de  Ph.  Ix.  271.) 

Chlorides  of  Tungsten.  —  Tungsten  and  chlorine  unite  in  two  proportions. 
When  metallic  tungsten  is  heated  in  chlorine  gas,  it  takes  fire  and  yields 
the  bichloride.  The  compound  appears  in  the  form  of  delicate  needles,  of  a 
deep  red  colour,  resembling  wool,  but  more  frequently  as  a  deep  red  fused 
mass  which  has  the  brilliant  fracture  of  cinnabar.  When  heated,  it  fuses, 
boils,  and  yields  a  red  vapour.  By  water  it  is  changed  into  hydrochloric 
acid  and  binoxide  of  tungsten.  It  is  entirely  dissolved  by  solution  of  pure 
potassa,  with  disengagement  of  hydrogen  gas,  yielding  tungstate  of  potassa 
and  chloride  of  potassium.  A  similar  change  is  produced  by  ammonia,  ex- 
cept that  some  binoxide  of  tungsten  is  left  undissolved. 

Its  eq.  is  165-64;  symb.  W-f2Cl,  or  WC1-. 

Another  chloride  has  been  described  by  Wohler.  It  is  formed  at  the  same 
time  as  the  first  ;  by  the  action  of  water  it  is  converted  into  hydrochloric  and 
tungstic  acids.  It  is  the  most  beautiful  of  aH  these  compounds,  existing  in 
long  transparent  crystals  of  a  fine  red  colour.  It  is  very  fusible  and  volatile, 
and  its  vapour  is  red  like  that  of  nitrous  acid.  The  difference  between  this 
compound  and  the  chloride  first  described  is  not  yet  satisfactorily  determined  5 
for  although  the  analysis  of  Malaguti,  in  his  paper  above  referred  to,  would 
indicate  its  constitution  to  be  similar  to  that  of  his  blue  oxide,  and,  therefore, 
W2C15  ;  still  the  errors  into  which  he  fell  in  reference  to  the  terchloride 
throw  suspicion  on  this  result.  The  production  of  tungstic  acid  by  its  de- 
composition with  water  strengthens  this  suspicion. 

Sulphurets  of  Tungsten.  —  The  bisulphuret  is  obtained  as  a  black  powder 
by  transmitting  hydrosulphurie  acid  gas,  or  the  vapour  of  sulphur,  over 
tungstic  acid  heated  to  whiteness  in  a  tube  of  porcelain.  The  tersulphuret  is 
prepared  by  dissolving  tungstic  acid  in  a  solution  of  sulphuret  of  potassium 
or  hydrosulphate  of  ammonia,  and  adding  an  excess  of  hydrosulphuric  acid. 
ft  falls  as  a  brown  precipitate,  which  becomes  black  in  drying.  It  is  soluble 
to  a  certain  extent  in  water  which  is  free  from  saline  matter. 

Oxychloride  of  Tungsten.  —  Formerly  described  as  the  terchloride.  It  was 
discovered  by  Wohler,  and  prepared  by  heating  the  binoxide  of  tungsten  in 
a  stream  of  dry  chlorine  gas.  The  action  is  attended  witb  the  appearance 
t)f  combustion,  dense  fumes  arise,  and  a  thick  sublimate  is  obtained  in  the 
form  of  scales,  like  native  boracic  acid.  It  is  volatile  at  a  low  temperature 
without  previous  fusion.  According  to  Rose,  who  has  determiued  its  com- 
position, (Pog.  An.  xl.  395.)  it  is  resolved,  when  suddenly  heated,  into  tung- 
stic acid,  bichloride  of  tungsten,  and  chlorine, 

Its  eq.  is  438-66  ;  symb. 


COLUMBJUM. 

Hist.  —  This  metal  was  dicovered  in  1801  by  Hatchctt,  who  detected  it  in 
a  black  mineral  belonging  to  the  British  Museum,  supposed  to  have  come 
from  Massachusetts  in  North  America;  and  from  this  circumstance  applied 
to  it  the  name  of  columbium.  About  two  years  after,  M.  Ekeberg,a  Swedish 
chemist,  extracted  the  same  substance  from  tantalite  and  yttro-tantalite  ; 
and,  on  the  supposition  of  its  being  different  from  columbium,  described  it 
under  the  name  of  tantalum.  The  identity  .of  these  metals,  however,  was 
established  in  the  year  1809  by  Wollaston. 

Prep.  —  Colum-bie  acid  is  with  difficulty  reduced  to  the  metallic  state  by 
the  action  of  heat  and  charcoal  ;  but  Berzelius  succeeded  in  obtaining  this 
metal  by  the  same  process  which  he  employed  in  the  preparation  of  zirco- 
nium and  silicon,  nanaely,  by  heating  potassium  with  the  double  fluoride  of 
potassium  and  calumbium.  On  washing  the  reduced  mass  with  hot  water, 
in  order  to  remove  the  fluoride  of  potassium,  columbium  is  left  in  the  form 
of  a  black  powder. 

Prop.  —  As  a  powder  it  does  not  conduct  electricity  ;  but  in  a  denser  state 

,3Q* 


354  COLUMBIUM, 

it  is  a  perfect  conductor.  By  pressure  it  acquires  metallic  lustre,  and  has  an 
iron-gray  colour.  It  is  not  fusible  at  the  temperature  at  which  glass  is  fused. 
When  heated  in  the  open  air  it  takes  fire  considerably  below  the  temperature 
of  ignition,  and  glows  with  a  vivid  light,  yielding  columbic  acid.  It  is 
scarcely  at  all  acted  on  by  the  sulphuric,  hydrochloric,  or  nitro-hydrochloric 
acid;  whereas  it  is  dissolved  with  heat  and  disengagement  of  hydrogen  gas 
by  hydrofluoric  acid,  and  still  more  easily  by  a  mixture  of  nitric  and  hydro- 
fluoric acids.  It  is  also  converted  into  columbic  acid  by  fusion  with  hydrate 
of  potassa,  the  hydrogen  gas  of  the  water  being  evolved. 

From  the  experiments  of  Berzelius  on  the  composition  of  the  oxide  and 
acid  of  columbium,  its  eq.  may  be  estimated  at  185.  Its  syrnb.  is  Ta.  The 
compounds  described  in  this  section  are  thus  constituted : 

Columbium.  Equiv.  Formulae. 

Binoxide  185  1  eq.-f  Oxygen     16      2  eq.=201       Ta-f  2O  or  TaO2. 

Columbic  acid  185  1  eq.-f  do.  24       3  eq.=209       Ta-f  3O  or  TaO3. 

Terchloride  185  1  eq.-f. Chlorine  106-26  3  eq.  =291-26  Ta-f3Cl or  TaCK 
Terfluoride  185  1  eq.-f  Fluorine  56-04  3  eq.=241-04Ta-f  3F  or  TaF*. 
Sulphuret  Composition  uncertain. 

Binoxide  of  Columbium. — It  is  generated  by  placing  columbic  acid  in  a 
crucible  lined  with  charcoal,  luting  carefully  to  exclude  atmospheric  air,  and 
exposing  it  for  an  hour  and  a  half  to  intense  heat.  The  acid,  where  in  direct 
contact  with  charcoal,  is  entirely  reduced  ;  but  the  film  of  metal  is  very 
thin.  The  interior  portions  are  pure  binoxide  of  a  dark  gray  colour,  very 
hard  and  coherent.  When  reduced  to  powder  its  colour  is  dark  brown.  It 
is  not  attacked  by  any  acid,  even  by  the  nitro-hydrofluoric ;  but  it  is  con- 
verted into  columbic  acid,  either  by  fusion  with  hydrate  of  potassa,  or  defla- 
gration with  nitre.  When  heated  to  low  redness  it  takes  fire  and  glows, 
yielding  a  light  gray  powder;  but  in  this  way  it  is  never  completely  oxi- 
dized. Berzelius  states  that  this  oxide,  in  union  with  protoxide  of  iron  and 
a  little  protoxide  of  manganese,  occurs  at  Kimito  in  Finland,  and  may  be 
distinguished  from  the  other  ores  of  columbium  by  yielding  a  chestnut- 
brown  powder. 

Its  eq.  is  201  ;  symb.  Ta-f  2O,  Ta,  or  TaO. 

Columbic  Acid. — Columbium  exists  in  most  of  its  ores  as  an  acid,  united 
either  with  the  oxides  of  iron  and  manganese,  as  in  tantalite,  or  with  the 
earth  yttria,  as  in  the  yttro-tantalite.  This  acid  is  obtained  by  fusing  its  ore 
with  three  or  four  times  its  weight  of  carbonate  of  potassa,  when  a  soluble 
columbate  of  that  alkali  results,  from  which  columbic  acid  is  precipitated  as 
a  white  hydrate  by  acids.  Berzelius  also  prepares  it  by  fusion  with  bisul- 
phate  of  potassa. 

Hydrated  columbic  acid  is  tasteless,  and  insoluble  in  water ;  but  when 
placed  on  moistened  litmus  paper,  it  communicates  a  red  tinge.  It  is  dis- 
solved by  sulphuric,  hydrochloric,  and  some  vegetable  acids  ;  but  it  does  not 
diminish  their  acidity,  or  appear  to  form  definite  compounds  with  them. 
With  alkalies  it  unites  readily  ;  and  though  it  does  not  neutralize  their  pro- 
perties completely,  crystallized  salts  may  be  obtained  by  evaporation. 
When  the  hydrated  acid  is  heated  to  redness,  water  is  expelled,  and  the  an- 
hydrous columbic  acid  remains.  In  this  state  it  is  attacked  by  alkalies  only. 

Its  eq.  is  209 ;  symb.  Ta-f  3O,  Ta,  or  TaQ3. 

Terchloride  of  Columbium. — When  columbium  is  heated  in  chlorine  gas, 
it  takes  fire  and  burns  actively,  yielding  a  yellow  vapour,  which  condenses  in 
the  cold  parts  of  the  apparatus  in  the  form  of  a  white  powder  with  a  tint  of 
yellow.  Its  texture  is  not  in  the  least  crystalline.  By  contact  with  water, 
it  is  converted,  with  a  hissing  noise  and  increase  of  temperature,  into  colum- 
bic and  hydrochloric  acids.  Hence  its  eq.  is  considered  to  be  291-26;  symb. 
Ta  +  3Cl,  orTaCR 


ANTIMONY.  355 

Terfluoride  of  Columbium. — Hydrofluoric  acid  lakes  up  hydrated  columbic 
acid,  and  forms  with  it  a  compound  of  terfluoride  of  columhium  and  hydro- 
fluoric acid,  which,  by  evaporation  at  75°,  is  deposited  in  crystals,  which  are 
soluble  in  water  and  effervesce  in  the  air.  By  gently  evaporating  the  solu- 
tion, an  uncrystalline  mass,  white  and  opaque,  is  left,  which  Berzelins  con- 
siders  to  be  the  terfluoride  of  columbium.  By  water  part  of  it  is  converted 
into  columbic  and  hydrofluoric  acids,  the  latter  soluble  and  the  former  inso- 
luble ;  but  both  of  these  acids  retain  some  terfluoride  in  combination.  Its 
eq.  is  241-04;  symb.  Ta-+-3F,  or  TaF3. 

Sulphuret  of  Columbium. — This  compound,  first  prepared  by  Rose,  is  ge- 
nerated, with  the  phenomena  of  combustion,  when  columbium  is  heated  to 
commencing  redness  in  the  vapour  of  sulphur  ;  or  by  transmitting  the  va- 
pour of  bisulphuret  of  carbon  over  columbic  acid  in  a  porcelain  tube  at  a 
white  heat,  carbonic  oxide  being  also  evolved. 


SECTION  XVIII. 


ANTIMONY. 

Hist. — FIRST  made  known  as  a  metal  in  the  15th  century  by  Basil  Valen- 
tine, and  is  said  to  derive  its  name  (afui-wtoine,  anti-monk}  from  having 
proved  fatal  to  some  monks  to  whom  it  was  given  as  a  medicine.  It  some- 
times occurs  native ;  but  its  only  ore  which  is  abundant,  and  from  which  the 
antimony  of  commerce  is  derived,  is  the  sulphuret.  This  ore,  the  stibium 
of  the  ancients,  was  long  regarded  as  the  metal  itself,  and  was  called  anti- 
mony, or  crude  antimony ;  while  the  pure  metal  was  termed  the  regulus  of 
antimony. 

Prep. — Either  by  heating  the  native  sulphuret  in  a  covered  crucible  with 
half  its  weight  of  iron  filings;  or  by  mixing  it  with  two-thirds  of  its  weight 
of  cream  of  tartar  and  one  third  of  nitre,  and  throwing  the  mixture,  in  small 
successive  portions,  into  a  red-hot  crucible.  By  the  first  process  the  sulphur 
unites  with  iron,  and  in  the  second  it  is  expelled  in  the  form  of  sulphurous 
acid;  while  the  fused  antimony,  which  in  both  cases  collects  in  the  bottom 
of  the  crucible,  may  be  drawn  off  and  received  in  moulds.  The  antimony, 
thus  obtained,  is  not  absolutely  pure  ;  and,  therefore,  for  chemical  purposes, 
should  be  procured  by  heating  the  sesquioxide  with  an  equal  weight  of  cream 
of  tartar. 

Prop. — A  brittle  metal,  of  a  white  colour  running  into  bluish  gray,  and  is 
possessed  of  considerable  lustre.  Its  sp.  gr.  is  6'702.  At  810°  it  fuses,  and 
on  cooling  acquires  a  highly  lamellated  texture,  and  sometimes  yields 
crystals:  like  arsenic,  but  unlike  most  other  rnetals,  its  primary  form  is  a 
rhombohedron.  It  is  volatile  at  a  very  intense  temperature.  Its  surface 
tarnishes  by  exposure  to  the  atmosphere;  and  by  the  continued  action  of 
air  and  moisture,  a  dark  matter  is  formed,  which  Berzelius  regards  as  a 
definite  compound.  It  appears,  however,  to  be  merely  a  mixture  of  the 
sesquioxide  and  metallic  antimony.  Heated  to  a  white  or  even  full  red  heat 
in  a  covered  crucible,  and  then  suddenly  exposed  to  the  air,  it  inflames,  and 
burns  with  a  white  light.  During  the  combustion  a  white  vapour  rises, 
which  condenses  on  cool  surfaces,  frequently  in  the  form  of  small  shining 
needles  of  silvery  whiteness.  These  crystals  were  formerly  called  argentine 
flowers  of  antimony,  and  in  chemical  works  are  generally  described  as  anti- 
monious  acid;  but  they  are  correctly  considered  by  Berzelius  as  the  scsqui- 
oxide. 

From  the  experiments  of  Berzelius  on  the  composition  of  the  oxide  and 
acids  of  antimony  (An  de  Ch.  et  de  Ph.  xvii%  the  eq.  of  this  metal  may  be 


356 


estimated  at  64-6.    Its  symb.  is  Sb.    The  composition  of  its  compounds 
described  in  this  section  is  as  follows : — 


Two  eq. 
Antimony. 

Sesquioxide    129-2  4.  Oxygen 
Antimoni-      129.2+do  32 


24 


ous  acid 
Antimonic 
acid 


Bichlo- 
ride 


Equiv.  Formulee. 

153-2    2Sb-f3O  or  Sb2Q3. 

161-2   2Sb-f  4O  or 


3  eq. 

4  eq.= 

129-2  -f  do.  40        5eq.==169-2   2Sb  -f 5O  or  SbsO*. 

SSHde    |l29'2+Chlorine     106-26    3  eq. 
i  129-2  +  do.  141-68   4  eq. 

Composition  uncertain. 

48-3      3  eq. 


Bromide 


:  270-88  2Sb  +  4Cl  or  SbSCH. 
=306-3   2Sb-f-5ClorSb2C15. 


Bisulphuret  129-2-f-do. 
Persulphuret  129'2-j-do. 
Oxychlor.  J  Sesquiehloride 

of  antirn.  (  Sesquioxide 
Oxysulph.  S  Sesquisulphuret 

of  antim.  /  Sesquioxide 


64-4 
80-5 
470-92 
1378-8 
355 
153-2 


4  eq. 

5  eq. 
2eq. 
9  eq. 
2eq. 
leq. 


=177-5   2Sb-|-3S  or  Sb2S3. 

d93-6  2Sb-f4S  or  Sb2S4. 
=209-7  2Sb-r-5S  or  Sb2S5. 
=1849  72 )  2Sb2Cl3 

»508  -2 


Sesquioxide. — When  sesquiehloride  of  antimony,  made  by  boiling  the 
native  sulphuret  in  hydrochloric  acid  (page  252)  is  poured  into  water,  a 
white  curdy  precipitate  subsides,  formerly  called  powder  of  Algaroth,  which 
consists  of  sesquioxide  of  antimony  combined  with  undeeomposed  sesqui- 
chloride.  On  decomposing  the  latter  by  digestion  with  carbonate  of  potassa 
and  then  washing  with  water,  the  sesquioxide  is  obtained  in  a  state  of  purity. 
It  may  also  be  procured  by  adding  carbonate  of  potassa  or  soda  to  a  solution 
of  tartar  emetic,  and  by  sublimation  during  the  combustion  of  antimony, 
When  slowly  sublimed  it  condenses  in  fine  needles  of  silvery  whiteness.  It 
occurs  as  a  mineral,  the  oxide  of  antimony  of  mineralogists,  the  primary 
form  of  which  is  a  right  rhombic  prism,  isomorphous  with  the  crystals  of 
arsenious  acid  lately  observed  by  Wohler.  (Page  332.) 

Prop. — When  prepared  in  the  moist  way,  it  is  a  white  powder  with  a 
somewhat  dirty  appearance.  When  heated  it  acquires  a  yellow  tint,  and  at 
a  dull  red  heat  in  close  vessels  it  is  fused,  yielding  a  yellow  fluid,  which  be- 
comes an  opaque  grayish  crystalline  mass  on  cooling.  Its  sp.  gr.  is  5-566. 
It  is  very  volatile,  and  if  protected  from  atmospheric  air  may  be  sublimed 
without  change.  When  heated  in  open  vessels  it  absorbs  oxygen  ;  and  when 
the  temperature  is  suddenly  raised,  and  the  oxide  is  porous,  it  takes  fire  and 
burns.  In  both  cases  antimonious  acid  is  generated.  It  is  the  only  oxide 
of  antimony  which  forms  regular  salts  with  acids,  and  is  the  base  of  the 
medicinal  preparation  tartar  emetic,  the  tartrate  of  antimony  and  potassa. 
Most  of  its  salts,  however,  are  either  insoluble  in  water,  or,  like  chloride  of 
antimony,  are  decomposed  by  it,  owing  to  the  affinity  of  that  fluid  for  the 
acid  being  greater  than  that  of  the  acid  for  sesquioxide  of  antimony.  This 
oxide  is,  therefore,  a  feeble  base;  and,  indeed,  possesses  the  property  of 
uniting  with  alkalies.  To  the  foregoing  remark,  however,  tartrate  of  anti- 
mony and  potassa  is  an  exception ;  for  it  dissolves  readily  in  water  without 
change.  By  excess  of  tartaric  or  hydrochloric  acid,  the  insoluble  salts  of 
antimony  may  be  rendered  soluble  in  water. 

The  presence  of  antimony  in  solution  is  easily  detected  by  hydrosulphuric 
acid.  This  gas  occasions  an  orange-coloured  precipitate,  hydrated  sesqui- 
sulphuret  of  antimony,  which  is  soluble  in  pure  potassa,  and  is  dissolved 
srith  disengagement  of  hydrosulphuric  acid  gas  by  hot  hydrochloric  acid,. 


ANTIMONY.  357 

forming  a  solution  from  which  the  white  oxychloride  (powder  of  Jllgarotfc) 
is  precipitated  by  water. 

In  trying  the  effect  of  reagents  on  solutions  of  sesquioxide  of  antimony,  it 
is  convenient  to  employ  tartar  emetic,  from  its  property  of  dissolving  in  pure 
water  without  decomposition.  From  a  solution  of  this  salt,  when  moderately 
concentrated,  a  little  pure  potassa  throws  down  the  sesquioxide,  but  excess 
of  the  alkali  redissolves  the  precipitate.  The  oxide  is  more  perfectly  sepa- 
rated by  alkaline  carbonates.  Lime-water  causes  a  white  precipitate,  a 
mixed  tartrate  of  lime  and  sesquioxide  of  antimony  ;  and  earthy  and  metallic 
salts  decompose  tartar  emetic  by  forming,  like  lime,  sparingly  soluble  com- 
pounds with  tartaric  acid.  Decomposition  is  also  occasioned  by  most  acids, 
which  throw  down  a  sparingly  soluble  salt  of  antimony  and  cream  of  tartar; 
and  a  recently  made,  pretty  strong,  infusion  of  gall-nuts  gives  a  yellowish- 
white  precipitate,  which  consists  of  tannic  acid  and  sesquioxide  of  antimony. 
But  these  appearances  are  by  no  means  to  be  relied  on  as  tests  of  the  pre- 
sence of  antimony  :  a  mixture  of  other  substances  might  be  similarly  influ- 
enced by  the  same  reagents.  In  a  moderately  dilute  solution  of  tartar  emetic 
most  of  them  produce  no  effect  whatever;  aad  the  too  free  addition  of  a  pure 
alkali  or  of  an  acid,  even  to  a  strong  solution,  may  altogether  prevent  that 
precipitate  from  forming,  which  a  smaller  quantity  of  the  same  reagents 
would  have  produced.  The  only  certain  method  of  bringing  the  antimony 
into  view,  even  in  a  very  weak  solution,  is  to  acidulate  with  tartaric  acid, 
and  then  transmit  through  the  liquid  a  current  of  hydrosulphuric  acid  gas. 
The  hyd rated  sesquisulphuret  of  antimony,  of  a  characteristic  orange-red 
colour,  is  im mediately  formed. 

The  detection  of  antimony  in  mixed  fluids,  as  when  tartar  emetic  is  mixed 
with  articles  of  food,  is  conducted  in  the  following  manner : — The  substances 
are  first  digested  in  water  acidulated  with  about  a  drachm  of  hydrochloric 
and  tartaric  acids,  which  coagulate  some  organic  matters,  and  give  complete 
solubility  to  the  sesquioxide  of  antimony.  Through  the  filtered  liquid,  hydro- 
sulphuric  acid  is  then  transmitted,  when  the  orange-red  sesquisulphuret  of 
antimony  subsides,  which  preserves  its  characteristic  tint  even  when  depo- 
sited from  coloured  solutions,  and  may  be  further  recognized  by  solution  in 
hot  hydrochloric  acid  and  precipitation  by  water.  The  metal  itself  may  in 
general  be  obtained  by  placing  the  dry  sulphuret  in  a  glass  tube,  transmitting- 
through  it  a  current  of  hydrogen  gas,  and  then,  when  all  the  atmospheric  air 
is  displaced,  heating  the  sulphuret  by  the  flame  of  a  spirit-larnp.  The  sul- 
phur is  carried  off  in  the  form  of  hydrosulphuric  acid  gas,  and  the  metallic 
antimony,  recognizable  by  its  lustre,  remains.  The  metal  is  principally  found 
where  the  sulphuret  lay  ;  but  if  the  current  of  gas  during  the  reduction  hap- 
pen to  be  rapid,  it  causes  mechanically  a  spurious  sublimation  of  antimony, 
which  lines  part  of  the  tube  with  a  thin  film  of  metal.  When  much  organic 
matter  is  mixed  with  the  sulphuret,  the  metal  is  sometimes  indistinctly  seen. 
In  that  case  it  should  be  dissolved  in  a  few  drops  of  nitro-hydrochloric  acid 
with  heat,  and  be  precipitated  by  water ;  it  may  then  be  redissolved  by  tar- 
taric acid,  and  again  precipitated  with  its  characteristic  tint  by  hydrosul- 
phuric acid.  Orfila  recommends  that  the  metal  should  be  obtained  from  the 
sesquisulphuret  by  fusion  with  black  flux ;  but  I  have  elsewhere  shown  the 
process  to  be  very  precarious,  and  my  opinion  is  supported  by  the  experi- 
ence of  Christison.  (Treatise  on  Poisons,  2nd  ed.  429.)  It  may  be  detected, 
when  present  even  in  small  quantity,  by  decomposing  the  antimoniuretted 
hydrogen,  formed  as  described  at  page  336,  where  the  characters  by  which 
it  is  distinguished  from  arsenic,  are  given. 

Its  eq.  153-2  ;  symb.  2Sb-f3O,  Sb,  or  Sb^CX 

Antimonious  Acid. — When  metallic  antimony  is  digested  in  strong  nitric 
acid,  the  metal  is  oxidized  at  the  expense  of  the  acid,  arid  hydrated  antimonic 
acid  is  formed  ;  and  on  exposing  this  substance  to  a  red  heat,  it  gives  out 
water  and  oxygen  gas,  and  is  converted  into  antimonious  acid.  It  is  also 


358  ANTIMONY. 

generated  when  the  oxide  is  exposed  to  heat  in  open  vessels.  Thus,  on  heating 
sulphuret  of  antimony  with  free  exposure  to  the  air,  sulphurous  acid  and 
sesquioxide  of  antimony  are  generated;  but  on  continuing  the  roasting 
after  all  the  sulphur  is  burned,  the  sesquioxide  gradually  absorbs  oxygen 
and  passes  into  antimonious  acid.  Hence  this  acid  is  formed  in  the  process 
for  preparing  the  Pulvis  Antimonialis  of  the  Pharmacopoeia.  Antimonious 
acid  is  white  while  cold,  but  acquires  a  yellow  tint  when  heated,  is  very 
infusible,  and  fixed  in  the  fire,  two  characters  by  which  it  is  readily  dis- 
tinguished from  the  sesquioxide.  It  is  insoluble  in  water,  and  likewise  in 
acids  after  being  heated  to  redness.  It  combines  in  definite  proportions  with 
alkalies,  and  its  salts  are  called  antimonites.  Antimonious  acid  is  pre- 
cipitated from  these  salts  by  acids  as  a  hydrate,  which  reddens  litmus  paper, 
and  is  dissolved  by  hydrochloric  and  tartaric  acids,  though  without  appear- 
ing to  form  with  them  definite  compounds. 

Its  eq.  is  161-2  ;  symb.  2Sb-f4O,  Sb,  or  Sb2Q4. 

Antimonic  Acid,  sometimes  called  peroxide  of  antimony,  is  obtained  as  a 
white  hydrate,  either  by  digesting  the  metal  in  strong  nitric  acid,  or  by  dis- 
solving it  in  nitro-hydrochloric  acid,  concentrating  by  heat  to  expel  excess  of 
acid,  and  throwing  the  solution  into  water.  When  recently  precipitated  it 
reddens  litmus  paper,  and  may  then  be  dissolved  in  water  by  means  of  hy- 
drochloric or  tartaric  acid.  It  does  not  enter  into  definite  combination  with 
acids,  but  with  alkalies  forms  salts,  which  are  called  antimoniates.  When 
hydrated  antimonic  acid  is  exposed  to  a  temperature  of  500°  or  600°  F., 
the  water  is  evolved,  and  the  anhydrous  acid  of  a  yellow  colour  remains. 
In  this  state  it  resists  the  action  of  acids.  When  exposed  to  a  red  heat,  it 
parts  with  oxygen,  and  is  converted  into  antimonious  acid. 

Its  eq.  is  169-2 ;  symb.  2Sb-j-5O,  Sb,  or  SbsO. 

Chlorides  of  Antimony. — When  antimony  in  powder  is  thrown  into  a  jar 
of  chlorine  gas,  combustion  ensues,  and  the  sesquichloride  of  antimony  is 
generated.  The  same  compound  may  be  formed  by  distilling  a  mixture  of 
antimony  with  about  twice  and  a  half  its  weight  of  corrosive  sublimate, 
when  the  volatile  sesquichloride  of  antimony  passes  over  into  the  recipient, 
and  metallic  mercury  remains  in  the  retort.  At  common  temperatures  it  is 
a  soft  solid,  thence  called  butter  of  antimony,  which  is  liquefied  by  gentle 
heat,  and  crystallizes  on  cooling.  It  deliquesces  on  exposure  to  the  air; 
and  when  "mixed  with  water,  hydrochloric  acid  and  sesquioxide  are  ge- 
nerated,  and  the  latter,  combined  with  undecomposed  chloride,  subsides. 

Its  eq.  is  235-46  ;  symb.  2Sb-f-3Cl,  or  Sb«Cl». 

The  bichloride  of  antimony,  is  formed  by  acting  on  hydrated  antimonious 
by  hydrochloric  acid,  when  a  solution  is  formed,  which  appears  to  be  a 
compound  of  bichloride  of  antimony  and  hydrochloric  acid.  It  possesses 
little  permanence,  and  on  the  addition  of  water,  antimonious  acid  subsides, 
and  hydrochloric  acid  remains  in  solution. 

The  perchloride  is  generated  by  passing  dry  chlorine  gas  over  heated 
metallic  antimony.  It  is  a  transparent  volatile  liquid,  which  emits  fumes 
on  exposure  to  the  air.  Mixed  with  water,  it  is  converted  into  hydrochloric 
acid,  and  hydrated  antimonic  acid  which  subsides.  (Rose,  in  the  Annals  of 
Philosophy,  'N.  S.  x.) 

Bromide  of  Antimony. — The  union  of  bromine  and  antimony  is  attended 
with  disengagement  of  heat  and  light,  and  the  compound  is  readily  obtained 
by  distillation,  as  in  the  process  for  preptiring  bromide  of  arsenic.  It  is 
solid  at  common  temperatures,  is  fused  at  206°,  and  boils  at  518°  F.  It  is 
colourless,  and  crystallizes  in  needles ;  it  attracts  moisture  from  the  air,  and 
is  decomposed  by  water. 

Sesquisulphuret  of  Antimony. — This  is  by  far  the  most  abundant  ore  of 
antimony,  and  is  hence  employed  in  making  the  preparations  of  antimony. 


ANTIMONY.  359 

Though  generally  compact  or  earthy,  it  sometimes  occurs  in  acicular  crys- 
tals and  in  rhombic  prisms.  Its  sp.  gr.  is  4-62,  colour  red-gray,  and  its  lustre 
metallic.  When  heated  in  close  vessels,  it  enters  into  fusion  without  under,- 
going  any  other  change.  It  may  be  formed  artificially  by  fusing  together 
antimony  and  sulphur,  or  by  transmitting  a  current  of  hydrosulphuric  acid 
gas  through  a  solution  of  tartar  emetic  :  in  this  case  it  falls  as  a  hydrate  of 
an  orange-red  colour,  and  does  not  acquire  its  dark  colour  till  its  water  is 
expelled  by  heat. 

Its  eq.  is  177-5;  symb.  2Sb+3S,  orSb2Ss. 

The  bisulphuret  is  formed,  according  to  Rose,  by  transmitting  hydrosul- 
phuric acid  gas  through  a  solution  of  antimonious  acid  in  dilute  hydrochlo- 
ric  acid.  (An.  of  Phil.  N.  S.  x.) 

Its  eq.  is  193-6;  symb.  2Sb-f-4S,  or  Sb«S*. 

Rose  formed  the  persulphuret  by  the  action  of  hydrosulphuric  acid  on  a 
solution  of  antimonic  acid.  The  golden  sulphuret,  prepared  by  boiling  sul- 
phuret  of  antimony  and  sulphur  in  solution  of  potassa,  a  process  which  is 
not  adopted  by  either  of  our  colleges,  is  a  persulphuret.  Its  eq.  is  209*7  ; 
symb.  2Sb+5S,  or  S&2S5. 

Oxychloride  of  Antimony. — This  compound  has  lately  been  studied  by 
Malaguti  and  Johnston.  When  an  acid  solution  of  the  sesquichloride  of 
antimony  is  thrown  into  a  large  quantity  of  water,  a  white  voluminous  pre- 
cipitate forms.  Allowing  it  to  subside,  it  contracts  considerably  during 
thirty  or  forty  hours,  and  then  consists  of  a  thick  bed  of  minute  crystals. 
These  crystals  are  small  prismatic  needles,  of  a  white  colour  and  brilliant 
lustre;  they  are  decomposed  by  boiling  in  water,  by  continued  washings, 
and  by  the  alkaline  carbonates,  being  thus  converted  into  sesquioxide.  They 
have  been  analyzed  by  Johnston,  according  to  whom  they  are  composed  of 
two  eq.  of  the  sesquichloride  united  with  nine  eq.  of  the  sesquioxide;  a  com- 
position which  corresponds  closely  with  the  analysis  of  Malaguti.  Hence 
the  eq.  is  1849-72;  symb  2SbsCl«+9Sb2Os. 

Oxysulphuret  of  Antimony. — Hist,  and  Prep. — Rose  has  shown  that  this 
compound  occurs  in  the  mineral  kingdom,  being  the  red  antimony  ore  (roth- 
spiesglanzerz)  of  mineralogists.  The  pharmaceutic  preparations,  known  by 
the  terms  glass,  liver,  and  crocus  of  antimony,  are  of  a  similar  nature, 
though  less  definite  in  composition.  They  are  made  by  roasting  the  native 
sesquisulphuret,  so  as  to  form  sulphurous  acid  and  sesquioxide  of  antimony, 
and  then  vitrefying  the  oxide  together  with  undecomposed  ore,  by  means  of 
a  strong  heat.  The  product  will  of  course  differ  according  as  more  or  less 
of  the  sulphuret  escapes  oxidation  during  the  process. 

When  sesquisulphuret  of  antimony  is  boiled  in  a  solution  of  potassa  or 
soda,  a  liquid  is  obtained,  from  which  on  cooling  an  orange-red  matter  called 
kermes  mineral  is  deposited ;  and  on  subsequently  neutralizing  the  cold  s%lu- 
tion  with  an  acid,  an  additional  quantity  of  a  similar  substance,  the  golden 
sulphuret  of  the  Pharmacopoeia,  subsides.  These  compounds  may  also  be 
obtained  by  igniting  sesquisulphuret  of  antimony  with  an  alkali  or  alkaline 
carbonate,  and  treating  the  product  with  hot  water  ;  or  by  boiling  the  mine- 
ral in  a  solution  of  carbonate  of  soda  or  potassa.  The  finest  kermes  is  ob- 
tained, according  to  M.  Cluzei,  from  a  mixture  of  4  parts  of  sulphuret  of  an- 
timony, 90  of  crystallized  carbonate  of  soda,  and  1000  of  water.  These  mate- 
rials are  boiled  for  half  or  three  quarters  of  an  hour ;  the  hot  solution  is 
filtered  into  a  warm  vessel,  in  order  that  it  may  cool  slowly ;  and  after  24 
hours  the  deposite  is  collected  on  a  filter,  moderately  washed  with  cold  wa- 
ter, and  dried  at  a  temperature  of  70°  or  80°  F. 

Prop. — Very  great  diversity  of  opinion  has  long  existed  among  chemists 
as  to  the  nature  of  kermes.  Berzelius  and  Rose  gave  experiments  to  show 
that  it  is  a  hydrated  sesquisulphuret,  differing  from  the  native  sulphuret 
solely  in  being  combined  with  water.  Subsequently  Gay-Lussac  and  others 
observed  that  kermes  contains  sesquioxide  of  antimony,  which  may  be  re- 
moved by  digestion  with  cream  of  tartar ;  and  Gay-Lussac  inferred  from  the 


360  URANIUM. 

quantity  of  water  formed  when  kermes,  previously  rendered  anhydrous,  is 
reduced  by  hydrogen  gas,  that  it  is  a  hydrated  oxysulphuret,  identical,  when 
deprived  of  its  water,  with  the  red  ore  of  antimony  above  referred  to.  Still 
more  recently  Berzelius  has  explained,  that  the  ordinary  process  for  making 
kermes  leads  to  the  separation  of  a  compound  of  sesquioxide  of  antimony 
and  potassa,  which  tenaciously  adheres  to  kermes,  but  is  not  chemically 
united  with  it :  he  rightly  argues  that  the  question  is  not  whether  sesquioxide 
of  antimony  is  sometimes  or  generally  present  in  kermes,  but  whether  the 
latter  can  exist  without  sesquioxide  of  antimony.  This  question  he  has  an- 
swered affirmatively.  He  fused  sesquisulphuret  of  antimony  with  black  flux, 
boiled  the  residue  in  water,  and  set  aside  the  solution  to  cool :  a  perfect 
kerrnes  was  deposited,  which  he  considers,  and  I  apprehend  with  good  rea- 
son, to  be  quite  free  from  sesquioxide  of  antimony.  (Pog.  Annalen,  xx.  364.) 
The  theory  of  the  preparation  of  kermes,  as  given  by  Berzelius,  is  the  fol- 
lowing.— When  sesquisulphuret  of  antimony  is  fused  with  potassa,  part  of 
each  interchanges  elements  with  the  other  in  such  a  ratio  that 

1  eq.  sesquisulp't  of  ant.,  2Sb-j-3S,  2   1  eq.  sesquioxide  of  antimony,  2Sb-f-3O, 
and  3  eq.  potassa,  3(K+O),  -^  &3eq.  sulphuret  of  potassium,  3(K-|-S). 

The  sulphuret  of  potassium  unites  with  undecomposed  sesquisulphuret  of 
antimony,  forming  a  sulphur-salt  which  will  be  again  referred  to  hereafter, 
and  sesquioxide  of  antimony  with  undecomposed  potassa;  and  on  adding 
hot  water  both  compounds  are  dissolved,  and  coexist  independently  of  each 
other  in  the  solution.  As  the  solution  cools,  the  sesquisulphuret  of  anti- 
mony subsides,  simply  because  the  solvent  power  of  sulphuret  of  potassium 
is  thereby  diminished ;  but  a  variable  quantity  of  potassa  and  sesquioxide  of 
antimony  falls  with  the  deposite,  and  cannot  be  entirely  removed  by  washing 
with  water.  The  cold  solution  still  contains  a  double  sulphuret  of  antimony 
and  potassium,  together  with  sesquioxide  of  antimony  united  with  potassa  : 
on  acidulating  with  sulphuric  acid,  the  sulphuret  of  potassium  is  resolved, 
by  decomposition  of  water,  into  potassa  and  hydrosulphuric  acid,  and  the 
sesquioxide  of  antimony  is  deprived  of  its  potassa;  and,  therefore,  the  ses- 
quisulphuret and  sesquioxide  of  antimony,  both  losing  at  the  same  instant 
the  principles  which  gave  them  solubility,  are  thrown  down  either  in  com- 
bination or  in  mixture  with  each  other.  Berzelius  believes  the  same  change 
to  occur  when  the  ingredients  are  boiled  instead  of  fused  together.  The 
golden  sulphuret  differs  from  kermes,  in  the  absence  of  potassa,  in  contain- 
ing more  sesquioxide  of  antimony,  and  perhaps  in  being  or  containing  an 
oxysulphuret.  It  commonly  contains  free  sulphur,  derived  apparently  from 
the  oxidizing  influence  of  the  air  on  the  sulphuret  of  potassium.  When  alka- 
line carbonates  are  employed  instead  of  pure  alkalies,  the  same  phenomena 
ensue,  except  that  carbonic  acid  is  evolved. 
Its  eq.  is  508-2 ;  symb.  2Sb2S3-r-Sb2Q3. 


SECTION    XIX. 


URANIUM    AND   CERIUM. 

URANIUM. 

Hist,  and  Prep. — THIS  metal  was  discovered  in  1798  by  the  German 
analyst  Klaproth,  who  named  it  after  the  new  planet  Uranus,  the  discovery 
of  which  took  place  in  the  same  year.  It  was  obtained  from  a  mineral  of 
Saxony,  called  from  its  black  colour  pitchblende,  which  consists  of  protoxide 


URANIUM.  361 

of  uranium  and  oxide  of  iron.  From  this  ore  the  uranium  may  be  conve- 
niently extracted  by  the  following1  process: — After  heating  the  mineral  to 
redness,  and  reducing  it  to  fine  powder,  it  is  digested  in  pure  nitric  acid  di- 
luted with  three  or  four  parts  of  water,  taking-  the  precaution  to  employ  a 
larger  quantity  of  the  mineral  than  the  nitric  acid  present  can  dissolve.  By 
this  mode  of  operating,  the  protoxide  is  converted  into  sesquioxide  of  ura- 
nium, which  unites  with  the  nitric  acid  almost  to  the  total  exclusion  of  the 
iron.  A  current  of  hydrosulphuric  acid  gas  is  then  transmitted  through  the 
solution,  in  order  to  separate  lead  and  copper,  the  sulphurets  of  which  are 
always  mixed  with  pitchblende.  The  solution  is  boiled  to  expel  free  hydro- 
sulphuric  acid,  and,  after  being  concentrated  by  evaporation,  is  set  aside  to 
crystallize.  The  nitrate  of  sesquioxide  of  uranium  is  gradually  deposited  in 
flattened  four-sided  prisms  of  a  beautiful  lemon-yellow  colour. 

Prop. — The  properties  of  metallic  uranium  are  as  yet  known  imperfectly. 
Its  sp.  gr.,  according  to  Buchholz,  is  9.  It  was  prepared  by  Arfwedson  by 
conducting  hydrogen  gas  over  the  protoxide  of  uranium  heated  in  a  glass 
tube.  The  substance  obtained  by  this  process  was  crystalline,  of  a  me- 
tallic lustre,  and  of  a  reddish-brown  colour.  It  suffered  no  change  on  expo- 
sure to  air  at  common  temperatures;  but  when  heated  in  open  vessels,  it 
absorbed  oxygen,  and  was  reconverted  into  the  protoxide.  From  its  lustre 
it  was  inferred  to  be  metallic  uranium. 

From  the  experiments  of  Arfwedson  and  Berzelius  on  the  oxides  of  uranium, 
the  eq.  of  the  metal  may  be  estimated  at  217.  (An.  of  Ph.  N.  S.  vii.  258)  ;  its 
symb.  is  U.  Its  compounds  described  in  this  section  are  thus  constituted: — 

Uranium.  Equiv.  Formulae. 

Protoxide  217  1  eq.  4.  Oxygen       8       1  eq.=225         U+O  or  UO. 

Sesquioxide       434  2  eq.-j-do.  24       3  eq.=458       2U+3O  or  UKK 

Protochloride    217  1  eq.-{- Chlorine   3542  1  eq.=252-42    U-f-Cl  or  UC1. 
Sesquichloride  434  2  eq.  4- do.          106-26  3  eq.=54O26  2U+3C1  or  U^Cls. 
Sulphuret          Composition  unknown. 

Protoxide. — This  oxide  is  of  a  very  dark  green  colour,  and  is  obtained  by 
exposing  nitrate  of  the  sesquioxide  to  a  strong  heat.  It  is  exceedingly  infu- 
sible, and  bears  any  temperature  hitherto  tried  without  change.  It  unites 
with  acids,  forming  salts  of  a  green  colour.  It  is  readily  oxidized  by  nitric 
acid,  yielding  a  nitrate  of  the  sesquioxide.  The  protoxide  is  employed  in 
the  arts  for  giving  a  black  colour  to  porcelain. 

Its  eq.  is  225 ;   symb.  U+O,  U,  or  UO. 

Sesquioxide  of  Uranium  is  of  a  yellow  or  orange  colour,  and  most  of  its 
salts  have  a  similar  tint.  It  not  only  combines  with  acids,  but  likewise  unites 
with  alkaline  bases,  a  property  which  was  first  noticed  by  Arfwedson.  It  is 
precipitated  from  acids  as  a  yellow  hydrate  by  pure  alkalies,  fixed  or  vola- 
tile ;  but  retains  a  portion  of  these  bases  in  combination.  It  is  thrown  down 
as  a  carbonate  by  alkaline  carbonates,  but  is  redissolved  by  an  excess  of 
carbonate  of  soda  or  ammonia,  a  circumstance  which  affords  an  easy  method 
of  separating  uranium  from  iron.  It  is  not  precipitated  by  hydrosulphurie 
acid,  but  acquires  a  green  tint  from  partial  deoxidation.  With  ferrocya- 
nuret  of  potassium  it  gives  a  brownish-red  precipitate,  very  like  ferrocyanuret 
of  copper. 

Sesquioxide  of  uranium  is  decomposed  by  a  strong  heat,  and  converted 
into  the  protoxide.  From  its  affinity  for  alkalies,  it  is  difficult  to  obtain  it  in|a 
state  of  perfect  purity.  It  is  employed  in  the  arts  for  giving  an  orange  co- 
lour to  porcelain. 

Its  eq.  is  458 ;  symb.  2U  +  3O,  U,  or  UsQs. 

Chlorides. — These  compounds  are  obtained  in  solution  by  dissolving  the 
corresponding  oxides  in  hydrochloric  acid.  The  protochloride  is  green,  very 
soluble,  and  does  not  crystallize.  The  sesquichloride  is  yellow,  deliquescent, 
soluble  in  alcohol,  ether,  and  water,  and  yields  yellow  solutions. 

31 


362  CERIUM. 

Sulphuret  of  Uranium  may  be  formed  by  transmitting  the  vapour  of  bi- 
sulphuret  of  carbon  over  protoxide  of  uranium  strongly  heated  in  a  tube  of 
porcelain.  (Rose.)  It  is  of  a  dark-gray  or  nearly  black  colour,  is  converted  into 
protoxide  of  uranium  when  heated  in  the  open  air,  and  is  readily  dissolved 
by  nitric  acid.  Hydrochloric  acid  attacks  it  feebly. 

CERIUM. 

Cerium,  named  after  the  planet  Ceres,  was  discovered  in  the  year  1803  by 
Hisinger  and  Berzelius,  in  a  rare  Swedish  mineral  known  by  the  name  of 
cerite,  and  its  existence  was  recognized  about  the  same  time  by  Klaprotb. 
Thomson  has  since  found  it  to  the  extent  of  thirty-four  percent  in  a  mineral 
from  Greenland,  called  Allanite,  in  honour  of  the  late  Mr.  Allan,  who  first 
distinguished  it  as  a  distinct  species. 

The  properties  of  cerium  are  in  a  great  measure  unknown.  It  appears 
from  the  experiments  of  Vauquelin,  who  obtained  it  in  minute  buttons  not 
larger  than  the  head  of  a  pin,  that  it  is  a  white  brittle  metal,  which  resists  the 
action  of  nitric,  but  is  dissolved  by  nitro-hydrochloric  acid.  According  to  an 
experiment  made  by  Children  and  Thomson,  metallic  cerium  is  volatile  in 
very  intense  degrees  of  heat.  (An.  of  Phil,  ii.) 

From  the  experiments  of  Hisinger,  the  eq.  of  cerium  may  be  estimated  at 
46 ;  its  symb.  is  Ce  ;  and  its  compounds  described  in  this  section  are  thus 
constituted : — 

Cerium.  Equiv.         Formulae. 

Protoxide  46    1  eq.  4-  Oxygen     8      1  cq.=  54         Ce-fOorCeO. 

Sesquioxide       !)2    2eq.-f-do.  24      3eq.=  116       2Ce-f.3O  orCe2(X 

iProtochloride    46    1  eq.-f  Chlorine  35-42  1  eq.=  81-42    Ce-f-Cl  or  CeCl. 
Sesquichloride  92   2  eq.-fdo.          106-26  3  eq-=198-26  2Ce-j-3ClorCe2Cls. 
Sulphuret          46   1  eq.-j-  Sulphur   16-1    leq.==62-l      Ce-f-SorCeS. 

Protoxide. — This  oxide  is  a  white  powder,  which  is  insoluble  in  water,  and 
forms  salts  with  acids,  all  of  which,  if  soluble,  have  an  acid  reaction.  Ex- 
posed to  the  air  at  common  temperatures  it  suffers  no  change  ;  but  if  heated 
in  open  vessels,  it  absorbs  oxygen  and  is  converted  into  the  sesquioxide.  It 
is  precipitated  from  its  salts  as  a  white  hydrate  by  pure  alkalies  ;  as  a  white 
carbonate  by  alkaline  carbonates,  but  is  redissolved  by  the  precipitant  in 
excess;  and  as  a  white  oxalate  by  oxalate  of  ammonia. 

Its  eq.  is  54 ;  symb.  Ce-f-O,  Ce,  or  CeO. 

Sesquioxide. — The  most  convenient  method  of  extracting  sesquioxide  of 
cerium  from  cerite  is  by  the  process  of  Laugier.  After  reducing  cerite  to 
powder,  it  is  dissolved  in  nitro-hydrochloric  acid,  arid  the  solution  is  eva- 
porated to  perfect  dryness.  The  soluble  parts  are  then  redissolved  by  water, 
and  an  excess  of  ammonia  is  added.  The  precipitate  thus  formed,  consisting 
of  the  oxides  of  iron  and  cerium,  is  well  washed,  and  afterwards  digested  in 
a  solution  of  oxalic  acid,  which  dissolves  the  iron,  and  forms  an  insoluble 
oxalate  with  the  cerium.  By  heating  this  oxalate  to  redness  in  an  open  fire, 
the  acid  is  decomposed,  and  the  sesquioxide  of  cerium  is  obtained  in  a  pure 
state.  It  has  a  fawn-red  colour  ;  is  dissolved  by  several  of  the  acids,  but  is  a 
weaker  base  than  the  protoxide.  Digested  in  hydrochloric  acid,  chlorine  is 
disengaged  and  a  protochloride  results. 

Its  eq.  is  116;  symb.  2Ce-f3O,  Ce,  or  Ce^O*. 

Chlorides  of  Cerium- — The  prot ochloride  is  obtained  as  a  porous  white  mass 
by  heating  sulphuret  of  cerium  in  a  current  of  dry  chlorine  gas.  It  is 
fusible  at  a  low  red  heat,  deliquesces  in  the  air,  and  is  soluble  in  water  and 
alcohol.  Its  solution  is  colourless ;  but  in  open  vessels  it  becomes  yellow 
from  the  formation  of  sesquichloride,  undergoing  the  same  kind  of  change 
as  the  protochlorides  of  iron  and  tin. 

Its  eq.  is  81-42;  symb.  Ce-j-Cl,  or  CeCl. 


BISMUTH.  363 

The  sesquichloride  is  formed  by  dissolving  sesquioxide  of  cerium  in  hy- 
drochloric acid,  and  it  forms  an  orange-yellow  solution. 

Its  eq.  is  198-26;  symb.  2Ce-f3Cl,  or  Ce^CK 

Sulphuret  of  Cerium. — Mosander  has  succeeded  in  forming  this  compound 
by  two  different  processes.  The  first  method  is  by  transmitting  the  vapour 
of  bisulphuret  of  carbon  over  carbonate  of  protoxide  of  cerium  at  a  red  heat; 
and  the  second  is  by  fusing  protoxide  of  cerium  at  a  white  heat  with  a  large 
excess  of  persulphuret  of  potassium,  and  afterwards  removing  the  soluble 
parts  by  water.  The  product  of  the  first  operation  is  porous,  light,  and  of  a 
red  colour  like  red  lead  ;  and  that  of  the  second  is  in  small  brilliant  scales, 
and  of  a  yellow  colour,  like  bisulphuret  of  tin.  These  sulphurets,  though 
different  in  appearance,  are  similar  in  point  of  composition,  containing  26 
per  cent,  of  sulphur.  They  are  insoluble  in  water,  but  are  dissolved  in  acids 
with  evolution  of  hydrosulphuric  acid  gas,  without  any  residuum  of  sul- 
phur. (Philos.  Mag.  and  Annals,  i.  71.)  Its  eq.  is  62-1 ;  symb.  Ce-f  S,  or 
CeS. 


SECTION    XX. 


BISMUTH,  TITANIUM  AND  TELLURIUM. 

BISMUTH. 

Hist,  and  Prep. — THIS  metal  was  known  to  the  ancients,  though  often 
confounded  by  them  with  lead  and  tin ;  but  it  appears  to  have  derived  the 
name  of  bismuth,  or  properly  wismuth,  from  the  German  miners.  It  occurs 
in  the  earth  both  native  and  in  combination  with  other  substances,  such  as 
sulphur,  oxygen,  and  arsenic.  That  which  is  employed  in  the  arts  is  de- 
rived chiefly  from  native  bismuth,  and  commonly  contains  small  quantities 
of  sulphur,  iron,  and  copper.  It  may  be  obtained  pure  for  chemical  purposes 
by  heating  the  protoxide  or  subnitrate  to  redness  along  with  charcoal. 

Prop. — Bismuth  has  a  reddish-white  colour  and  considerable  lustre.  Its 
structure  is  highly  lamellated,  and  when  slowly  cooled,  it  crystallizes  in 
cubes  or  octahedrons.  It  density  9 '822.  It  is  brittle  when  cold,  but  may  be 
hammered  into  plates  while  warm.  At  476°  it  fuses,  and  sublimes  in  close 
vessels  at  a  red  heat.  It  is  a  less  perfect  conductor  of  heat  than  most  other 
metals. 

Bismuth  undergoes  little  change  by  exposure  to  air  at  common  tempera- 
tures.  When  fused  in  open  vessels,  its  surface  becomes  covered  with  a  gray 
film,  which  is  a  mixture  of  metallic  bismuth  with  the  protoxide  of  the  metal. 
Heated  to  its  subliming  point,  it  burns  with  a  bluish-white  flume,  and  emits 
copious  fumes  of  protoxide  of  bismuth.  The  metal  is  attacked  with  difficulty 
by  hydrochloric  or  sulphuric  acid,  but  it  is  readily  oxidized  and  dissolved  by 
nitric  acid. 

The  eq.  of  bismuth,  deduced  by  Lagerjelm  from  the  composition  of  its 
protoxide,  is  71  (An.  of  Phil.  iv.  357) ;  its  symb.  is  Bi.  Its  compounds  de- 
scribed in  this  section  are  thus  constituted : — 

Bismuth.  Equiv.         Formulae. 

Protoxide        71     1  eq.-f  Oxygen        8       1  eq.=  79         Bi-fOorBiO. 

Sesquioxide  142    2  eq.-f  do.  24      3  eq.=166      2Bi+3O  or  BiOs. 

Chloride          71     1  eq.-f  Chlorine  35-42  1  eq.=106-42    Bi-f  Cl  or  BiCl. 

Bromide          71     1  eq.-f  Bromine  78-4    1  eq.=149-4      Bi -f  Br  or  BiBr. 

Sulphuret        71     1  eq.-f  Sulphur  16-1    1  eq.=  87-1      Bi-fS  or  BiS. 


364  TITANIUM. 

Protoxide  of  Bismuth. — This  compound  is  readily  prepared  by  heating 
to  redness  the  nitrate  or  subnitrate  of  protoxide  of  bismuth.  Its  colour  is 
yellow;  at  a  full  red-heat  it  is  fused  into  a  brown  liquid,  which  on  cooling 
becomes  a  yeltew  transparent  glass  of  sp.  gr.  8-211.  At  intense  tempera- 
tures' it  is  sublimed.  It  unites  with  acids,  and  most  of  its  salts  are  white. 

When  nitrate  of  protoxide  of  bismuth,  either  in  solution  or  in  crystals,  is 
put  into  water,  a  copious  precipitate,  the  subnitrate,  of  a  beautifully  white 
colour,  subsides,  which  was  formerly  called  the  magistery  of  bismuth. 
From  its  whiteness  it  is  sometimes  employed  as  a  paint  for  improving  the 
complexion  ;  but  it  is  an  inconvenient  pigment,  owing  to  the  facility  with 
which  it  is  blackened  by  hydrosulphuric  acid.  If  the  nitrate  with  which 
it  is  made  contains  no  excess  of  acid,  and  a  large  quantity  of  water  is  em- 
ployed, nearly  the  whole  of  the  bismuth  is  separated  as  a  subnitrate.  By 
this  character  bismuth  may  be  both  distinguished  and  separated  from  other 
metals. 

Its  eq.  is  79  ;  symb.  Bi+O,  Bi,  or  BiO. 

Sesquioxide. — This  oxide  was  first  noticed  by  Buchholz  and  Brandes,  but 
its  nature  and  composition  have  been  recently  examined  by  A.  Stromeyer. 
It  is  generated  when  hydrate  of  potassa  is  fused  at  a  moderate  heat  with 
protoxide  of  bismuth  ;  but  the  best  mode  of  preparation  is  first  to  prepare  the 
protoxide  by  igniting  the  subnitrate,  and  then  gently  heating  it  for  some  time 
in  a  solution  of  chloride  of  potassa  or  soda.  After  washing  with  water,  any 
unchanged  protoxide  is  dissolved  by  a  solution  made  with  one  part  of  nitric 
acid  (quite  free  from  nitrous  acid)  and  nine  of  water. 

As  thus  prepared,  sesquioxide  of  bismuth  is  a  heavy  powder  of  a  brown  co- 
lour, very  like  peroxide  of  lead,  manifests  little  disposition  to  unite  either 
with  acids  or  alkalies,  and  is  reconverted  by  heat  with  loss  of  oxygen  into 
the  protoxide.  Heated  with  sulphuric  or  phosphoric  acid,  it  gives  off  oxygen 
gas,  and  a  sulphate  or  phosphate  of  the  protoxide  is  formed  ;  and  with  hydro- 
chloric acid,  chlorine  is  evolved,  and  the  protochloride  produced  (An.  de  Ch. 
et  de  Ph.  li.  267). 

Its  eq.  is  166  ;  symb.  2Bi4-3O,J3i,or  Bi^CX 

Chloride  of  Bismuth. — When  bismuth  in  fine  powder  is  introduced  into 
chlorine  gas,  it  takes  fire,  burns  with  a  pale  blue  light,  and  is  converted  into 
a  chloride,  formerly  termed  butter  of  bismuth.  It  may  be  prepared  con- 
veniently by  heating  two  parts  of  corrosive  sublimate  with  one  of  bismuth, 
and  afterwards  expelling  the  excess  of  the  former,  together  with  the  metallic 
mercury,  by  heat. 

Chloride  of  bismuth  is  of  a  grayish-white  colour,  opaque,  and  of  a  granular 
texture.  It  fuses  at  a  temperature  a  little  above  that  at  which  the  metal 
itself  is  liquefied,  and  bears  a  red  heat  in  close  vessels  without  subliming. 

Its  eq.  is  106-42  ;  symb.  Bi+Cl,  or  Bid. 

Bromide  of  Bismuth  is  prepared  by  heating  the  metal  with  a  large  excess 
of  bromine  in  a  long  tube  ;  when  a  gray-coloured  bromide  results,  similar  in 
its  aspect  to  fused  iodine.  At  392°  it  enters  into  fusion,  and  at  a  low  red 
heat  sublimes.  With  water  it  is  converted  into  protoxide  of  bismuth  and 
hydrobromic  acid,  the  former  of  which  combines  with  some  undecomposed 
bromide  of  bismuth  as  an  oxy bromide.  (Serullas.) 

Its  eq.  is  149-4;  symb.  Bi+Br,  or  BiBr. 

Sulphuret  of  Bismuth. — This  sulphuret  is  found  native,  and  may  be 
formed  artificially  by  fusing  bismuth  with  sulphur,  or  by  the  action  of  hy- 
drosulphuric acid  on  the  salts  of  bismuth.  It  is  of  a  lead-gray  colour  and 
metallic  lustre. 

Its  eq.  is  87-1  ;  symb.  Bi+S,  or  BiS. 

TITANIUM. 

Hist. — This  metal  was  first  recognized  as  a  new  substance  by  Mr.  Gregor 
of  Cornwall,  and  its  existence  was  afterwards  established  by  Klaproth,  who 


TITANIUM.  365 

HJr  *'  '  fP\ 

fancifully  gave  it  the  name  of  titanium,  after  the  Titans  of  ancient  fable. 

(Contributions,  i.)  But  the  properties  of  the  metal  were  not  ascertained  in  a 
satisfactory  manner  until  the  year  1822,  when  Wollaston  was  led  to  examin< 
some  minute  crystals  which  were  found  in  a  slag  at  the  bottom  of  a  smelting 
furnace  at  the  great  iron  works  at  Merthyr  Tydvil  in  Wales,  and  pre- 
sented to  him  by  Buckland.  (Philosophical  Transactions,  1823.)  These 
crystals,  which  have  since  been  found  at  other  iron  works,  are  of  a  cubic 
form,  and  in  colour  and  lustre  resemble  burnished  copper.  They  are  found 
in  the  blast  furnaces,  and  are  probably  derived  principally  from  the  hearth- 
stone,  which  contains  them  abundantly.  They  conduct  electricity,  and  are 
attracted  slightly  by  the  magnet,  a  property  which  seems  owing  to  the  pre- 
sence of  a  minute  quantity  of  iron.  Their  sp.  gr.  is  5'3 ;  and  their  hardness 
is  so  great,  that  they  scratch  a  polished  surface  of  rock  crystal.  They  are 
exceedingly  infusible ;  but  when  exposed  to  the  united  action  of  heat  and 
air,  their  surface  becomes  covered  with  a  purple-coloured  film,  which  is  an 
oxide.  They  resist  the  action  of  nitric  and  nitro-hydrochloric  acids,  but  are 
completely  oxidized  by  being  strongly  heated  with  nitre.  They  are  then 
converted  into  a  white  substance,  which  possesses  all  the  properties  of  titanic 
acid. 

Prep. — Liebig  prepares  metallic  titanium  by  putting  fragments  of  recently 
made  chloride  of  titanium  and  ammonia  into  a  glass  tube  half  an  inch  wide 
and  two  or  three  feet  long,  transmitting  through  it  a  current  of  perfectly 
dry  ammonia,  and,  when  atmospheric  air  is  entirely  displaced,  applying  heat 
until  the  glass  softens.  Complete  decomposition  ensues,  nitrogen  gas  is 
disengaged,  hydrochlorate  of  ammonia  sublimes,  and  metallic  titanium  is 
left  in  the  state  of  a  deep  blue-coloured  powder.  If  exposed  to  the  air  while 
warm,  it  is  apt  to  take  fire. 

The  eq.  of  titanium,  determined  by  Rose  from  his  analysis  of  the  bichloride, 
is  24-3 ;  its  symb.  is  Ti.  The  composition  of  its  compounds  described  in 
this  section  is  as  follows  : — 

One  eq. 

Titanium.  Equiv.        Formulae. 

Oxide  (probably)  24-3-J-Oxygen       8  1  eq.=  32-3    Ti-fO  or  TiO. 

Titanic  acid    .    24-3-j-do.  16  2  eq.=40-3    Ti+2O  or  TiO^. 

Bichloride       .    24-3-j-Chlorine  70-84  2  eq.=95-14  Ti+2Cl  or  TiCl«, 

Bisulphuret     .    24-3-f  Sulphur  32-2  2  eq.=56-5    Ti+2S  or  TiS*. 

Oxide  of  Titanium. — When  titanic  acid  is  exposed  to  a  strong  heat  in  a 
black  lead  crucible,  a  mass  is  obtained,  the  exterior  crust  of  which  is  me- 
tallic titanium,  but  the  interior  parts  consist  of  the  supposed  oxide.  As  thus 
prepared  it  is  a  black  mass,  which  has  an  earthy  fracture,  is  quite  insoluble 
in  all  acids,  and  is  very  difficult  to  oxidize.  Oxide  of  titanium  is  formed  in 
the  moist  way,  when  a  fragment  of  zinc  or  iron  is  introduced  into  a  solution 
of  titannic  acid  in  hydrochloric  acid.  The  solution  soon  acquires  a  purple 
tint,  and  after  a  time  the  whole  of  the  titanic  acid  is  thrown  down  in  the 
form  of  a  deep  purple  powder.  This  cannot  be  collected,  owing  to  the  fa- 
cility with  which  it  is  reconverted  into  titanic  acid ;  hence  its  composition 
and  chemical  properties  are  unknown. 

Titanic  Acid. — Hist,  and  Prep. — This  compound,  called  also  peroxide  of 
titanium,  has  been  carefully  studied  by  H.  Rose,  who  first  pointed  out  its  acid 
properties.  It  occurs  in  a  nearly  pure  state  in  the  minerals  rutile  and  anatase, 
which  are  remarkable  for  presenting  the  same  chemical  compound,  crystal., 
lized  in  unconnected  forms.  It  also  exists  in  titanite  or  sphene  as  titanate 
and  silicate  of  lime,  and  in  menaccanite  as  titanate  of  the  oxides  of  iron  and 
manganese,  in  the  latter  of  which  titanium  was  originally  discovered  by  Gre» 
gor.  It  is  best  prepared  from  rutile.  The  mineral,  after  being  reduced  to 
an  exceedingly  fine  powder,  is  fused  in  a  platinum  crucible  with  three  times 
its  weight  of  carbonate  of  potassa,  and  the  mass  afterwards  washed  with  wa, 
ter  to  remove  the  excess  of  alkali.  A  gray  mass  remains,  which  consists  of 

31* 


366  TITANIUM. 

potassa  and  titanic  acid.  This  compound  is  dissolved  in  concentrated  hydro- 
chloric acid  ;  and  on  diluting  with  water,  and  boiling  the  solution,  the  greater 
part  of  the  titanic  acid  is  thrown  down.  It  is  then  collected  on  a  filter,  and 
well  washed  with  water  acidulated  with  hydrochloric  acid.  In  this  state  it 
is  not  quite  pure  ;  but  contains  a  little  oxide  of  manganese  and  iron,  derived 
from  the  rutile.  The  best  mode  of  separating  these  impurities  is  to  digest  the 
precipitate,  whtfe  still  moist,  with  hydrosulphate  of  ammonia,  which  con- 
verts the  oxides  of  iron  and  manganese  into  sulphurets,  but  does  not  act  on 
the  titanic  acid.  The  two  sulphurets  are  readily  dissolved  by  dilute  hydro- 
chloric acid  ;  and  the  titanic  acid,  after  being  collected  on  a  filter  and  well 
washed  as  before,  may  be  dried  and  heated  to  redness.  This  method,  pro- 
posed by  Rose  of  Berlin,  has  been  thus  simplified  by  himself.  Either  rutile 
or  titaniferous  iron,  after  being  pulverized  and  washed,  is  exposed  in  a  por- 
celain tube,  at  a  very  strong  red  heat,  to  a  current  of  hydrosulphuric  acid 
gas,  which  acts  upon  the  oxide  of  iron,  giving  rise  to  water  and  sulphuret  of 
iron.  As  soon  as  the  water  ceases  to  appear,  the  process  is  discontinued,  the 
mass  digested  in  hydrochloric  acid  to  remove  the  iron,  and  the  titanic  acid 
separated  from  adhering  sulphur  by  heat.  A  little  iron  is  still  usually  re- 
tained; but  the  whole  may  be  removed  by  a  repetition  of  the  same  process. 
(An.  de  Ch.  et  de  Ph.  xxiii.  and  xxxviii.  131.) 

Prop. — Titanic  acid,  when  pure,  is  quite  white.  It  is  exceedingly  infusi- 
ble ;  and  after  being  once  ignited  it  ceases  to  be  soluble  in  acids,  except  in  the 
hydrofluoric.  In  its  chemical  relations  it  is  analogous  to  silicic  acid,  being 
a  feeble  acid,  insoluble  in  water,  without  action  on  test  paper,  but  combining 
with  metallic  oxides.  In  the  state  of  hydrate,  as  when  precipitated  from  hy- 
drochloric acid  by  boiling,  or  when  combined  with  an  alkali  after  fusion,  it 
has  a  singular  tendency  to  pass  through  the  pores  of  a  filter  when  washed 
with  pure  water  ;  but  the  presence  of  a  little  acid,  alkali,  or  salt,  prevents  this 
inconvenience. 

If  previously  ignited  with  carbonate  of  potassa,  titanic  acid  is  soluble  in 
dilute  hydrochloric  acid  ;  but  it  is  retained  in  solution  by  so  feeble  an  attrac- 
tion, that  it  is  precipitated  merely  by  boiling.  It  is  likewise  thrown  down 
by  the  pure  and  carbonated  alkalies,  both  fixed  arid  volatile.  A  solution  of 
gall-nuts  causes  an  orange-red  colour,  which  is  very  characteristic  of  titanic 
acid ;  an  effect  which  appears  owing  to  tannic,  and  not  to  gallic  acid.  When 
a  rod  of  zinc  is  suspended  in  the  solution,  a  purple-coloured  powder,  probably 
the  oxide,  is  precipitated,  which  is  gradually  converted  into  titanic  acid.  Its 
eq.  is  40-3  ;  symb.  Ti+2O,  Ti,  or  TiO. 

Bichloride  of  Titanium. — This  substance  was  discovered  in  the  year  1824 
by  Mr.  George  of  Leeds,  by  transmitting  dry  chlorine  gas  over  metallic  tita- 
nium at  a  red  heat.  Rose  prepared  it  for  his  analysis  by  heating  a  mixture 
of  titanic  acid  and  charcoal  in  a  tube,  through  which  dry  chlorine  gas  was 
passing  :  the  resulting  bichloride  was  purified  from  adhering  free  chlorine  by 
agitation  either  with  mercury  or  potassium,  and  repeated  distillation.  At 
common  temperatures  it  is  a  transparent  colourless  fluid  of  considerable  sp. 
gr.,  boils  violently  at  a  temperature  a  little  above  212°,  and  condenses  again 
without  change.  Dumas  has  shown  that  the  density  of  its  vapour  may  be 
estimated  at  6-615.  In  open  vessels  it  is  attacked  by  the  moisture  of  the  at- 
mosphere, and  emits  dense  white  fumes  of  a  pungent  odour  similar  to  that  of 
chlorine,  but  not  so  offensive.  On  adding  a  few  drops  of  water  to  a  few 
drops  of  the  liquid,  combination  ensues  with  almost  explosive  violence,  from 
the  evolution  of  intense  heat ;  and  if  the  water  is  not  in  excess,  a  solid  hydrate 
is  obtained.  On  exposure  to  the  air  it  deliquesces,  and  on  adding  water  the 
greater  part  is  dissolved.  The  bichloride,  when  exposed  to  an  atmosphere  of 
dry  ammonia,  absorbs  a  large  quantity  of  the  gas,  and  becomes  solid.  It 
was  from  this  compound  Liebig  prepared  metallic  titanium.  Its  eq.  is  95-14; 
symb.  Ti-r-2Cl,  or  TICK  - 

Bisulphuret  of  Titanium. — This  compound  was  discovered  by  Rose,  who 


TELLURIUM.  367 

prepared  it  by  transmitting  the  vapour  of  bisulphuret  of  carbon  over  titanic 
acid,  heated  to  whiteness  in  a  tube  of  porcelain.  It  occurs  in  thick  green 
masses,  which  by  the  least  friction  acquire  a  dark  yellow  colour  and  metallic 
lustre.  When  heated  in  the  open  air  it  is  converted  into  sulphurous  and 
titanic  acids.  By  acids  it  is  slowly  decomposed,  and  is  dissolved  by  hydro- 
chloric acid  with  disengagement  of  hvdrosulphuric  acid  gas. 
Its  eq.  is  56-5  ;  symb.  Ti+28,  or 


TELLURIUM. 

Hist.  —  A  rare  metal,  hitherto  found  only  in  the  gold  mines  of  Transylvania, 
and  even  there  in  very  small  quantity.  Its  existence  was  inferred  by  M  filler 
in  the  year  1782,  and  fully  established  in  1798  by  Klaproth,  who  gave  it  the 
name  of  tellurium,  from  tellus,the  earth,  suggested  by  the  source  from  which 
he  drew  the  name  of  uranium.  (Contributions,  iii.)  It  occurs  in  the  metallic 
state,  chiefly  in  combination  with  gold  and  silver. 

Prop.  —  It  has  a  tin-white  colour  running  into  lead-gray,  a  strong  metallic 
lustre,  and  lamellated  texture.  It  is  very  brittle,  and  its  density  is  6  115.  It 
fuses  at  a  temperature  below  redness,  and  at  a  red  heat  is  volatile.  When 
heated  before  the  blowpipe,  it  takes  fire,  burns  rapidly  with  a  blue  flame 
bordered  with  green,  and  is  dissipated  in  gray-coloured  pungent  inodorous 
fumes.  The  odour  of  decayed  horse-radish  is  sometimes  emitted  during  the 
combustion,  and  was  thought  by  Klaproth  to  be  peculiar  to  tellurium  ;  but 
Berzelius  ascribes  it  solely  to  the  presence  of  selenium. 

From  some  experiments  of  Berzelius,  the  eq.  of  tellurium  is  64-2;  its 
symb.  is  Te.  The  compounds  described  in  this  section  are  thus  con- 
stituted :  — 

One  eq. 

Tellurium.  Equiv.  Formulae. 

Tellurous  acid       64-2-f-Oxygen     16          2  eq.=  80-2      Te-}-2O  or  TeO. 
Telluric  acid         64-2-f-do.  24          3  eq.=  88-2       Te  +  3O  or  TeOs. 

Protochloride         64-2-fChIorine    35-42    ]  eq.=  99-62     Te-f-Cl  or  TeCl. 
Bichloride  64-2-f-do.  70.84    2  eq.=  135-04     Te-f2Cl  or  TeCls. 

Bisulphuret          64-2  -f-  Sulphur     32-2     2  eq.=  96-4      Te  -j-  2S  or  TeS  *. 
Persulphuret          Composition  uncertain. 
Hydrotelluric  acid  64  2-|-Hydrogen  1         1  eq.=   65  2       Te-f  H  or  TeH. 

Tellurous  Acid  —  This  compound,  also  called  oxide  of  tellurium,  is  ge. 
nerated  by  the  action  of  nitric  acid  on  tellurium,  by  which  acid  it  is  dis- 
solved; but  the  solution  possesses  such  little  permanence  that  mere  affusion 
of  water  precipitates  part  of  it,  and  the  rest  is  obtained  by  evaporating  to 
dryness.  In  this  state  it  is  a  white  granular  anhydrous  powder,  which 
slowly  reddens  moist  litmus  paper,  and  is  insoluble  in  water  and  acids.  By 
pure  potassa  or  soda  in  solution  it  is  dissolved,  and  is  rendered  soluble  by 
fusion  with  the  alkaline  carbonates,  forming  with  those  alkalies  crystallizable 
salts.  Acids,  added  in  slight  excess  to  the  alkaline  solutions,  throw  down 
tellurous  acid  as  a  white  flaky  hydrate,  which  if  washed  in  ice-cold  water, 
and  dried  at  a  temperature  not  exceeding  53°,  may  be  preserved  unchanged. 
In  this  state  it  is  freely  soluble  in  acids,  in  ammonia,  in  the  alkaline  car- 
bonates, from  which  it  expels  carbonic  acid,  and  even  to  considerable  extent 
in  pure  water.  Its  aqueous  solution  reddens  litmus  paper  :  it  becomes  turbid 
at  68°,  and  the  acid  which  falls  is  no  longer  soluble  in  acids.  In  these  pro- 
perties tellurous  acid  closely  resembles  the  titanic  and  several  other  feeble 
acids,  which  have  a  soluble  hydrated  state  easily  convertible  into  an  insoluble 
anhydrous  one.  Its  salts  are  precipitated  black  by  hydrosulphuric  acid, 
bisulphuret  of  tellurium  being-  formed.  It  is  deoxidized,  and  metallic  tel- 
lurium falls  as  a  black  powder,  when  a  piece  of  zinc,  tin,  iron,  or  anti- 
mony is  left  in  its  solution.  Its  eq.  is  80-2  ;  symb.  Te+20,  Te,  or  TeQ3. 

Telluric  Acid.  —  The  process  which  Berzelius  recommends  for  preparing 


368  TELLURIUM. 

this  compound  is  either  to  deflagrate  tellurous  acid  with  nitre,  or  to  mix  pure 
potassa  freely  with  a  solution  of  tellurite  of  potassa,  and  to  saturate  fully 
with  chlorine.  Nitric  acid  in  slight  excess  and  a  little  chloride  of  barium 
are  added,  in  order  to  precipitate  any  traces  of  sulphuric  and  selenic  acids ; 
and  after  separating  the  precipitate  by  filtration,  the  liquid  is  exactly  neu- 
tralized with  ammonia,  and  chloride  of  barium  added  as  long  as  it  causes  a 
precipitate.  The  tellurate  of  baryta  is  washed,  dried  by  a  gentle  heat,  and 
then  digested  with  a  fourth  of  its  weight  of  strong  sulphuric  acid  previously 
diluted  with  water :  the  filtered  solution  is  then  concentrated  by  a  water 
bath,  and,  on  cooling  or  subsequent  spontaneous  evaporation,  yields  hydrated 
telluric  acid  in  the  form  of  flat  six-sided  prisms.  Adhering  sulphuric  acid  is 
removed  by  alcohol. 

This  hydrate  consists  of  one  eq.  of  acid  and  three  eq.  of  water.  When 
heated  at  212°  it  loses  two  of  its  eq.  of  water  ;  and  on  heating  still  further 
all  its  water  is  expelled,  and  the  anhydrous  acid  of  a  lemon-yellow  colour 
remains.  In  this  state  it  is  insoluble  in  all  fluids,  whereas  the  hydrated  acid 
is  soluble  in  water ;  and  the  salts  of  the  former  differ  from  those  which  the 
latter  forms  with  the  same  bases.  Hence  heat  modifies  the  character  of 
telluric  acid  much  in  the  same  way  as  that  of  phosphoric  acid.  At  a  heat 
beyond  that  required  to  render  it  anhydrous,  telluric  acid  loses  oxygen  and 
is  reduced  to  tellurous  acid.  (Pog.  Annalen,  xxviii.  392.) 

Its  eq.  is  88-2;  symb.  Te+3O,  Te,  or  TeCM. 

Protochloride. — Rose  obtained  it  by  passing  a  feeble  current  of  chlorine 
gas  over  tellurium  at  a  strong  heat,  when  the  chloride  passes  over  as  a  violet 
vapour,  which  at  first  condenses  into  a  black  liquid,  and  when  quite  cold  be- 
comes a  solid  of  the  same  colour.  By  the  action  of  water  it  deposites  metallic 
tellurium,  and  the  bichloride  is  dissolved.  Its  eq.  is  99-62  ;  symb.  Te-f-Cl, 
or  TeCl. 

Bichloride. — Rose  obtained  this  in  the  same  manner  as  the  preceding 
chloride,  except  using  a  lower  heat  and  a  more  liberal  supply  of  chlorine. 
The  bichloride  is  also  volatile,  and  after  being  purified  from  free  chlorine  by 
agitation  with  mercury,  and  a  second  distillation,  it  condenses  into  a  white 
crystalline  solid.  By  a  gentle  heat  it  yields  a  brown  liquid,  but  recovers  its 
whiteness  on  cooling.  (Pog.  Annalen,  xxi.  443.) 

Its  eq.  is  135-04  ;  symb.  Te-{-2Cl,  or  TeCR 

Bisulphuret. — This  compound  falls  of  a  dark  brown,  nearly  black  colour, 
when  hydrosulphuric  acid  gas  is  transmitted  through  a  solution  of  bichloride 
of  tellurium,  tellurous  acid,  or  any  soluble  tellurite.  This  sulphuret  is  what 
Berzelius  calls  a  sulphur-acid,  forming  a  soluble  sulphur-salt  by  uniting  with 
sulphuret  of  potassium.  Hence  a  solution  of  caustic  potassa  dissolves  bisul- 
phuret  of  tellurium,  producing  the  same  kind  of  change  as  on  sesquisulphuret 
of  antimony.  (Page  360.) 

Its  eq.  is  96-4 ;  symb.  Te-f-2S,  or  TeS3. 

Persulphuret. — This  compound  falls  of  a  deep  yellow  colour,  when  a  salt 
of  telluric  acid  is  mixed  in  solution  with  persulphuret  of  potassium.  Its  ex- 
istence is  but  transient,  as  it  is  quickly  transformed  into  bisulphuret  and  be- 
comes black. 

Hydrolelluric  Acid. — This  gas,  discovered  by  Davy  in  1809,  is  formed  by 
acting  with  hydrochloric  acid  on  an  alloy  of  tellurium  with  zinc  or  tin.  It 
has  the  properties  of  a  feeble  acid,  very  analogous  in  odour,  and  apparently 
in  composition,  to  hydrosulphuric  acid  ;  It  is  absorbed  by  water,  forming  a 
claret-coloured  solution  ;  and  it  precipitates  many  metallic  salts,  yielding 
an  alloy  of  tellurium  with  the  other  metal.  It  is  deprived  of  its  hydrogen 
by  chlorine,  nitric  acid,  or  oxygen  of  the  atmosphere,  tellurium  being  sepa- 
rated. 

Its  eq.  is  65-2;  symb.  Te+H,  or  TeH. 


369 


SECTION   XXI. 


COPPER. 

Hist,  and  Prep. — ONE  of  the  most  abundant  of  the  metals,  and  was  well 
known  to  the  ancients.  Native  copper  is  by  no  means  uncommon,  being1 
found  more  or  less  in  most  copper  mines :  it  occurs  in  large  amorphous 
masses  in  some  parts  of  America,  and  is  sometimes  met  with  in  octohedral 
crystals  or  in  some  of  the  forms  allied  to  the  octohedron.  Stromeyer  has 
lately  discovered  it  in  several  specimens  of  meteoric  iron,  but  in  a  quantity 
not  exceeding  2-1000ths  of  the  mass.  The  copper  of  commerce  is  extracted 
chiefly  from  the  native  sulphuret ;  especially  from  copper  pyrites,  a  double 
sulphuret  of  iron  and  copper.  The  first  part  of  the  process  consists  in  roast- 
ing the  ore,  so  as  to  burn  off  some  of  the  sulphur,  and  leave  the  remainder 
as  a  subsulphate  of  the  oxides  of  iron  and  copper.  The  mass  is  next  heated 
with  some  unroasted  ore  and  siliceous  substances,  by  which  means  much  of 
the  iron  unites  in  the  state  of  black  oxide  with  silicic  acid,  and  rises  as  a 
fusible  slag  to  the  surface ;  while  most  of  the  copper  returns  to  the  state  of 
sulphuret.  It  is  then  subjected  to  long-continued  roasting,  when  the  greater 
part  of  the  sulphur  escapes  as  sulphurous  acid,  and  the  metal  is  oxidized  ; 
after  which  it  is  reduced  by  charcoal,  and  more  of  the  iron  separated  as  a 
silicate  by  the  addition  of  sand.  Lastly,  the  metal  is  strongly  heated  while 
a  current  of  air  plays  upon  its  surface:  the  impurities,  chiefly  sulphur  and 
iron,  being  more  oxidable  than  copper,  combine  with  oxygen  by  preference, 
and  the  copper  is  at  length  left  in  a  state  of  purity  sufficient  for  the  purposes 
of  commerce. 

Prop. — Distinguished  from  all  other  metals,  titanium  excepted,  by  having 
a  red  colour.  It  receives  a  considerable  lustre  by  polishing.  Its  density, 
when  fused,  is  8-895,  and  it  is  increased  by  hammering.  It  is  both  ductile 
and  malleable,  and  in  tenacity  is  inferior  only  to  iron.  It  is  hard  and  elastic, 
and  consequently  sonorous.  Its  point  of  fusion  is  1996°  F.  according  to 
Daniell,  being  less  fusible  than  silver  and  more  so  than  gold. 

It  undergoes  little  change  in  a  perfectly  dry  atmosphere,  but  is  rusted  in  a 
short  time  by  exposure  to  air  and  moisture,  being  converted  into  a  green 
substance,  carbonate  of  the  black  oxide  of  copper.  At  a  red  heat  it  absorbs 
oxygen,  and  is  converted  into  black  scales  of  protoxide.  It  is  attacked  with 
difficulty  by  hydrochloric  and  sulphuric  acids,  and  not  at  all  by  solutions  of 
the  vegetable  acids,  if  atmospheric  air  be  excluded ;  but  if  air  have  free  ac- 
cess, the  metal  absorbs  oxygen  with  rapidity,  the  attraction  of  the  acid  for 
the  protoxide  of  copper  co-operating  with  that  of  the  copper  for  oxygen. 
Nitric  acid  acts  with  violence  on  copper,  forming  a  nitrate  of  the  black 
oxide. 

The  most  trustworthy  experiments  for  determining  the  eq.  of  copper  are 
those  of  Berzelius  on  the  reduction  of  the  black  oxide  by  means  of  hydrogen 
gas  at  a  red  heat.  According  to  the  best  of  his  analyses,  8  parts  of  oxygen 
unite  with  31'6  parts  of  copper  to  constitute  the  black  oxide;  and, therefore, 
if  this  oxide  be  formed  of  an  atom  of  oxygen  united  with  an  atom  of  copper, 
the  eq.  of  this  metal  will  be  31-6.  This  opinion,  which  I  have  adopted,  is 
maintained  by  Thomson,  Berzelius,  and  many  continental  chemists.  Others 
consider  it  as  a  binoxide,  regarding  red  oxide  of  copper  as  the  real  protoxide ; 
and  these  take  twice  31*6  or  63-2  as  the  eq.  of  copper.  The  principal  arguments 
in  favour  of  the  former  view  are  these: — 1,  the  red  oxide  has  very  much  the 
character  of  a  suboxide,  a  term  frequently  used  to  designate  an  oxide  which 
has  little  or  no  tendency  to  unite  with  acids,  and  which  contains  less  than 
one  atom  of  oxygen  to  one  atom  of  metal ;  2,  the  product  of  the  eq.  and 
specific  heat  of  most  metals  is  a  constant  quantity,  and  copper  coincides  with 


370 


the  law,  provided  the  black  oxide  contain  an  atom  of  each  element  (page  35) ; 
3,  the  salts  of  the  black  oxide  are  isomorphous  with  the  salts  of  protoxide  of 
iron,  which  gives  a  strong  presumption  that  these  oxides  possess  the  same 
atomic  constitution. 

Its  symb.  is  Cu. 

The  composition  of  the  compounds  described  in  this  section  is  as  fol- 
lows : — 


Copper, 

Red  or  dioxide         63-2 
Black  or  protoxide  31-6 


Superoxide 

Dichloride 

Protochloride 

Diniodide 

Disulphuret 

Protosulphuret 

Triphosphuret 

Subsesquiphosph. 


31-6 
632 
31-6 
63-2 
63-2 
31-6 
94-8 
94-8 


Equiv.    Formulae. 

2  eq.-f  Oxygen      8  1  eq.=  71-2    2Cu-fO. 

1  eq.-f  do.  8  1  eq.=  39-6       Cu-fO. 

1  eq.-f  do.  16  2eq.=  47-6      Cu-f2O. 

2  eq.  -J-  Chlorine  35-42  1  eq.=  98-62  2Cu-f  Cl. 

1  eq.-f  do.  35-42  1  eq.=-  67-02     Cu-fCl. 

2  eq.-f  Iodine     126-3  1  eq.=189-5     2Cu-fI- 

2  eq.-f  Sulphur    16-1  1  eq.=  79-3     2Cu-fS. 
1  eq.-f  do.             16-1  1  eq.=:  47-7       Cu-f  S. 
3eq.-|-Phosph.     15-7  1  eq.=  110-5     3Cu-fP. 

3  eq.-f  do.  31-4  2  eq.=  126-2     3Cu+2P. 


Red  or  Dioxide. — Hist,  and  Prep. — This  compound  occurs  native  in  the 
form  of  octohedral  crystals,  and  is  found  of  peculiar  beauty  in  the  mines  of 
Cornwall.  It  may  be  prepared  artificially  by  heating  in  a  covered  crucible  a 
mixture  of  31'6  parts  of  copper  filings,  with  39-6  of  the  black  oxide ;  or  still 
better  by  arranging  thin  copper-plates  one  above  the  other  with  interposed 
strata  of  the  black  oxide,  and  exposing  them  to  a  red  heat  carefully  protected 
from  the  air.  Another  method  is  by  boiling  a  solution  of  acetate  of  protoxide 
of  copper  with  sugar,  when  the  dioxide  subsides  as  a  red  powder ;  and  ano- 
ther is  to  fuse  at  a  low  red  heat  the  dichloride  of  copper  with  about  an  equal 
weight  of  carbonate  or  bicarbonate  of  soda,  subsequently  dissolving  the  sea- 
salt  by  water,  and  drying  the  red  powder. 

In  this  case,  by  an  interchange  of  elements, 

1  eq.  dichloride  of  copper,  2Cu-fCl,3  1  eq.  red  oxide,   ....     2Cu+O, 
and  1  eq.  soda,  ....     Na-f  O, -^and  1  eq.  chloride  of  sodium,  Na-fCl. 

Malaguti  recommends  the  following  process : — 100  parts  of  sulphate  of 
copper,  and  57  of  carbonate  of  soda,  both  in  crystals,  are  fused  at  a  gentle 
heat ;  and  the  mass  left,  when  all  water  is  expelled,  is  pulverized  and  mixed 
with  25  parts  of  copper  filings.  The  mixture  is  pressed  into  a  crucible  and 
exposed  for  20  minutes  to  a  white  heat.  The  result  is  again  pulverized  and 
carefully  washed  (An.  de  Ch.  et  de  Ph.  liv.  216). 

Prop. — The  red  or  dioxide  of  copper  has  a  sp.  gr.  of  6*093,  and  in  colour 
is  very  similar  to  copper.  It  may  be  preserved  in  a  dry  atmosphere;  but  at 
a  red  heat  it  absorbs  oxygen  and  is  converted  into  the  protoxide.  Dilute 
acids  act  on  it  very  slowly ;  and  the  resulting  solution,  as  is  indicated  by  its 
tint,  does  not  arise  from  the  union  of  the  red  oxide  itself  with  the  acid,  but 
from  its  being  resolved,  like  other  suboxides,  into  metal  and  a  protoxide. 
With  strong  nitric  acid  it  is  oxidized,  binoxide  of  nitrogen  escapes,  and  a 
nitrate  of  the  black  oxide  is  formed.  Strong  hydrochloric  acid  forms  with  it 
a  colourless  solution,  from  which  alkalies  throw  it  down  as  a  hydrate  of  an 
orange  tint.  In  this  state  it  readily  absorbs  oxygen  from  the  air.  The  red 
oxide  of  copper  is  soluble  in  ammonia,  and  the  solution  is  quite  colourless ; 
but  it  becomes  blue  with  surprising  rapidity,  by  free  exposure  to  air,  owing 
to  the  formation  of  the  black  oxide. 

Its  eq.  is  71-2 ;  symb.  2Cu-f  O,  or  Cu2O. 

Black  or  Protoxide. — Hist,  and  Prep. — This  compound,  the  copper  black 
of  mineralogists,  is  sometimes  found  native,  being  formed  by  the  spontaneous 
oxidation  of  other  ores  of  copper.  It  may  be  prepared  artificially  by  calcining 
metallic  copper,  by  precipitation  from  the  salts  of  copper  by  means  of  pure 
polassa,  and  by  heating  nitrate  of  copper  to  redness. 


COPPER.  371 

Prop. — It  varies  in  colour  from  a  dark  brown  to  a  bluish-black,  according 
to  the  mode  of  formation;  its  sp.gr.  is  6'401.  It  undergoes  no  change  by 
heat  alone,  but  is  readily  reduced  to  the  metallic  state  by  heat  and  combusti- 
ble matter.  It  is  insoluble  in  water,  and  does  not  affect  the  vegetable  blue 
colours.  It  combines  with  nearly  all  the  acids,  forming  salts  which  have  a 
green  or  blue  tint.  It  is  soluble  likewise  in  ammonia,  forming  with  it  a  deep 
blue  solution,  a  property  by  which  protoxide  of  copper  is  distinguished  from 
all  other  substances.  Its  salts  are  distinguished  from  most  substances 
by  their  colour,  and  are  easily  recognized  by  reagents.  When  pure  soda  or 
potassa  is  mixed  with  a  solution  of  sulphate  of  the  protoxide,  a  greenish-blue 
disulphate  at  first  subsides ;  but  as  soon  as  the  alkali  is  added  in  excess,  a 
blue  bulky  hydrate  of  the  protoxide  is  formed,  which  is  decomposed  by  boil- 
ing,  and  consequently  becomes  black.  Pure  ammonia  also  throws  down  the 
disulphate  when  carefully  added;  but  an  excess  of  the  alkali  instantly  redis- 
solves  the  precipitate,  and  forms  a  deep  blue  solution.  Alkaline  carbonates 
cause  a  bluish-green  precipitate,  carbonate  of  the  protoxide,  which  is  redis- 
solved  by  an  excess  of  carbonate  of  ammonia.  It  is  precipitated  as  a  dark 
brown  sulphuret  by  hydrosulphuric  acid,  and  as  a  reddish-brown  ferrocya- 
nuret  by  ferrocyanuret  of  potassium.  It  is  thrown  down  of  a  yellowish- 
white  colour  by  albumen,  and  M.  Orfila  has  proved  that  this  compound  is 
inert ;  so  that  albumen  is  an  antidote  to  poisoning  by  copper. 

Copper  is  separated  in  the  metallic  state  by  a  rod  of  iron  or  zinc.  The 
copper  thus  obtained,  after  being  digested  in  a  dilute  solution  of  hydrochloric 
acid,  is  almost  chemically  pure.' 

The  best  mode  of  detecting  copper,  when  supposed  to  be  present  in  mixed 
fluids,  is  by  hydrosulphuric  acid.  The  sulphuret,  after  being  collected,  and 
heated  to  redness  in  order  to  char  organic  matter,  should  be  placed  on  a  piece 
of  porcelain,  and  be  digested  in  a  few  drops  of  nitric  acid.  Sulphate  of  prot- 
oxide of  copper  is  formed,  which,  evaporated  to  dryness,  strikes  the  charac- 
teristic deep  blue  tint  on  the  addition  of  ammonia. 

Its  eq.  is  39-6  ;  symb.  Cu-j-O,  Cu,  or  CuO. 

Superoxide. — This  oxide  was  prepared  by  Thenard  by  the  action  of  perox- 
ide of  hydrogen  diluted  with  water  on  the  hydrated  black  oxide.  It  suffers 
spontaneous  decomposition  under  water ;  but  it  may  be  dried  in  vacua  by 
means  of  sulphuric  acid. 

Its  eq.  is  47-6 ;  symb.  Cu+2O,  Cu,  or  CuO. 

Dichloride.— Prep. — When  copper  filings  are  introduced  into  an  atmos- 
phere of  chlorine  gas,  the  metal  takes  fire  spontaneously,  and  both  the  chlo- 
rides are  generated.  The  dichloride  may  be  conveniently  prepared  by  heating 
copper  filings  with  twice  their  weight  of  corrosive  sublimate.  In  this  way  it 
was  originally  made  by  Boyle,  who  termed  it  resin  of  copper,  from  its  resem- 
blance to  common  resin.  Proust,  who  called  it  uihite  muriate  of  copper,  pro- 
cured it  by  the  action  of  protochloride  of  tin  on  protochloride  of  copper;  and 
also  by  decomposing  the  protochloride  by  heat,  air  being  excluded.  It  is 
slowly  deposited  in  crystalline  grains  when  the  green  solution  of  protochloride 
of  copper  is  kept  in  a  corked  bottle  in  contact  with  metallic  copper. 

Prop. — The  dichloride  of  copper  is  fusible  at  a  heat  just  below  redness, 
and  bears  a  red  heat  in  close  vessels  without  subliming.  It  is  insoluble  in 
water,  but  dissolves  in  hydrochloric  acid,  and  is  precipitated  unchanged  by 
water  as  a  white  powder.  Its  colour  varies  with  the  mode  of  preparation, 
being  white,  yellow,  or  dark  brown.  It  is  apt  to  absorb  oxygen  from  the 
atmosphere,  forming  a  green-coloured  compound  of  protoxide  and  proto- 
chloride of  copper ;  a  change  to  which  the  dichloride,  prepared  in  the  moist 
way,  is  peculiarly  prone. 

Its  eq.  is  98-62 ;  symb.  2Cu+Cl,  or  Cu5Cl. 

Protochloride. — The  protochloride  of  copper  is  obtained  in  solution  of  a 
green  colour  by  dissolving  protoxide  of  copper  in  hydrochloric  acid,  and 
crystallizes  by  due  concentration  in  green  needles  which  are  deliquescent 
and  very  soluble  in  alcohol.  When  heated  they  fuse,  lose  water,  and  the 


372  LEAD. 

anhydrous  chloride  in  form  of  a  yellow  powder  is  left;  but  the  heat  must  not 
exceed  400°,  as  beyond  that  degree  the  chloride  loses  half  its  chlorine,  and 
is  converted  into  the  dichloride.  Its  eq.  is  67'02 ;  symb.  Cu-j-Cl,  or  CuCl. 

Diniodide  of  Copper. — This  substance  is  obtained  by  adding-  iodide  of  po- 
tassium to  a  solution  made  of  the  sulphate  of  the  protoxides  of  copper  and 
iron,  both  in  crystals,  in  the  ratio  of  1  to  2^,  when  the  protoxide  of  iron 
takes  the  oxygen  of  the  protoxide  of  copper,  and  the  iodine  the  metallic 
copper,  forming  a  white  precipitate,  the  diniodide.  It  may  be  dried,  and 
will  bear  a  high  temperature  in  close  vessels,  without  change;  but  if  heated 
with  the  oxides  of  iron,  manganese,  or  copper,  iodine  is  expelled  and  the 
copper  oxidized.  (Page  228.)  Its  eq.  is  189-5;  symb.  2Cu-{-I,  or  Cu3I. 

Protiodide  of  Copper  is  scarcely  known.  For  on  mixing  a  salt  of  prot- 
oxide of  copper  with  iodide  of  potassium,  iodine  is  set  free  and  the  diniodide 
of  copper  falls.  A  small  quantity  of  protoxide  of  copper  remains  in  so- 
lution. 

Sulphur ets  of  Copper. — The  disulphuret  is  a  natural  production,  well 
known  to  mineralogists  under  the  name  of  copper  glance ;  and  in  combination 
with  protosulphuret  of  iron,  it  is  a  constituent  of  variegated  copper  ore.  It 
is  formed  artificially  by  heating  copper  filings  with  a  third  of  their  weight 
of  sulphur,  the  combination  being  attended  with  such  free  disengagement  of 
heat,  that  the  mass  becomes  vividly  luminous. 

Its  eq.  is  79-3 ;  symb.  2Cu+S,  or  Cu^S. 

The  protosulphuret  is  formed  by  the  action  of  hydrosulphuric  acid  on  a 
salt  of  copper.  When  ignited  without  exposure  to  the  air,  it  loses  half  of  its 
sulphur,  and  is  converted  into  the  disulphuret. 

Its  eq.  is  47-7;  symb.  Cu-fS,  or  CuS. 

Phosphurets  of  Copper — Rose  states  that  the  triphosphuret  is  generated 
by  the  action  of  phosphuretted  hydrogen  gas  on  dichloride  of  copper ;  the 
mutual  interchange  of  elements  being  such  that 

3  eq.  dichloride  of  copper,  3(2Cu-f-Cl),  2  2  eq.  triphosphuret,  2(3Cu-|-P), 
and  1  eq.  phosphuretted  hyd.,*  3H+2P,  -^  &  3  eq.  hydrochl.  acid,  3(H-|-C1). 

The  subsesquiphosphuret  is  formed  by  a  similar  interchange  between  proto- 
chloride  of  copper  and  phosphuretted  hydrogen,  so  that 

3  eq.  protochloride  of  copper,  and  1  eq.  phosph.  hyd., 
3(Cu  +  CI)  3H  +  2P 

yield 

1  eq.  subsesquiphosphuret,  and  3  eq.  hydrochloric  acid. 
3Cu+2P  3(H-f-Cl). 

Rose  obtained  the  protophosphuret  by  the  action  of  hydrogen  gas  on  phos- 
phate of  protoxide  of  copper  at  a  red  heat.  All  these  phosphurets  resemble 
each  other,  being  pulverulent,  of  a  gray  colour,  insoluble  in  hydrochloric 
acid,  oxidized  and  dissolved  by  nitric  acid,  and  burn  with  a  phosphorus  flame 
before  the  blowpipe.  A  phosphuret  of  copper  is  also  obtained  by  transmitting 
phosphuretted  hydrogen  gas  through  a  solution  of  sulphate  of  protoxide  of 
copper;  but  the  dark  precipitate  which  fails  seems  to  be  a  variable  mixture 
of  different  phosphurets,  phosphoric  acid  being  generated  at  the  same  time. 
(An.  de  Ch.  et  de  Ph.  li.  47.) 


SECTION   XXII. 

LEAD. 

Hist,  and  Prep. — THIS  metal  was  well  known  to  the  ancients.  As  a  na- 
tive production  it  is  very  rare;  but  in  combination  with  sulphur  it  occurs  in 
great  quantity.  All  the  lead  of  commerce  is  extracted  from  the  native 


"V   -  LEAD.  373 

sulphuret,  the  galena  of  mineralogists.  This  ore,  in  the  state  of  a  coarse 
powder,  is  heated  in  a  reverberatory  furnace ;  when  part  of  it  is  oxidized, 
yielding  sulphate  of  protoxide  of  lead,  sulphuric  acid,  which  is  evolved,  and 
Jree  protoxide  of  lead.  These  oxidized  portions  then  react  on  sulphuret  of 
lead  :  by  the  reaction  of  two  eq.  of  protoxide  of  lead  and  one  of  the  sul- 
phuret, three  eq.  of  metallic  lead  and  one  of  sulphurous  acid  result;  while  one 
equivalent  of  the  sulphuret  and  one  of  sulphate  mutually  decompose  each 
other,  giving-  rise  to  two  eq.  of  sulphurous  acid  and  two  of  metallic  lead. 
The  slag  which  collects  on  the  surface  of  the  fused  lead  contains  a  large 
quantity  of  sulphate  of  protoxide  of  lead,  and  is  decomposed  by  the  addition 
of  quicklime,  the  oxide  so  separated  reacting  as  before  on  sulphuret  of  lead. 
The  lead  of  commerce  commonly  contains  silver,  iron,  and  copper. 

Prop. — It  has  a  bluish -gray  colour,  and  when  recently  cut,  a  strong  metallic 
lustre  ;  but  it  soon  tarnishes  by  exposure  to  the  air,  acquiring  a  superficial 
coating  of  carbonate  of  protoxide  of  lead.  (Christison.)  Its  sp.  gr.  is  11*352. 
It  is  soft,  flexible,  and  inelastic.  It  is  both  malleable  and  ductile,  possessing 
the  former  property  in  particular  to  a  considerable  extent.  In  tenacity,  it  is 
inferior  to  all  ductile  metals.  It  fuses  at  about  612°,  and  when  slowly  cooled 
forms  octohedral  crystals.  It  may  be  heated  to  whiteness  in  close  vessels 
without  subliming. 

Lead  absorbs  oxygen  quickly  at  high  temperatures.  When  fused  in  open 
vessels,  a  gray  film  is  formed  upon  its  surface,  which  is  a  mixture  of  me- 
tallic lead  and  protoxide  ;  and  when  strongly  heated,  it  is  dissipated  in  fumes 
of  the  protoxide.  In  distilled  water,  previously  boiled  and  preserved  in  close 
vessels,  it  undergoes  no  change;  but  in  open  vessels  it  is  oxidized  with  con- 
siderable rapidity,  yielding  minute,  shining,  brilliantly  white,  crystalline 
scales  of  carbonate  of  the  protoxide,  the  oxygen  and  carbonic  acid  being 
derived  from  the  air.  The  presence  of  saline  matter  in  water  retards  the 
oxidation  of  the  lead ;  and  some  salts,  even  in  very  minute  quantity,  pre- 
vent it  altogether.  The  protecting  influence,  exerted  by  certain  substances, 
was  first  noticed  by  Guyton  Morveau ;  but  it  has  been  minutely  investigated 
by  Christison  of  Edinburgh,  who  has  discussed  the  subject  in  his  excellent 
Treatise  on  Poisons.  He  finds  that  the  preservative  power  of  neutral  salts 
is  materially  connected  with  the  insolubility  of  the  compound  which  their 
acid  is  capable  of  forming  with  lead.  Thus,  phosphates  and  sulphates,  as 
well  as  chlorides  and  iodides,  are  highly  preservative  ;  so  small  a  quantity  as 
1 -30,000th  part  of  phosphate  of  soda  or  iodide  of  potassium  in  distilled  water 
preventing  the  corrosion  of  lead.  In  a  preservative  solution,  the  metal 
gains  weight  during  some  weeks,  in  consequence  of  its  surface  gradually 
acquiring  a  superficial  coating  of  carbonate,  which  is  slowly  decomposed  by 
the  saline  matter  of  the  solution.  The  metallic  surface  being  thus  covered 
with  an  insoluble  film,  which  adheres  tenaciously,  all  further  change  ceases. 
Many  kinds  of  spring  water,  owing  to  the  salts  which  they  contain,  do  not 
corrode  lead ;  and  hence,  though  intended  for  drinking,  it  may  be  safely 
collected  in  leaden  cisterns.  Of  this  the  water  of  Edinburgh  is  a  remarkable 
instance. 

Lead  is  not  attacked  by  the  hydrochloric  or  the  vegetable  acids,  though 
their  presence,  at  least  in  some  instances,  accelerates  the  absorption  of  oxygen 
from  the  atmosphere  in  the  same  manner  as  with  copper.  Cold  sulphuric 
acid  does  not  act  upon  it ;  but  when  boiled  in  that  liquid,  the  lead  is  slowly 
oxidized  at  the  expense  of  the  acid.  The  only  proper  solvent  for  lead  is  nitric 
acid.  This  reagent  oxidizes  it  rapidly,  and  forms  with  its  protoxide  a  salt 
which  crystallizes  in  opaque  octohedrons  by  evaporation. 

From  my  experiments  on  the  composition  of  the  protoxide  of  lead,  and  of 
the  nitrate  and  sulphate  of  that  oxide,  I  have  deduced  103-6  as  the  eq.,  a 
number  which  agrees  very  closely  with  the  researches  of  Berzelius  on  the 
same  subject.  (Phil.  Trans.  ]833,  part  ii.)  Its  symb.  is  Pb.  The  composi- 
tion of  its  compounds  described  in  this  section  is  as  follows: — 

32 


374 


LEAD. 


Dinoxide 
Protoxide 
Peroxide 

Red  oxide 
d  °Xlde 

Chloride 

Iodide 

Bromide 

Fluoride 

Sulphuret 

Phosphuret 

Carburet 


Lead.  Equiv.  Formula?, 

207-2  2  eq.-f  Oxygen       8  1  eq.=215-2  2Pb-+-O. 

103-6  1  eq.-f-do.  8  1  eq.=-lll-6      Pb-f-2O. 

103-6  1  eq.-f  do.  16  2  eq.=  119-6      Pb-f-20. 

310'8  3  eq-  +  do-  32  4  eq-  I  _q4o.ft  J  3Pb+40. 

or  protox.22T-22eq.+perox.ll9-6  1  eq.  ]  ~342  8  )  2PbO+PbO* 

103-6  1  eq.  4-  Chlorine  35-42  1  eq.=139-02  Pb+Cl. 

103-6  leq.  4.  Iodine     126-3  1  eq.=229-9  Pb+T. 

103-6  1  eq.  4.  Bromine    78-4  1  eq.=182  Pb-fBr. 

103-6  1  eq.-f  Fluorine  18-68  1  eq.=122-28  Pb+F. 

103-6  1  eq.-f  Sulphur    16-1  1  eq.—  119-7  Pb+S 
)  ^ 
ComPosltlon  uncertain. 


Dinoxide  of  Lead,  —  Dulong  observed  that  on  heating  dry  oxalate  of 
protoxide  of  lead  in  a  glass  tube  to  low  redness,  air  being  excluded,  a  mix- 
ture of  carbonic  acid  and  carbonic  oxide  gases  is  evolved,  and  a  suboxide  re- 
mains of  a  dark  gray,  nearly  black,  colour.  Boussingault  has  lately  proved 
that  it  is  a  dinoxide.  It  does  not  unite  with  acids,  but  is  resolved  by  them 
into  a  salt  of  the  protoxide  with  separation  of  metallic  lead.  (An.  de  Ch.  et 
de  Ph.  liv.  263.)  Its  eq.  is  215-2  ;  symb.  2Pb+O,  or  Pb^O. 

Protoxide.  —  Prep.  —  This  oxide  is  prepared  on  a  large  scale  by  collecting- 
the  gray  film  which  forms  on  the  surface  of  melted  lead,  and  exposing  it  to 
heat  and  air  until  it  acquires  a  uniform  yellow  colour.  In  this  state  it  is  the 
massicot  of  commerce  ;  and  when  partially  fused  by  heat,  the  term  litharge 
is  applied  to  it  As  thus  procured  it  is  always  mixed  with  the  red  oxide.  It 
may  be  obtained  pure  by  adding  ammonia  to  a  cold  solution  of  nitrate  of 
protoxide  of  lead  until  it  is  faintly  alkaline,  washing  the  precipitated  subni- 
trate  with  cold  water,  and  when  dry,  heating  it  to  moderate  redness  for  an 
hour  in  a  platinum  crucible.  An  open  fire  should  be  used,  and  great  care 
taken  to  prevent  combustible  matter  in  any  form  from  contact  with  the 
oxide. 

Prop.  —  It  is  red  while  hot,  but  has  a  rich  lemon-yellow  colour  when  cold, 
is  insoluble  in  water,  fuses  at  a  bright  red  heat,  and  is  fixed  and  unchange- 
able in  the  fire.  Its  sp.  gr.  is  9-4214.  The  fused  protoxide  has  a  highly  fo- 
liated texture,  and  is  very  tough,  so  as  to  be  pulverized  with  difficulty.  By 
transmitted  light  it  is  yellow  ;  but  by  reflected  light  it  appears  green  in  some 
parts,  and  yellow  in  others.  Heated  with  combustible  matters,  it  parts  with 
oxygen  and  is  reduced.  From  its  insolubility  it  does  not  change  the  vegeta- 
ble colours  under  common  circumstances;  but  when  rendered  soluble  by  a 
small  quantity  of  acetic  acid,  it  has  a  distinct  alkaline  reaction.  It  unites 
with  acids,  and  is  the  base  of  all  the  salts  of  lead,  most  of  which  are  of  a 
white  colour.  From  its  solutions  it  is  precipitated  by  pure  alkalies  as  a 
white  hydrate,  which  is  redissolved  by  potassa  in  excess  ;  as  a  white  carbo- 
nate, which  is  the  well-known  pigment  white  lead,  by  alkaline  carbonates  ; 
as  a  white  sulphate  by  soluble  sulphates  ;  as  a  dark  brown  sulphuret  by  hy- 
drosulphnric  acid  ;  and  as  yellow  iodide  of  lead  by  hydriodic  acid  or  iodide  of 
potassium. 

With  regard  to  the  poisonous  property  of  the  salts  of  lead,  a  remakable 
fact  has  been  observed  by  my  colleague  Dr.  A  T.  Thomson,  who  has  proved 
that  of  all  the  ordinary  preparations  of  load,  the  carbonate  is  by  far  the  most 
virulent  poison.  Any  salt  of  lead  which  is  easily  convertible  into  the  car- 
bonate, as  for  instance  the  subacetate,  is  also  poisonous  ;  but  he  has  given 
large  doses  of  the  nitrate  of  the  protoxide  and  chloride  of  lead  to  rabbits 
without  producing  perceptible  inconvenience.  He  finds  that  acetate  of  prot- 
oxide of  lead,  mixed  with  vinegar  to  prevent  the  formation  of  any  carbonate, 
may  be  freely  and  safely  administered  in  medical  practice. 

The  best  method  of  detecting  the  presence  of  lead  in  wine  or  other  sus- 
pected mixed  fluids  is  by  means  of  hydrosulphuric  acid.  The  sulphuret  of 
lead,  after  being  collected  on  a  filter  and  washed,  is  to  be  digested  in  nitric 


LEAD.  375 

acid  diluted  with  twice  its  weight  of  water,  until  the  dark  colour  of  the  sul- 
phuret  disappears.  The  solution  of  the  nitrate  should  then  be  brought  to 
perfect  dryness  on  a  watch-glass,  in  order  to  expel  the  excess  of  nitric  acid, 
and  the  residue  be  redissolved  in  a  small  quantity  of  cold  water.  On  drop- 
ping a  particle  of  iodide  of  potassium  into  a  portion  of  this  liquid,  yellow 
iodide  of  lead  will  instantly  appear. 

Protoxide  of  lead  unites  readily  with  earthy  substances,  forming  with 
them  a  transparent  colourless  glass.  Owing  to  this  property  it  is  much  em- 
ployed for  glazing  earthenware  and  porcelain.  It  enters  in  large  quantity 
into  the  composition  of  flint  glass,  which  it  renders  more  fusible,  transparent, 
and  uniform. 

Lead  is  separated  from  its  salts  in  the  metallic  state  by  iron  or  zinc.  The 
best  way  of  demonstrating  this  fact  is  by  dissolving  1  part  of  acetate  of 
protoxide  of  lead  in  24  of  water,  and  suspending  a  piece  of  zinc  in  the  so- 
lution by  means  of  a  thread.  The  lead  is  deposited  upon  the  zinc  in  a 
peculiar  arborescent  form,  giving  rise  to  the  appearance  called  arbor  Saturni. 

Its  eq.  is  111-6;  symb.  Pb-f  O,  Pb,  or  PbO. 

Red  Oxide. — Prep. — This  compound,  the  minium  of  commerce,  is  em- 
ployed as  a  pigment,  and  in  the  manufacture  of  flint  glass.  It  is  formed  by 
oxidizing  lead  by  heat  and  air  without  allowing  it  to  fuse,  and  then  exposing 
it  in  open  vessels  to  a  temperature  of  600°  or  700°,  while  a  current  of  air 
plays  upon  its  surface.  It  slowly  absorbs  oxygen  and  is  converted  into 
minium. 

Prop, — This  oxide  does  not  unite  with  acids.  When  heated  to  redness  it 
gives  off  pure  oxygen  gas,  and  is  reconverted  into  the  protoxide.  When  di- 
gested in  nitric  acid  it  is  resolved  into  protoxide  and  peroxide  of  lead,  the 
former  of  which  unites  with  the  acid,  while  the  latter  remains  as  an  insoluble 
powder.  From  the  facility  with  which  this  change  is  effected  even  by  acetic 
acid,  most  chemists  consider  red  lead,  not  so  much  as  a  definite  compound 
of  lead  and  oxygen,  but  as  a  salt  composed  of  the  protoxide  and  peroxide,  as 
stated  at  page  374.  This  oxide  had  been  long  considered  as  a  sesquioxide, 
an  error  first  corrected  by  Dalton  (New  System  of  Chemistry,  ii.  41,)  whose 
observation  has  been  confirmed  by  Dumas  and  Phillips.  (An.  de  Ch.  et  de 
Ph.  xlix.  398,  and  Phil.  Mag.  N.  S.  iii.  125.)  Dumas  shows  that  the  minium 
is  not  uniform  in  composition,  but  consists  of  variable  mixtures  of  the  prot- 
oxide with  real  red  lead.  The'former  may  be  oxidized  by  continued  exposure 
to  air  and  heat,  and  may  be  dissolved  by  acetic  acid  very  much  diluted  with 
cold  water. 

Its  eq.  is  342-8  ;  symb.  2PbO-f  PbO*. 

Peroxide. — Prep. — This  oxide  may  be  obtained  by  the  action  of  nitric 
acid  on  minium,  as  just  mentioned;  by  fusing  protoxide  of  lead  with  chlorate 
of  potassa,  at  a  temperature  short  of  redness,  and  removing  the  chloride  of 
potassium  by  solution  in  water;  and  by  transmitting  a  current  of  chlorine 
gas  through  a  solution  of  acetate  of  the  protoxide  of  lead.  In  the  last,  the 
reaction  is  such,  that 

1  eq.  chlorine  and  2  eq.  protox.  lead  2  1  eq.  perox.  lead  and  1  eq.  chloride  lead. 
Cl  2(Pb-fO)         -^          Pb-f  20  Pb+Cl. 

The  chloride  is  removed  by  washing  with  warm  water. 

Prop. — It  is  of  a  puce  colour,  is  insoluble  in  water,  and  is  resolved  by 
strong  oxacids,  such  as  the  sulphuric  and  nitric,  into  a  salt  of  the  protoxide 
and  oxygen  gas.  With  hydrochloric  acid  it  yields  chlorine  gas  and  chloride 
of  lead.  At  a  red  heat  it  emits  oxygen  gas  and  is  converted  into  the  prot- 
oxide. 

Its  eq.  is  119-6;  symb.  Pb-f  2O,  Pb,  or  PhO*. 

Chloride  of  Lead. — This  compound,  sometimes  called  horn  lead,  is  slowly 
formed  by  the  action  of  chlorine  gas  on  thin  plates  of  lead,  and  may  be  ob- 
tained more  easily  by  adding  hydrochloric  acid  or  a  solution  of  sea-salt  to 
acetate  or  nitrate  of  protoxide  of  lead  dissolved  in  water.  This  chloride 
dissolves  to  a  considerable  extent  in  hot  water,  especially  when  acidulated 


376  LEAD. 

with  hydrochloric  acid,  and  separates  on  cooling  in  small  acicular  anhydrous 
crystals  of  a  white  colour.  It  fuses  at  a  temperature  below  redness,  and 
forms  as  it  cools  a  semi-traneparent  mass,  which  has  a  density  of  5-133.  It 
bears  a  full  red  heat  in  close  vessels  without  subliming ;  but  in  open  vessels 
it  smokes  from  spurious  evaporation,  loses  some  of  its  chlorine  and  absorbs 
oxygen,  yielding  an  oxychloride  of  a  yellow  colour. 

Itseq.  is  139-02;  symb.  Pb-f  CI,  or  PbCl. 

Iodide  of  Lead  is  easily  formed  by  mixing  a  solution  of  hydriodic  acid  in 
excess  with  the  nitrate  of  protoxide  of  lead  dissolved  in  water.*  It  is  of  a 
rich  yellow  colour.  It  is  dissolved  by  boiling  water,  forming  a  colourless 
solution,  and  is  deposited  on  cooling  in  yellow  crystalline  scales  of  ^  brilliant 
lustre. 

Its  eq.  is  229-9  ;  symb.  Pb-f  I,  or  Pbl. 

Bromide  of  Lead. — It  falls  as  a  white  crystalline  powder,  of  sparing  solu- 
bility in  water,  when  a  soluble  salt  of  lead  is  mixed  with  bromide  of  potas- 
sium in  solution.  Exposed  to  heat  it  fuses  into  a  red  liquid  which  becomes 
yellow  when  cold. 

Its  eq.  is  182;  symb.  Pb-f  Br,  or  PbBr. 

Fluoride  of  Lead  is  formed  by  mixing  hydrofluoric  acid  with  acetate  of 
protoxide  of  lead,  and  falls  as  an  uncrystalline  white  powder  of  very  sparing 
solubility.  It  is  soluble  in  nitric  and  hydrochloric  acids,  but  is  decomposed 
when  the  solution  is  evaporated. 

Its  eq.  is  122-28  ;  symb.  Pb-f  F,  or  PbF. 

Sulphuret  of  Lead. — It  is  probable  that  lead  unites  with  sulphur  in  seve- 
ral different  proportions;  but  the  only  one  of  these  compounds  well  known 
to  chemists  is  the  native  sulphuret,  galena,  which  occurs  in  cubic  crystals, 
or  in  forms  allied  to  the  cube.  It  may  be  formed  artificially  by  fusing  lead 
with  sulphur,  or  by  the  action  of  hydrosulphuric  acid  on  a  salt  of  lead. 

Its  eq.  is  119-7 ;  symb,  Pb-f  S,  or  PbS. 

Phosphuret  of  Lead  has  been  little  examined.  It  may  be  formed  by  heat- 
ing phosphate  of  protoxide  of  lead  with  charcoal,  by  mixing  a  solution  of 
phosphorus  in  alcohol  or  ether  with  the  solution  of  a  salt  of  lead,  or  by  the 
action  of  phosphuretted  hydrogen  on  a  similar  solution. 

Carburet  of  Lead  may  be  obtained  by  reducing  protoxide  of  lead,  in  a  state 
of  fine  division  and  intimate  admixture  with  charcoal.  It  is  also  generated 
when  salts  of  lead,  which  contain  a  vegetable  acid,  are  decomposed  by  heat 
in  close  vessels.  (Berzelius.) 


*  An  easier  method  of  forming  this  iodide  is  by  double  decomposition  be- 
tween  solutions  of  iodide  of  potassium  and  nitrate  of  lead.  Iodide  of  lead 
precipitates,  and  nitrate  of  polassa  remains  in  solution. -^Ed. 


377 


CLASS  II. 
ORDER  III. 


METALS,  THE    OXIDES  OF  WHICH  ARE  REDUCED  TO  THE 
METALLIC  STATE  BY  A  RED  HEAT. 


SECTION     XXIII. 


MERCURY  OR  QUICKSILVER. 

Hist,  and  Prep. — THIS  metal  was  well  known  to  the  ancients.  The  prin- 
cipal mines  from  which  it  is  obtained  are  those  of  Idria  in  Carniola,  and 
Almaden  in  Spain,  where  it  is  found  both  in  the  native  state,  and  combined 
with  sulphur  as  cinnabar,  the  latter  being  the  most  abundant.  From  this  ore 
the  metal  is  extracted  by  heating  it  with  lime  or  iron  filings,  by  which 
means  the  mercury  is  volatilized  and  the  sulphur  retained.  As  prepared  on 
a  large  scale  it  is  usually  mixed  in  small  quantity  with  other  metals,  from 
which  it  may  be  purified  by  cautious  distillation. 

Prop. — Distinguished  from  all  other  metals  by  being  fluid  at  common 
temperatures.  It  has  a  tin-white  colour  and  strong  metallic  lustre.  It  be- 
comes solid  at  a  temperature  which  is  39  or  40  degrees  below  zero ;  and  in 
congealing  it  evinces  a  strong  tendency  to  crystallize  in  octohedrons.  It 
contracts  greatly  at  the  moment  of  congelation ;  for  while  its  density  at 
47°  is  13-568,  that  of  frozen  mercury  is  15-612.  When  solid  it  is  malleable, 
and  may  be  cut  with  a  knife.  At  662°  or  near  that  degree,  it  enters  into 
ebullition,  and  condenses  again  on  cool  surfaces  into  metallic  globules. 

Mercury,  if  quite  pure,  is  not  tarnished  in  the  cold  by  exposure  to  air  and 
moisture ;  but  if  it  contain  other  metals,  the  amalgam  of  those  metals  ox- 
idizes readily,  and  collects  as  a  film  upon  its  snrface.  It  is  said  to  be  oxidized 
by  long  agitation  in  a  bottle  half  full  of  air,  and  the  oxide  so  formed  was 
called  by  Boerhaave  ethiops  per  se ;  but  it  is  very  probable  that  the  oxidation 
of  mercury  observed  under  these  circumstances  was  solely  owing  to  the 
presence  of  other  metals.  When  exposed  to  air  or  oxygen  gas,  while  in  the 
form  of  vapour,  it  slowly  absorbs  oxygen,  and  is  converted  into  peroxide  of 
mercury. 

The  only  acids  that  act  on  mercury  are  the  sulphuric  and  nitric  acids, 
The  former  has  no  action  whatever* in  the  cold;  but  on  the  application  of 
heat,  the  mercury  is  oxidized  at  the  expense  of  the  acid,  pure  sulphurous  acid 
gas  is  disengaged,  and  a  sulphate  of  mercury  is  generated.  Nitric  acid  acts 
energetically  upon  mercury  both  with  and  without  the  aid  of  heat,  oxidizing 
and  dissolving  it  with  evolution  of  binoxide  of  nitrogen. 

From  some  late  analyses  of  the  peroxide  and  chloride  of  mercury,  I  have 
inferred  that  its  equivalent  is  202  (Phil.  Trans.  1833,  part  ii.) ;  its  symb, 
is  Hg.  The  composition  of  its  compounds  described  in  this  section  is  as 
follows  :— • 


378  MERCURY. 

Mercury.  Equiv.        Formulae. 

Protoxide          202  1  eq.-f  Oxygen     8       1  eq.=210       Hg-f  O  or  HgO. 
Peroxide  202  1  eq.-f  do.  16      2  cq.=218       Hg-f  2O  or  HgO*. 

Protochloride   202  1  eq.-f  Chlorine  35-42  1  eq.=237  -42  Hg-f  Cl  or  HgCl. 
Bichloride        202  1  eq.-f  do.  70-842  eq.  =272-84  Hg-f2Cl  or  HgCK 

Protiodide        202  1  eq.-f  Iodine  1263    1  eq.=  328-3    Hg-f  I  or  Hgl. 
Sesquiodide      404  2  eq.-f  do.        378-9    3  eq.=782-9  2Hg-f  31  or  HgsK 
Biniodide          202  1  eq.-f  do.        252-6    2  eq.=454-6    Hg-f  21  or  HgR 
Protobromide   202  1  eq.-f  Bromine  78-4    1  eq.  =280-4    Hg-f  Br  or  HgBr. 
Bibromide        202  1  eq.-f  do.        156-8    2  eq.  =358-8    Hg-f  2Br  or  HgBr ?. 
Protosulphuret202  1  eq.-f  Sulphur  16-1    1  eq.=218-l    Hg-fS  or  HgS. 
Bisulphuret      202  1  eq--f  do.          32-2    2  eq.  ==234-2    Hg-f  2S  or  HgS3. 
loduretted  bichloride  S  Bichlor.     5456-8  20  eq.  >        ^QQ  i   onu  ni«  i  T 

of  mercury  }  Iodine         126-3     1  eq.  $  =  ****'*  »»IMN-*- 

lodo-bichloride  of       S  Bichlor.  10913-6  40  eq.  S      HQAQO  ^ntr  <^i  > •  H^Ta 

mercury  )  Biniodide    454-6     ]  ^  }  =U368-2  40HgCl -f  Hgl* 

Protoxide. — Prep. — Best  by  the  process  recommended  by  Donovan  (An. 
of  Phil,  xiv.) :  this  consists  in  mixing  calomel  briskly  in  a  mortar  with  pure 
potassa  in  excess,  so  as  to  effect  its  decomposition  as  rapidly  as  possible ;  the 
protoxide  is  then  washed  with  cold  water,  and  dried  spontaneously  in  a  dark 
place.  These  precautions  are  rendered  necessary  by  the  tendency  of  the 
protoxide  to  resolve  itself  into  the  peroxide  and  metallic  mercury,  a  change 
which  is  easily  effected  by  heat,  by  the  direct  solar  rays,  and  even  by  day- 
light. It  is  on  this  account  very  difficult  to  procure  protoxide  of  mercury 
in  a  state  of  absolute  purity. 

Prop. — A  black  powder,  which  is  exceedingly  prone  to  decomposition,,  is 
insoluble  in  water,  unites  with  acids,  but  is  a  weak  alkaline  base.  It  is  pre- 
cipitated from  a  solution  of  its  salts,  of  which  the  nitrate  is  the  most  inte- 
resting, as  the  black  protoxide  by  pure  alkalies  ;  as  a  white  carbonate,  which 
soon  becomes  dark  from  the  loss  of  carbonic  acid,  by  alkaline  carbonates;  as 
calomel  by  hydrochloric  acid  or  any  soluble  chloride ;  and  as  the  black  proto- 
sulphuret  by  hydrosulphuric  acid.  Of  these  tests,  the  action  of  hydrochloric 
acid  is  the  most  characteristic.  The  oxide  is  reduced  to  the  metallic  state  by 
copper,  phosphorous  acid,  or  protochloride  of  tin. 

Its  eq.  is  210;  symb.  Hg+O,  Hg,  or  HgO. 

Peroxide— r-Prep.-^— Either  by  the  combined  agency  of  heat  and  air,  as  already 
mentioned,  or  by  dissolving  mercury  in  nitric  acid,  and  exposing  the  nitrate 
so  formed  to  a  temperature  just  sufficient  for  expelling  the  whole  of  the 
nitric  acid.  It  is  commonly  known  by  the  name  of  red  precipitate.  The 
peroxide  prepared  from  the  nitrate  almost  always  contains  a  trace  of  nitric 
acid,  which  may  be  detected  by  heating  it  in  a  clean  glass  tube  by  means 
of  a  spirit-lamp  :  a  yellow  ring,  formed  of  subnitrate  of  peroxide  of  mercury, 
collects  within  the  tube  just  above  the  part  which  is  heated.  (Clarke.) 

As  thus  prepared,  it  is  commonly  in  the  form  of  shining  crystalline  scales 
of  a  nearly  black  colour  while  hot,  but  red  when  cold:  when  very  finely  levi- 
gated, the  peroxide  has  an  orange  colour.  It  is  soluble"  to  a  small  extent  in 
water,  forming  a  solution  which  has  an  acrid  metallic  taste,  and  communi- 
cates a  green  colour  to  the  blue  infusion  of  violets.  When  heated  to  redness, 
it  is  converted  into  metallic  mercury  and  oxygen.  Long  exposure  to  light  has 
a  similar  effect,  (Guibourt.) 

Some  of  the  neutral  salts  of  this  oxide,  such  as  the  nitrate  and  sulphate, 
are  converted  by  water,  especially  at  a  boiling  temperature,  into  insoluble 
yellow  subsalts,  leaving  a  strongly  acid  solution,  in  which  a  little  of  the  ori- 
ginal salt  is  dissolved.  This  oxide  is  separated  from  all  acids  as  a  red,  or 
when  hydratic  as  a  yellow  precipitate,  by  the  pure  and  carbonated  fixed  al- 
kalies. Ammonia  and  its  carbonate  cause  a  white  precipitate,  which  is  a  dou- 
ble salt,  consisting  of  one  equivalent  of  the  acid,  one  equivalent  of  the  per- 
oxide, and  one  equivalent  of  ammonia.  The  oxide  is  readily  reduced  to  the 


MERCURY.  379 

metallic  stale  by  metallic  copper.  Hydrosulphuric  acid,  phosphorous  acid, 
and  protochloride  of  tin  reduce  the  peroxide  into  the  protoxide  ;  and  when 
added  in  larger  quantity,  the  first  throws  down  a  black  sulphuret,  and  the 
two  hitter  metallic  mercury.  The  action  of  hydrosulphuric  acid  on  a  solution 
of  corrosive  sublimate  is,  however,  peculiar  ;  for  at  first  it  occasions  a  white 
precipitate  which,  according  to  Rose,  is  a  compound  of  two  equivalents  of 
bisulphuret  to  one  of  bichloride  of  mercury.  This  gas  acts  on  bibrornide 
and  biniodide  of  mercury  in  a  similar  manner.  (An.  de  Ch.  et  de  Ph.  xl. 
46.) 

Its  eq.  is  218;  symb.  Hg-f2O,  Hg,  or  HgOa. 

Protochloride. — Prep. — Protochloride  of  mercury,  or  calomel,  is  a  rare 
mineral  production,  called  horn  quicksilver,  which  occurs  crystallized  in 
quadrangular  prisms  terminated  by  pyramids.  It  is  always  generated  when 
chlorine  comes  in  contact  with  mercury  at  common  temperatures ;  and  also 
by  the  contact  of  metallic  mercury  and  the  bichloride.  It  may  be  made  by 
precipitation,  by  mixing  nitrate  of  protoxide  of  mercury  in  solution  with 
hydrochloric  acid  or  any  soluble  chloride.  It  is  more  commonly  prepared  by 
sublimation.  This  is  conveniently  done  by  mixing  272-84  parts  or  one 
eq.  of  the  bichloride,  with  202  parts  or  one  eq.  of  mercury,  until  the  metallic 
globules  entirely  disappear,  and  then  subliming.  When  first  prepared  it  is 
always  mixed  with  some  corrosive  sublimate,  and,  therefore,  should  be  re- 
duced to  powder  and  well  washed  before  being  employed  for  chemical  or 
medical  purposes. 

Prop. — When  obtained  by  sublimation  it  is  in  semi-transparent  crystalline 
cakes  ;  but  as  formed  by  precipitation  it  is  a  white  powder.  Its  sp.  gr.  is 
7-2,  At  a  heat  short  of  redness,  but  higher  than  the  subliming  point  of  the 
bichloride,  it  rises  in  vapour  without  previous  fusion  ;  but  during  the  sub- 
limation a  portion  is  always  resolved  into  mercury  and  the  bichloride.  It  is 
yellow  while  warm,  but  recovers  its  whiteness  on  cooling.  It  is  distinguished 
from  the  bichloride  by  not  being  poisonous,  by  having  no  taste,  and  by  being 
exceedingly  insoluble  in  water.  Acids  have  little  effect  upon  it;  but  pure 
alkalies  decompose  it,  separating  the  black  protoxide  of  mercury.  When 
calomel  is  boiled  in  a  solution  of  hydrochlorate  of  ammonia  it  is  converted 
into  corrosive  sublimate  and  metallic  mercury.  Chloride  of  sodium  has  a 
similar  effect,  though  in  a  less  degree.  Its  eq.  is  237«42 ;  symb.  Hg-fCl,  or 
HgCl. 

Bichloride. — Prep. — When  mercury  is  heated  in  chlorine  gas,  it  takes 
fire,  and  burns  with  a  pale  red  flame,  forming  the  well-known  medicinal 
preparation  and  virulent  poison,  corrosive  sublimate  or  bichloride  of  mercury. 
It  is  prepared  for  medical  purposes  by  subliming  a  mixture  of  bisulphate  of 
the  peroxide  of  mercury  with  chloride  of  sodium  or  sea-salt.  The  exact 
quantities  required  for  mutual  decomposition  are  298-2  parts  or  one  eq.  of 
the  bisulphate,  to  117-44  parts  or  two  eq.  of  the  chloride.  Thus, 


1  eq.  Bisulphate  of  Mercury. 
Sulphuric  acid         80-2  or  2  eq.  2SO. 
Peroxide  of  mere.  218    or  1  eq.  HgQs. 


298-2  HgO*+2SO->. 


2  eq.  Chloride  of  Sodium. 
Chlorine     .     70-84  or  2  eq.       2C1. 
Sodium      .     46.6    or  2  eq.       2Na. 

117-44  2(Na+Cl). 


And  by  mutual  interchange  of  elements  they  produce 


1  eq.  Bichloride  of  Mercury. 
Mercury     .     202       or  1  eq.     .    Hg. 
Chlorine     .      70-84  or  2  eq.     .    2C1. 

272-84  Hg+2Cl. 


2  eq.  Sulphate  of  Soda. 
Soda     .     .        62-6  or  2  eq.       2NaO. 
Sulphuric  acid  80*2  or  2  eq.       2SO. 


14-2-8       2(NaO+SO3). 


The  products  have  exactly  the  same  weight  (272-84-f- 142-8=  415-64)  as 
the  compounds  (298-2-r-117-44=415'64)  from  which  they  were  prepared. 

Prop.—" When  obtained  by  sublimation,  it  is  a  semi-transparent  colourless 
substance  of  a  crystalline  texture.  It  has  an  acrid,  burning  taste,  and 


380  MERCURY. 

leaves  a  nauseous  metallic  flavour  on  the  tongue.  Its  sp  gr.  is  5'2.  When 
exposed  to  a  heat  short  of  incandescence,  it  is  fused,  enters  into  ebullition 
from  the  rapid  formation  of  vapour,  and  is  deposited  without  further  change 
on  cool  surfaces  as  a  white  crystalline  sublimate.  It  requires  twenty  times 
its  weight  of  cold,  and  only  twice  its  weight  of  boiling  water  for  solution, 
and  is  deposited  from  the  latter,  as  it  cools,  in  the  form  of  prismatic  crystals. 
Strong  alcohol  and  ether  dissolve  it  in  the  same  proportion  as  boiling  water; 
and  it  is  soluble  in  half  its  weight  of  concentrated  hydrochloric  acid  at  the 
temperature  of  70°.  With  the  chlorides  of  potassium  and  sodium,  hydro- 
chlorate  of  ammonia,  and  several  other  bases,  it  enters  into  combination, 
forming  double  salts,  which  are  more  soluble  than  the  chloride  itself.  When 
its  solution  in  water  is  agitated  with  ether,  the  latter  abstracts  the  bichloride, 
and  rises  with  it  to  the  surface  of  the  former,  thus  affording  strong  evidence 
of  the  bichloride  having  existed  as  such  in  the  water.  Its  aqueous  solution 
is  gradually  decomposed  by  light,  calomel  being  deposited. 

The  pure  and  carbonated  fixed  alkalies  throw  down  the  peroxide  of  mer- 
cury from  a  solution  of  corrosive  sublimate.  Ammonia,  on  the  contrary, 
causes  the  deposition  of  a  white  matter,  which  is  commonly  known  under 
the  name  of  the  white  precipitate.  This  substance  has  been  recently  ex- 
amined by  Kane  (Trans.  Irish  Academy,  xvii.)  He  finds  that  on  adding  a 
slight  excess  of  ammonia,  just  one  half  of  the  chlorine  of  the  corrosive  sub- 
limate falls,  the  other  half  remaining  in  the  solution  with  ammonia.  The 
precipitate  nevertheless  does  not  contain  calomel,  as  is  proved  by  its  complete 
solubility  in  hydrochloric  and  nitric  acids.  From  his  analysis  it  is  com- 
posed of 

Mercury         .         .  78-6       Ammonia         .         .         .      ~.  6*77 

Chlorine     '    .         .  13-85     Hygrometric  water,  loss  and  oxygen      .78 

Its  atomic  constitution  would  appear  from  this  analysis  to  contain  the  com- 
pound radical  which  is  the  base  of  the  amides.  By  the  action  of  boiling 
water,  it  loses  half  its  chlorine  and  ammonia,  peroxide  of  mercury  being  at 
the  same  time  formed,  and  a  canary-yellow  powder  is  produced.  Kane  finds 
that  on  treating  calomel  with  ammonia,  it  too  loses  only  one-half  its  chlorine, 
and  a  compound  analogous  to  white  precipitate  is  obtained. 

The  presence  of  mercury,  in  a  fluid  supposed  to  contain  corrosive  sub- 
limate, may  be  detected  by  concentrating  and  digesting  it  with  an  excess  of 
pure  potassa.  Peroxide  of  mercury,  which  subsides,  is  then  sublimed  in  a 
small  glass  tube  by  means  of  a  spirit-lamp,  and  obtained  in  the  form  of  me- 
tallic  globules.  But  in  cases  of  poisoning,  when  the  bichloride  is  mixed  with 
organic  substances,  Christison  recommends  that  the  liquid,  without  previous 
filtration,  be  agitated  with  a  fourth  of  its  volume  of  ether,  which  separates 
the  poison  from  the  aqueous  part,  and  rises  to  the  surface.  The  ethereal 
solution  is  then  evaporated  on  a  watch-glass,  the  residue  dissolved  in  hot  water, 
and  the  mercury  precipitated  in  the  metallic  state  by  protochloride  of  tin  at 
a  boiling  temperature.  If,  as  is  probable,  most  of  the  poison  is  already  con- 
verted into  calomel  and  thereby  rendered  insoluble,  as  many  vegetable  fibres 
should  be  picked  out  as  possible,  and  the  whole  at  once  digested  with  proto- 
chloride of  tin.  The  organic  substances  are  then  dissolved  in  a  hot  solution 
of  caustic  potassa,  and  the  insolublo  parts  washed  and  sublimed  to  separate 
the  mercury.  (Christison  on  Poisons.) 

A  very  elega.nt  method  of  detecting  the  presence  of  mercury  is  to  place  a 
drop  of  the  suspected  liquid  on  polished  gold,  and  to  touch  the  moistened  sur- 
face with  a  piece  of  iron  wire  or  the  point  of  a  penknife,  when  the  part  touched 
instantly  becomes  white,  owing  to  the  formation  of  an  amalgam  of  gold. 
This  process  was  originally  suggested  by  Sylvester,  and  has  since  been  sim- 
plified by  Paris.  (Medical  Jurisprudence,  by  Paris  and  Fonblanque.) 

Many  animal  and  vegetable  solutions  convert  bichloride  of  mercury  into 
calomel,  a  portion  of  hydrochloric  acid  being  set  free  at  the  same  time.  Some 
substances  eff?ct  this  change  slowly;  while  others,  and  especially  albumen, 
produce  it  in  an  instant.  Thus,  when  a  solution  of  corrosive  sublimate  is 


MERCURY.  381 

mixed  with  albumen,  a  white  flocculent  precipitate  subsides,  which  Orfila 
has  shown  to  be  a  compound  of  calomel  and  albumen,  and  which  he  has 
proved  experimentally  to  be  inert.  (Toxicologie,  vol.  i.)  Consequently,  a 
solution  of  the  white  of  eggs  is  an  antidote  to  poisoning  by  corrosive  sub- 
limate. The  muscular  and  membranous  parts,  even  of  a  living  animal,  pro- 
duce a  similar  effect;  and  the  causticity  of  corrosive  sublimate  seems  owing 
to  the  destruction  of  the  animal  fibre,  by  which  the  decomposition  of  the 
bichloride  is  accompanied,  and  which  constitutes  an  essential  part  of  the 
chemical  change. 

Its  eq.  is  272-84;  symb.  Hg-f.  2C1,  or  HgCR 

Protiodide  of  Mercury. — This  compound  is  obtained  by  mixing  nitrate  of 
protoxide  of  mercury  in  solution  with  iodide  of  potassium.  It  is  a  green 
powder,  insoluble  in  water,  and  disposed  to  resolve  itself,  under  the  influence 
of  heat  or  solar  light,  into  mercury  and  the  biniodide.  However,  when  the 
heat  is  quickly  applied,  it  is  fused  and  sublimed  without  material  change. 

Its  eq.  is  32S-3 ;  symb.  Hg+I,  or  Hgl. 

Sesquiodide. — This  compound  falls  as  a  yellow  powder  when  iodide  of 
potassium  is  added  in  solution  to  the  mixed  nitrates  of  the  protoxide  and 
peroxide  of  mercury,  the  latter  being  in  excess.  The  precipitate  is  digested 
with  a  solution  of  sea-salt,  which  takes  up  any  binoidide  which  may  have 
fallen. 

Its  eq.  is  782-9  ;  symb.  2Hg-j-3I,  or  Hg2R 

Biniodide. — This  compound  is  formed  by  mixing  nitrate  of  the  peroxide, 
or  bichloride  of  mercury  with  iodide  of  potassium  in  solution,  and  falls  as  a 
rich  red- coloured  powder  of  a  tint  which  vies  in  beauty  with  that  of  ver- 
milion, though,  unfortunately,  the  colour  is  less  permanent.  Though  insoluble 
in  water,  it  dissolves  freely  in  an  excess  of  either  of  its  precipitants.  If  taken 
up  in  a  hot  solution  of  nitrate  of  peroxide  of  mercury,  the  biniodide  crystal- 
lizes  out  on  cooling  in  scales  of  a:  beautiful  red  tint.  The  same  crystals 
separate  from  a  solution  in  iodide  of  potassium  ;  but  if  the  liquid  be  concen- 
trated, a  double  iodide  of  mercury  and  potassium  subsides. 

The  biniodide,  when  exposed  to  a  moderate  heat,  gradually  becomes  yellow ; 
and  the  particles,  though  previously  in  powder,  acquire  a  crystalline  appear- 
ance. At  about  400°  it  forms  a  yellow  liquid  which  slowly  sublimes  in 
small  transparent  scales,  or  in.  large  rhombic  tables,  when  a  considerable 
quantity  is  sublimed.  The  crystals  retain  their  yellow  colour  at  60°  if  kept 
very  tranquil,  but  if  the  temperature  be  below  a  certain  point,  or  they 
are  rubbed  or  touched,  they  quickly  become  red.  This  phenomenon  is  en- 
tirely due  to  a  change  in  molecular  arrangement:  the  different  colours  so 
often  witnessed  in  the  same  substances  at  different  temperatures,  as  in  per- 
oxide of  mercury,  and  the  protoxides  of  lead  and  zinc,  appear  to  be  phe- 
nomena of  the  same  nature. 

Its  eq.  is  454-6 ;  symb.  Hg-f-2I,  or  Hgfo 

loduretted  Bichloride  of  Mercury. — This  compound  has  recently  been  de- 
scribed by  Lassaigne.  (An.  deCh.  et  de  Ph.  Ixiii.  106).  It  is  formed  by  ad- 
ding to  an  alcoholic  solution  of  iodine,  a  solution  of  corrosive  sublimate,  when 
the  deep  colour  of  the  iodine  gradually  disappears,  and  a  colourless  solution 
is  obtained.  It  is  remarkable,  that  in  this  combination  the  iodine  cannot  be 
detected  by  starch  and  chlorine  or  sulphurous  acid,  as  in  its  other  combina- 
tions. The  compound  is  decomposed  by  heat,  but  may  be  obtained  in  crystals 
by  evaporating  a  concentrated  solution  at  a  moderate  temperature.  Its  eq.  is 
5583-1;  symb.  20HgC12+I. 

lodo-bichloride  of  Mercury. — This  compound  was  described  by  Boulay 
(An.  de  Ch.  et  de  Ph.  xxxvi.  366).  It  is  formed  by  dissolving  biniodide  of 
mercury  in  corrosive  sublimate,  when  a  colourless  crystalline  compound  is 
obtained.  It  is  composed  of  forty  eq.  of  the  bichloride  and  one  of  the 
biniodide. 

Its  eq.  is  11368-2;  symb.  40HgC12+Hgl2. 

Protobromide  of  Mercury. — It  is  precipitated  as  a  white  insoluble  powder 


382  SILVER. 

by  mixing  nitrate  of  protoxide  of  mercury  with  bromide  of  potassium.  Its 
eq.  is  280-4  ;  symb.  Hg+Br,  or  HgBr. 

The  bibromide  is  a  white  crystallizable  compound,  soluble  in  water  and 
alcohol,  fusible  and  volatile,  and  in  many  respects  analogous  to  the  bichlo- 
ricfe.  It  is  formed  by  acting  on  peroxide  of  mercury  with  hydrobromic  acid, 
or  digesting  the  preceding  compound  with  bromine. 

Its  eq.  is  358-8;  symb.  Hg+2Br,  or  HgBr2. 

Sulphurcts  of  Mercury. — The  protosulphurel  may  be  prepared  by  trans- 
milling  a  current  of  hydrosulphuric  acid  gas  through  a  dilute  solution  of  ni- 
trate of  protoxide  of  mercury,  or  through  water  in  which  calomel  is  sus- 
pended. It  is  a  black-coloured  substance,  which  is  oxidized  by  digestion  in 
strong  nitric  acid.  When  exposed  to  heat  it  is  resolved  into  the  bisulphuret 
and  metallic  mercury.  Its  eq.  is  218-1 ;  symb.  Hg-f-S,  or  HgS. 

The  bisulphuret  is  formed  by  fusing  sulphur  with  about  six  times  its 
weight  of  mercury,  and  subliming  in  close  vessels.  When  procured  by  this 
process  it  has  a  red  colour,  and  is  known  by  the  name  of  factitious  cinnabar. 
Its  tint  is  greatly  improved  by  being  reduced  to  powder,  in  which  state  it 
forms  the  beautiful  pigment  vermilion.  It  may  be  obtained  in  the  moist  way 
by  pouring  a  solution  of  corrosive  sublimate  into  an  excess  of  hydrosulphate 
of  ammonia.  A  black  precipitate  subsides,  which  acquires  the  usual  red  co- 
lour of  cinnabar  when  sublimed.  The  black  precipitate,  formed  by  the  action 
of  hydrosulphuric  acid  on  bicyanuret  of  mercury,  is  likewise  a  bisulphuret. 
Cinnabar,  as  already  mentioned,  occurs  native. 

When  equal  parts  of  sulphur  and  mercury  are  triturated  together  until 
metallic  globules  cease  to  be  visible,  the  dark-coloured  mass  called  ethiops 
mineral  results,  which  Mr.  Brande  has  proved  to  be  a  mixture  of  sulphur 
and  bisulphuret  of  mercury.  (Journal  of  Science,  vol.  xviii.  p.  294.) 

Cinnabar  is  not  attacked  by  alkalies,  or  any  simple  acid;  but  it  is  dis- 
solved by  the  nitro-hydrochlonc,  with  formation  of  sulphuric  acid  and  per- 
oxide of  mercury. , 

Its  eq.  is  234-2  ;  symb.  Hg-f  2S,  or  HgS3. 


SECTION   XXIV. 

SILVER. 

Hist. — THIS  metal  was  known  to  the  ancients.  It  frequently  occurs  native 
in  silver  mines,  both  massive  and  in  octohedral  or  cubic  crystals.  It  is  also 
found  in  combination  with  gold,  tellurium,  antimony,  copper,  arsenic,  amd 
sulphur.  In  the  state  of  snlphuret  it  so  frequently  accompanies  galena,  that 
the  lead  of  commerce  is  rarely  quite  free  from  traces  of  silver. 

Prep. — Silver  is  extracted  from  its  ores  by  two  processes  which  are  es- 
sentially distinct ;  one  of  them  being  contrived  to  separate  it  from  lead,  the 
other,  the  process  by  amalgamation,  being  especially  adapted  to  those  ores 
which  are  free  from  lead.  The  principle  of  its  separation  from  lead  is  founded 
on  the  different  oxidability  of  lead  and  silver,  and  on  the  ready  fusibility  of 
litharge.  The  lead,  obtained  from  those  kinds  of  galena  which  are  rich  in 
sulphuret  of  silver,  is  kept  at  a  red  heat  in  a  flat  furnace,  with  a  draught  of 
air  constantly  playing  on  its  surface:  the  lead  is  thus  rapidly  oxidized;  and 
as  the  oxide,  at  the  moment  of  its  formation,  is  fused,  and  runs  off  through 
an  aperture  in  the  side  of  the  furnace,  the  production  of  litharge  goes  on  un- 
interruptedly until  all  the  lead  is  removed.  The  button  of  silver  is  again 
fused  in  a  smaller  furnace,  resting  on  a  porous  earthen  dish,  made  with 
lixiviated  wood-ashes,  called  a  test,  the  porosity  of  which  is  so  great,  that  it 
absorbs  any  remaining  portions  of  litharge  which  may  be  formed  on  the 
silver. 


SILVER.  383 

The  ores  commonly  employed  in  the  process  of  amalgamation,  which  has 
been  long  used  at  Freyberg  in  Saxony,  and  is  extensively  practised  in  the 
silver  and  gold  mines  of  South  America,  are  native  silver  and  its  sulphuret. 
At  Freyberg  the  ore  in  fine  powder  is  mixed  with  sea-salt,  and  carefully 
roasted  in  a  reverbcratory  furnace.  The  production  of  Mphuric  acid  leads 
to  the  formation  of  sulphate  of  soda,  while  the  chlorine  of  the  sea-salt  com- 
bines with  silver.  The  roasted  mass  is  ground  to  a  fine  powder,  and,  together 
with  mercury,  water,  and  fragments  of  iron,  is  put  into  barrels,  which  are 
made  to  revolve  by  machinery.  In  this  operation,  intended  to  insure  perfect 
contact  between  the  materials,  chloride  of  silver  is  decomposed  by  the  iron, 
the  silver  unites  with  the  mercury,  and  the  chloride  of  iron  is  dissolved  by 
the  water.  The  mercury  is  then  squeezed  through  leathern  bags,  the  pores 
of  which  permit  the  pure  mercury  to  pass,  but  retain  the  amalgam  of  silver. 
The  combined  mercury  is  then  distilled  off  in  close  vessels,  and  the  metal 
obtained  in  a  separate  state. 

Goldsmiths'  silver  commonly  contains  copper  and  traces  of  gold,  the  lat- 
ter appearing  in  dark  flocks  when  the  metal  is  dissolved  in  nitric  acid.  It 
may  be  obtained  pure  for  chemical  uses  by  placing  a  clean  piece  of  copper 
in  a  solution  of  nitrate  of  oxide  of  silver,  washing  the  precipitate  with  pure 
water,  and  then  digesting  it  in  ammonia,  in  order  to  remove  any  adhering 
copper.  A  better  process  is  to  decompose  chloride  of  silver  by  means  of  car- 
bonate of  potassa.  For  this  purpose  precipitate  a  solution  of  nitrate  of  oxide 
of  silver  with  chloride  of  sodium,  wash  the  precipitate  with  water,  and  dry 
it.  Then  put  twice  its  weight  of  carbonate  of  potassa  into  a  clean  Hessian  or 
black-lead  crucible,  heat  it  to  redness,  and  throw  the  chloride  by  successive 
portions  into  the  fused  alkali.  Effervescence  takes  place  from  the  evolution 
of  carbonic  acid  and  oxygen  gases,  chloride  of  potassium  is  generated,  and 
metallic  silver  subsides  to  the  bottom.  The  pure  metal  may  be  granulated, 
by  pouring  it  while  fused  from  a  height  of  seven  or  eight  feet  into  a  vessel  of 
water. 

Prop. — It  has  the  clearest  white  colour  of  all  the  metals,  and  is  susceptible 
of  receiving  a  lustre  surpassed  only  by  polished  steel.  In  malleability  and 
ductility  it  is  inferior  only  to  gold,  and  its  tenacity  is  considerable.  It  is 
very  soft  when  pure,  so  that  it  may  be  cut  with  a  knife.  Its  density  after 
being  hammered  is  10-51.  At  a  full  red  heat,  corresponding  to  1873°  F.  ac- 
cording to  Daniell,  it  enters  into  fusion.  It  does  not  rust  by  exposure  to  air 
and  moisture.  When  fused  in  open  vessels  it  absorbs  oxygen  in  considerable 
quantity,  amounting  sometimes  to  22  times  its  volume;  but  it  parts  with  the 
whole  of  it  in  the  act  of  becoming  solid.  This  fact,  first  noticed  by  M.  Lucas, 
has  been  studied  by  Gay-Lussac,  who  attributes  to  it  the  peculiarly  beauti- 
ful aspect  of  granulated  silver:  he  observed  the  absorption  and  subsequent 
evolution  of  oxygen  to  be  most  abundant  in  the  purest  silver,  and  is  entirely 
prevented  by  a  very  small  per  centage  of  copper.  If  silver  is  heated  to  red- 
ness, without  fusing,  in  contact  with  glass  or  porcelain,  it  readily  absorbs 
oxygen,  and  the  oxide  fuses  with  the  earthy  matters,  forming  a  yellow  ena- 
mel. When  silver  in  the  form  of  leaves  or  fine  wire  is  intensely  heated  by 
means  of  electricity,  galvanism,  or  the  oxy-hydrogen  blowpipe,  it  burns  with 
vivid  scintillations  of  a  greenish-white  colour. 

The  only  pure  acids  that  act  on  silver  are  the  sulphuric  and  nitric  acids, 
by  both  of  which  it  is  oxidized,  forming  with  the  first  a  sulphate,  and  with 
the  second  a  nitrate  of  oxide  of  silver.  It  is  not  attacked  by  sulphuric  acid 
unless  by  the  aid  of  heat.  Nitric  acid  is  its  proper  solvent,  and  forms  with 
its  oxide  a  salt,  which,  after  fusion,  is  known  by  the  name  of  lunar  caustic. 

From  recent  experiments  on  the  composition  of  the  chloride  and  nitrate  of 
the  oxide  of  silver,  I  have  deduced  108  as  the  eq.  of  silver,  an  estimate  closely 
corresponding  with  the  previous  researches  of  Berzelius.  (Phil.  Trans.  1833, 
part  ii.)  Its  symb.  is  Ag.  The  compounds  of  silver  described  in  this  sec- 
tion are  thus  constituted : — 


384  SILVER. 

Silver.  Equm  Formulae. 

Oxide     .     .     108  1  eq.-f  Oxygen  8  1  eq.*==116  Ag+O  or  AgO. 

Chloride     .     108  1  eq.+Chlorine  3542  1  eq.==  143-42  Ag-fCl  or  AgCl. 

Iodide    .     .     108  1  eq.-f  Iodine  126-3  1  eq.^234-3  Ag+I  or  Agl. 

Sulphurct   .     108  1  eq.+Sulphur  161  1  eq.=  124-1  Ag-}-S  or  ASS- 

Oxide  of  Silver. — This  oxide  is  best  procured  by  mixing  a  solution  of  pure 
baryta  with  nitrate  of  oxide  of  silver  dissolved  in  water.  It  is  of  a  brown 
colour,  insoluble  in  water,  and  is  completely  reduced  by  a  red  heat.  Silver 
is  separated  from  its  solution  in  nitric  acid  by  pure  alkalies  and  alkaline 
earths  as  the  brown  oxide,  which  is  rcdissolved  by  ammonia  in  excess ;  by 
alkaline  carbonates  as  a  white  carbonate,  which  is  soluble  in  an  excess  of 
carbonate  of  ammonia;  as  a  dark  brown  sulphuret  by  hydrosulphuric  acid; 
and  as  a  white  curdy  chloride  of  silver,  which  is  turned  violet  by  light  and 
is  very  soluble  in  ammonia,  by  hydrochloric  acid  or  any  soluble  chloride. 
By  the  last  character,  silver  may  be  both  distinguished  and  separated  from 
other  metallic  bodies. 

Silver  is  precipitated  in  the  metallic  state  by  most  other  metals.  When 
mercury  is  employed  for  this  purpose,  the  silver  assumes  a  beautiful  arbores- 
cent appearance,  called  arhor  Diana.  A  very  good  proportion  for  the 
experiment  is  20  grains  of  lunar  caustic  to  6  drachrns  or  an  ounce  of  water. 
The  silver  thus  deposited  always  contains  mercury. 

When  oxide  of  silver,  recently  precipitated  by  baryta  or  lime-water,  and 
separated  from  adhering  moisture  by  bibulous  paper,  is  left  in  contact  for 
10  or  12  hours  with  a  strong  solution  of  ammonia,  the  greater  part  of  it  is 
dissolved ;  but  a  black  powder  remains  which  detonates  violently  from  heat 
or  percussion.  This  substance,  which  was  discovered  by  Berthollet,  (An.de 
Chimie,  i.)  appears  to  be  a  compound  of  ammonia  and  oxide  of  silver ;  for 
the  products  of  its  detonation  are  metallic  silver,  water,  and  nitrogen  gas. 
It  should  be  made  in  very  small  quantity  at  a  time,  and  dried  spontaneously 
in  the  air. 

On  exposing  a  solution  of  oxide  of  silver  in  ammonia  to  the  air,  its  sur- 
face becomes  covered  with  a  pellicle,  which  Faraday  considers  to  be  an  oxide 
containing  a  smaller  proportion  of  oxygen  than  that  just  described.  This 
opinion  he  has  made  highly  probable  ;  but  further  experiments  are  requisite 
before  the  existence  of  this  oxide  can  be  regarded  as  certain. 

Its  eq.  is  116 ;  symb.  Ag-f-O,  Ag,  or  AgO. 

Chloride  of  Silver. — Prep. — This  compound,  which  sometimes  occurs  in 
silver  mines,  and  constitutes  the  horn  silver  of  mineralogists,  is  always 
generated  when  silver  is  heated  in  chlorine  gas,  and  may  be  prepared  con- 
veniently by  mixing  hydrochloric  acid,  or  any  soluble  chloride,  with  a  solution 
of  nitrate  of  oxide  of  silver.  As  formed  by  precipitation  it  is  quite  white  ; 
but  by  exposure  to  the  direct  solar  rays  it  becomes  violet,  and  almost  black, 
in  the  course  of  a  few  minutes;  and  a  similar  effect  is  slowly  produced  by 
diffused  day-light.  Hydrochloric  acid  is  set  free  during  this  change,  and, 
according  to  Berthollet,  the  dark  colour  is  owing  to  separation  of  oxide  of 
silver.  (Statique  Chimique,  vol.  i.  p.  195.) 

Prop. — It  is  insoluble  in  water,  and  is  dissolved  very  sparingly  by  the 
strongest  acids;  but  it  is  soluble  in  ammonia.  Hyposulphurous  acid  like- 
wise dissolves  it.  At  a  temperature  of  about  500°  it  fuses,  and  forms  a 
semitransparent  horny  mass  on  cooling,  which  has  a  density  of  5*524.  It 
bears  any  degree  of  heat,  or  even  the  combined  action  of  pure  charcoal  and 
heat,  without  decomposition  ;  but  hydrogen  gas  decomposes  it  readily  with 
formation  of  hydrochloric  acid.  Its  eq.  is  143-42  ;  symb.  Ag-}-Cl,  or  AgCl. 

Iodide  of  Silver. — This  compound  is  formed  when  iodide  of  potassium  is 
mixed  with  a  solution  of  nitrate  of  oxide  of  silver.  It  is  of  a  greenish-yellow 
colour,  and  is  insoluble  in  water  and  ammonia. 

Its  eq.  is  234-3  ;  symb.  Ag+I,  or  Agl. 

Sulphuret  of  Silver.— Silver  has  a  strong  affinity  for  sulphur.  This  metal 
tarnishes  rapidly  when  exposed  to  an  atmosphere  containing  hydrosulphuric 


GOLD.  385 

acid  ga?,  owing  to  the  formation  of  a  sulphuret.  On  transmitting  a  current 
of  this  gas  through  a  solution  of  lunar  caustic,  a  dark  brown  precipitate 
subsides,  which  is  a  sulphuret  of  silver.  The  silver  glance  of  mineralogists 
is  a  similar  compound,  and  the  same  sulphuret  may  be  prepared  by  heating 
thin  plates  of  silver  with  alternate  layers  of  sulphur.  This  sulphuret  is  re- 
markable for  being  soft  and  even  malleable. 

Its  eq.  is  124-1 ;  symb.  Ag-4-S,  or  AgS. 

Silver  unites  also  by  the  aid  of  heat  with  phosphorus,  forming  a  soft, 
brittle,  crystalline  compound. 


SECTION    XXV. 


GOLD. 

Hist,  and  Prep. — GOLD  appears  to  have  been  known  to  the  earliest  races 
of  man,  and  to  have  been  esteemed  by  them  as  much  as  by  the  moderns. 
It  has  hitherto  been  found  only  in  the  metallic  state,  either  pure  or  in  com- 
bination with  other  metals.  It  occurs  massive,  capillary,  in  grains,  and 
crystallizes  in  octohedrons  and  cubes,  or  their  allied  forms.  It  is  sometimes 
found  in  primary  mountains ;  but  more  frequently  in  alluvial  depositions, 
especially  among  sand  in  the  beds  of  rivers,  having  been  washed  by  water 
out  of  disintegrated  rocks  in  which  it  originally  existed.  There  are  few 
countries  in  which  gold  washings  have  not  formerly  existed ;  but  the  prin- 
cipal supply  of  gold  is  from  South  America,  from  the  gold  mines  of  Hungary, 
and  from  the  Uralian  mountains  of  Siberia,  especially  on  the  Asiatic  side  of 
the  chain,  where  separate  masses  in  sand  have  been  found  weighing  18  or 
20  pounds.  Rich  deposites  of  gold  appear  also  to  exist  in  some  of  the 
southern  provinces  of  North  America.  Gold  is  generally  separated  from 
accompanying  impurities  by  the  process  of  amalgamation,  similar  to  that 
described  in  the  last  section;  by  which  means  it  is  freed  from  iron  and  all 
associated  metals,  excepting  silver.  In  Hungary  the  gold  is  purified  by  cu- 
pellation.  The  silver,  which  in  variable  quantity  is  present  in  native  gold, 
may  be  brought  into  view  by  dissolving  the  gold  in  nitro-hydrochloric  acid. 
The  best  mode  of  separation  consists  in  fusing  the  gold  with  so  much  silver 
that  the  former  may  constitute  one-fourth  -of  the  mass  :  nitric  acid  will  then 
dissolve  ajl  the  silver,  and  leave  the  gold.  The  silver  may  also  be  removed 
by  digestion  in  sulphuric  acid. 

Prop. — Gold  is  the  only  metal  which  has  a  yellow  colour,  a  character  by 
which  it  is  distinguished  from  all  other  simple  metallic  bodies.  It  is  capa- 
ble of  receiving  a  high  lustre  by  polishing,  but  is  inferior  in  brilliancy  to 
steel,  silver,  and  mercury.  In  ductility  and  malleability  it  exceeds  all  other 
metals ;  but  it  is  surpassed  by  several  in  tenacity.  Its  density  is  19'257 ; 
when  pure  it  is  exceedingly  soft  and  flexible;  and  it  fuses  according  to 
Daniell  at  2016°. 

Gold  may  be  exposed  for  ages  to  air  and  moisture  without  change,  nor  is 
it  oxidized  by  being  kept  in  a  state  of  fusion  in  open  vessels.  When  in- 
tensely ignited  by  means  of  electricity  or  the  oxy-hydrogen  blowpipe,  it 
burns  with  a  greenish-blue  flame,  and  is  dissipated  in  the  form  of  a  purple 
powder,  which  is  supposed  to  be  an  oxide. 

Gold  is  not  oxidized  or  dissolved  by  any  of  the  pure  acids ;  for  it  may  be 
boiled  even  in  nitric  acid  without  undergoing  any  change.  Its  best  solvents 
are  chlorine  and  nitro-hydrochloric  acid ;  and  it  appears  from  the  observa- 
tions of  Davy  that  chlorine  is  the  agent  in  both  cases,  since  nitro-bydro- 
chloric  acid  does  not  dissolve  gold,  except  when  it  gives  rise  to  the  formation 
of  chlorine.  (Page  216.)  It  is  to  be  inferred,  therefore,  that  the  chlorine 

33 


386  GOLD. 

unites  directly  with  the  gold.    It  is  also  readily  attacked  by  fluorine  (page 
240.) 

The  most  convenient  method  of  dissolving  it  is  to  digest  fragments  of  the 
metal  in  a  mixture  composed  of  two  measures  of  hydrochloric  and  one  of 
nitric  acid,  until  the  acid  is  saturated.  The  excess  of  acid  is  then  expelled 
by  evaporating  the  orange-coloured  solution  until  a  ruby-red  liquid  remains, 
which  is  the  neutral  terchloride  of  gold.  On  adding  water,  the  chloride  is 
dissolved,  forming  a  solution  of  a  gold-yellow  colour. 

The  eq.  of  gold,  estimated  from  the  analysis  of  the  terchloride  by  Berze- 
lius,  is  199-2  ;  its  symb.  is  Au.    The  composition  of  its  compounds  described 
in  this  section  is  as  follows : — 
One  eq. 

Gold.  Equiv.         Formulae. 

Protoxide        199-2  +  Oxygen        8        1  eq.=  207-2     Au+O  or  AuO. 
Binoxide         199-2  -f  do.  16        2eq,=  215-2     Au+2O  or  AuO2. 

Teroxide          199-2  +  do.  24         3eq.=  223-2     Au-f3O  or  AuO3. 

Protochloride  199-2  +  Chlorine     35-42    1  eq.=?  234-62  Au+Cl  or  AuCl. 
Terchloride     199-2  +  do.  106-26    3  eq.=  305-46  Au+3Cl  or  AuCR 

Tersulphuret  199-2  +  Sulphur      48-3      3  eq.=247-5     Au+33  or  AuS3. 
Protiodide       199-2  +  Iodine       126-3      1  eq.=325-5    Au+I  or  Aul. 
Teriodide       199-2  +  do.  378-9      3eq.=578-l    Au+31  or  Aul*. 

Protoxide  of  Gold. — It  is  obtained  by  the  action  of  a  cold  solution  of 
potassa  on  the  protochloride  of  gold,  and  is  separated  as  a  green  precipitate, 
which  is  partially  soluble  in  the  alkaline  solution.  It  spontaneously  changes 
soon  after  its  preparation  into  metallic  gold  and  the  teroxide. 

Its  eq,  is  207-2 ;  symb.  Au+O,  Au,  or  AuO. 

The  binoxide  is  supposed  to  be  the  purple  oxide  which  is  formed  by  the 
combustion  of  gold ;  but  its  composition  has  not  been  demonstrated  by 
analysis, 

Teroxide. — Prep. — This,  the  only  well-known  oxide  of  gold,  is  prepared 
by  the  action  of  alkalies  on  the  terchloride,  but  is  obtained  quite  pure  with 
difficulty.  Pelletier  recommends  that  it  should  be  formed  by  digesting  a 
solution  of  the  terchloride  with  pure  magnesia,  washing  the  precipitate  with 
water,  and  removing  the  excess  of  magnesia  by  dilute  nitric  acid.  It  is  apt, 
however,  to  retain  magnesia,  and  I  am  informed  by  Wagner,  of  Pesth  in 
Hungary,  that  the  most  certain  mode  of  procuring  the  teroxide  is  the  follow- 
ing : — Dissolve  one  part  of  gold  in  the  usual  way,  render  it  quite  neutral  by 
evaporation,  and  redissolve  in  twelve  parts  of  water :  to  the  solution  add  one 
part  of  carbonate  of  potassa  dissolved  in  twice  its  weight  of  water,  and  di- 
gest at  about  170°.  Carbonic  acid  gradually  escapes,  and  the  hydrated 
teroxide  of  a  brownish-red  colour  subsides.  After  being  well  washed  it  is 
dissolved  in  colourless  nitric  acid  of  specific  gravity  1-4,  and  the  solution 
decomposed  by  admixture  with  water.  The  hydrated  teroxide  is  thus  ob- 
tained quite  pure,  and  is  rendered  anhydrous  by  a  temperature  of  212°. 

Prop. — Yellow  in  the  state  of  hydrate,  and  nearly  black  when  anhydrous, 
is  insoluble  in  water,  and  completely  decomposed  by  solar  light  or  a  red 
heat.  Hydrochloric  acid  dissolves  it  readily,  yielding  the  common  solution 
of  gold;  but  it  forms  no  definite  compound  with  any  acid  which  contains 
oxygen.  It  may  indeed  be  dissolved  by  nitric  and  sulphuric  acids  ;  but  the 
affinity  is  so  slight  that  the  oxide  is  precipitated  by  the  addition  of  water.  It 
combines,  on  the  contrary,  with  alkaline  bases,  such  as  potassa  and  baryta, 
apparently  forming  regular  salts,  in  which  it  acts  the  part  of  a  weak  acid. 
This  property,  which  constitutes  the  difficulty  of  procuring  teroxide  of  gold 
quite  pure,  induced  Pelletier  to  deny  that  the  teroxide  of  gold  is  a  salifiable 
base,  and  to  propose  for  it  the  name  of  auric  acid,  its  compounds  with  alka- 
lies being  called  aurates.  (An.  de  Ch.  et  de  Ph.xv.) 

When  recently  precipitated  teroxide  of  gold  is  kept  in  strong  ammonia  for 


GOLD.  387 

about  a  day,  a  detonating  compound  of  a  deep  olive  colour  is  generated,  ana- 
logous to  the  fulminating  silver  described  in  the  last  section.  According  to 
the  analysis  of  Dumas,  its  elements  are  in  the  ratio  of  one  eq.  of  gold,  two 
of  nitrogen,  six  of  hydrogen,  and  three  of  oxygen,  as  expressed  by  the  sym- 
bols Au-f-2N-f-  6 H-|-3O.  With  regard  to  the  mode  in  which  these  ele- 
ments are  arranged,  different  opinions  may  be  formed.  Dumas  thinks  the 
real  combination  is  indicated  by  the  formula  (Au+N)  -f-  (3H-J-N)  -|-  3H, 
being  a  hydrated  nituret  of  gold  united  with  ammonia;  but  it  appears  more 
simple  to  consider  it  as  a  diaurate  of  ammonia,  expressed  by  the  formula 
2(3H-|.N)-j~  AuO3.  Its  detonation  should  give  rise  to  metallic  gold,  water, 
nitrogen,  and  ammonia.  A  similar  compound  is  obtained,  and  this  is  the 
ordinary  mode  of  procuring  fulminating  gold,  by  digesting  terchloride  of 
gold  with  an  excess  of  ammonia:  a  yellow  precipitate  subsides,  the  fulmi- 
nating ingredient  of  which  appears  identical  with  that  above  described;  but 
a  subchloride  of  gold  and  ammonia  falls  at  the  same  time,  and  adheres  so 
obstinately  that  it  cannot  be  wholly  removed  by  boiling  water.  Fulminating 
gold  may  be  dried  at  212°;  but  friction,  or  a  heat  suddenly  raised  to  about 
290°  or  upwards,  produces  a  violent  detonation.  It  is  best  to  make  it  in 
small  quantities  at  a  time,  and  to  dry  it  in  the  open  air.  (An.  de  Ch.  et  de 
Ph.  xliv.  167.) 

Its  eq.  is  223-2;  symb.  Au-f  3O,  Au,  or  AuCK 

Chlorides  of  Gold. — On  concentrating  the  solution  of  gold  to  a  sufficient 
extent  by  evaporation,  the  terchloride  may  be  obtained  in  ruby-red  prismatic 
crystals,  which  are  very  fusible.  It  deliquesces  on  exposure  to  the  air,  and 
is  dissolved  readily  by  water  without  residue.  It  is  also  soluble  in  alcohol 
and  ether ;  and  the  latter  withdraws  it  from  the  aqueous  solution.  It  begins 
to  lose  chlorine  at  a  temperature  of  about  400°,  being  changed  into  a  brown 
dry  mass,  which  is  a  mixture  of  the  protochloride  and  terchloride,  soluble  in 
water.  At  about  600°  the  terchloride  is  completely  resolved  into  the  yellow 
insoluble  protochloride,  which  by  boiling  in  water  is  changed  into  metallic 
gold  and  the  soluble  terchloride.  At  a  red  heat  the  protochloride  loses  its 
chlorine  altogether,  and  metallic  gold  remains.  Its  eq.  is  234'62 ;  symb. 
Au+Cl,  or  AuCl. 

The  terchloride  of  gold  is  the  usual  and  most  convenient  form  of  obtaining 
a  solution  of  gold  and  examining  its  properties  in  that  state.  On  adding  to 
the  solution  sulphate  of  protoxide  of  iron,  a  brown  precipitate  ensues,  which 
is  gold  in  very  fine  division,  and  the  solution  contains  tersulphale  of  sesqui- 
oxide  of  iron,  and  sesquichloride  of  iron.  The  action  is  such  that 

6  eq.  sulphate  of  protoxide  of  iron  6(Fe-f-S) 

and  1  eq.  terchloride  of  gold  Au-f-3Cl 

yield 

2  eq.  tersulphate  of  sesquioxide  of  iron  2(Fe-f-3S) 

1  eq.  sesquichloride  of  iron  2Fe+3Cl 

and  1  eq.  of  gold  Au. 

The  precipitate,  when  duly  washed  with  dilute  hydrochloric  acid  in  order 
to  separate  adhering  iron,  is  gold  in  a  state  of  perfect  purity.  A  similar  re- 
duction  is  effected  by  most  of  the  metals,  by  sulphurous  and  phosphorous 
acids,  and  by  oxalic  acid  with  escape  of  carbonic  acid  gas.  When  a  piece 
of  charcoal  is  immersed  in  a  solution  of  gold,  and  exposed  to  the  direct  solar 
rays,  its  surface  acquires  a  coating  of  metallic  gold ;  and  ribands  may  be 
gilded  by  moistening  them  with  a  dilute  solution  of  gold,  and  exposing  them 
to  a  current  of  hydrogen  or  phosphuretted  hydrogen  gas.  When  a  strong 
aqueous  solution  of  gold  is  shaken  in  a  phial  with  an  equal  volume  of  pure 
ether,  two  fluids  result,  the  lighter  of  which  is  an  ethereal  solution  of  gold. 
From  this  liquid  flakes  of  metal  are  deposited  on  standing,  especially  by  ex- 
posure to  light,  and  substances  moistened  with  it  receive  a  coating  of  metal- 


388  GOLD. 

lie  gold.*  The  reduction  in  most  of  these  instances  is  owing  to  the  chlorine 
quitting  the  gold  in  obedience  to  some  stronger  attraction :  metals  deprive 
it  directly  of  its  chlorine;  and  deoxidizing  agents  do  so  indirectly  by  com- 
bining with  the  oxygen  of  water,  while  its  hydrogen  acts  on  the  chlorine. 

When  protochloride  of  tin  is  added  to  a  dilute  aqueous  solution  of  terchlo- 
ride  of  gold,  a  purple-coloured  precipitate,  called  the  purple  of  Cassius,  is 
thrown  down  ;  and  the  same  substance  may  be  prepared  by  fusing  together 
150  parts  of  silver,  20  of  gold,  and  35-1  of  tin,  and  acting  on  the  alloy  with 
nitric  acid,  which  dissolves  out  the  silver  and  leaves  a  purple  residue  con- 
taining  the  tin  and  gold  which  were  employed.  To  prevent  the  oxidation  of 
the  tin  during  fusion,  the  three  metals  should  be  projected  into  a  red-hot 
black-lead  crucible,  which  contains  a  little  melted  borax.  When  the  powder 
of  Cassius  is  fused  with  vitreous  substances,  such  as  flint-glass,  or  a  mixture 
of  sand  and  borax,  it  forms  with  them  a  purple  enamel,  which  is  employed 
in  giving-  pink  colours  to  porcelain.  The  essential  cause  of  the  colour  is 
probably  a  compound  of  the  purple  or  supposed  binoxide  of  gold  with  earthy 
matters,  similar  to  the  enamel  formed  by  glass  and  oxide  of  silver.  The  oxide 
of  tin  is  not  essential,  since  finely  divided  metallic  gold  alone  will  give  the 
same  tint  of  purple. 

The  chemical  nature  of  the  purple  of  Cassius  is  very  obscure.  From  its 
formation  by  protochloride  of  tin  it  is  inferred  to  contain  binoxide  of  tin, 
and  gold  either  in  the  metallic  state  or  oxidized  to  a  degree  inferior  to  the 
teroxide.  According  to  Berzelius  its  sole  loss  when  heated  to  redness  is 
7-65  per  cent  of  water,  and  the  residue  has  a  brick-red  colour  arising  from  a 
mechanical  mixture  of  metallic  gold  and  binoxide  of  tin,  a  statement  which 
is  confirmed  by  Gay-Lussac.  (An  de  Ch.  et  de  Ph.  xlix.  396.)  The  proportion 
of  these  products  corresponds  to  five  equivalents  of  binoxide  of  tin,  one  of 
gold,  and  six  of  water.  Nevertheless,  the  purple  of  Cassius,  as  is  indicated 
both  by  its  colour  and  its  solubility  in  ammonia,  is  not  a  mechanical  mixture 
of  these  ingredients  ;  nor  can  it  well  be  regarded  as  a  chemical  compound  of 
gold  and  binoxide  of  tin,  since  no  definite  compound  of  the  kind  is  known 
to  chemists.  The  more  probable  supposition  is,  that  it  is  a  hydrated  double 
salt,  composed  of  binoxide  of  tin  as  the  acid,  united  with  protoxide  of  tin 
and  binoxide  of  gold  as  bases,  in  such  proportion  that  the  oxygen  of  the 
gold  exactly  suffices  to  convert  the  protoxide  into  binoxide  of  tin.  A  com- 
pound of  this  nature  is  expressed  by  the  formula  2(kSn-}-Sn)-f-(Au-|-Sn) 
-f6H. 

Its  eq.  is  305-46;  symb.  Au-f  3C1,  or  AuCK 

Tersulphuret  of  Gold. — On  transmitting  a  current  of  hydrosulphuric  acid 
gas  through  a  solution  of  gold,  a  black  precipitate  is  formed,  which  is  the 
tersulphuret.  It  is  resolved  by  a  red  heat  into  gold  and  sulphur. 

Its  eq.  is  247-5 ;  symb.  Au  -J-3S,  or  AuSa. 

The  compounds  of  gold  with  the  other  non-metallic  bodies  have  been  little 
examined. 

Iodides  of  Gold. — These  compounds  have  recently  been  studied  by  Johnston 
(Phil,  Mag.  and  An.  ix.  266.)  The  protiodide  falls  as  a  greenish-yellow 
powder,  when  iodide  of  potassium  is  added  in  excess  to  a  solution  of  the 
terchloride  of  gold.  Though  insoluble  in  water,  it  dissolves  in  a  dilute  hot 
solution  of  iodide  of  potassium,  from  which  it  crystallizes  on  cooling  in 
golden-yellow  scales  with  triangular  and  square  faces.  These  crystals 
generally  contain  about  12  per  cent  of  metallic  gold  mechanically  mixed 
with  them.  They  gradually  lose  iodine  at  common  temperatures,  freely  at 
150°,  and  are  almost  wholly  decomposed  at  230°. 

Its  eq.  is  325-5 :  symb.  Au  4-  I,  or  Aul. 


*  With  respect  to  the  revival  of  gold  from  its  solutions,  the  reader  may 
consult  an  Essay  on  Combustion  by  Mrs.  Fulhame,  and  a  paper  by  Count 
Rumford,  in  the  Philosophical  Transactions  for  1798. 


PLATINUM.  389 

The  teriodide  is  formed  when  terchloride  of  gold  is  added  to  a  solution  of 
iodide  of  potassium.  It  falls  as  a  dark  green  precipitate,  which  is  insoluble  in 
water,  but  is  soluble  in  hydriodic  acid,  and  in  solutions  of  the  iodides  of  potas- 
sium and  sodium.  It  is  very  prone  to  decomposition  from  the  easy  loss  of 
iodine.  It  is  a  haloid  acid,  and  forms  crystallizable  compounds  with  haloid 
bases.  Thus,  on  setting-  aside  the  solution  formed  by  digesting  it  in  iodide 
of  potassium,  the  auro-iodide  of  potassium  is  deposited  in  dark  brownish-red, 
nearly  black  needles.  These  crystals  are  anhydrous,  are  more  stable  than 
the  teriodide,  and  may  be  dried  at  100°  without  decomposition.  The  cor* 
responding-  salt  of  sodium  is  deliquescent. 

Its  eq.  is  578-1 ;  symb.  Au-f  31,  or  AuR 


SECTION  XXVI. 

PLATINUM. 

Hist. — THIS  valuable  metal  occurs  only  in  the  metallic  state,  associated  or 
combined  with  various  other  metals,  such  as  copper,  iron,  lead,  titanium, 
chromium,  gold,  silver,  palladium,  rhodium,  osmium,  and  iridium.  It  has 
hitherto  been  found  chiefly  in  Brazil,  Peru,  and  other  parts  of  South  America, 
in  the  form  of  rounded  or  flattened  grains  of  a  metallic  lustre,  and  white 
colour,  mixed  with  sand  and  other  alluvial  depositions.  The  particles  rarely 
occur  so  large  as  a  pea;  but  they  are  sometimes  larger,  and  a  specimen 
brought  from  South  America  by  Humboldt  was  rather  larger  than  a  pigeon's 
egg,  and  weighed  1088-6  grains.  In  the  year  1826,  however,  Boussingault 
discovered  it  in  a  syenitic  rock  in  the  province  of  Antioquia  in  South  Ame- 
rica, where  it  occurs  in  veins  associated  with  gold.  Rich  mines  of  gold  and 
platinum  have  also  been  discovered  in  the  Uralian  Mountains.  (Edinburgh 
Journal  of  Science,  v.  323.) 

Prop. — Pure  platinum  has  a  white  colour  very  much  like  silver,  but  of 
inferior  lustra.  It  is  the  heaviest  of  known  metals,  its  density  after  forging, 
being  about  21-25,  and  21-5  in  the  state  of  wire.  Its  malleability  is  consi- 
derable, though  far  less  than  that  of  gold  and  silver.  It  may  be  drawn  into 
wires,  the  diameter  of  which  does  not  exceed  the  2000th  part  of  an  inch.  It 
is  a  soft  metal,  and  like  iron  admits  of  being  welded  at  a  high  tempeaature. 
Wollaston*  observed  that  it  is  a  less  perfect  conductor  of  heat  than  several 
other  metals. 

Platinum  undergoes  no  change  from  the  combined  agency  of  air  and 
moisture ;  and  it  may  be  exposed  to  the  strongest  heat  of  a  smith's  forge 
without  suffering  either  oxidation  or  fusion.  On  heating  a  small  wire  of  it 
by  means  of  galvanism  or  the  oxy-hydrogen  blowpipe,  it  is  fused,  and  after. 
wards  burns  with  the  emission  of  sparks.  Smithson  Tennant  showed  that  it 
is  oxidized  when  ignited  with  nitre  (Phil.  Trans.  1797) ;  and  a  similar  effect 
is  occasioned  by  pure  potassa  and  lithia.  It  is  not  attacked  by  any  of  the 
pure  acids.  Its  solvents  are  chlorine,  or  solutions,  such  as  nitro-hydro. 
chloric  acid,  which  supply  chlorine;  and  it  is  dissolved  with  greater  difficulty 
than  gold. 

*  The  reader  will  find,  in  the  Philosophical  Transactions  for  1829,  some 
important  directions  by  Dr.  Wollaston,  both  as  to  the  mode  of  extracting 
platinum  from  its  ores,  and  of  communicating  to  the  pure  metal  its  highest 
degree  of  malleability.  The  essay  receives  additional  interest,  from  being 
one  of  those  which  were  composed  during  the  last  illness  of  this  truly  illus* 
trious  philosopher, 

33* 


390  PLATINUM. 

The  remarkable  property  observed  by  Dobereiner  in  spongy  platinum  of 
causing  the  union  of  oxygen  and  hydrogen  gases,  was  mentioned  at  page 
159  ;  a  property  which  Dulong  and  Thenard  showed  to  be  also  possessed, 
though  in  a  lower  degree,  by  platinum  in  its  compact  form  of  wire  or  foil, 
and  by  several  other  metals.  (An.  de  Ch.  et  de  Ph.  xxiii.  and  xxiv.)  Faraday 
(Phil.  Trans.  1834,  part  i.)  has  lately  discussed,  with  his  wonted  ability  and 
success,  both  the  conditions  required  for  the  effective  action  of  platinum,  and 
the  cause  of  the  phenomenon.  The  sole  conditions  are  purity  of  the  gases 
and  perfect  cleanliness  of  the  platinum.  By  cleanliness  is  meant  perfect  ab- 
sence of  foreign  matter,  pure  water  excepted ;  and  this  condition  is  easily 
secured  by  fusing  pure  potassa  on  its  surface,  washing  off  the  alkali  by  pure 
water,  then  dipping  the  platinum  in  hot  oil  of  vitriol,  and  again  washing 
with  water.  In  this  state  platinum  foil  acts  so  rapidly  at  common  tempera- 
tures on  oxygen  and  hydrogen  gases  mixed  in  the  ratio  of  1  to  2,  that  it  often 
becotnes  red-hot  and  kindles  the  mixture.  Handling  the  platinum,  wiping  it 
with  a  towel,  or  exposing  it  to  the  atmosphere  for  a  few  days,  suffices  to  soil 
the  surface  of  the  rnetal,  and  thereby  diminish  or  prevent  its  action.  These 
phenomena  are  supposed  to  result  from  the  concurring  influence  of  two 
forces,  the  self-repulsive  energy  of  similar  gaseous  particles,  and  the  adhesive 
attraction  exerted  between  them  and  the  platinum.  Each  gas,  repulsive  to 
itself  and  not  repelled  by  the  platinum,  comes  into  the  most  intimate  con- 
tact with  that  metal,  and  both  gases  are  so  condensed  upon  its  surface  that  they 
are  brought  within  the  sphere  of  their  mutual  attraction  and  combine.  Fara- 
day has  given  several  instances,  similar  to  those  which  I  had  occasion  to 
describe  some  years  ago  (Jameson's  Journal,  xi.  99  and  311),  where  the  ac- 
tion of  platinum  is  retarded  or  altogether  prevented  by  small  quantities  of 
certain  gases,  such  as  hydrosulphuric  acid,  carbonic  oxide,  and  olefiant 
gases.  One  would  be  tempted  to  suppose  that  these  gases  act  by  soiling 
the  metallic  surface,  though  in  some  respects  this  explanation  is  not  satis- 
factory. 

The  eq.  of  platinum,  deduced  by  Berzelius  from  the  analysis  of  the  bichlo- 
ride, is  98-8 ;  its  symb  is  Pt.  The  composition  of  its  compounds  described 
in  this  section  is  as  follows  ; — 

Platinum.  Equiv.        Formulae. 

Protoxide  98-8  1  eq.-f  Oxygen     8  1  eq.=  106-8    Pt+O  or  PtO. 

Binoxide  .         98-8  1  eq.-f-do.  16  2  eq.=114-8     Pt+2O  or  PtO*. 

Sesquioxide  ?    197-6  2  eq.+do.  24  3  eq.  =221-6  2Pt-f  3O  or  Pt2O3. 

Protochloride    98-8  1  eq.-r-Chlorine  35-42  1  eq.=  134-22  Pt-f  Cl  or  PtCl. 

Bichloride          89-8  1  eq.+do.  70-84  2  eq.=169-64  Pt-f2Clor  PtCl2. 

Protiodide          98-8  1  eq.-}-Iodine  126-3  1  eq.=225-l     Pt+IorPtl. 

Biniodide  98-8  1  eq.-fdo.        252-6  2  eq.  =351-4    Pt  4.  21  or  Ptl2. 

Protosulphuret  98-8  1  eq.-hSulphur  16-1  1  eq.=114-9     Pt-j-S  or  PtS. 

Bisulphuret       98-8  1  eq.-r-do.          32-2  2  eq.=131       Pt-p-2S  or  PtS2. 

Protoxide  of  Platinum. — This  oxide  is  prepared  by  digesting  protochlo- 
ride  of  platinum  in  a  solution  of  pure  potassa,  avoiding  a  large  excess  of  the 
alkali,  since  it  dissolves  a  portion  of  the  oxide  and  thereby  acquires  a  green 
colour.  In  this  state  it  is  a  hydrate  which  loses  first  its  water  and  then  oxy- 
gen when  heated,  and  dissolves  slowly  in  acids,  yielding  solutions  of  a 
brownish-green  tint. 

Its  eq.  is  106-8  ;  symb.  Pt-f-O,  Pt,  or  PtO. 

Binoxide' — This  oxide  is  prepared  with  difficulty,  owing  to  its  disposition, 
like  teroxide  of  gold,  to  act  rather  as  an  acid  than  an  alkaline  base,  and  either 
to  fall  in  combination  with  any  alkali  by  which  it  is  precipitated,  or  to  re- 
main with  it  altogether  in  solution.  Berzelius  recommends  that  it  should 
be  prepared  by  exactly  decomposing  sulphate  of  binoxide  of  platinum  with 
nitrate  of  baryta,  and  adding  pure  soda  to  the  filtered  solution,  so  as  to  preci- 
pitate about  half  of  the  oxide ;  since  otherwise,  a  sub-salt  would  subside. 
The  oxide  falls  in  the  form  of  a  bulky  hydrate,  of  a  yellowish-brown  colour ; 


PLATINUM.  391 

it  resembles  rust  of  iron  when  dry,  and  is  nearly  black  when  rendered  an- 
hydrous. 

Its  eq.  is  114-8;  symb.  Pt+20,  Pt,  or  Pt(X 

Sesquioxide. — This  oxide,  of  a  gray  colour,  is  prepared,  according  to  its 
discoverer  Mr.  E.  Davy,  by  heating  fulminating  platinum  with  nitrous  acid ; 
but  the  nature  of  the  compound  so  formed  has  not  yet  been  decisively  deter- 
mined.  (Phil.  Trans.  1320.) 

Protochloride. — When  the  bichloride  is  heated  to  450°,  half  of  its  chlorine 
is  expelled,  and  the  protochloride  of  a  greenish-gray  colour  remains.  It  is 
insoluble  in  water,  sulphuric  acid,  and  nitric  acid;  but  hydrochloric  acid 
partially  dissolves  it,  yielding  a  red  solution.  At  a  red  heat  its  chlorine  is 
driven  off,  and  metallic  platinum  is  left.  It  is  dissolved  by  a  solution  of  the 
bichloride. 

Its  eq.  is  134-22  ;  symb.  Pt+Cl,  or  PtCl. 

Bichloride  of  Platinum. — This  chloride  is  obtained  by  evaporating  the 
solution  of  platinum  in  nitro-hydrochloric  acid  to  dryness  at  a  very  gentle 
heat,  when  it  remains  as  a  red  hydrate,  which  becomes  brown  when  its  water 
is  expelled.  It  is  deliquescent,  and  very  soluble  in  water,  alcohol,  and  ether ; 
its  solution,  if  free  from  the  chlorides  of  palladium  and  iridium,  being  of  a 
pure  yellow  colour.  Its  ethereal  solution  is  decomposed  by  light,  metallic 
platinum  being  deposited. 

A  solution  of  platinum  is  recognized  by  the  following  characters  j — When 
to  an  alcoholic  or  concentrated  aqueous  solution  of  the  bichloride,  a  solution  of 
chloride  of  potassium  is  added,  a  crystalline  double  chloride  of  a  pale  yellow 
colour  subsides,  which  is  insoluble  in  alcohol,  and  sparingly  soluble  in  water: 
at  a  red  heat  it  yields  chlorine  gas,  and  the  residue  consists  of  metallic  pla- 
tinum and  chloride  of  potassium  With  a  solution  of  hydrochlorate  of  am- 
monia a  similar  yellow  salt  falls,  which  when  ignited  leaves  pure  platinum 
in  the  form  of  a  delicate  spongy  mass,  the  power  of  which  in  kindling  an 
explosive  mixture  of  oxygen  and  hydrogen  gases  has  already  been  men- 
tioned. 

Its  eq.  is  169-64  ;  symb.  Pt-f  2C1,  or  PtCl3. 

Protiodide  of  Platinum. — Lassaigne  prepared  this  compound  by  digesting 
the  protochloride  of  platinum  in  a  rather  strong  solution  of  iodide  of  potas- 
sium, when  the  protiodide  gradually  appeared  in  the  form  of  a  black  powder, 
which  is  insoluble  in  water  and  alcohol.  It  is  unchanged  by  sulphuric,  ni- 
tric, and  hydrochloric  acids,  decomposed  by  the  alkalies,  and  at  a  red  heat 
gives  off  its  iodine.  Its  eq.  is  225-1 ;  symb.  Pt-f- 1,  or  PtI. 

Biniodide  of  Platinum. — Lassaigne  prepares  this  compound  by  the  action 
of  iodide  of  potassium  on  a  rather  dilute  solution  of  bichloride  of  platinum. 
At  first  the  liquid  acquires  an  orange-red  and  then  a  claret  colour^  without 
any  precipitation  ;  but  when  the  solution  is  boiled,  a  black  precipitate  sub- 
sides, which  should  be  washed  with  hot  water  and  dried  at  a  heat  not  ex- 
ceeding 212°.  This  biniodide  is  a  black  powder,  sometimes  crystalline,  is 
tasteless  and  inodorous,  insoluble  in  water,  and  may  be  boiled  in  water 
without  change.  By  alcohol  it  is  sparingly  dissolved,  especially  when  heated. 
Acids  act  feebly  upon  it ;  but  it  is  decomposed  by  alkalies,  and  begins  to 
lose  iodine  at  270°.  (An.  de  Ch.  et  de  Ph.  li.  113.)  Its  eq.  is  351-4  ;  symb. 
Pl  +  2I,orPtR 

Protosulphuret  of  Platinum. — It  is  formed  by  heating  in  a  retort  the 
yellow  ammoniacal  chloride  of  platinum  with  half  its  weight  of  sulphur  until 
all  the  sal  ammoniac  and  excess  of  sulphur  are  expelled.  The  protosulphuret 
is  then  left  as  a  gray  powder  of  a  metallic  lustre.  It  may  also  be  formed  by 
the  action  of  hydrosulphuric  acid  on  protochloride  of  platinum. 

Its  eq.  is  114-9;  symb.  Pt-j-S,  or  PtS. 

Bisulphuret. — It  is  formed  as  a  brown  precipitate,  which  becomes  black 
when  dried,  by  letting  fall  a  solution  of  bichloride  of  platinum,  drop  by  drop, 
into  a  solution  of  sulphuret  of  potassium,  or  by  transmitting  hydrosulphuric 
acid  gas  into  a  solution  of  the  double  chloride  of  platinum  and  sodium. 


PALLADIUM. 


(Berzelius.)  It  should  be  dried  in  vacuo  by  aid  of  sulphuric  acid,  since  by 
exposure  to  the  air  in  a  moist  state  sulphuric  acid  is  generated. 

Its  eq.  is  131;  symb.  Pt  +  2S,  or  PtS2. 

Fulminating  platinum  may  be  prepared  by  the  action  of  ammonia  in  slight 
excess  on  a  solution  of  sulphate  of  protoxide  of  platinum  (E.  Davy.)  It  is 
analogous  to  the  detonating  compounds  which  ammonia  forms  with  the  oxides 
of  gold  and  silver. 


SECTION    XXVII. 

PALLADIUM,  RHODIUM,  OSMIUM,  AND  IRIDIUM. 

THE  four  metals  to  be  described  in  this  section  are  all  contained  in  the  ore 
of  platinum,  and  have  hitherto  been  procured  in  very  small  quantity.  When 
the  ore  is  digested  in  nitro-hydrochloric  acid,  the  platinum,  together  with 
palladium,  rhodium,  iron,  copper,  and  lead,  is  dissolved ;  while  a  black  pow- 
der is  left  consisting  of  osmium  and  iridium,  mixed  in  general  with  a  con- 
siderable quantity  of  titanate  of  iron,  and  siliceous  minerals. 


PALLADIUM. 

Hist,  and  Prep.— DISCOVERED  in  1803  by  Wollaston  (Phil.  Trans.  1804 
and  1 805.)  On  adding  bicyariuret  of  mercury  dissolved  in  water  to  a  neutral 
solution  of  the  ore  of  platinum,  either  before  or  after  the  separation  of  that 
metal  by  hydrochlorate  of  ammonia,  a  yellowish-white  flocculent  precipitate 
is  gradually  deposited,  which  is  cyanuret  of  palladium.  When  this  com- 
pound is  heated  to  redness,  the  cyanogen  is  expelled,  and  pure  palladium 
remains.  In  order  to  obtain  it  in  a  malleable  state,  the  metal  should  be  heated 
with  sulphur,  and  the  resulting  sulphuret  purified  by  cupellation  in  an  open 
crucible  with  borax  and  a  little  nitre.  It  is  then  roasted  at  a  low  red  heat  on 
a  flat  brick,  and  when  reduced  to  a  pasty  cansistence,  it  is  pressed  into  a 
square  or  oblong  perfectly  flat  cake.  It  is  again  to  be  roasted  very  patiently 
at  a  low  red  heat,  until  it  becomes  spongy  on  the  surface ;  and  when  quite 
cold,  it  is  condensed  by  frequent  tappings  with  a  light  hammer.  By  alter- 
nate roastings  and  tappings  the  sulphur  is  burned  off,  and  the  metal  rendered 
sufficiently  dense  to  be  laminated.  Thus  prepared  it  is  rather  brittle  while 
hot,  which  Wollastan  supposed  to  arise  from  a  small  remnant  of  sulphur. 
(Phil.  Trans.  1829,  p.  7.) 

Prop. — It  resembles  platinum  in  colour  and  lustre.  It  is  ductile  as  well 
as  malleable,  and  is  considerably  harder  than  platinum.  Its  sp.  gr.  varies 
from  1 1*3  to  11'8.  In  fusibility  it  is  intermediate  between  gold  and  platinum, 
and  is  dissipated  in  sparks  when  intensely  heated  by  the  oxy-hydrogcn 
blowpipe.  At  a  red  heat  in  oxygen  gas  its  surface  acquires  a  fine  blue  colour, 
owing  to  superficial  oxidation;  but  the  increase  of  weight  is  so  slight  as 
not  to  be  appreciated.  It  is  oxidized  and  dissolved  by  nitric  acid,  and  even 
the  sulphuric  and  hydrochloric  acids  act  upon  it  by  the  aid  of  heat ;  but  its 
proper  solvent  is  nitro-hydrochloric  acid.  Its  protoxide  forms  beauiful  red- 
coloured  salts,  from  which  metallic  palladium  is  precipitated  by  sulphate  of 
protoxide  of  iron,  and  by  all  the  metals  described  in  the  foregoing  sections, 
excepting  silver,  gold,  and  platinum. 

From  the  analysis  by  Berzelius  of  the  double  chloride  of  palladium  and 


RHODIUM.  393 

potassium,  the  eq.  of  palladium  is  inferred  to  be  53-3.    Its  symb.  is  Pd.    The 
composition  of  its  compounds  described  in  this  section  is  as  follows : — 

Palladium.  Equiv.        Formulas. 

Protoxide  53-3  1  eq.-f.  Oxygen     8        1  eq.=  61-3     Pd-f-OorPdO. 

Binoxide  53-3  1  eq.-f  do.          _16        2  eq.=  69-3     Pd-f-20  or  PdO3. 

Protochloride     53-3  1  eq.-f  Chlorine  35-42  1  eq.=  88-72  Pd-f  Cl  or  PdCl. 
Bichloride          53-3  1  eq.-f  do.  70-84  2  eq.  =124-14  Pd-f-2Cl  or  PdCR 

Protosulphuret  53-3  1  eq.  -f  Sulphur   16-1     1  eq.=  69-4    Pd-f  S  or  PdS. 

Protoxide  of  Palladium. — This  oxide  is  obtained  as  a  hydrate  of  a  deep 
brown  colour  by  decomposing  its  salts  with  an  excess  of  carbonate  of  potassa 
or  soda ;  and  by  washing  and  heating  to  low  redness,  the  anhydrous  prot- 
oxide of  a  black  colour  is  left.  It  is  also  obtained  by  heating  the  nitrate  at 
a  low  red  heat.  In  the  anhydrous  state  it  is  dissolved  with  difficulty  by  acids, 
When  strongly  heated  it  parts  with  its  oxygen.  Berzelius  says  it  falls  from 
its  salts  on  the  addtion  of  the  alkalies  as  a  subsalt,  which  is  dissolved  by  the 
alkali  in  excess. 

Its  eq.  is  61-3 ;  symb.  Pd-f  O,  Pd,  or  PdO. 

Binoxide. — To  prepare  this  oxide  Berzelius  recommends  that  a  solution  of 
potassa  or  its  carbonate  in  excess  should  be  poured,  by  little  and  little,  on  the 
solid  bichloride  of  palladium  and  potassium,  and  the  materials  be  well  inter- 
mixed:  water  is  not  first  added,  because  it  decomposes  the  double  chloride; 
and  the  akali  is  not  added  all  at  once,  because  the  binoxide  would  then  be 
dissolved  at  first,  and  afterwards  separate  out  as  a  gelatinous  hydrate,  which 
could  not  be  purified  by  washing.  When  prepared  with  the  foregoing  direc- 
tions, the  binoxide  is  obtained  as  a  hydrate  of  a  deep  yellowish-brown  colour, 
which  retains  a  little  potassa  in  combination ;  but  on  heating  the  solution  to 
212°,  the  alkali  is  dissolved  and  the  anhydrous  black  oxide  left. 

Its  eq.  is  69-3  ;  symb.  Pd-f  2O,  Pd,  or  PdO*. 

Protochloride  of  Palladium. — It  is  obtained  by  evaporating  to  dryness  a 
solution  of  palladium  in  nitro-hydrochloric  acid,  being  left  as  a  brown  crys- 
talline hydrate,  which  becomes  black  when  its  water  is  expelled.  It  loses  its 
chlorine  when  strongly  heated,  and  is  soluble  in  water. 

Its  eq.  is  88-72;  symb.  Pd-f  Cl,  or  PdCI. 

The  bichloride  is  formed  by  digesting  the  protochloride  in  nitro-hydro- 
chloric acid,  and  exists  only  in  solution,  the  colour  of  which  is  of  so  deep  a 
brown  as  to  appear  nearly  black.  It  is  readily  distinguished  from  the  pro- 
tochloride by  yielding  with  chloride  of  potassium  a  double  chloride  of  a  red 
colour ;  whereas  that  formed  with  the  protochloride  is  yellow. 

Its  eq.  is  124-14;  symb.  Pd+2Cl,  or  PdCl«. 

Protosulphuret  of  Palladium. — It  is  readily  formed  by  heating  the  metal 
with  sulphur,  and  is  a  fusible  brittle  compound  of  a  gray  colour. 

Its  eq.  is  69-4;  symb.  Pd-fS,  or  PdS. 


RHODIUM. 

Hist,  and  Prep. — This  metal  was  discovered  by,Wollaston  at  the  time  he 
was  occupied  with  the  discovery  of  palladium.  On  immersing  a  thin  plate 
of  clean  iron  into  the  solution  from  which  palladium  and  the  greater  part  of 
the  platinum  have  been  precipitated,  the  rhodium,  together  with  small 
quantities  of  platinum,  copper,  and  lead,  is  thrown  down  in  the  metallic 
state;  and  on  digesting  the  precipitate  in  dilute  nitric  acid,  the  two  last 
metals  are  removed.  The  rhodium  and  platinum  are  then  dissolved  by 
means  of  nitro-hydrochloric  acid,  and  the  solution,  after  being  mixed  with 
some  chloride  of  sodium,  is  evaporated  to  dryness.  Two  double  chlorides 
result,  that  of  platinum  and  sodium,  and  of  rhodium  and  sodium,  the  former 
of  which  is  soluble,  and  the  latter  insoluble  in  alcohol ;  and  they  may,  there- 
fore, be  separated  from  each  other  by  this  menstruum.  The  double  chloride 


394  RHODIUM. 

of  rhodium  is  then  dissolved  in  water,  and  metallic  rhodium  precipitated  by 
insertion  of  a  rod  of  zinc. 

Prop. — Thus  procured,  it  is  in  the  form  of  a  black  powder,  which  requires 
the  strongest  heat  that  can  be  produced  in  a  wind  furnace  for  fusion,  and 
when  fused  has  a  white  colour  and  metallic  lustre.  It  is  brittle,  extremely 
hard,  and  has  a  sp.  gr.  of  about  11.  It  attracts  oxygen  at  a  red  heat,  a 
mixture  of  sesquioxide  and  protoxide  being  formed.  It  is  not  attacked  by 
any  of  the  acids  when  in  its  pure  state;  but  if  alloyed  with  other  metals, 
such  as  copper  or  lead,  it  is  dissolved  by  nitre-hydrochloric  acid,  a  circum- 
stance which  accounts  for  its  presence  in  the  solution  of  crude  platinum.  It 
is  oxidized  by  being  ignited  either  with  nitre,  or  bisulphate  of  potassa. 
When  heated  with  the  latter,  sulphurous  acid  gas  is  evolved,  and  a  double 
sulphate  of  sesquioxide  of  rhodium  and  potassa  is  generated,  which  dissolves 
readily  in  hot  water,  and  yields  a  yellow  solution.  The  presence  of  rhodium 
in  platinum,  iridiurn,  and  osmium  may  thus  be  detected,  and  by  repeated 
fusion  a  perfect  separation  be  accomplished.  (Berzelius.) 

Chemists  are  acquainted  with  two  oxides  of  rhodium.  The  protoxide  is 
black,  and  the  sesquioxide,  which  is  the  base  of  the  salts  of  rhodium,  is  of  a 
yellow  colour.  Most  of  its  salts  are  either  red  or  yellow. 

From  the  composition  of  the  double  chloride  of  rhodium  and  potassium, 
Berzelius  considers  52-2  as  the  eq.  of  rhodium  ;  its  symb.  is  R,  and  its  com- 
pounds described  in  this  section  are  thus  constituted : — 

Rhodium.  Equiv.        Formulae. 

Protoxide          52-2  1  eq.  4.  Oxygen       8      1  eq.=  60-2      R-fOorRO. 
Sesquioxide     104.4  2  eq.-j-do.  24      3  eq.=  128-4    2R  +  3O  or  BXX 

Protochloride    52-2  1  eq.-f  Chlorine  35-42  1  eq.=  87-62    R-fCl  or  RC1. 
Sesquichlor.     104-4  2  eq.-f- do.          106-26  3  eq.=21 0-66 2R  +  3C1  or  RsCK 
Sulphuret          Probably  a  protosulphuret. 

Oxides  of  Rhodium. — The  first  grade  of  oxidation  has  not  yet  been  in- 
sulated. The  sesquioxide  is  generated  when  pulverulent  rhodium  is  heated 
to  redness  in  a  silver  crucible  mixed  with  hydrate  of  potassa  and  a  little 
nitre,  when  the  rhodium  is  oxidized  and  acquires  a  coffee-brown  colour.  To 
remove  the  potassa  united  with  the  sesquioxide,  the  mass  is  first  washed 
with  water  and  then  digested  in  hydrochloric  acid,  when  it  acquires  a 
greenish-gray  colour,  and  is  left  as  a  pure  hydrate  of  the  sesquioxide.  In  this 
state  it  is  insoluble  in  acids.  If  an  excess  of  carbonate  of  potassa  or  soda 
is  added  to  the  double  chloride  of  rhodium  and  potassium,  and  the  solution 
is  evaporated,  a  gelatinous  hydrate  falls;  but  on  attempting  to  dissolve  in 
acid  the  potassa  combined  with  the  sesquioxide,  the  latter  is  also  dissolved. 

Its  eq.  is  128-4;  symb.  2R+3O,  R,  or  R2Q3. 

Chlorides  of  Rhodium. — The  only  chloride  which  has  yet  been  insulated 
is  the  sesquichloride,  which  Berzelius  obtained  by  adding  to  a  solution  of  the 
double  chloride  of  rhodium  and  potassium,  silico-hydrofluoric  acid  as  long  as 
the  double  fluoride  of  potassium  and  silicon  was  generated,  after  which  the 
filtered  liquid  was  evaporated  to  dryness,  and  redissolved  in  water.  This 
sesquichloride  when  dry  has  a  dark  brown  colour,  is  uncrystalline,  and  de- 
composed by  a  full  red  heat  into  chlorine  and  metallic  rhodium.  It  deli- 
quesces in  the  air  into  a  brown  liquid,  and  its  aqueous  solution  has  a  fine 
red  colour,  whence  the  name  of  rhodium  (from  'goJW,  a  rose)  is  derived. 
(An.  deCh  et  de  Ph.  xl.  51.) 

Its  eq.  is  210-66 :  symb.  2R+3C1,  or  R2C13. 

Sulphuret  of  Rhodium. — It  may  be  formed  by  heating  rhodium  directly 
with  sulphur,  fuses  at  a  white  heat  without  decomposition,  and  has  a  bluish- 
gray  colour  with  a  metallic  lustre.  Wollaston  made  use  of  it  for  procuring 
the  metal  in  a  coherent  state,  in  the  same  manner  as  sulphuret  of  palladium, 


OSMIUM  AND  IRIDIUM.  395 


OSMIUM  AND  IRIDIUM. 

Hist. — These  metals  were  discovered  by  the  late  Mr.  Tennant  in  the  year 
1803  (Phil.  Trans.  1804),  and  the  discovery  of  indium  was  made  about  the 
same  time  by  Descotils  in  France.  The  black  powder  mentioned  at  the 
beginning  of  this  section  is  a  compound  of  osmium  and  iridium,  an  alloy 
which  Wollaston  detected  in  the  form  of  flat  white  grains  among  fragments 
of  crude  platinum.  This  alloy,  which  is  quite  insoluble  in  nitro-hydrochloric 
acid,  is  the  source  from  which  osmium  and  iridium  are  extracted. 

Preparation. — Osmium  and  iridium  are  obtained  from  the  pulverulent 
residue  of  the  ores  of  platinum,  after  that  metal,  together  with  palladium 
and  rhodium,  has  been  removed  by  digestion  in  nitro-hydrochloric  acid. 
Wollaston  has  recommended  the  following  process  (Phil.  Trans.  1829,  p.  8): 
— The  residue  is  ground  into  a  fine  powder  with  a  third  of  its  weight  of 
nitre,  and  the  mixture  heated  to  redness  in  a  silver  crucible  until  it  is  reduced 
to  a  pasty  state,  when  the  characteristic  odour  of  osmic  acid  will  be  percep- 
tible. Dissolve  the  soluble  parts,  which  contain  osmic  acid  in  combination  with 
potassa,  in  the  smallest  possible  quantity  of  water,  and  acidulate  the  solution, 
introduced  into  a  retort,  with  sulphuric  acid  diluted  with  its  own  weight  of 
water.  By  distilling  rapidly  into  a  clean  receiver  as  long  as  osmic  fumes 
pass  over,  the  acid  will  be  collected  on  its  sides  in  the  form  of  a  white  crust ; 
and,  there  melting,  it  will  run  down  in  drops  beneath  the  watery  solution, 
forming  a  fluid  flattened  globule  at  the  bottom.  As  the  receiver  cools,  the 
acid  becomes  solid  and  crystallizes.  Osmium  is  precipitated  from  the  solu- 
tion of  its  acid  by  all  the  metals  excepting  gold  and  silver.  A  convenient 
mode  of  reduction  is  to  agitate  it  with  mercury,  adding  hydrochloric  acid  to 
decompose  the  protoxide  of  mercury  which  is  formed,  and  then  expelling  the 
mercury  and  calomel  by  heat.  The  osmium  is  left  as  a  black  porous  powder 
which  acquires  metallic  lustre  by  friction. 

The  insoluble  parts  contain  the  iridium  as  oxide  in  combination  with  po- 
tassa. On  digesting  the  mass  in  hydrochloric  acid,  a  blue  solution  is  ob- 
tained; but  it  afterwards  becomes  of  an  olive-green  hue,  and  subsequently 
acquires  a  deep-red  tint.  This  variety  of  colour,  which  suggested  the  name 
of  iridium  (iris,  the  rainbow)  is  owing  to  the  successive  production  of  dif- 
ferent compounds.  The  iridium  may  be  precipitated  from  the  solution  by 
any  metal  except  gold  and  platinum,  or  it  may  be  obtained  by  exposing  the 
chloride  to  a  red  heat.  Wohler  has  proposed  a  very  elegant  process  by  which 
both  rnetals  may  be  obtained  on  a  large  scale  (Pog.  An.  xxxi.  161.)  The 
great  advantage  of  his  method  is,  that  it  leaves  the  titanate  of  iron  and  other 
foreign  minerals  undecomposed.  He  mixes  the  residue  with  an  equal  weight 
of  fused  sea-salt  in  fine  powder.  The  mixture  is  introduced  into  a  long  and 
wide  green  glass  tube,  which  is  connected  at  one  extremity  with  an  apparatus 
for  developing  chlorine,  at  the  other  with  a  tubulated  receiver.  The  latter 
is  furnished  with  a  small  tube,  the  extremity  of  which  is  made  to  dip  into  a 
weak  solution  of  ammonia.  The  tube  containing  the  mixture  of  salt  and 
ore  being  then  brought  to  a  low  red  heat,  the  chlorine  is  developed  and  the 
gas  transmitted  in  a  moderate  stream  through  the  glowing  mass,  by  which 
in  the  first  part  of  the  process  it  is  abundantly  and  completely  absorbed. 
The  operation  is  to  be  continued  until  the  chlorine  is  observed  to  pass  pretty 
freely  into  the  solution  of  ammonia.  The  changes  which  occur  are  owing 
to  the  formation  of  two  haloid  acids,  by  the  combination  of  the  chlorine  with 
both  metals  of  the  ore;  and  as  these  instantly  combine  with  the  chloride  of 
sodium,  two  soluble  salts,  the  iridio-chloride  of  sodium  and  the  osmio-chloride 
of  sodium,  are  produced.  But  by  the  moisture  of  the  chlorine  gas  the  latter 
compound  is  decomposed,  the  chloride  of  osmium  giving  rise  to  the  formation 
of  osmic  and  hydrochloric  acids,  and  the  deposition  of  a  part  of  the  osmium 
in  the  metallic  state.  This  by  again  combining  with  chlorine  gives  rise  to 
a  repetition  of  the  same  changes,  and  to  the  production  of  an  additional 
quantity  of  osmic  acid,  which,  being  volatile,  passes  on  and  is  deposited  in 


396  OSMIUM. 

crystals  in  the  receiver.  The  solution  of  ammonia  prevents  the  loss  of  any 
acid  which  might  escape  condensation.  The  solid  matter  in  the  tube  is  then 
digested  in  water,  when  a  deep  brown  solution  is  obtained,  and  the  clear 
liquid  is  separated  by  decantation  from  the  insoluble  parts,  which  consist 
principally  of  titanate  of  iron.  As  the  solution  still  contains  some  osmic  acid, 
it  is  submitted  to  a  distillation,  until  one-half  has  passed  over  into  a  weak 
solution  of  ammonia.  The  remainder  is  then  evaporated  in  an  open  dish, 
while  carbonate  of  soda  is  at  the  same  time  added  in  successive  portions  until 
a  considerable  excess  is  present.  On  evaporating  to  dryness,  a  black  mass 
is  obtained,  which  is  to  be  exposed  to  a  low  red  heat  in  a  Hessian  crucible. 
When  cold,  the  saline  matter  is  removed  by  boiling  water,  and  the  sesqui- 
oxide  of  iridium  is  left  in  the  form  of  a  black  powder.  It  is  readily  reduced 
to  the  metallic  state  by  a  stream  of  hydrogen  gas. 

OSMIUM. — As  obtained  by  precipitation  it  is  a  black  porous  powder,  which 
acquires  metallic  lustre  by  friction.  After  exposure  to  a  very  gentle  heat, 
its  sp.  gr.  is  7.  It  takes  fire  when  heated  in  the  open  air,  and  is  readily 
oxidized  and  dissolved  by  fuming  nitric  acid ;  but  a  red  heat  gives  it  greater 
compactness,  and  in  that  state  it  ceases  to  be  attacked  by  acids,  and  may  be 
freely  heated  without  oxidation.  In  its  densest  state  Berzelius  found  its  sp. 
gr.  to  be  10.  (An.  de  Ch.  et  de  Ph.  xl.  257,  and  xliii.  185.)  Its  symb.  is  Os. 

Berzelius,  from  his  late  researches  on  the  compounds  of  osmium,  considers 
99-7  to  be  its  eq.,  and  gives  the  composition  of  its  oxides,  chlorides,  and 
sulphurets  as  follows : — 

Osmium.  Equiv.         Formulae. 

Protoxide         99-7  1  eq.-f.  Oxygen      8       1  eq.=107-7     Os-fOorOsO. 
Sesquioxide    1994  2  eq.-f  do.  24       3eq.=223-4   2Os  -f  3O  or  OssQs. 

Binoxide          99-7  1  eq.-f  do.  16       2eq.=  115-7     Os-f  2O  or  O=-O^. 

Teroxide          99-7  leq.-j-do.  24       3eq.=123-7     Os-f3Oor OsOs. 

Osmic  acid      99-7  I  eq. 4. do.  32       4eq.=131-7      Os-f4O  or  OsO*. 

Protochlor.      99-7  1  eq.  -f  Chlorine  35-42  1  eq.=  135-12    Os -f  Cl  or  OsCl. 
Sesquichlor.  199-4  2  eq  -f  do.          106-26  3eq.=  305-66  2Os -f 3C1  or Os'-'CP. 
Bichloride       99-7  1  eq.-f  do.  70-84  2  eq.  =170-54    Os-j-2Clor  O.Cls. 

Terchloride    99-7  1  eq. -f- do.          106-26  3  eq,=205-96    Os-f  SClorOsCls. 
Protosulph't.  99-7  1  eq.-f. Sulphur    16-1     leq.=  115-8       Os-fS  or  OsS. 
Sesquisulp't.  199-4  2  eq.-f  do.  48-3    3  eq.=  247-7     2Os-j-3S  or  Ofi«S?." 

Bisulphuret    99-7  1  eq.-j-do.  322    2  eq.=131-9       Os-f-2S  or  OsS2. 

Tersulphuret  99-7  1  eq.-f  do.  48-3    3eq.=148          Os  -f  3S  or  OsS*. 

Oxides  of  Osmium — For  a  minute  description  of  these  compounds  I  refer 
to  the  essays  of  Berzelius  above  cited.  The  protoxide  is  precipitated  hy 
pure  alkalies  from  the  protochloride,  and  falls  as  a  deep  green,  nearly  black, 
hydrate,  which  is  soluble  in  acids,  and  detonates  when  heated  with  com- 
bustible matter.  The  binoxide  is  thrown  down  as  a  hydrate  of  a  deep  brown 
colour,  when  a  saturated  solution  of  the  bichloride  is  heated  with  carbonate 
of  soda.  It  retains  a  little  alkali  in  combination  ;  but  the  soda  is  easily 
removed  by  dilute  hydrochloric  acid,  without  the  binoxide  being  dissolved. 
The  teroxide  is  prepared  in  like  manner  from  the  terchloride.  The  ses- 
qv-ioxide  has  not  been  obtained  in  a  separate  state ;  but  it  is  procured  in 
combination  with  ammonia  when  the  binoxide  is  treated  with  a  large  excess 
of  pure  ammonia,  nitrogen  gas  being  disengaged  at  the  same  time. 

Osmic  Acid. — The  highest  stage  of  oxidation  is  the  volatile  compound 
called  osmic  acid,  which  is  the  product  of  the  oxidation  of  osmium  by  acids, 
by  combustion,  or  by  fusion  with  nitre  or  alkalies ;  and  it  may  be  procured 
by  the  process  above  mentioned  in  colourless  transparent  elongated  crystals, 
or  as  a  colourless  solution  in  water.  Its  vapour  is  very  acrid,  exciting  cough, 
irritating  the  eyes,  and  producing  a  copious  flow  of  saliva ;  and  its  odour  is 
disagreeable  and  pungent,  somewhat  like  that  of  chlorine  ;  a  property  which 
suggested  the  name  of  osmium  (from  OP/UK,  odour.)  It  does  not  combine 
with  acids :  on  the  contrary,  though  it  has  no  acid  reaction,  it  unites  with 


1RIDIUM.  397 

alkalies,  and  the  compound  sustains  a  strong  heat  without  decomposition. 
When  touched,  it  communicates  a  stain  which  cannot  be  removed  by 
washing.  With  the  infusion  of  gall-nuts  it  yields  a  purple  solution,  which 
afterwards  acquires  a  deep  blue  tint;  a  character  which  forms  a  sure  and 
extremely  delicate  test  for  osmic  acid.  By  sulphurous  acid  it  is  deoxidized, 
and  the  colour  of  the  solution  passes  through  the  shades  of  yellow,  orange, 
brown,  green,  and  lastly  blue,  when  it  resembles  sulphate  of  indigo.  These 
changes  correspond  to  sulphates  of  the  different  oxides  of  osmium,  the  last 
or  blue  oxide  being  a  compound  of  protoxide  and  sesquioxide  of  osmium. 

Chlorides  of  Osmium. — Berzelius  has  described  four  chlorides  of  osmium, 
corresponding  to  the  four  first  degrees  of  oxidation  above  mentioned.  When 
osmium  is  heated  in  a  tube  in  a  current  of  dry  chlorine  gas,  a  deep  green 
sublimate  is  formed,  which  is  the  protochloride.  On  continuing  the  process 
it  yields  a  red  sublimate,  which  is  the  bichloride.  For  the  remaining  details, 
which  are  rather  minute,  I  may  refer  to  the  essay  already  cited.  Several 
of  these  chlorides  yield  double  chlorides  with  sodium,  potassium,  and  am- 
monia. 

Osmium  unites  with  sulphur  in  the  dry  way,  or  when  precipitated  from  the 
chlorides  by  hydrosulphuric  acid.  The  sulphurets  obviously  correspond  to 
the  number  of  the  oxides.  (Berzelius.) 

IHIDIUM. — Prop. — A  brittle  rnetal,  and  apt  to  fall  into  powder  when  bur- 
nished; but  with  care  it  may  be  polished,  and  then  acquires  the  appearance 
of  platinum.  Of  all  known  metals  it  is  the  most  infusible.  Children,  by  means 
of  his  large  galvanic  battery,  fused  it  into  a  globule  of  a  brilliant  metallic 
lustre  and  white  colour,  having  a  density  of  18-68;  but  the  attempts  at  fusion 
by  Berzelius  were  unsuccessful.  Its  greatest  sp.  gr.  in  the  unfused  state  is 
15-8629.  It  is  oxidized  at  a  red  heat  in  the  open  air,  if  in  a  state  of  fine 
division,  but  not  otherwise;  and  it  is  attacked  with  difficulty  even  by  nitro- 
hydrochloric  acid. 

The  eq.  of  iridium  is  estimated  by  Berzelius  at  98-8,  being  identical  with 
that  of  platinum.  It  forms  with  oxygen  four  oxides  exactly  analogous  in 
composition  to  the  first  four  oxides  of  osmium  in  the  foregoing  table,  and  its 
four  chlorides  correspond  to  those  of  osmium.  Its  sulphurets  have  been  little 
examined,  but  they  doubtless  correspond  to  the  oxides.  (An.  de  Ch.  et  de 
Ph.  xl.  257,  and  xliii.  185.)  Its  symb.  is  Ir. 

Oxides  of  Iridium. — The  protoxide,  sesquioxide,  and  teroxide  are  precipi- 
tated by  alkalies  from  the  chloride,  to  which  each  is  respectively  proportional. 
The  protoxide  is  greenish-gray  as  a  hydrate,  and  black  when  anhydrous. 
The  sesquioxide  is  bluish-black  in  the  dry  state,  and  deep  brown  as  a  hydrate. 
The  hyd rated  teroxide  is  of  a  yellowish-brown  or  greenish  colour.  The  bin- 
oxide  has  not  hitherto  been  insulated.  Berzelius  has  not  fully  decided  the 
nature  of  the  compound  which  is  considered  as  the  blue  oxide,  that  which 
forms  a  blue  solution  with  acids ;  but  he  believes  it  to  be  a  compound  of  the 
protoxide  and  sesquioxide.  This  variety  of  oxides,  together  with  the  facility 
with  which  they  appear  to  pass  from  one  to  the  other,  amply  accounts  for 
the  diversity  of  tints  sometimes  observed  in  solutions  of  iridium. 

Chlorides  of  Iridium. — The  protochloride  is  obtained  as  a  light  powder  of 
a  deep  olive-green  colour,  by  transmitting  chlorine  gas  over  pulverulent  iridium 
heated  to  a  commencing  red  heat.  When  heated  to  redness  its  chlorine  is 
expelled.  It  is  insoluble  in  water,  and  but  sparingly  dissolved  by  acids,  even 
the  nitro-bydrochloric;  but  when  the  hydrated  protoxide  is  digested  in  hy- 
drochloric acid,  the  protochloride  is  reproduced  and  dissolved,  forming  pro- 
bably a  soluble  compound  of  the  protochloride  and  hydrochloric  acid.  Its 
solution  is  a  mixture  of  brown,  green,  and  yellow.  (Berzelius.) 

The  sesquichloride  is  best  obtained  by  calcining  iridium  with  nitre,  digest- 
ing the  product  in  nitric  acid,  and,  after  washing,  dissolving  the  residual 
oxide  in  hydrochloric  acid.  Its  solution  has  a  dark  yellowish-brown  tint, 
which  is  so  intense  that  a  small  quantity  renders  water  opake.  By  evapora- 
tion it  yields  a  black  mass,  wholly  uncrystalline,  and  deliquescent  in  the 
air. 

34 


398 


METALLIC   COMBINATIONS. 


The  bichloride  is  formed  by  digesting  at  a  moderate  heat  the  sesquichloride 
in  nitro-hydrocliloric  acid.  It  is  deliquescent  and  very  soluble,  yielding  a 
solution  of  a  dark  reddish-brown  colour.  When  its  solution  is  evaporated 
to  dryness,  except  at  a  heat  not  exceeding  104°,  it  loses  chlorine,  and  is  re- 
converted into  the  sesquichloride. 

The  terchloride  has  not  been  obtained  in  a  separate  form,  but  only  as  a 
double  chloride  of  iridium  and  potassium.  It  appears  to  be  the  principal 
compound  formed  in  the  process  above  given  for  extracting  iridium  from  its 
ore,  and  is  recognized  by  its  rose-red  tint. 

Iridium  has  a  considerable  affinity  for  carbon,  combining  with  it  when  a 
piece  of  the  metal  is  held  in  the  flame  of  a  spirit-lamp.  The  resulting  car- 
buret contains  19-8  per  cent,  of  carbon. 


SECTION  XXVIII. 

METALLIC  COMBINATIONS. 

HAVING  completed  the  history  of  the  individual  metals,  and  of  the  com- 
pounds resulting  from  their  union  with  the  simple  non-metallic  bodies,  I  shall 
treat  briefly  in  the  present  section  of  the  combinations  of  the  metals  with 
each  other.  These  compounds  are  called  alloys;  and  to  those  alloys,  of 
which  mercury  is  a  constituent,  the  term  amalgam  is  applied.  It  is  probable 
that  each  metal  is  capable  of  uniting  in  one  or  more  proportions  with  every 
other  metal,  and  on  this  supposition  the  number  of  alloys  would  be  exceed- 
ingly numerous.  This  department  of  chemistry,  however,  owing  to  its  having 
been  cultivated  with  less  zeal  than  most  other  branches  of  the  science,  is  as 
yet  limited,  and  our  knowledge  concerning  it  imperfect.  On  this  account  I 
shall  mention  'those  alloys  only  to  which  some  particular  interest  is  at- 
tached. 

Metals  do  not  combine  with  each  other  in  their  solid  state,  owing  to  the 
influence  of  chemical  affinity  being  counteracted  by  the  force  of  cohesion. 
It  is  necessary  to  liquefy  at  least  one  of  them,  in  which  case  they  always 
unite,  provided  their  mutual  attraction  is  energetic.  Thus,  brass  is  formed 
when  pieces  of  copper  are  put  into  melted  zinc ;  and  gold  unites  with  mer- 
cury at  common  temperatures  by  mere  contact. 

Metals  appear  to  unite  with  one  another  in  every  proportion,  precisely  in 
the  same  manner  as  sulphuric  acid  and  water.  Thus  there  is  no  limit  to  the 
number  of  alloys  of  gold  and  copper.  It  is  certain,  however,  that  metals 
have  a  tendency  to  combine  in  definite  proportion  ;  for  several  atomic  com- 
pounds  of  this  kind  occur  native.  The  crystallized  amalgam  of  silver,  for 
example,  is  composed,  according  to  the  analysis  of  Klaproth,  of  64  parts  of 
mercury  and  36  of  silver;  numbers  which  are  so  nearly  in  the  ratio  of  202 
to  108,  that  the  amalgam  may  be  inferred  to  contain  one  eq.  of  each  of  its 
elements.  It  is  indeed  possible  that  the  variety  of  proportion  in  alloys  is 
rather  apparent  than  real,  arising  from  the  mixture  of  a  few  definite  com- 
pounds with  each  other,  or  with  uncombined  metal ;  an  opinion  not  only 
suggested  by  the  mode  in  which  alloys  are  prepared,  but  in  some  measure 
supported  by  observation.  Thus,  on  adding  successive  small  quantities  of 
silver  to  mercury,  a  great  variety  of  fluid  amalgams  are  apparently  produced  ; 
but,  in  reality,  the  chief,  if  not  the  sole  compound,  is  a  solid  amalgam,  which 
is  merely  diffused  throughout  the  fluid  mass,  and  may  be  separated  by  press- 
ing  the  liquid  mercury  through  a  piece  of  thick  leather. 

This  view  is  strengthened  by  some  late  experiments  by  Rudberg  (An.  de 
Cii.  et  de  Ph.  xlviii.  363.)  He  finds  that  variable  mixtures  of  metals  in  cooling 
after  fusion  have  generally  two  periods  when  the  thermometer  is  stationary. 


AMALGAMS.  399 

In  alloys  of  lead  and  tin  one  of  these  points  is  uniformly  at  368£°  for  all 
mixtures,  while  the  other  point  varies  according  as  one  or  the  other  metal  is 
predominant,  and  is  near  the  fusing-  point  of  the  predominating  metal.  From 
this  it  is  inferred  that  the  latter  point  is  caused  by  the  congelation  of  the 
predominating  metal,  and  the  constant  point  is  the  congealing  temperature 
of  an  alloy  of  uniform  composition  present  in  all  the  mixtures.  This  alloy 
is  composed  of  three  eq.  of  tin  and  one  eq.  of  lead,  its  congealing  point  be- 
ing 368^°,  In  variable  mixtures  of  bismuth  and  tin  the  constant  point  is 
289^°,  which  is  the  congealing  temperature  of  an  alloy  composed  of  single 
eq.  of  tin  and  bismuth. 

Alloys  are  analogous  to  metals  in  their  chief  physical  properties.  They 
are  opaque,  possess  the  metallic  lustre,  and  are  good  conductors  of  heat  and 
electricity.  They  often  differ  materially  in  some  respects  from  the  elements 
of  which  they  consist.  The  colour  of  an  alloy  is  sometimes  different  from 
that  of  its  constituents,  of  which  brass  is  a  remarkable  example.  The  hard- 
ness of  a  metal  is  in  general  increased  by  being  alloyed,  and  for  this  reason 
its  elasticity  and  sonorousness  are  frequently  improved.  The  malleability 
and  ductility  of  metals,  on  the  contrary,  are- usually  impaired  by  combina- 
tion. Alloys  formed  of  two  brittle  metals  are  always  brittle;  and  an  alloy 
composed  of  a  ductile  and  a  brittle  metal  is  generally  brittle,  especially  if 
the  latter  predominate.  An  alloy  of  two  ductile  metals  is  sometimes 
brittle. 

The  density  of  an  alloy  is  sometimes  less,  sometimes  greater,  than  the 
mean  density  Of  the  rnetals  of  which  it  is  composed. 

The  fusibility  of  metals  is  greatly  increased  by  being  alloyed.  Thus  pure 
platinum,  which  cannot  be  completely  fused  in  the  most  intense  heat  of  a 
wind  furnace,  forms  a  very  fusible  alloy  with  arsenic. 

The  tendency  of  metals  to  unite  with  oxygen  is  considerably  augmented 
by  being  alloyed.  This  effect  is  particularly  conspicuous  when  dense  me- 
tals are  liquefied  by  combination  with  quicksilver.  Lead  and  tin,  for  in- 
stance, when  united  with  mercury,  are  soon  oxidized  by  exposure  to  the 
atmosphere ;  and  even  gold  and  silver  combine  with  oxygen,  when  the  amal- 
gams of  those  metals  are  agitated  with  air.  The  oxidability  of  one  metal  in 
an  alloy  appears  in  some  instances  to  be  increased  in  consequence  of  a  gal- 
vanic action.  Tims,  Faraday  observed  that  an  alloy  of  steel  with  100th  of 
its  weight  of  platinum  was  dissolved  with  effervescence  in  dilute  sulphuric 
acid,  which  was  so  weak  that  it  scarcely  acted  on  common  steel ;  an  effect 
which  he  ascribes  to  the  steel  in  the  alloy  being  rendered  positive  by  the 
presence  of  the  platinum.  De  la  Rive  has  noticed  a  similar  instance  in  com- 
mercial zinc,  the  oxidability  of  which  is  increased  by  the  presence  of  small 
quantities  of  iron.  In  these  cases,  however,  the  effect"  is  due  rather  to  one 
metal  being  mechanically  enveloped  in  another  than  to  actual  combination. 

AMALGAMS. 

Quicksilver  unites  with  potassium  when  agitated  in  a  glass  tube  with  that 
metal,  forming  a  solid  amalgam.  When  the  amalgam  is  put  into  water,  the 
potassium  is  gradually  oxidized,  hydrogen  gas  is  disengaged,  and  the  mer- 
cury resumes  its  liquid  form.  A  similar  compound  may  be  obtained  with 
sodium.  These  amalgams  may  also  be  procured  by  placing  the  negative 
wire  in  contact  with  a  globule  of  mercury  during  the  process  of  decomposing 
potassa  and  soda  by  galvanism. 

A  solid  amalgam  of  tin  is  employed  in  making  looking  glasses;  and  an 
amalgam  made  of  one  part  of  lead,  one  of  tin,  two  of  bismuth,  and  four 
parts  of  mercury,  is  used  for  silvering  the  inside  of  hollow  glass  globes. 
This  amalgam  is  solid  at  common  temperatures ;  but  it  is  fused  by  a  slight 
degree  of  heat. 

The  amalgam  of  zinc  and  tin,  used  for  promoting  the  action  of  the  elec- 
trical machine,  is  made  by  fusing  one  part  of  zinc  with  one  of  tin,  and  then 
agitating  the  liquid  mass  with  two  parts  of  hot  mercury  placed  in  a  wooden 


400  ALLOYS. 

box.  Mercury  evinces  little  disposition  to  unite  with  iron,  and,  on  this  ac- 
count, it  is  usually  preserved  in  iron  bottles. 

The  amalgam  of  silver,  as  already  mentioned,  is  a  mineral  production. 
The  process  of  separating  silver  from  its  ores  by  amalgamation,  practised  on 
a  large  scale  at  Freyberg  in  Germany,  is  founded  on  the  affinity  of  mercury 
for  silver.  On  exposing  the  amalgam  to  heat,  the  quicksilver  is  volatilized, 
and  pure  silver  remains, 

Gold  unites  with  remarkable  facility  with  mercury,  forming  a  white-col- 
oured compound.  An  amalgam  composed  of  one  part  of  gold  and  eight  of 
mercury  is  employed  in  gilding  brass.  The  brass,  after  being  rubbed  with 
nitrate  of  peroxide  of  mercury  in  order  to  give  it  a  thin  film  of  quicksilver, 
is  covered  with  the  amalgam  of  gold,  and  then  exposed  to  heat  for  the  pur- 
pose of  expelling  the  mercury. 

ALLOYS  OF  ARSENIC. 

Arsenic  has  a  tendency  to  render  the  metals,  with  which  it  is  alloyed, 
both  brittle  and  fusible.  It  has  the  property  of  destroying  the  colour  of 
gold  and  copper.  An  alloy  of  copper,  with  a  tenth  part  of  arsenic  is  so  very 
similar  in  appearance  to  silver,  that  it  has  been  substituted  for  it.  The 
whiteness  of  this  alloy  affords  a  rough  mode  of  testing  for  arsenic;  for  if 
arsenious  acid  and  charcoal  be  heated  between  two  plates  of  copper,  a  white 
stain  afterwards  appears  upon  its  surface,  owing  to  the  formation  of  an 
arseniuret  of  copper. 

The  presence  of  arsenic  in  iron  has  a  very  pernicious  effect ;  for  even 
though  in  small  proporion,  it  renders  the  iron  brittle,  especially  when 
heated. 

The  alloy  of  tin  and  arsenic  is  employed  for  forming  arseniuretted  hy- 
drogen gas  by  the  action  of  hydrochloric  acid.  The  tin  of  commerce  some- 
times contains  a  minute  quantity  of  this  alloy. 

An  alloy  of  platinum  with  ten  parts  of  arsenic  is  fusible  at  a  heat  a  little 
above  redness,  and  may,  therefore,  be  cast  in  moulds.  On  exposing  the  alloy 
to  a  gradually  increasing  temperature  in  open  vessels,  the  arsenic  is  oxidized 
and  expelled,  and  the  platinum  recovers  its  purity  and  infusibility. 

ALLOYS  OF  TIN,  LEAD,  ANTIMONY,  AND  BISMUTH. 

Tin  and  lead  unite  readily  when  fused  together,  constituting  solder,  of 
which  two  kinds  are  distinguished.  The  alloy  called  fine  solder  consists  of 
two  parts  of  tin  and  one  of  lead,  fuses  at  about  360°,  and  is  much  employed 
in  tinning  copper.  The  coarse  solder  contains  l-4th  of  tin,  fuses  at  about 
500°,  and  is  the  substance  used  for  soldering  by  glaziers.  Thus,  by  varying 
the  relative  quantity  of  the  metals,  a  solder  of  different  fusibility  may  be 
obtained.  The  process  of  hard  soldering  or  brazing,  by  which  two  surfaces 
of  copper  are  cemented  together,  is  done  with  hard  solder,  which  is  made  by 
fusing  together  brass  and  zinc  :  the  copper  requires  to  be  heated,  when  this 
solder  is  used,  to  near  its  point  of  fusion. 

It  has  been  observed  by  Kupfer  that  most  of  the  alloys  of  tin  and  lead, 
made  in  atomic  proportion,  have  a  sp.  gr.  less  than  their  calculated  density  ; 
from  which  it  is  manifest  that  they  expand  in  uniting.  The  amalgams  of 
lead  and  tin,  on  the  contrary,  occupy  less  space,  when  combined,  than  their 
elements  did  previously. 

Tin,  alloyed  with  small  quantities  of  antimony,  copper  and  bismuth, 
forms  the  best  kind  of  pewter.  Inferior  sorts  contain  a  large  proportion  of 
lead. 

Tin,  lead,  and  bismuth  form  an  alloy  which  is  fused  at  a  temperature  be- 
low 212°.  The  best  proportion,  according  to  D'Arcet,  is  eight  parts  of  bis- 
muth, five  of  lead,  and  three  of  tin. 

An  alloy  of  three  parts  of  lead  to  one  of  antimony  constitutes  the  sub- 
stance  of  which  types  for  printing  are  made. 


ALLOYS.  401 

A  native  alloy  of  antimony  and  nickel,  found  at  Andreasberg  in  the  Harz, 
was  found  by  Stromeyer  to  consist  of  29'5  parts  or  one  eq.  of  nickel,  and 
64-6  parts  or  one  eq.  of  antimony. 

ALLOYS  OF  COPPER. 

Copper  forms  with  tin  several  valuable  alloys,  which  are  characterized  by 
their  sonorousness.  Bronze  is  an  alloy  of  copper  with  about  eight  or  ten 
per  cent,  of  tin,  together  with  small  quantities  of  other  metals,  which  are 
not  essential  to  the  compound.  Canons  are  cast  with  an  alloy  of  a  similar 
kind. 

The  best  bell-metal  is  composed  of  80  parts  of  copper  and  20  of  tin; — the 
Indian  gong,  celebrated  for  the  richness  of  its  tones,  contains  copper  and  tin 
in  this  proportion.  A  specimen  of  English  bell-metal  was  found  by  Dr. 
Thomson  to  consist  of  80  parts  of  copper,  10gl  of  tin,  5'6  of  zinc,  and  4-3  of 
lead.  Lead  and  antimony,  though  in  small  quantity,  have  a  remarkable 
effect  in  diminishing  the  elasticity  and  sonorousness  of  the  compound.  Spe- 
culum-metal^ with  which  mirrors  for  telescopes  are  made,  consists  of  about 
two  parts  of  copper  and  one  of  tin.  The  whiteness  of  the  alloy  is  improved 
by  the  addition  of  a  little  arsenic. 

Copper  and  zinc  unite  in  several  proportions,  forming  alloys  of  great  im- 
portance in  the  arts.  The  best  brass  consists  of  four  parts  of  copper  to  one 
of  zinc;  and  when  the  latter  is  in  a  greater  proportion,  compounds  are  gene- 
rated which  are  called  tombac,  Dutch-gold,  and  pinchbeck.  The  white  copper 
of  the  Chinese  is  composed,  according  to  the  analysis  of  Fyfe,  of  40-4  parts 
of  copper,  25-4  of  zinc,  31-6  of  nickel,  and  2-6  of  iron. 

The  art  of  tinning  copper  consists  in  covering  that  metal  with  a  thin 
layer  of  tin,  in  order  to  protect  its  surface  from  rusting.  For  this  purpose, 
pieces  of  tin  are  placed  upon  a  well-polished  sheet  of  copper,  which  is  heated 
sufficiently  for  fusing  the  tin.  As  soon  as  the  tin  liquefies,  it  is  rubbed  over 
the  whole  sheet  of  copper,  and  if  the  process  is  skilfully  conducted,  adheres 
uniformly  to  its  surface.  The  oxidation  of  the  tin,  a  circumstance  which 
would  entirely  prevent  the  success  of  the  operation,  is  avoided  by  employing 
fragments  of  resin  or  muriate  of  ammonia,  and  regulating  the  temperature 
with  great  eare.  The  two  metals  do  not  actually  combine ;  but  the  adhesion 
is  certainly  owing  to  their  mutual  affinity.  Iron,  which  has  a  weaker  at- 
traction than  copper  for  tin,  is  tinned  with  more  difficulty  than  that  metal. 

ALLOYS  OF  STEEL. 

Messrs.  Stodart  and  Faraday  have  succeeded  in  making  some  very  im- 
portant alloys  of  steel  with  other  metals.  (Phil.  Trans,  for  1822.)  Their  ex- 
periments  induced  them  to  believe  that  the  celebrated  Indian  steel,  called 
wootz,  is  an  alloy  of  steel  with  small  quantities  of  silicon  and  aluminium  ; 
and  they  succeeded  in  preparing  a  similar  compound,  possessed  of  all  the 
properties  of  wootz.  They  ascertained  that  silver  combines  with  steel,  form- 
ing an  alloy,  which,  although  it  contains  only  l-500th  of  its  weight  of  silver, 
is  superior  to  wootz  or  the  best  cast  steel  in  hardness.  The  alloy  of  steel 
with  100th  part  of  platinum,  though  less  hard  than  that  with  silver,  possesses 
a  greater  degree  of  toughness,  and  is,  therefore,  highly  valuable  when  tena- 
city as  well  as  hardness  is  required.  The  alloy  of  steel  with  rhodium  even 
exceeds  the  two  former  in  hardness.  The  compound  of  steel  with  palladium, 
and  of  steel  with  iridium  and  osmium,  is  likewise  exceedingly  hard ;  but 
these  alloys  cannot  be  employed  extensively,  owing  to  the  rarity  of  the  metals 
of  which  they  are  composed. 

ALLOYS  OF  SILVER. 

Silver  is  capable  of  uniting  with  most  other  metals,  and  suffers  greatly  in 
malleability  and  ductility  by  their  presence.  It  may  contain  a.  large  quantity 

34* 


402  GENERAL  REMARKS  ON  SALTS. 

of  copper  without  losing  its  white  colour.  The  standard  silver  for  coinage 
contains  about  l-13th  part  of  copper,  which  increases  its  hardness,  and  thus 
renders  it  more  fit  for  coins  and  many  other  purposes. 

ALLOYS  OF  GOLD. 

The  presence  of  other  metals  in  gold  has  a  remarkable  effect  in  impairing 
its  malleability  and  ductility.  The  metals  which  possess  this  property  in  the 
greatest  degree  are  bismuth,  lead,  antimony,  and  arsenic.  Thus,  when  gold 
is  alloyed  with  l-1920th  part  of  its  weight  of  lead,  its  malleability  is  surpris- 
ingly diminished.  A  very  small  proportion  of  copper  has  an  influence  over 
the  colour  of  gold,  communicating  to  it  a  red  tint,  which  becomes  deeper  as 
the  quantity  of  copper  increases.  Pure  gold,  being  too  soft  for  coinage  and 
many  purposes  in  the  arts,  is  always  alloyed  either  with  copper  or  an  alloy 
of  copper  and  silver,  which  increases  the  hardness  of  the  gold  without  ma- 
terially affecting  its  colour  or  tenacity.  Gold  coins  contain  about  l-12th  of 
copper. 

Nearly  all  the  gold  found  in  nature  is  alloyed  more  or  less  with  silver. 
In  a  late  elaborate  investigation  into  the  constituents  of  the  Uralian  ores  of 
gold,  G.  Rose  found  one  specimen  with  0-16  per  cent,  of  silver,  and  another 
with  38*38  per  cent.;  but  most  of  the  specimens  contained  8  or  9  per  cent,  of 
silver.  It  has  been  maintained  that  the  native  alloys  of  gold  and  silver  are 
usually  in  atomic  proportion.  This  statement,  however,  has  been  amply 
disproved  by  G.  Rose :  these  metals  appear  to  be  isomorphous,  and  hence, 
like  other  isomorphous  bodies,  they  crystallize  with  each  other  in  proportions 
altogether  indefinite.  (Pog.  An.  xxiii.  161.) 


SALTS. 

GENERAL  REMARKS  ON  SALTS. 

THE  preceding  pages  contain  the  description  either  of  elementary  prin- 
ciples, or  of  compounds  immediately  resulting  from  the  union  of  those 
elements.  These  compounds  are  chiefly  bi-elemcntary,  that  is,  arise  from 
the  union  of  two  elements  :  their  constituents  are  regarded,  according  to  the 
electro-chemical  theory,  as  possessing  opposite  electric  energies,  and  as 
combined  by  virtue  of  such  energies ;  and  the  names  applied  to  them  are 
partly  constructed  in  reference  to  this  theory.  Thus  in  compounds  of 
oxygen  and  chlorine,  chlorine  and  iodine,  sulphur  and  potassium,  the  term 
expressive  of  the  genus  or  class  of  bodies  to  which  each  compound  belongs, 
is  derived  from  the  electro-negative  element ;  so  that  we  do  not  say,  chloride 
of  oxygen,  iodide  of  chlorine,  and  potassiuret  of  sulphur, — but  oxide  of 
chlorine,  chloride  of  iodine,  and  sulphuret  of  potassium  ;  because  oxygen 
has  a  higher  electro-negative  energy  than  chlorine,  chlorine  than  iodine,  and 
sulphur  than  potassium.  The  metals  as  a  class  are  electro- positive  to  the 
non-metallic  elements ;  but  in  relation  to  each  other,  some  of  the  metals  are 
electro-positive,  and  others  electro-negative.  To  the  former  belongs  those 
metals,  the  oxides  of  which  are  strong  alkaline  bases,  such  as  potassium, 
sodium,  and  calcium  ;  and  among  the  latter  are  enumerated  those,  such  as 
arsenic,  antimony,  and  molybdenum,  which  are  prone  to  form  acids  when 
they  unite  with  oxygen. 

Some  of  the  bi-elementary  compounds  above  referred  to,  though  composed 
of  very  energetic  elements,  are  themselves  chemically  indifferent,  manifesting 
little  disposition  to  unite  with  any  other  body  whatever;  of  which  the  per- 
oxides of  manganese  and  lead,  and  some  of  the  chlorides,  are  examples. 


GENERAL  REMARKS  ON  SALTS.  403 

Others,  on  the  contrary,  are  surprisingly  energetic  in  their  chemical  relations, 
and  have  an  extensive  range  of  affinity.  The  most  remarkable  instances  of 
this  are  found  among  those  oxidized  bodies  called  acids  and  alkalies,  the 
characters  of  which  fixed  the  attention  of  chemists  long  before  their  com- 
position was  understood.  The  acids  and  alkalies,  however,  are  indifferent  to 
elementary  substances :  their  affinities  are  exerted  towards  each  other,  and 
by  uniting  they  give  rise  to  compounds  more  complex  than  themselves,  as 
containing  at  least  three  elements,  and  which  are  known  by  the  name  of 
salts.  Acids  and  alkalies  possess  opposite  electric  energies  in  relation  to 
each  other,  the  former  being  negative  and  the  latter  positive.  The  electric 
energies  evinced  by  them  are  related  to  the  electric  energies  of  their  ele- 
ments. Thus  acids  generally  abound  in  the  electro-negative  oxygen,  and  if 
they  contain  a  metal,  it  is  usually  an  electro-negative  metal;  whereas  the 
powerful  alkalies  are  the  protoxides  of  electro-positive  metals. 

Acids  and  alkalies  neutralize  each  other  more  or  less  completely,  so  that 
the  resulting  salt  is  generally  neither  acid  nor  alkaline,  and  is  far  less  ener- 
getic as  a  chemical  agent  than  acids  and  alkalies.  Most  of  them,  however, 
unite  in  definite  proportion  with  certain  substances,  such  as  water,  alcohol, 
ammonia,  and  with  other  salts,  forming  the  extensive  family  of  double  salts. 
To  these  compounds  the  electro-chemical  theory  may  be  extended  :  the  two 
simple  salts  which  constitute  a  double  salt,  may  be  viewed  as  two  molecules, 
united  by  virtue  of  electric  energies  of  an  opposite  character. 

In  the  early  period  of  modern  chemistry  an  acid  was  considered  to  be  an 
oxidized  body  which  has  a  sour  taste,  reddens,  litmus  paper,  and  neutralizes 
alkalies.  But  subsequent  experience  has  shown  the  propriety  of  extending 
the  definition  of  an  acid.  For,  first,  the  discovery  of  the  hydracids  proved 
that  oxygen  is  not  essential  to  acidity.  Secondly,  some  compounds,  owing 
to  their  insolubility,  neither  taste  sour  nor  redden  litmus,  and  yet  from  their 
chemical  relations  are  regarded  as  acids.  Thirdly,  some  acknowledged  acids, 
such  as  the  carbonic  and  hydrosulphuric,  are  unable  fully  to  destroy  the 
alkaline  reaction  of  potassa.  Facts  of  this  kind  have  induced  chemists  to 
consider  as  acids  all  those  compounds  which  unite  with  potassa  or  ammonia, 
and  give  rise  to  bodies  sirnilar  in  their  constitution  and  general  character  to 
the  salts  which  the  sulphuric  or  some  admitted  acid  forms  with  those 
alkalies. 

A  similar  extension  is  given  to  the  notion  of  alkalinity,  the  characters  of 
which,  as  exhibited  in  their  most  perfect  form  in  potassa  and  soda,  are  caus- 
ticity, a  peculiar  pungent  alkaline  taste,  alkaline  reaction  with  test  paper, 
and  power  both  of  neutralizing  acids  and  of  forming  with  them  neutral  saline 
compounds.  Of  these,  chemists  agree  to  consider  the  last  as  the  most  cha- 
racteristic, and  place  among  the  alkaline  or  salifiable  bases,  all  those  bodies 
which  unite  definitely  with  admitted  acids,  such  as  the  sulphuric  and  nitric, 
and  form  with  them  compounds  analogous  in  constitution  to  the  salts  which 
admitted  alkalies  form  with  the  acids.  Thus,  magnesia  is  a  very  strong" 
alkaline  base,  seeing  that  2O7  parts  of  it  neutralize  as  much  sulphuric  acid 
as  47-15  of  potassa ;  and  yet  magnesia,  from  being  insoluble,  is  all  but  taste- 
less, and  has  barely  any  alkaline  reaction. 

The  progress  of  chemistry,  which  has  gradually  developed  sounder  views 
of  the  nature  of  acids  and  alkalies,  is  also  causing  an  extension  in  the  idea 
of  a  salt.  The  great  mass  of  salts  are  compounds  of  oxidixed  bodies,  both 
the  acid  and  the  base  containing  oxygen.  But  ammonia,  though  not  an  oxide, 
has  all  the  characters  of  alkalinity  in  an  eminent  degree,  and  its  compounds 
with  acids  were  at  once  admitted  into  the  list  of  salts.  Then  came  the  dis- 
covery of  the  hydracids,  such  as  the  hydrochloric  and  hydriodic,  which  are 
-so  powerfully  acid,  that  their  compounds  with  alkaline  bases  were  readily 
adopted  as  salts.  Hence  arose  the  division  of  the  salts,  as  a  class,  into  two 
orders,  one  containing  oxygen  or  oxy-salts,  and  the  other  hydrogen  or  hydro- 
salts.  Again,  the  gaseous  terfluoride  of  boron,  which  contains  neither  oxygen 
nor  hydrogen,  combines  definitely  with  ammonia,  and  forms  with  it  a  neutral 
compound,  which  was  esteemed  a  salt  as  soon  as  it  was  known. 


404  GENERAL  REMARKS  ON  SALTS. 

The  notion  of  a  bait  has  of  late  been  still  further  extended.  Chemists 
have  long  known  that  metallic  sulphurets  occasionally  combine  together, 
and  constitute  what  is  called  a  double  sulphuret.  In  these  compounds  Ber- 
zelius,  whose  labours  have  greutly  added  to  their  number,  has  traced  an  exact 
analogy  with  the  salts,  and  applied  to  them  the  name  of  sulphur-salts.  The 
simple  sulphurets,  by  the  union  of  which  a  sulphur-salt  is  formed,  are  bi-ele- 
mentary  compounds,  strictly  analogous  in  their  constitution  to  acids  and 
alkaline  bases,  and  which,  like  them,  are  capable  of  assuming  opposite  electric 
energies  in  relation  to  each  other.  Electro-positive  sulphurets,  termed  sulphur- 
bases^  are  usually  the  protosulphurets  of  electro-positive  metals,  and,  there- 
fore, correspond  to  the  alkaline  bases  of  those  rnetals ;  and  the  electro-nega- 
tive sulphurets,  sulphur- acids ,  are  the  sulphurets  of  electro-negative  metals, 
and  are  proportional  in  composition  to  the  acids  which  the  same  metals  form 
with  oxygen.  Hence,  if  the  sulphur  of  a  sulphur-salt  were  replaced  by  an 
equivalent  quantity  of  oxygen,  an  oxy-salt  would  result.  (An.  de  Ch.  et  de 
Ph.  xxxii.  60.) 

The  compounds  which  Berzelius  has  enumerated  as  sulphur-acids,  are  the 
sulphurets  of  arsenic,  antimony,  tungsten,  molybdenum,  tellurium,  tin  and 
gold.  To  these  he  has  added  the  sulphurets  of  several  other  substances  not 
metallic,  such  as  sulphuret  of  selenium,  bisulphuret  of  carbon,  and  the  hy- 
drosulphuric  and  hydrosulphocyanic  acids.  He  mentions,  also,  that  just  as 
two  electro-positive  oxides  may  combine,  one  becoming  electro-negative  in 
regard  to  the  other,  so  may  a  sulphur-salt  be  generated  by  the  union  of  elec- 
tro-positive sulphurets.  The  native  double  sulphuret  of  copper  and  iron, 
and  a  considerable  number  of  similar  compounds,  are  instances  of  this 
nature.  These  analogies  are  rendered  much  closer  by  the  facts  that  hydro- 
sulphuric  and  hydrosulphocyanic  acids  act  as  hydracids  with  ammonia,  and 
as  sulphur-acids  with  sulphur-bases;  and  that  all  the  sulphurets  which  are 
remarkable  as  sulphur-acids,  have  likewise  the  property  of  combining  with 
ammonia.  I  shall  accordingly  place  the  double  sulphurets  as  a  third  order 
of  the  class  of  salts,  and  describe  them  under  the  name  of  sulphur-salts. 

A  fourth  order  of  salts  has  been  formed  by  Berzelius,  comprising  for  the 
most  part  bi-elementary  compounds,  which  consist  of  a  metal  on  the  one  hand, 
and  of  chlorine,  iodine,  bromine,  fluorine,  and  the  radicals  of  the  hydracids 
on  the  other.  He  has  applied  to  them  the  name  of  haloid  salts  (from  axe 
sea-salt,  and  «;/&;  form,)  because  in  constitution  they  are  analogous  to  sea- 
salt.  The  whole  series  of  the  metallic  chlorides,  iodides,  bromides,  and 
fluorides,  such  as  chloride  of  sodium,  iodide  of  potassium,  and  fluor  spar,  as 
well  as  the  cyanurets,  sulphocyanurets,  and  ferrocyanurets,  are  included  in 
his  list  of  haloid  salts.  (An.  de  Ch.  et  de  Ph.  xxxii.  60.)  The  reader  will 
at  once  perceive  that  these  haloid  salts,  as  bi-elementary  compounds,  differ  in 
composition  from  other  salts,  and  are  analogous  to  oxides  and  sulphurets. 
This  resemblance  will  appear  still  more  intimate  if  he  turn  to  the  tables  of 
composition  given  in  the  sections  on  the  metals,  where  the  number  and  con. 
stitution  of  the  chlorides  and  iodides  are  shown  to  be  strikingly  similar  to 
the  number  and  constitution  of  the  oxides  and  sulphurets.  But  Berzelius, 
though  he  has  himself  traced  and  fully  admits  these  analogies,  considers  his 
haloid  salts  to  differ  so  much  in  their  chemical  relations  from  oxides  and  sul- 
phurets, that  they  ought  not  to  stand  in  the  same  class  of  compounds.  Soda, 
for  instance,  is  caustic,  strongly  alkaline,  and  endowed  with  powerful  affini- 
ties; while  chloride  of  sodium  is  a  neutral  substance,  of  a  taste  and  appea- 
rance precisely  like  ordinary  salts,  and  indifferent  in  its  chemical  relations. 
The  difference  is  here  certainly  very  striking;  but  on  extending  the  compa- 
rison to  other  oxides  and  chlorides,  the  result  is  by  no  means  the  same.  Surely 
the  terchloride  of  gold  is  at  least  as  energetic  an  agent  as  the  teroxide,  and 
the  bichloride  of  platinum  as  the  corresponding  oxide.  The  bichloride  and 
bicyanuret  of  mercury  are  more  energetic  as  chemical  agents  than  bisul- 
phuret of  mercury,  and  perhaps  fully  as  much  so  as  the  peroxide.  Chemists 
are  only  beginning  to  be  acquainted  with  the  numerous  compounds  which 
metallic  cyanurets  are  capable  of  forming  with  each  other. 


GENERAL  REMARKS  ON  SALTS.  405 

If  the  difference  between  all  oxides  and  chlorides  were  as  strong  as  be- 
tween soda  and  sea-salt,  chemists  would  have  to  consider  whether  they 
should  adopt,  as  a  principle  of  classification,  analogy  of  composition  or  of 
character.  But  as  the  case  now  stands  they  are  scarcely  left  to  this  alternative. 
In  point  of  composition  the  chlorides  are  as  remote  from  salts  as  they  are 
allied  to  oxides;  and  in  their  chemical  agencies,  the  haloid  salts  of  Berzelius, 
taken  collectively,  appear  to  me  to  be  as  closely  related  to  oxides  and  sulphu- 
rets  as  to  salts.  It  seems  then  fair  to  conclude  that  the  chlorides  and  simi- 
lar bi-elementary  compounds  stand  to  each  other  in  the  relation  of  acids^ind 
bases,  btfing  capable  of  assuming"  opposite  electric  energies,  and  of  forming1 
compounds  analogous  to  salt?.  I  shall  describe  them  as  a  fourth  order  of 
salts  under  the  name  of  haloid  salts,  because  the  electro-positive  and  electro- 
negative compounds  which  form  them,  Ihe,  haloid  bases  and  acids,  have  the 
same  kind  of  composition  as  sea-salt.  The  haloid  salts  of  Berzclius  are  my 
haloid  acids  and  bases ;  and  what  I  term  a  haloid  salt,  is  a  double  haloid  salt 
to  Berzelius.  The  doctrine  here  adopted  was  first  proposed  and  ably  illus- 
trated by  Bonsdorff.*  (An.  de  Ch.  et  de  Ph.  xliv.  189.) 

Consistently  with  the  views  developed  in  the  preceding  pages,  I  have 
grouped  together  all  saline  compounds  which  have  a  certain  similarity  of 
composition  into  one  great  class  of  salts^  which  is  divided  into  the  four  fol- 
lowing orders : — 

Order  I.  The  oxy-salts.  This  order  includes  no  salt  the  acid  or  base  of 
which  is  not  an  oxidized  body. 

Order  II.  The  hydro-salts.  This  order  includes  no  salt  the  acid  or  base 
of  which  does  not  contain  hydrogen. 

Order  III.  The  sulphur-salts.  This  order  includes  no  salt  the  electro- 
positive or  negative  ingredient  of  which  is  not  a  sulphuret. 

Order  IV.  The  haloid  salts.  This  order  includes  no  salt  the  electro- 
positive or  negative  ingredient  of  which  is  not  haloidal. 

The  nomenclature  of  the  first  order  of  salts  was  explained  on  a  former 
occasion  (page  123).  The  insufficiency  of  the  division  into  neutral,  super, 
and  SM^salts,  will  be  made  apparent  by  the  following  remarks.  In  the  first 
place,  some  alkaline  bases  form  more  than  one  super-salt,  in  which  case  two 
or  more  different  salts  would  be  included  under  the  same  name.  Secondly, 
some  salts  have  an  acid  reaction,  and  might,  therefore,  be  denominated  super- 
salts,  although  they  do  not  contain  an  excess  of  acid.  Nitrate  of  protoxide 
of  lead,  for  instance,  has  the  property  of  reddening  litmus  paper ;  whereas  it 
consists  of  one  eq.  of  protoxide  of  lead  and  one  eq.  of  nitric  acid,  and,  there- 
fore in  composition  is  precisely  analogous  to  nitrate  of  potassa,  which  is  a 
neutral  salt.  The  fact  was  noticed  some  years  ago  by  Berzelius,  who  ac- 
counted for  the  circumstance  in  the  following  manner  : — The  colour  of  litmus 
is  naturally  red,  and  it  is  only  rendered  blue  by  the  colouring  matter  com- 
bining with  an  alkali.  If  an  acid  be  added  to  the  blue  compound,  the  colour- 
ing matter  is  deprived  of  its  alkali,  and  thus,  being  set  free,  resumes  its  red 
tint.  Now  on  bringing  litmus  paper  in  contact  with  a  salt,  the  acid  and  base 
of  which  have  a  weak  attraction  for  each  other,  it  is  possible  that  the  alkali 
contained  in  the  litmus  paper  may  have  a  stronger  affinity  for  the  acid  of 
the  salt  than  the  base  has  with  which  it  was  combined  ;  and  in  that  case 
the  alkali  of  the  litmus  being  neutralized,  its  red  colour  will  necessarily  be 
restored.  It  is  hence  apparent  that  a  salt  may  have  an  acid  reaction  with- 
out having  an  excess  of  acid. 

The  nomenclature  of  thf1  hydro-salts  is  framed  on  the  same  principles  as 
that  applied  to  the  salts  which  contain  oxygen.  With  respect  to  the  third 

*  This  same  doctrine  was  proposed  and  ably  supported  by  Dr.  Hare,  in  a 
letter  on  the  Berzelian  nomenclature,  addressed  to  Professor  Silliman,  and 
dated  in  June,  1834.  Dr.  Hare  had  entertained  his  peculiar  views  for  some 
time  before  the  dale  of  his  letter,  and  before  he  was  aware  that  Bonsdorff 
had  held  similar  opinions. — Ed. 


406  GENERAL  REMARKS  ON  SALTS. 

and  fourth  order  of  salts,  no  general  principle  of  nomenclature  has  yet  been 
agreed  on.  Berzelius  has  extended  to  them  the  same  nomenclature  which 
he  employs  for  the  oxy-salts,  and  some  chemists  seem  disposed  to  follow  his 
example;  but  as  new  views  are  apt  to  be  obscured,  and  their  intrinsic  value 
overlooked,  by  being  expressed  in  new  language,  I  shall  confine  myself  as 
much  as  possible  to  terms  with  which  every  chemist  is  familiar.  It  is  worthy 
of  consideration  whether  the  nomenclature  of  the  sulphur  and  haloid  salts, 
instead  of  being  purposely  assimilated  to  that  of  the  other  salts,  should  not 
designedly  be  kept  distinct,  in  order  the  more  readily  to  distinguish  between 
analogous  compounds. 

Nearly  all  salts  are  solid  at  common  temperatures,  and  most  of  them  are 
capable  of  crystallizing.  The  colour  of  salts  is  very  variable,  having  no 
necessary  connexion  with  the  colour  of  their  elements.  Salts  composed  of  a 
colourless  acid  and  base  are  colourless  ;  but  a  salt,  though  formed  of  a  co- 
loured oxide  or  acid,  may  be  colourless  ;  or,  if  coloured,  the  tint  may  differ 
from  that  of  both  its  constituents. 

All  soluble  salts  are  more  or  less  sapid,  while  those  that  are  insoluble  in 
water  are  insipid.  Few  salts  are  possessed  of  odour  :  the  most  remarkable 
one  for  this  property  is  carbonate  of  ammonia. 

Salts  differ  remarkably  in  their  affinity  for  water.  Thus,  some  salts,  such 
as  the  nitrates  of  lime  and  magnesia,  are  deliquescent,  that  is,  attract  mois- 
ture from  the  air,  and  become  liquid.  Others,  which  have  a  less  powerful 
attraction  for  water,  undergo  no  change  when  the  air  is  dry,  but  become 
moist  in  a  humid  atmosphere;  and  others  may  be  exposed  without  change 
to  an  atmosphere  loaded  with  watery  vapour. 

Salts  differ  likewise  in  the  degree  of  solubility  in  water.  Some  dissolve  in 
less  than  their  weight  of  water;  while  others  require  several  hundred  times 
their  weight  of  this  liquid  for  solution,  and  others  are  quite  insoluble.  This 
difference  depends  on  two  circumstances,  namely,  on  their  affinity  for  water, 
and  on  their  cohesion  ;  their  solubility  being  in  direct  ratio  with  the  first,  and 
in  inverse  ratio  with  the  second.  One  salt  may  have  a  greater  affinity  for 
water  than  another,  and  yet  be  less  soluble;  an  effect  which  may  be  pro- 
duced by  the  cohesive  power  of  the  salt  which  has  the  stronger  attraction  for 
water  being  greater  than  that  of  the  salt  which  has  a  less  powerful  affinity 
for  that  liquid.  The  method  proposed  by  Gay-Lussac  for  estimating  the 
relative  degrees  of  affinity  of  salts  for  water  (An.  de  Ch.  Ixxxii )  is  by  dis- 
solving equal  quantities  of  salts  in  equal  quantities  of  water,  and  applying 
heat  to  the  solutions.  That  salt  which  has  the  greatest  affinity  for  the  men- 
struum will  retain  it  with  most  force,  and  will,  therefore,  require  the  highest 
temperature  for  boilingf. 

Salts  which  are  soluble  in  water  crystallize  more  or  less  regularly  when 
their  solutions  are  evaporated.  If  the  evaporation  is  rendered  rapid  by  heat, 
the  salt  is  usually  deposited  in  a  confused  crystalline  mass  ;  but  if  it  take 
place  slowly,  regular  crystals  are  formed.  The  best  mode  of  conducting  the 
process  is  to  dissolve  a  salt  in  hot  water,  and  when  it  has  become  quite  cold 
to  pour  the  saturated  eolution  into  an  evaporating  basin,  which  is  to  be  set 
aside  for  several  days  or  weeks  without  being  moved  As  the  water  eva- 
porates, the  salt  assumes  the  solid  form ;  and  the  slower  the  evaporation,  the 
more  regular  are  the  crystals.  Some  salts  which  are  much  more  soluble  in 
hot  than  in  cold  water,  crystallize  with  considerable  regularity  when  a  boiling 
saturated  solution  is  slowly  cooled.  The  form  which  salts  assume  in  crys- 
tallizing is  constant  under  the  same  circumstances,  and  constitutes  an  ex- 
cellent character  by  which  they  may  be  distinguished  from  one  another. 

Many  salts  during  the  act  of  crystallizing  unite  chemically  with  a  definite 
portion  of  water,  which  forms  an  essential  part  of  the  crystal,  but  not  of  the 
salt,  and  is  termed  water  of  crystallization.  The  quantity  of  combined 
water  is  very  variable  in  different  saline  bodies,  but  is  uniform  in  the  same 
salt.  A  salt  may  contain  more  than  half  its  weight  of  water,  and  yet  be 
quite  dry.  On  exposing  a  salt  of  this  kind  to  heat,  it  is  dissolved,  if  soluble, 
in  its  own  water  of  crystallization,  undergoing  what  is  termed  the  watery 


GENERAL  REMARKS  ON  SALTS.  407 

fusion.  By  a  strong  heat,  the  whole  of  the  water  is  expelled;  for  no  salt 
can  retain  its  water  of  crystallization  when  heated  to  redness.  Some  salts, 
such  as  sulphate  and  phosphate  of  soda,  lose  a  portion  of  theiT  water,  and 
crumble  down  into  a  white  powder,  by  mere  exposure  to  the  air;  a  change 
which  is  called  efflorescence.  The  tendency  of  salts  to  undergo  this  change 
depends  on  the  dry  ness  and  coldness  of  the  air;  for  a  salt  which  effloresces 
rapidly  in  a  moderately  dry  and  warm  atmosphere,  may  often  be  kept  with- 
out change  in  one  which  is  damp  and  cold. 

The  water  of  crystallization  is  retained  by   a  very  feeble  affinity,  as  is 
proved  by  the  phenomena  of  efflorescence,  and  by  the  facility  with  which 
such  water  is  separated  from  the  saline  matter  by  a  moderate  heat,  or  by 
exposure  to  the  vacuum  of  an  air-purnp  at  common  temperatures.     It  is  fre- 
quently observed,  however,  that  a  portion  of  the  water  is  retained  with  such 
obstinacy  that  it  cannot  be  expelled  by  a  temperature  short  of  that  at  which 
the  salt  is  totally  decomposed.     This  water,  as  in  the  case  of  the  hydrated 
acids,  is  considered  to  act  the  part  of  a  base,  and  is  hence  commonly  called 
basic  water,  as  has  already  been  explained  in  the  section  on  phosphorus,  (p. 
202.)     But  from  the  observations  of  Graham  it  would  appear  that  the  water 
thus  retained  does  not  always  act  the  part  of  a  base,  but   is  in  a  peculiar 
state  of  combination  characteristically  different  both  from  basic  water  and 
water  of  crystallization  (Ph.  Tr.  Ed.  xii.  297).     In  his  original  paper  he  dis- 
tinguished it  as  saline  water  ;  but  in  a  recent  report  read  to  the  meeting  of 
the  British  Association  in  Liverpool,  he  has  called  it  constitutional  water.  It 
is  readily  distinguished  from  water  of  crystallization,  by  being  retained  by  a 
stronger  affinity,  and  by  being  essential  to  the  existence  of  the  salt  of  which 
it  constitutes  a  part.  From  basic  water  it  differs  by  not  being  removed  from 
its  combinations  even  by  the  most  powerful  alkalies,  whereas  it  is  readily  re- 
moved, and  its  place  in  the  compound  assumed,  by  certain  anhydrous  salts : 
it  is  also  expelled  from  an  acid  more  readily  than  the  basic  water.    From  an 
example,  the  character  of  water  in  these  different  states  of  combination  will 
be  readily  understood.     The  crystals  of  the  common  phosphate  of  soda  are 
composed  of  one  eq.  of  phosphoric  acid,  two  eq.  of  soda,  and  twenty-five  eq. 
of  water.     On  exposing  them  to  a  temperature  of  212°,  twenty-four  eq.  of 
the  water  are  readily  expelled  ;  but  the  twenty-fifth  eq.  is  retained  with  such 
power,  that  a  red  heat  is  necessary  to  effect  its  complete  separation.     By  the 
loss  of  the  twenty-four  eq.  of  water,  the  crystalline  form  and  texture  of  the 
salt  are  entirely  destroyed,  but  the  residual  amorphous  mass  has  all  the  pro- 
perties of  the  common  phosphate;  whereas  by  the  loss  of  the  twenty-fifth  eq. 
an  entirely  different  salt,  the  pyrophosphate  of  soda,  is  produced.     It  will 
hence  appear,  that  the  twenty-four  eq.  of  water  which  were  lost  at  212°  were 
only  essential  to  the  existence  of  the  crystal,  while  the  loss  of  the  twenty-fifth 
eq.  affected  that  of  the  salt. 

The  same  thing  is  observed  in  the  case  of  sulphate  of  protoxide  of  zinc. 
Its  common  crystals  are  composed  of  one  eq.  of  sulphuric  acid,  one  eq.  of 
protoxide  of  zinc,  and  seven  eq.  of  water,  six  of  which  are  readily  lost  at 
212°,  the  crystal  being  at  the  same  time  destroyed,  while  the  seventh  eq.  is 
not  expelled  until  the  temperature  rises  above  410°.  Thus  far  the  seventh 
eq.  of  water  in  sulphate  of  zinc  appears  analogous  to  the  twenty-fifth  in  the 
common  phosphate  of  soda ;  but  Graham  has  pointed  out  the  remarkable 
difference  that,  in  the  latter  salt,  the  eq.  of  water  is  readily  removed  from  its 
combination  by  an  eq.  of  any  base  which  supplies  its  place  in  the  compound  ; 
while  in  sulphate  of  zine,  the  eq.  of  water  is  not  affected  by  bases,  but  may 
be  removed  by  anhydrous  sulphates,  which  occupy  its  place  and  give  rise  to 
the  formation  of  double  salts.  The  former,  as  acting  the  part  of  a  base,  is 
called  basic  water  ;  the  latter,  as  influencing  the  constitution  of  a  salt,  is  called 
constitutional  water.  The  difference  is  denoted  in  symbols,  by  writing  the 
basic  water,  as  is  the  case  with  all  bases,  on  the  left  side  of  the  acid  with  which 
it  is  combined,  and  the  constitutional  water  on  the  right.  Hence  the  symb. 
of  the  crystals  of  phosphate  of  soda  is  2NaO.  HO,  P2O5+24Aq.;  and  of  the 
sulphate  of  zinc,  ZnO,SOs,HO  -f.  6Aq.  In  the  phosphate  the  water  may  be 


408  GENERAL  REMARKS  ON  SALTS. 

removed    by  soda,  forming  3NaO.P-O5-r-24Aq. ;    in  the   sulphate,  by    an- 
hydrous sulphate  of  potassa,  forming  the  double  salt  ZnO,SO:*,  (KO,SO3). 

In  pursuing  the  study  of  this  subject,  Graham  has  been  led  to  the  conclu- 
sion that  all  salts  are  neutral  in  their  constitution  with  the  exception  of  cer- 
tain classes.  Thus  he  finds  that  the  bisulphate  of  potassa  is  a  double  salt, 
formed  by  the  constitutional  water  of  sulphate  of  water  being  replaced  by 
sulphate  of  potassa :  thus 

HO,  SO3,HO  J    .  . ,  J  HO,  SO3,  (KO,  SO3) 

&  KO,  SO3   (  yield  )  &  HO. 

•* 

To  illustrate  the  constitution  of  a  subsalt,  the  nitrates  were  selected.  Nitric 
acid  of  sp.  gr.  T42  he  considers  to  be  nitrate  of  wafer,  with  three  eq.  of  con- 
stitutional water;  its  symb.  is,  therefore,  HO,  NO5,  3HO.  But  water  corres- 
ponds with  the  class  of  isomorphous  oxides,  of  which  magnesia,  and  the  prot- 
oxides of  zinc  and  copper  may  be  taken  as  the  type.  Hence  these  oxides  are 
capable  of  supplying  the  place  of  water  in  either  state  of  combination,  as  is 
seen  in  the  neutral  and  subnitrate  of  copper ;  in  the  former  of  which  the  basic 
water  is  removed  by  an  eq.  of  protoxide  of  copper,  while  in  the  subsalt  the 
three  eq.  of  constitutional  water  are  replaced  by  three  eq.  of  protoxide  of 
copper.  Their  constitution  is,  therefore,  represented  by  the  formulee, 

CuO,  NO*,  3 HO, 
&  HO,  NO5,  3CuO. 

In  applying  thsse  views  in  other  cases,  however,  difficulties  arise,  owing 
to  the  existence  of  anhydrous  bisalts,  as  the  anhydrous  bisulphate  and  bichro- 
mate of  potassa.  These  are  accounted  for  by  Graham,  by  supposing  the 
existence  of  a  class  of  bodies,  called  by  him  basic  adjuncts,  which  admit  of 
being  attached  to  the  oxide  of  hydrogen,  or  to  the  oxides  of  metals — the  only 
true  bases;  The  arguments  in  support  of  this  view  are  principally  drawn 
from  the  composition  of  the  ammoniacal  salts.  It  must  be  remembered, 
however,  that  the  whole  subject  is  in  many  respects  hypothetical,  and  has 
not  yet  been  sufficiently  tested  by  experiment. 

Salts,  in  crystallizing,  frequently  enclose  mechanically,  within  their  texture, 
particles  of  water,  by  the  expansion  of  which,  when  heated,  the  salt  is  burst 
with  a  crackling  noise  into  smaller  fragments.  This  phenomenon  is  known 
by  the  name  of  decrepitation.  Berzelius  has  correctly  remarked  that  those 
crystals  decrepitate  most  powerfully,  such  as  the  nitrates  of  baryta  and  prot- 
oxide of  lead,  which  contain  no  water  of  crystallization. 

The  atmospheric  pressure  is  said  to  have  considerable  influence  on  the 
crystallization  of  salts.  If,  for  example,  a  concentrated  solution,  composed 
of  about  three  parts  of  sulphate  of  soda  in  crystals  and  two  of  water,  is  made 
to  boil  briskly,  and  the  flask  which  contains  it  is  then  tightly  corked,  while 
its  upper  part  is  full  of  vapour,  the  solution  will  cool  down  to  the  tempera- 
ture of  the  air  without  crystallizing,  and  may  in  that  state  be  preserved  for 
months  without  change.  Before  removal  of  the  cork,  the  liquid  may  often 
be  briskly  agitated  without  losing  its  fluidity;  but  on  re-admitting  the  air, 
crystallization  commonly  commences,  and  the  whole  becomes  solid  in  the 
course  of  a  few  seconds.  The  admission  of  the  air  sometimes,  indeed,  fails 
in  causing  the  effect;  but  it  may  be  produced  with  certainty  by  agitation,  or 
the  introduction  of  a  solid  body.  The  theory  of  this  phenomenon  is  not 
very  apparent.  Gay-Lussac  has  shown  that  it  does  not  depend  on  atmos- 
pheric pressure  (An.  dc  Ch.  vol.  Ixxxvii.);  for  he  finds  that  the  solution  may 
be  cooled  in  open  vessels  without  becoming  solid  provided  its  surface  be 
covered  with  a  film  of  oil;  and  I  have  frequently  succeeded  in  the  same  ex- 
periment without  the  use  of  oil,  by  causing  the  air  of  the  flask  to  communi- 
cate with  the  atmosphere  by  means  of  a  moderately  narrow  tube.  It  appears 
from  some  experiments  of  Graham  (Phil.  Trans.  Edin.  1828,)  that  the  in- 
fluence of  the  air  may  be  ascribed  to  its  uniting  chemically  with  water ;  for  he 
has  proved  that  gases  which  are  more  freely  absorbed  than  atmospheric  air,  act 
more  rapidly  in  producing  crystallization.  Indeed,  the  rapidity  of  cryetalliza- 


CRYSTALLIZATION.  409 

tion,  occasioned  by  the  contact  of  gaseous  matter,  seems  proportional  to  the 
degree  of  its  affinity  for  water. 

The  same  quantity  of  water  may  hold  several  different  salts  in  solution, 
provided  they  do  not  mutually  decompose  each  other.  The  solvent  power  of 
water  with  respect  to  one  salt  is,  indeed,  sometimes  increased  by  the  presence 
of  another,  owing  to  combination  taking  place  between  the  two  salts. 

Most  salts  produce  cold  during  the  act  of  solution,  especially  when  they 
are  dissolved  rapidly  and  in  large  quantity.  The  greatest  reduction  of  tem- 
perature is  occasioned  by  those  which  contain  water  of  crystallization. 

All  the  oxy-salts  are  decomposed  by  Voltaic  electricity,  provided  they  are 
either  moistened  or  in  solution.  The  acid  appears  at  the  positive  pole  of  the 
battery,  and  the  oxide  at  its  opposite  extremity ;  or  if  the  oxide  is  of  easy 
reduction,  the  metal  itself  goes  over  to  the  negative  side,  and  its  oxygen  ac- 
companies the  acid  to  the  positive  wire. 

The  hydro-salts,  and  doubtless  also  the  sulphur  and  haloid  salts,  are  sub- 
ject to  a  similar  change ;  but  the  phenomena,  as  respects  the  two  last  orders 
of  salts,  have  been  little  examined. 

CRYSTALLIZATION. 

The  particles  of  liquid  and  gaseous  bodies,  during  the  formation  of  solids 
sometimes  cohere  together  in  an  indiscriminate  manner,  and  give  rise  to  ir- 
regular shapeless  masses ;  but  more  frequently  they  attach  themselves  to 
each  other  in  a  certain  order  so  as  to  constitute  solids  possessed  of  a  sym- 
metrical form.  The  process  by  which  such  a  body  is  produced  is  called 
crystallisation;  the  solid  itself  is  termed  a  crystal ;  and  the  science,  the  object 
of  which  is  to  study  the  form  of  crystals,  is  crystallography. 

Most  bodies  crystallize  under  favourable  circumstances.  The  condition  by 
which  the  process  is  peculiarly  favoured  is  the  slow  and  gradual  change  of 
a  fluid  into  a  solid,  the  arrangement  of  the  particles  being  at  the  same  time 
undisturbed  by  motion.  This  is  exemplified  during  the  slow  cooling  of  a 
fused  mass  of  sulphur  or  bismuth,  or  the  spontaneous  evaporation  of  a  saline 
solution  ;  and  the  origin  of  the  numerous  crystals,  which  are  found  in  the 
mineral  kingdom,  may  be  ascribed  to  the  influence  of  the  same  cause. 

All  substances  are  limited  in  the  number  of  their  crystalline  forms.  Thus, 
calcareous  spar  crystallizes  in  rhombohedrons,  fluor-spar  in  cubes,  and  quartz 
in  six-sided  pyramids;  and  these  forms  are  so  far  peculiar  to  those  substances, 
that  fluor-spar  never  crystallizes  in  rhombohedrons  or  six-sided  pyramids, 
nor  calcareous  spar  or  quartz  in  cubes.  Crystalline  form  may,  therefore, 
serve  as  a  ground  of  distinction  between  different  substances.  It  is  accord- 
ingly employed  by  mineralogists  for  distinguishing  one  mineral  species  from 
another ;  and  it  is  very  serviceable  to  the  chemist  as  affording  a  physical 
character  for  salts.  On  this  account  I  have  thought  it  would  be  useful, 
before  describing  the  individual  salts,  to  introduce  a  few  pages  on  crystal- 
lization ;  but  from  the  great  extent  of  the  subject,  which  now  constitutes  a 
separate  science,  my  remarks  must  necessarily  be  limited,  and  comprehend 
little  else  than  a  brief  outline  of  its  more  important  principles.  To  those 
who  are  desirous  of  more  ample  information,  I  may  recommend  the  "  Ele- 
ments of  Crystallography,"  by  Gustav  Rose,  or  Mr.  WhewelPs  Essay  in  the 
Phil.  Trans,  of  London  for  1825. 

Every  perfect  crystal  is  bounded  by  plane  surfaces,  which  are  called  its  faces. 
The  straight  line  formed  by  the  intersection  of  two  faces  is  called  an  edge  ; 
the  meeting  of  three  or  more  edges  in  a  point  forms  a  solid  angle.  Thus  in 
the  octohedron,  fig.  1,  the  bounding  planes  are  the  faces,  the  lines  formed  by 
their  intersection  the  edges,  the  meeting  of  four  of  which  in  the  same  point 
produces  a  solid  angle  of  the  crystal. 

The  forms  of  crystals  are  exceedingly  diversified.  They  are  divided  by 
crystallographers  into  simple  and  compound:  a  simple  form  has  all  its  faces 
equal  and  similar  to  each  other,  while  a  compound  form  is  bounded  by  at 
least  two  different  classes  of  faces.  Thus,  figs.  1,  2,  and  3,  are  simple 

•JO 


410 


Fig.  1. 


CRYSTALLIZATION. 
Fig.  2. 


Pig.  3. 


forms ;  for  the  first  is  bounded  by  eight  faces,  each  of  which  is  an  equi- 
lateral triangle,  the  second  by  six  squares,  and  the  third  by  twelve  equal  and 
similar  rhombi.  The  forms  represented  by  4,  5,  and  6,  are,  on  the  contrary, 


Fig.  5. 


Fig.  6. 


compound  crystals  :  for  fig.  4  is  composed  of  two  classes  effaces,  eight  which 
are  hexagonal,  and  six  square ;  while  fig.  6  contains  three  classes,  eight 
faces  being  hexagonal,  six  octagonal,  and  twelve  quadratic.  This  division 
into  compound  and  simple  is  not  artificial,  but  is  founded  on  the  fact  that  the 
compound  forms  are  really  produced  by  the  combination  of  two  or  more  of 
the  simple  crystals;  as  will  be  seen  by  a  careful  inspection  of  the  forms  and 
relative  situations  of  the  faces  in  the  accompanying  figures.  The  character 
of  the  faces  in  figs.  1,  2,  and  3,  which  represent  respectively  the  regular 
octohedron,  the  cube,  and  the  rhombic  dodecahedron,  is  too  obvious  to  demand 
comment ;  but  to  obtain  a  correct  idea  of  the  relative  positions  of  the  faces 
in  these  three  forms  requires  a  more  careful  investigation. 

It  will  be  observed  that  in  each  of  these  figures,  three  right  lines,  which 
are  equal  in  length,  perpendicular  to  each  other,  and  pass  through  the  centre 
of  the  crystal,  may  be  obtained ; — in  the  octohedron  by  joining  the  opposite 
angles,  in  the  cube  by  joining  the  centres  of  the  opposite  faces,  and  in  the 
rhombic  dodecahedron  by  connecting  the  opposite  angles  formed  by  the 
meeting  of  four  edges,  these  angles  being  six  in  number  and  corresponding 
in  situation  to  the  six  angles  of  the  octohedron.  The  lines  around  which 
the  different  parts  of  the  crystals  are  thus  symmetrically  grouped  are  called 
crystalline  axes-  Hence  the  above  forms  are  connected  by  being  possessed 
of  the  same  axes  of  crystallization,  arid  proceeding  from  these  three  equal 
and  rectangular  axes,  either  the  octohedron,  the  cube,  or  the  rhombic  dode- 
cahedron may  be  constructed,  the  resulting  form  being  solely  dependent  on 
the  law  in  accordance  with  which,  planes  are  symmetrically  arranged  or 
grouped  around  the  axes.  The  octohedron  (fig.  1)  results  from  the  law  that 
every  plane  shall  pass  through  an  extremity  of  each  axis :  it  will  be  evident 
that  one,  and  only  one,  plane,  fulfilling  the  required  condition,  may  be  in- 


CRYSTALLIZATION.  411 

troduced  into  each  of  the  eight  octants  formed  by  the  intersection  of  the 
three  axes.  This  law,  therefore,  limits  the  number  effaces  to  eight;  and  as 
these  intersect  each  other  in  the  lines  joining-  the  extremities  of  the  axes, 
each  face  is  an  equilateral  triangle,  and  the  resulting  form  is  the  regular 
octohedron.  The  cube  (fig.  2)  results  from  the  law  that  each  plane  shall 
pass  through  an  extremity  of  one  axis,  and  be  parallel  to  the  other  two :  as 
each  of  the  three  axes  has  two  extremities,  six,  and  only  six,  planes  can  be 
grouped  around  them  in  accordance  with  this  law,  and  by  their  intersection 
the  hexahedron  or  cube  as  it  is  more  commonly  called,  is  produced.  In 
a  similar  manner  may  the  rhombic  dodecahedron  (fig.  3)  be  shown  to  be 
formed  according  to  the  law  that  each  plane  shall  pass  through  the  extrem- 
ities of  two  axes,  and  be  parallel  to  the  third. 

The  groups  of  simple  forms,  which  are  thus  associated  by  being  reducible 
from  the  same  axes,  constitute  what  is  called  by  crystallographers  a  system 
of  crystallization.  Thus  the  octohedron,  the  cube,  and  the  rhombic  dodeca- 
hedron, are  three  forms  of  what  is  called  the  octohedral  or  regular  system. 
Such  forms  are  associated  not  merely  by  the  similiarity  of  their  axis,  but  are 
connected  still  more  intimately  by  the  remarkable  fact,  that  any  substance 
which  in  crystallizing  assumes  one  form  of  a  system,  may,  and  frequently 
does,  assume  other  forms  belonging  to  that  system.  Examples  of  this  may 
be  seen  in  the  well-known  salt  alum,  and  in  the  black  oxide  of  iron,  the 
magnetic  ore  of  mineralogists;  the  former  gonerally  crystallizing  in  the  oc- 
tohedrori  (fig.  1),  but  it  may  also  be  obtained  in  the  form  of  the  cube  (fig.  9) ; 
and  the  magnetic  iron  ore  is  found  not  only  in  the  form  of  octohedrons  and 
cubes,  but  likewise  in  that  of  the  rhombic  dodecahedron  (fig.  3).  But,  what 
is  still  more  remarkable,  the  same  substance  is  not  only  capable  of  assuming 
different  forms  of  the  same  system,  but,  during  the  act  of  crystallization,  the 
faces  of  two,  three,  four,  and  in  some  cases  even  more,  of  these  forms  are 
simultaneously  developed,  whereby  compound  crystals  of  the  greatest  diver- 
sity of  form  and  appearance  are  produced.  Thus,  in  the  crystallization  of 
alum  either  the  cube  or  octohedron  may  be  formed,  but  it  is  by  far  more 
common  that  the  faces  of  both  be  produced,  giving  rise  to  the"  compound 
crystal  represented  in  fig.  4,  where  the  faces  of  the  cube  appear  truncating 
the  angles  of  the  octohedron.  Another  form  frequently  observed  in  alum  is 
represented  by  fig.  5,  where,  in  addition  to  the  octohedron,  the  faces  of  the 
rhombic  dodecahedron  are  also  developed ;  and  as  these  are  twelve  in  num- 
ber, and  correspond  in  situation  to  the  twelve  edges  of  the  octohedron,  their 
development  removes,  or,  as  it  is  technically  expressed,  truncates  the  twelve 
edges  of  the  latter  form.  Fig.  6  represents  a  combination  of  all  three  forms. 
Similar  and  still  more  complicated  combinations  are  observed  on  magnetic 
iron  ore. 

The  importance  of  a  knowledge  of  all  the  simple  forms  of  a  system,  as 
being  those  in  which  the  same  substance  may  occur,  "and  which  alone  can 
give  rise  to  compound  crystals,  for  simple  forms  of  different  systems  are 
never  combined,  will  be  felt  from  what  has  already  been  stated.  The  first 
person  who  proved  the  existence  of  a  mathematical  connexion  between  them 
was  the  celebrated  crystallographer  Haily ;  but  it  is  to  Weiss,  Professor  of 
Mineralogy  in  Berlin,  that  we  are  indebted  to  the  distinction  of  the  system 
of  crystallization, — a  discovery  which  justly  entitles  him  to  the  honour  of 
being  the  founder  of  modern  crystallography.  He  has  shown  that  all  crys- 
talline forms  may  be  brought  under  one  of  the  six  following  systems,  which 
may  be  conveniently  distinguished  as, 

1.  The  octohedral,  or  regular  system  of  crystallization, 

2.  The  square  prismatic  system. 

3.  The  right  prismatic  system. 

4.  The  oblique  prismatic  system. 

5.  The  doubly  oblique  system. 

6.  The  rhornbohedral  system. 

The  Octohedral  System.— This  system  is  characterized  by  the  three  equal 
and  rectangular  axes,  which  have  already  been  described  at  p.  410.   Let  them 


412  CRYSTALLIZATION. 

be  distinguished  as  the  axes,  a,  6,  and  c ;  and  for  the  convenience  of  reference, 
let  us  consider  that  the  figure  be  brought  into  such  a  position  that  two  of 
them,  a  and  b,  be  horizontal,  and  c  vertical.  The  figs.  1,  2,  and  3  are  drawn 
under  this  supposition.  The  law  of  crystalline  symmetry  is  such,  that  if  a 
face  of  a  crystal  be  observed  to  bear  a  certain  relation  to  one  of  the  axes  a, 
other  faces  must  fulfil  the  same  condition  to  the  equal  axes  b  and  c.  Thus, 
if  a  plane  be  seen  to  pass  through  the  extremity  of  0,  or  be  parallel  to  it, 
other  planes  miist  pass  through  the  extremity  of  b  and  c,  or  be  parallel  to 
them.  Owing  to  the  perfect  symmetry  in  the  different  parts  of  the  crystal, 
this  group  is  frequently  called  the  regular  system  of  crystallization. 

It  consists  of  but  few  simple  forms,  the  number  being  necessarily  limited  to 
the  number  of  different  ways  in  which  a  plane  can  intersect  the  three  axes. 
These,  it  will  be  seen,  are  only  seven : 

1.  The  plane  may  cut  each  at  an  equal  distance  from  the  centre.  The  crystal 
the  faces  of  which  obey  this  law  is  the  octohedron,  fig.  1. 

2.  The  plane  may  cut  two  axes  at  an  equal,  and  the  third  at  a  greater 
distance  from  the  centre.     The  resulting  form  is  called  the  triakisoctohedron. 

3.  The  plane  may  cut  two  axes  at  an  equal,  and  the  third  at  a  less  distance 
from  the  centre.     The  resulting  form  is  the  ikositetrahedron.    -\ 

4.  The  plane  may  cut  all  three  axes  unequally.     The  form  is  the  herakis- 
octohedron. 

5.  The  plane  may  cut  two  a^res  at  unequal  distances  from  the  centre,  and 
be  parallel  to  the  third.     The  resulting  crystal  is  the  tetrakishexahedron. 

6.  The  plane  may  cut  two  axes  in  points  equally  distant  from  the  centre, 
and  be  parallel  to  the  third.     The  form  is  the  rhombic  dodecahedron,  fig.  3. 

7.  The  plane  may  cut  one  axis,  and  be  parallel  to  the  other  two.    This  law 
gives  rise  to  the  cube  or  hexahedron  fig.  2. 

Of  these  forms,  1,  6,  and  7  are  of  frequent  occurrence;  but  the  others  are 
usually  found  only  in  combination,  when  their  faces  are  generally  small,  and 
appear  symmetrically  arranged  around  the  angles  and  on  the  edges  of  the 
former,  Hence,  in  most  compound  crystals  of  this  system,  the  faces  either 
of  the  octohedron,  cube,  or  rhombic  dodecahedron  may  be  readily  recognized ; 
and  as  these  suffice  to  fix  the  position  of  the  crystalline  axes,  they  serve  as  a 
guide  to  determine  the  forms  of  the  combination.  Their  prevalence  presents 
also  a  remarkable  instance  of  the  tendence  to  simplicity  which  may  be  ob- 
served in  all  the  processes  of  nature.  This  is  not  only  seen  in  the  greater 
simplicity  of  exterior  form,  but  in  the  more  definite  nature  of  the  laws  by 
which  the  faces  of  these  three  crystals  are  determined ;  for  while  a  plane 
has  but  one  position  in  which  it  can  satisfy  the  laws,  1,  6,  and  7,  an  un- 
lirnfted  number  of  planes  may  be  found  to  satisfy  the  conditions  expressed 
by  2,  3,  4,  and  5.  Thus,  for  example,  there  is  but  one  way  in  which  a  plane 
can  satisfy  the  law  1 ;  while  there  are  as  many  ways  of  satisfying  the  law  4, 
as  there  are  of  taking  three  lines  which  shall  be  unequal.  Hence  it  follows 
that  there  can  be  but  one  octohedron,  while  the  number  of  herakisoctohe- 
drons  is  unlimited,  and  the  faces  of  two  different  ones  have  been  observed 
on  the  same  crystals.  The  latter  observation  also  applies  to  the  forms  pro- 
duced according  to  the  laws  2,  3,  and  5 ;  but  the  number  of  varieties  which 
have  been  observed  is  very  limited,  and  the  relative  lengths  of  the  unequal 
axes  may  be  expressed,  almost  without  an  exception,  by  the  numbers  I,.*.,  ^., 
J.,and|.  Fig.  7. 

It  is  frequently  observed  in  crystals  of  this 
system,  that  one-half  of  the  faces  of  the  crystals 
is  much  more  developed  than  the  other.  This 
may  be  seen  in  fig.  7,  a  crystal  of  the  red  oxide 
of  copper,  where  four  out  of  the  eight  faces  of 
the  octohedron  have  increased,  and  the  other  four 
proportionally  diminished.  The  faces  which 
increase,  as  well  as  those  which  diminish,  always 
form  two  similar  and  symmetrically  arranged 
groups,  the  increasing  faces  or  groups  of  faces 


CRYSTALLIZATION. 


413 


Fig.  9. 


touching  each  other  at  the  angular  points  Pig.  8. 

of  the  crystal.     Thus,  in  the  octohedron,  the 

four  alternating  faces  which  do  not  intersect 

in  edges,  but  merely  touch  each  other  in  the 

angular  points,  increase,  as  represented  in 

figure  7,  and  by  increasing  till  they  form  a 

perfect  figure,  give  rise  to  the  well-known 

crystal,  the  tetrahedron,  fig.  8.     These  forms 

are  called  hemihedral,  as  denoting  their  origin: 

hence  the  tetrahedron  is  commonly  known 

as  the  herni-octohedron.     Each  of  the  simple 

forms  of  this  system,  with  the  exception  of  the 

cube  and  rhombic  dodecahedron,  give  rise  to 

hemihedral  crystals :   the  exception  evidently  results  from  the  impossibility 

of  dividing  the  faces  of  the  cube  and  rhombic  dodecahedron  into  two  groups, 

which  fulfil  the  necessary  conditions. 

The  Square  Prismatic  System.— The  forms  of  this  system  are,  like  those 
of  the  preceding,  characterized  by  three  axes,  which  intersect  each  other  at 
right  angles  ;  but  they  differ  from  them  by  two  only  out  of  the  three  being 
equal.  Let  the  third,  which  may  be  either  greater  or  less  than  the  two 
equal  axes,  be  called  c,  and  let  it  be  placed  in  a  vertical  position.  The  octo- 
hedron formed  by  joining  the  extremities  of  these  axes  is  either  longer  or 
shorter  in  the  direction  of  the  axis  c  than  in  that  of  its  horizontal  axis,  as 
is  seen  in  fig.  9.  From  this  it  follows 
that  these  octohedrons  may  be  compared 
to  a  double  four-sided  pyramid  construct- 
ed on  cither  side  of  a  square  base.  The 
parts  of  the  crystal  about  this  base  are, 
therefore,  similar  to  each  other,  but  differ 
from  those  about  its  upper  or  lower 
extremity;  and  as  this  observation  applies 

equally  to  all  forms  of  this  system,  it  is 

the  character  by  which  the  system  is 

best  distinguished.     This  difference  is 

owing  to  the  inequality  of  the  vertical  axis,  which  causes  the  relations  of  the 

faces  to  it  to  be  unconnected  with  those  they  bear  to  the  two  horizontal  axes 

Hence  it  is  common  to  find  the  lateral  edges  truncated  without  those  connected 

with  the  extremities  of  the  crystal  being  affected,  whereby  a  square  prism 

terminated  by  four-sided 

pyramids,  as  represented  Fig.  10.  Fig.  11. 

in  fig.  10,  is  produced. 

The  same  may  occur  on 

the  lateral  angles  as  well 

asedgesasinfig.il.  In 

other  cases,  the  termina- 

ledges  and  angles  are  mo 

dified,  but  always  in  a 

different    manner    from 

the  lateral. 

The  Right .  Prismatic 

System — The  crystals  of 

this  system  are  like  the 

preceding,  characterized 

by  three  rectangular  axes, 

and     are     distinguished 

from  both  by  no  two  of 

these  axes  being  equal. 

Its  forms  are,  therefore,  not  only  distinguished  by  a  difference  in  the  lateral 

and  terminal  parts,  but  are  still  further  marked  by  the  difference  between  the 

front  and  back  of  the  crystal,  as  compared  with  its  sides.    Thus  in  figs.  12, 

35* 


414 


Fig.  12. 


CRYSTALLIZATION. 
Fig.  13. 


Fig.  14. 


Fig.  16. 


13,  and  14,  which  represent  three  of  the  FiS- 15' 

common   forms  of  sulphur,   the    different 

magnitude  in  the  parts  of  the  crystals  about 

each  axis  is    perceptible,  and    sufficiently 

marks  the  different  crystalline  values  of  the 

three  axes.     But  this  is  still  better  po'inted 

out  by  the  three  different  and  independent 

modifications  of  the  rhombic    octohedron, 

which  forms  the  basis  of  all  three  crystals. 

The  Oblique  Prismatic  System. — The  crys- 
tals of  this  system,  of  which  an  example  may 
be  seen  in  sulphate  of  protoxide  of  iron,  fig 
15,  differ  from  those  of  the  right  prismatic 
system  by  the  front  and  back  parts  being 
dissimilar.  This  difference  is  owing  to  two 
of  the  axes  intersecting  each  other  obliquely,  while  the 
third  still  remains  perpendicular  to  both. 

The  Double  Oblique  System. — This  system  is  readily 
recognized  by  the  complete  absence  of  all  symmetry  in 
its  crystalline  forms.  This  results  from  all  three  axes 
•intersecting  each  other  obliquely  ;  owing  to  which  the 
left  and  right  sides,  as  well  as  the  back  and  front,  are 
of  different  crystalline  values.  From  this  it  follows  that 
no  two  faces  are  connected  except  those  which  are 
parallel,  and  all  symmetry  of  form  disappears,  as  ob- 
served in  fig.  1 6,  which  represents  a  crystal  of  the  sul- 
phate of  the  protoxide  of  copper. 

Jhe  Rhombohedral  System. — The  forms  of  this  system  of  crystallization 
are,  like  the  octohedral,  characterized  by  three  equal  and 
similar  axes ;  but  these  axes  intersect  each  other  at  equal, 
but  not  at  right  angles.     Its   most  simple  form  is  the 
rhombohedron,  fig.  17,  which  is  bounded  by  six  equal  and 
similar  rhombic  faces.    The  axes  are  obtained  by  joining 
the  centre  of  the  opposite  faces.     Although  the  faces  of  6< 
the   rhombohedron  are   equal,  two  only   of  its   angles,  ,1 
marked  a,  are  regular,  being  formed  by  the  meeting  of 
three  equal  edges,  while  the  other  six  are  irregular.  The 
line  joining  a  a  is  called  the  principal  axis  of  the  rhom- 
bohedron, the  angles  a  the  terminal,  and  b  the  lateral 
angles  of  the  rhombohedron. 


Fig.  17. 


CRYSTALLIZATION.  415 

The  form  which  most  commonly  occurs  associated  Fig.  18. 

with  the  rhombohedron,  is  a  hexagonal  prism,  fig.  18, 
two  of  which  are  observed,  the  one  truncating  the  six 
angles,  the  other  the  lines  joining  these  angles,  the 
faces  of  the  prism  being  in  both  cases  parallel  to  the 
rhombohedral  axes  aa.  The  terminal  angles  a  are 
frequently  truncated  by  terminal  planes. 

The  different  forms  of  the  system  may  be  advantageously  studied  on  crys- 
tals of  quartz  and  calcareous  spar. 

Besides  the  distinction  arising  from  external  form,  minerals  are  further 
distinguished  by  differences  in  the  mechanical  connexion  of  their  particles, 
peculiarities  which  mineralogists  designate  by  the  name  of  structure.  The 
structure  of  a  mineral  arises  from  its  particles  adhering  at  some  parts  less 
tenaciously  than  at  others,  and  consequently  yielding  to  force  in  one  direction 
more  readily  than  in  another.  Structure  is  sometimes  visible  by  holding  a 
mineral  between  the  eye  and  the  light;  but  in  general  it  is  brought  into 
view  by  effecting  the  actual  separation  of  parts  by  mechanical  means. 

The  structure  of  minerals  may  be  regular  or  irregular.  It  is  regular  when 
the  separation  takes  place  in  such  a  manner,  that  the  detached  surfaces  are 
smooth  and  even  like  the  planes  of  a  crystal ;  and  it  is  irregular,  when  the 
new  surface  does  not  possess  this  character. 

A  mineral  which  possesses  a  regular  structure  is  said  to  be  cleavable,  or 
to  admit  of  cleavage  ;  the  surfaces  exposed  by  splitting  or  cleaving  a  mineral 
are  termed  the  faces  of  cleavage ;  and  the  direction  in  which  it  may  be 
cleaved  is  called  the  direction  of  cleavage.  Sometimes  a  mineral  is  cleavablc 
only  in  one  direction,  and  is  then  said  to  have  a  single  cleavage.  Others  may 
be  cleaved  in  two,  three,  four,  or  more  directions,  and  are  said  to  have  a 
double,  treble,  fourfold  cleavage,  and  so  ont  according  to  their  number. 

Minerals  that  are  cleavable  in  more  than  two  directions  may,  by  the  re- 
moval of  layers  parallel  to  the  planes  of  their  cleavage,  be  often  made  to 
assume  regular  forms,  though  they  may  originally  have  possessed  a  different 
figure.  Calcareous  spar  for  example,  occurs  in  rhombohedrons  of  different 
kinds,  in  hexagonal  prisms,  in  six-sided  pyramids,  and  in  various  combina- 
tions of  these  forms  ;  but  it  has  three  sets  of  cleavage,  which  are  so  inclined 
to  each  other  as  to  constitute  a  rhombohedron  of  invariable  dimensions,  and 
into  that  form  every  crystal  of  calcareous  spar  may  be  reduced.  Lead  glance 
possesses  a  treble  cleavage,  the  planes  of  which  are  at  right  angles  to  each 
other ;  and  hence  it  is  always  convertible  by  cleavage  into  the  cube.  The 
cleavages  of  fluor-spar  are  fourfold,  and  in  a  direction  parallel  to  the  planes 
of  the  regular  octohedron,  into  which  form  every  cube  of  fluor-spar  may  be 
converted. 

Since  the  forms  enumerated  as  belonging  to  the  octohedral  system  of 
crystallization  are  possessed  of  fixed  invariable  dimensions,  it  is  obvious  that 
minerals,  or  other  crystallized  bodies  included  in  that  system,  must  often  in 
their  primary  forms  be  identical  with  each  other.  In  the  other  systems  of 
crystallization  this  identity  is  not  necessary,  because  the  dimensions  of  their 
forms  are  variable.  Thus  octohedrons  with  a  square  base  may  be  distin- 
guished by  the  relative  length  of  their  axis,  some  being  flat  and  others  acute. 
Rhombic  octehedrons  may  be  distinguished  from  each  other  by  the  relative 
length  of  their  axis,  and  the  angles  of  their  base.  By  Hatty  it  was  regarded 
as  an  axiom  in  crystallography,  that  minerals  not  belonging  to  the  octohedral 
system  are  characterized  by  their  form  :  that  though  two  minerals  may  in 
form  be  analogous,  each  for  instance  being  a  rhombic  prism,  the  dimensions 
of  those  prisms  are  different.  Identity  of  form  in  crystals  not  included  in 
the  octohedral  system  was  thought  to  indicate  identity  of  composition.  But 
in  the  year  1819,  a  discovery,  extremely  important  both  to  mineralogy  and 
chemistry,  was  made  by  Mitscherlich  of  Berlin,  relative  to  the  connexion 
between  the  crystalline  form  and  composition  of  bodies.  It  appears  from  his 


416 


CRYSTALLIZATION. 


researches,*  that  certain  substances  have  the  property  of  assuming  the  same 
crystalline  form,  and  may  he  substituted  for  each  other  in  combination  with- 
out affecting  the  external  character  of  the  compound.  Thus  minerals  having 
the  crystallization  and  structure  of  garnet,  and  which  from  their  appearance 
were  believed  to  be  such,  have  been  found  on  analysis  to  contain  different 
ingredients.  Crystals  possessed  of  the  form  and  aspect  of  alum  may  be  made 
with  sulphates  of  potassa  and  sesquioxide  of  iron,  without  a  particle  of  alu- 
minous earth ;  and  a  crystal  composed  of  selenic  acid  and  soda  will  have  a 
perfect  resemblance  to  Glauber's  salt.  The  axiom  of  Hatty,  therefore,  re- 
quires an  essential  modification. 

To  the  new  branch  of  science  laid  open  by  the  discovery  of  Mitscherlich, 
the  term  isomorphism  (from  uro5  equal,  and  f*o£<f>n  form)  is  applied;  and 
those  substances  which  assume  the  same  figure  are  said  to  be  isomorphous. 
Of  these  isomorphous  bodies  several  distinct  groups  have  been  described  by 
Mitscherlich.  One  of  the  most  instructive  of  these  includes  the  salts  of  ar- 
senic and  phosphoric  acid.  Thus,  the  neutral  phosphate  and  biphosphate  of 
soda  have  exactly  the  same  form  as  the  arseniate  and  b'marseniate  of  soda ; 
phosphate  and  biphosphate  of  ammonia  correspond  to  arseniate  and  binarse- 
riiate  of  ammonia  ;  and  the  biphosphate  and  binarseniate  of  potassa  have  the 
same  form.  Each  arseniate  has  a  corresponding  phosphate,  possessed  of  the 
same  form,  possessing  the  same  number  of  eq.  of  acid,  alkali,  and  water  of 
crystallization,  and  differing  in  fact  in  nothing,  except  that  one  series  con- 
tains arsenic  and  the  other  an  equivalent  quantity  of  phosphoros.  A  second 
remarkable  group  contains  the  salts  of  sulphuric,  selenic,  chromic,  and  man- 
ganic acids.  The  salts  of  baryta,  strontia,  arid  protoxide  of  lead  constitute  a 
third  group;  and  a  fourth  consists  of  lime,  magnesia,  and  the  protoxides  of 
manganese,  iron,  cobalt,  nickel,  zinc,  and  copper.  A  fifth  includes  alumina, 
sesquioxide  of  iron,  and  the  green  or  sesquioxide  of  chromium;  and  a  sixth 
group  includes  the  salts  of  permanganic  and  perchloric  acids.  In  comparing 
together  isomorphous  bodies  of  the  same  group,  identity  of  form  is  not  to  be 
expected  unless  there  is  similarity  of  composition.  A  neutral  phosphate  does 
not  correspond  to  a  binarseniate,  nor  a  biphosphate  to  a  neutral  arseniate. 
An  anhydrous  sulphate  is  not  comparable  to  a  hydrated  seleniate  of  the  same 
base ;  nor  is  sulphate  of  protoxide  of  iron,  with  six  eq.  of  water,  isomorphous 
with  sulphate  of  protoxide  of  manganese  with  five  eq.  In  all  such  instances, 
if  chemical  composition  differ,  crystalline  form  is  also  different. 

The  following  table  contains  the  principal  groups  of  isomorphous  sub- 
stances at  present  observed  by  chemists  :  a  more  extended  one,  partly  theo- 
retical, has  been  drawn  up  by  Professor  Johnston,  of  Durham,  in  his  Report 
on  Chemistry  to  the  British  Association : — 


1. 

5. 

Silver    . 

.             Ag. 

Salts  of 

Gold 

.        .     Aii. 

Sulphuric  acid 

SO*. 

2. 

Selenic  acid 

SeOs. 

Arsenious  acid 

.   As2O3. 

Chromic  acid 

CrO3. 

in  its  unusual  form 

(page  332.) 

Manganic  acid  .         . 

MnO3. 

Sesquioxide  of  antimony 

Sb2O3. 

6. 

3. 

Salts  of 

Alumina 

.     A12O3. 

Perchloric  acid     .  .-.^  i$s$j$ 

C1O7. 

Sesquioxide  of  iron 

Fe203. 

Permanganic  acid     . 

Mn2O7. 

4. 

7. 

Salts  of 

Salts  of 

Phosphoric  acid 

.      P2Q5. 

Potassa         .         . 

KO- 

Arsenic  acid     . 

As205. 

Ammonia  with  one  eq.  of  water 

H4NO- 

*  Annales  de  Ch.  et  dc  Physique,  vol.  xiv.  1,72,  xix.  350,  and  xxiv.  264 
and  355. 


CRYSTALLIZATION. 


417 


Salts  of 
Soda 
Oxide  of  silver 


9. 


Salts  of 

Protoxide  of  iron 

FeO. 

NaO. 

manganese, 

MnO. 

AgO 

zinc 

ZnO. 

nickel 

NiO. 

cobalt     , 

CoO. 

BaO. 

copper 

CuO. 

SrO. 

CaO. 

lead     in    plumbo- 
calcite    . 

(PbO. 

PbO. 

11. 

Salts  of 

Alumina 

A12Q*. 

CaO. 

Sesquioxide  of  iron 
Sesquioxide  of  chromium 

Fe203. 
Cr2O3. 

MgO. 

Sesquioxide  of  manganese        MnsO°. 

Salts  of 
Baryta 
Strontia 

Lime  (in  Arragonitc) 
Protoxide  of  lead    . 

10. 

Salts  of 
Lime 
Magnesia       .         »    "  ^-^ 

The  facts  above  mentioned  afford  indubitable  proof  that  the  form  of  crys- 
tals is  materially  dependent  on  their  atomic  constitution  ;  and  they  at  first 
induced  Mitscherlich  to  suspect  that  crystalline  form  is  determined  solely  by 
the  number  and  arrangement  of  atoms,  quite  independently  of  their  nature. 
Subsequent  observation,  however,  induced  him  to  abandon  this  view ;  and  his 
opinion  now  appears  to  be,  that  certain  elements,  which  are  themselves  isomor- 
phous, when  combined  in  the  same  manner  with  the  same  substance,  com- 
municate the  same  form.  Similarly  constituted  salts  of  arsenic  and  phos- 
phoric acid  yield  crystals  of  the  same  figure,  because  the  acids,  it  is  thought, 
are  themselves  isomorphous;  and  as  the  atomic  constitution  of  these  acids  is 
similar,  each  containing  the  same  number  of  atoms  of  oxygen  united  with 
the  same  number  of  atoms  of  the  other  ingredient,  it  is  inferred  that  phos- 
phorus is  isomorphous  with  arsenic.  In  like  manner  it  is  believed  that  selenic 
acid  must  be  isomorphous  with  sulphuric  acid,  and  selenium  with  sulphur; 
and  the  same  identity  of  form  is  ascribed  to  all  those  oxides  above  enume- 
rated, the  salts  of  which  are  isomorphous.  The  accuracy  of  this  ingenious 
view  has  not  yet  been  put  to  the  test  of  extensive  observation,  because  the 
crystalline  forms  of  the  substances  in  question  are  for  the  most  part  un- 
known. But  our  knowledge,  so  far  as  it  goes,  is  favourable;  for  sesquioxide 
of  iron  and  alumina,  the  salts  of  which  possess  the  same  form,  are  them- 
selves isomorphous.  It  may  hence  be  inferred  as  probable,  that  isomorphous 
compounds  in  general  arise  from  isomorphous  elements  uniting  in  the  same 
manner  with  the  same  substance. 

Isomorphous  substances  have  often  very  close  points  of  resemblance,  quite 
independently  of  form.  Thus,  arsenic  and  phosphorus  have  the  same  odour, 
they  both  form  gaseous  compounds  with  hydrogen,  they  differ  from  nearly 
all  other  bodies  in  their  mode  of  combining  with  oxygen,  and  yet  agree  with 
one  another,  and  their  salts  are  disposed  to  combine  with  the  same  quantity 
of  water  of  crystallization.  A  similar  analogy  subsists  between  selenium  and 
sulphur,  both  being  fusible,  volatile,  and  combustible  in  nearly  the  same  de- 
gree, forming  with  hydrogen  colourless  gases  which  are  similar  in  odour  and 
in  their  chemical  relations,  and  giving  rise  to  analogous  compounds  with 
oxygen.  The  characters  of  sulphuric  and  selenic  acids  in  particular  are  very 
similar  ;  and  the  salts  of  these  acids  are  equally  allied.  Sulphate  of  soda,  for 
example,  has  the  unusual  property  of  being  less  soluble  in  water  at  212°  than 
at  100°,  and  the  very  same  peculiarity  is  observable  in  seleniate  of  soda. 
The  same  intimacy  of  relation  exists  between  baryta  and  strontia,  between 
lime  and  magnesia,  and  between  cobalt  and  nickel. 

Isomorphous  substances,  owing  doubtless  to  the  various  points  of  resem- 
blance which  have  just  been  traced,  crystallize  together  with  great  readiness, 
and  are  separated  from  each  other  with  difficulty.  Daubeny  has  remarked 
that  a  weak  solution  ot  lime,  which  in  pure  water  would  be  instantly  indi- 
cated by  oxalate  of  ammonia,  is  very  sluggishly  affected  by  that  test  when 
much  sulphate  of  magnesia  is  present;  and  I  find  that  chloride  of  manganese 


418  CRYSTALLIZATION. 

cannot  be  purified  from  lime  by  oxalate  of  ammonia.  A  mixture  of  the  sul- 
phates of  the  protoxides  of  copper  and  iron  yields  crystals  which  have  the 
same  quantity  of  water  of  crystallization  (six  equivalents),  and  the  same  form 
as  groen  vitriol,  though  they  may  contain  a  large  quantity  of  copper.  The 
sulphates  of  the  protoxides  of  zinc  and  copper,  of  copper  and  magnesium,  of 
copper  and  nickel,  of  zinc  and  manganese,  and  of  magnesium  and  manga- 
nese, crystallize  together,  contain  six  equivalents  of  water,  and  have  the  same 
form  as  green  vitriol,  without  containing  a  particle  of  iron.  These  mixed 
salts  may  be  crystallized  over  and  over  again  without  the  ingredients  being 
separated  from  each  other,  just  as  it  is  extremely  difficult  to  purify  alum 
from  sesquioxide  of  iron,  with  which  alumina  is  isomorphous.  In  these  in- 
stances the  isomorphous  salts  do  not  occur  in  definite  proportions :  they  are 
not  chemically  united  as  double  salts,  but  merely  crystallize  together. 

The  same  intermixture  of  isomorphous  substances  which  takes  place  in 
artificial  salts  is  found  to  occur  in  minerals,  and  affords  a  luminous  explana- 
tion of  the  great  variety  both  in  the  kind  and  proportion  of  substances  which 
may  coexist  in  a  mineral  species,  without  its  external  character  being 
thereby  essentially  affected.  Thus,  garnet  is  a  double  silicate  of  alumina  and 
lime,  expressed  by  the  formula  (A12Q3.f  SiO3)-f-3(CaO.fSiO3) ;  but  in  gar- 
net,  as  in  alum,  the  alumina  may  be  replaced  by  sesquioxide  of  iron,  yielding 
the  compound  (Fe2O3^SiO3)4-3(CaO-fSiO3),  or  they  may  be  both  present 
in  any  proportion,  provided  that  their  sum  is  equivalent  to  either  singly.  So, 
while  sesquioxide  of  iron  displaces  the  alumina,  the  lime  may  be  exchanged 
for  protoxide  of  iron;  and  a  mineral  would  result,  ^FeaO3-j-SiO3)-f.3(FeO 
-}-SiO3)  which  contains  neither  alumina  nor  lime,  though  it  has  still  the 
form  of  garnet.  Instead  of  protoxide  of  iron,  the  lime  may  be  replaced  by 
magnesia,  protoxide  of  manganese,  or  any  other  isomorphous  base  ;  or  any 
equivalent  quantity  of  some  or  all  of  these  may  take  the  place  of  the  lirne, 
without  the  crystallographic  character  being  destroyed.  In  like  manner 
epidote  is  a  double  silicate  of  alumina  and  lime,  expressed  by  (Al2O3-f-SiO3) 
-|-(CaO-|-SiO3);  and  here  again  varieties  of  epidote  are  to  be  expected,  in 
which  alumina  and  lime  are  replaced  partially  or  wholly  by  an  equivalent 
quantity  of  isomorphous  bases. 

The  discovery  of  Mitscherlich,  while  it  accounts  for  difference  of  compo- 
sition in  the  same  mineral,  and  serves  as  a  caution  to  mineralogists  against 
too  exclusive  reliance  on  crystallographic  character,  is  in  several  other  re- 
spects of  deep  interest  to  the  chemist.  It  tends  to  lay  open  new  paths  of 
research  by  unfolding  analogies  which  would  not  otherwise  have  been  per- 
ceived. The  tendency  of  isomorphous  bodies  to  crystallize  together  accounts 
for  the  difficulty  of  purifying  mixtures  of  isomorphous  salts  by  crystalliza- 
tion. The  same  property  sets  the  chemist  on  his  guard  against  the  occur- 
rence of  isomorphous  substances  in  crystallized  minerals.  The  native  phos- 
phates, for  example,  frequently  contain  arsenic  acid,  and  conversely  the  native 
arseniates  phosphoric  acid,  without  the  form  of  the  crystals  being  thereby 
affected  in  the  slightest  degree.  It  is  a  useful  guide  in  discovering  the 
atomic  constitution  of  compounds.  All  chemists  are  agreed,  from  the  com- 
position of  the  oxides  of  iron,  and  from  the  compounds  which  this  metal 
forms  with  other  bodies,  that  the  sesquioxide  consists  of  two  atoms  of  iron 
and  three  atoms  of  oxygen  ;  and,  therefore,  it  is  inferred  that  alumina,  which 
is  isomorphous  with  sesquioxide  of  iron,  has  a  similar  constitution.  The 
green  oxide  and  acid  of  chromium,  the  oxygen  of  which  is  as  1  to  2,  affords 
a  still  better  illustration.  As  the  chromates  and  sulphates  are  isomorphous, 
it  was  inferred  that  chromic,  like  sulphuric,  acid  was  composed  of  one  atom 
of  the  combustible  to  three  atoms  of  oxygen.  On  this  presumption  it  follows 
that  the  green  oxide,  containing  half  as  much  oxygen  as  the  acid,  must  con- 
tain two  atoms  of  chromium  to  three  atoms  of  oxygen  ;  and  agreeably  to 
this  inference,  it  is  found  that  the  green  oxide  is  isomorphous  with  alumina 
and  sesquioxide  of  iron.  The  phenomena  presented  by  isomorphous  bodies 
afford  a  powerful  argument  in  favour  of  the  atomic  theory.  The  only  mode 
of  satisfactorily  accounting  for  the  striking  identity  of  crystalline  form  ob- 


OXY-SALTS.  419 

servable,  first,  between  two  substances,  and,  secondly,  between  all  their  com- 
pounds which  have  an  exactly  similar  composition,  is  by  supposing  them  to 
consist  of  ultimate  particles,  possessed  of  the  same  figure,  and  arranged  in 
precisely  the  same  order.  Hence  it  appears,  that,  in  accounting  for  the  con- 
nexion  between  form  and  composition,  it  is  necessary  to  employ  the  very 
same  theory,  by  which  alone  the  laws  of  chemical  union  can  be  adequately 
explained. 

It  has  been  objected  to  some  of  the  facts  adduced  in  favour  of  isomorphism, 
that  the  forms  of  substances  considered  isomorphous  are  sometimes  approxi- 
mate rather  than  identical.  The  "primary  form  of  sulphate  of  strontia  is  a 
rhombic  prism  very  similar  to  that  of  sulphate  of  baryta;  but  on  measuring 
the  inclination  of  corresponding  sides  in  each  prism,  the  difference  is  found 
to  exceed  two  degrees ;  and  similar  differences  are  observable  in  the  rhom- 
bohedron  of  the  carbonates  of  lime  and  protoxide  of  iron*  This  has  induced 
Professor  Miller  of  Cambridge  to  indicate  this  approximation  by  the  term 
plesiomorphism  (CTXHCT/O?,  near);  and  it  has  been  brought  forward  in  a  clever 
essay  by  Brooke,  as  an  argument  against  the  whole  doctrine  of  isomorphism, 
an  essay  which  has  received  an  able  reply  from  the  pen  of  Whewell.  (Phil. 
Mag.  and  An.  N.  S.  x.  161  and  401.) 

In  one  of  the  essays  above  referred  to  Mitscherlich  observed  that  biphos- 
phate  of  soda  is  capable  of  yielding  two  distinct  kinds  of  crystals,  which, 
though  different  in  form,  in  composition  appear  to  be  identical.  The  more 
uncommon  of  the  two  forms  resembled  binarseniate  of  soda;  but  the  more 
usual  form  is  quite  dissimilar.  He  has  since  discovered,  that  sulphur  is 
capable  of  yielding  two  distinct  kinds  of  crystals.  The  crystals  of  carbonate 
of  lime  in  calcareous  spar  and  in  Arragonite  belong  to  different  systems  of 
crystallization,  the  former  being  rhombohedral,  and  the  latter  derived  from  a 
rhombic  prism.  Arsenious  acid,  and  probably  metallic  arsenic  also,  affords 
an  instance  of  the  same  kind  (p.  332.)  It  would  thus  seem  that  elementary 
and  compound  bodies  are  capable  of  assuming  two  distinct  crystalline  forms. 
In  the  case  of  biphosphate  of  soda,  an  explanation  may  be  derived  from  the 
experiments  of  Graham  on  metaphosphoric  acid ;  but  the  fact  that  an  ele- 
mentary substance  is  susceptible  of  assuming  different  forms  is  wholly  unex- 
plained. 

Mitscherlich  has  also  noticed  that  the  form  of  salts  is  sometimes  changed 
by  heat,  without  their  losing  the  solid  state.  This  change  was  first  noticed 
in  sulphate  of  magnesia,  and  also  in  the  sulphates  of  the  protoxides  of  zinc 
and  iron.  It  appears,  in  these  instances  at  least,  to  be  owing  to  decomposition 
of  the  hydrous  salt  effected  by  increased  temperature ;  a  change  of  com- 
position  which  is  accompanied  with  a  new  arrangement  in  the  molecules  of 
the  compound. 


SECTION   I. 

CLASS  OF  SALTS.  ORDER  I. 

OXY-SALTS. 

THIS  order  of  salts  includes  no  compound  the  acid  or  base  of  which  does 
not  contain  oxygen.  With  the  exception  of  the  ammoniacal  salts,  both  the 
acid  and  base  of  the  salts  described  in  this  section  are  oxidized  bodies.  As 
each  acid,  with  few  exceptions,  is  capable  of  uniting  with  every  alkaline 
base,  and  frequently  in  |wo  or  more  proportions,  it  is  manifest  that  the  salts 
must  constitute  a  very  numerous  class  of  bodies.  It  is  necessary,  on  this 
account,  to  facilitate  the  study  of  them  as  much  as  possible  by  classification. 
They  may  be  conveniently  arranged  by  placing  together  those  salts  which 


420  OXY-SALTS. 

contain  either  the  same  salifiable  base  or  the  same  acid.  It  is  not  very 
material  which  principle  of  arrangement  is  adopted;  but  I  give  the  preference 
to  the  latter,  because,  in  describing  the  individual  oxides,  I  have  already 
mentioned  the  characteristic  features  of  their  salts,  and  have  thus  anticipated 
the  chief  advantage  that  arises  from  the  former  mode  of  classification.  I 
shall,  therefore,  divide  the  salts  into  families,  placing  together  those  saline 
combinations  which  consist  of  the  same  acid  united  with  different  salifiable 
bases.  The  salts  of  each  family,  in  consequence  of  containing  the  same  acid, 
possess  certain  characters  in  common  by  which  they  may  all  be  distinguished  ; 
and,  indeed,  the  description  of  many  salts,  to  which  no  particular  inte- 
rest is  attached,  is  sufficiently  comprehended  in  that  of  its  family,  and  may, 
therefore,  be  omitted. 

All  the  powerful  alkaline  bases,  excepting  ammonia,  are  the  protoxides  of 
an  electro-positive  metal,  such  as  potassium,  barium,  or  iron  ;  so  that  if  M 
represent  an  eq.  of  any  one  of  those  rnetals,  M-j-O  or  MO  is  the  strongest 
alkaline  base,  and  often  the  only  one,  which  that  metal  can  form.  A  single 
eq.  of  acid  neutralizes  MO,  forming  with  it  a  neutral  salt.  Thus,  indicating 
an  equivalent  of  sulphuric  and  nitric  acid  by  the  signs  SO3  and  NO-1,  all  the 
neutral  sulphates  and  nitrates  of  protoxides  are  indicated  by  MO-j-SO3  and 
MO+NO*.  There  is,  therefore,  in  the  neutral  protosalts  of  each  family,  a 
constant  ratio  in  the  oxygen  of  the  base  and  acid,  resulting  from  the  com- 
position of  each  acid,  that  ratio  for  sulphates  being  as  1  to  3,  and  for 
nitrates  as  1  to  5.  If  the  metal  M  of  a  neutral  sulphate  pass  into  a  higher 
grade  of  oxidation,  becoming  a  binoxide  MO3,  then  will  that  binoxide  be 
disposed  to  unite  with  two  eq.  of  acid,  and  form  a  bisalt,  MO2-J-2SO3,  in 
which  the  oxygen  of  the  base  and  acid  is  still  as  1  to  3 ;  and  if  the  metal 
yield  a  sesquioxide,  M2O*,  then,  if  sufficient  acid  be  supplied,  the  resulting 
salt  will  consist  of  M9OH-3SOs,  the  ratio  of  1  to  3  being  preserved.  This 
curious  law  relative  to  oxy-salts,  which  is  very  general,  was  first  noticed  by 
Gay-Lussac  (Memoires  d'Arcueil,  ii.);  and  Berzelius  has  found  it  to  hold  in 
earthy  minerals,  and  employed  it  as  a  guide  in  studying  their  composition. 

The  combination  of  salts  with  one  another  gives  rise  to  compounds  which 
were  formerly  called  triple  salts ;  but  as  the  term  double  salt,  proposed  by 
Berzelius,  gives  a  more  correct  idea  of  their  nature  and  constitution,  it  will 
always  be  employed  by  preference.  These  salts  may  be  composed  of  one 
acid  and  two  bases,  of  two  acids  and  one  base,  and  of  two  different  acids  and 
two  different  bases.  Most  of  the  double  salts  hitherto  examined  consist  of 
the  same  acid  and  two  different  bases. 

The  difference  in  the  constitution  of  ammonia  and  that  of  all  other  bases 
capable  of  uniting  with  oxacids,  gives  great  interest  to  its  salts.  In  page 
246,  the  probable  existence  of  a  compound  radical  formed  of  one  eq.  of 
nitrogen  and  four  of  hydrogen,  and  called  by  Berzelius  ammonium,  was 
pointed  out.  The  oxide  of  this  radical,  which  has  not  yet  been  obtained  in 
an  uncombined  state,  he  considers  as  the  base  of  the  oxy-salts  of  ammonia. 
This  view  is  not  supported  by  analogy  alone,  but  is  based  on  the  remarkable 
fact,  that  in  all  the  neutral  salts  of  ammonia,  the  quantity  of  water  necessary 
to  convert  the  ammonia  into  oxide  of  ammonium  is  always  present;  nor  can 
it  be  removed  without  the  total  decomposition  of  the  salt.  H.  Rose  has 
indeed  succeeded  in  obtaining  anhydrous  compounds  of  ammonia  with  the 
oxacids  ;  but  he  has  at  the  same  time  shown  that  they-cannot  be  considered 
as  salts,  for  although  containing  the  elements  for  forming  an  anhydrous  and 
neutral  salt  of  ammonia,  and  produced  by  direct  combination,  neither  the  acid 
nor  the  alkali  is  present  in  the  compound.  This  he  has  proved  particularly 
in  the  substance  formed  by  the  union  of  anhydrous  sulphuric  acid  with 
ammonia  (An.  de  Ch.  et  de  Ph.  Ixii.  389.)  Strong  evidence  in  its  favour  is 
likewise  obtained  from  the  views  of  isomorphism.  It  has  been  proved  by 
Mitscherlich  that  in  all  the  crystallized  salts  of  potSssa,  whether  simple  or 
double,  the  potassa  may  be  replaced  either  partially  or  completely  by  an 
equivalent  quantity  of  protohydrate  of  ammonia,  without  any  change  in  the 
form  of  the  crystal.  Ammonia  with  an  eq.  of  water  is,  therefore,  isomorphous 


SULPHATES,  421 

with  potassa.  But  all  isomorphous  substances,  with  this  exception,  have  the 
?ame  chemical  constitution,  and  it  is  incompatible  with  the  theory  of  iso- 
morphism to  suppose  one  alkali  to  be  isomorphous  with  the  hydrate  of  another. 
But  that  the  oxide  of  a  compound  radjcal  should  be  isomorphous  with  the 
oxide  of  a  simple  metal,  is  consistent  with — nay,  might  be  expected  from, 
their  known  analogies. 

Another  view  of  the  constitution  of  the  oxy-salts  of  ammonia  has  recently 
been  proposed  by  Graham.  He  supposes  ammonia  not  to  be  a  base,  but  to 
be  one  of  a  class  of  bodies  which  he  calls  basic  adjuncts;  a  term  used  to 
denote  a  substance,  which,  without  being  a  base,  is  capable  of  entering  into 
the  constitution  of  a  salt  by  attaching  itself  to  other  bases.  Thus,  the  oxy- 
salts  of  ammonia  he  conceives  to  be  salts  of  water,  to  the  base  of  which 
ammonia  is  added  as  an  adjunct.  It  is  scarcely  necessary  to  remark,  that 
this  view  is  not  only  inconsistent  with  the  theory  of  isomorphism,  but  that 
the  existence  of  adjunct  bases  is  hypothetical,  and  arises  from  an  endeavour 
to  support  another  hypothesis,  that  all  salts  are  neutral  in  composition. 

SULPHATES. 

The  salts  of  sulphuric  acid  in  solution  may  be  detected  chloride  of  barium. 
A  white  precipitate,  sulphate  of  baryta,  invariably  subsides,  which  is  insolu- 
ble in  acids  and  alkalies;  a  character  by  which  the  presence  of  sulphuric 
acid,  whether  free  or  combined,  may  always  be  recognized-  An  insoluble 
sulphate,  such  as  sulphate  of  baryta  or  strontia,  may  be  detected  by  mixing 
it,  in  fine  powder,  with  three  times  its  weight  of  carbonate  of  potassa  or  soda, 
and  exposing  the  mixtures  in  a  platinum  crucible  for  half  an  hour  to  a  red 
heat.  Double  decomposition  ensues;  and  on  digesting  the  residue  in  water, 
filtering  the  solution,  neutralizing  the  free  alkali  by  pure  hydrochloric,  nitric, 
or  acetic  acid,  and  adding  chloride  of  barium,  the  insoluble  sulphate  of  that 
base  is  precipitated. 

Several  sulphates  exist  in  nature,  but  the  only  ones  which  are  abundant 
are  the  sulphates  of  lime  and  baryta.  All  of  them  may  be  formed  by  the 
action  of  sulphuric  acid  on  the  metals  themselves,  on  the  metallic  oxides  or 
their  carbonates,  or  by  way  of  double  decomposition. 

The  solubility  of  the  sulphates  is  very  variable.  There  are  six  only  which 
may  be  regarded  as  really  insoluble ;  namely,  the  sulphates  of  baryta,  and  of 
the  oxides  of  tin,  antimony,  bismuth,  lead,  and  mercury.  The  sparingly 
soluble  sulphates  are  those  of  strontia,  lime,  zirconia,  yttria,  and  of  the  oxides 
of  cerium  and  silver.  All  the  others  are  soluble  in  water. 

All  the  sulphates,  those  of  potassa,  soda,  lithia,  baryta,  strontia,  and  lime 
excepted,  are  decomposed  by  a  white  heat.  One  part  of  the  sulphuric  acid 
of  the  decomposed  sulphate  escapes  unchanged,  and  another  portion  is  re- 
solved into  sulphurous  acid  and  oxygen.  Those  which  are  easily  decom- 
posed by  heat,  such  as  sulphate  of  protoxide  of  iron,  yield  the  largest  quan- 
tity of  undecomposed  sulphuric  acid. 

When  a  sulphate,  mixed  with  carbonaceous  matter,  is  ignited,  the  oxygen 
both  of  the  acid  and  of  the  oxide  unites  with  carbon,  carbonic  acid  is  disen- 
gaged, and  a  metallic  sulphuret  remains.  A  similar  change  is  produced  by 
hydrogen  gas  at  a  red  heat,  with  formation  of  water,  and  frequently  of  some 
hydrosulphuric  acid.  In  some  instances  the  hydrogen  entirely  deprives  the 
metal  of  its  sulphur. 

The  composition  of  neutral  protosulphates  is  expressed,  as  above  stated, 
by  the  formula  MO-|-SO3.  Consequently  the  acid  contains  three  times  as 
much  oxygen  as  the  base ;  and  if  both  were  deprived  of  their  oxygen,  a 
metallic  protosulphuret  would  result  as  indicated  by  the  formula  M-f-S. 

In  accordance  with  the  views  of  Graham  already  given  (page  407,)  the 
sulphates  may  be  divided  into  three  classes ; — the^first  consisting  of  the  anhy- 
drous sulphates,  being  such  as  can  exist  without  the  eq.  of  constitutional 
water;  the  second,  those  in  which  the  constitutional  water  forms  an  essential 
part ;  and  the  third  composed  of  the  double  salts,  which  he  considers  as 
produced  from  the  second  by  the  eq.  of  constitutional  water  beingr  replace 

36 


422 


SULPHATES. 


by  an  eq.  of  a  sulphate  of  the  first  class.  ,  If  dilute  sulphuric  acid  be  exposed 
in  an  open  dish  to  a  temperature  not  exceeding  380°,  the  evaporation  proceeds 
without  the  slightest  loss  of  acid  until  the  sp.  gr.  is  raised  to  1-78,  when  it  ceases 
entirely,  and  there  remains  a  definite  compound  of  one  eq.  of  sulphuric  acid 
and  two  eq.  of  water.  One  of  these*  he  considers  as  basic,  the  other  as  con- 
stitutional water,  the  acid  of  the  mentioned  strength  being  a  salt,  the  consti- 
tution of  which  is  represented  by  the  formula  HO,SO3,  HO.  From  it  any 
one  of  the  three  classes  of  sulphates  may  be  formed,  the  eq.  of  basic  water 
being  readily  replaced  by  any  stronger  base;  while  the  eq.  of  constitutional 
water  can  only  be  removed  by  a  neutral  salt  producing  the  double  salts,  among 
which  the  bisulphates  must  also  be  included.  There  are,  however,  excep- 
tions to  the  last  observation,  as  Graham  has  remarked  that  magnesia  and  its 
class  of  isomorphous  oxides  are  capable  of  acting  the  part  of  constitutional 
water.  Although  it  would  be  highly  advantageous  to  treat  of  the  sulphates 
under  the  three  classes  above  mentioned,  it  cannot  yet  be  attempted ;  for  al- 
though the  constitutional  water  of  several  of  them  has  been  determined  by 
Graham  in  his  valuable  essay  already  quoted,  many  of  them  have  not  yet  been 
examined  in  reference  to  this  point.  The  following  table  represents  the  con- 
stitution of  the  more  important,  both  in  their  amorphous  and  crystallized 
state : — 


SIMPLE  SUPHATKS. 


Names.  Base.  Acid.  Equiv. 

Sulphate  of  potassa        47-15  1  eq.-}-  40-1     1  eq.=  87-25 
Sesquisulph.  polassa       94-3     2  eq.-f  120-3     3  eq.  =214-6 
Do.     in  crystals  with    9  or  1  eq.  of  water  =223-6 

Bisulph.  potassa  47-15  1  eq.-f  80-2    2  eq.  =127-35 

Do.  with    9  or  1  eq.  of  water  =136-35 

Sulph.  soda  31-3     1  eq.-f  40-1     1  eq.=  71-4 

Do.     in  crystals  with  90  or  10  eq.  of  water          =161-4 
Bisulph.  soda  31-3     1  eq.-f  80-2    2  eq.=lll-5 

Do.    in  crystals  with  36  or  4  eq.  of  water          =147-5 
Sulph.  lithia  14-44  1  eq.-f  40-1     1  eq.=  54-54 

Do.    in  crystals  with    9  or  1  eq.  of  water  =  63-54 

Sulph.  ox.  ammonium     26-15  1  eq.-f  40-1     1  eq.=  6625 
Do.     in  crystals  with    9  or  1  eq.  of  water          =  75-25 
Sulph.  baryta  76-7     1  eq.-f  40-1     1  eq.«116-8 

Sulph.  strontia  51-8    1  eq.-f  40-1     1  eq.=  91'9 

Sulph.  lime  28-5     1  eq.-f  40-1     1  eq.=  68-6 

Do.     as  gypsum  with  18  or  2  eq.  of  water          «=  86-6 
Sulph.  magnesia  20-7     1  eq.-f  40-1     leq. 

+  9  aq.  1  eq.  =  69-8 

Do.     in  crystals  with  54  or  6  eq.  of  water          =123-8 

Sulph.  alumina  51-4     1  eq.-f  40-1     1  eq.=  91-5 

Do.     in  crystals  with  81   or  9  eq.  of  water  =172-5 

Tersulph.  alumina          51-4     1  eq.-f  120-3    3  eq.=171-7 

Do.  in  crystals  with  162  or  18  eq.  of  water         .=333-7 

Sulph.  protox.  mang.      35-7     1  eq.-f  40-1     leq. 

+9aq.leq.  =  84-8 

Do.     in  crystals  with  36  or  4  eq.  of  water          «=120-8 
Sulph.  protox.  iron          36       1  eq.-f  40-1     leq. 

-f  9  aq.  1  eq.  =  85-1 

Do.    in  crystals  with  45  or  5  eq.  of  water  =130-1 

Tersulph.  sesquiox.  iron  80        1  eq.  -f  120-3     3  eq.=200-3 

Disulph.  sesquiox.  iron  160       2  eq.  -f  40-1     1  eq.=200-l 

Do.  as  a  hydrate  with  54  or  6  eq.  of  water          =254-1 

Sulph.  protox.  zinc        40-3     1  eq.-f  40-1     leq. 

+9  aq.  1  eq.  =  89-4 

Do.    in  crystals  with  54  or  6  eq.  of  water          =143-4 


Formulae, 
KO-fSO3. 
2KO+3S03. 

KO-f2SOs. 

NaO-fS03. 

NaO-f2SO3. 

LO+S03. 

H4NO+SO3 

BaO-fSO3. 
SrO+SO3. 
CaO-fSO3. 

MgO-fS03HO, 

A12O3+SO3. 
A12O3+3SO3. 

MnO-fSOsHO. 

FeO-fSO3HO. 

Fe2O3-f3SO3. 


ZnO-f  SO3HO. 


SULPHATES. 


423 


Names. 
Sulph.  protox.  nickel 


Base.  Acid. 

37-5     1  eq.-f.  40-1 

+9  aq.  1  eq. 
Do.    in  crystals  with  54  or  6  eq.  of  water 
Sulph.  protox.  cobalt       37-5     1  eq.  -f   40-1 

-f-9  aq.  1  eq. 

Do.     in  crystals  with  45  or  5  eq.  of  water 
Tersulph.  sesquiox.  J     g()        1  e     r  120.3 

chromium  \ 

Sulph.  prolox.  copper     39-6     1  eq.-j-  40-1 

-f-9  aq.  1  eq. 

Do.  in  crystals  with  36  or  4  eq.  of  water 
Disulph.  protox.  copper  79-2  2  eq.-f.  40-1 
Sulph.  protox.  mere.  210  1  eq.-f.  4O1 
Subsulph.  perox.  mere.  872  4  eq,-j-12O3 
Bisulph.  perox.  mere.  218  1  eq.-f.  80-2 
Sulph.  oxide  silver  116  1  eq.-f.  40-1 


Equiv. 

leq. 

=  86-6 
=140-6 

1  eq. 

=  86-6 
=131-6 

3  eq.=200-3 

leq. 

=  88-7 
=124-7 

1  eq.  =-119-3 

1  eq.=250-l 
3  eq.=992  3 

2  eq.  =298-2 
1  eq.=156-l 


Formulae. 
NiO-j-S03HO. 

CoO-f-SO3HO. 

Cr2O3-{-3SO3. 

CuO+SO3HO. 

2CuO+SO3. 
HgO+SO3. 
4HgO3+3SO3. 
HgQ2-|-2S03. 
AgO+S03. 


Names. 
Sulphate  soda 

and  lime 
Sulph.  potassa 
&  magnesia 

Do. 
Sulph.  oxide 


Sulph.  soda  & 
magnesia 

Do. 

Sulph.  potassa 
&  alumina 

Do 

Sulph.  soda  & 
alumina 

Do. 

Sulph.  oxide 
am'm  and 
alumina 

Do. 

Sulph.  potassa 
and  protox. 
mang. 
Do. 

Sulph.  oxide 
am'm  and 
protox.  mang. 
Do. 


DOUBLE  SULPHATES. 

Constit.  Salts. 
Sulph.  soda  71  -4 

Sulph.  lime  68-6 

\  Sulph.  potassa  87-25 

)  Sulph.  magnesia,  60-8 
with  54  or  6  eq.  of  water 

S  Sulph.  ox.  ammon'm  66-25 
"l  Sulph.  magnesia         60-8 

with  54  or  6  eq.  of  water 
^  Sulph.  soda  71-4 

)  Sulph.  magnesia         60-8 
with  54  or  6  eq.  of  water 
<  Sulph.  potassa  87-25 

I  Tersulph.  alumina  171-7 
with  21 6  or  24  eq.  of  water 
\  Sulph.  soda  71-4 

)  Tersulph.  alumina  171-7 
with  234  or  26  eq.  of  water 

\  Sulph.  ox.  arnmon'm  66-25 
i  Tersulph.  alumina   171-7 

with  216  or  24  eq.  of  water 

S  Sulph.  potassa  87-25 

1  Sulph.  protox.  mang.  75-8 

with  54  or  6  eq.  of  water 
j  Sulph.  ox.  ammon'm  66-25 


Equiv. 


with  54  or  6  eq.  of  water 


Formulae. 
NaO,SO3 
-4-CaO,SO3. 
KO,SO3 
4-MgO,SOs. 

H4NO,SO3 

\  +MgO,SO3. 

NaO,S03 
+MgO,S03. 

J  KO,S03+ 
AM)3,3S03. 

5  NaO,SO3-h 
A12O3,3SO3 

H4NO,S03-f 
A12Q3,3SO3. 


KO,S03 
+MnO,SO3. 

S  H4NO,SO3 
+MnO,SQ3. 


The  protoxides  of  iron,  zinc,  nickel,  and  cobalt  yield  with  potassa  and 
oxide  of  ammonium,  double  salts  exactly  agreeing  in  form  and  composition 
with  the  preceding  double  salts  of  magnesia  and  protoxide  of  manganese 
with  the  same  alkalies. 

Sulphate  of  Potassa.  —  This  salt  is  easily  prepared  artificially  by  neutraliz* 
ing  carbonate  of  potassa  with  sulphuric  acid  ;  and  it  is  procured  abundantly 
by  neutralizing  with  carbonate  of  potassa,  the  residue  of  the  operation  for 
preparing  nitric  acid,  (Page  182.)  Its  taste  is  saline  and  bitter.  It  crys- 


4'24  SULPHATES. 

tallizes  in  forms  belonging  to  the  right  prismatic  system,  and  its  general 
form  closely  resembles  the  regular  hexagonal  prism,  terminated  by  pyramids 
with  six  sides;  the  size  of  which  is  said  to  be  much  increased  by  the  presence 
of  a  little  carbonate  of  potassa.  According  to  Mitscherlich  it  is  isomorphous 
with  chromate  and  seleniate  of  potassa.  (Pog.  Annalen,  xviii.  168.)  The 
crystals  contain  no  water  of  crystallization,  and  suffer  no  change  by  exposure 
to  the  air.  They  decrepitate  when  heated,  and  enter  into  fusion  at  a  red 
heat.  They  require  sixteen  times  their  weight  of  water  at  60°,  and  five  of 
boiling  water  for  solution. 

Bisulphate  of  Potassa  is  easily  formed  by  exposing  the  neutral  sulphate 
with  half  its  weight  of  strong  sulphuric  acid  to  a  heat  just  below  redness,  in 
a  platinum  crucible,  until  acid  fumes  cease  to  escape.  It  is  obtained  in  crys- 
tals from  a  concentrated  solution  at  high  temperatures,  as  in  the  cold  the 
neutral  sulphate  is  formed.  The  form  is  a  right  rhombic  prism,  which  is  in 
general  so  flattened  as  to  be  tabular.  According  to  Graham  they  contain 
one  eq.  of  water,  which  he  considers  to  be  basic ;  the  bisulphate  being  a  double 
sulphate  of  water  and  potassa.  The  anhydrous  bisulphate  has  been  prepared 
by  Rose.  It  has  a  strong  sour  taste,  and  reddens  litmus  paper.  It  is  much 
more  soluble  than  the  neutral  sulphate,  requiring  for  solution  only  twice  its 
weight  of  water  at  60°,  and  less  than  an  equal  weight  at  212°  F.  It  is 
resolved  by  heat  into  sulphuric  acid  and  the  neutral  sulphate. 

Phillips  has  described  a  sesquisulphate,  obtained  in  the  form  of  acicular 
crystals  like  asbestos,  from  the  residue  of  the  process  for  making  nitric  acid. 
The  conditions  for  ensuring  its  production  have  riot  been  determined.  (Phil. 
Mag.  and  Annals,  ii.  421.) 

Sulphate  of  Soda. — This  compound,  commonly  called  Glauber's  salt,  is 
occasionally  met  with  on  the  surface  of  the  earth,  and  is  frequently  contained 
in  mineral  springs.  It  may  be  made  by  the  direct  action  of  sulphuric  acid 
on  carbonate  of  soda;  and  it  is  procured  in  large  quantity  as  a  residue  in  the 
processes  for  forming  hydrochloric  acid  and  chlorine.  (Pages  212  and  214.) 

Sulphate  of  soda  has  a  cooling,  saline,  and  hitter  taste.  It  commonly  yields 
forms  belonging  to  the  right  prismatic  system,  and  containing  ten  eq.  of  water 
of  crystallization,  the  whole  of  which  is  rapidly  lost  by  efflorescence  on 
exposure  to  the  air.  When  heated  they  readily  undergo  the  watery  fusion. 
At  32°,  100  parts  of  water  dissolve  12  parts  of  the  crystals,  48  parts  at  64-5°, 
100  parts  at  77°,  270  at  89-5°,  and  322  at  91-5°.  On  increasing  the  heat 
beyond  this  point,  a  portion  of  the  salt  is  deposited,  being  less  soluble  than 
at  91*5°.  (Gay-Lussac.)  If  a  solution  saturated  at  91-5°  is  evaporated  at  a 
higher  temperature,  the  salt  is  deposited  in  opaque  anhydrous  prisms,  uncon- 
nected, but  of  the  same  system  as  the  hydrous  crystals.  Its  sp,  gr.  in  this 
state  is  2-462.  (Haidinger.) 

Bisulphate  of  Soda  may  be  formed  in  the  same  manner  as  the  analogous 
salt  of  potassa, 

Sulphate  of  Lithia. — This  salt  is  very  soluble  in  water,  fuses  by  heat 
more  readily  than  the  sulphates  of  the  other  alkalies,  and  crystallizes  in  flat 
prisms,  which  resemble  sulphate  of  soda  in  appearance,  but  do  not  effloresce 
on  exposure  to  the  air.  Its  taste  is  saline,  without  being  bitter. 

Sulphate  of  Oxide  of  Ammonium. — This  salt  is  easily  prepared  by  neu- 
tralizing carbonate  of  oxide  of  ammonium  with  dilute  sulphuric  acid ;  and 
it  is  contained  in  considerable  quantity  in  the  soot  from  coal.  It  crystallizes 
in  long  flattened  six-sided  prisms.  It  dissolves  in  two  parts  of  water  at  60°, 
and  in  an  equal  weight  of  boiling  water.  In  a  warm  dry  air  it  effloresces  and 
loses  one  eq.  of  water.  When  sharply  heated,  it  fuses  and  is  decomposed, 
yielding  nitrogen  gas,  water,  and  sulphate  of  oxide  of  ammonium. 

The  anhydrous  compound  was  formed  by  Rose  by  conducting  dry  ammo- 
niacal  gas  into  a  glass  vessel  coated  by  a  thin  film  of  perfectly  anhydrous 
sulphuric  acid.  When  no  excess  of  aeid  is  present  it  undergoes  no  change 
in  the  air,  and  is  soluble  without  change  in  water,  from  which  it  crystallizes 
irregularly,  but  in  forms  different  from  those  of  the  common  sulphate.  It  is 
remarkable  that  the  sulphuric  acid  is  only  partially  precipitated  by  chloride 


SULPHATES.  425 

of  barium  in  the  cold,  and  no  precipitate  whatever  is  produced  by  chlorides 
of  strontium  or  calcium  until  heat  is  applied,  and  even  then  the  action  is 
imperfect.  Nor,  on  the  other  hand,  can  the  ammonia  be  separated  by  the 
chloride  of  platinum.  From  this  it  follows  that  neither  the  sulphuric  acid 
nor  the  ammonia  can  be  present  in  the  solution,  although  their  elements  are 
present  in  equivalent  proportions.  It  is  not  improbable  it  may  be  an  amide, 
and  formed  H^NSO-f  HO. 

Sulphate  of  Baryta. — Native  sulphate  of  baryta,  commonly  called  heavy 
spar,  occurs  abundantly,  chiefly  massive,  but  sometimes  in  anhydrous  crys- 
tals, the  form  of  which  is  variable,  being  sometimes  prismatic  and  sometimes 
tabular,  deducible  from  a  right  rhombic  prism.  Its  density  is  about  4*4.  It 
is  easily  formed  artificially  by  double  decomposition.  This  salt  bears  an 
intense  heat  without  fusing  or  undergoing  any  other  change,  and  is  one  of 
the  most  insoluble  substances  with  which  chemists  are  acquainted.  It  is 
sparingly  dissolved  by  hot  and  concentrated  sulphuric  acid,  but  is  precipitated 
by  the  addition  of  water. 

Sulphate  of  Strontia. — This  salt,  the  celestine  of  mineralogists,  is  less 
abundant  than  heavy  spar.  It  occurs  in  anhydrous  prismatic  crystals  of 
peculiar  beauty  in  Sicily,  and  is  isomorphous  with  the  sulphate  of  baryta. 
Its  density  is  3-858.  As  obtained  by  the  way  of  double  decomposition,  it  is 
a  white  heavy  powder,  very  similar  to  sulphate  of  baryta,  and  requires  about 
3840  times  its  weight  of  boiling  water  for  solution. 

Sulphate  of  Lime. — This  salt  is  easily  formed  by  mixing  in  solution  a  salt 
of  lime  with  any  soluble  sulphate.  It  occurs  abundantly  as  a  natural  pro- 
duction. The  mineral  called  anhydrite  is  anhydrous  sulphate  of  lime ;  and 
all  the  varieties  of  gypsum  are  composed  of  the  same  salt,  united  with  water. 
The  pure  crystallized  specimens  of  gypsum  are  sometimes  called  selenite ; 
and  the  white  compact  variety  is  employed  in  statuary  under  the  name  of 
alabaster.  The  crystals  of  anhydrite  belong  to  the  right  prismatic  system, 
and  are  isomorphous  with  the  sulphates  of  baryta  and  strontia,  while  the 
forms  of  gypsum  are  oblique  prismatic.  The  latter,  which  are  by  far  the 
more  general,  are  readily  recognized  by  the  perfect  cleavage  plane  which 
truncates  the  acute  angle  of  the  prism.  They  contain  two  eq.  of  water,  one 
only  of  which  is  considered  by  Graham  to  be  water  of  crystallization,  the 
other  being  constitutional.  The  former  is  readily  lost  by  exposing  pounded 
gypsum  to  a  temperature  of  212°  in  vacuo,  and  the  whole  water  is  expelled 
by  a  temperature  below  300°.  Thus  dried,  it  constitutes  the  well-known 
plaster  of  Paris,  which,  when  mixed  with  a  proper  proportion  of  water, 
rapidly  becomes  dry  and  solid,  owing  to  the  reproduction  of  gypsum.  It  is 
remarkable,  however,  that  gypsum  which  has  lost  only  one  eq.  of  water,  as 
well  as  that  which  is  dried  by  a  heat  exceeding  270°,  will  not  act  in  a  similar 
manner.  In  the  latter  case,  the  powder  is  a  perfect  anhydrite.  (Phil.  Mag. 
vi.  417.) 

Sulphate  of  lime  has  hardly  any  taste.  It  is  considerably  more  soluble 
than  the  sulphate  of  baryta  or  strontia,  requiring  for  solution  about  500  parts 
of  cold,  and  450  of  boiling  water.  Owing  to  this  circumstance,  and  to  its 
existing  so  abundantly  in  the  earth,  it  is  frequently  contained  in  spring  water, 
to  which  it  communicates  the  property  called  hardness.  When  freshly 
precipitated,  it  may  be  dissolved  completely  by  dilute  nitric  acid.  It  is 
commonly  believed  to  sustain  a  white  heat  without  decomposition;  but. 
Thomson  states,  that  it  parts  with  some  of  its  acid  when  heated  to  redness, 

Sulphate  of  Magnesia. — This  sulphate,  generally  known  by  the  name  of 
Epsom  salt,  is  frequently  contained  in  mineral  springs.  It  may  be  made 
directly,  by  neutralizing  dilute  sulphuric  acid  with  carbonate  of  magnesia ; 
but  it  is  procured  for  the  purposes  of  commerce  by  the  action  of  dilute 
sulphuric  acid  on  magnesian  limestone, — native  carbonate  of  HmQ  and  mag- 
nesia. 

Sulphate  of  magnesia  has  a  saline,  bitter,  and  nauseous  taste.  It  crys» 
tallizes  readily  in  small  quadrangular  prisms,  which  effloresce  slightly  in  a 
dry  air.  It  is  obtained  also  in  larger  crystals,  the  principal  form  in  which 

36* 


130  SULPHATESv 

is  a  right  rhombic  prism,  the  angles  of  which  are  90°  30'  and  89°  30'.  (Brooke 
Its  crystals  are  soluble  in  an  equal  weight  of  water  at  60°,  and  in  three-fourths 
of  their  weight  of  boiling  water.  They  undergo  the  watery  fusion  when 
heated ;  and  the  anhydrous  salt  is  deprived  of  a  portion  of  its  acid  at  a  white 
heat.  Dried  at  212°  it  retains  two  eq.  of  water;  but  one  of  these  is  expelled 
at  270°,  while  the  other  is  retained  till  the  temperature  rises  to  460°. 

Sulphates  of  Alumina. — The  tersulphate  is  prepared  by  saturating  dilute 
sulphuric  acid  withhydrated  alumina,  and  evaporating.  It  crystallizes  with 
difficulty  in  thin  flexible  plates  of  a  pearly  lustre,  which  contain  eighteen  eq. 
of  water,  and  require  twice  their  weight  of  water  for  solution.  Berzelius 
says  it  occurs  native  at  Milo  in  the  Grecian  Archipelago.  It  has  an  acid 
reaction. 

The  hydrated  sulphate  is  known  to  mineralogists  under  the  name  of 
aluminite,  which  occurs  at  Halle  on  the  river  Saal,  and  at  Newhaven,  in 
Sussex  ;  and  Berzelius  says  the  same  compound  falls  when  ammonia  is  added 
to  a  solution  of  the  tersulphate.  It  is  insoluble  in  water,  and  by  heat  is  first 
rendered  anhydrous,  and  then  its  acid  is  expelled,  leaving  pure  alumina. 
The  composition  given  in  the  table  is  from  an  analysis  of  alurninite  from 
both  its  localities  by  Stromeyer. 

Sulphate  of  Protoxide  of  Manganese.— This  salt  is  best  obtained  by  dis- 
solving pure  carbonate  of  manganese  in  moderately  dilute  sulphuric  acid, 
and  setting  the  solution  aside  to  crystallize  by  spontaneous  evaporation.  The 
crystals  are  transparent,  and  of  a  slight  rose  tint,  in  taste  resemble  Glauber's 
salt,  and  belong  to  the  doubly  oblique  prismatic  system.  It  is  insoluble  in 
alcohol,  but  dissolves  in  twice  and  a  half  its  weight  of  cold  water-  If  the 
heat  is  gradually  applied,  it  may  be  increased  to  redness  without  expelling 
any  of  the  acid. 

Sulphates  of  the  Oxides  of  Iron. — Sulphate  of  the  protoxide,  commonly 
called  green  vitriol,  is  formed  by  the  action  of  dilute  sulphuric  acid  on 
metallic  iron  (page  162,)  or  by  exposing  protosulphuret  of  iron  in  fragments 
to  the  combined  agency  of  air  and  moisture.  The  salt  has  a  strong  styptic, 
inky  taste.  When  perfectly  pure  it  does  not  change  vegetable  blue  colours, 
though  generally  stated  to  do  so,  the  reddening  effect  being  only  produced 
when  some  of  the  iron  passes  into  a  higher  state  of  oxidation,  as  has  been 
shown  by  Bonsdorff  (Pogg.  Ann.  xxxi.  81.)  He  finds  that  the  oxidation, 
which  occurs  with  extreme  facility  in  a  perfectly  neutral  solution,  is  com- 
pletely prevented  by  a  few  drops  of  sulphuric  acid  in  excess,  and  the  resulting 
crystals  have  a  distinctly  blue  colour.  The  common  green  tint  is  conse- 
quently a  delicate  test  of  the  presence  of  sesquioxide  of  iron.  The  crystals 
belong  to  the  oblique  prismatic  system,  and  contain  six  eq.  of  water,  one  of 
which  is  retained,  according  to  Graham,  till  the  temperature  rises  to  535°. 
By  operating  carefully  it  may  be  rendered  anhydrous  without  the  loss  of  acid, 
It  is  soluble  in  two  parts  of  cold  and  in  three-fourths  of  its  weight  of  boiling 
water.  This  salt  is  employed  in  the  manufacture  of  fuming  sulphuric  acid. 
(Page  194.) 

The  tersulphate  of  the  sesquioxide  is  formed  by  mixing  with  a  solution  of 
the  protosulphate  exactly  half  as  much  sulphuric  acid  as  that  salt  contains, 
and  adding  to  the  mixture  in  a  boiling  state  successive  portions  of  nitric 
acid  until  nitrous  acid  fumes  cease  to  appear.  The  solution  is  then  evapo- 
rated to  dry  ness  to  expel  the  excess  of  nitric  acid,  and  the  tersulphate  remains 
as  a  white  salt.  Afler  being  strongly  heated,  it  dissolves  slowly  in  water ; 
but  if  evaporated  at  a  gentle  heat,  it  is  deliquescent,  and  very  soluble  in  water 
and  alcohol,  but  insoluble  in  strong  sulphuric  acid.  At  a  red  heat  it  gives 
out  all  its  acid,  and  sesquioxide  of  iron  is  left.  Its  solution  in  water  has  an 
orange  colour,  which  is  yellow  when  much  diluted. 

The  disulphate  of  the  sesquioxide  falls  as  a  hydrate  of  an  ochreous  colour, 
when  a  solution  of  the  protosulphate  is  kept  in  an  open  vessel. 

Sulpliate  of  Protoxide  of  Zinc. — This  salt  frequently  called  white  vitriol,  is 
the  residue  of  the  process  for  forming  hydrogen  gas  by  the  action  of  dilute 
sulphuric  acid  on  metallic  zinc;  but  it  is  also  made,  for  the  purposes  of  com- 


SULPHATES.  427 

merce,  by  roasting  native  sulphuret  of  zinc.  It  crystallizes  by  spontaneous 
evaporation  in  transparent  flattened  four-sided  prisms  of  the  right  prismatic 
system,  and  isomorphous  with  Epsom  salt.  The  crystals  dissolve  in  two 
parts  and  a  half  of  cold,  and  are  still  more  soluble  in  boiling-  water.  The 
taste  of  this  salt  is  strongly  styptic.  It  reddens  vegetables  blue  colours,  though 
in  composition  it  is  a  strictly  neutral  salt. 

Sulphate  of  Protoxide  of  Nickel. — This  salt,  like  the  salts  of  nickel  in 
general,  is  of  a  green  colour,  and  crystallizes  from  its  solution  in  pure 
water  in  right  rhombic  prisms,  exactly  similar  to  the  sulphates  of  zinc 
and  magnesia.  If  an  excess  of  sulphuric  acid  is  present,  the  crystals  are 
square  prisms,  which,  according  to  R.  Phillips  and  Cuoper,  contain  rather 
less  water  and  more  acid  than  the  preceding;  though  the  difference  is  not  so 
great  as  to  indicate  a  different  atomic  constitution.  (Annals  of  Philosophy, 
xxii.  439.)  Thomson  says  he  analyzed  both  kinds,  and  found  their  composi- 
tion identical.  It  is  soluble  in  about  three  times  its  weight  of  water  at 
60°  F. 

Sulphate  of  Protoxide  of  Cobalt — When  protoxide  of  cobalt  is  digested  in 
dilute  sulphuric  acid,  a  red  solution  is  formed,  which  by  evaporation  deposites 
crystals  of  the  same  colour.  Mitscherlich  has  shown  that  the  crystals  are 
identical  in  composition  with  sulphate  of  protoxide  of  iron;  and  Brooke's 
measurements  prove  these  salts  to  be  isomorphous.  (An.  of  Phil.  N.  S.  vi. 
120.)  They  are  insoluble  in  alcohol,  and  dissolves  in  about  24  parts  of  cold 
water, 

Tersulphate  of  Sesquioxide  of  Chromium. — This  salt  may  be  formed  by 
saturating  diluted  sulphuric  acid  with  hydrated  sesquioxide  of  chromium  ; 
but  it  has  not  been  obtained  in  crystals. 

Sulphates  of  the  Oxides  of  Copper. — Sulphate  of  the  red  oxide  of  copper 
has  not  been  obtained  in  a  separate  state.  The  sulphate  of  the  black  or 
protoxide,  blue  vitriol,  employed  by  surgeons  as  an  escharotic  and  astringent, 
may  be  prepared  by  roasting  the  native  sulphuret ;  but  it  is  more  generally 
made  by  directly  dissolving-  the  protoxide  in  dilute  sulphuric  acid,  and  crys- 
tallizing by  evaporation.  This  salt  forms  crystals  of  a  blue  colour,  reddens 
litmus  paper,  and  is  soluble  in  about  four  of  cold,  and  in  two  parts  of  boiling 
water.  The  crystals  contain  five  eq  of  water,  four  of  which  are  lost  at  212° 
in  a  dry  air,  but  the  fifth  is  retained  till  the  temperature  exceeds  430°.  It  is 
then  a  white  powder,  which  combines  readily  with  water,  with  the  develope- 
ment  of  considerable  heat.  It  is  isomorphous  with  sulphate  of  protoxide  of 
manganese. 

When  pure  potassa  is  added  to  a  solution  of  the  sulphate  of  protoxide  of 
copper,  in  a  quantity  insufficient  for  separating  the  whole  of  the  acid,  a  pale 
bluish-green  precipitate,  the  disulphate,  is"  thrown  down. 

Sulphate  of  protoxide  of  copper  and  ammonia  is  generated  by  dropping 
pure  ammonia  into  a  solution  of  the  sulphate,  until  the  subsalt  at  first  thrown 
down  is  nearly  all  dissolved.  It  forms  a  dark  blue  solution,  from  which, 
when  concentrated,  crystals  are  deposited  by  the  addition  of  alcohol.  It  may 
be  formed  also  by  rubbing  briskly  in  a  mortar  two  parts  of  crystallized 
sulphate  of  protoxide  of  copper  with  three  parts  of  carbonate  of  ammonia, 
until  the  mixture  acquires  a  uniform  deep  blue  colour.  Carbonic  acid  gas  is 
disengaged  with  effervescence  during  the  operation,  and  the  mass  becomes 
moist,  owing  to  the  water  of  the  blue  vitriol  being  set  free. 

This  compound,  which  is  the  ammoniuret  of  copper  of  the  Pharmacopoeia, 
contains  sulphuric  acid,  protoxide  of  copper,  and  ammonia ;  but  its  precise 
nature  has  not  been  determined  in  a  satisfactory  manner.  It  parts  gradually 
with  ammonia  by  exposure  to  the  air. 

Sulphates  of  the  Oxides  of  Mercury. — When  two  parts  of  mercury  are 
gently  heated  in  three  parts  of  strong  sulphuric  acid,  so  as  to  cause  slow 
effervescence,  a  sulphate  of  the  protoxide  of  mercury  is  generated.  But  if  a 
strong  heat  is  employed  in  such  a  manner  as  to  excite  brisk  effervescence, 
and  the  mixture  is  brought  to  dry  ness,  a  bisulphate  of  the  peroxide  results, 
both  being  anhydrous.  (Donovan  in  An.  of  Phil,  xiv.)  When  this  bisulphate. 


428  DOUBLE   SULPHATES. 

which  is  the  salt  employed  in  making-  corrosive  sublimate,  is  thrown  into  hot 
water,  decomposition  ensues,  and  a  yellow  subsalt,  formerly  called  turpeth. 
mineral,  subsides.  This  salt  is  said  by  Phillips  to  consist  of  three  eq.  of  acid 
and  four  eq.  of  the  peroxide.  The  hot  water  retains  some  of  the  bisulphate 
in  solution,  together  with  free  sulphuric  acid. 

Sulphate  of  Oxide  of  Silver. — As  this  salt  is  rather  sparingly  soluble  in 
water,  it  may  be  formed  by  double  decomposition  from  concentrated  solutions 
of  nitrate  of  oxide  of  silver  and  sulphate  of  soda.  It  may  also  be  procured 
by  dissolving  silver  in  sulphuric  acid  which  contains  about  a  tenth  part  of 
nitric  acid,  or  by  boiling  silver  in  an  equal  weight  of  concentrated  sulphuric 
acid.  It  requires  about  80  times  its  weight  of  hot  water  for  solution,  and 
the  greater  part  is  deposited  in  small  needles  on  cooling.  By  slow  evapora- 
tion from  a  solution  containing1  a  little  nitric  acid,  Milscherlich  obtained  it  in 
the  form  of  a  rhombic  octohedron,  the  angles  of  which  are  almost  identical 
with  those  of  anhydrous  sulphate  of  soda.  Seleniate  of  oxide  of  silver  is 
isomorphous  with  the  sulphate. 

Sulphate  of  oxide  of  silver  forms  with  ammonia  a  double  salt,  which  crys- 
tallizes in  rectangular  prisms,  the  solid  angles  and  lateral  edges  of  which  are 
commonly  replaced  by  tangent  planes.  It  consists  of  one  eq.  of  oxide  of 
silver,  one  of  acid,  and  two  of  ammonia ;  and  it  is  formed  by  dissolving 
sulphate  of  oxide  of  silver  in  a  hot  concentrated  solution  of  ammonia,  from 
which  on  cooling  the  crystals  are  deposited.  This  salt  is  isomorphous  with 
the  double  chrornate  and  seleniate  of  oxide  of  silver  and  ammonia,  which 
have  a  similar  constitution,  and  are  formed  in  the  same  manner.  (Mitscherlich 
in  An.  de  Ch.  et  de  Ph.  xxxviii.  62.) 

DOUBLE  SULPHATES. 

Sulphate  of  Soda  and  Lime. — This  compound,  the  Glauberite  of  minera- 
logists, occurs  in  very  flat  oblique  rhombic  prisms.  Berthier  prepared  it  by 
fusing  together  sulphate  of  soda  with  sulphate  of  lime  in  the  ratio  of  their 
equivalents.  Sulphate  of  soda,  fused  in  similar  proportions  with  the  sulphates 
of  magnesia,  baryta,  and  oxide  of  lead,  gives  analogous  compounds.  In 
these  instances,  however,  the  affinity  is  so  feeble,  that  it  is  overcome  by  the 
mere  action  of  water.  (An.  de  Ch.  et  de  Ph.  xxxviii.  255.) 

Sulphate  of  Potassa  and  Magnesia. — On  mixing  solutions  of  these  salts  in 
atomic  proportion,  the  double  salt  is  formed  either  by  spontaneous  evapora- 
tion or  on  cooling  from  a  hot  rather  concentrated  solution.  The  crystals  are 
prismatic,  and  of  a  complicated  form,  belonging  to  the  oblique  prismatic  sys- 
tem. (Brooke.)  A  similar  double  salt,  isomorphous  with  the  preceding,  is 
formed  by  substituting  oxide  of  ammonium  for  potassa.  Their  composition 
is  given  in  the  table  (page  423). 

Similar  pairs  of  double  salts  may  be  formed  with  the  protoxides  of  iron, 
zinc,  cobalt,  and  nickel.  These  salts  have  the  same  form  and  composition  as 
the  corresponding  salt  of  magnesia. 

Mum. — This  well-known  substance  is  a  double  sulphate  of  potassa  and 
alumina,  which  crystallizes  with  great  facility  from  a  solution  containing  its 
elements.  It  is  prepared  in  this  country  from  alum-slate,  an  argillaceous 
slaty  rock  highly  charged  with  pyrites :  on  roasting  this  rock,  the  sulphuret 
of  iron  is  oxidized,  the  resulting  sulphuric  acid  unites  with  alumina  and  po- 
tassa present  in  the  slate,  and  the  alum  is  dissolved  out  by  water.  By  fre- 
quent crystallization  it  is  purified  from  the  sesquioxide  of  iron,  which  obsti- 
nately adheres  to  it.  In  Italy  it  is  prepared  from  alum-stone,  which  occurs 
at  Tolfa  near  Rome,  and  in  most  volcanic  districts,  being  formed  apparently 
by  the  action  of  sulphurous  acid  vapours  on  felspatic  rocks.  The  materials 
of  the  alum  exist  in  the  stone  ready  formed ;  and  they  are  extracted  by  gently 
heating  the  rock,  exposing  it  for  a  time  to  the  air,  and  lixiviation.  The  alum 
from  this  source  has  been  long  prized,  in  consequence  of  being  quite  free 
from  iron.  In  both  of  these  processes  the  alkali  contained  in  the  alum-rock 
is  inadequate  for  uniting  with  the  sulphate  of  alumina  which  is  obtained,  and 
hence  a  salt  of  potassa  must  be  added, 


DOUBLE    SULPHATES,  439 

Alum  has  a  sweetish  astringent  taste,  arid  reddens  litmus  paper.  It  is  sol- 
uble in  five  parts  of  water  at  60°,*  and  a  little  more  than  its  own  weight  of 
boiling  water.  It  crystallizes  readily  in  octohedrons,  or  in  segments  of  the 
octohedron,  and  the  crystals  contain  twenty-four  eq.  or  almost  50  per  cent, 
of  water  of  crystallization.  On  being  exposed  to  heat,  they  froth  up  re- 
markably, and  part  with  all  the  water,  forming  anhydrous  alum,  the  Alumen 
Ustum  of  the  Pharmacopoeia.  At  a  full  red  heat  the  alumina  is  deprived  of 
its  acid. 

Alum  is  employed  in  the  formation  of  a  spontaneously  inflammable  mix- 
ture, long  known  under  the  name  of  Homberg's  pyrophorus.  It  is  made  by 
mixing  equal  weights  of  alum  and  brown  sugar,  and  stirring  the  mass  over 
the  fire  in  an  iron  or  other  convenient  vessel  till  quite  dry  :  it  is  then  put 
into  a  glass  tube  or  bottle,  and  heated  to  moderate  redness  without  exposure 
to  the  air,  until  inflammable  gas  ceases  to  be  evolved.  A  more  convenient 
mixture  is  made  with  three  parts  of  lampblack,  four  of  burned  alum,  and 
eight  of  carbonate  of  potassa.  When  the  pyrophorus  is  well  made,  it  speedily 
becomes  hot  on  exposure  to  the  air,  takes  fire,  and  burns  like  tinder ;  but 
the  experiment  frequently  fails  from  the  difficulty  of  regulating  the  tempe- 
rature. 

From  some  recent  experiments  by  Gay-Lussac,  it  appears  that  the  essential 
ingredient  of  Homberg's  pyrophorus  is  sulphuret  of  potassium  in  a  state  of 
minute  division.  The  charcoal  and  alumina  act  only  by  being  mechanically 
interposed  between  its  particles  ;  but  when  the  mass  once  kindles,  the  char- 
coal takes  fire  and  continues  the  combustion.  He  finds  that  an  excellent 
pyrophorus  is  made  by  mixing  27  parts  of  sulphate  of  potassa  with  15  parts 
of  calcined  lampblack,  and  heating  the  mixture  to  redness  in  a  common 
Hessian  crucible,  of  course  excluding  the  air  at  the  same  time.  (An.  de,  Ch. 
et  de  Ph.  xxxvii.  415.) 

Alum,  having  exactly  the  same  form,  composition,  appearance,  and  taste 
as  the  salt  just  described,  may  be  made  with  ammonia,  the  sulphate  of  which 
replaces  sulphate  of  potassa.  It  is  met  with  occasionally  as  a  natural  pro- 
duct, and  may  be  prepared  by  evaporating  a  solution  of  sulphate  of  ammonia 
with  tersulphate  of  alumina. 

A  soda  alum  may  also  be  prepared,  similar  in  form  and  composition  to  the 
preceding  alums,  except  that  it  contains  twenty-six  equivalents  of  water. 
(Berzelius.)  This  salt  is  disposed  to  effloresce  in  the  air. 

Iron  Alum. — By  mixing-  sulphate  of  potassa  with  tersulphate  of  sesquioxide 
of  iron,  and  crystallizing  by  spontaneous  evaporation,  crystals  are  obtained 
similar  to  common  alum  in  form,  colour,  taste,  and  composition.  This  salt 
has  often  a  pink  tint,  but  is  sometimes  quite  colourless.  A  similar  double 
salt,  quite  colourless,  may  be  made  with  ammonia  instead  of  potassa.  In 
both  these  alums,  the  alumina  is  simply  replaced  by  an  equivalent  quantity  of 
sesquioxide  of  iron. 

Chrome  Alums. — The  tersulphate  of  sesquioxide  of  chromium  forms  with 
the  sulphates  of  potassa  and  ammonia  double  salts,  which  are  exactly  similar 
in  form  and  composition  to  the  preceding  varieties  of  alurn.  They  appear 
black  by  reflected,  but  ruby-red  by  transmitted  light. 

Manganese  Alum. — Mitscherlich  obtained  this  salt  by  mixing  a  solution 
of  tersulphate  of  sesquioxide  of  manganese  with  sulphate  of  potassa,  and 
evaporating  to  the  consistence  of  syrup  by  a  very  gentle  heat.  On  cooling, 
octohedral  crystals  of  a  brownish-violet  colour  were  deposited,  which  were 
similar  in  composition  to  common  alurn.  The  tersulphate  used  for  the  pur- 
pose is  prepared  by  macerating  sesquioxide  of  manganese  in  very  fine  powder 
with  strong  sulphuric  acid :  it  is  made  with  difficulty,  owing  to  the  indispo- 
sition of  that  oxide  to  unite  with  acids,  and  to  its  ready  conversion  by  heat 
into  sulphate  of  the  protoxide. 

*  The  solubility  of  alum  in  cold  water  is  probably  not  so  great  as  is  here 
mentioned.  Berzelius  states  it  to  be  soluble  in  about  eighteen  parts  of  cold 
water,  and  Thenard  in  between  fourteen  and  fifteen  parts. — Ed. 


430  DOUBLE  SULPHATES. 

From  the  descriptions  of  the  salts  to  which  the  term  alum  has  been  ap- 
plied, it  will  be  observed  that  they  are  characterized  by  two  common  proper- 
ties: they  all  crystallize  in  the  octohedral  system,  and  they  are  all  constituted 
as  represented  by  the  formula  ROSOs-f  R2O3SO34-24  Aq.;  where  RO  re- 
presents an  eq.  of  potassa,  or  oxide  of  ammonium,  and  RsO ',  any  one  of  the 
isomorphous  sesquioxides  of  aluminium,  iron,  manganese,  and  chromium. 
As  Berzelius  has  ably  remarked,  the  formula  and  crystalline  form  serve  to 
determine  the  genus  alum,  and  the  oxidized  bases  its  species. 

Sulphate  of  Protoxide  of  Iron  and  Alumina, — This  salt,  which  has  recently 
been  formed  by  Klauer,  is  obtained  by  the  spontaneous  evaporation  of  a 
mixture  of  sulphate  of  protoxide  of  iron  and  tersulphate  of  alumina  in  eq. 
proportions,  a  large  excess  of  sulphuric  acid  being  present  (Lieb.  An.  xiv. 
261.)  The  salt  is  deposited  in  long  acicular  crystals,  the  constitution  of 
which,  being  FeOSO3+Al^O33SO3-f  24HO,  is  similar  to  that  of  an  alum; 
but  as  the  crystals  do  not  belong  to  the  octohedral  system,  it  has  been  impro- 
perly described  as  one  of  that  class. 

A  similar  salt  of  magnesia  was  obtained  in  the  same  manner;  and  it  is 
exceedingly  probable  that  a  similar  compound  might  be  formed  with  the 
isomorphous  oxides  of  zinc,  copper,  nickel,  and  cobalt,  and  with  lime.  These, 
in  their  turn,  might  again  be  varied  by  substituting  for  the  alumina,  the  ses- 
quioxides of  iron,  manganese,  and  chromium. 

Anhydrous  Sulphates  with  Ammonia. — Rose  has  observed  that  some  sul- 
phates possess  the  property  of  absorbing  ammonia,  and  of  forming  with  Lt 
definite  compounds,  which  differ  from  sulphates  of  ammonia  prepared  in  the 
moist  way,  both  by  containing  no  water  of  crystallization,  and  by  the  facility 
with  which  the  alkali  is  again  given  out.  They  are  formed  by  placing  the 
anhydrous  sulphate  in  a  glass  tube,  and  transmitting  over  it  at  common  tem- 
peratures ammoniacal  gas,  well  dried  by  fused  potassa,  as  long  as  any  increase 
of  weight  is  observed :  some  sulphates  absorb  the  gas  very  rapidly  at  first, 
and  with  disengagement  of  heat :  but  the  absorption  afterwards  becomes  slow, 
and  requires  a  day  or  two  in  order  to  be  complete.  The  salts  most  remarka- 
ble for  this  property  are  those  which,  in  solution,  are  disposed  to  unite  with 
ammonia. — Sulphate  of  protoxide  of  copper  greedily  absorbs  ammonia,  and 
acquires  a  deep  blue  colour  similar  to  the  ammoniuret  of  copper,  prepared  with 
moisture ;  but  the  former  compound  consists  of  two  eq.  of  sulphate  of  prot- 
oxide of  copper  and  five  eq.  of  ammonia,  while  the  latter  contains  one  eq.  of 
sulphate  of  copper,  two  of  ammonia,  and  one  eq.  of  water.  Sulphate  of  protox- 
ide of  cobalt,  as  well  as  that  of  nickel,  unites  with  three  eq.  of  ammonia; 
that  of  zinc  with  two  and  a  half,  and  that  of  manganese  with  two  eq.  The 
latter  when  heated  loses  all  its  ammonia,  and  returns  to  its  original  condition ; 
whereas  most  of  the  other  ammoniaco-sulphates  suffer  partial  decomposition 
at  the  same  time.  Sulphate  of  oxide  of  silver  unites  with  one  eq.  of  ammo- 
nia ;  and  a  similar  compound  was  prepared  by  C.  G.  Mitscherlich,  but  with 
two  eq.  of  ammonia.  With  most  of  the  other  anhydrous  sulphates  ammonia 
refuses  to  unite. 

On  considering  the  nature  of  these  compounds,  one  is  at  first  disposed  to 
associate  them  with  double  salts,  supposing  the  acid  to  be  divided  between 
the  two  bases.  But  this  opinion  is  rendered  unlikely  by  the  large  quantity 
of  combined  ammonia,  by  the  facility  with  which  the  alkali  is  given  off,  and 
by  the  absence  of  water,  so  constantly  present  in  other  ammoniacal  sulphates. 
Rose,  with  much  plausibility,  compares  these  compounds  to  hydrates:  water 
acts  as  a  feeble  base  to  saline  compounds,  combining  with  some  in  one  or 
more  proportions,  and  not  at  all  with  others,  differing  greatly  in  the  ratio  in 
which  it  combines  with  different  salts,  and  being  abandoned  with  great  fa- 
cility, often  by  mere  exposure  to  the  air.  The  same  features  characterize 
the  combinations  of  ammonia  with  the  anhydrous  sulphates.  (Pog.  Annalen, 
xx.  149.) 

The  sulphates  are  not  the  only  salts  which  absorb  ammonia.  Rose  found 
that  the  nitrate  of  oxide  of  silver  unites  with  three  eq.  of  ammonia,  and  the 
gas,  if  freely  supplied,  is  at  first  absorbed  with  such  rapidity,  and  the  cor, 


SULPHITES. — NITRATES.  431 

responding  increase  of  temperature  is  so  great,  that  the  salt  enters  into  fusion. 
Heat  expels  the  ammonia  before  the  nitrate  of  oxide  of  silver  is  decom- 
posed. A  similar  compound,  but  with  less  ammonia,  was  formed  by  C.  Mits- 
cherlich. 

SULPHITES. 

The  salts  of  sulphurous  acid  have  not  hitherto  been  minutely  examined. 
The  sulphites  of  potassa,  soda,  and  ammonia,  which  are  made  by  neutral- 
izing- those  alkalies  with  sulphurous  acid,  are  soluble  in  water  ;  but  most  of 
the  other  sulphites,  so  far  as  is  known,  are  of  sparing  solubility.  The  sul- 
phites of  baryta,  strontia,  and  lime  are  very  insoluble;  and  consequently  the 
soluble  salts  of  these  earths  decompose  the  alkaline  sulphites. 

The  stronger  acids,  such  as  the  sulphuric,  hydrochloric,  phosphoric,  and 
arsenic  acids,  decompose  all  the  sulphites  with  effervescence,  owing  to  the 
escape  of  sulphurous  acid,  which  may  easily  be  recognized  by  its  odour. 
Nitric  acid,  by  yielding  oxygen,  converts  the  sulphites  into  sulphates. 

When  the  sulphites  of  the  fixed  alkalies  and  alkaline  earths  are  strongly 
heated  in  close  vessels,  a  sulphate  is  generated,  and  a  portion  of  sulphur  sub- 
limed. In  open  vessels  at  a  high  temperature  they  absorb  oxygen,  and  are 
converted  into  sulphates;  and  a  similar  change  takes  place  even  in  the  cold, 
especially  when  they  are  in  solution.  Gay-Lussac  has  remarked,  that  a  neu- 
tral sulphite  always  forms  a  neutral  sulphate  when  its  acid  is  oxidized  ;  a 
fact  from  which  it  may  be  inferred  that  neutral  sulphites  consist  of  one  eq. 
of  the  acid  and  one  eq.  of  the  base. 

The  kyposulphates  and  hyposulphites  are  of  such  little  practical  importance, 
that  it  is  unnecessary  to  describe  individual  salts :  their  general  character 
has  been  already  given.  (Pages  196  and  197.)  For  a  particular  description 
of  the  hyposulphates,  the  reader  is  referred  to  an  essay  by  Heeren.  (An.  de 
Ch.  et  de  Ph.  xl.  30.) 

NITRATES. 

The  nitrates  may  be  prepared  by  the  action  of  nitric  acid  on  metals,  on 
the  salifiable  bases  themselves,  or  on  carbonates.  As  nitric  acid  forms  solu- 
ble salts  with  all  alkaline  bases,  the  acid  of  the  nitrates  cannot  be  precipitated 
by  any  reagent.  They  are  readily  distinguished  from  other  salts,  however, 
by  the  characters  already  described.  (Page  184.) 

All  the  nitrates  are  decomposed  without  exception  by  a  high  temperature  ; 
but  the  changes  which  ensue  are  modified  by  the  nature  of  the  oxide.  Ni- 
trate of  oxide  of  palladium  is  decomposed  at  such  a  moderate  temperature, 
that  a  great  part  of  the  acid  passes  off  unchanged.  Nitrate  of  protoxide  of 
lead  requires  a  red  heat,  by  which  it  is  resolved,  as  already  mentioned  (page 
180,)  into  oxygen  and  nitrous  acid.  In  some  instances  the  changes  are  more 
complicated.  With  nitre,  for  example,  nitrite  of  potassa  is  at  first  generated, 
with  escape  of  oxygen  gas  :  as  the  heat  increases,  the  nitrous  acid  is  resolved 
into  binoxide  of  nitrogen  and  oxygen,  the  former  of  which  remains  in  com- 
bination with  potassa;  the  binoxide  is  then  resolved  into  protoxide  of  nitro- 
gen and  oxygen,  the  farmec  being  retained  by  the  alkali ;  and,  lastly,  nitro- 
gen gas  is  disengaged,  and  peroxide  of  potassium  remains.  If  the  operation 
is  performed  in  an  earthen  vessel,  the  peroxide  will  be  more  or  less  decom- 
posed, in  consequence  of  the  affinity  of  the  earthy  substances  for  potassa. 
The  preceding  facts  have  been  chiefly  collected  from  the  observations  of 
Phillips  and  Berzelius.  The  tendency  of  potassa  and  soda  to  unite  with  pro- 
toxide of  nitrogen  was  first  observed  by  Davy;  and  Hess  has  lately  remark- 
ed that  similar  compounds  are  obtained  with  soda,  baryta,  and  lime,  as  well 
as  potassa,  when  their  nitrates  are  heated  until  the  disengaged  gas  is  found 
to  extinguish  a  light. 

As  the  nitrates  are  easily  decomposed  by  heat  alone,  they  must  necessarily 
suffer  decomposition  by  the  united  agency  of  heat  and  combustible  matter. 
The  nitrates  on  this  account  are  much  employed  as  oxidizing  agents,  and 


432  NITRATES. 

frequently  act  with  greater  efficacy  even  than  nitre-hydrochloric  acid.  Thus 
metallic  titanium,  which  resists  the  action  of  these  acids,  combines  with  oxy- 
gen when  heated  with  nitre.  The  efficiency  of  this  salt,  which  is  the  nitrate 
usually  employed  for  the  purpose,  depends  not  only  on  the  affinity  of  the 
combustible  for  oxygen,  but  likewise  on  that  of  the  oxidized  body  for  potassa. 
The  process  for  oxidizing  substances  by  means  of  nitre  is  called  deflagration, 
and  is  generally  performed  by  mixing  the  inflammable  body  with  an  equal 
weight  of  the  nitrate,  and  projecting  the  mixture  in  small  portions  at  a  time 
into  a  red-hot  crucible. 

All  the  neutraPnitrates  of  the  fixed  alkalies  and  alkaline  earths,  together 
with  most  of  the  neutral  nitrates  of  the  common  metals,  are  composed  of  one 
eq.  of  nitric  acid,  and  one  eq.  of  a  protoxide.  Consequently,  the  oxygen  of 
the  oxide  and  acid  in  all  such  salts  must  be  in  the  ratio  of  1  to  5,  the  gene- 
ral formula  being  MO-f-NO5. 

The  only  nitrates  found  native  are  those  of  potassa,  soda,  lime,  and  mag- 
nesia. 

The  composition  of  the  principal  nitrates  is  exhibited  in  the  following 
table  :— 

Names.  Base.  Acid.  Equiv.       Formulae. 

Nitrate  of  potassa       -       47-15  1  eq.-f  54-15  1  eq.=  101-3  KO-j-NO.     . 

Do.      soda  -       31-3     1  eq.-f  54-15  1  eq.=  85-45  NaO+NCX 

Do.      ox.  ammonium     26-15  1  eq.-f  54-15  1  eq.=  80-3  H^NO-j-NO*. 

Do.     baryta  •       76-7     1  eq.-f-  54-15  1  eq.  =130-85  BaO-fN(K 

Do.     strontia  -       51-8     1  eq.-j-  54-15  1  eq.=  105-95  SrO-f-NO. 

Do.  in  pris.  with  45  or  5  eq.  of  water  =150-95 

Do.     lime  -       28-5     1  eq.  +  54-15  I  eq,=  82-65  CaO-fNO. 

Do.     magnesia  20-7     1  eq.  -f  54-15  1  eq.=  74-85  MgO-J-NO*. 

Do.     protox.  copper       39-6     1  eq.-f  54-15  1  eq.=  93-75  CuO-fNO. 

Do.  in  pris.  with  63  or  7  eq.  of  water  ?         —156-75 

Do.     protox.  lead          111-6     1  eq.-J-54-15  1  eq.=  165-75  PbO-fN(X 

Dinitrate  of  protox.  lead  223-2     2  eq.  +  54-1S  1  eq.=277-35  2PbO  -f  NO«. 

Nitrateof  protox.  merc.210        1  eq.-f-54.15  1  eq.=264-15  HgO-f-NOfi. 

Do.  in  crys.with  18  or  2  eq.  of  water  =282-15 

Do.      perox.  mercury  218        1  eq.-f  54-15  1  eq.  =272-15 


436     -  2  eq.-f  54.15     1  eq.=490-15 
Nitrate  of  ox.  silver       116        1  eq.-f  54-15     1  eq.  =170-15     AgO-fNCK 

Nitrate  of  Potassa.  —  This  salt  isxgenerated  spontaneously  in  the  soil,  and 
crystallizes  upon  its  surface,  in  several  parts  of  the  world,  and  especially  in 
the  East  Indies,  whence  the  greater  part  of  the  nitre  used  in  Britain  is  de- 
rived. In  some  parts  of  the  Continent,  it  is  prepared  artificially  from  a 
mixture  of  common  mould  or  porous  calcareous  earth  with  animal  and  vege- 
table remains  containing  nitrogen.  When  a  heap  of  these  materials,  pre- 
served moist  and  in  a  shady  situation,  is  moderately  exposed  to  the  air,  nitric 
acid  is  gradually  generated,  and  unites  with  the  potassa,  lime,  and  magnesia, 
which  are  commonly  present  in  the  mixture.  On  dissolving  these  salts  in 
water,  and  precipitating  the  two  earths  by  carbonate  of  potassa,  a  solution  is 
formed  which  yields  crystals  of  nitre  by  evaporation.  The  nitric  acid  is 
probably  generated  under  these  circumstances  by  the  nitrogen  of  the  organic 
matters  combining  during  putrefaction  with  oxygen  of  the  atmosphere,  a 
change  which  must  be  attributed  to  the  affinity  of  oxygen  for  nitrogen,  aided 
by  that  of  nitric  acid  for  alkaline  bases.  The  nitre  made  in  France  is  often 
said  to  be  formed  by  this  process;  but  the  greater  part  is  certainly  obtained 
by  lixiviation  from  certain  kinds  of  plaster  of  old  houses,  where  nitrate  of 
lime  is  gradually  generated. 

Nitrate  of  potassa  is  a  colourless  salt,  which  crystallizes  readily  in  six- 
sided  prisms.  Its  taste  is  saline,  accompanied  with  an  impression  of  cool- 
ness. It  requires  for  solution  seven  parts  of  water  at  60°,  and  its  own  weight 


NITRATES.  433 

of  boiling  water.  It  contains  no  water  of  crystallization,  but  its  crystals 
are  never  quite  free  from  water  lodged  mechanically  within  them.  At  616° 
it  undergoes  the  igneous  fusion,  and  like  all  the  nitrates,  is  decomposed  by  a 
red  heat. 

Nitre  is  chiefly  employed  in  chemistry  as  an  oxidizing  agent,  and  in  the 
formation  of  nitric  acid.  Its  chief  use  in  the  arts  is  in  making  gunpowder, 
which  is  a  mixture  of  nitre,  charcoal,  and  sulphur.  In  the  East  Indies  it 
is  employed  for  the  preparation  of  cooling  mixtures:  an  ounce  of  powdered 
nitre  dissolved  in  five  ounces  of  water  reduces  its  temperature  by  fifteen 
degrees.  It  possesses  powerful  antiseptic  properties,  and  is,  therefore,  much 
employed  in  the  preservation  of  meat  and  animal  matters  in  general. 

Nitrate  of  Soda. — This  salt  is  analogous  in  its  chemical  properties  to  the 
preceding  compound.  It  sometimes  crystallizes  in  oblique  rhombic  prisms; 
but  it  more  commonly  occurs  as  an  obtuse  rhombohedrori.  (Brooke.)  It  is 
plentifully  found  in  the  soil  in  some  parts  of  India ;  and  at  Atacama  in  Peru 
it  covers  large  districts,  and  occurs  in  immense  quantity.  With  charcoal 
and  sulphur  it  forms  a  mixture  which  burns  much  slower  than  common  gun- 
powder, and,  therefore,  cannot  he  substituted  for  nitre ;  but  it  may  be  advan- 
tageously used  in  the  manufacture  both  of  sulphuric  and  nitric  acid.  It  is 
disposed  to  deliquesce  in  the  air,  and  is  soluble  in  twice  its  weight  of  cold 
water,  and  still  more  freely  by  the  aid  of  heat. 

Nitrate  of  Oxide  of  Ammonium. — It  may  be  formed  by  neutralizing  dilute 
nitric  acid  by  carbonate  of  ammonia,  and  evaporating  the  solution.  This 
salt  may  be  procured  in  three  different  states,  which  have  been  described  by 
Davy.  (Researches  concerning  the  Nitrous  Oxide.)  If  the  evaporation  is 
conducted  at  a  temperature  not  exceeding  100°,  the  salt  is  obtained  in  pris- 
matic crystals  isomorphous  with  nitre.  If  the  solution  is  evaporated  at  212°, 
fibrous  crystals  are  procured;  and  if  the  heat  be  gradually  increased  to  300°, 
it  forms  a  brittle  compact  mass  on  cooling.  The  fibrous  and  compact  varie- 
ties still  contain  water,  the  former  8-2  per  cent.,  and  the  latter  5'7.  All  these 
varieties  deliquesce  in  a  moist  air,  and  are  very  soluble  in  water. 

The  change  which  nitrate  of  ammonia  undergoes  at  a  temperature  vary- 
ing between  400°  and  500°  has  already  been  explained.  (Page  174.)  When 
heated  to  600°,  it  explodes  with  violence,  being  resolved  into  water,  nitrous 
acid,  binoxide  of  nitrogen,  and  nitrogen.  The  fibrous  variety  was  found  by 
Davy  to  yield  the  largest  quantity  of  protoxide  of  nitrogen.  From  one 
pound  of  this  salt  he  procured  nearly  three  cubic  feet  of  the  gas. 

Nitrate  of  Baryta, — This  salt  is  sometimes  used  as  a  reagent  and  for 
preparing  pure  baryta.  It  is  easily  prepared  by  digesting  the  native  carbo- 
nate, reduced  to  powder,  in  nitric  acid  diluted  with  8  or  10  times  its  weight 
of  water.  The  salt  crystallizes  readily  by  evaporation  in  transparent  anhy- 
drous octohedrons,  and  is  very  apt  to  decrepitate  by  heat  unless  previously 
reduced  to  powder.  It  requires  12  parts  of  water  at  60°  and  3  or  4  of  boiling 
water  for  solution,  but  is  insoluble  in  alcohol.  It  undergoes  the  igneous 
fusion  in  the  fire  before  being  decomposed. 

Nitrate  of  Strontia. — This  salt  may  be  made  from  strontianite  in  the 
same  manner  as  the  foregoing  compound,  to  which  it  is  exceedingly  analo- 
gous. It  commonly  crystallizes  in  anhydrous  octohedrons  which  undergo 
no  change  in  a  moderately  dry  atmosphere,  and  are  insoluble  in  alcohol;  but. 
sometimes  it  contains  30  per  cent,  of  water  of  crystallization,  and  then  as- 
sumes the  form  of  the  oblique  prismatic  system. 

Nitrates  of  Lime  and  Magnesia. — These  salts  crystallize  in  hydrated 
prisms  when  their  solutions  are  concentrated  to  the  consistence  o,f  syrup,  but 
the  quantity  of  water  which  they  contain  is  not  ascertained.  They  deliquesce 
rapidly  in  the  air,  are  very  soluble  in  water,  and  are  dissolved  by  alcohol, 
the  nitrate  of  lime  more  freely  than  nitrate  of  magnesia. 

Nitrate  of  Protoxide  of  Copper. — This  salt  is  prepared  by  the  action  of 
nitric  acid  on  copper.  (Page  176.)  It  crystallizes,  though  with  some  diffi- 
culty, in  prisms  of  a  deep  blue  colour,  which  are  very  soluble  in  water  and 
alcohol,  and  deliquesce  on  exposure  to  the  air.  The  green  insoluble  subsalt, 

37 


434  NITRATES. 

procured  by  exposing  the  neutral  nitrate  to  a  heat  of  400°,  or  by  dropping  an 
alkali  into  a  solution  of  that  salt,  the  latter  being  in  excess,  is  a  trinitrate, 
consisting  of  three  eq.  of  protoxide  of  copper,  one  eq.  of  acid,  and  one  eq.  of 
water.  From  the  observations  of  Graham,  the  neutral  salt  contains  three  eq. 
of  constitutional  water,  and,  therefore,  may  be  represented  by  the  formula 
CuO-f-NO53HO  :  from  this  it  would  appear  that  the  subsalt  is  similarly  con- 
stituted,  being  a  nitrate  of  water  with  three  eq.  of  constitutional  protoxide  of 
copper.  It  is  on  this  supposition  represented  by  the  formula  HO-j-NO53CuO. 
It  is  probable  that  the  nitrates  of  lime  and  magnesia  are  similarly  constituted, 
as  has  been  shown  to  be  the  case  with  nitric  acid  of  sp.  gr.  1-42.  When 
heated  to  redness  it  yields  pure  protoxide  of  copper. 

Nitrate  of  Protoxide  of  Lead. — This  salt  is  formed  by  digesting  litharge 
in  dilute  nitric  acid,  and  crystallizes  readily  in  octohedrons,  which  are  anhy- 
drous and  almost  always  opaque.  It  has  an  acid  reaction,  but  is  neutral  in 
composition. 

A  dinitrate  was  formed  by  Berzelius  by  adding  to  a  solution  of  the  neutral 
nitrate,  a  quantity  of  pure  ammonia  insufficient  for  separating  the  whole  of 
the  acid. 

Nitrates  of  the  Oxides  of  Mercury. — The  protonitrate  is  conveniently 
formed  by  digesting  mercury  in  nitric  acid  diluted  with  three  or  four  parts 
of  water,  until  the  acid  is  saturated,  and  then  allowing  the  solution  to  eva- 
porate spontaneously  in  an  open  vessel.  The  solution  always  contains,  at 
first,  some  nitrate  of  the  peroxide;  but  if  metallic  mercury  is  left  in  the  liquid, 
a  pure  protonitrate  is  gradually  deposited.  The  salt  thus  formed  has  hitherto 
been  regarded  as  the  neutral  protonitrate ;  but  according  to  the  analysis  of 
M.  C.  Mitscherlich  (Pog.  Annalen,  ix.  387),  it  is  a  subsalt,  in  which  the  prot- 
oxide and  acid  are  in  the  ratio  of  208  to  36.  This  result,  however,  requires 
confirmation.  The  neutral  protonitrate  is  said  by  C.  Mitscherlich  to  be  ob- 
tained in  crystals,  by  dissolving  the  former  salt  in  pure  water  acidulated 
with  nitric  acid,  and  evaporating  spontaneously  without  the  contact  of  me- 
tallic mercury  or  uncombined  oxide.  These  salts  dissolve  completely  in 
water  slightly  acidulated  with  nitric  acid,  but  in  pure  water  a  small  quantity 
of  a  yellow  subsalt  is  generated. 

When  mercury  is  heated  in  an  excess  of  strong  nitric  acid,  it  is  dissolved 
with  brisk  effervescence,  owing  to  the  escape  of  binoxide  of  nitrogen,  and 
transparent  prismatic  crystals  of  the  pernitrate  are  deposited  as  the  solution 
cools.  When  put  into  hot  water  it  is  resolved  into  a  soluble  salt,  the  compo- 
sition of  which  is  unknown,  and  into  a  yellow  dinitrate  of  the  peroxide.  (An. 
de  Ch.  et  de  Phys.  xix.) 

Nitrate  of  Oxide  of  Silver. — Silver  is  readily  oxidized  and  dissolved  by 
nitric  acid  diluted  with  two  or  three  times  its  weight  of  water,  forming  a 
solution  which  yields  transparent  tabular  crystals  by  evaporation.  These 
crystals,  which  are  anhydrous,  undergo  the  igneous  fusion  at  426°,  and  yield 
a  crystalline  mass  in  cooling ;  but  when  the  temperature  reaches  600°  or 
700°,  complete  decomposition  ensues,  the  acid  being  resolved  into  oxygen 
and  nitrous  acid,  while  metallic  silver  is  left.  When  liquefied  by  heat,  and 
received  in  small  cylindrical  moulds,  it  forms  the  lapis  infernalis  or  lunar 
caustic,  employed  by  surgeons  as  a  cautery.  The  nitric  acid  appears  to  be 
the  agent  which  destroys  the  animal  texture,  and  the  black  stain  is  owing  to 
the  separation  of  oxide  of  silver.  It  is  sometimes  employed  for  giving  a 
black  colour  to  the  hair,  and  is  the  basis  of  the  indelible  ink  for  marking 
linen. 

The  pure  nitrate,  whether  fused  or  in  crystals,  is  colourless  and  transpa- 
rent, and  does  not  deliquesce  by  exposure  to  the  air ;  but  common  lunar 
Caustic  is  dark  and  opaque,  and  dissolves  imperfectly  in  water,  owing  to 
some  of  the  nitrate  being  decomposed  during  its  preparation.  It  is  impure 
also,  always  containing  nitrate  of  protoxide  of  copper,  and  frequently  traces 
of  gold.  The  pure  salt  is  soluble  in  its  own  weight  of  cold,  and  in  half  its 
weight  of  hot  water.  It  dissolves  also  in  four  times  its  weight  of  alcohol. 
Its  aqueous  solution,  if  preserved  in  clean  glass  vessels,  undergoes  little  or 


NITRITES. — CHLORATES.  435 

no  change  even  in  the  direct  solar  rays ;  but  when  exposed  to  light,  especially 
to  sunshine,  in  contact  with  paper,  the  skin,  or  any  organic  substance,  a 
black  stain  is  quickly  produced,  owing  to  decomposition  of  the  salt  and  reduc- 
tion of  its  oxide  to  the  metallic  state.  This  change  is  so  constant,  that  nitrate 
of  oxide  of  silver  constitutes  an  extremely  delicate  test  of  the  presence  of  or- 
ganic mutter,  and  has  been  properly  recommended  as  such  by  Dr.  Davy.  Its 
solution  is  always  kept  in  the  laboratory  as  a  test  for  chlorine  and  hydro- 
chloric acid. 

Nitrate  of  oxide  of  silver,  even  after  fusion,  reddens  vegetable  colouring 
matters ;  but  it  is  quite  neutral  in  composition. 

NITRITES. 

Little  is  known  with  certainty  concerning  the  compounds  of  nitrous  acid 
with  alkaline  bases.  Nitrite  of  potassa  is  formed  by  heating  nitre  to  redness, 
and  removing  it  from  the  fire  before  the  decomposition  is  complete.  On 
adding  a  strong  acid  to  the  product,  red  fumes  of  nitrous  acid  are  disengaged, 
a  character  which  is  common  to  all  the  nitrites.  The  nitrite  of  soda,  baryta, 
and  strontia  may  be  obtained  in  the  same  manner,  and  dombtless  several 
others.  Two  nitrites  of  protoxide  of  lead  have  been  described  in  the  Annales 
de  Chimie,  Ixxxiii.  by  Chevreul  and  Berzelius.  It  is  possible,  however,  that 
these  compounds  are  hyponitrites. 

CHLORATES. 

The  salts  of  chloric  acid  are  very  analogous  to  the  nitrates.  As  the  chlo- 
rates of  the  alkalies,  alkaline  earths,  and  most  of  the  common  metals  are 
composed  of  one  eq.  of  chloric  acid  and  one  eq.  of  a  protoxide,  MO-J-C1O5, 
it  follows  that  the  oxygen  of  the  oxide  to  that  of  the  acid  is  in  the  ratio  of 
1  to  5.  The  chlorates  are  decomposed  by  a  red  heat,  nearly  all  of  them  being 
converted  into  metallic  chlorides,  with  evolution  of  pure  oxygen  gas.  They 
deflagrate  with  inflammable  substances  with  greater  violence  than  nitrates, 
yielding  oxygen  with  such  facility  that  an  explosion  is  produced  by  slight 
causes.  Thus,  a  mixture  of  sulphur  with  three  times  its  weight  of  chlorate 
of  potassa  explodes  when  struck  between  two  hard  surfaces.  With  charcoal 
and  the  sulphurets  of  arsenic  and  antimony,  this  salt  forms  similar  explosive 
mixtures  ;  and  with  phosphorus  it  detonates  violently  by  percussion.  One 
of  the  mixtures,  employed  in  the  percussion  locks  for  guns,  consists  of  sul- 
phur and  chlorate  of  potassa,  with  which  a  little  charcoal  or  gunpowder  is 
mixed;  but  as  the  use  of  these  materials  is  found  corrosive  to  the  lock,  ful- 
minating mercury  is  now  generally  preferred. 

All  the  chlorates  hitherto  examined  are  soluble  in  water,  excepting  the 
chlorate  of  protoxide  of  mercury,  which  is  of  sparing  solubility.  The  salts 
are  distinguished  by  the  action  of  strong  hydrochloric  and  sulphuric  acids, 
the  former  of  which  occasions  the  disengagement  of  chlorine  and  protoxide 
of  chlorine,  and  the  latter  of  chlorous  acid. 

None  of  the  chlorates  are  found  native,  and  the  only  ones  that  require 
particular  description  are  those  of  potassa  and  baryta. 

Chlorate  of  Potassa. — This  salt,  formerly  called  oxymuriate  or  hyper  oxy- 
muriate  of  potassa,  is  colourless,  and  crystallizes  in  four  and  six-sided  scales 
of  a  pearly  lustre.  Its  forms  are  stated  by  Brooke  to  belong  to  the  oblique 
prismatic  system.  It  is  soluble  in  sixteen  times  its  weight  of  water  at  60°, 
and  in  two  and  a  half  of  boiling  water.  It  is  quite  anhydrous,  and  when  ex- 
posed to  a  temperature  of  400°  or  500°  undergoes  the  igneous  fusion.  On 
increasing  the  heat  almost  to  redness,  effervescence  ensues,  and  pure  oxygen 
gas  is  disengaged,  phenomena  which  have  been  explained  in  the  section  on 
oxygen.  It  can  bear  a  heat  of  600°  without  decomposition. 

Chlorate  of  potassa  is  made  by  transmitting  chlorine  gas  through  a  con- 
centrated solution  of  pure  potassa,  until  the  alkali  is  completely  neutralized. 
The  solution  which,  after  being  boiled  for  a  few  minutes,  contains  nothing 
but  chloride  of  potassium  and  chlorate  of  potassa  (page  220),  is  gently  evapo- 
rated till  a  pellicle  forms  upon  its  surface,  and  is  then  allowed  to  cool.  The 
greater  part  of  the  chlorate  crystallizes,  while  the  chloride  remains  in  solu? 


436  CHLORITES. 

tion.    The  crystals,  after  being  washed  with  cold  water,  may  be  purified  by 
a  second  cr}7stallization. 

Chlorate  of  Baryta  is  of  interest,  as  being  the  compound  employed  in  the 
formation  of  chloric  acid  ;  and  the  readiest  mode  of  preparing-  it  is  by  the  pro- 
cess of  Wheeler.  On  digesting  for  a  few  minutes  a  concentrated  solution  of 
chlorate  of  potassa  with  a  slight  excess  of  silicated  hydrofluoric  acid,  the 
alkali  is  precipitated  in  the  form  of  an  insoluble  double  fluoride  of  silicon 
and  potassium,  while  chloric  acid  remains  in  solution.  The  liquid  after  fil- 
tration is  neutralized  by  carbonate  of  baryta,  which  throws  down  the  excess 
of  silicated  hydrofluoric  acid,  and  chlorate  of  baryta  is  left  in  solution.  By 
evaporation  it  yields  prismatic  crystals,  which  require  for  solution  four  times 
their  weight  of  cold,  and  a  still  smaller  quantity  of  hot  water.  They  are 
composed  of  76*7  parts  or  one  eq.  of  baryta,  75'42  or  one  eq.  of  chloric  acid, 
and  9  or  one  eq.  of  water. 

Perchlorates. — The  neutral  protosalts  of  perchloric  acid  consist  of  one  eq. 
of  acid  and  base,  as  is  expressed  by  the  formula  MO-f-ClO7.  Most  of  these 
salts  are  deliquescent,  very  soluble  in  water,  and  soluble  in  alcohol :  four  only 
were  found  by  Serullas  to  be  not  deliquescent, — the  perchlorates  of  potassa, 
ammonia,  protoxide  of  lead,  and  protoxide  of  mercury.  When  heated  to 
redness  they  yield  oxygen  gas  and  metallic  chlorides ;  and  they  are  distin- 
guished from  the  chlorates  by  not  acquiring  a  yellow  tint  on  the  addition  of 
hydrochloric  acid.  The  perchlorate  of  potassa  is  prepared  from  the  chlorate 
by  the  action  of  heat  and  sulphuric  acid,  as  already  mentioned.  (Page  219.) 
It  is  the  most  insoluble  of  the  perchlorates,  and  on  this  account  perchloric 
acid  precipitates  potassa  from  its  salts,  being  a  test  of  about  the  same  deli- 
cacy as  tartaric  acid.  The  other  perchlorates  are  made  by  neutralizing  the 
base  with  perchloric  acid.  The  solubility  in  alcohol  of  the  perchlorates  of 
baryta,  soda,  and  oxide  of  silver  is  a  property  which  the  analytical  chemist 
may  avail  himself  of  in  analysis  for  the  separation  of  potassa  and  soda  from 
each  other. 

CHLORITES. 

The  alkaline  salts  of  chlorous  acid  are  readily  made,  as  mentioned  at  page 
219,  by  transmitting  a  current  of  chlorous  acid  gas  into  a  solution  of  the 
pure  alkalies.  All  that  have  as  yet  been  examined  are  soluble  in  water,  and 
are  remarkable  for  their  high  bleaching  and  oxidizing  properties.  By  the 
latter  properties  and  the  evolution  of  chlorous  acid  on  the  addition  or  any 
of  the  stronger  acids,  their  presence  is  readily  recognized. 

Hypochlorites. — The  hypochlorites  may  be  produced  by  the  action  of  chlo- 
rine gas  on  the  salifiable  bases.  The  most  important  of  them  is  the  hypo- 
chlorite  of  lime,  the  well-known  bleaching  powder,  which  has  commonly  been 
described  as  the  oxy muriate  or  chloride  of  lime.  It  is  prepared  for  com- 
mercial purposes  by  exposing  thin  strata  of  recently  slaked-lime  in  fine  pow- 
der to  an  atmosphere  of  chlorine.  The  gas  is  absorbed  in  large  quantity, 
and  chloride  of  calcium  and  hypochlorite  of  lime  are  produced  in  equivalent 
proportions. 

It  is  a  dry  white  powder,  which  smells  faintly  of  chlorine,  and  has  a  strong 
taste.  It  dissolves  partially  in  water,  and  the  solution  possesses  powerful 
bleaching  properties,  and  contains  both  chlorine  and  lime ;  while  the  undis- 
solved  portion  is  hydrate  of  lime,  retaining  a  small  quantity  of  chlorine. 
The  aqueous  solution,  when  exposed  to  the  atmosphere,  is  gradually  decom- 
posed ;  chlorine  is  set  free,  and  carbonate  of  lime  generated.  On  boiling  the 
liquid,  chloride  of  calcium  and,  I  presume,  chlorate  of  lime  are  formed ;  and 
by  long  keeping,  the  dry  chloride  appears  to  undergo  a  similar  change, — at 
least  chloride  of  calcium  is  produced  in  large  quantity.  It  is  also  decom- 
posed by  a  strong  heat :  at  first,  chlorine  is  evolved  ;  but  pure  oxygen  is 
afterwards  disengaged,  and  chloride  of  calcium  remains  in  the  retort. 

The  composition  of  chloride  of  lime  was  first  carefully  investigated  by 


IODATES.  437 

Dalton,*  and  it  has  since  been  analyzed  by  Thomson,t  Welter,:}:  and 
Ure.§  The  three  first-mentioned  chemists  infer  from  their  researches 
that  bleaching1  powder  is  a  hydrated  subchloride  or  dichloride  of  lime, 
in  which  one  equivalent  of  chlorine  is  united  with  two  equivalents  of 
lime.  They  are  also  of  opinion,  that  on  mixing  this  dichloride  with 
water,  the  chloride  is  dissolved,  and  one  equivalent  of  lime  separated  as  an 
insoluble  powder.  Dr.  Ure,  on  the  contrary,  denies  that  bleaching  powder 
is  a  dichloride,  and  maintains  that  the  elements  of  this  powder  do  not  con- 
stitute a  regular  atomic  combination.  He  found  that  the  quantity  of  chlo- 
rine absorbed  by  hydrate  of  lime  is  variable,  depending  not  only  on  the  pres- 
sure and  degree  of  exposure,  but  on  the  quantity  of  water  present.  From 
these  experiments  it  appears  that  the  commercial  bleaching  powder  is  essen- 
tially a  hypochlorite  with  single  equivalents  of  its  elements,  but  mixed  with 
variable  quantities  of  hydrate  of  lime. 

Several  methods  have  been  proposed  for  estimating  the  value  of  different 
specimens  of  bleaching  powder.     Perhaps  the  most  convenient  for  the  artist 
is  that  of  Welter,  which  consists  in  ascertaining  the  power  of  the  bleaching 
liquid  to  deprive  a  solution  of  indigo  of  known  strength  of  its  colour;  and 
directions  have  been  drawn  up  by  Gay-Lussac  for  enabling  manufacturers  to 
employ  this  method  with  accuracy.  (Annals  of  Philosophy,  xxiv.  218.)     For 
analytical  purposes,  the  best  method  is  to  decompose  chloride  of  lime,  con. 
fined  in  a  glass  tube  over  mercury,  by  means  of  hydrochloric  acid.   Chloride   I 
of  calcium  is  generated,  and  the  chlorine  being  set  free,  its  quantity  may   ; 
easily  be  measured. 

IODATES. 

From  the  close  analogy  in  the  composition  of  chloric  and  iodic  acids,  it 
follows  that  the  general  character  of  the  iodates  must  be  similar  to  that  of 
the  chlorates.  Thus  in  all  neutral  protiodates  the  oxygen  contained  in  the 
oxide  and  acid  is  in  the  ratio  of  1  to  5.  They  form  deflagrating  mixtures 
with  combustible  matters ;  and  on  being  heated  to  low  redness,  oxygen  gas 
is  disengaged  and  a  metallic  iodide  remains.  As  the  affinity  of  iodine  for 
metals  is  less  energetic  than  that  of  chlorine,  many  of  the  iodates  part  with 
iodine  as  well  as  oxygen  when  heated,  especially  if  a  high  temperature  is 
employed. 

The  iodates  are  easily  recognized  by  the  facility  with  which  their  acid  is 
decomposed  by  deoxidizing  agents.  Thus,  the  sulphurous,  phosphorous,  hy- 
drochloric, and  hydriodic  acids  "deprive  iodic  acid  of  its  oxygen,  and  set 
iodine  at  liberty.  Hydrosulphuric  acid  not  only  decomposes  the  acid  of  these 
salts,  but  occasions  the  formation  of  an  iodide  of  the  metal  in  the  base. 
Hence  iodate  of  potassa  may  be  converted  into  iodide  of  potassium  by  trans- 
mitting a  current  of  hydrosulphuric  acid  gas  through  its  solution.  None  of  the 
iodates  have  been  found  native.  They  are  all  of  very  sparing  solubility,  or 
actually  insoluble  in  water,  excepting  the  iodates  of  the  alkalies. 

Iodate  of  Potassa. — This  salt  may  be  procured  by  adding  iodine  to  a  con- 
centrated hot  solution  of  pure  potassa,  until  the  alkali  is  completely  neutra. 
lized.  The  liquid,  which  contains  an  iodate  and  iodide  (page  229),  is  evapor 
rated  to  dryness  by  a  gentle  heat,  and  the  residue,  when  cold,  is  treated  by 
repeated  portions  of  boiling  alcohol.  The  iodate,  which  is  insoluble  in  that 
menstruum,  is  left,  while  the  iodide  of  potassium  is  dissolved.  A  better  pro- 
cess has  been  recommended  by  M.  Henry,  jun.,  founded  on  the  property 
which  iodide  of  potassium  possesses,  of  absorbing  oxygen  while  in  the  act  of 
escape  from  decomposing  chlorate  of  potassa.  For  this  purpose  iodide  of 
potassium  is  fused  in  a  capacious  Hessian  crucible,  and  when,  after  removal 
from  the  fire,  it  is  yet  semi-fluid,  successive  portions  of  pulverized  chlorate 
of  potassa  are  projected  into  it,  stirring  well  after  each  addition.  The  ma» 

*  Annals  of  Philosophy,  i.  15,  and  ii,  6.        t  Ibid,  xv.  401. 
f  Ann.  de  Ch.  et  Ph.  vol.  viii.  §  Quarterly  Journal,  xui<  I; 

37* 


438  BROMATES. — PHOSPHATES. 

lerials  froth  up  considerably,  and  when  the  action  is  over,  a  white,  opaque, 
cellular  mass  remains,  easily  separable  from  the  crucible :  tepid  water  dis- 
solves  out  the  chloride  of  potassium,  and  leaves  the  iodate.  Convenient  pro- 
portions are  one  part  of  iodide  of  potassium,  and  rather  more  than  one  and  a 
half  of  chlorate  of  potassa.  (Journ.  de  Pharmacie,  July  1832.) 

All  the  insoluble  iodates-may  be  procured  from  this  salt  by  double  decom- 
position. Thus  iodate  of  baryta  may  be  formed  by  mixing  chloride  of  barium 
with  a  solution  of  iodate  of  potassa. 

A  biniodate  of  potassa  has  been  described  by  Serullas.  It  is  formed  by 
incompletely  neutralizing  a  hot  solution  of  chloride  of  iodine  with  potassa  or 
its  carbonate,  and  setting  it  aside  to  cool.  A  peculiar  compound  of  chloride 
of  potassium  and  biniodate  of  potassa  falls  ;  but  on  dissolving  this  substance, 
filtering,  arid  exposing  the  solution  to  a  temperature  of  77°,  the  biniodate  is 
gradually  deposited  in  right  rhombic  prisms,  terminated  by  dihedral  sum- 
mits. It  is  soluble  in  75  times  its  weight  of  water  at  59°. 

A  teriodate  may  be  formed  by  mixing  a  large  "excess  of  sulphuric  acid 
with  a  moderately  dilute  solution  of  iodate  of  potassa.  On  evaporating  at 
77°,  the  teriodate  is  deposited  in  regular  rhomboidal  crystals,  which  require 
25  times  their  weight  of  water  at  60°  for  solution. 

Serullas  states  that  the  compound  of  chloride  of  potassium  and  biniodate 
of  potassa,  above  mentioned,  may  be  formed  by  the  action  of  hydrochloric 
acid  on  iodate  of  potassa.  By  spontaneous  evaporation  it  is  obtained,  some- 
times in  brilliant,  transparent,  elongated  prisms,  and  at  other  limes  in  hexa- 
gonal laminae;  but  generally  it  crystallizes  in  right  quadrangular  prisms 
with  their  lateral  edges  truncated,  und  terminated  by  four-sided  summits. 
(An.  de  Ch.  et  de  Ph.  xliii.  113.) 

BROMATES. 

These  compounds  have  many  characters  in  common  with  the  chlorates 
artd  iodates ;  but  hitherto  they  have  been  but  partially  examined. 

PHOSPHATES. 

In  studying  these  salts,  the  reader  must  bear  in  mind  that  there  are 
three  isomeric  modifications  of  the  same  acid,  which  have  been  described 
under  the  names  of  phosphoric,  pyrophosphoric,  and  meta phosphoric  acid  (page 
201);  and,  therefore,  it  will  be  necessary  to  have  three  corresponding  fami- 
lies of  salts,  the  phosphates,  pyrophosphates,  and  met  a  phosphates.  This  dis- 
tinction, and  the  other  facts  lately  recorded  by  Graham,  render  it  necessary 
either  to  change  the  names  of  the  phosphates,  or  to  retain  their  old  names 
in  opposition  to  the  principles  of  nomenclature.  The  most  consistent  con- 
duct will  be  to  describe  each  salt  under  its  scientific  name,  and  add  at  the 
same  time  its  ordinary  one.  An  eq.  of  each  of  the  three  acids  is  a  com- 
pound of  314  parts  or  two  eq.  of  phosphorus-J-40  parts  or  five  eq.  of  oxygen 
=714,  expressed  by  the  formula  PflQs.  To  form  a  salt  neutral  in  composi- 
tion, one  eq.  of  an  alkaline  base  is  requisite;  and  in  the  case  of  any  protox- 
ide, indicated  by  MO,  the  general  formula  will  be  MO-4-P2O5.  If  two  eq. 
of  a  protoxide  are  united  with  one  of  the  acid,  we  have  a  disaU,  2MO-J-P3 
O5;  and  if  three  eq.  of  a  base  combine  with  one  eq.  of  the  acid,  it  is  a  tri- 
salt,  3MO-^-P3O5.  It  seems  also  that  water  plays  the  part  of  an  alkaline 
base  towards  each  of  the  three  acids,  either  alone  or  conjointly  with  another 
base.  The  salts  with  such  compound  bases  can  scarcely  be  viewed  in  the 
light  of  double  salts  (pages  202  and  203) ;  since  the  two  bases  act  together 
as  one  electro-positive  element 

All  the  protophosphates  which  are  neutral  in  composition  are  soluble  in 
water,  and  redden  litmus  paper;  whence  they  are  commonly  called  super- 
phosphates. The  tri phosphates,  except  those  of  the  pure  alkalies,  are  either 
sparingly  soluble  or  insoluble  in  water ;  but  they  are  all  dissolved  by  dilute  ni- 
tric or  phosphoric  acid,  being  converted  into  the  soluble  phosphates.  All  the 
triphospkates  with  fixed  and  strong  bases  bear  a  red  heat  without  change;  but 


PHOSPHATES. 


439 


the  phosphates  and  di  phosphates,  to  judge  from  experiments  on  the  soda 
salts,  are  converted  into  metaphosphales  and  pyrophosphates.  Most  of  the 
phosphates  of  the  second  class  of  metals  are  resolved  into  phosphurets  by 
the  conjoint  agency  of  heat  and  combustible  matter.  The  phosphates  of  the 
alkalies  are  only  partially  decomposed  under  these  circumstances,  and  the 
phosphates  of  baryta,  strontia,  and  lime  undergo  no  change. 

The  presence  of  a  soluble  phosphate  may  be  distinguished  by  the  tests 
already  mentioned  (page  203)  for  phosphoric  acid.  The  insoluble  phosphates 
are  decomposed  when  boiled  with  a  strong  solution  of  carbonate  of  potassa 
or  soda,  the  acid  uniting  with  the  alkali  so  as  to  form  a  soluble  phosphate: 
the  earthy  phosphates,  indeed,  are  decomposed  with  difficulty,  requiring  con- 
tinued ebullition,  and  should  preferably  be  fused  with  an  alkaline  carbonate, 
like  an  insoluble  sulphate. 

Several  phosphates  are  met  with  in  nature,  such  as  those  of  lime,  alumina, 
and  the  oxides  of  manganese,  iron,  uranium,  copper,  and  lead. 

The  composition  of  the  principal  phosphates  is  given  in  the  following 
table  :  — 


Names.                    Base. 

Acid. 

Equiv. 

Formulae. 

Triphos.  soda        -          93-9     3  eq.     -J-  71-4 
Do.  in  crystals  with  216  or  24  eq.  of  water 

leq.=165-3    3NaO  +  paO5, 
=381-3 

Triphos.  soda  )  «    ,          />0  ~ 
r  i     ,          f  feoda        v&'u 

wlr^lw^       9 

?:qq:(+T1-4 

leq.=143    < 

2NaO.HO 

Do.  in  crystals  with  216  or 

24  eq.  of  water 

=359 

Do.        -        -           126  or 

14  eq.  of  water 

=269 

Acid    triphos.  i  «   ,         g    . 

A            A  k        V  OOUd           OL  O 

soua  ana  Da-  /•  TTT  ,        -.  0 
i  W  ater    lo 

2^:|+71'4 

1  eq.=120-7  ) 

NaO,2HO 

Do.  in  crystals  with  18  or 

2  eq.  of  water 

=138-7 

Triphos.  potassa    -         141-45 

3eq.     +71-4 

1  eq.=212-85 

3KO-fP2O5, 

Triphos_potas.Jp 
wate"^    *{*««•«      9 

i%fe* 

1  eq.=174-7) 

2KO.HO 
-I-P2O5. 

Acid  triphos.  1  Potassa  47.15 
pkwaTerS^161-    18 

1  eq.  f    -  7-1  ,j 
2eq.^+714 

1  eq.  =136-55  < 

KO,2HO 

Triphos.  soda"j  ^    i          qi.q 

i  e     1 

f 

ox.  ammo-  1  Q°  a        Ofi.i  5 

1  eq.'  i  +71-4 

1 
1  eq.=137'85^ 

NaO,H4NO, 
HO4-P2Q5 

basic  water  j 

leq.J 

1 

Do.  in  crystals  with  72  or 

8  eq.  of  water 

^20985 
/ 

TriPh°Sl  "x:    Ox.  am.    52-3     2  eq. 


Bone-phos.  lime 
Triphos.  lime 
Triphos    lime 

water 


wte 


2H4NO-HO 


8Ca04-3P2Q5. 
3CaO4-P2O5. 

2CaO.HO 


CaO,2HO 
+P2Q5. 


The  triphosphate  of  baryta,  strontia,  and  of  the  protoxides  of  manganese, 
iron,  copper,  lead,  silver,  &c.  precisely  correspond  to  the  triphosphate  of 


440  PHOSPHATES. 

lime,  simply  substituting1  three  eq.  of  those  oxides.  These  oxides  in  like 
manner  form  soluble  phosphates  analogous  in  composition  to  that  of  lime. 

Triphosphate  of  Soda. — This  salt,  described  by  Graham  as  the  subsesqui- 
phosphate,  is  made  by  adding  pure  soda  to  a  solution  of  the  succeeding  com- 
pound until  the  liquid  feels  soapy  to  the  fingers,  an  excess  of  soda  not  being 
injurious.  The  liquid  is  then  evaporated  until  a  pellicle  appears,  and  the 
crystals  which  form  on  cooling  are  quickly  redissolved  in  water  and  recrys- 
tallized.  Though  the  crystals  do  not  change  in  the  air,  the  solution  absorbs 
carbonic  acid,  and  the  resulting  carbonate  of  soda  adheres  to  the  triphos- 
phate. 

This  salt  crystallizes  in  colourless  six-sided  slender  prisms,  which  have  a 
strong  alkaline  taste  and  reaction,  require  5  times  their  weight  of  water  at 
60°,  and  still  less  of  hot  water,  for  solution,  and  at  170°  fuse  in  their  water 
of  crystallization.  They  may  be  exposed  to  a  red  heat  without  losing  the 
characters  of  a  phosphate.  The  feeblest  acids  deprive  the  salt  of  one-third  of 
its  soda. 

When  this  salt  is  mixed  in  solution  with  nitrate  of  oxide  of  silver  in  ex- 
cess, there  is  an  exact  interchange  of  elements,  such  that 

1  eq.  triphosphate  of  soda  and  3  eq.  nitrate  of  silver 
3NaO-HP2Q5  3(AgO  4.  NQ5) 

yield 

1  eq.  triphos.  of  silver  and  3  eq.  nitrate  of  soda. 
3  AgO  -f.  P2Q5  3(NaO  -j-  NQ5). 

The  resulting  solution  is,  therefore,  quite  neutral.  The  triphosphate  of 
oxide  of  lead,  and  other  insoluble  triphosphates,  may  be  prepared  in  like 
manner. 

Triphosphate  of  Soda  and  Basic  Water. — This  salt  is  the  most  common  of 
the  phosphates,  being  manufactured  on  a  large  scale  by  neutralizing  with 
carbonate  of  soda,  the  acid  phosphate  of  lime  procured  by  the  action  of  sul- 
phuric acid  on  burned  bones  (p.  198).  It  is  generally  described  as  the  neu- 
tral phosphate  of  soda,  and  for  distinction's  sake  is  sometimes  termed 
.rhombic  phosphate,  from  its  crystals  having  the  form  of  oblique  rhombic 
prisms. 

This  salt  crystallizes  best  out  of  an  alkaline  solution ;  but  however  pre- 
pared, it  is  always  alkaline  to  test  paper,  and  requires  a  considerable  quantity 
of  acid  before  losing  its  alkalinity.  The  crystals  effloresce  on  exposure  to  the 
air,  and  require  four  times  their  weight  of  cold,  and  twice  their  weight  of 
hot  water  for  solution.  It  often  contains  traces  of  sulphuric  acid,  from  which 
it  may  be  purified  by  repeated  solution  and  crystallization.  When  mixed 
with  nitrate  of  oxide  of  silver,  the  interchange  of  elements  is  such  that 

1  eq.  rhombic  phosphate  and  3  eq.  nitrate  of  silver 
2NaO.HO-r-P2O5  3(AgO  +  NQ5) 

yield 

1  eq.  triphosphate  of  silver  and  2  eq.  nitrate  of  soda. 
3  AgO-f  P2Q5  2(NaO  +  NO5). 

The  yellow  triphosphate  of  oxide  of  silver  falls  exactly  as  with  the  former 
salt,  but  one  eq.  of  nitric  acid  is  left  free  in  the  solution. 

When  a  solution  of  the  rhombic  phosphate  is  evaporated  at  a  temperature  of 
90°,  it  crystallizes  with  fourteen  instead  of  twenty-four  equivalents  of  water, 
and  the  crystals  differ,  as  might  be  expected,  from  the  other  salt  in  figure, 
and  are  permanent  in  the  air.  Both  salts  lose  their  basic  water  at  a  red  heat, 
and  are  converted  into  a  pyrophosphate. 

Acid  Triphosphate  of  Soda  and  Water. — This  salt,  commonly  called 
biphosphate  of  soda  from  its  acid  reaction,  may  be  formed  by  adding  phos- 
phoric acid  to  a  solution  of  carbonate  of  soda,  or  to  either  of  the  preceding 
phosphates,  until  it  ceases  to  give  a  precipitate  with  chloride  of  barium.  Be 
ing  very  soluble  in  water,  the  solution  must  be  concentrated  in  order  that  it 
may  crystallize.  This  salt  is  capable  of  yielding  two  different  kinds  of  crys- 


PHOSPHATES.  441 

tals  without  varying  its  composition.  The  more  unusual  form,  isomorphous 
with  binarscniate  of  soda,  is  a  right  rhombic  prisrn,  the  smaller  lateral  edge 
of  which  is  78°  30',  terminated  by  pyramidal  planes.  The  form  of  its  ordi- 
nary crystals  is  a  right  rhombic  prism,  the  larger  angle  of  which  is 
93o  54'. 

The  crystals  of  this  salt  consist,  as  stated  at  page  439,  of  NaO,2HO.P O 
-J-2HO.  When  heated  to  212°,  the  water  of  crystallization  is  expelled,  and 
the  anhydrous  salt  remains,  still  yielding  a  yellow  precipitate  with  silver 
when  neutralized  by  ammonia ;  but  if  exposed  to  a  heat  of  400°,  it  loses  half 
its  basic  water,  being  reduced  to  NaO.HO,P9Os,  and  has  the  character  of 
acid  dipyrophosphate  of  soda  and  water.  At  a  red  heat  it  is  converted  into 
metaphosphate  of  soda. 

Triphosphate  of  Potassa. — Groharn  formed  this  salt  by  adding  caustic  po- 
tassa  in  excess  to  a  solution  of  phosphoric  acid,  as  well  as  by  fusing  phos- 
phoric acid  with  a  slight  excess  of  carbonate  of  potassa.  He  obtained  it  in 
acicular  crystals,  which  were  very  soluble  in  water  but  not  deliquescent. 

Triphosphate  of  Potassa  and  Basic  Water. — This  salt  may  be  prepared 
by  neutralizing  the  superphosphate  of  lime  from  bones  with  carbonate  of 
potassa.  It  is  deliquescent,  and  has  not  been  obtained  in  regular  crystals. 

Acid  Triphosphate  of  Potassa  and  Basic  Water  may  be  formed  by  adding 
phosphoric  acid  to  carbonate  of  potassa  until  the  liquid  ceases  to  give  a  pre- 
cipitate with  chloride  of  barium,  and  setting  it  aside  to  crystallize.  The 
crystals  belong  to  the  square  prismatic  system,  and  usually  occur  in  square 
prisms  terminated  by  the  planes  of  an  octohedron.  They  are  acid  to  test 
paper. 

When  this  compound  is  nentralized  by  carbonate  of  soda,  and  the  solution 
set  to  crystallize,  a  phosphate  of  soda  and  potassa  is  deposited  in  crystals,  the 
form  of  which  is  an  oblique  rhombic  prism,  which  frequently  occurs  without 
any  modification. 

Triphosphate  of  Soda,  Oxide  of  Ammonium,  and  Basic  Water. — This  salt  is 
easily  prepared  by  mixing  together  one  eq.  of  hydrochlorate  of  ammonia  and 
two  eq.  of  the  rhombic  phosphate  of  soda,  each  being  previously  dissolved  in 
a  small  quantity  of  boiling  water.  As  the  liquid  cools,  prismatic  crystals  of 
the  double  phosphate  are  deposited,  while  chloride  of  sodium  remains  in  so- 
lution. Their  form  is  an  oblique  rhombic  prism.  This  salt  has  been  long 
known  by  the  name  of  microcosmic  salt,  and  is  much  employed  as  a  flux  in 
experiments  with  the  blowpipe.  When  heated  it  parts  with  its  water  and 
ammonia,  and  a  very  fusible  metaphosphate  of  soda  remains. 

Triphosphate  ofOxiHe  of  Ammonium  and  Basic  Water. — This  salt  is  formed 
by  adding  ammonia  to  concentrated  phosphoric  acid  until  a  precipitate  ap- 
pears. On  applying  heat,  the  precipitate  is  dissolved,  and  on  abandoning  the 
solution  to  itself,  the  neutral  salt  crystallizes.  The  form  of  the  crystals  is  an 
oblique  rhombic  prism,  the  smaller  angle  of  which  is  84°  30'.  They  often 
occur  in  rhombic  prisms  with  dihedral  summits.  (Mitscherlich.) 

The  acid  triphosphate  is  made  in  the  same  manner  as  the  acid  triphosphate  of 
potassa.  The  crystals  are  less  soluble  than  the  preceding  salt,  and  undergo 
no  change  on  exposure  to  the  air.  Their  form  is  an  octohedron  with  a 
square  base;  but  the  right  square  prism,  terminated  by  the  faces  of  the  octo- 
hedron, is  the  most  frequent. 

Phosphates  of  Lime. — The  peculiar  compound  called  the  bone-phosphate, 
exists  in  bones  after  calcination,  and  falls  as  a  gelatinous  precipitate  on 
pouring  chloride  of  calcium  into  a  solution  of  the  rhombic  phosphate  of 
soda,  or  on  adding  ammonia  to  a  solution  of  any  phosphate  of  lime  in  acids. 

Triphosphate  of  Lime  cannot  be  formed  by  precipitation,  but  occurs  in 
hexagonal  prisms  in  the  mineral  called  apatite. 

Triphosphate  of  Lime  and  Basic  Water,  commonly  called  neutral  phos- 
phate, falls  as  a  granular  precipitate,  consisting  of  fine  crystalline  particles, 
when  the  rhombic  phosphate  of  soda  is  added  in  solution  drop  by  drop  to 
chloride  of  calcium  in  excess.  The  residual  liquid  reddens  litmus,  owing  to 
a  small  quantity  of  triphosphate  of  lirne  being  generated. 


442  PYROPHOSPHATES. 

Acid  Triphosp/iate  of  Lime  and  Basic  Water,  called  the  biphosphate  from 
its  acid  reaction,  is  formed  by  dissolving  either  of  the  preceding  salts  in  a 
slight  excess  of  phosphoric  acid.  The  compound  is  deliquescent,  very  solu- 
ble, and  crystallizes  with  great  difficulty.  It  exists  in  the  urine.  The  solu- 
tion formed  by  the  action  of  sulphuric  acid  on  bones  is  probably  a  com- 
pound of  lime  with  two  or  more  eq.  of  phosphoric  acid,  being  really  a 
superphosphate. 

Triphosphate  of  Magnesia  and  Basic  Water. — It  is  formed  by  mixing 
together  hot  saturated  solutions  of  the  rhombic  phosphate  of  soda  and  sul- 
phate of  magnesia,  and  separates  on  cooling  in  small  crystals  which  contain 
thirteen  eq.  of  water  to  one  of  the  salt.  The  triphosphate  of  magnesia  is  princi- 
pally formed  when  the  solutions  are  intermixed  in  the  cold.  These  salts 
have  been  but  little  examined. 

The  phosphate  of  ammonia  and  magnesia  subsides  as  a  pulverulent  granular 
precipitate  from  neutral  or  alkaline  solutions,  containing  phosphoric  acid, 
ammonia,  and  magnesia.  It  is  readily  dissolved  by  acids,  and  is  sparingly 
soluble  in  pure  water,  especially  when  carbonic  acid  is  present;  but  it  is  in 
soluble  in  a  solution  of  most  neutral  salts,  such  as  hydrochlorate  of  ammonia. 
It  constitutes  one  variety  of  urinary  concretions.  According  to  Berzelius  it 
consists  of 

Phosphoric  acid            -  -  71-4.  1  eq.  PO*. 

Magnesia             -         -  -  41-4  2  eq.  2MgO. 

Ammonia            -        -  -  34-3  2  eq.  2H3N. 

Water              .:*•'-  -  90  10  eq.  10HO. 

The  mode  in  which  these  elements  are  arranged  is  unknown.  When 
heated  to  redness  it  loses  its  water  and  ammonia,  and  the  residue  is  diphos- 
phate  of  magnesia,  which  contains  36-67  per  cent,  of  pure  magnesia.  At  a 
strong  red  heat  it  fuses,  and  appears  when  cold  as  a  white  enamel. 

When  the  materials  for  forming  the  preceding  salt  are  mixed  while  hot, 
small  acicular  crystals  subside  on  cooling,  which  are  said  by  Berzelius  to 
contain  less  of  the  two  bases  than  the  other  salt. 

Phosphates  of  Protoxide  of  Lead. — The  triphosphate  is  precipitated  when 
acetate  of  protoxide  of  lead  is  mixed  with  a  solution  of  the  rhombic  ^phos- 
phate of  soda,  acetic  acid  being  set  free.  The  triphosphate  with  basic  water 
is  best  formed  by  adding  the  rhombic  phosphate  of  soda  gradually  to  a  hot 
solution  of  chloride  of  lead.  The  nitrate  should  not  be  used  for  the  purpose, 
as  it  combines  with  the  precipitate.  Both  these  phosphates  are  white,  and 
are  frequently  formed  at  the  same  time.  The  latter  fuses  readily  into  a  yel- 
low bead,  which  in  cooling  acquires  crystalline  facettes. 

Triphosphate  of  Oxide  of  Silver. — This  compound  subsides,  of  a  charac- 
teristic yellow  colour  (page  203,)  when  the  rhombic  phosphate  of  soda  is 
mixed  in  solution  with  nitrate  of  oxide  of  silver,  nitric  acid  being  set  free  at 
the  same  time.  It  is  apt  to  retain  some  of  the  nitrate  in  combination.  This 
salt  is  very  soluble  in  nitric  and  phosphoric  acid,  forming-  the  soluble  phos- 
phate,, and  in  ammonia.  By  exposure  to  light  it  is  speedily  blackened ;  but 
when  protected  from  this  agent,  it  yields  on  drying  an  anhydrous  yellow 
powder,  which  has  a  sp.  gr.  of  7-321  (Stroymeyer.)  Its  colour  changes  on 
the  application  of  heat  to  a  reddish-brown,  but  its  original  tint  returns  on 
cooling.  It  bears  a  red  heat  without  fusion  :  at  a  white  heat  it  fuses,  and  if 
kept  for  some  time  in  a  fused  state,  a  portion  of  pyrophosphate  is  generated. 

PYROPHOSPHATES. 

The  discovery  of  these  salts  by  Clarke  has  also  been  mentioned  (page  203.) 
That  modification  of  phosphoric  acid,  termed  pyrophosphoric  acid,  is  procured 
by  forcing,  with  the  aid  of  heat,  phosphoric  acid  to  combine  with  two  eq. 
either  of  water  or  some  fixed  base.  The  only  pyro  phosphates  which  have  as  yet 


METAPHOSPHATES.  443 

been  studied  are  those  of  soda  and  oxide  of  silver.    These  salts  are  thus 
constituted : — 

Names.                    Base.                    Acid.          Equiv.  Formulae. 

Dipyrophos.  soda                 62-6       2  eq.     +71-4  1  eq.  =134  2NaO+P2Q5. 

Do.     in  crystals  with  90  or  10  eq,  of  water  =224 

Acid 1  dipyrophos.  )  goda     31>3      l        J  )  NaO,HO 

water"  \ Water     9         l  e*  \  "^          \         ™ 

Pyrophos.  soda  -        31-3      1  eq.     4-71-4  1  eq.=102-7 

Dipyrophos.  oxide  silver  232         2  eq.     4. 71-4  1  eq.  =303-4 

Dipyrophosphate  of  Soda. — This  is  the  compound  first  prepared  by  Clarke 
from  the  rhombic  phosphate  (page  203,)  by  expelling  its  basic  water.  When 
the  residual  mass  is  dissolved  in  water  and  set  to  evaporate,  crystals  are  ob- 
tained, having  the  outline  of  an  irregular  six-sided  prism,  derived  from  a 
rhombic  prism.  These  crystals  are  permanent  in  the  air,  much  less  soluble 
in  water  than  the  original  rhombic  phosphate,  and  quite  neutral  to  test  paper. 
Ignited  with  carbonate  of  soda,  a  phosphate  is  reproduced,  because  the  acid 
is  forced  to  unite  with  three  eq.  of  a  base. 

Dipyrophosphate  of  soda  is  permanent  both  in  crystals  and  in  solution  in 
the  cold ;  but  by  long  boiling,  or  quickly  when  boiled  with  an  acid,  a  phos- 
phate is  reproduced.  With  a  salt  of  lead  it  yields  a  white  dipyrophosphate 
of  protoxide  of  lead;  and  on  washing  the  precipitate  and  decomposing  by  hy- 
drosulphuric  acid  gas,  a  solution  of  pyrophosphoric  acid  is  obtained,  which 
again  forms  dipyrophosphate  of  soda  when  neutralized  with  soda. 

The  oxides  of  most  metals  of  the  second  class  yield  with  pyrophosphoric 
acid  insoluble  or  sparingly  soluble  salts,  which  may  be  prepared  by  double 
decomposition  with  dipyrophosphate  of  soda.  It  should  be  held  in  view, 
however,  as  Stromeyer  has  remarked,  that  most  of  these  salts  are  more  or 
less  soluble  in  an  excess  of  dipyrophosphate  of  soda;  and  that  some  of  them, 
such  as  the  dipyrophosphate  of  the  oxides  of  lead,  copper,  nickel,  cobalt, 
uranium,  bismuth,  manganese,  and  mercury,  are  dissolved  by  it  with  great 
facility. 

Acid  Dipyrophosphate  of  Soda  and  Water. — This  salt  is  formed  by  expos- 
ing, as  stated  at  page  441,  the  acid  triphosphate  to  a  heat  of  400°,  when  it 
loses  one-half  of  its  basic  water,  and  acquires  the  character  of  a  pyrophos- 
phate.  This  salt  dissolves  readily  in  water,  has  an  acid  reaction,  and  has  not 
been  obtained  in  crystals. 

Pyrophosphate  of  Soda. — When  the  preceding  salt,  NaO,HO-f-P2O5,  is- 
heated  to  600°  or  a  little  higher,  it  loses  its  basic  water,  and  yet  the  acid 
does  not  lose  the  character  of  pyrophosphoric  acid.  It  is  left,  therefore,  as 
a  simple  pyrophosphate  of  soda,  NaO-f-P2O5.  On  adding  water,  part  of  it 
dissolves,  and  part  is  left  as  an  insoluble  white  powder.  The  solution  is 
quite  neutral  to  test  paper ;  but  on  adding  nitrate  of  oxide  of  silver,  the  dipy- 
rophosphate of  that  oxide  falls,  and  free  nitric  acid  remains  in  solution.  The 
soluble  and  insoluble  pyrophosphate  of  soda  appear  identical  in  composition, 
and  the  former  at  a  heat  just  short  of  redness  may  be  wholly  converted  into 
the  latter. 

Dipyrophosphate  of  Oxide  of  Silver. — This  salt  is  readily  formed  by  double 
decomposition  between  dipyrophosphate  of  soda  and  nitrate  of  oxide  of 
silver,  the  residual  liquid  being  quite  neutral  to  test  paper.  It  falls  as  a 
snow-white  granular  precipitate,  which  fuses  readily  at  a  heat  short  of  incan- 
descence into  a  dark  brown  liquid,  which  becomes  a  crystalline  enamel  on 
cooling. 

METAPHOSPHATES. 

The  only  metaphosphates  which  have  yet  been  examined,  are  those  of 
jsoda,  baryta,  and  oxide  of  silver,  which  are  thus  constituted  : — 


444  ARSENIATES. 

Names.  Base.                  Acid.             Equiv.       Formulae. 

Metaphosphateofsoda  31-3     1  eq.-f   71'4  1  eq.=  102-7     NaO-J-PaO. 

baryta  76-7     1  eq.-f   714  1  eq.=  148-1 

oxide  of  silver  116        1  eq.-j-   71-4  1  eq.=187-4 

SubmetaphoB.  of  ox.  of  j  34g        3  eq  +  ^  2  eqi=490.8 

Metaphosphate  of  Soda. — When  the  pyrophosphate  or  acid  dipyrophosphate 
of  soda  is  heated  to  low  redness,  it  fuses,  and  on  cooling'  becomes  a  transpa- 
rent glass,  which  deliquesces  in  a  damp  air,  and  is  very  soluble.  The  solu- 
tion has  a  feeble  acid  reaction.  When  mixed  with  nitrate  of  oxide  of  silver, 
the  metaphosphate  of  that  oxide  falls  in  gelatinous  flakes,  wholely  unlike  the 
pyrophosphate,  and  aggregates  together  as  a  soft  solid  when  heated  to  near 
212°.  The  metaphosphate  of  soda  does  not  change  by  keeping,  and  has  not 
hitherto  been  made  to  crystallize.  When  its  solution  is  evaporated,  and  kept 
for  some  time  at  400°,  it  is  reconverted  into  the  acid  dipyrophosphate  of  soda 
and  basic  water.  All  the  preceding  facts  are  drawn  from  Graham's  essay. 
(Phil.  Trans.  1833,  Part  ii.) 

Metaphosphate  of  Baryta  falls  in  gelatinous  flakes,  on  adding  metaphos- 
phate of  soda  to  a  solution  of  chloride  of  barium,  the  latter  being  in  excess, 
as  the  soda  salt  dissolves  the  precipitate.  By  long  continued  boiling  meta- 
phosphate  of  baryta  is  at  length  dissolved,  and  at  the  same  time  converted 
into  a  phosphate. 

The  metaphosphate  of  silver  is  obtained  by  precipitation,  as  above  stated. 
When  put,  while  rnoist,  into  boiling  water,  part  of  its  acid  is  removed,  and 
the  submetaphosphate  is  generated. 

ARSENIATES. 

Arsenic  acid  resembles  the  phosphoric  in  composition  and  in  many  of  its 

'properties,  but  as  far  as  is  yet  known   is  only  capable  of  forming   tribasic 

salts.     Those  which  contain  two  eq.  of  basic  water  are,  like  the  phosphates, 

soluble  in  water  and  redden  litmus,  whence  they  are  commonly  considered 

>  as  bisalts.  If  only  one  eq.  of  basic  water  be  present,  in  which  case  the  oxygen 

/     of  the  alkaline  base  and  acid  is  as  2  to  5,  the  salt  is  usually  termed  a  neutral 

arseniate.     When  no  basic  water  is  present,  the  salt  is  usually  described  as 

a  subarseniate.     The  two  last  series  of  salts,  except  those  with  the  alkalies, 

are  of  sparing  solubility   in  water  ;    but  they  are  dissolved  by  phosphoric 

or  nitric  acid,  as  well  as  most  acids  which  do  not  precipitate  the  base  of  the 

salt. 

Many  of  the  arseniat.es  bear  a  red  heat  without  decomposition,  or  being 
otherwise  modified  in  their  characters ;  but  they  are  all  decomposed  when 
heated  to  redness  along  with  charcoal,  metallic  arsenic  being  set  at  liberty. 
The  arseniates  of  the  fixed  alkalies  and  alkaline  earths  require  a  rather  high 
temperature  for  seduction  ;  while  the  arseniates  of  the  second  class  of  metals, 
as  of  lead  and  copper,  are  easily  reduced  in  a  glass  tube  by  means  of  a 
spirit-lamp,  without  danger  of  melting  the  glass.  Of  all  the  arseniates  that 
of  protoxide  of  lead  is  the  most  insoluble. 

The  soluble  arseniates  are  easily  recognized  by  the  tests  described  in  the 
section  on  arsenic  (page  336) ;  and  the  insoluble  arseniates,  when  boiled  in 
a  strong  solution  of  the  fixed  alkaline  carbonates,  are  deprived  of  their  acid, 
which  may  then  be  detected  in  the  usual  manner.  The  free  alkali,  however, 
should  first  be  exactly  neutralized  by  pure  nitric  acid. 

The  arseniates  of  lime,  and  of  the  oxides  of  nickel,  cobalt,  iron,  copper, 
and  lead,  are  natural  productions. 

The  composition  of  the  principal  arseniates  is  contained  in  the  following 
table  :— 

Names.  Base.  Acid.  Equiv.        Formulae. 

Triarsen.  soda  93-9      3  eq-+115-4  1  eq.=209-3     3NaO-r-As3O5. 

Do.     in  crystals  with  21 6  or  24  eq.  of  water         =425-3 


ARSENIATES. 

Names.                     Base.                  Acid. 
Triarsen.  soda   )  Soda     62-6    2  eq.  J    ,  ^5.4 
&>  basic  water  \  Water    9       1  eq.  £  "• 
Do.     in  crystals  with  216  or  24  eq.  of  water 

1 

eq. 

Equiv. 
=  187 
=403 

445 

Formulae. 
S  2NaO.HO 

Do.     in  crystals  with  126  or  14  eq. 

of  water 

=313 

Acid  triarsen. 

( 

WaL 

31-3 

1 
2 

eq. 
eq. 

\ 

+  115-4 

1 

cq 

.=  164-7 

(  NaO,2HO 

Do.  in  crystals  with  18 

or 

2 

eq. 

of  water 

=182-7 

Triarsen.  potassa 

141-45 

3 

eq.+     115-4 

1 

eq.=  256-85    3KO  +  As2O5. 

Triarsen.  po- 
tassa   and 

Potassa 

94-3 

2 
i 

eq. 

J 

+  115-4 

1 

eq 

,-218-7 

\  2KO.HO 

basic  water     ' 

Water 

* 

JL 

efl. 

) 

f 

Acid  triarsen. 
potassa   and 
basic  water 

f  Potassa  47-15  1  eq. 

i 

+  115-4  leq.=180-55 

5  KO,2HO 
\  +As2O5. 

Triarsen.  ox. 
am'm    and 

?  Ox.  am.  52-3  2  eq. 

?  Wntpr         Q       1    f>n. 

+  115-4 

1 

eq. 

=  176-7 

S  2H4NO.HO 

basic  water 

} 

f 

Acid  triarsen. 
ox.  am'm  & 
basic  water 

I 

Ox.  am. 

Water 

26-15  leq- 
18      2eq- 

1 

+  115-4 

1 

eq 

.=159-55 

S  H4NO,2HO 
1  +As2O5. 

Triarsen.  baryta 

230-1 

3 

eq. 

+  115-4 

1 

eq 

.=345-5 

3BaO+As2O5. 

Triarsen.  bary- 
ta and    basic 
water 

( 

Baryta  153-4  2 
Water      9     1 

eq. 

i 

+  115-4 

1 

ti 

.=277.8 

\  +As2O5. 

Acid  triarsen. 
baryta  &  ba- 
sic water 

Baryta 

76-7 

18 

1 
2 

eq. 
eq. 

+  115-4 

1 

eq 

.=210-1 

S  BaO,2HO 
j  +As2Q5. 

Triarsen.  lime 

85-5 

3 

eq. 

+  115-4 

1 

cq. 

=200-9 

3CaO+As2O5 

Triarsen.  lime 
and  basic 
water 

( 

Lime 
Water 

9 

2 
1 

eq. 

eq. 

i 

+  115-4 

1 

eq 

.=  181-4 

^2CaO.HO 
\  +As2O5. 

Acid  triarsen. 
lime  and  ba- 
sic water 

\ 

Water 

is' 

31 
2 

eq. 
eq. 

\ 

+  115-4 

1 

eq.=  161-9 

(  CaO,2HO 
1  +As2O5. 

Triarsen.  protox.  lead  334-8 

3 

eq. 

+  115-4 

1 

eq 

.=450-2 

3PbO+As2Os. 

Triarsen.  prot- 
ox. lead  and 
basic  water 

( 

Water' 

>23-2  2  eq. 
9  1  eq. 

\ 

+  115-4 

1 

eq. 

-347-6 

^  2PbO.HO 
i+AsaO5. 

Triarsen.  ox.  silver      348 

3  eq. 

+  115-4 

1  eq.: 

=4634 

3AgO  +  As2O5, 

Arseniates  of  Soda. — The  triarseniate  is  made  in  the  same  manner  as 
triphosphate  of  soda,  with  which  it  is  isomorphous.  At  60°,  100  parts  of 
water  dissolve  28  of  the  crystals,  and  still  more  by  the  aid  of  heat.  At  186° 
they  fuse  in  their  water  of  crystallization. 

The  triarseniate  of  soda  and  basic  water  corresponds  precisely  in  form 
and  constitution  with  the  corresponding  phosphate,  and  like  it  parts  with  its 
last  eq.  of  water  at  a  red  heat ;  but  does  not,  on  losing1  it,  receive  any  change 
in  its  characters.  It  is  efflorescent  and  alkaline  to  test  paper,  and  crystal- 
lizes best  out  of  an  alkaline  solution.  It  is  prepared  by  adding  soda  or  its 
carbonate  in  slight  excess  to  a  solution  of  arsenic  acid.  The  salt  with  four- 
teen eq.  of  water  coincides  with  the  corresponding  phosphate. 

The  acid  triarseniate  of  soda  and  basic  water  is  prepared  like  the  corres- 
ponding phosphate. 

The  same  observation  applies  to  the  arseniates  of  potassa  and  ammonia, 
each  having  its  isomorphous  phosphate.  The  triarseniate  of  potassa  crys- 
tallizes in  needles  and  with  difficulty,  like  the  corresponding  triphosphate. 
The  arseniate  of  pntsssa  may  be  formed  by  heating  nitre  to  redness  mixed 
with  an  equal  weight  of  arsenious  acid. 

38 


446  ARSENtTES. 

The  double  arseniate  of  potassa  and  soda  agrees  in  form  and  composition 
with  the  phosphate  of  those  bases. 

Arseniates  of  Baryta. — The  triarseniate  is  best  prepared  by  gradually 
adding  in  solution  triarseniate  of  soda  to  chloride  of  barium  in  excess,  and 
falls  as  a  pulverulent  heavy  precipitate,  which  is  apt  to  contain  a  little  triar- 
seniate of  baryta  and  basic  water  as  well  as  the  soda  salt,  and  should,  there- 
fore,  be  well  washed  with  boiling  water.  On  adding  chloride  of  barium  to 
an  excess  of  triarseniate  of  soda,  the  latter  salt  always  falls  with  the  preci- 
pitate. 

To  prepare  the  triarseniate  of  baryta  and  basic  water ',  a  solution  of  the 
rhombic  triarseniate  of  soda  is  added  drop  by  drop  to  chloride  of  barium  in 
solution,  when  the  triarseniate  soon  appears  in  white  crystalline  scales, 
which  contain  three  eq.  of  water.  On  reversing  the  process  by  adding  chlo- 
ride of  barium  to  the  arseniate,  the  precipitate  is  a  mixture  of  the  triarseniate 
of  baryta,  and  triarseniate  of  baryta  and  water.  By  the  continued  action 
of  hot  water  on  the  latter,  it  is  partly  changed  into  the  acid  triarseniate  and 
insoluble  triarseniate.  The  acid  triarseniate  is  obtained  by  dissolving  either 
of  the  two  former  salts,  in  a  moist  state,  by  dilute  arsenic  acid. 

Triarseniates  of  Lime. — The  three  salts  analogous  to  those  of  baryta  arc 
obtained  by  precisely  similar  processes.  The  triarseniate  of  lirne  and  basic 
water  occurs  in  silky  acicular  crystals  as  a  rare  mineral  named  pharmacolite, 
which  contains  five  eq.  of  water  of  crystallization. 

Triarseniates  of  Protoxide  of  Lead. — The  triarseniate  is  formed  by  ad- 
ding in  solution  acetate  of  protoxide  of  lead  gradually  to  an  excess  of  triarsen- 
iate of  soda.  The  same  salt  falls  when  acetate  of  protoxide  of  lead  and  the 
rhombic  triarseniate  of  soda  are  intermixed,  acetic  acid  being  set  free. 
It  is  a  white  very  insoluble  powder,  which  at  a  low  red  heat  acquires  a  yel- 
low tint,  which  it  loses  again  on  cooling. 

The  triarseniate  with  basic  water  may  be  made  by  a  similar  process  as  for 
forming  the  corresponding  triphosphate,  and  is  a  white  insoluble,  easily 
fusible  powder. 

Triarseniate  of  Oxide  of  Silver. — This  salt  falls  as  a  brick-red  powder 
when  nitrate  of  oxide  of  silver  is  mixed  in  solution  with  triarseniate  of  soda 
or  the  rhombic  triarseniate,  in  the  latter  case  nitric  acid  being  set  free.  It 
is  apt  to  retain  some  of  the  nitrate,  which  cannot  be  removed  by  washing;  a 
property  which  the  yellow  phosphate  of  oxide  of  silver  also  possesses, 

ARSENITES. 

These  salts  have  as  yet  been  but  little  examined.  The  arsenites  of  potassu, 
soda,  and  ammonia  may  be  prepared  by  acting  with  those  alkalies  on  arsen- 
ious  acid  :  they  are  very  soluble  in  water,  have  an  alkaline  reaction,  and 
have  not  been  obtained  in  regular  crystals.  Most  of  the  other  arsenites  are 
insoluble,  or  sparingly  soluble,  in  pure  water ;  but  they  are  dissolved  by  an 
excess  of  their  own  acid,  with  great  facility  by  nitric  acid,  and  by  most  other 
acids  with  ^vhich  their  bases  do  not  form  insoluble  compounds.  The  insolu- 
ble arsenites  are  easily  formed  by  double  decomposition. 

All  the  arsenites  are  decomposed  when  heated  in  close  vessels,  being  either 
deprived  of  the  arsenious  acid  which  is  dissipated  in  vapour,  or  converted, 
with  disengagement  of  some  metallic  arsenic,  into  arseriiates.  Heated  with 
charcoal  or  black  flux,  the  acid  is  reduced  with  facility.  (Page  334.) 

The  soluble  arseniates,  if  quite  neutral,  are  characterized  by  forming  a 
yellow  arsenite  of  oxide  of  silver  when  mixed  with  the  nitrate  of  that  base, 
and  a  green  arsenite  of  protoxide  of  copper,  Scheele's  green,  with  sulphate 
of  that  oxide.  When  acidulated  with  acetic  or  hydrochloric  acid,  hydrosul- 
phuric  acid  causes  the  formation  of  orpiment.  The  insoluble  arsenites  are 
all  decomposed  when  boiled  in  a  solution  of  carbonate  of  potassa  or  soda. 

The  arsenite  of  potassa  is  the  active  principle  of  Fowler's  arsenical  solu- 
tion. 


CIIROMATES.  447 


CHROMATES. 

The  salts  of  chromic  acid  are  mostly  either  of  a  yellow  or  red  colour,  the 
latter  tint  predominating  whenever  the  acid  is  in  excess.  The  chromates  of 
oxides  of  the  second  class  of  metals  are  decomposed  by  a  strong  red  heat, 
by  which  the  acid  is  resolved  into  the  green  or  sesquioxide  of  chromium  and 
oxygen  gas;  but  the  chromates  of  the  fixed  alkalies  sustain  a  very  high 
temperature  without  decomposition.  They  are  all  decomposed  without  ex- 
ception by  the  united  agency  of  heat  and  combustible  matter.  The  neutral 
chromates  of  protoxides  are  similar  in  constitution  to  the  sulphates,  being 
formed  of  one  eq.  of  the  base  and  one  of  chromic  acid,  the  formula  being 
MO+CrOs. 

The  chromates  are  in  general  sufficiently  distinguished  by  their  colour. 
They  may  be  known  chemically  by  the  following  character: — On  boiling  a 
chromate  in  hydrochloric  acid  mixed  with  alcohol,  the  chromic  acid  is  at 
first  set  free,  and  then  decomposed,  a  green  solution  of  the  chloride  of  chro- 
mium being  generated. 

The  only  native  chromate  hitherto  discovered  is  the  red  dichromate  of 
protoxide  of  lead  from  Siberia,  in  the  examination  of  which  Vauquelin  made 
the  discovery  of  chromium. 

Chromates  of  Potassa.— The  neutral  chromate  from  which  all  the  com- 
pounds of  chromium  are  directly  or  indirectly  prepared,  is  made  by  heating 
to  redness  the  native  oxide  of  chromium  and  iron,  commonly  called  'chromate 
of  iron,  with  nitrate  of  potassa,  when  chromic  acid  is  generated,  and  unites 
with  the  alkali  of  the  nitre.  The  object  to  be  held  in  view  is  to  employ  so 
small  a  proportion  of  nitre,  that  the  whole  of  the  alkali  may  combine  with 
chromic  acid,  and  constitute  a  neutral  chromate,  which  is  easily  obtained 
pure  by  solution  in  water  and  crystallization.  For  this  purpose  the  chromate 
of  iron  is  mixed  with  about  a  fifth  of  its  weight  of  nitre,  and  exposed  to  a 
strong  heat  for  a  considerable  time ;  and  the  process  is  repeated  with  those 
portions  of  the  ore  which  are  not  attacked  in  the  first  operation.  It  is  de- 
posited from  its  solution  in  sma.ll  prismatic  anhydrous  crystals  of  a  lemon- 
yellow  colour,  which,  according  to  Brooke,  belong  to  the  right  prismatic 
system. 

Chromate  of  potassa  has  a  cool,  bitter,  and  disagreeable  taste.  It  is  solu- 
ble to  great  extent  in  boiling  water,  and  in  twice  its  weight  of  that  liquid  at 
60°;  but  it  is  insoluble  in  alcohol.  It  has  an  alkaline  reaction,  and  on  this 
account  Tassaert*  regards  it  as  a  subsalt;  but  Thomson  has  proved  that  it  is 
neutral  in  composition,  consisting  of  52  parts  or  one  eq.  of  chromic  acid, 
and  47*15  parts  or  one  eq.  of  potassa. f 

Bichromate  of  potassa,  which  is  made  in  large  quantity  at  Glasgow  for 
dyeing,  is  prepared  by  acidulating  the  neutral  chromate  with  sulphuric,  or 
still  better  with  acetic  acid,  and  allowing  the  solution  to  crystallize  by  spon- 
taneous evaporation.  When  slowly  formed  it  is  deposited  in  four-sided  tabular 
crystals,  the  form  of  which  is  an  oblique  rhombic  prism.  They  have  an 
exceedingly  rich  red  colour,  are  anhydrous,  and  consist  of  one  eq.  of  the 
alkali,  and  two  eq.  of  chromic  acid.  (Thomson.)  They  are  soluble  in  about 
ten  times  their  weight  of  water  at  60°,  and  the  solution  reddens  litmus 
paper. 

The  insoluble  salts  of  chromic  acid,  such  as  the  chromates  of  baryta  and 
of  the  oxides  of  zinc,  lead,  mercury,  and  silver,  are  prepared  by  mixing  the 
soluble  salts  of  those  bases  with  a  solution  of  chromate  of  potassa.  The  three 
former  are  yellow,  the  fourth  orange-red,  and  the  fifth  deep  red  or  purple. 
The  yellow  chromate  of  lead,  which  consists  of  one  eq.  of  acid  and  one  eq. 
of  protoxide,  is  now  extensively  used  as  a  pigment,  and  the  chromate  of  prot- 
oxide of  zinc  may  be  used  for  the  same  purpose. 


An.  de  Ch.  et  Ph.  vol.  xxii.  t  Annals  of  Philosophy,  vol.  xvi. 


448  BORATES. 

A  dichromate,  composed  of  one  eq.  of  chromic  acid  and  two  eq.  of  prot- 
oxide of  lead,  may  be  formed  by  boiling  the  carbonate  of  that  oxide  with 
excess  of  chrornate  of  potassa.  It  is  of  a  beautiful  red  colour,  and  has  been 
recommended  by  Badams  as  a  pigment.  (An.  of  Phil.  xxv.  303.)  It  may  be 
also  made  by  boiling  the  neutral  chromate  with  ammonia  or  lime-water. 
Liebeg  and  Wohler  prepare  it  by  fusing  nitre  at  a  low  red-heat,  and  adding 
chromate  of  protoxide  of  lead  by  degrees  until  the  nitre  is  nearly  exhausted. 
The  chromate  of  potassa  and  nitre  are  then  removed  by  water,  and  the  di- 
chromate  is  left  crystalline  in  texture,  and  of  so  beautiful  a  tint  that  it  vies 
with  cinnabar.  (Pog.  An.  xxi.  580.) 

Ckromates  of  Silver. — When  a  soluble  salt  of  chromic  acid  is  added  to  a 
solution  of  nitrate  of  silver,  a  deep  red-coloured  precipitate  is  obtained,  which 
has  usually  been  considered  as  the  neutral  chromate  of  silver.  But  it  has 
recently  been  proved  by  Warrington  (Phil.  Mag.  xi.  489)  that  if  the  precipi- 
tation be  made  with  acid  solutions,  a  bichromate  is  formed.  He  also  obtained 
the  latter  salt  by  the  direct  oxidation  of  metallic  silver  by  a  solution  of  bichro- 
mate of  potassa  acidulated  with  sulphuric  acid.  The  silver  is  oxidized  at 
the  expense  of  a  part  of  the  chromic  acid;  while  another  part,  by  uniting 
with  the  resulting  oxide,  forms  the  bichromate,  which  is  deposited  in  tabular 
crystals  of  a  rich  crimson  colour.  A  chrome  alum  is  at  the  same  lime  formed ; 
and  the  oxidation  of  the  silver  would  appear  to  be  induced  by  the  affinity  of 
the  sulphuric  acid  for  the  sesquioxide  of  chromium. 

On  boiling  the  bichromate  in  distilled  water,  a  part  is  dissolved  and  separ- 
ated as  the  solution  cools  in  beautiful  micaceous  crystals;  but,  at  the  same 
time  a  portion  of  the  salt  is  decomposed  into  chromic  acid  and  neutral  chro- 
mate of  silver.  As  thus  formed,  the  latter  is  of  a  dark  green  colour  :  it  is 
crimson,  however,  by  transmitted  light,  and  yields  by  trituration  a  powder 
similar  in  colour  to  the  precipitated  chromate. 

Bichromate  of  Chloride  of  Potassium. — Peligot  has  described  a  crystalline 
compound  in  which  chloride  of  potassium  acts  the  part  of  an  alkaline  base 
in  relation  to  chromic  acid.  It  is  prepared  from  bichromate  of  potassa  arid 
concentrated  hydrochloric  acid  in  the  ratio  by  weight  of  about  3  to  4,  which 
are  to  be  boiled  together  for  some  time  in  a  rather  small  quantity  of  water; 
and  it  is  deposited  in  flat  quadrangular  prisms  of  the  same  colour  as  bichro- 
mate of  potassa. 

In  this  process  there  is  a  mutual  interchange  between  the  elements  of 
potassa  and  hydrochloric  acid  ;  such  that 

2  eq.  chromic  acid       2(Cr-j-3O)  i  I  2  eq.  chromic  acid       2(Cr-J-3O) 

I  eq.  potassa  K-f-O    >  yield  •?  1  eq.  chlo.  of  potassium     K-f-Cl 

1  eq.  hydrochloric  acid      H-j-Cl  3  f  1  eq.  water  H-j-O. 

For  this  change  to  ensue  there  ought  to  be  a  certain  excess  of  hydrochloric 
acid,  and  yet  not  so  much  as  to  decompose  the  chromic  acid. 

This  salt  should  be  dried  on  bibulous  paper.  It  is  permanent  in  the  air. 
In  pure  water  it  is  decomposed,  the  materials  from  which  it  was  formed, 
bichromate  of  potassa  and  hydrochloric  acid,  being  reproduced  ;  but  it  may 
be  dissolved  without  such  change  in  water  acidulated  by  hydrochloric  acid. 
Peligot  has  made  similar  bichromates  with  the  chlorides  of  sodium,  calcium, 
and  magnesium,  and  with  hydrochlorate  of  ammonia ;  this  last  salt  being 
exactly  similar  in  appearance  to  the  bichromate  of  chloride  of  potassium. 
(An.  de  Ch.  et  de  Ph.  Hi.  267.) 

BORATES. 

As  the  boracic  is  a  feeble  acid,  it  neutralizes  alkalies  imperfectly,  and  hence 
the  borates  of  soda,  potassa,  and  oxide  of  ammonium  have  always  an  alka- 
line reaction.  For  the  same  reason,  when  the  borates  are  digested  in  any 
of  the  more  powerful  acids,  such  as  the  sulphuric,  nitric,  or  hydrochloric, 
the  boracic  acid  is  separated  from  its  base.  This  docs  not  happen,  however 


CARBONATES.  449 

at  high  temperatures;  for  boracic  acid, owing  to  its  fixed  nature,  decomposes 
at  a  red  heat  all  salts,  not  excepting  sulphates,  the  acid  of  which  is  volatile. 

The  borates  of  the  alkalies  are  soluble  in  water,  but  most  of  the  other  salts 
of  this  acid  are  of  sparing-  solubility.  They  are  not  decomposed  by  heat, 
and  the  alkaline  and  earthy  borates  resist  the  action  of  heat  and  combustible 
matter.  They  are  remarkably  fusible  in  the  fire,  a  property  obviously  owing 
to  the  great  fusibility  of  boracic  acid  itself. 

The  borates  are  distinguished  by  the  following  character: — By  digesting 
any  borate  in  a  slight  excess  of  strong  sulphuric  acid,  evaporating  to  dryness, 
and  boiling  the  residue  in  strong  alcohol,  a  solution  is  formed  which  has  the 
property  of  burning  with  a  green  flame.  (Page  205.) 

Biborate  of  Soda. — This  salt,  the  only  borate  of  importance,  occurs  native 
in  some  of  the  lakes  of  Thibet  and  Persia,  and  is  extracted  from  this  source 
by  evaporation.  It  is  imported  from  India  in  a  crude  state,  under  the  name 
of  tincal,  which,  after  being  purified,  constitutes  the  refined  borax  of  com- 
merce. It  is  frequently  called  subborate  of  soda,  a  name  suggested  by  the 
inconsistent  and  unphilosophical  practice,  now  quite  inadmissible,  of  regulat- 
ing the  nomenclature  of  si'lts  merely  by  their  action  on  vegetable  colouring 
matter.  It  crystallizes  in  prisms  of  the  oblique  system,  which  effloresce  on  ex- 
posure to  the  air,  and  require  twenty  parts  of  cold  and  six  of  boiling  water  for 
solution.  When  exposed  to  heat,  the  crystals  are  first  deprived  of  their  water 
of  crystallization,  and  then  fused,  forming  a  vitreous  transparent  substance 
called  glass  of  borax.  The  crystals  are  composed  of  69-8  parts  or  two  eq.  of 
boraric  acid,  31-3  or  one  eq.  of  soda,  and  90  or  ten  eq.  of  water. 

The  chief  use  of  borax  is  as  a  flux,  and  for  the  preparation  of  boracic  acid. 
Biborate  of  magnesia  is  a  rare  natural  production,  which  is  known  to  miner- 
alogists by  the  name  of  boracite.  «  -. 

A  new  biborate  of  soda,  which  contains  half  as  much  water  of  crystalliza- 
tion as  the  preceding,  has  been  lately  described  by  Buran.  It  is  harder  and 
denser  than  borax,  is  not  efflorescent,  and  crystallizes  in  regular  octohedrons. 
It  is  made  by  dissolving  borax  in  boilirtg  water  until  the  sp.  gr.  of  the 
solution  is  at  30°  or  32°  of  Baume's  hydrometer :  the  solution  is  then  very 
slowly  cooled ;  and  when  the  temperature  descends  to  about  133°,  the  new 
salt  is  deposited.  It  is  found  to  be  more  convenient  for  the  use  of  jewellers 
than  common  borax.  (An.  de  Ch.  et  de  Ph.  xxxvii.  419.) 

The  neutral  borate  of  soda  has  been  obtained  by  Berzelius  by  the  action 
of  boracic  acid  on  carbonate  of  soda  at  a  boiling  heat,  when  carbonic  acid  is 
evolved.  The  solution  on  cooling  yields  crystals  of  the  oblique  prismatic 
system,  and  containing  eight  cq.  of  water.  Their  constitution  is,  therefore, 
NaO,BO--4-8HO.  They  are  powerfully  alkaline,  and  on  exposure  to  the  air 
readily  attract  carbonic  acid,  forming  the  carbonate  and  biborate  of  soda. 
He  also  obtained  the  neutral  borate  of  potassa,  but  was  prevented  by  its  great 
solubility  from  procuring  it  in  crystals. 

CARBONATES. 

The  carbonates  are  distinguished  from  other  salts  by  being  decomposed 
with  effervescence,  owing  to  the  escape  of  carbonic  acid  gas,  by  nearly  all 
the  acids ;  and  all  of  them,  except  the  carbonates  of  potassa,  soda,  and  lithia, 
may  be  deprived  of  their  acid  by  heat.  The  carbonates  of  baryta  and  strontia, 
especially  the  former,  require  an  intense  white  heat  for  decomposition ;  those 
of  lime  and  magnesia  are  reduced  to  the  caustic  state  by  a  full  red  heat;  and 
the  other  carbonates  part  with  their  carbonic  acid  when  heated  to  dull  red- 
ness. 

All  the  carbonates,  except  those  of  potassa,  soda,  and  ammonia,  are  of 
sparing  solubility  in  pure  water;  but  all  of  them  are  more  or  less  soluble 
in  an  excess  of  carbonic  acid,  owing  doubtless  to  the  formation  of  super- 
salts. 

Several  of  the  carbonates  occur  native,  among  which  may  be  enumerated 
the  carbonates  of  soda,  baryta,  strontia,  lime,  magnesia,  and  the  protoxides 
of  manganese,  iron,  copper,  and  lead ;  together  with  some  double  carbonates 

38* 


450  CARBONATES. 

such  as  Dolomite  or  the  double  carbonate  of  lime  and  magnesia,  and  baryto- 
calcite  or  the  double  carbonate  of  baryta  and  lime. 

The  composition  of  the  principal  carbonates  is  stated  in  the  following 
table  : 

SIMPLE  CARBONATES. 

Names.  Base.  Acid.  Equiv.  Formulae. 

Carbonate  of  potassa         47-15  1  eq.-f  22-12     1  cq.=  69-27  KO-f  CO. 

Bicarb,  of  potassa  47-15  1  eq.-f  44-24     2  eq.=  91-39  KO-J.2CQ2. 

Do.  in  crystals  with    9  or  1  eq.  of  water          =100-39 

Carbonate  of  soda  31-3     1  eq.-f  22-12      1  eq.=  53-42  NaO-f  CCR 

Do.  in  crystals  with  90  or  10  eq.-j-of  water        =143-42 

Do.  in  crystals  with  63  or  7  eq.-f  of  water        =116-42 

Bicarb,  of  soda  31-3     1  eq.-|-44-24    2  eq.=  75-54  NuO-f2CQ2. 

Do.  in  crystals  with    9  or  1  eq.  of  water  =  84-54 

Carbonate  of  ammonia     17-15  1  eq.-f22-12     1  eq.=  39-27  H3N-f  CO. 

Bicarb,  of  ammonia          17-15  1  eq.-f  44-24    2  eq.=  61-39  H3N-f2CO. 

Carbonate  of  baryta          76-7     1  eq.-f  22-12     1  eq,=  98-82  BaO-j-CX)2. 

Carbonate  of  strontia       51-8     1  eq.-f  22-12     1  eq.=  73-92  SiO-fCOs. 

Carbonate  of  lime  28-5     1  eq.-f-22-12     1  cq.=  50-62  CaO-fCO2. 

Carbonate  of  magnesia    20-7     1  eq.-f  22-12     1  eq.=  42-82  MgO-f  CC>2. 

Do.    in  crystals  with  27  or  3  eq.  of  water          =69-82 

Carbonate  of  protox.  iron  36        1  eq.-f22-12     1  cq.=  58-12  FeO-fCO2. 

Dicarb.  of  protox.  copper  79-2    2  eq.-|-22-12     1  eq.=101-32  2CuO-f  CQ2. 

Do.  in  malachite  with  9  or  1  eq.  of  water          =110-32 
Carb.  of  protox.  lead      111-6     1  eq.4-22-12     1  eq.=133-72 

Dicarb.  of  perox.  mere.  436       2  eq.-f  22-  12     1  eq.  =458-12  2HgO2-fCCR 

DOUBLE  CARBONATES. 

Names.  Const.  Salts.  Equiv.        Formulae. 


Carbonate  of  lime  ?  Carb.  lime          50-62  1  eq.  (  _  qo.44  S  MgO,CQ2 

and  magnesia      5  Carb.  magnesia  42-82  1  eq.  (  "  I  -f  CaO,CO2. 

Carb.  of  baryta  and  (Carb.  baryta       98-82  1  eq  .(      ,  A(].AA  )  CaO,CO2 

lime  I  Carb.  lime          50-62  1  eq.  \  =  )  -f-BaO,CO2. 


I  Carbonate  of  Potassa.  —  This  salt  is  procured  in  an  impure  form  by  burn- 
ing land  plants,  lixiviating  their  ashes,  and  evaporating  the  solution  to  dry- 
ness,  a  process  which  is  performed  on  a  large  scale  in  Russia  and  America. 
The  carbonate,  thus  obtained,  is  known  in  commerce  by  the  names  of  potash 
und  pearlash,  and  is  much  employed  in  the  arts,  especially  in  the  formation 
of  soap  and  the  manufacture  of  glass.  When  derived  from  this  source  it 
always  contains  other  compounds,  such  as  sulphate  of  potassa  and  chloride 
of  potassium;  and,  therefore,  for  chemical  purposes,  it  should  be  prepared 
from  cream  of  tartar.  On  heating  this  salt  to  redness,  the  tartaric  acid  is 
decomposed,  and'a  pure  carbonate  of  potassa  mixed  with  charcoal  remains. 
The  carbonate  is  then  dissolved  in  water,  and,  after  filtration,  is  evaporated 
to  dryness  in  a  capsule  of  platinum  or  silver. 

Pure  carbonate  of  potassa  lias  a  taste  strongly  alkaline,  is  slightly  caustic, 
and  communicates  a  green  lint  to  the  blue  colour  of  the  violet.  It  dissolves 
in  less  than  an  equal  weight  of  water  at  60°,  deliquesces  rapidly  on  exposure 
to  the  air,  and  crystallizes  with  much  difficulty  from  its  solution.  In  pure 
alcohol  it  is  insoluble.  It  fuses  at  a  full  red  heat,  but  undergoes  no  other 
change. 

It  is  often  necessary,  for  commercial  purposes,  to  ascertain  the  value  of 
different  samples  of  pearlash  ;  that  is,  to  determine  the  quantity  of  real  car- 
Donate  of  potassa,  contained  in  a  given  weight  of  impure  carbonate.  A  con- 
venient mode  of  effecting  this  object  is  described  by  Faraday  in  his  excellent 
work  on  Chemical  Manipulation.  Into  a  tube  sealed  at  one  end,  9£  inches 


CARBONATES. 


451 


1000 


Potassa  -        — 


long,  fths  of  an  inch  in  diameter,  and  as  cylindrical  as  possible  in  its  whole 
length,  pour  1000  grains  of  water,  and  with  a  file  or  diamond  mark  the  place 
where  its  surface  reaches,  and  divide  the  space  occupied  by  the  water  into 
100  equal  parts,  as  is  &hown  in  the  annexed  wood  cut.  Opposite  to  the 
numbers  23-44,  48  96,  54*63,  and  65,  draw  a  line,  and  at  the  first  write  soda, 
at  the  second  potassa,  at  the  third  carbonate  of  soda,  and  at  the  fourth  carbo- 
nate of  potassa.  Then  prepare  a  dilute  acid  having  the  specific  gravity  of 
1-127  at  60°,  which  may  be  made  by  mixing  one  measure  of  concentrated 
sulphuric  acid  with  four  measures  of  distilled  water.  This  is  the  standard 
acid  to  be  used  in  all  the  experiments,  being  of  such  strength  that  when 
poured  into  the  tube  till  it  reaches  either  of  the  four  marks  just  mentioned, 
we  shall  obtain  the  exact  quantity  necessary  for  neutralizing  100  grains  of 
the  alkali  written  opposite  to  it.  li\  when  the  acid  reaches  the  word  carb, potas- 
sa, and  when,  consequently,  we  have  the  exact 
quantity  which  will  neutralize  100  grains  of 
that  carbonate,  pure  water  be  added  until  it 
reaches  0,  or  the  beginning  of  the  scale,  each 
division  of  this  mixture  will  neutralize  one 
grain  of  carbonate  of  potassa.  All  that  is 
now  required,  in  order  to  ascertain  the  quan- 
tity of  real  carbonate  in  any  specimen  of  pearl- 
ash,  is  to  dissolve  100  grains  of  the  sample  in  Soda 
warm  water,  filter  to  remove  all  the  insoluble 
parts,  and  add  the  dilute  acid  in  successive 
small  quantities,  until,  by  the  test  of  litmus 
paper,  the  solution  is  exactly  neutralized. 
Each  division  of  the  mixture  indicates  a  grain 
of  pure  carbonate.  It  is  convenient,  in  con- 
ducting this  process,  to  set  aside  a  portion  of  Carb  soda  — 
the  alkaline  liquid,  in  order  to  neutralize  the 
acid,  in  case  it  should  at  first  be  added  too  ~ 
freely.  To  this  instrument  the  term  alka-  ^rb.potassa 
limeter  is  given,  a  name  obviously  derived 
from  the  use  to  which  it  is  applied. 

Bicarbonate  of  Potassa  is  made  by  trans- 
mitting a  current  of  carbonic  acid  gas  through 
a  solution  of  the  carbonate  ;  or  by  evaporating 
a  mixture  of  the  carbonates  of  ammonia  and 
potassa,  the  ammonia  being  dissipated  in  a 
pure  state.  By  slow  evaporation,  the  bicar- 
bonate is  deposited  from  the  liquid  in  hydra  ted  prisms  with  eight  sides,  ter- 
minated with  dihedral  summits. 

Bicarbonate  of  potassa,  though  far  milder  than  the  carbonate,  is  alkaline 
both  to  the  taste  and  to  test  paper.  It  does  not  deliquesce  on  exposure  to 
the  air.  It  requires  four  times  its  weight  of  water  at  60°  for  solution,  and 
is  much  more  soluble  at  212°;  at  this  temperature  it  has  been  stated  to  be 
converted  into  sesquicarbonate,  but  H.  Rose  has  shown  that,  though  gradu- 
ally, it  at  length  parts  with  half  its  carbonic  acid.  The  escape  of  the  gas  he 
finds  to  be  much  retarded  by  pressure,  that  of  one  inch  of  mercury  making 
a  difference ;  hence  the  loss  of  carbonic  acid  is  much  more  rapid  when  a 
cold  solution  is  evaporated  in  vacuo,  both  the  gas  and  aqueous  vapour  being 
absorbed  by  quicklime  (Pog.  An.  xxxiv.  149).  Ai  a  low  red  heat  it  is  con- 
verted into  the  carbonate. 

Thomson,  in  his  "First  Principles,"  has  described  a  sesquicarbonate, 
which  was  discovered  by  Nimmo  of  Glasgow.  Its  crystals  contain  twelve 
eq.  of  water,  as  denoted  by  the  formula  2KO.3CO  -f  I2HO. 

Carbonate  of  Soda. — The  carbonate  of  commerce  is  obtained  by  lixiviating 
the  ashes  of  sea-weeds.  The  best  variety  is  known  by  the  name  of  barilla, 
and  is  derived  chiefly  from  the  salsola  soda  and  salicornia  herbacea.  A  very 
inferior  kind,  known  by  the  name  of  kelp,  is  prepared  from  sea- weeds  on  the 


0 
5 
10 
15 
20 
25 
30 
35 
40 
45 
50 
55 
60 
65 
70 
75 
80 
85 
90 
95 
100 


^  452  CARBONATES. 

northern  shores  of  Scotland.  The  purest  barilla,  however,  though  well  fitted 
for  making  soap  and  glass,  and  for  other  purposes  in  the  arts,  always  con- 
tains the  sulphates  of  potassa  and  soda,  and  the  chlorides  of  potassium  and 
sodium.  A  purer  carbonate  is  prepared  by  heating  a  mixture  of  sulphate  of 
soda,  saw-dust,  and  lime  in  a  reverberatory  furnace.  By  the  action  of  car- 
bonaceous matter,  the  sulphuric  acid  is  decomposed;  its  sulphur  partly 
uniting  with  calcium  and  partly  being  dissipated  in  the  form  of  sulphurous 
acid,  while  the  carbonic  acid,  which  is  generated  during  the  process,  unites 
with  the  soda.  The  carbonate  of  soda  is  then  obtained  by  lixiviation  and 
crystallization.  It  is  difficult  to  obtain  this  salt  quite  free  from  sulphuric 
acid. 

It  crystallizes  in  rhombic  octohedrons,  the  acute  angles  of  which  are  gene- 
rally truncated.  The  crystals  effloresce  on  exposure  to  the  air,  and,  when 
heated,  dissolve  in  their  water  of  crystallization.  By  continued  heat  they  are 
rendered  anhydrous  without  loss  of  carbonic  acid.  They  dissolve  in  about 
two  parts  of  cold,  and  in  rather  less  than  their  weight  of  boiling  water,  and 
the  solution  has  a  strong  alkaline  taste  and  reaction.  The  crystals  com- 
monly found  in  commerce  contain  ten  eq.  of  water ;  but  when  formed  at  a 
temperature  of  about  80°,  they  retain  only  seven  eq. 

The  purity  of  different  specimens  of  barilla,  or  other  carbonates  of  soda, 
may  be  ascertained  by  means  of  the  alkalimeter  above  described. 

Bicarbonate  of  Soda. — This  salt  is  made  by  the  same  processes  as  bicar- 
bonate of  potassa,  and  is  deposited  in  hydrated  crystalline  grains  by  evapora- 
tion. Though  still  alkaline,  it  is  much  milder  than  the  carbonate,  and  far 
less  soluble,  requiring  about  ten  times  its  weight  of  water  at  60°  for  solution. 
It  is  found  by  Rose  to  undergo  the  same  changes  on  boiling  as  the  bicarbo- 
nate of  potassa;  it  is  converted  into  the  carbonate  by  a  red  heat. 

Sesquicarbonate. — This  compound  occurs  native  on  the  banks  of  the  lakes 
of  soda  in  the  province  of  Sukena  in  Africa,  whence  it  is  exported  under  the 
nameofiromz.  It  was  first  distinguished  from  the  two  other  carbonates  by 
Phillips,  (Journal  of  Science,  vii.)  whose  analysis  corresponds  with  that  of 
Klaproth.  Its  formula  is  2NaO.3CO2_|_4HO. 

Carbonate  of  Ammonia. — The  only  method  of  obtaining  the  substance  so 
called  is  by  mixing  perfectly  dry  carbonic  acid  and  ammoniacal  gases.  In 
whatever  proportion  the  two  gases  be  mixed,  they  unite  only  in  the  ratio  of 
one  volume  of  the  former  to 'two  of  the  latter,  and  condense  into  a  white 
light  powder.  This  substance,  therefore,  contains  carbonic  acid  and  ammonia 
in  equivalent  proportions,  but  it  is  probable  that  the  elements  are  not  ar- 
ranged as  expressed  by  the  name.  By  the  action  of  water  it  is  instantly  de. 
composed  into  ammonia  and  the  sesquicarbonate. 

Bicarbonate  of  Oxide  of  Ammonium. — This  salt  was  formed  by  Berthollet 
by  transmitting  a. current  of  carbonic  acid  gas  through  a  solution  of  the 
common  carbonate  of  ammonia  of  the  shops.  On  evaporating  the  liquid  by 
a  gentle  heat,  the  bicarbonate  is  deposited  in  small  prisms  of  the  right  rhom- 
bic system,  which  have  no  smell,  and  very  little  taste.  Berthollet  ascertained 
that  it  contains  twice  as  much  acid  as  the  carbonate.  It  cannot  exist  without 
the  presence  of  water,  of  which  it  contains  £2-7  per  cent.  (Berzelius),  OF  two 
eq.  It  may,  therefore,  be  considered  as  carbonate  of  basic  water,  and  carbo- 
nate of  oxide  of  ammonium,  or  HO,COl-'-f-H^NO,CO2. 

Sesquicarbonate,  of  Oxide  of  Annnonium.—The  common  carbonate  of  am- 
monia of  the  shops,  Sub-carbonas  Ammonia  of  the  Pharmacopoeia,  is  different 
from  both  these  compounds.  It  is  prepared  by  heating  a  mixture  of  one  part 
of  hydrochlorate  of  ammonia  with  one  part  and  a  half  of  carbonate  of  lime, 
carefully  dried.  Double  decomposition  ensues  during  the  process;  chloride 
of  calcium  remains  in  the  retort,  and  hydrated  sesquicarbonate  of  ammonia 
is  sublimed.  The  carbonic  acid  and  ammonia  are,  indeed^in  proper  propor- 
tion  in  the  mixture  for  forming  the  real  carbonate  ;  but,  owing  to  the  pre- 
sence of  water,  generated  by  the  combination  of  the  oxygen  of  the  lime  with 
the  hydrogen  of  the  hydrochloric  acid,  part  of  the  ammonia  is  disengaged  in 
a  free  state. 


CARBONATES.  453 

The  salt  thus  formed  consists,  according  to  the  analysis  of  Phillips,  Ure, 
and  Thomson,  of  34*3  parts  or  two  eq.  of  ammonia,  66*36  parts  of  three  eq- 
of  carbonic  acid,  and  18  parts  or  two  eq.  of  water.  It  is,  therefore,  anhydrous 
sesquicarbonate  of  oxide  of  ammonium,  or  2H>NO4-3CO3.  When  recently 
prepared,  it  is  hard,  compact,  translucent,  of  a  crystalline  texture,  and  pun- 
gent ammoniacal  odour;  but  if  exposed  to  the  air,  it  loses  weight  rapidly 
from  the  escape  of  pure  ammonia,  and  becomes  an  opaque  brittle  mass, 
which  is  the  bicarbonate. 

Carbonate  of  Baryta  occurs  abundantly  in  the  lead  mines  of  the  north  of 
England,  where  it  was  discovered  by  Dr.  Withering,  and  has  hence  re- 
ceived the  name  of  Wilherite.  It  may  be  prepared  by  way  of  double  decom- 
position, by  mixing  a  soluble  salt  of  baryta  with  any  of  the  alkaline  carbo- 
nates or  bicarbonates.  It  is  anhydrous,  exceedingly  insoluble  in  distilled 
water,  requiring  4300  times  its  weight  of  water  at  60°,  and  2300  of  boiling 
water  for  solution  ;  but  when  recently  precipitated,  it  is  dissolved  much  more 
freely  by  a  solution  of  carbonic  acid.  It  is  highly  poisonous. 

Carbonate  of  strontia,  which  occurs  native  at  Strontian  in  Argyleshire, 
and  is  known  by  the  name  of  strontianite,  may  be  prepared  in  the  same 
manner  as  carbonate  of  baryta.  It  is  anhydrous,  and  very  insoluble  in  pure 
water,  but  is  dissolved  by  an  excess  of  carbonic  acid. 

Carbonate  of  Lime. — This  salt  is  a  very  abundant  natural  production,  and 
occurs  under  a  great  variety  of  forms,  such  as  common  limestone,  chalk, 
marble,  and  Iceland  spar,  and  in  regular  anhydrous  crystals,  the  density  of 
which  is  2-7.  It  may  also  be  formed  by  precipitation.  Though  sparingly 
soluble  in  pure  water,  it  is  dissolved  by  carbonic  acid  in  excess ;  and  hence 
the  spring-water  of  limestone  districts  always  contains  carbonate  of  lime, 
which  is  deposited  when  the  water  is  boiled. 

Daniell  noticed  that  an  aqueous  solution  of  sugar  and  lime  deposited  crys- 
tallized carbonate  of  lime  by  exposure  to  the  air.  Gay-Lussac  has  proved 
that  the  sugar  merely  acts  as  a  solvent,  presenting  lime  in  a  favourable  state 
for  combining  with  the  carbonic  acid  of  the  atmosphere ;  and  that  all  the 
lime  is  deposited  in  acute  rhombohedrons,  which  contain  five  eq.  of  water  to 
one  eq.  of  carbonate  of  lime.  These  crystals  are  insoluble  and  remain  un- 
changed in  cold  water,  but  in  water  at  86°,  or  in  air,  they  lose  their  com- 
bined water,  and  fall  to  powder.  When  boiled  in  alcohol  they  retain  their 
form,  but  lose  two  eq.  of  water  and  retain  three  eq.  in  combination.  (An.  de 
Ch.  et  Ph.  de  xlviii.  301.) 

Carbonate  of  Magnesia. — It  is  met  with  occasionally  in  rhornbohedral 
crystals,  and  in  a  pulverulent  earthy  state,  but  more  commonly  as  a  compact 
mineral  of  an  earthy  fracture  called  magnesite.  A  specimen  of  magnesite 
from  the  East  Indies,  where,  I  am  informed,  it  is  abundant,  has  been  analysed 
by  Henry,  who  found  it  to  be  nearly  pure  anhydrous  carbonate  of  magnesia: 
it  is  of  a  snow-white  colour,  of  density  2-56,  and  so  hard  that  it  strikes  fire 
with  steel.  (An.  of  Phil.  xvii.  252.)  It  is  obtained  in  minute  transparent 
hexagonal  prisms  with  three  eq.  of  water,  when  a  solution  of  bicarbonate  of 
magnesia  evaporates  spontaneously  in  an  open  vessel.  The  crystals  lose 
their  water  and  become  opaque  by  a  very  gentle  heat,  and  even  in  a  dry  air 
at  60°.  By  cold  water  they  are  decomposed,  yielding  a  soluble  bicarbonate, 
and  an  insoluble  white  compound  of  hydrate  and  carbonate  of  magnesia;  and 
hot  water  produces  the  same  change  with  disengagement  of  carbonic  acid, 
without  dissolving  any  magnesia.  (Berzelius.) 

When  carbonate  of  potassa  is  added  in  excess  to  a  hot  solution  of  sulphate 
of  magnesia,  a  white  precipitate  falls,  which  after  being  well  washed  has  been 
long  considered  as  pure  carbonate  of  magnesia  ;  but  Berzelius  has  shown 
that  it  consists  of  the  following  ingredients : — 

Magnesia  44-75  82-8    or  4  eq.  J  D    u  u i    c         i    • 

TarhnnJP  nnM          ^.77  RK  Q«    I  Q    2  (  Probable  formula  is 

i^arooniC  acid          do-77  bb' Jo  or  3  eq. 

Water  19-48  36      or  4  eq. 

100-00          185-16  or  1  eq. 


454  CARBONATES. 

This  compound  is  said  to  require  2493  parts  of  cold,  and  9000  of  hot  water 
for  solution.  It  is  freely  dissolved  by  a  solution  of  carbonic  acid,  bicarbo- 
nate of  magnesia  being-  generated;  but  on  allowing  the  solution  to  evaporate 
spontaneously,  carbonic  acid  is  given  off,  and  crystals  of  the  hydrated  car- 
bonate above  mentioned  are  obtained. 

Carbonate  of  Protoxide  of  Iron. — Carbonic  acid  does  not  form  a  definite 
compound  with  sesquioxide  of  iron,  but  with  the  protoxide  it  constitutes  a 
salt  which  is  an  abundant  natural  production,  occurring-  sometimes  massive, 
and  at  other  times  crystallized  in  rhombohedrons.  This  protocarbonate  is 
contained  also  in  most  of  the  chalybeate  mineral  waters,  being  held  in  solu- 
tion by  free  carbonic  acid ;  and  it  may  be  formed  by  mixing  an  alkaline  car- 
bonate with  the  sulphate  of  protoxide  of  iron.  When  prepared  by  precipita- 
tion it  attracts  oxygen  rapidly  from  the  atmosphere,  and  the  protoxide  of  iron, 
passing  into  the  state  of  sesquioxide,  parts  with  carbonic  acid.  For  this 
reason,  the  carbonate  of  iron  of  the  Pharmacopoeia  is  of  a  red  colour,  and 
consists  chiefly  of  the  sesquioxide. 

Bicarbonate  of  Protoxide  of  Copper. — It  occurs  as  a  hydrate  in  the  beau- 
tiful green  mineral  called  malachite;  and  the  same  compound,  as  a  green 
powder,  the  rffineral  green  of  painters,  may  be  obtained  by  precipitation  from 
a  hot  solution  of  sulphate  of  protoxide  of  copper,  by  carbonate  of  soda  or 
potassa.  When  obtained  from  a  cold  solution,  it  falls  as  a  bulky  hydrate  of 
a  greenish-blue  colour,  which  contains  more  water  than  the  green  precipitate. 
By  careful  drying  its  water  may  be  expelled.  When  the  hydrate  is  boiled 
for  a  long  time  in  water,  it  loses  both  carbonic  acid  and  combined  water,  and 
the  colour  changes  to  brown.  The  rust  of  copper,  prepared  by  exposing 
metallic  copper  to  air  and  moisture,  is  a  hydrated  dicarbonate*. 

The  blue-coloured  mineral,  called  Hue  copper  ore,  appears  to  be  a  hydrate 
and  carbonate  of  the  protoxide  of  copper,  and  consists,  according  to  the 
analysis  of  Phillips,  of,  (Quarterly  Journal  of  Science,  iv.} 

Protoxide  of  copper        69-08  118-8     3  eq.  ) 

Carbonic  acid   P  25-46  44-24  2  eq. 

Water  5-46  91  eq. 


100-00  172-04  1  eq. 

The  blue  pigment  called  verier,  prepared  by  decomposing  nitrate  of  prot- 
oxide of  copper  with  chalk,  has  a  similar  composition.  (Phillips.) 

Carbonate  of  Protoxide  of  Lead. — This  salt,  which  is  the  white  lead  or 
ceruse  of  painters,  occurs  native  in  white  prismatic  crystals  derived  from  a 
right  rhombic  prism,  the  sp.  gr.  of  which  is  6*72.  It  is  obtained  as  a  white 
pulverulent  precipitate  by  mixing  solutions  of  an  alkaline  carbonate  with 
acetate  of  protoxide  of  lead ;  and  it  is  prepared  as  an  article  of  commerce 
from  the  subacetate  by  a  current  of  carbonic  acid  ;  by  exposing  metallic  lead 
in  minute  division  to  air  and  moisture;  and  by  the  action  on  thin  sheets  of 
lead  of  the  vapour  of  vinegar,  by  which  the  metal  is  both  oxidized  and  con- 
verted  into  a  carbonate. 

Dicarbonate  of  Peroxide  of  Mercury. — When  a  solution  of  the  nitrate  of 
peroxide  of  mercury  is  decomposed  by  carbonate  of  soda,  an  ochre-yellow 
precipitate  falls,  which  Phillips  finds  to  be  a  dicarbonate.  The  protoxide  ap- 
pears to  form  no  compound  with  carbonic  acid;  for  when  a  nitrate  of  that 
oxide  is  decomposed  by  any  alkaline  carbonate,  the  precipitate  is  either  black 
at  first  or  speedily  becomes  so,  and  after  being  washed  is  quite  free  from  car- 
bonic acid. 

Double  Carbonates. — One  of  the  most  remarkable  of  these  is  the  double 
carbonate  of  lime  and  magnesia,  which  constitutes  the  minerals  called  bitter- 
spar,  pearl-spar,  and  Dolomite.  The  two  former  occur  in  rhombohedrons  of 
nearly  the  same  dimensions  as  carbonate  of  lime.  The  latter  is  met  with  in 
great  perfection  in  the  Alps,  and  there  usually  occurs  in  white  masses  of  3 
granular  texture;  the  grains  often  cohere  loosely,  but  other  specimens  are 
hard  and  compact,  and  when  broken  present  the  crystalline  aspect  of  marble. 


HYDRO-SALTS.  455 

Its  density  is  2-884.  Some  specimens  consist  of  the  two  constituent  car- 
bonates in  the  ratio  of  their  eq.,  as  stated  in  the  table ;  but  the  ratio  of  the 
ingredients,  as  may  be  expected,  is  very  variable,  since  isomorphous  sub- 
stances crystallize  tog-ether  in  all  proportions.  Carbonate  of  protoxide  of 
manganese  is  often  associated  with  them.  The  rock  called  magnesian  lime- 
stone may  be  viewed  as  an  impure  earthy  variety  of  Dolomite. 

The  double  carbonate  of  baryta  and  lime  constitutes  the  mineral  called 
baryto-calcite,  which  Mr.  Children  found  to  contain  the  two  carbonates  in 
atomic  proportion. 

Berthier  has  made  some  interesting  experiments  on  the  production  of 
double  carbonates  by  fusion.  Carbonate  of  soda,  when,  fused  with  carbonate 
of  baryta,  strontia,  or  lime,  in  the  ratio  of  their  eq.,  yields  uniform  crystal- 
line compounds,  which  have  all  the  appearance  of  being  definite.  An  eq.  of 
Dolomite  fuses  in  like  manner  with  four  eq.  of  carbonate  of  soda.  Five  parts 
of  carbonate  of  potassa  and  four  of  carbonate  of  soda,  corresponding  to  an 
eq.  of  each,  fuse  with  remarkable  facility ;  and  this  mixture,  by  reason  of  its 
fusibility,  may  be  advantageously  employed  in  the  analysis  of  earthy  min- 
erals. 

Compounds  similar  to  the  foregoing  may  be  generated  by  heating  sulphate 
of  soda  with  carbonate  of  baryta,  strontia,  or  lirne,  in  the  ratio  of  their  eq.; 
or  by  employing  the  sulphate  of  these  bases  arid  carbonate  of  soda.  In  like 
manner  carbonate  of  soda  fuses  with  chloride  of  barium  or  calcium ;  and 
chloride  of  sodium  with  carbonate  of  baryta  or  lime.  (An.  deCh.  et  de  Ph. 
xxxviii.) 


SECTION    II. 

CLASS  OF  SALTS.    ORDER  II. 

HYDRO-SALTS. 

IN  this  section  are  included  those  salts  only,  the  acid  or  base  of  which. is 
a  compound  containing  hydrogen  as  one  of  its  elements.  For  reasons  already 
assigned  (page  273)  I  have  already  described  all  those  salts  which  were 
formerly  called  muriates  or  kyctrochlorates  of  metallic  oxides,  as  chlorides  of 
metals,  considering  that  in  general  the  neutralizing  power  of  hydrochloric 
acid  is  not  due  to  its  direct  combination  with  an  oxide,  but  to  chlorine  unit- 
ing with  the  metal  itself.  The  same  remark  applies  to  the  hydriodic  and 
other  hydracids,  the  salts  of  which  are  consequently  reduced  to  a  small 
number.  The  only  salts,  indeed,  which  are  included  in  this  section,  are 
compounds  of  the  hydracids  with  ammonia  arid  phosphuretted  hydrogen. 
Some  of  the  compounds  which  might,  as  containing  an  hydracid,  be  com- 
prehended in  this  section,  may  with  greater  propriety  be  placed  in  the  fourth, 
seeing  that  in  them  the  hydracid  acts  rather  as  a  base  or  electro-positive  in- 
gredient, than  as  an  acid  or  electro-negative  substance.  This  double  func- 
tion, which  chemists  have  long  recognized  in  certain  metallic  oxides,  such 
as  alumina  and  protoxide  of  zinc,  appears  to  be  performed  even  by  so  pow- 
erful an  acid  as  the  hydrochloric.  Some  judicious  observations  on  this  sub- 
ject have  been  made  by  Professor  Kane  of  Dublin.  (Dublin  Journal  of  Science, 
i.  265.) 

The  compounds  of  ammonia  with  the  hydracids  may  be  described  as  chlo- 
rides of  the  hypothetical  radical  ammonium.  The  argument  for  doing  so  is 
derived  from  the  similarity  of  the  hydrochlorate  of  ammonia  to  the  chloride  of 


456  AMMONIACAL  SALTS. 

potassium  in  its  crystalline  form,  and  all  its  relations  to  other  chlorides.  But 
the  argument  does  not  apply  with  equal  force  in  both  cases ;  for  to  suppose  a 
direct  compound  of  ammonia  and  an  hydracid  is  perfectly  consistent  with 
observation,  whereas  the  existence  of  a  compound  of  ammonia  and  an  oxacid 
is  directly  opposed  to  it.  In  the  former  case,  therefore,  we  have  two  ways  of 
of  accounting  for  the  phenomena  observed ;  in  the  latter  we  have  but  one, 
and  that  one,  therefore,  though  hypothetical  must  be  adopted.  As  this 
necessity  does  not  exist  in  the  compounds  of  ammonia  with  the  hydracids, 
they  are  treated  as  direct  binary  combinations  of  their  constituents. 

Ammonia  unites  with  fluoride  of  boron,  bisulphuret  of  carbon,  and  some 
other  bi-elemenlary  compounds,  which  contain  neither  oxygen  nor  hydrogen, 
constituting  saline  combinations,  which  are  included  in  this  section,  and  to 
which,  considering  the  distinct  alkaline  character  of  ammonia,  the  ordinary 
nomenclature  of  salts  is  applicable. 

AMMONIACAL  SALTS. 

These  compounds  are  readily  recognized  by  the  addition  of  pure  potassa 
or  lime,  when  the  odour  of  ammonia  may  be  perceived.  Those  which  con- 
tain a  volatile  acid  may  in  general  be  sublimed  without  decomposition;  but 
the  ammonia  is  expelled  by  heat  from  those  acids  which  are  much  more 
fixed  than  Uself.  The  most  important  of  these  salts  are  thus  constituted : — 

Names.  Base.  Acid.  Equiv.     Formulae. 

Hydrochlorate  of  ammonia  17-15  1  eq.-f-  36-42  1  eq.=  53-57    H3N-f.HCl. 

Hydriodate  do.  17-15  1  eq.+127-3     1  eq.  =144-45    H8N-fHI. 

Hydrobromate  do.  17-15  1  cq.+  79-4     1  eq.=  96-55    HJN-f-HBr. 

Hydrofluate  do.  17-15  1  eq.-f-  19-68  1  eq.=  36-83    H3N-f  HF. 

Hydrosulphate  do.  17-15  1  eq.-f   17-1     1  eq.=  34-25    H3N  +  HS. 

Triflnoborate  do.  51-45  3  eq.+  66-94  1  eq.=118-39  SHaN-f-BF*. 

Pifluoborate  do.  34-3     2  eq.-h  66-94  1  cq.=l 01-24  2H3N-f-BF,3. 

Fluoborate  do.  17-15  1  eq.-j-  66-94  1  eq.=  84-09    HsN-j-BF3. 

Fluosilicate  do.  17-15  1  eq.+  78-54  1  eq.=  95-69    H  N+ SiF3. 

Carbosulphate  do.  17-15  1  eq.-f  38-32  1  eq.=  55-47    HSN-fCSa. 

Hydrochlorate  of  Ammonia. — -This  salt,  the  sal  ammoniac  of  commerce, 
was  formerly  imported  from  Egypt,  where  it  is  procured  by  sublimation  from 
the  soot  of  camels'  dung;  but  it  is  now  manufactured  in  Europe  by  several 
processes.  The  most  usual  is  to  decompose  sulphate  of  oxide  of  ammonium 
by  the  chloride  either  of  sodium  or  magnesium,  when  double  decomposition 
ensues,  giving  rise  in  both  cases  to  hydrochlorate  of  ammonia,  and  to  sul- 
phate of  soda  when  chloride  of  sodium  is  used,  and  to  sulphate  of  magnesia 
when  chloride  of  magnesium  is  employed.  The  sal  ammoniac  is  afterwards 
obtained  in  a  pure  state  by  sublimation.  The  method  now  generally  used  in 
this  country  for  obtaining  sulphate  of  oxide  of  ammonium  is  to  decompose 
with  sulphuric  acid  the  hydrosulphate  and  hydrocyanate  of  ammonia  which 
is  collected  in  the  manufacture  of  coal-gas;  but  it  may  also  be  procured 
either  from  lixiviating  the  soot  of  coal,  which  contains  sulphate  of  oxide  of 
ammonium  in  considerable  quantity, or  by  digesting,  with  gypsum,  impure 
sesquicarbonate  of  oxide  of  ammonium,  procured  from  the  destructive  distil- 
lation of  bones  and  other  animal  substances,  so  as  to  form  an  insoluble  car- 
bonate of  lime  and  a  soluble  sujphate  of  oxide  of  ammonium. 

Hydrochlorate  of  ammonia  has  a  pungent  saline  taste,  a  density  of  1-45, 
and  it  is  tough  and  difficult  to  be  pulverized.  It  is  soluble  in  alcohol  and 
water,  requiring  for  solution  three  times  its  weight  of  water  at  60°,  and  an 
equal  weight  of  212°.  It  usually  crystallizes  from  its  solution  in  feathery 
crystals,  but  sometimes  in  cubes  or  octohcdrons.  At  a  temperature  below 
that  of  ignition  it  sublimes  without  fusion  or  decomposition,  and  condenses 
on  cool  surfaces  as  an  anhydrous  salt,  which  absorbs  humidity  in  a  damp 


AMMONIACAL   SALTS.  457 

atmosphere,  but  is  not  deliquescent.     It  is  generated  by  the  direct  union  of 
hydrochloric  acid  gas  and  arnmoniacal  gas  which  unite  in  equal  volumes. 

Hydriodate  of  Ammonia. — It  is  formed  as  a  white  powder  by  the  direct 
union  in  equal  measures  of  hydriodic  acid  gas  and  ammoniacal  gas,  or  by 
neutralizing  a  solution  of  hydriodic  acid  with  ammonia,  and  evaporating.  It 
crystallizes  with  difficulty  in  anhydrous  cubes,  is  very  soluble  in  water,  and 
deliquesces  in  a  moist  atmosphere.  In  close  vessels  it  may  be  sublimed 
without  change ;  but  it  suffers  partial  decomposition  when  heated  in  the 
open  air. 

When  a  concentrated  solution  of  this  salt  is  digested  with  iodine,  a  brown 
solution  is  obtained,  the  nature  of  which  is  not  understood. 

Hydrobromate  of  Ammonia  is  a  white  anhydrous  salt,  which  may  be 
formed  by  similar  processes  as  the  hydriodate.  It  is  soluble  in  water,  and 
crystallizes  by  evaporation  in  quadrilateral  prisms. 

Hydrofluate  of  Ammonia. — It  is  prepared  by  mixing  1  part  of  sal  ammo- 
niac with  2 1  of  fluoride  of  sodium,  both  dry  and  in  fine  powder,  gently  heat- 
ing the  mixture  in  a  platinum  vessel,  and  receiving-  the  sublimed  salt  in  a 
second  platinum  vessel,  the  temperature  of  which  is  riot  allowed  to  exceed 
212°.  Chloride  of  sodium  is  generated,  and  hydrofluate  of  ammonia  is  ob- 
tained in  small  anhydrous  prismatic  crystals  which  may  be  preserved  un- 
changed in  the  air,  is  partly  soluble  in  alcohol,  and  dissolves  readily  in  water. 
At  an  elevated  temperature  it  fuses  before  subliming.  It  acts  powerfully  on 
glass  even  in  its  dry  state. 

When  this  salt  is  introduced  in  a  dry  state  into  ammoniacal  gas,  absorp- 
tion ensues,  and  the  resulting  salt  appears  to  be  a  dihydrofluate  of  ammonia. 
By  sublimation  it  loses  ammonia  and  becomes  neutral.  An  acid  salt,  appa- 
rently a  bihydrofluate,  is  obtained  by  evaporating  the  aqueous  solution  of  the 
neutral  hydrofluate,  ammonia  being  disengaged.  If  the  evaporation  take 
place  at  100°,  it  separates  in  crystalline  grains,  which  redden  litmus,  and 
deliquesce  rapidly  at  common  temperatures. 

Hydrosulphate  of  Ammonia. — This  salt,  also  called  hydrosulphuret  of  am- 
monia, and  formerly  the  fuming  liquor  of  Boyle,  is  prepared  by  heating  a 
mixture  of  one  part  of  sulphur,  two  of  sal  ammoniac,  and  two  of  unslaked 
lirne.  The  changes  which  ensue  have  been  explained  by  Gay-Lussac.  The 
volatile  products  are  ammonia  and  hydrosulphate  of  ammonia;  and  the  fixed 
residue  consists  of  sulphate  of  lime,  with  chloride  and  sulphuret  of  calcium. 
The  hydrosulphuric  acid  is  formed  from  the  hydrogen  of  hydrochloric  acid 
uniting  with  sulphur,  and  the  oxygen  of  the  sulphuric  acid  is  derived  from 
decomposed  lime,  the  calcium  of  which  is  divided  between  the  chlorine  of 
the  hydrochloric  acid,  and  the  sulphur.  Hydrosulphate  of  ammonia  may  also  be 
formed  by  the  direct  union  of  its  constituent  gases,  and  if  they  are  mixed  in 
a.  glass  globe  kept  cool  by  ice,  the  salt  is  deposited  in  crystals.  It  is  much 
used  as  a  reagent,  and  for  this  purpose  is  usually  prepared  by  saturating 
solution  of  ammonia  with  hydrosulphuric  acid  gas. 

Fluoborates  of  Ammonia. — Fluoboric  acid  combines  with  three  times  and 
with  twice  its  volume  of  ammoniacal  gas,  forming  a  trifluoborate  and  difluo- 
borate,  which  are  liquid  at  common  temperatures.  The  neutral  fluoborate 
is  formed  of  equal  volumes  of  its  constituent  gases,  and  is  a  white  volatile 
salt,  soluble  in  water,  but  which  cannot  be  recovered  from  the  solution;  for 
on  evaporation,  a  subfluoborate  of  ammonia  is  expelled,  and  boracic  acid  is 
left  in  solution.  The  neutral  fluoborate  is  formed  by  heating  gently  either 
of  the  subfluoborates. 

FLuosilicate  of  Ammonia. — Fluosilicic  acid  and  ammoniacal  gases  unite 
by  volume  in  the  ratio  of  one  to  two,  forming  a  white  volatile  salt  which  is 
decomposed  by  water. 

Carbosulphate  of  Ammonia. — When  dry  ammoniacal  gas  is  brought  into 
contact  with  bisulphuret  of  carbon,  direct  combination  ensires,  and  there  re- 
suits  an  uncrystalline  solid  mass  of  straw-yellow  colour  which  may  be  sub- 
limed without  decomposition.  By  contact  with  water,  or  exposure  to  a  moist 
air,  an  interchange  ensues  between  the  elements  of  water  and  bisulphuret 

39 


458  SULPHUR-SALTS. 

of  carbon,  giving  rise  to  hydrosulphuric  und  carbonic  acids;  and  a  sulphur- 
salt  of  an  orange-yellow  colour,  the  hydro-carbosulphuret  of  ammonia,*  is 
generated. 

Arsenio-per sulphate  of  Ammonia. — Berzelius  states  that  when  dry  persul- 
phuret  of  arsenic  is  exposed  to  ammoniacal  gas,  absorption  ensues,  and  a 
yellowish-white  compound  results ;  but  the  elements  are  united  by  a  feeble 
attraction,  and  on  mere  exposure  to  the  air,  the  ammonia  escapes. 

SALTS  OF  PHOSPHURETTED  HYDROGEN. 

Rose  has  lately  called  the  attention  of  chemists  to  the  close  analogy  which 
exists  in  the  composition  of  ammonia  and  phosphuretted  hydrogen,  and  in 
some  of  their  properties.  The  latter  is  a  feeble  alkaline  base,  which  com- 
bines with  some  of  the  hydracids.  The  salt  best  known  is  the  hydriodate  or 
phosphuretted  hydrogen,  first  noticed  by  Gay-Lussac,  which  is  formed  of 
127-3  parts  of  one  eq.  of  acid  and  344  parts  or  one  eq.  of  base,  and  crystal- 
lizes in  cubes.  The  crystals  are  permanent  while  quite  dry;  but  with  water 
or  the  moisture  of  the  air,  they  yield  a  solution  of  hydriodic  acid,  and  phos 
phuretted  hydrogen  gas  escapes.  These  salts  are  all  decomposed  by  water 
and  exist  only  in  the  anhydrous  state. 


SECTION  III. 

CLASS  OF  SALTS.  ORDER  III. 

SULPHUR-SALTS. 

THE  compounds  described  in  this  section  are  double  sulphurets,  just  as 
the  oxy-salts  in  general  are  double  oxides.  Their  resemblance  in  composi- 
tion to  salts  is  perfect.  The  principal  sulphur-bases  are  the  protosulphurets 
of  potassium,  sodium,  lithium,  barium,  strontium,  calcium,  and  magnesium, 
and  hydrosulphate  of  ammonia;  and  the  principal  sulphur-acids  are  the  sul- 
phurets of  arsenic,  antimony,  tungsten,  molybdenum,  tellurium,  tin,  and 
gold,  together  with  hydrosulphuric  acid,  bisulphuret  of  carbon,  and  sulphuret 
of  selenium.  The  sulphur-salts  with  two  metals  are  so  constituted,  that  if 
the  sulphur  in  each  were  replaced  by  an  eq.  quantity  of  oxygen,  an  oxy-salt 
would  result.  The  analogy  between  oxy-salts  and  sulphur-salts  is  rendered 
still  closer  by  the  circumstance  that  hydrosulphuric  and  hydrosulphoeyanic 
acids  have  the  characteristic  properties  of  acidity,  and  unite  both  with  am- 
monia and  with  sulphur-bases. 

Tlie  sulphur-salts  may  be  divided  into  families,  characterized  by  contain 
jng  the  same  sulphur-acid.  For  the  purpose  of  indicating  that  such  salts  are 
double  sulphurets,  as  well  as  to  distinguish  them  readily  from  other  kinds  of 
salts,  I  shall  construct  the  generic  name  of  each  family  from  the  sulphur- 
acid  terminated  with  sulphuret.  Thus  the  salts  which  contain  persulphuret 
of  arsenic  or  hydrosulphuric  acid  as  the  sulphur-acid  are  termed  arsenio- 
sulphurets  and  hydro-sulphurets ;  and  a  salt  composed  of  each  of  these 
sulphur-acids  with  sulphuret  of  potassium  is  termed  arsenio-sulphuret  and 
hydro-sulphur et  of  sulphuret  of  potassium.  For  the  sake  of  brevity  the  metal 


*  It  is  not  very  clear  what  combination  Dr.  Turner  intends  by  the  name, 
hydro-car bosulphuret  of  ammonia  ;  but  it  is  probable  that  he  means  to  desig- 
nate the  sulphur-salt  called  further  on,  carbo- sulphur et  of  hydrosulphate  of 
ammonia.  See  page  460. — Ed. 


HYDRO-SULPHURETS. 


459 


of  the  base  may  alone  be  expressed,  it  being  understood  that  the  positive 
metal  in  a  sulphur-salt  enters  as  a  protosulphuret  into  the  compound.* 

HYDRO-SULPHURETS. 

The  sulphur-salts  contained  in  this  group  have  hydrosulphuric  acid  for 
their  electro-negative  ingredient.  Most  of  them  which  have  been  studied 
are  soluble  in  water,  and  may  be  obtained  in  crystals  by  evaporation.  They 
are  decomposed  by  exposure  to  the  air,  yielding  at  first  bisulphurets  of  the 
metal,  and  then  a  hyposulphite.  By  acids  the  hydrosulphuric  acid  is  ex- 
pelled with  effervescence.  They  are  thus  constituted  : — 


Sulphur- 
Names,              base. 

Sulphur- 
acid. 

Equiv. 

Formulae. 

Hydrosulphuret  of  ) 
potassium  V 

55-25 

"I'. 

eq.+  17-l 

1 

eq 

.=72-35 

KS+HS. 

Do. 

sodium 

39-4 

1 

eq.+17-l 

] 

Cq 

.= 

56-5 

NaS4-HS. 

Do. 

lithium 

22-54 

1 

eq.-j-17-l 

1 

cq 

.  — 

39-64 

LS+HS. 

Do. 

barium 

84-8 

1 

eq.-j-17-l 

1 

eq 

.=101-9 

BaS-l-HS. 

Do. 

strontium 

59-9 

1 

eqH-17-l 

1 

eq 

.= 

77 

SrSO-HS. 

Do. 

calcium 

36-6 

1 

eq.+17-l 

1 

cq 

.= 

53-7 

CaS4-HS. 

Do. 

magnesium 

28-8 

1 

eq.+17-l 

1 

eq 

fr? 

45-9 

MgS-f-HS. 

HydrO'Sulphuret  of  Potassium. — This  salt  is  obtained  in  the  anhydrous 
state  by  introducing  anhydrous  carbonate  of  potassa  into  a  tubulated  retort, 
transmitting  through  it  a  current  of  hydrosulphuric  acid  gas,  and  heating 
the  salt  to  low  redness.  The  mass  becomes  black,  fuses,  and  boils  from  the 
escape  of  carbonic  acid  gas  and  aqueous  vapour  ;  and  after  the  ebullition  has 
ceased,  the  gas  is  continued  to  be  transmitted,  until  the  retort  is  quite  cold. 
The  resulting  anhydrous  hydro-sulphuret  of  potassium,  though  black  while 
in  fusion,  is  white  when  cold,  and  of  a  crystalline  texture;  but  if  air  had  not 
been  perfectly  excluded,  it  has  a  yellow  tint,  owing  to  the  presence  of  some 
bisulphuret  of  potassium. 

The  same  salt  is  prepared  in  the  moist  way  by  introducing  a  solution  of 
pure  potassa,  free  from  carbonic  acid,  into  a  tubulated  retort,  expelling  at- 
mospheric air  by  a  current  of  hydrogen  gas,  and  then  saturating  the  solution 
with  hydrosulphuric  acid.  At  first  the  potassa,  as  in  the  former  process,  in- 
terchanges elements  with  the  gas,  yielding  water  and  protosulphuret  of  po- 
tassium ;  after  which  the  protosulphuret  unites  with  hydrosulphuric  acid. 
The  solution  should  be  evaporated  in  the  retort  to  the  consistence  of  syrup,  a 
current  of  hydrogen  gas  being  transmitted  through  the  apparatus  the  whole 
time;  and  on  cooling  the  salt  crystallizes  in  large  four  or  six-sided  prisms, 
which  are  colourless  if  air  was  perfectly  excluded.  The  crystals  contain 
water  of  crystallization,  have  an  acrid,  alkaline,  and  bitter  taste,  deliquesce  in 
open  vessels,  and  dissolve  freely  in  water  and  alcohol.  On  exposure  to  the 
air  it  acquires  a  yellow  colour,  from  the  formation  of  bisulphuret  of  potas- 
sium. 


*  Dr.  Hare  has  adopted  an  ingenious  plan  for  naming  the  sulphur-salts, 
founded  on  the  nomenclature  of  the  oxy-salts.  Considering  the  electro- 
negative sulphuret  in  the  sulphur-salts  as  performing  the  part  of  an  acid,  he 
calls  it  an  acid,  and  forms  its  name  by  changing  the  termination  of  the  ele- 
ment with  which  the  sulphur  is  combined  into  ic,  and  prefixing  sulph  or 
sulpha.  Thus,  taking1  the  examples  given  by  Dr.  Turner,  he  calls  persul- 
phuret  of  arsenic,  sulpharsenic  acid,  and  its  sulphur-salts,  sulpharseniates ; 
while  he  denominates  hydrosulphuric  acid,  sulphydric  acid,  and  its  salts 
Bulphydrates.  In  indicating  the  sulphur-base,  Dr.  Hare  has  adopted  the 
same  plan  which  Dr.  Turner  recommends  in  the  text,  of  expressing  the 
metal  only  of  the  sulphur-base,  the  metal  being  understood  to  be  in  the 
state  of  protosulphuret,'— Ed, 


460 


CARBO-SULPHURETS. 


Hydro-sulphuret  of  Sodium.  —  It  is  prepared  on  the  same  principles  as  the 
former  salt,  and  yields  by  evaporation  colourless  crystals.  When  a  hot  con- 
centrated solution  is  mixed  with  a  solution  of  hydrate  of  soda  also  concen- 
trated, the  mixture  on  cooling  deposites  four-sided  prisms,  which  are  proto- 
sulphuret  of  sodium  with  water  of  crystallization.  The  interchange  of 
elements  is  such  that 


1  eq.  hydro-sulphuret  and  1  eq.  soda  J  3 
(Na  +  S)  +  (H  +  S)        Na-fO 


2  eq.  sulphuret  and  1  eq.  water. 
2(Na+S)  H  +  O. 

Hydro-sulphuret  of  Lithium  may  be  prepared  in  the  same  way  as  the 
two  former  salts,  and  is  left  by  evaporation  as  a  crystalline  solid.  When 
heated  in  close  vessels  it  parts  with  its  water  of  crystallization,  and  like  the 
two  former  salts  retains  its  acid  even  at  a  red  heat. 

Hydro-sulphuret  of  Barium.  —  It  is  prepared  by  the  action  of  hydrosul- 
phuric  acid  on  a  solution  of  baryta  with  the  precautions  already  mentioned 
for  excluding  atmospheric  air,  and  crystallizes  by  evaporation  in  four-sided 
prisms,  which  are  very  soluble  in  water,  but  dissolve  sparingly  in  alcohol. 
The  crystals  part  with  their  water  of  crystallization  when  heated,  and  at 
a  commencing  red  heat  give  out  hydrosulphuric  acid,  leaving  pure  sulphuret 
of  barium. 

Hydro-sulphuret  of  Strontium  is  prepared  like  the  former  salt,  and  crystal- 
lizes in  large  radiated  prisms,  which  when  quite  dry  may  be  kept  several 
days  exposed  to  the  air  without  change.  When  heated  it  loses  its  water  and 
acid,  and  protosulphuret  of  strontium  as  a  white  powder  is  left. 

Hydro-sulphuret  of  Calcium  is  formed  in  the  same  manner  as  the  pre- 
ceding salts;  but  it  exists  only  in  solution  ;  for  on  attempting  to  crystallize 
by  evaporation,  hydrosulphuric  acid  is  driven  off,  and  the  sulphuret  of  cal- 
cium, in  prisms  of  a  silky  lustre,  is  deposited.  The  hydro-sulphuret  of  mag- 
nesium likewise  exists  only  in  solution. 

CARBO-SULPHURETS. 

The  acid  of  these  sulphur-salts  is  bisulphuret  of  carbon;  and  the  salts 
themselves  are  thus  constituted  : 


Sulphur- 
Names,  base. 
Carbo-sulphuret  of  )  55.35 

potassium          ^    c 
Do.  sodium  39-4 

Do.  lithium  22-54 

Do.  hydrosulphate 
of  ammonia 
Do.  barium  84-8 

Do.  strontium  59-9 

Do.  calcium  36-6 

Do.  magnesium          28  8 


Sulphur- 
acid. 

1  eq.-|-38-32     1  eq. 

1  eq.-}-38-32     1  eq.: 
1  eq.+38'33     1  eq/ 


Equiv. 
=  93-57 


Formulae. 


1  eq.4-38-32 

1  eq.-|-38-32 
1  eq.-f38-32 
1  eq.-r-38-32 
1  eq.-|-38  32 


1  eq.= 

1  eq.; 
1  eq.= 
1  eq.= 
1  eq  = 


KS  +  CS2 

NaS-f-CS\ 

LS4.CS2. 

(IPN-fHS) 

J-CS*. 
BaS-fCS*. 
SrS-f-CS*. 


=  77-72 
=  60-86 

--  72-57$ 

=123-12 

=  98-22 
=  74-92 
=  67-12  MgS+CSs. 


Carbo-sulphuret  of  Potassium. — On  agitating  bisulphuret  of  carbon  with 
a  strong  alcoholic  solution  of  protosulphuret  of  potassium,  the  liquid  when 
set  at  rest  separates  into  three  layers,  the  lowest  of  which  is  carbo-sulphuret 
of  potassium,  and  is  of  the  consistence  of  syrup.  Another  process  is  to  di- 
gest bisulphuret  of  carbon  at  86°  in  a  corked  bottle,  full  of  a  strong  aqueous 
solution  of  protosulphuret  of  potassium,  until  the  latter  is  saturated.  A  con- 
centrated solution  of  this  salt  is  of  a  deep  orange,  almost  red,  colour;  and 
when  evaporated  at  86°  to  the  consistence  of  syrup,  a  deliquescent  yellow 
crystalline  salt  is  deposited,  which  is  sparingly  soluble  in  alcohol.  On  heat- 
ing it  to  150°  it  gives  off  water  of  crystallization  ;  and  when  more  strongly 
heated  it  is  resolved  into  tersulphuret  of  potassium  and  charcoal. 

Carbo-sulphuret  of  Sodium. — It  is  prepared  like  the  former  salt,  and  sepa- 


ARSENIO-SULPHURETS.  461 

rates  in  yellow  crystals  from  a  very  concentrated  solution.  It  is  deliquescent, 
and  dissolves  readily  in  alcohol  as  well  as  water. 

Car  bo-sulphur  et  of  Lithium  resembles  the  preceding  salt,  and  is  very  solu- 
ble in  water  and  alcohol. 

Carbo-sulphuret  of  Hydrosulphate  of  Ammonia.  —  Zeisse  prepares  this  salt 
by  filling  a  bottle,  with  ten  measures  of  nearly  absolute  alcohol,  saturated 
.with  amrnoniacal  gas,  and  one  measure  of  bisulphuret  of  carbon,  and  insert- 
ing- a  tight  cork.  As  soon  as  the  liquid  has  acquired  a  yellowish-brown 
colour,  the  botlle  is  plunged  into  ice-cold  water,  when  the  carbo-sulphuret  is 
deposited  either  in  yellow  penniform  crystals,  or  as  a  crystalline  powder. 
The  whole  "is  thrown  upon  a  linen  filter,  and  the  salt  after  being  washed,  first 
with  absolute  alcohol  and  then  with  ether,  is  dried  by  pressure  within  folds 
of  bibulous  papqr.  This  salt  is  very  volatile,  passing  oft  entirely  at  common 
temperatures,  and  can  only  be  preserved  in  well-corked  bottles.  Exposed  to 
the  air  it  absorbs  humidity  and  acquires  a  red  colour.  Its  solution  may  be 
kept  unchanged  in  bottles  filled  with  it  and  tightly  corked. 

The  carbo-sulphurets  of  barium,  strontium,  and  calcium  may  be  obtained 
oy  acting  on  bisulphuret  of  carbon  with  a  solution  of  the  protosulphurets  of 
those  metals.  The  resulting  solutions  are  of  an  orange  or  brown  colour, 
and  the  salts  deposited  by  evaporation  are  of  a  citron-yellow  when  quite  dry. 
The  carbo-sulphuret  of  barium  is  of  sparing  solubility.  The  carbo-sulphuret 
of  magnesium  is  best  prepared  by  adding  sulphate  of  magnesia  to  a  solution 
of  carbo-sulphuret  of  barium.  Berzelius  has  also  prepared  several  carbo- 
sulphurets  of  the  metals  of  the  second  class. 

ARSENIO-SULPHURETS. 

Borzelius  finds  that  each  of  the  three  sulphurets  of  arsenic  (page  338)  is 
capable  of  acting  as  a  sulphur-acid,  giving  rise  to  three  distinct  families  of 
sulphur-salts,  distinguishable  by  the  terms  arsenio-persulphurets,  arsenio-ses- 
quisulphurets,  and  arsenio-protosulphurets. 

Persulphuret  of  arsenic  is  a  very  powerful  sulphur-acid,  violently  displac- 
ing hydrosulphuric  acid  from  its  combinations  with  sulphur-bases,  even  at 
common  temperatures;  and  when  digested  with  earthy  or  alkaline  carbon- 
ates, it  expels  carbonic  acid.  The  salts  of  this  sulphur-acid  may  be  prepared 
by  several  different  methods:  — 

1.  By  digesting-  the  persulphuret  of  arsenic  in  a  solution  of  a  sulphur- 
base,  such  as  protosulphuret  of  potassium  or  sodium,  until  it  is  saturated. 
The  resulting  soluble  arsenio-persulphuret  may  be  employed  to  prepare  inso- 
luble salts  of  the  same  sulphur-acid  by  means  of  double  decomposition.  If 
a  persulphuret  of  potassium  is  used,  sulphur  is  deposited. 

^2.  By  decomposing  a  hydrosulpfmret  of  a  sulphur-base  with  persulphuret 
of  arsenic,  in  which  case  hydrosulphuric  acid  gas  is  disengaged  with  efferves- 
cence. 

3.  By  decomposing  a  solution  of  an  arseniate  by  means  of  hydrosulphuric 
acid  or  hydrosulphate  of  ammonia. 

4.  By  dissolving  persulphuret  of  arsenic  in  a  solution  of  caustic  alkali,  such 
as  potassa  ;  when  an  interchange  of  elements  between  portions  of  the  alkali 
and  persulphuret  ensues,  whereby  arsenic  acid  and  protosulphuret  of  potassium 
are  generated.     In  this  case 

1  eq.  persulph,  &  5  eq.  potassa  )    .  ,  ,  $  1  eq.  arsenic  acid  &  5  eq.  protosulph. 
2As+5S  5(K+0)    $yield)        2AS+50 


Two  salts  are  thus  generated  and  co-exist  in  the  solution,  namely,  arseniate 
of  potassa  and  arsenio-porsulphuret  of  potassium.  Similar  changes  invaria- 
bly occur  when  sesquisulphuret  of  arsenic,  sesquisulphuret  of  antimony,  and 
other  sulphur-acids  are  boiled  with  alkaline  solutions  :  an  oxy-salt,  the  acid 
of  which  is  formed  of  oxygen  and  the  electro-negative  metal,  is  always  gen- 
erated ;  and  this  salt,  if  soluble  in  water,  remains  together  with  the  sul- 
phur-salt in  solution.  An  alkaline  carbonate  may  be  substituted  for  a  pure 

39* 


462  ARSENIO-SULPHURETS. 

alkali,  but  then  carbonic  acid  is  expelled.    These  principles  are  concerned 
in  the  production  of  kermes,  as  already  explained  (page  359.) 

5.  The  last  method  which  requires  mention,  is  by  exposing  a  mixture 
of  persulphuret  of  arsenic  and  an  alkaline  carbonate  to  a  red  heat  in  a 
covered  vessel.  Carbonic  acid  gas  is  disengaged;  and  an  interchange  of 
elements,  similar  to  that  just  explained,  takes  place  between  a  portion  of  the 
alkali  and  the  persulphuret.  The  fused  mass,  accordingly,  contains  an  arsen- 
iate  of  the  alkali,  as  well  as  a  sulphur-salt.  This  tendency  to  the  formation 
of  a  double  sulphuret  is  the  reason  why,  in  decomposing  orpiment  by  black 
flux,  the  whole  of  the  arsenic  is  never  sublimed  :  a  part  is  uniformly  re- 
tained in  the  form  of  a  sulphur-salt,  the  arsenio-sesquisulphuret  of  sulphuret 
of  potassium. 

Most  of  the  arsenio-persulphurets  of  the  second  class  of  metals  are  insol- 
uble; but  those  of  the  metals  of  the  alkalies  and  alkaline  earths  are  very 
soluble  in  water,  have  a  lemon-yellow  colour  in  the  anhydrous  state,  and 
are  colourless  when  combined  with  water  of  crystallization  or  in  solution. 
When  exposed  to  heat  in  close  vessels  they  give  off  sulphur,  and  an  arsenio- 
sesquisulphuret  is  generated.  In  the  solid  state  they  are  very  permanent  in 
the  air,  and  even  in  solution  oxidation  takes  place  with  great  slowness. 
When  decomposed  by  an  acid,  persulphuret  of  arsenic  subsides,  hydrosul- 
phuric  acid  gas  escapes,  and  a  salt  of  the  alkali  is  generated.  Some  chemists 
may  doubt  the  possibility  of  the  arsenio-persulphurets  dissolving  as  such  in 
water;  they  may  consider  the  arsenic,  and  the  metal  of  the  sulphur-base  to 
be  united  with  oxygen,  and  all  the  sulphur  with  hydrogen  ;  but  this  suppo- 
sition, if  followed  out,  leads  into  such  complex  and  improbable  modes  of 
combination,  that  I  see  no  alternative  but  implicitly  to  admit  the  views  here 
adopted. 

The  following  table  exhibits  the  composition  of  the  principal  arsenio-per- 
sulphurets : 

Sulphur-         Sulphur- 
Names.  base.  acid.  Equiv.        Formulae. 


leq.=321-65  3KS  +  As<2S5. 

Diarsenio.  persulph.  do.   110-5    2  eq.-j-155-9  1  eq.=266-4    2KS-J-AS2S5. 
Arsenio-persulph.  do.       55-25     1  eq.+155'9  1  eq.=211-15     KS-fAs2S5. 

3  eq.+155-9  1 


Do.     in  crystals  with  270  or  30  eq.  of  water   =544-1 

Diarsenio-persulph.  do.      78-8    2  eq.4-155-9  1  eq.=234-7    2NaS-fAs2S5. 

Arsenio-persulph.  do.         39-4     1  eq-4-155-9  1  eq.=193-3       NaS-f  AsSS*. 

Triarsenio-persulph.  of  J  10o.7r  o  pn   ,  irr.q  i  pn  _o*Q.fis  5  3(H3N-fHS) 

hydrosulph.  amm.     ^02753eq.+l.     )  1  eq._        ^    +Ag2S5. 

Diarsenio-persulph.  do.      68-5     2  eq.+155-9  1  eq.=224-4    j 
Arsenio-persulph.  do.        34-25  1  eq.+155-9  1  eq.=190  15 

Arsenio-persulphurets  of  Potassium.  —  The  diarsenio-persulphuret  is  best 
obtained  by  the  action  of  hydrosulphuric  acid  gas  on  the  diarseniate  of  po- 
tassa,  and  yields  a  colourless  solution.  By  evaporation  in  vacuo  it  is  reduced 
to  a  yellowish  viscid  mass  which  dries  imperfectly,  but,  when  exposed  for 
some  time  to  the  open  air,  at  length  becomes  a  crystalline  mass  of  a  lemon- 
yellow  colour,  in  which  rhomboidal  tables  are  perceptible.  When  this  salt 
is  mixed  with  alcohol,  it  is  resolved  into  the  triarsenio-persulphuret,  which  is 
insoluble  in  the  alcohol,  and  the  arsenio-persulphuret,  which  remains  in  solu- 
tion. The  latter  has  not  been  obtained  in  the  solid  state.  The  former  is 
deliquescent  and  very  soluble  in  water  ;  but  when  its  solution  is  gently  eva- 
porated, the  residue  has  a  radiated  crystalline  texture. 

Arsenio-persulphurets  of  Sodium.  —  The  diarsenio-persulphuret  is  formed 
like  the  corresponding  salt  of  potassium,  is  very  soluble  in  water,  and  by 


MOLYBDO-SULPHURKTS,  463 

evaporation  yields  a  lemon-yellow  mass,  which  attracts  humidity  from  the 
air.  On  mixing  its  solution  with  alcohol  it  is  resolved  into  the  arsenio-per- 
sulphuret and  triarscnio-persulphuret  of  sodium,  and  the  latter  falls  in  scaly 
crystals  of  snowy  whiteness,  which  may  be  collected  on  a  filter,  washed  with 
alcohol,  and  dried  without  change.  This  salt  by  solution  in  water  and  eva- 
poration may  be  obtained  in  rhomboidal  tables,  or  prisms  derived  from  a 
rhombic  prism.  The  crystals  undergo  no  change  in  the  air,  and  contain 
thirty  eq.  of  water.  The  arsenio-persulphuret  has  been  obtained  only  in  so- 
lution. The  arsenio-persulphurets  of  lithium  are  very  analogous  to  those  of 
sodium. 

Arsenio-persulphurets  of  Hydrosulphate  of  Ammonia.  —  The  diafsenio-per- 
sulphuret  is  obtained  as  a  colourless  solution  by  decomposing  with  hydrosul- 
phuric  acid  gas,  a  solution  of  triarseniate  of  oxide  of  ammonium  and  basic  water. 
By  spontaneous  evaporation  it  becomes  a  viscid  mass  of  a  reddish-yellow 
colour,  and  which  cannot  be  fully  dried  without  decomposition.  When  its 
solution  is  mixed  with  hydrosulphate  of  ammonia  and  agitated  with  hot  alco- 
hol, the  triarsenio-sulphuret  is  deposited  in  colourless  prisms,  which,  after 
being  well  washed  with  alcohol  and  dried  on  bibulous  paper,  undergo  no 
change  by  exposure  to  the  air.  The  arsenio-persulphuret  remains  in  the 
alcoholic  solution. 

Analogous  salts  may  be  similarly  prepared  with  barium,  strontium,  cal- 
cium, and  magnesium  ;  and  insoluble  compounds  of  the  same  nature  may  be 
formed  by  way  of  double  decomposition  by  mixing  soluble  arsenio-persul- 
phurets with  oxy-salts  of  the  second  class  of  metals. 

The  salts  in  which  sesquisulphuret  of  arsenic  acts  as  an  acid,  resemble 
those  of  the  persulphuret  both  in  their  general  characters  and  mode  of  forma- 
tion. Those  formed  with  the  protosulphuret  of  arsenic  cannot  be  made  n 
the  moist  way  by  direct  union  of  their  ingredients  ;  but  when  solutions  of 
the  arsenio-sesquisulphurets  are  evaporated,  spontaneous  decomposition  takes 
place,  the  salts  of  protosulphuret  of  arsenic  of  a  reddish-brown  colour  sub- 
sides, while  arsenio-persulphurets  remain  in  solution. 

MOLYBDO-SULPHURETS. 

The  electro-negative  ingredient  of  these  salts  is  the  tersulphuret  of  molybde- 
num, and  the  most  remarkable  of  them  is  the  molybdo-sulphuret  of  potassium  , 
which  is  readily  formed  by  decomposing  with  hydrosulphuric  acid  gas  a 
rather  strong  solution  of  molybdate  of  potassa.  If  no  iron  is  present,  the 
liquid  acquires  a  beautiful  red  colour  like  the  solution  of  bichromate  of  potassa, 
and  on  evaporation  prismatic  crystals  with  four  and  eight  sides  are  deposited. 
Berzelius  describes  this  compound  as  one  of  the  most  beautiful  which  chem- 
istry can  produce  :  the  crystals,  by  transmitted  light,  are  ruby-red,  and 
•  their  surfaces,  while  moist  with  the  solution  which  yielded  them,  shine  like 
the  wings  of  certain  insects  with  a  metallic  lustre  of  a  rich  green  tint.  The 
crystals  are  anhydrous,  dissolve  readily  in  water,  but  are  insoluble  in  alco- 
hol. On  the  addition  of  sulphuric  or  any  of  the  stronger  acids,  a  salt  of  po- 
tassa is  generated  with  escape  of  hydrosulphuric  acid,  and  precipitation  of 
tersulphuret  of  molybdenum. 

Soluble  molybdo-sulphuret  s  af  sodium,  lithium,  and  hydrosulphale  of  ammo- 
nia  of  a  red  colour,  may  be  obtained  by  a  process  similar  to  that  for  pre- 
paring the  preceding  compound.  The  composition  of  these  salts  is  as 
follows  :  — 

Sulphur-        Sulphur- 
Names.  base.  acid.  Equiv.          Formulae. 


55-25    1  eq.+96     1  eq.=15M5   '     KS  +  MoS3. 
39'4      le*+96    1^=135-4          NaS  +  MoS3. 

LS+MoS3. 


4 64  HALOID  SALTS. 

Similarly  constituted  soluble  salts  of  a  red  or  orange  colour  may  be  ob- 
tained by  boiling  solutions  of  sulphuret  of  barium,  strontium,  and  calcium 
with  an  excess  of  tersulphuret  of  molybdenum.  The  insoluble  molybdo- 
sulphurets  may  be  prepared  from  the  former  by  way  of  double  decompo- 
sition. 

ANTIMONIO-SULPHURETS. 

When  two  parts  of  carbonate  of  potassa  are  intimately  mixed  with  four  of 
sesquisulphuret  of  antimony  and  one  part  of  sulphur,  and  the  mixture  is  fused, 
an  antimonio-persulphuret  of  potassium  is  generated.  On  digesting  in  water, 
a  subantimonio-persulphuret  is  dissolved,  and  is  deposited  by  gentle  evapora- 
tion in  large  colourless  tetrahedrons,  which  become  yellow  on  exposure  to 
the  air.  The  salts  which  persulphuret  of  antimony  forms  with  other  bases 
have  not  been  examined. 

A  sulphur-salt  of  potassium,  in  which  sesquisulphuret  of  antimony  is  the 
acid,  remains  in  solution  after  the  kermes  is  deposited  (page  360),  and  may 
be  obtained  by  evaporation  in  vacuo  in  colourless  irregular  crystals  which 
deliquesce  rapidly  in  the  air. 

TUNGSTO-SULPHURETS. 

The  best  known  of  these  salts  is  that  of  potassium,  in  which  tersulphuret 
of  tungsten  is  combined  with  protosulpburet  of  potassium.  It  is  formed 
when  a  solution  of  tungstate  of  potassa  is  decomposed  by  hydrosulphuric 
acid,  and  crystallizes  by  evaporation  in  flat  quadrilateral  prisms,  which  are 
anhydrous,  and  are  of  a  pale  red  colour.  It  dissolves  sparingly  in  alcohol, 
but  is  freely  soluble  in  water,  yielding  an  orange-coloured  solution.  Whew 
mixed  with  a  quantity  of  acid  insufficient  for  entire  decomposition,  it  forms 
a  bitungsto-sulphuret  of  a  brown  colour. 

The  tungsto-sulphuret  of  potassium  unites  with  tungstate  of  potassa  as  a 
double  salt,  which  yields  a  yellow  solution,  and  crystallizes  in  rectangular 
tables  of  a  lemon-yellow  colour.  It  combines  also  with  nitrate  of  potassa, 
and  the  resulting  double  salt  crystallizes  in  large  transparent  crystals  of  a 
ruby-red  tint,  and  when  heated  detonates  like  gunpowder. 

The  tungsto-sulphuret  of  sodium  is  prepared  from  tungstate  of  soda  by 
hydrosulphuric  acid,  and  crystallizes  with  difficulty  in  irregular  crystals  of 
a  red  colour.  It  deliquesces  in  the  air,  and  is  soluble  in  water  and  alcohol. 


SECTION   IV. 

CLASS  OF  SALTS.  ORDER  IV. 

HALOID  SALTS. 

IN  this  section  are  included  substances  composed,  like  the  preceding  salts, 
of  two  hi-elemcntary  compounds,  one  or  both  of  which  are  analogous  in  com- 
position to  sea-salt.  The  principal  groups  consist  of  double  chlorides,  double 
iodides,  double  bromides,  and  double  fluorides.  In  these  the  haloid-bases 
belong  usually  to  the  electro-positive  metals,  and  the  haloid-acids  to  the  me- 
tals which  are  electro-negative.  I  shall  apply  to  them  the  same  principle  of 
nomenclature  as  to  the  sulphur-salts.* 


*  Dr.  Hare  has  adopted  for  these  compounds  the  same  plan  of  nomencla- 
ture as  for  the  sulphur-salts. — See  note,  page  459.  Viewing,  as  Dr.  Turner 
has  done,  the  double  haloid  salts  of  Berzelius  as  simple  salts,  consisting  of 


DOUBLE  CHLORIDES.  465 


DOUBLE  CHLORIDES. 

Hydrargo-Bichlorides. 

The  haloid-acid  of  this  family  is  bichloride  of  mercury,  which  reddens 
litmus  paper,  and  loses  the  property  when  a  haloid-base  is  present,  thus  bear- 
ing1 a  close  analogy  to  ordinary  acids.  Its  principal  salts  which  have  been 
examined  are  thus  constituted  :  — 

Basic  Bichlor. 

Names.  Chloride.  Mercury.  Equiv.       Formulae. 

J149'14    2eq.4-272.84    1  eq.^421-98  2KCl  +  HgCl*. 
Do.  in  rhombic  prisms  with  18  or  2  eq.  of  water  =439-98 
Hydrargo-bichlo.     >    ?4<57     j       +272.84     i  eq.  =347-41     KCl4-HgCR 
ride  of  potassium    S 
Do.  in  acicular  crystals  with  18  or  2  eq.  of  water  =365*41 

®&^$S*1   74'57    le*+545-68    2eq.=620.25    KO+SHgCR. 
Do.  in  acicular  crystals  with  36  or  4  eq.  of  water  =656'25 

58'72     1  '-H-272'84    *  eq.=331-S6    NaCl+HgCR 


Do.  in  crystals  with  36  or  4  eq.  of  water  =367'56 

Dihydrargo-bichlo-  ) 

ride  of  hydrochl.  >  10714    2  eq.+272-84     1  eq.=379-98 
of  ammonia  S 

Do.  in  flat  rhom.  prisms  with  18  or  2  eq.  of  water  =397-98 

The  preceding  salts,  except  the  last,  were  first  prepared  and  examined  by 
BonsdorfF  (An.  de  Ch.  et  de  Ph.  xliv.  189)  ;  and  they  are  obtained  by  mixing 
the  ingredients  in  the  ratio  for  combining,  and  setting  aside  the  solution  to 
crystallize.  The  ammoniacal  salt  has  long  been  known  under  the  name  of 
salt  of  alembroth.  BonsdorfF  obtained  similar  compounds  with  the  chlorides 
of  lithium,  barium,  strontium,  calcium,  magnesium,  manganese,  iron,  cobalt, 
nickel,  and  copper.  Those  of  lithium,  calcium,  magnesium,  and  zinc  are 
deliquescent.  The  hydrargo-bichlorides  of  iron  and  manganese  are  isomor- 
phous,  and  crystallize  in  rhombic  prisms.  Hydrochloric  acid  combines  with 
bichloride  of  mercury,  and  yields  a  very  soluble  salt,  which  may  be  obtained 
in  *  crystals  :  the  electro-positive  ingredient  is  here  probably  hydrochloric 
acid,  and  as  such  will  be  considered  as  chloride  of  hydrogen,  with  properties 
analogous  to  the  chlorides  of  electro-positive  metals. 

Auro-Chlorides. 
These  salts,  the  electro-negative  ingredient  of  which  is  the  terchloride  of 

two  bi-elementary  compounds,  the  more  electro-negative  compound  acting 
the  part  of  an  acid,  the  other  of  a  base,  he  has  applied  to  the  former  the 
generic  appellation  of  acid,  and  named  the  salts  themselves  on  the  same  plan 
as  the  oxy-salts.  Accordingly,  he  gives  the  usual  acid  termination  to 
the  name  of  the  more  electro-positive  element  of  the  compound  acting  as 
the  acid,  considering  this  element  as  the  radical,  and  prefixes  to  it  syllables 
indicating  the  other  element.  Where  oxygen  is  the  electro-negative  ele- 
ment of  an  acid,  it  is  understood  to  be  present,  without  any  syllables  being 
prefixed  to  indicate  its  presence  ;  but  where  other  elements  replace  oxygen 
in  compounds  having  the  nature  of  ordinary  acids,  it  is  obviously  necessary 
to  indicate  the  replacing  element.  Adopting  these  principles  of  nomencla- 
ture, Dr.  Hare  has  chlorohydrargyrates,  chloroaurates,  iodoplatinatcs,  bro- 
mohydrargyrates,  fluohydrates,  fluoborates,  fluosilicates,  &c.,  corresponding 
with  Dr.  Turner's  hydrargo-chlorides,  auro-chlorides,  platino-iodides,  hy. 
drargo-bromides,  hydro-fluorides,  boro-fluorides,  silico-fluorides,  &c.  —  Ed* 


466  PLATING-CHLORIDES. 

gold  have  been  studied  by  Berzelius,  Johnston,  and  Bonsdorflf.  They  are  pre- 
pared by  mixing  the  chlorides  in  atomic  proportions,  and  setting  aside  the  so- 
lution to  crystallize. 

Most  of  them  have  an  orange  or  yellow  colour,  and  consist  of  single  equi- 
valents of  their  constituent  chlorides,  as  is  exemplified  by  the  composition  of 
the  three  following  salts  :  — 

Basic  Terchl. 

Names.          Chloride.  Gold.  Equiv.       Formulae. 

74'57     le<H-305<46     leq.=380-03     KCl  +  AuCP. 
Do.  in  prisms  with  45  or  5  eq.  of  water         =425f03 

58'72    le<l-+305'46    leq.=364-18    NaCl+AuCR 


Do.  in  4-sided  prisms  with  36or4eq.  of  water  =400-18 
Auro-chloride  of?    „  e?     i         ,  on-  AK     i  QSO  no    5  (H3N+HCI) 

hydroehl.amm.l    53'57     *«HWJ*     X  e*=359'°  ^  +AuC13. 
Do.  in  acic.  crys.  with  36  or  4  eq.  of  water  =395-03 

Auro-chloride  of  Potassium.  —  This  salt  crystallizes  either  in  striated 
prisms  or  thin  hexagonal  tables,  which  effloresce  in  a  dry  air,  and  lose  all 
their  water  at  212°.  At  a  red  heat,  the  terchloridc  of  gold  is  decomposed, 
leaving  chloride  of  potassium  and  metallic  gold.  This  salt  is  soluble  both 
in  water  and  alcohol. 

Auro-chloride  of  Sodium  crystallizes  in  long  quadrilateral  prisms,  which 
may  be  exposed  to  the  air  without  change,  and  fuse  readily  in  their  water 
of  crystallization.  The  aurochloride  of  lithium  is  deliquescent. 

Auro-chloride  of  Hydrochlorate  of  Ammonia.  —  It  crystallizes  in  transparent 
needles  or  small  prisms,  which  become  opaque  by  exposure  to  the  air,  and 
are  soluble  in  water  and  alcohol. 

Auro-chloride  of  Hydrogen.  —  In  this  compound  hydrochloric  acid  is  pro- 
bably the  positive  chloride.  It  crystallizes  readily  in  long  acicular  crystals 
of  a  light  yellow  colour,  when  an  acid  solution  of  gold  is  cautiously  evapora- 
ted. The  crystals  undergo  no  change  in  dry  air,  but  in  a  moist  atmosphere 
deliquesce  into  a  yellow  liquid. 

Bonsdorffhas  prepared  the  auro-chlorides  of  barium,  strontium,  calcium, 
magnesium,  manganese,  zinc,  cadmium,  cobalt,  and  nickel.  Most  of  them 
crystallize  in  prisms  and  contain  water  of  crystallization. 

Platino-  Chlorides. 

Both  the  protochloride  and  bichloride  of  platinum  act  as  haloid-acids. 
Magnus  prepared  the  platino-protochloride  of  potassium  by  mixing  chloride 
of  potassium  with  a  solution  of  protochloride  of  platinum  in  hydrochloric 
acid.  It  crystallizes  by  evaporation  in  red,  anhydrous,  four-sided  prisms, 
which  are  insoluble  in  alcohol,  but  dissolve  readily  in  water.  It  consists  of 
single  equivalents  of  its  constituent  chlorides. 

The  'platino-protochloride  of  Sodium  may  also  be  prepared,  is  soluble  in 
water  and  alcohol,  and  crystallizes  with  difficulty.  A  similar  salt  may  be 
formed  with  hydrochlorate  of  ammonia,  and  is  isomorphous  with  that  of 
potassium,  which  it  also  resembles  in  its  properties,  composition,  and  mode 
of  preparation. 

The  solution  of  protochloride  of  platinum  in  hydrochloric  acid,  which 
has  a  deep  red  tint,  is  doubtless  a  double  chloride  ;  but  it  has  not  been  obtained 
in  crystals. 

The  principal  salts  of  bichloride  of  platinum  are  those  of  potassium,  so- 
dium, and  hydrochlorate  of  ammonia,  which  are  thus  constituted  :  — 

Basic  Bichl. 

Names.  Chloride.  Platinum.  Equiv.        Formulae. 

°f(74'57     leq.+  169-64    1  eq.=  244-21     KCl  +  PlCl*. 


PALLADIO-CHLORIDE8.  —  RHODIO-CHLOR1DKS.  467 

Basic  Bichl, 

Names,  Chloride.  Platinum.  Equiv.        Formulas 

Platino-bichloride  of>58.72    i  eq>.j_  169-64    1  eq.=228-36    NaCl+PtCR 

Do.  in  prisms  of  54  or  6  eq.  water  =282-36 

Platino-bichloride   of>53.57     l       +  16g.64    1  eq.=  223-21  5 
hydrochl.  amm.    $ 


Platino-bichloride  of  Potassium.  —  The  production  of  this  salt  by  mixing 
itfconstituents  in  solution,  constitutes  one  of  the  best  tests  for  potassa  (page 
280.)  It  is  commonly  obtained  as  a  powder  of  a  pale  lemon-yellow  colour; 
but  by  slow  evaporation  it  yields  small  octohedrons  of  a  brilliant  lustre.  It 
is  anhydrous,  insoluble  in  alcohol,  and  is  sparingly  dissolved  by  cold,  but 
more  freely  by  hot  water.  Heated  to  redness  it  yields  chlorine,  and  the  resi- 
due consists  of  platinum  and  chloride  of  potassium. 

Platino-bichloride  of  Sodium.  —  This  salt  crystallizes  in  fine  transparent 
prisms  of  a  deep  yellow  colour,  which  are  soluble  in  water  and  alcohol. 
When  gently  heated  it  loses  its  water  of  crystallization,  and  becomes  a  pale 
yellow  powder. 

PlatinO'bichloride  of  Hydrochlorate  of  Ammonia  falls  as  a  lemon-yellow  pow- 
der when  sal  ammoniac  is  mixed  with  a  strong  solution  of  bichloride  of 
platinum.  It  resembles  the  double  salt  of  potassium  in  its  properties  and 
form,  crystallizing  in  small  anhydrous  octohedrons  when  its  aqueous  solution 
is  slowly  evaporated.  This  salt  is  employed  in  the  preparation  of  platinum, 
and  when  heated  to  redness  leaves  that  metal  in  a  spongy  state. 

Bonsdorff  has  prepared  the  platino-bichlorides  of  barium,  strontium,  cal- 
cium, and  several  other  metals.  Most  of  them  crystallize  with  water  of 
crystallization,  and  have  a  yellow  or  orange  colour. 

Palladio-  Chlorides. 

Both  of  the  chlorides  of  palladium  act  as  holoid-acids,  combining  with 
many  of  the  metallic  chlorides,  when  their  respective  solutions  are  mixed 
and  evaporated.  The  principal  palladio-chlorides  which  have  been  examined 
are  those  with  the  chlorides  of  potassium  and  sodium,  and  with  hydrochlo- 
rate  of  ammonia,  which  consist  of  single  equivalents  of  their  ingredients. 

The  palladio-protochloride  of  potassium  crystallizes  in  four-sided  prisms  of 
a  dirty  yellow  colour,  which  are  anhydrous,  insoluble  in  alcohol,  and  freely 
soluble  in  water.  The  corresponding  salt  of  sodium  is  deliquescent  and  solu- 
ble both  in  water  and  alcohol.  That  of  hydrochlorate  of  ammonia  is  iso- 
morphous  with  the  salt  of  potassium,  which  it  resembles  in  its  other  proper- 
ties. 

The  palladio-bichloride  of  potassium  is  obtained  by  evaporating  the  palla- 
dio-protochloride with  nitro-hydrochloric  acid,  when  microscopic  crystals  of 
a  cinnabar-red  colour  are  deposited,  which  by  a  glass  are  found  to  be  regular 
octohedrons.  It  is  anhydrous,  insoluble  in  alcohol,  and  nearly  so  in  water. 
When  heated,  or  by  continued  ebullition,  it  is  reconverted  into  the  palladio- 
protochloride  of  potassium.  The  corresponding  salt  of  hydrochlorate  of 
ammonia  is  obtained  in  a  similar  manner,  and  resembles  the  former  in  form 
and  other  properties. 

Rhodio-  Chlorides. 

The  sesquichloride  of  rhodium  combines  with  the  chlorides  of  potassium 
and  sodium,  and  the  resulting  salts  are  thus  constituted  :  — 

Basic  Sesquichl. 

Names.  Chloride.          Rhodium.  Equiv.      Formula), 


»'"    2eq.+210-66     1.,, 

Do.  in  four  sided  prisms  with  18  or  2  eq.  of  water  =377-8 
Trirhodio-chloride  of  )  17fi  1A     Q         iom££     i  «        ^Q^fio 
sodium  £176-16    3eq.+210-66     1  eq.=386-82 

Do.  in  prisms  with  162  or  18  eq.  of  water  =548-82 


468  IRIDIO,  OSMIO,  4ND  OXY-CHLORIDES. 

Dirhodio-Chloride  of  Potassium. — It  is  obtained  by  mixing  the  respective 
chlorides  in  the  ratio  above  assigned,  and  crystallizes  in  four-sided  rectangu- 
lar prisms",  which  are  of  a  deep  red  colour,  insoluble  in  alcohol,  and  contain 
18  parts  or  two  eq.  of  water  combined  with  359'8  parts  or  one  eq.  of  the 
salt. 

Hydrochlorate  of  ammonia  yields  a  similar  double  salt,  analogous  in  its 
properties  to  the  preceding. 

Trirhodio-chloride  of  Sodium. — This  salt  crystallizes  in  large  prismatic 
crystals  of  a  deep  red  colour,  which  lose  part  of  their  water  in  a  dry  air,  and 
become  covered  with  a  red  powder.  They  are  insoluble  in  alcohol. 

Iridio-  Chlorides. 

The  chlorides  of  iridium  acfas  haloid-acids.  The  most  remarkable  of  their 
salts  is  the  iridio-bichloride  of  potassium,  which  in  form  and  properties  re- 
sembles the  platino-bichloride  of  potassium,  crystallizing  in  brilliant  octohe- 
drons,  but  of  a  black  colour,  which  are  sparingly  soluble  in  water.  Hydro- 
chlorate  of  ammonia  forms  with  it  a  similar  salt,  which  is  of  a  deep  cherry 
red  colour. 

Osmio-  Chlorides. 

Berzelius  has  described  the  osmio-bichloride  of  potassium,  which  resembles 
in  form,  composition,  and  most  of  its  properties,  the  corresponding  salts  of 
platinum  and  iridium.  It  is  insoluble  in  alcohol,  and  but  sparingly  dissolved 
in  water ;  but  its  aqueous  solution,  when  gently  evaporated,  yields  oetohe- 
dral  crystals  of  a  deep  brown  colour. 

OXYCHLORIDES. 

Chemists  are  acquainted  with  a  considerable  number  of  compounds  in 
which  a  metallic  oxide  is  united  with  a  chloride  either  of  the  same  metal, 
which  is  the  most  frequent,  or  of  some  other  metal.  These  compounds  are 
commonly  termed  submuriates,  on  the  supposition  that  they  consist  of  hydro- 
chloric acid  combined  with  two  or  more  eq.  of  an  oxide. 

Oxychlorides  of  Iron. — When  the  crystallized  protochloride  of  iron  is 
heated  without  exposure  to  the  air,  the  last  portions  of  its  water  exchange 
elements  with  part  of  the  chloride  of  iron,  yielding  hydrochloric  acid  which 
is  evolved,  and  protoxide  of  iron.  On  raising  the  heat  so  as  to  expel  the 
pure  chloride  of  iron,  a  deep  green  oxychloride  in  scaly  crystals  remains. 
(Berzelius.) 

The  ochreous  matter  which  falls  when  a  solution  of  the  protochloride  of 
iron  is  exposed  to  the  air,  is  hydrated  sesquioxide  of  iron  combined  with 
some  sesquichloride.  A  similar  hydrate  is  obtained  by  mixing  with  a  solution 
of  the  sesquichloride  of  iron,  a  quantity  of  alkali  insufficient  for  complete 
decomposition.  When  a  solution  of  the  sesquichloride  is  evaporated  to  dry- 
ness  without  exposure  to  the  air,  the  last  portions  of  water  exchange  ele- 
ments with  the  sesquichloride,  hydrochloric  acid  is  disengaged,  and  after 
subliming  the  pure  anhydrous  sesquichloride,  a  compound  in  large,  brown, 
shining  laminae  is  left,  which  consists  of  sesquioxide  and  sesquichloride  of 
iron.  (Berzelius.) 

Mr.  Phillips  has  described  a  soluble  oxychloride,  which  appears  to  consist 
of  one  eq.  of  sesquichloride  of  iron  with  nine  eq.  of  the  sesquioxide.  It  is 
prepared  by  digesting  hydrochloric  acid  with  the  required  proportion  of  the 
moist  hydrated  sesquioxide.  The  solution  is  of  a  brownish-red  colour,  and  a 
precipitate  is  occasioned  either  by  a  little  more  of  the  sesquioxide  or  a  little 
acid,  indicating  the  formation  of  other  oxychlorides  which  are  insoluble. 
(Phil.  Mag.  and  An.  viii.  406.) 

Oxychlorides  of  Tin. — When  a  large  quantity  of  water  is  poured  on  crys- 
tallized protochloride  of  tin,  a  portion  of  water  and  protochloride  exchange 
elements,  an  acid  solution  is  formed,  containing  the  double  chloride  of  tin 
and  hydrogen,  and  a  white  powder  subsides,  which  is  a  compound  of  the 
protoxide  and  protochloride  of  tin. 


CHLORIDES  WITH  AMMONIA.  469 

Oxycldoride  of  Chromium. — This  compound,  which  was  long  considered 
as  the  terchloride,  was  first  shown  to  be  an  oxychloride  by  Rose.  .,  It  has 
already  been  mentioned  at  page  343.  ^^^fc 

Oxychloride  of  Tungsten. — This  compound,  the  nature  of  which  was  first 
pointed  out  by  Rose,  has  already  been  described  at  page  353. 

Oxychloride  of  Molybdenum. — Formerly  described  as  the  terchloride,  but 
shown  by  Rose  to  be  really  similar  in  constitution  to  the  two  preceding 
compounds  (page  351). 

Oxychloride  of  Antimony. — It  falls  as  a  white  curdy  precipitate  when 
sesquichloride  of  antimon}7  is  thrown  into  water  (page  359),  and,  according 
to  an  analysis  by  Phillips,  contains  about  7-8  per  cent,  of  chlorine. 

Oxychloride  of  Cerium. — This  compound  is  generated  by  heating  the 
hydrated  protochloride,  just  as  when  the  protochloride  of  iron  is  distilled. 

Oxychloride  of  Bismuth. — It  is  prepared  by  pouring  a  neutral  solution  of 
nitrate  of  protoxide  of  bismuth  into  a  concentrated  solution  of  sea-salt;  and  a 
similar  compound,  but  with  more  protoxide,  is  formed  when  a  dilute  solu- 
tion of  sea-salt  is  used.  They  are  both  heavy  insoluble  powders  of  a  very 
white  colour. 

Oxychloride  of  Copper. — This  compound  falls  as  a  green  hydrate,  when 
potassa  is  added  to  a  solution  of  protochloride  of  copper  insufficient  for  its 
complete  decomposition.  When  its  water  is  expelled  it  becomes  of  a  liver- 
brown  colour.  Berzelius  states  it  to  consist  of  one  eq.  of  protochloride  and 
three  eq.  of  protoxide  of  copper.  It  is  used  as  a  pigment  under  the  name 
of  Brunswick  green,  being  prepared  for  that  purpose  by  exposing  metallic 
copper  to  hydrochloric  acid  or  a  solution  of  sal  ammoniac.  The  same  com- 
pound is  generated  during  the  corrosion  of  copper  in  sea-water, 

Oxychloride  of  Lead. — A  compound  of  one  eq,  chloride  to  two  eq.  of  prot- 
oxide of  lead  has  been  found  as  a  colourless  mineral.  Another  oxychloride 
with  three  eq.  of  the  protoxide*ls  prepared  by  adding  pure  ammonia  to  a  hot 
solution  of  chloride  of  lead.  It  falls  as  a  heavy  white  hydrate  ;  but  on  ex- 
pelling its  water  by  heat,  it  acquires  a  pale  yellow  colour.  A  third  oxychlo- 
ride with  a  still  larger  proportion  of  protoxide  is  used  as  a  pigment  under  the 
name  of  mineral  or  patent  yellow ;  and  it  is  prepared  by  the  action  of  moist 
sea-salt  on  litharge,  by  which  means  portions  of  the  protoxide  and  sea-salt 
exchange  elements,  yielding  soda  and  chloride  of  lead.  After  washing  away 
the  alkali,  the  mixed  protoxide  and  chloride  are  dried  and  fused. 

Oxychloride  of  Mercury. — This  compound  is  obtained  as  a  shining  crystal- 
line powder  of  a  brownish-black  colour,  when  peroxide  of  mercury  is  boiled 
with  a  solution  of  the  bichloride.  It  is  anhydrous,  and  consists  of  single 
equivalents  of  the  oxide  and  chloride. 

CHLORIDES  WITH  AMMONIA. 

Several  interesting  compounds  of  chlorides  with  ammonia  have  been  stu- 
died by  Persoz  and  Rose.  (An.  de  Ch.  et  de  Ph.  xliv.  315  and  li.  5,  and  Pog- 
Annalen,  xx.  149.)  The  bichlorides  of  tin  and  titanium,  the  sesquichlorides 
of  antimony  and  iron,  and  the  oxychloride  of  chromium  absorb  ammonia  at 
common  temperatures;  and  most  of  the  other  chlorides  absorb  it  when 
gently  warmed.  The  chlorides  of  potassium,  sodium,  and  barium  do  not 
absorb  ammonia ;  while  those  of  strontium  and  calcium  combine  with  four 
eq.  of  the  alkali.  Protochloride  of  copper  absorbs  three  eq.,  and  acquires  the 
same  deep  blue  tint  as  the  ammoniaco-sulphate  of  copper.  Chloride  of  nickel 
unites  with  three,  and  chloride  of  cobalt  with  two  eq.  of  ammonia,  Chloride 
of  silver  takes  up  slowly  one  and  a  half  eq.  Calomel  absorbs  half  an  eq.and 
forms  a  black. compound  ;  but  on  exposure  to  the  air  the  ammonia  flies  off, 
and  pure  white  calomel  remains.  Corrosive  sublimate,  by  the  aid  of  heat, 
rapidly  absorbs  half  an  eq.  of  ammonia,  and  forms  a  white  compound,  which 
is  insoluble  in  water,  and  bears  a  considerable  temperature  without  decom- 
position :  the  white  precipitate  of  pharmacy  is  probably  analogous  in  nature, 
though  the  ratio  of  its  ingredients  is  different.  Bichloride  of  titanium  com- 
bines with  two  eq.  and  that  of  tin  with  one.  The  bromides  and  iodides  as 

40 


470 


CHLORIDES  WITH  PHOSPHURETTED  HYDROGEN. — DOUBLE  IODIDES. 


well  as  the  bicyanuret  of  mercury  absorb  ammonia  in  the  same  manner  as 
the  chlorides.  Nearly  all  of  these  compounds  depend  on  very  feeble  affinities. 
Most  of  them  lose  their  ammonia  by  mere  exposure  to  the  air,  and  it  is  ex- 
pelled from  nearly  all  by  a  very  moderate  heat :  in  some,  as  with  bichloride 
of  titanium,  heat  occasions  reactions  between  the  chlorine  and  ammonia,  and 
the  metal  is  insulated ;  but  in  general  the  alkali  is  simply  expelled,  and  the 
chloride  returns  to  its  former  condition.  Though  these  amrnoniacal  chlorides 
may  be  viewed  as  salts  in  which  a  metallic  chloride  acts  as  an  acid,  they 
appear  to  be  more  closely  allied  to  those  singular  compounds  of  ammonia 
with  the  oxysalts  which  have  already  been  noticed  (page  430).  To  this  re- 
mark some  of  them,  of  which  the  arnmoniacal  chloride  of  mercury  is  an  in- 
stance, are  probably  exceptions. 

CHLORIDES  WITH  PHOSPHURETTED  HYDROGEN. 

The  analogy  which  Rose  has  traced  between  ammonia  and  phosphuretted 
hydrogen  is  especially  remarkable  in  the  compounds  which  they  both  form 
with  metallic  chlorides.  He  has  examined  the  compounds  of  phosphuretted 
hydrogen  with  the  bichlorides  of  titanium  and  tin,  and  the  sesquichlorides  of 
antimony,  iron,  and  aluminium,  all  of  which  correspond  to  ammoniacal  chlo- 
rides of  similar  composition.  The  phosphuretted  hydrogen  is  in  all  readily 
displaced  by  water,  or  a  solution  of  ammonia.  Rose  observed  that  the  result- 
ing chloride  is  the  same  in  character  and  composition  whichever  of  the  two 
kinds  of  phosphuretted  hydrogen  was  used  in  its  preparation.  He  also  found 
that  the  gas,  when  displaced  from  bichloride  of  titanium  by  water,  does  not 
inflame  spontaneously ;  whereas,  if  displaced  by  a  solution  of  potassa  or  its 
carbonate,  by  carbonate  of  ammonia  or  hydrochloric  acid,  the  gas  is  spon- 
taneously inflammable.  He  was  thus  able  to  disengage  at  will  either  variety 
of  phosphuretted  hydrogen  from  the  same  compound,  without  reference  to 
the  kind  which  had  been  used  in  its  preparation.  These  facts  first  led  Rose 
to  the  opinion  that  the  two  gases  of  phosphorus  and  hydrogen  must  be  similar 
in  composition.  (Page  256.) 

DOUBLE  IODIDES. 

These  compounds  have  not  yet  been  closely  studied ;  but  there  is  no  doubt 
that  the  iodides  are  capable  of  forming  with  each  other  an  extensive  series 
of  compounds.  Bonsdorff  obtained  the  hydrargo-biniodide  of  potassium  by 
saturating  a  strong  solution  of  iodide  of  potassium  with  biniodide  of  mer- 
cury :  it  may  also  be  formed  by  dissolving  corrosive  sublimate  in  a  solution 
of  iodide  of  potassium,  evaporating  to  dryness,  and  digesting  in  alcohol,  when 
the  double  iodide  is  dissolved,  and  chloride  of  potassium  is  left.  A  variety  of 
double  iodides  have  been  described  by  Boullay,  and  among  them  a  compound 
of  biniodide  of  mercury  and  hydriodic  acid.  (An.  de  Ch.  et  de  Ph.  xxxiv.)  In 
general  the  hydrargo-biniodides  contain  single  equivalents  of  the  respective 
iodides.  Liebig  obtained  a  compound  of  the  bichloride  and  biniodide  of 
mercury,  consisting  of  two  eq.  of  the  former  to  one  eq.  of  the  latter,  as  indi- 
cated by  the  formula  HgP-}-2HgCl2. 

Platino-biniodides. 

Several  compounds  of  biniodide  of  platinum  with  other  iodides  have  been 
studied  by  Mr.  Kane  of  Dublin,  and  Lassaigne.  (Dublin  Journal  of  Science, 
i.  304,  and  An.  de  Ch.  et  de  Ph.  li.  125.)  The  compounds  at  present  known 
are  thus  constituted : — 

Biniod. 
Platinum.  Equiv.       Formulae. 

leq.^351-4    1  eq.=516'85    KI-f-PtR 
l'eq.H-351-4     1  eq.=501 
1  eq.+351-4    1  eq.=495-85 

Do.  of  barium  '  195          1  eq.4-351-4    1  eq.=546'4 

Do.  of  zinc  158-6       1  eq.-f-351-4     1  eq.=510 

Do.  of  hydrogen  127-3       1  eq.4-351-4    1  eq.  =478-7    HI-f-PtR 


Basic 

Names.  Iodide. 

Plalino-biniodide  of    )  155.45 

potassium          ^ 
Do.  of  sodium  149*6 

Do.  of  hydriodate  of   >  144.45 


5  (H3N+HI) 
}  +PtR 
Bal  +  Ptls. 


OXYIODIDES. — DOUBLE  BROMIDES. DOUBLE  FLUORIDES.  471 

The  platino-liriiodide  of  potassium  is  prepared  by  digesting-  an  excess  of 
biniodide  of  platinum  in  a  rather  concentrated  solution  of  iodide  of  potassium. 
By  spontaneous  evaporation  it  crystallizes  in  small  rectangular  plates  sur- 
mounted sometimes  with  a  four-sided  pyramid,  which  are  anhydrous,  un- 
changed in  the  air,  and  insoluble  in  alcohol.  The  colour  of  the  crystals  is 
black  with  a  metallic  lustre,  and  they  yield  a  deep  claret-coloured  solution 
with  water.  The  biniodide  of  platinum  appears  to  combine  also  with  the 
protiodide^  of  platinum;  but  the  compound  has  only  been  obtained  in  so- 
lution. 

The  platino-biniodides  of  sodium,  barium,  and  zinc  are  obtained  in  the 
same  manner  as  that  of  potassium,  crystallize  with  difficulty,  are  deliquescent 
in  the  air,  and  dissolve  in  water  and  alcohol.  The  ammoniacal  salt  is  ana- 
logous in  its  properties  to  that  of  potassium,  with  which  it  appears  also  to  be 
isomorphous. 

Platino-biniodide  of  Hydrogen. — This  compound  consists  of  hydriodic  acid 
and  biniodide  of  platinum,  in  which  the  former  is  regarded  as  the  electro- 
positive ingredient.  It  ie  prepared  by  acting  on  biniodide  of  platinum  with 
a  cold  dilute* solution  of  hydriodic  acid,  which  gradually  acquires  a  deep 
claret  colour,  and  by  evaporation  under  a  bell-jar  with  quicklime,  deposites 
black  acicular  crystals.  The  crystals  become  moist  by  exposure  to  the  air. 

OXYIODIDES. 

The  principal  oxyiodides  at  present  known  to  chemists  'are  those  formed 
by  the  protoxide  and  iodide  of  lead.  When  iodide  of  potassium  is  mixed  with 
acetate  of  protoxide  of  lead  in  excess,  the  yellow  iodide  at  first  formed  com- 
bines with  protoxide  of  lead  and  [acquires  a  white  colour;  and  the  same 
compound  is  obtained  directly  by  employing  a  subacetate.  Denot  finds  that 
there  are  three  oxyiodides,  in  which  one  eq.  of  iodide  of  lead  is  united  with 
onef  two,  and  five  eq.  of  protoxide  of  lead. 

DOUBLE  BROMIDES. 

These  compounds  have  not  yet  been  studied  ;  but  Bonsdorff  has  proved 
the  possibility  of  forming  compounds  similar  in  composition  and  properties 
to  the  double  chlorides.  He  obtained  the  hydrargo-bibromide  of  potassium 
in  crystals,  consising  of  an  eq.  of  each  bromide  united  with  two  eq.  of  water. 

DOUBLE  FLUORIDES. 

The  researches  of  Berzelius  have  led  to  the  formation  of  several  extensive 
families  of  double  fluorides,  in  which  the  fluorides  of  boron  and  silicon,  of 
titanium  and  other  electro-negative  metals  are  the  acids,  and  the  fluorides  of 
electro-positive  metals  are  bases.  In  some  instances  hydrofluoric  acid  is  a 
haloid-acid  ;  but  more  commonly  it  acts  the  part  of  a  base. 

Hydro -fluorides. 

In  this  family  hydrofluoric  acid  is  combined  with  the  fluorides  of  electro- 
positive metals.  If  an  equivalent  of  any  electron-positive  metal  be  indicated 
by  M,  then  the  general  formula  for  this  family  is  MF-j-HF. 

Hydro.Jluoride  of  Potassium  is  made  by  mixing  hydrofluoric  acid  with  a 
solution  of  fluoride  of  potassium,  and  evaporating  by  a  gentle  heat  in  a  plati- 
num capsule^  It  commonly  crystallizes  in  confused  laminae,  but,  by  slow 
evaporation,  in  square  tables  or  cubes,  which  are  anhydrous  and  dissolve 
freely  in  pure  water.  It  fuses  readily  when  heated,  and  loses  all  its  hydror 
fluoric  acid  at  a  low  red  heat. 

Hydro-Jluoride  of  Sodium  is  prepared  as  the  preceding  salt,  and  by  spon- 
taneous evaporation  yields  anhydrous  rhombohedral  crystals.  It  is  sparingly 
soluble  in  cold,  but  much  more  freely  in  hot  water.  The  hydro-fluoride  of 
lithium  is  also  of  sparing  solubility.  The  fluorides  of  barium,  strontium, 
calciuin,  and  magnesium  (Jo  not  combine  with  hydrofluoric  add 


472  BORO-FLUORIDES. — SILICO-FLUORIDES. 

Boro -fluorides. 

Boro-fluoride  of  Hydrogen. — When  the  terfluoride  of  boron  (fluoborie 
acid  gas)  is  acted  upon  by  water,  one  out  of  every  four  eq.  of  the  gas  inter- 
changes  elements  with  water,  giving  rise  to  hydrofluoric  and  boracic  acids, 
the  former  of  which  combines  as  a  haloid-base  with  undecomposed  ter- 
fluoride of  boron,  constituting  the  boro-hydrofluoric  acid  (page  243),  but 
which  may  be  viewed  as  the  boro-fluoride  of  hydrogen.  This  change  is 
such  that 

4  eq.  terfluoride  of  boron  4(B+  3F)  ^       3  eq.  terfluoride  of  boron  3(B-f3F) 

'»       3  eq.  hydrofluoric  acid    3(H*|-  F) 
&  3  eq.  of  water  3(H-|~O)  *>»  &  1  eq.  boracic  acid  B+3O. 

By  careful  concentration  and  cooling,  the  boracic  acid  separates  as  a  crys- 
talline powder,  and  the  boro-fluoride  of  hydrogen  remains  in  solution.  It  is 
stronj/ly  acid  to  test  paper,  and  its  composition  is  indicated  by  the  formula 
HF-f*BF3,  being  an  eq.  of  each  fluoride.  On  adding  potassa  to  this  com- 
pound, it  interchanges  elements  with  hydrofluoric  acid,  and  there  results  the 
boro-fluoride  of  potassium,  KF-f~BF3,  the  hydrogen  being  simply  displaced 
by  potassium.  The  protoxides  of  most  other  metals  act  precisely  like  potassa, 
and,  therefore,  the  general  formula  of  these  compounds  isMFHhBFs.  When 
exposed  to  a  strong  heat,  they  all  give  off  terfluoride  of  boron,  and  a  metallic 
fluoride  is  left. 

Boro-fluoride  of  Potassium. — It  is  prepared  by  dropping  boro-fluoride  of 
hydrogen  drop  by  drop  into  a  solution  of  a  salt  of  potassa,  and  falls  as  a  gela- 
tinous transparent  hydrate,  which  is  a  white  very  fine  powder  when  dried, 
It  has  a  slightly  bitter  taste,  and  is  quite  neutral  to  test  paper,  is  very 
sparingly  soluble  in  alcohol  and  cold  water,  but  is  dissolved  freely  by  hot 
water,  and  subsides  on  cooling  in  small  brilliant  anhydrous  crystals.  At  a 
strong  red  heat  it  gives  off  the  terfluoride  of  boron,  and  fluoride  of  potassium 
remains. 

Boro-fluoride  of  Sodium  is  very  soluble  in  water,  and  is,  therefore,  best  ob- 
tained pure  by  the  direct  action  of  boro-fluoride  of  hydrogen  on  fluoride  of 
sodium.  It  crystallizes  by  slow  evaporation  in  large  rectangular  prisms, 
which'redden  litmus  paper  strongly.  The  b&ro-ftuoride  of  lithium  also  crys- 
tallizes in  large  prisms,  is  very  soluble  in  water,  and  deliquesces  in  the  air. 

Bow-fluoride  of  Barium  is  prepared  by  adding  carbonate  of  baryta  to  boro- 
fluoride  of  hydrogen  till  it  ceases  to  be  dissolved,  avoiding  any  further  addi- 
tion. On  evaporating  to  the  consistence  of  a  syrup  long  acicular  crystals 
form,  and  by  keeping  the  solution  in  a  warm  place  it  yields  flat,  four-sided, 
rectangular  prisms.  It  is  acid  to  test  paper,  and  deliquescent.  The  boro- 
fluorides  of  calcium  and  magnesium  may  be  prepared  in  a  similar  manner, 
and  are  soluble  in  water.  Lead  forms  a  soluble  boro-fluoride,  which  crystal- 
lizes in  the  same  manner  as  the  boro-fluoride  of  barium. 

Silico-fluorides. 

Subsesquisilico-fluoride  of  Hydrogen. — -The  acid  solution,  called  silica- 
hydrofluoric  acid  (page  244)  may  be  viewed  as  the  subsesquisilico-fluoride  of 
hydrogen,  a  compound  of  157-08  parts  or  two  eq.of  terfluoride  of  silicon,  and 
59'04  or  three  eq.  of  fluoride  of  hydrogen  (hydrofluoric  acid),  as  indicated 
by  the  formula  3HF  +  2SiF3.  When  the  solution  is  neutralized  with  potassa, 
the  alkali  interchanges  elements  with  the  fluoride  of  hydrogen,  water  and 
fluoride  of  potassium  are  generated,  and  the  latter  combines  with  the  terflu- 
oride of  silicon.  This  double  fluoride  consists,  therefore,  of  157*08  parts  or 
two  eq.  of  terfluoride  of  silicon,  and  173-49  or  three  eq.  of  fluoride  of  potas- 
sium, the  formula  of  which  is  3KF4"2SiF3.  A  similar  change  ensues  with 
the  protoxides  of  most  other  metals,  and  hence  the  general  formula  of  the 
silico-fluoride  is  3MF4-2SiF3.  On  exposing  these  compounds  to  a  red  heat, 
fluoride  of  silicon  is  disengaged. 

Silico -fluoride  of  Potassium.-^-  This  salt  falls  as  a  very  transparent  jelly, 
which  has  the  property  of  reflecting  the  colours  of  the  rainbow ;  but  when 


T1TANO -FLUORIDES. OXTFLUORrDES.  473 

collected  on  a  filter  and  dried,  it  becomes  a  white  powder.  By  evaporating 
a  saturated  aqueous  solution,  it  separates  in  minute  anhydrous  crystals.  It  is 
sparingly  soluble  in  hot  water,  and  still  less  so  in  cold  water. 

Silica-fluoride  of  Sodium  resembles  the  former  salt,  but  is  much  more  so- 
luble in  hot  water.  By  evaporation  it  is  obtained  in  minute  anhydrous  hex- 
agonal prisms.  The  silico-fluoride  of  lithium  forms  similar  crystals,  but  is 
more  soluble  in  water. 

SilicQ-fluoiide  of  Barium  gradually  falls  in  microscopic  crystals,  which 
through  a  glass  appear  as  elongated  prisms,  when  chloride  of  barium  is 
mixed  with  the  silico-fluoride  of  hydrogen,  hydrochloric  acid  remaining  in 
solution.  This  salt  is  very  sparingly  soluble  in  water  whether  hot  or  cold. 

The  silico-fluorides  of  strontium,  calcium,  magnesium,  and  lead  are  best 
prepared  by  dissolving  their  respective  carbonates  in  silico-fluoride  of  hydro- 
gen. The  salt  of  strontium  crystallizes  in  short  quadrilateral  prisms,  which 
lose  their  water  of  crystallization  at  a  gentle  heat  and  become  opaque.  For 
complete  solubility  in  water,  they  require  a  slight  excess  of  hydrofluoric  acid 
to  be  present,  and  then  they  dissolve  freely.  The  salt  of  calcium  crystallizes 
in  regular  quadrilateral  prisms.  It  dissolves  readily  in  water  acidulated  with 
hydrofluoric  or  hydrochloric  acid,  but  is  decomposed  by  pure  water,  yielding 
an  acid  soluble  salt,  and  an  insoluble  subsalt.  The  salts  of  magnesium  and 
lead  are  very  soluble,  and  leave  a  gummy  mass  by  evaporation. 

The  silico-fluorides  of  manganese,  iron,  zinc,  cobalt,  nickel,  and  copper  are 
soluble  in  water,  and  crystallize  in  similar  hexagonal  prisms,  probably  iso- 
morphous,  which  contain  respectively  one  eq.  of  the  silico-fluoride,  and  seven 
eq.  of  water  of  crystallization. 

Tita  no-fluorides. 

Hydrofluoric  acid  dissolves  titanic  acid,  and  forms  with  it  an  acid  solution 
which  may  be  viewed  as  the  titano-fluoride  of  hydrogen,  consisting  of  61-66 
parts  or  one  eq.  of  bifluoride  of  titanium,  and  19-68  or  one  eq.  of  fluoride  of 
hydrogen,  expressed  by  the  formula  HF  +  TiF2.  When  mixed  with  potassa, 
water  and  fluoride  of  potassium  are  generated,  and  the  titano-fluoride  of 
potassium  results,  the  formula  of  which  is  KF-}~TiF2.  By  substituting  most 
other  protoxides  for  potassa,  similar  salts  may  be  prepared,  the  general  for- 
mula being  MF-f-TiF8. 

Few  of  the  titano-fluorides  have  as  yet  been  studied.  That  of  potassium 
crystallizes  by  evaporation  in  scales  like  boracic  acid,  which  are  anhydrous, 
and  but  sparingly  soluble  in  cold  water.  The  titano-fluoride  of  sodium  is 
very  soluble,  and  crystallizes  with  difficulty. 

Similar  double  fluorides  may  be  formed,  in  which  the  fluorides  of  molyb- 
denum, tellurium,  and  platinum  act  as  the  electro-negative  ingredients.  Few 
of  them,  however,  have  as  yet  been  studied.  Berzelius  has  prepared  the 
alurnino-fluorides  of  potassium  and  sodium,  and  the  zircono-fluoride  of  potas- 
sium. He  employed  the  latter  in  the  preparation  of  metallic  zirconium. 
The  alumino-fluoride  of  sodium  is  found  in  nature  as  a  rare  mineral  called 
cryolite. 

OXYFLUORIDES. 

Several* fluorides  combine  with  oxides  in  the  same  manner  as  chlorides 
and  iodides.  An  oxyfluoride  of  aluminium  is  prepared  as  an  insoluble  gela- 
tinous hydrate,  by  digesting  hydrate  of  alumina  in  a  solution  of  the  sesqui- 
rluoride  of  aluminium.  This  oxyfluoride,  combined  with  silicate  of  alumina, 
constitutes  the  topaz.  The  neutral  fluorides  of  cobalt,  nickel,  and  copper  are 
decomposed  by  hot  water,  being  resolved  into  soluble  hydro-fluorides,  and  in- 
soluble oxyfluorides.  Several  other  fluorides  doubtless  undergo  a  similar 
change.  The  oxyfluoride  of  lead  is  generated  either  by  digesting  fluoride 
of  lead  in  solution  of  ammonia,  or  by  fusing  together  the  fluoride  and  prot- 
oxide of  lead.  It  is  more  soluble  than  the  fluoride,  and  the  solution,  by  ex- 
posure to  the  air,  gives  a  precipitate  of  carbonate  of  protoxide  of  lead.  The 
fluoride  of  lead  also  combines  by  fusion  with  chloride  of  lead.  Fluoride  of 
calcium  forms  a  very  fusible  compound  with  sulphate  of  lime. 

40* 


PART  III. 

ORGANIC  CHEMISTRY. 


THE  department  of  organic  chemistry  comprehends  the  history  of  those 
compounds  which  are  of  animal  or  vegetable  origin,  and  which  are  hence 
called  organic  substances.  These  bodies,  viewed  collectively,  form  a  re- 
markable  contrast  with  those  of  the  mineral  kingdom.  Such  substances  in 
general  are  characterized  by  containing  some  principle  peculiar  to  each. 
Thus  the  presence  of  nitrogen  in  nitric,  and  of  sulphur  in  sulphuric  acid, 
establishes  a  wide  distinction  between  these  acids;  and  although  in  many 
instances  two  or  more  inorganic  bodies  consist  of  the  same  elements,  as  is 
exemplified  by  the  compounds  of  sulphur  and  oxygen,  or  of  nitrogen  and 
oxygen,  they  are  always  few  in  number,  and  distinguished  by  a  well-marked 
difference  in  the  proportion  in  which  they  are  united.  The  products  of  ani- 
mal and  vegetable  life,  on  the  contrary,  consist  essentially  of  the  same  ele- 
mentary principles,  the  number  of  which  is  very  limited.  They  are  nearly 
all  composed  of  carbon,  hydrogen,  and  oxygen,  in  addition  to  which  some 
of  them  contain  nitrogen.  Besides  these,  portions  of  phosphorus,  sulphur, 
iron,  silicic  acid,  potassa,  lime,  and  other  substances  of  a  like  nature,  may 
sometimes  be  detected ;  but  their  quantity  is  exceedingly  minute  when  com- 
pared with  the  principles  above  mentioned.  In  point  of  composition,  there- 
fore, most  organic  substances  differ  only  in  the  proportion  of  their  consti- 
tuents, and  on  this  account  may  not  unfrequently  be  converted  into  one 
another. 

The  elements  of  organic  bodies  are  united  with  each  other  in  definite 
proportion,  and,  therefore,  the  same  laws  of  combination  which  regulate  the 
composition  of  mineral  substances,  must  likewise  influence  that  of  organic 
compounds.  In  the  latter,  however,  the  modes  of  combination  are  generally 
of  a  complex  kind.  A  single  molecule  of  a  metallic  oxide  or  a  chloride,  as 
determined  bv  its  combining  weight,  consists  of  two  elements,  and  usually 
of  two  or  three  atoms  only.  Thus,  in  an  equivalent  of  potassa,  the  chemist 
has  to  do  with  a  single  equivalent  of  potassium  and  of  oxygen,  between 
which  one  kind  of  combination  only  is  practicable.  In  an  equivalent  of 
sulphuric  acid  there  are  four  atoms,  which  admit  of  three  different  arrange- 
ments; for  S  and  3O  may  be  united  as  S  +  SO,  or  S  +  2O,  or  S-f  O.  But 
here,  guided  by  the  third  law  of  combination  (page  137),  and  by  the  other 
compounds  of  sulphur  and  oxygen,  chemists  infer  with  confidence  that 
S-f.3O  is  the  true  mode  in  which  the  elements  of  that  acid  are  united. 
But  in  organic  compounds  a  single  combining  molecule  is  often  made  up  of 
so  many  elementary  particles,  that  one  is  bewildered  by  the  multiplicity  of 
possible  modes  of  combination.  An  equivalent  of  tartaric  acid  contains 
four  eq.  of  carbon,  two  eq.  of  hydrogen,  and  five  eq.  of  oxygen,  which  it  is 
obvious  may  be  arranged  in  a  variety  of  ways ;  and  an  equivalent  of  quinia 
is  composed  of  twenty-one  eq.  of  carbon,  twelve  eq.  of  hydrogen,  one  eq.  of 
nitrogen,  and  two  eq.  of  oxygen.  The  difficulty  of  assigning  any  one  ar- 
rangement of  so  many  elements  in  preference  to  others  equally  probable,  or 
sometimes  of  agreeing  on  any  arrangement  which  is  probable,  formerly  led 
chemists  to  suspect  that  the  modes  of  combination  in  organic  and  inorganic 
bodies  were  essentially  distinct.  But  the  progress  of  analytical  chemistry 
has  in  a  great  degree  corrected  this  opinion,  and  is  daily  destroying  the  dis* 


ORGANIC  CHEMISTRY.  475 

tinction  between  these  two  classes  of  substances.  The  late  researches  of 
Liebig  and  Wohler  on  the  radical  of  benzole  acid,  and  those  of  Dumas  on 
camphene,  have  indisputably  established  the  existence  of  compound  inflam- 
mable or  electro- positive  substances,  which  like  cyanogen  are  susceptible  of 
uniting  with  oxygen,  chlorine,  sulphur,  and  other  energetic  principles,  and 
of  being  transferred  from  one  to  the  other  without  a  change  in  their  own 
constitution.  Many  vegetable  substances  appear  to  consist  of  electro-posi- 
tive compounds  of  carbon  and  hydrogen,  which  in  some  bodies  exist  mere- 
ly as  oxides,  and  in  others  act  as  bases  in  relation  to  water,  carbonic  oxWe, 
carbonic  acid,  or  similar  compounds.  In  the  constitution  of  animal  mat- 
ters, cyanogen  appears  to  act  an  important  function,  as  may  be  inferred 
from  the  history  of  urea  and  uric  acid. 

When  organic  substances  are  heated  to  redness  with  pure  potassa  or  sodar 
they  invariably  yield  alkaline  carbonates ;  but  at  a  temperature  of  about 
400°  or  450°,  many  of  them  are  decomposed  with  formation  of  oxalic  acid. 
This  fact  has  been  noticed  by  Gay-Lussac,  who  observed  it  with  cotton, 
saw-dust,  sugar,  starch,  gum,  sugar  of  milk,  and  tartaric,  citric,  and  mucic 
acids.  The  other  products  of  course  vary  with  the  nature  of  the  substance  ; 
but  water  and  acetic  acid  are  generally  formed.  (Quarterly  Journal  of  Sci- 
ence, N.  S.  vi.  413.) 

Organic  substances,  owing  to  the  energetic  affinities  with  which  their 
elements  are  endowed,  are  very  prone  to  spontaneous  decomposition.  The 
prevailing  tendency  of  carbon  and  hydrogen  is  to  appropriate  to  themselves 
so  much  oxygen  as  shall  convert  them  into  carbonic  acid  and  water :  and 
hence,  in  whatever  manner  these  three  elements  may  be  mutually  combined 
in  a  vegetable  substance,  they  are  always  disposed  to  resolve  themselves 
into  the  compounds  just  mentioned.  If,  at  the  time  this  change  occurs, 
there  is  an  insufficient  supply  of  oxygen  to  oxidize  the  hydrogen  and  carbon 
completely,  then,  in  addition  to  carbonic  acid  and  water,  carbonic  oxide  and 
carburetted  hydrogen  gases  will  probably  be  generated.  One  or  both  of 
these  combustible  products  must  in  every  case  be  formed,  except  when  oxy- 
gen is  freely  supplied  from  extraneous  sources ;  because  organic  bodies  are 
so  constituted  that  their  oxygen  is  never  in  sufficient  quantity  for  convert- 
ing the  carbon  into  carbonic  acid,  and  the  hydrogen  into  water. 

If  substances  composed  of  oxygen,  hydrogen,  and  carbon,  are  liable  to 
spontaneous  decomposition,  that  tendency  should  become  much  stronger 
when  nitrogen  is  also  present.  Other  and  powerful  affinities  are  then  super- 
added  to  those  above  enumerated,  and  especially  that  of  hydrogen  for  nitro- 
gen. Such  compounds  are  very  prone  to  decomposition,  and  the  usual  pro- 
ducts are  water,  carbonic  acid,  hydrocyanic  acid,  and  ammonia. 

Another  circumstance  which  is  characteristic  of  organic  products  is  the 
impracticability  of  forming  them  artificially  by  direct  union  of  their  ele- 
ments, the  tendency  of  those  eleme»ts  being  to  unite  so  as  to  form  water 
and  carbonic  acid.  Some  organic  bodies  are  developed  during  the  decompo- 
sition of  others,  as,  for  instance,  oxalic  acid  from  most  substances  when 
digested  in  nitric  acid,  alcohol  from  sugar,  and  acetic  acid  in  the  distillation 
of  wood ;  but  these  results  do  not  strictly  form  exceptions  to  the  preceding 
remark. 

Animal  and  vegetable  substances  are  decomposed  by  a  red  heat,  and 
nearly  all  are  partially  affected  by  a  temperature  far  below  ignition.  When 
heated  in  the  open  air,  or  with  substances  which  yield  oxygen  freely,  they 
burn,  and  are  converted  into  water  and  carbonic  acid ;  but  if  exposed  to 
heat  in  vessels  from  which  atmospheric  air  is  excluded,  very  complicated 
products  ensue.  A  compound,  consisting  of  carbon,  hydrogen,  and  oxygen, 
yields  water,  carbonic  acid,  carbonic  oxide,  carburetted  hydrogen  of  various 
kinds,  and  probably  pure  hydrogen.  Besides  these  products,  some  acetic 
acid  is  commonly  generated,  together  with  a  volatile  oil  which  has  a  dark 
colour  and  burnt  odour,  and  is  hence  called  empyreumatic  oil.  An  azotized 
substance,  in  addition  to  these,  yields  ammonia,  cyanogen,  and  probably 
free  nitrogen. 


476  VEGETABLE   CHEMISTRY. 

From  the  foregoing  remarks,  it  appears  that  organic  products  are  char- 
acterized  by  the  following  circumstances: — 1st,  by  being  composed  of  the 
same  elements ;  2nd,  by  the  facility  with  which  they  undergo  spontaneous 
decomposition ;  3rd,  by  the  impracticability  of  forming  them  by  the  direct 
union  of  their  elements;  and  4th,  by  being  decomposed  at  a  red  heat. 

VEGETABLE  CHEMISTRY. 

All  bodies  which  are  of  vegetable  origin  are  termed  vegetable  substances. 
They  are  nearly  all  composed  of  oxygen,  hydrogen,  and  carbon,  and  in  a 
few  of  them  nitrogen  is  likewise  present.  Every  distinct  compound  which 
exists  ready  formed  in  plants,  is  called  a  proximate  or  immediate  principle 
of  vegetables.  Thus  sugar,  starch,  and  gum  are  proximate  principles. 
Opium,  though  obtained  from  a  plant,  is  not  a  proximate  principle;  but 
consists  of  several  proximate  principles  mixed  more  or  less  intimately  with 
each  other. 

The  proximate  principles  of  vegetables  are  sometimes  distributed  over 
the  whole  plant,  while  at  others  they  are  confined  to  a  particular  part.  The 
methods  by  which  they  are  procured  are  very  variable.  Thus  gum  exudes 
spontaneously,  and  the  saccharine  juice  of  the  maple-tree  is  obtained  by  in- 
cisions made  in  the  bark,  In  some  cases  a  particular  principle  is  mixed 
with  such  a  variety  of  others,  that  a  distinct  process  is  required  for  its  sepa- 
ration. Of  such  processes  consists  the  proximate  analysis  of  vegetables. 
Sometimes  a  substance  is  separated  by  mechanical  means,  as  in  the  prepa- 
ration of  starch.  On  other  occasions,  advantage  is  taken  of  the  volatility  of 
a  compound,  or  of  its  solubility  in  some  particular  menstruum.  Whatever 
method  is  employed,  it  should  be  of  such  a  nature  as  to  occasion  no  change 
in  the  composition  of  the  body  to  be  prepared. 

The  reduction  of  the  proximate  principles  into  their  simplest  parts  consti- 
tutes their  ultimate  analysis.  By  this  means  chemists  ascertain  the  quan- 
tity of  oxygen,  carbon,  and  hydrogen  present  in  any  compound.  The  former 
method  of  performing  this  operation  was  by  what  is  termed  destructive  dis- 
tillation; that  is,  by  exposing  the  compounds  to  a  red  heat  in  close  vessels, 
and  collecting  all  the  products.  So  many  different  substances,  however,  are 
procured  in  this  way,  such  as  water,  carbonic  acid,  carbonic  oxide,  carbu- 
retted  hydrogen,  and  the  like,  that  it  is  almost  impossible  to  arrive  at  a  satis- 
factory conclusion.  A  more  simple  and  effectual  method  was  proposed  by 
Gay-Lussac  and  Thenard  in  the  second  volume  of  their  celebrated  Re- 
cherches  Physico-Chirniques.  The  object  of  their  process,  which  is  applica- 
ble to  the  ultimate  analysis  of  animal  as  well  as  vegetable  substances,  is  to 
convert  the  whole  of  the  carbon  into  carbonic  acid,  and  the  hydrogen  into 
water,  by  means  of  some  compound  which  contains  oxygen  in  so  loose  a 
state  of  combination  as  to  give  it  up  to, those  elements  at  a  red  heat. 

The  agent  first  employed  by  these  chemists  was  chlorate  of  potassa.  This 
substance,  however,  is  liable  to  the  objection,  that  it  not  only  gives  oxygen 
to  the  substance  to  be  analyzed,  but  is  itself  decomposed  by  heat.  On  this 
account  it  is  now  very  rarely  employed  in  ultimate  analysis,  oxide  of  cop- 
per, proposed  by  Gay-Lussac,  having  been  substituted  for  it.  This  oxide,  if 
alone,  may  be  heated  to  whiteness  without  parting  with  oxygen ;  whereas  it 
yields  oxygen  readily  to  any  combustible  substance  with  which  it  is  ignited. 
It  is  easy,  therefore,  by  weighing  it  before  and  after  the  analysis,  to  discover 
the  precise  quantity  of  oxygen  which  has  entered  into  union  with  the  car- 
bon and  hydrogen  of  the  substances  submitted  to  examination. 

The  ultimate  analysis  of  organic  bodies  is  one  of  the  most  delicate  opera- 
tions with  which  the  analytical  chemist  can  be  engaged.  The  chief  cause 
of  uncertainty  in  the  process  arises  from  the  presence  of  moisture,  which  is 
retained  by  some  animal  and  vegetable  substances  with  such  force,  that  it 
can  be  expelled  only  by  a  temperature  which  endangers  the  decomposition 
of  the  compound  itself.  The  best  mode  of  drying  organic  matters  for  the 
purpose,  is  by  confining  them  with  sulphuric  acid  under  the  exhausted  re- 


VEGETABLE   CHEMISTRY.  477 

ceiver  of  an  air-pump,  and  exposing  them  at  the  same  time  to  a  temperature 
of  212°, — a  method  adopted  by  Berzelius,  and  for  which  a  neat  apparatus 
has  been  described  by  Dr.  Prout.  (An.  of  Phil.  vi.  272.)  Another  source  of 
difficulty  is  occasioned  by  atmospheric  air  within  the  apparatus,  owing  to 
the  presence  of  which  nitrogen  may  be  detected  in  the  products,  without 
having  been  contained  in  the  substance  analyzed. 

But  though  the  ultimate  analysis  of  organic  substances  is  difficult  in 
practice,  in  theory  it  is  exceedingly  simple.  It  consists  in  mixing  three  or 
four  grains  of  the  body  to  be  analyzed  with  about  two  hundred  grains  of 
oxide  of  copper,  heating  the  mixture  to  redness  in  a  glass  tube,  and  collect- 
ing the  gaseous  products  in  a  graduated  glass  jar  over  mercury.  From  the 
quantity  of  carbonic  acid  procured  by  measure,  its  weight  may  readily  be 
inferred  (page  187) ;  and  from  this,  the  quantity  of  carbonaceous  matter 
may  be  calculated,  by  recollecting  that  every  22'12  grains  of  the  acid  con- 
tain 16  of  oxygen  and  6*12  of  carbon. 

In  order  to  ascertain  the  quantity  of  hydrogen,  the  gaseous  products  are 
transmitted  through  a  tube  filled  with  fragments  of  fused  chloride  of  cal- 
cium, which  absorbs  all  the  watery  vapour;  and  by  its  increase  in  weight 
indicates  the  precise  quantity  of  that  fluid  generated.  Every  9  grains  of 
water  thus  collected  correspond  to  1  grain  of  hydrogen  and  8  of  oxygen. 

If  the  quantity  of  oxygen  contained  in  the  carbonic  acid  and  water  cor- 
responds precisely  to  that  lost  by  the  oxide  of  copper,  it  follows  that  the  or- 
ganic substance  itself  was  free  from  oxygen.  But  if,  on  the  other  hand, 
more  oxygen  exists  in  the  products  than  was  lost  by  the  copper,  it  is  obvious 
that  the  difference  indicates  the  amount  of  oxygen  contained  in  the  subject 
of  analysis. 

If  nitrogen  enter  into  the  constitution  of  the  organic  substance,  it  will 
pass  over  in  the  gaseous  state,  mixed  with  carbonic  acid ;  and  its  quantity 
may  be  ascertained  by  removing  the  carbonic  acid  by  means  of  a  solution  of 
pure  potassa.  In  order  to  prevent  the  production  of  binoxide  of  nitrogen, 
which  is  otherwise  apt  to  be  generated,  the  oxide  should  be  mixed  with 
some  metallic  copper;  or  the  latter  may  be  placed  on  the  surface  of  the 
oxide,  and  be  kept  at  a  red  heat,  in  order  that  any  oxide  of  nitrogen,  in 
passing  through  the  metallic  mass,  should  be  decomposed.  The  copper  for 
the  purpose  should  be  in  a  state  of  fine  division,  and  is  best  prepared  from 
the  oxide  by  means  of  hydrogen  gas. 

It  need  scarcely  be  observed,  that  if  the  analysis  has  been  successfully 
performed,  the  weight  of  the  different  products,  added  together,  should  make 
up  the  exact  weight  of  the  organic  substance  employed. 

In  analyzing  an  animal  or  vegetable  fluid,  the  foregoing  process  will  re- 
quire slight  modification.  If  the  fluid  is  of  a  fixed  nature,  it  may  be  made 
into  a  paste  with  oxide  of  copper,  and  heated  in  the  usual  manner.  But  if  it 
is  volatile,  a  given  weight  of  its  vapour  is  conducted  over  oxide  of  copper 
heated  to  redness  in  a  glass  tube. 

The  constitution  of  vegetable  substances  is  not  yet  sufficiently  known  to 
admit  of  their  being  classified  in  a  purely  scientific  order.  I  have  arranged 
them  into  seven  sections:  the  first  includes  the  vegetable  acids;  the  second, 
the  vegetable  alkalies ;  the  third  comprises  neutral  substances,  the  oxygen 
and  hydrogen  of  which  are  in  the  same  ratio  as  in  water;  the  fourth  con: 
tains  oleaginous,  resinous,  and  bituminous  principles;  the  fifth,  spirituous 
and  ethereal  principles;  the  sixth,  colouring  matters;  and  the  seventh  com* 
prehends  substances  not  referable  to  preceding  sections. 


478  VEGETABLE   ACIDS. 


SECTION  I. 


VEGETABLE  ACIDS. 

THOSE  compounds  are  regarded  as  vegetable  acids  which  possess  the  pro- 
perties of  an  acid,  and  are  peculiarly  the  product  of  vegetation.  These  acids, 
like  all  organic  principles,  are  decomposed  by  a  red  heat.  They  are  in  gene- 
ral less  liable  to  spontaneous  decomposition  than  other  vegetable  substances. 
They  are  nearly  all  decomposed  by  concentrated  hot  nitric  acid,  by  which 
they  are  converted  into  carbonic  acid  and  water.  They  do  not  possess  any 
constant  analogy  in  composition.  It  was  thought  at  one  time  that  their  oxy- 
gen was  always  more  than  sufficient  to  convert  all  their  hydrogen  into  water  ; 
but  several  acids  are  known  in  which,  as  in  sugar,  the  oxygen  and  hydro- 
gen are  in  the  same  ratio  as  in  water,  and  in  benzoic  acid  the  hydrogen  is 
actually  in  excess.  It  seems,  however,  to  be  true  that  all  vegetable  sub- 
stances are  acid,  which  contain  more  oxygen  than  suffices  to  form  water 
with  their  hydrogen.  The  following  table  exhibits  the  constituents  of  the 
principal  vegetable  acids,  and  will  serve  to  show  analogies  of  composition. 
The  formulae  merely  express  the  elements  contained  in  an  equivalent  of 
each  acid,  without  indicating  the  order  in  which  they  arc  arranged.  The 
composition,  where  not  otherwise  expressed,  indicates  the  anhydrous  acids, 
such  as  they  exist  in  combination  with  an  alkali :  the  numeral  attached  to  each 
symbol  expresses  the  number  of  equivalents  of  that  element  contained  in  the 
acid. 

Names  of  Acids.  Carb.  Hyd.  Oxyg.  Equiv.  Formulae. 

Oxalic  .  .  .  12-24+  0+24=  36-24  C3O3. 

Do.  sublimed  with  9  parts  or  1  eq.  of  water  =  45-24 

Do.  in  crystals  from  solution  with  27  parts  or  3  eq.  of  water=63-24 

Mellitic  .  .  .  24-48-4-  0+24=  48  48  C4O3. 

Croconic  .  .  .  306  +  0+32=  62-6  C5O4. 

Acetic  .  .  .  24-48+  3-|-24=  51-48  C4H3O3. 

Do.  in  crystals  with  9  parts  or  1  eq.  of  water  =  60-48 

Lactic  (in  lactate  of  oxide  of  zinc)  36-72+  5+40=  81-72  C6H5O5. 

Do.  dried  in  vacuo  from  solution  with  9  parts  or  1  eq.  of  water=90-72 

Do.  sublimed  .  .  36-72+  4+32=  72-72  C6H4O*. 

TCinic      ....  91-8  +10+80=181-8  C15H10O'°. 

Malic      ....  2448+  2+32=  58-48  C4H2O4. 

Citric      ....  24-48+  2+32=  58-48  C4H2O4. 

Pyrocitric  .  .  .  61-2  +  2+24=  87-2  C10IPO3. 

Tartaric  .  .  .  24-48+  2+40=  6648  C4H2O5. 

Do.  in  crystals  with  9  parts  or  1  eq.  of  water  =  75-48 

Racemic  .  .  .  24-48+  2+40=  66-48  C4H2O5. 

Do.  in  crystals  with  18  parts  or  2  eq.  of  water  =  84-48 

Benzoic  .  .  .  85-68+  5+24=114-68  C14H5O3. 

Do.  in  crystals  with  9  parts  or  1  eq.  of  water  =123-68 

Meconic  .  .  .  42  84+  2+56=100-84  C7H2O7. 

Metameconic       .  .  .  73-44+  4+80=157-44  C12H4O'°. 

Tannic  (from  catechu)     .  .  110-16+  9+64=183-16  C'8H9O8. 

(from  gall-nuts)  .  110-16+9+96=215-16  C18H9O12. 

Gallic      ....  42-84+  3+40=  85-84  C7H3O5. 

Do.  in  crystals  with  9  parts  or  1  eq.  of  water  =  94-84 

Pyrogallic  .  .  .  36-72+  3+24=  63-72  C8H3OS. 

Metagallic  .  .  .  73-44+  3+24=100-44  C12H3O3. 

Etlagic  .  .  .  42-84+  2+32=  76-84  C7H2O4. 

Succinie  .  .  .  24-43+  2+24=  50-48  C4H2O3. 


OXALIC    ACID.  479 

Names  of  Acids.  Carb.  Hyd.  Oxyg.  Equiv.  Formulas. 

Mucic     .  .  .  36-72+  54-64=105-72    C6H5O8. 

Camphoric  .  ,  .          122-4  +16+40=1784      C20H16O5. 

Valerianic  .  .  .  61-2  +  9+24=  94-2       C10H9O3. 

Rocellic  .  .  .  97-92+16+32=145-92    C'6HI6O4. 

Oxalic  Acid. 

Oxalic  acid  exists  ready  formed  in  several  plants,  especially  in  the  rumex 
acetosa  or  common  sorrel,  and  in  the  oxalis  acetosella  or  wood  sorrel ;  but  it 
almost  always  occurs  in  combination  either  with  lime  or  potassa.  These 
plants  contain  binoxalate  of  potassa;  and  the  oxalate  of  lime  has  been  found 
in  large  quantity  by  M.  Braconnot  in  several  species  of  lichen. 

Oxalic  acid  is  easily  made  artificially  by  digesting-  sugar  in  five  or  six 
times  its  weight  of  nitric  acid,  and  expelling  the  excess  of  that  acid  by  dis* 
tillation,  until  a  fluid  of  the  consistence  of  syrup  remain  in  the  retort.  The 
residue  in  cooling  yields  crystals  of  oxalic  ucid,  the  weight  of  which 
amounts  to  rather  more  than  half  the  quantity  of  the  sugar  employed. 
They  should  be  purified  by  repeated  solution  in  pure  water,  and  re-crystal- 
lization;  for  they  are  very  apt  to  retain  traces  of  nitric  acid,  the  odour  of 
which  becomes  obvious  when  the  crystals  are  heated.  In  the  conversion  of 
sugar  into  oxalic  acid,  changes  of  a  very  complicated  nature  ensue,  during 
which  a  large  quantity  of  binoxide  of  nitrogen  with  some  carbonic  acid  is 
disengaged :  water  is  freely  generated  at  the  same  time,  and  a  small  quan- 
.  tity  of  malic  and  acetic  acids  is  produced.  As  oxalic  acid  does  not  contain 
any  hydrogen,  and  has  a  smaller  proportional  quantity  of  carbon  than  sugar, 
there  can  be  no  doubt  that  the  production  of  this  acid  essentially  depends 
upon  the  sugar  being  deprived  of  all  its  hydrogen  and  a  portion  of  its  car- 
bon by  oxygen  derived  from  the  nitric  acid. 

Many  organic  substances  besides  sugar,  such  as  starch,  gum,  most  of  the 
vegetable  acids,  wool,  hair,  and  silk,  are  converted  into  oxalic  by  the  action 
of  nitric  acid ; — a  circumstance  which  is  explicable  on  the  fact  that  oxalic 
acid  contains  more  oxygen  than  any  other  principle,  whether  of  animal  or 
vegetable  origin.  It  is  also  generated  by  heating  organic  substances  with 
potassa.  (Page  475.) 

Oxalic  acid  crystallizes  in  slender,  flattened,  four  and  six-sided  prisms  ter- 
minated by  two-sided  summits;  but  their  primary  form  is  an  oblique 
rhombic  prism.  It  has  an  exceedingly  sour  taste,  reddens  litmus  paper 
strongly,  and  forms  neutral  salts  with  alkalies.  The  crystals,  which  consist 
of  one  equivalent  of  real  acid  and  three  of  water,  undergo  no  change  in 
ordinary  states  of  the  air;  but  when  the  atmosphere  is  very  dry,  or  the 
temperature  slightly  raised,  as  to  70°  or  80°,  partial  efflorescence  ensues, 
and  at  212°  they  lose  two  equivalents  of  water,  which  on  exposure  to  the 
air  while  cold  they  soon  recover.  Heated  in  a  tube  to  209°  they  fuse  in 
their  water  of  crystallization,  and  are  hence  soluble  in  boiling  water  with- 
out limit:  at  50°  they  dissolve  in  15.5  times  their  weight  of  water,  and  in 
9.5  times  at  57° ;  but  the  solubility  is  increased  by  the  presence  of  nitric 
acid.  They  are  dissolved  also  by  alcohol,  though  less  freely  than  in 
water. 

Oxalic  acid  possesses  considerable  volatility.  Mr.  Faraday  has  shown 
that  a  very  slow  sublimation  of  oxalic  acid  takes  place  at  common  tempe- 
ratures. At  212°  its  vaporization  goes  on  in  appreciable  quantities ;  and  at 
330°  the  acid,  when  deprived  of  two  equivalents  of  its  water  of  crystalliza- 
tion, sublimes  rapidly,  and  without  any  decomposition.  The  sublimed  acid 
crystallizes  in  transparent  acicular  crystals,  which  contain  one  equivalent  of 
water;  but  by  exposure  to  the  air  they  rapidly  absorb  moisture,  and  become 
opaque.  (An.  of  Phil.  N.  S.  x.  348.)  When  fully  hyd rated  oxalic  acid  is 
suddenly  heated  to  about  300°,  it  undergoes  decomposition,  and  yields 


480  OXALIC   ACID. 

water,  carbonic  acid  gas  mixed  with  carbonic  oxide  in  the  ratio  of  6  to  5, 
and  formic  acid.  To  this  change,  which  has  been  lately  studied  by  Gay- 
Lussac,  the  water  of  crystallization  essentially  contributes,  the  elements  of 
formic  acid  being  such,  that  it  rnay  be  considered  a  compound  of  two 
equivalents  of  carbonic  oxide  with  one  equivalent  of  water.  The  crystals, 
when  deprived  of  2-3ds  of  their  water,  are  much  more  stable,  not  suffering 
the  same  decomposition  until  the  heat  exceeds  330°,  and  even  then  a  consi- 
derable portion  is  sublimed. 

Oxalic  acid  is  a  powerful  and  rapidly  fatal  poison;  and  frequent  accidents 
have  occurred  from  its  being  sold  arid  taken  by  mistake  for  Epsom  salt, 
\vith  the  appearance  of  which  its  crystals  have  some  resemblance.  These 
substances  may  be  easily  distinguished,  however,  by  the  strong  acidity  of 
oxalic  acid,  which  may  be  tasted  without  danger,  while  sulphate  of  magnesia 
is  quite  neutral,  and  has  a  bitter  saline  taste.  In  cases  of  poisoning  with 
this  acid,  chalk  mixed  with  water  should  be  administered  as  an  antidote,  an 
insoluble  oxalatc  being  formed,  which  is  inert.  Chalk  was  first  suggested 
for  this  purpose  by  my  colleague,  Dr.  A.  T.  Thomson  ;  and  his  opinion  has 
been  since  fully  confirmed  by  the  experiments  of  Drs.  Christison  and  Coin- 
det,  who  have  recommended  the  use  of  magnesia  with  the  same  intention. 
(Christison  on  Poisons.) 

Oxalic  acid  is  easily  distinguished  from  all  other  acids  by  the  form  of  its 
crystals,  and  by  its  solution  giving  with  lime-water  a  white  precipitate, 
which  is  insoluble  in  an  excess  of  the  acid.  When  the  acid  is  contained  in 
mixed  fluids,  it  may  be  conveniently  precipitated  by  nitrate  of  oxide  of  lead, 
care  being  taken  beforehand  to  neutralize  the  solution  with  a  little  carbonate 
of  soda.  The  precipitated  oxalate  of  oxide  of  lead,  after  being  well  washed, 
and  while  yet  moist,  is  suspended  in  water,  and  decomposed  by  a  current  of 
hydrosulphuric  acid :  the  clear  liquid  is  poured  off  or  filtered  from  the  sul- 
phuret  of  lead,  and  concentrated  by  evaporation  that  crystals  may  form. 
These  may  be  purified  by  solution  in  pure  water  and  a  second  crystalli- 
zation. 

As  an  equivalent  of  oxalic  acid  contains  two  eq.  of  carbon  and  three  of 
oxygen,  it  may  be  regarded  cither  as  a  direct  compound  of  carbon  and 
oxygen,  indicated  by  the  formula  C  or  C2O3,  or  as  a  compound  of  carbonic 
oxide  and  carbonic  acid,  denoted  by  C-f"C.  The  latter  is  supported  by  the 
fact  observed  by  Dobereiner,  that  oxalic  acid  is  converted  into  carbonic 
oxide  and  carbonic  acid  gases  by  the  action  of  concentrated  sulphuric  acid. 
The  decomposition  takes  place  slowly  at  212°,  and  rapidly  at  230°. 

The  neutral  oxalates  of  protoxides  consist  of  36.24  parts  or  one  eq.  of 
oxalic  and  one  eq.  of  the  base,  the  general  formula  of  such  salts  being 
M-J-C,  or  M-j-O  (page  152.)  Most  of  these  compounds  are  either  insoluble 
or  sparingly  soluble  in  water;  but  they  are  all  dissolved  by  the  nitric,  and 
also  by  the  hydrochloric  acid,  except  when  the  latter  precipitates  the  base  of 
the  salts.  The  only  oxalates  which  are  remarkable  for  solubility  are  those 
of  potassa,  soda,  lithia,  ammonia,  alumina,  and  sesquioxide  of  iron. 

A  soluble  oxalate  is  easily  detected  by  adding  to  its  solution  a  neutral 
salt  of  lime  or  oxide  of  lead,  when  a  white  oxalate  of  those  bases  will  be 
thrown  down.  On  digesting  the  precipitate  in  a  little  sulphuric  acid,  an  in- 
soluble sulphate  is  formed,  and  the  solution  yields  crystals  of  oxalic  acid  on 
cooling.  All  insoluble  oxalates,  the  bases  of  which  form  insoluble  com- 
pounds with  sulphuric  acid,  may  be  decomposed  in  a  similar  manner.  All 
other  insoluble  oxalates  may  be  decomposed  by  potassa,  by  which  means  a 
soluble  oxalate  is  procured. 

The  oxalates,  like  ail  salts  which  contain  a  vegetable  acid,  are  decom- 
posed by  a  red  heat,  a  carbonate  being  left,  provided  the  oxide  can  retain 
carbonic  acid  at  the  temperature  which  is  employed.  As  oxalic  acid  is  so 
highly  oxidized,  its  salts  leave  no  charcoal  when  heated  in  close  vessels. 

Several  oxalates  are  reduced  to  the  metallic  state,  with  evolution  of  pure 


OXALIC   ACID.  481 

carbonic  acid,  when  heated  to  redness  in  close  vessels.  (Pages  326  and  329.) 
The  peculiar  constitution  of  oxalic  acid  accounts  for  this  change ;  for  one 
equivalent  of  the  acid,  to  be  converted  into  carbonic  acid,  requires  precisely 
one  equivalent  of  oxygen,  which  is  the  exact  quantity  contained  in  the  oxide 
of  a  neutral  protoxalate. 

Oxalates  of  Potassa. — Oxalic  acid  forms  with  potassa  three  compounds, 
which  were  first  described  by  Wollaston.  (Philos.  Trans.  1808.)  The  first 
is  the  neutral  oxalate,  which  is  formed  by  neutralizing  carbonate  of  potassa 
with  oxalic  acid.  It  crystallizes  in  oblique  quadrangular  prisms,  which 
have  a  cooling  bitter  taste,  require  about  twice  their  weight  of  water  at  60° 
for  solution,  and  contain  36-24  parts  or  one  eq.  of  oxalic  acid,  47-15  or  one 
eq.  of  potassa,  and  9  parts  or  one  eq.  of  water.  This  salt  is  much  employed 
as  a  reagent  for  detecting  lime.  The  binoxalate  is  contained  in  sorrel,  and 
may  be  procured  from  that  plant  by  solution  and  crystallization.  It  crys- 
tallizes readily  in  small  rhomboids,  which  are  less  soluble  in  water  than  the 
neutral  oxalate,  and  consist  of  72-48  parts  or  two  eq.  of  acid,  47-15  or  one 
eq.  of  potassa,  and  18  or  two  eq.  of  water.  It  is  often  sold  under  the  name 
of  essential  salt  of  lemons  for  removing  iron  moulds  from  linen  ; — an  effect 
which  it  produces  by  half  of  its  acid  uniting  with  the  sesquioxide  of  iron  and 
forming  a  soluble  oxalate.  The  quadroxalate  is  the  least  soluble  of  these 
salts,  and  is  formed  by  digesting  the  binoxalate  in  nitric  acid,  by  which  it 
is  deprived  of  half  of  its  base.  The  crystals  consist  of  144-96  parts  or  four 
eq.  of  acid,  47-15  or  one  eq.  of  potassa,  and  63  or  seven  eq.  of  water. 

Oxalate  of  Soda  may  be  made  in  the  same  manner  as  oxalate  of  potassa. 
It  likewise  forms  a  binoxalate,  but  no  quadroxalate  is  known. 

Oxalate  of  Ammonia. — This  salt,  prepared  by  neutralizing  ammonia  with 
oxalic  acid,  is  much  used  as  a  reagent.  It  is  very  soluble  in  hot  water, 
and  is  deposited  in  acicular  crystals  when  a  saturated  hot  solution  is  allow- 
ed to  cool.  The  crystals  contain  two  equivalents  of  water.  Dr.  Thomson 
has  likewise  described  a  binoxalate  of  ammonia,  which  is  less  soluble  than 
the  preceding,  and  contains  three  equivalents  of  water. 

During  the  decomposition  of  oxalate  of  ammonia  by  heat  an  interesting 
compound  is  generated,  which  was  discovered  and  described  by  Dumas, 
who  has  given  it  the  name  of  oxalammide  or  oxamide^  compounded  of  the 
words  oxalic  and  ammonia.  (An.  de  Ch.  et  de  Ph.  xliv.  129.)  On  putting 
oxalate  of  ammonia  into  a  retort  and  applying  heat,  the  crystals  at  first  lose 
water  and  become  opaque;  then  the  salt,  where  directly  in  contact  with  the 
hot  glass,  fuses,  boils,  and  disappears ;  and  this  action  goes  on  successively 
through  the  mass,  until,  excepting  traces  of  a  light  carbonaceous  matter, 
the  whole  is  expelled.  During  the  whole  course  of  the  distillation  gas  is 
disengaged:  at  first  ammonia  appears,  then  a  mixture  of  carbonic  acid  and 
carbonic  oxide,  the  former  of  which  unites  with  the  ammonia,  and  towards 
the  close  of  the  process  cyanogen  gas  is  generated.  The  oxamide,  which 
constitutes  but  a  small  part  of  the  products,  is  found  as  a  thick  deposite,  of 
a  dirty  white  colour,  in  the  neck  of  the  retort,  and  partly  floating  in  flakes 
in  the  water  of  the  recipient.  It  is  separated  from  adhering  carbonate  of 
ammonia  by  being  well  washed  with  cold  water. 

Oxamide  is  insoluble  in  cold  water :  at  212°  it  is  dissolved,  and  is  depo- 
sited unchanged  on  cooling  in  the  form  of  flocks  of  a  dirty  white  colour, 
and  of  a  confused  crystalline  appearance.  Heated  gently  in  an  open  tube  it 
speedily  rises  in  vapour,  and  is  condensed  again  on  the  cold  part  of  the  tube  ; 
but  when  sharply  heated  in  a  retort,  it  enters  into  fusion,  and  while  part 
sublimes,  another  portion  yields  cyanogen  gas,  and  leaves  a  very  bulky  car- 
bonaceous residue. 

The  elements  contained  in  oxamide  are  expressed  by  the  formula  2C+ 
N-f-2H-f-2O.  Nothing  certain  is  known  respecting  the  mode  in  which 
these  elements  are  arranged ;  but  the  three  following  hypotheses  are  most 
consistent  with  known  affinities : — it  may  be  a  compound  of 

41 


482  OXALIC  ACID. 

Cyanogen  and  water        ....        (2C-j-N)-f-2(H-f-O) 
Or  binoxide  of  nitrogen  and  olefiant  gas  (2H4-2C)-f-(N-r-2O) 

Or  dinituret  of  hydrogen  and  carbonic  oxide    (2H  -j-  N) +2(C  +  O). 

It  can  scarcely  be  thought  to  contain  either  oxalic  acid  or  ammonia.  But 
when  boiled  with  a  solution  of  potassa,  ammonia  after  a  short  time  is  evolved, 
and  oxalate  of  potassa  generated ;  and  when  heated  with  a  large  excess  of 
strong  sulphuric  acid,  a  mixture  of  carbonic  oxide,  and  carbonic  acid  gases, 
in  the  ratio  to  form  oxalic  acid,  is  evolved,  and  sulphate  of  ammonia  is  pro- 
duced. Under  the  influence  of  the  attraction  of  potassa  for  oxalic  acid,  or 
of  sulphuric  acid  for  ammonia,  oxamide  and  water  interchange  elements ; 
so  that 

1  eq.  oxamide  2C  +  N  +  2H-f- 2O    3     1  eq.  oxallic  acid          2C-f3O 
and  1  eq.  water         H-J-O  -^     and  1  eq.  ammonia       3H-f-N. 

Oxalate  of  Lime. — This  salt,  like  all  the  insoluble  oxalates,  is  easily  pre- 
pared by  way  of  double  decomposition.  It  is  a  white  finely  divided  powder, 
which  is  remarkable  for  its  extreme  insolubility  in  pure  water.  On  this  ac- 
count a  soluble  oxalate  is  an  exceedingly  delicate  test  for  lime.  It  is  soluble, 
however,  in  hydrochloric  and  nitric  acids.  It  is  composed  of  36-24  parts  or 
one  eq.  of  oxalic  acid,  and  28-5  or  one  eq.  of  lime.  It  may  be  exposed  to  a 
temperature  of  560°  without  decomposition,  and  is  then  quite  anhydrous. 
No  binoxalate  of  lime  is  known. 

This  salt  is  interesting  in  a  pathological  point  of  view,  because  it  is  a  fre- 
quent ingredient  of  urinary  concretions,  being  the  basis  of  what  is  called 
the  mulberry  calculus. 

Oxalate  of  Magnesia  may  be  prepared  by  mixing  oxalate  of  ammonia 
with  a  hot  concentrated  solution  of  sulphate  of  magnesia.  It  is  a  white  pow- 
der, which  is  very  sparingly  soluble  in  water ;  but,  nevertheless,  when  sul- 
phate of  magnesia  is  moderately  diluted  with  cold  water,  oxalate  of  ammonia 
occasions  no  precipitate.  On  this  fact  is  founded  the  best  analytic  process 
for  separating  lime  from  magnesia. 

Oxalate  of  Chromium  and  Potassa. — This  salt  was  discovered  by  my  bro- 
ther during  the  winter  of  1830-31,  by  adding  oxalic  acid  to  a  solution  of 
bichromate  of  potassa  until  effervescence  ceased,  and  then  evaporating.  The 
same  salt  has  been  prepared  independently,  and  by  a  better  process,  by  Dr. 
Gregory,  who  employs  190  parts  of  bichromate  of  potassa,  157-5  of  oxalic 
acid  in  crystals,  and  517-5  of  crystals  of  binoxalate  of  potassa,  pours  hot  wa- 
ter over  the  materials,  and  when  effervescence  has  ceased,  concentrates  very 
considerably.  This  beautiful  salt  crystallizes  in  thin  elongated  prisms, 
which  appear  black  by  reflection,  blue  by  transmitted  light,  and  green  when 
reduced  to  powder :  its  solution  is  green  and  red  at  the  same  time,  except 
by  candlelight,  when  it  is  of  a  pure  red.  Dr.  Gregory  considers  it  a  com- 
pound of  three  eq.  of  oxalic  acid,  two  of  potassa,  one  of  green  oxide  of  chro- 
mium, and  six  of  water. 

Mellitic  Acid. — This  acid  is  contained  in  the  rare  substance  called  honey- 
stone,  which  is  occasionally  met  with  at  Thuringia  in  Germany.  The  honey- 
stone,  according  to  Klaproth,  is  a  mellitate  of  alumina,  and  on  boiling  it  in 
a  large  quantity  of  water,  the  acid  is  dissolved,  and  the  alumina  subsides. 
On  concentrating  the  solution,  mellitic  acid  is  deposited  in  minute  acicular 
crystals.  From  its  rarity  it  has  been  little  studied.  Liebig  and  Wohler 
have  shown  (page  478)  that  it  has  the  same  composition  as  succinic  acid, 
hydrogen  cxcepted.  (An.  de  Ch.  et  de  Ph.  xliii.  200.) 

Croconic  Acid. — In  the  preparation  of  potassium  from  cream  of  tartar 
(page  276),  the  principal  products  are  potassium  and  carbonic  oxide  gas; 
but  these  are  accompanied  with  dense  fumes,  which  in  cool  vessels  deposite 
a  gray  flaky  substance.  On  the  addition  of  water  this  matter  becomes  red, 
and  on  exposure  to  the  air  a  reddish-yellow  solution  is  formed,  which  by 
gentle  evaporation  yields  croconate  of  potassa  in  crystals  of  the  same  colour 
as  the  solution :  the  residual  liquid  contains  bicarbonate  and  oxalate  of  po- 


ACETIC   ACID.  483 

tassa.  In  order  to  separate  croconic  acid,  the  crystals,  purified  by  a  second 
crystallization  and  reduced  to  fine  powder,  are  put  into  absolute  alcohol,  to 
which  sulphuric  acid  of  specific  gravity  1-78,  in  quantity  insufficient  for 
combining  witli  all  the  alkali  of  the  croconate,  is  added.  The  mixture  is  gen- 
tly warmed  during  several  hours,  and  frequently  shaken,  until  a  drop  of  the 
solution,  mixed  with  chloride  of  barium,  causes  no  turbidity.  The  yellow 
alcoholic  solution  of  croconic  acid  is  then  separated  from  the  sulphate  of 
potassa  by  filtration,  and  the  acid  obtained  by  expelling  the  alcohol.  (Gme- 
iin's  Handbuch.) 

Croconic  acid,  by  solution  in  water  and  spontaneous  evaporation,  yields 
transparent  prismatic  crystals  of  a  yellow  colour,  which  are  inodorous,  have 
an  acid  astringent  taste,  redden  litmus,  and  neutralize  alkaline  bases.  It 
bears  a  heat  of  212°  without  decomposition,  but  at  a  higher  temperature*  it  is 
decomposed,  giving  a  deposite  of  charcoal.  A  similar  facility  of  decompose 
tion  is  conspicuous  in  all  its  salts:  when,  for  instance,  croconate  of  potassa 
is  heated,  it  takes  fire  at  a  temperature  below  ignition,  the  whole  mass 
blackens,  and  is  found  to  be  a  mixture  of  charcoal  and  carbonate  of  potassa. 
As  it  consists  of  carbon  and  oxygen  in  the  ratio  of  five  eq.  of  carbon  to  four 
eq.  of  oxygen,  its  origin  seems  referable  to  the  deoxidizing  action  of  potas- 
sium on  carbonic  acid  and  carbonic  oxide. 

ACETIC  ACID. 

Acetic  acid,  exists  ready  formed  in  the  sap  of  many  plants,  either  free  or 
combined  with  lime  or  potassa :  it  is  generated  during  the  destructive  dis- 
tillation of  vegetable  matter,  and  is  an  abundant  product  of  the  acetous  fer- 
mentation. 

Common  vinegar,  the  acidifying  principle  of  which  is  acetic  acid,  is  com- 
monly prepared  in  this  country  by  fermentation  from  an  infusion  of  malt, 
and  in  France  from  the  same  process  taking  place  in  weak  wine.  Vinegar, 
thus  obtained,  is  a  very  impure  acetic  acid,  containing  the  saccharine,  mu- 
cilaginous, glutinous,  and  other  matters  existing  in  the  fluid  from  which  it 
was  prepared.  It  is  separated  from  these  impurities  by  distillation.  Distilled 
vinegar,  formerly  called  acetous  acid,  is  real  acetic  acid  merely  diluted  with 
water,  and  commonly  containing  a  small  portion  of  em  pyre  urn  a  tic  oil, 
formed  during  the  distillation,  and  from  which  it  receives  a  peculiar  flavour. 
It  may  be  rendered  stronger  by  exposure  to  cold,  when  a  considerable  part 
of  the  water  is  frozen,  while  the  acid  remains  liquid. 

The  acid  now  generally  employed  for  chemical  purposes  is  prepared  by 
the  distillation  of  wood,  and  is  sold  under  the  name  of  pyroligneous  acid. 
When  first  made  it  is  very  impure,  and  of  a  dark  colour,  holding  in  solution 
tar  and  volatile  oil.  In  this  state  it  is  mixed  with  chalk,  and  obtained  in  the 
state  of  acetate  of  lime,  which  is  decomposed  by  digestion  with  sulphate 
of  soda:  the  resulting  acetate  of  soda  is  then  fused  at  a  high  temperature, 
insufficient  to  decompose  the  salt,  but  sufficient  to  expel  or  char  the  impuri- 
ties. The  acetate  of  soda  is  thus  obtained  pure  and  in  crystals,  and  is  de- 
composed by  sulphuric  acid. 

Concentrated  acetic  acid  is  best  obtained  by  decomposing  the  acetates 
either  by  sulphuric  acid,  or  in  some  instances  by  heat.  A  convenient  pro- 
cess is  to  distil  acetate  of  potassa  with  half  its  weight  of  concentrated  sul- 
phuric acid,  the  recipient  being  kept  cool  by  the  application  of  ice.  The 
acid  is  at  first  contaminated  with  sulphurous  acid ;  but  by  mixing  it  with  a 
little  peroxide  of  manganese,  and  redistilling,  it  is  rendered. quite  pure.  A 
strong  acid  may  likewise  be  procured  from  acetate  of  oxide  of  copper  by 
the  sole  action  of  heat.  The  acid  when  first  collected  has  a  greenish  tint, 
owing  to  the  presence  of  copper,  from  which  it  is  freed  by  a  second  distilla- 
tion. Pyro-acetic  ether  is  formed  towards  the  close  of  the  process. 

Strong  acetic  acid  is  exceedingly  pungent,  and  even  raises  a  blister  when 
kept  for  some  time  in  contact  with  the  skin.  It  has  a  very  sour  taste  and  an 
agreeable  refreshing  odour.  Its  acidity  is  well  marked,  as  it  reddens  litmus 


484  ACETIC   ACID. 

paper  powerfully,  and  forms  neutral  salts  with  the  alkalies.  It  is  exceed- 
ingly volatile,  rising  rapidly  in  vapour  at  a  moderate  temperature  without 
undergoing  any  change.  Its  vapour  is  inflammable,  and  burns  with  a  white 
light.  In  its  most  concentrated  form  it  is  a  definite  compound  of  one  equi- 
valent of  water,  and  one  equivalent  of  acid  ;  and  in  this  state  it  crystallizes 
when  exposed  to  a  low  temperature,  retaining  its  solidity  until  the  thermo- 
meter rises  to  50°  F.  It  is  decomposed  by  being  passed  through  red-hot 
tubes ;  but  owing  to  its  volatility,  a  large  quantity  of  it  escapes  decompo- 
sition. 

The  only  correct  mode  of  estimating  the  strength  of  acetic  acid  is  by  its 
neutralizing  power.  Its  specific  gravity  is  no  criterion,  as  will  appear  from 
the  following  table  (Thomson's  First  Principles,  vol.  ii.  p.  135),  exhibiting 
the  density  of  acetic  acid  of  different  strengths. 

Acid.  Water.                                                         Sp.  gr.  at  60°  F. 

]  atom    4.   1  atom  .....  1-06296 

1  4.  2 1-07060 

1  4-3 1-07080 

1  +4 1-07132 

1  4.  5            .....  1-06820 

1  +6        •  ,.^   ;;>         -..   '    5'«  -  ,        .  1-06708 

1  +7         :  -v  ^        .            .          :v  '         .  1-06349 

I  4.  8        •  •  V'*    -V;           V:   >VJ        •  1-05974 

1  4-  9        m  fa*        ....  1-05794 

1  4-10                       .         >..^        .            .  1-05439  •v'f.  •: 

The  acetic  is  distinguished  from  all  other  acids  by  its  flavour,  odour,  and 
volatility.  Its  salts,  which  are  called  acetates,  are  all  soluble  in  hot  and  most 
of  them  in  cold  water,  are  destroyed  by  a  high  temperature,  and  are  decom- 
posed by  sulphuric  acid.  The  neutral  acetates  of  protoxides  consist  of  51-48 
parts  or  one  eq.  of  anhydrous  acetic  acid  and  one  eq.  of  base;  so  that  the  ge- 
neral formula  of  such  salts  is  M4~C'4H8O3,  or  M-f-A,  A  being  used  as  the 
symbol  of  one  equivalent  of  acetic  acid,  and  M  of  any  electro- positive  metal. 

Acetate  of  Potassa. — This  salt  is  made  by  neutralizing  the  carbonate  with 
acetic  acid,  or  by  decomposing  acetate  of  lime  with  sulphate  of  potassa. 
When  cautiously  evaporated,  it  forms  irregular  crystals,  which  are  obtained 
with  difficulty,  owing  to  the  deliquescent  property  of  the  salt.  According  to 
Dr.  Thomson,  the  crystals  are  composed  of  98-63  parts  or  one  eq.  of  neutral 
acetate  of  potassa,  and  18  or  two  eq.  of  water.  It  is  commonly  prepared  for 
pharmaceutic  purposes  by  evaporating  the  solution  to  dryness,  and  heating 
the  residue  so  as  to  cause  the  igneous  fusion.  On  cooling  it  becomes  a 
white  crystalline  foliated  mass,  which  is  generally  alkaline. 

This  salt  is  highly  soluble  in  water,  and  requires  twice  its  weight  of  boil- 
ing alcohol  for  solution. 

Dr.  Thomson  procured  a  binacetate  by  mixing  acetic  acid  and  carbonate 
of  potassa  in  the  proportion  of  two  equivalents  of  the  former  to  one  of  the 
latter.  On  confining  the  solution  along  with  sulphuric  acid  under  the  ex- 
hausted receiver  of  an  air-pump,  the  binacetate  was  deposited  in  large  trans- 
parent flat  plates.  The  crystals  contain  six  equivalents  of  water,  and  deli- 
quesce rapidly  on  exposure  to  the  air. 

Acetate  of  Soda  is  prepared  in  large  quantity  by  manufacturers  pf  pyro- 
ligneous  acid  by  neutralizing  the  impure  acid  with  chalk,  and  then  decom- 
posing the  acetate  of  lime  by  sulphate  of  soda.  It  crystallizes  readily  by 
gentle  evaporation,  and  its  crystals,  which  are  not  deliquescent,  are  composed 
of  51-48  parts  or  one  eq.  of  acetic  acid,  31-3  parts  or  one  eq.  of  soda,  and  54 
parts  or  six  equivalents  of  water.  (Berzelius  and  Thomson.)  The  form  of 
its  crystals  is  very  complicated,  and  derived  from  an  oblique  rhombic  prism. 
(Brooke.)  When  heated  to  550°,  it  is  deprived  of  its  water,  and  undergoes 
the  igneous  fusion  without  parting  with  any  of  its  acid,  At  600°  decompo- 
sition takes  place. 


ACETIC   ACID.  485 

Acetate  of  soda  is  much  employed  for  the  preparation  of  concentrated 
acetic  acid. 

Acetate  of  Ammonia  is  made  by  neutralizing-  the  carbonate  with  acetic 
acid.  It  crystallizes  with  difficulty  in  consequence  of  being-  deliquescent  and 
highly  soluble.  It  has  been  long  used  in  medicine  as  a  febrifuge  under  the 
name  of  spirit  of  Minder ervs. 

The  Acetates  of  Baryta,  Strontia,  and  Lime  are  of  little  importance.  The 
former,  which  is  occasionally  employed  as  a  reagent,  crystallizes  in  irregular 
six-sided  prisms  terminated  by  dihedral  summits,  the  primary  form  of  which 
is  a  right  rhomboidal  prism.  The  latter  crystallizes  in  very  slender  acicular 
crystals  of  a  silky  lustre,  and  is  chiefly  employed  in  the  preparation  of 
acetate  of  soda, 

Acetate  of  Alumina  is  formed  by  adding  acetate  of  oxide  of  lead  to  sul- 
phate of  alumina,  when  the  sulphate  of  oxide  of  lead  subsides,  and  acetate  of 
alumina  remains  in  solution.  It  is  used  by  dyers  and  calico-printers  as  a 
basis  or  mordant. 

Acetates  of  Protoxide  of  Lead. — The  neutral  acetate,  long  known  by  the 
names  of  sugar  of  lead  (saceharum  Saturni}  and  cerussa  acetata,  is  made  by 
dissolving  either  the  carbonate  or  litharge  in  distilled  vinegar.  The  solution 
has  a  sweet,  succeeded  by  an  astringent  taste,  does  not  redden  litmus  paper, 
and  deposites  shining  acicular  crystals  by  evaporation.  When  more  regu- 
larly crystallized,  it  occurs  in  six-sided  prismatic  crystals,  cleaveable  parallel 
to  the  lateral  and  terminal  planes  of  a  right  rhombic  prism,  which  may  be 
regarded  as  its  primary  form.  (Mr.  Brooke.)  The  crystals  effloresce  slowly 
by  exposure  to  the  air,  and  require  about  four  times  their  weight  of  water  at 
60°  for  solution.  They  consist  of  51-48  parts  or  one  eq.  of  the  acid,  111'6 
parts  or  one  eq.  of  protoxide  of  lead,  arid  2.7  parts  or  three  equivalents  of 
water. 

This  salt  is  partially  decomposed,  with  formation  of  carbonate  of  oxide  of 
lead,  by  water  which  contains  carbonic  acid,  or  by  exposure  to  the  air;  but 
a  slight  addition  of  acetic  acid  renders  the  solution  quite  clear.  It  is  much 
used  in  the  arts,  in  medical  and  surgical  practice  as  a  sedative  and  astrin- 
gent, and  in  chemistry  as  a  reagent. 

The  subacetatc,  commonly  called  extractum  Saturni,  is  prepared  by  boil- 
ing I  part  of  the  neutral  acetate,  and  2  parts  of  litharge,  deprived  of  carbonic 
acid  by  heat,  with  25  parts  of  water. 

This  salt  is  less  sweet  and  more  soluble  in  water  than  the  neutral  acetate, 
and  has  an  alkaline  reaction.  Thenard  has  obtained  it  by  evaporation  in 
opaque  white  tabular  crystals,  but  it  crystallizes  with  difficulty.  It  is  decom- 
posed by  a  current  of  carbonic  acid,  with  production  of  pure  carbonate  of 
oxide  of  lead;  and  forms  a  turbid  solution,  owing  to  the  formation  of  the 
carbonate,  when  it  is  mixed  with  water  in  which  carbonic  acid  is  present. 
It  consists  of  one  equivalent  of  acid,  and  threo  equivalents  of  protoxide  of 
lead,  and  is,  therefore,  a  triacetate.  (Berzelius.) 

A  diacetate  may  be  formed  by  boiling  with  water  a  mixture  of  litharge 
and  acetate  of  oxide  of  lead  in  atomic  proportion.  (Thomson.) 

Acetates  of  Protoxide  of  Copper. — These  salts  have  been  carefully  studied 
by  Berzelius  and  Phillips.  (An.  of  Phil.  N.  S.  i.  ii.  iv.  and  viii.)  Tiie  neutraj 
acetate  may  be  formed  either  by  dissolving  protoxide  of  copper  or  common 
verdigris  in  acetic  acid,  or  by  decomposing  the  sulphate  by  an  equivalent 
quantity  of  acetate  of  oxide  of  lead.  On  evaporation  it  readily  crystallizes  in 
rhombic  octohedrons  of  a  dark  green  colour,  which  are  soluble  in  20  times 
their  weight  of  cold  water,  in  5  of  boiling  water,  and  in  14  of  boiling  alcohol. 
The  crystals  consist  of  39  6  parts  or  one  eq.  of  the  black  oxide,  51-48  parts 
or  one  eq.  of  acetic  acid,  and  9  parts  or  one  equivalent  of  water. 

When  copper  plates  are  covered  with  a  layer  of  the  neutral  acetate,  made 
into  a  thin  paste  with  water,  and  are  then  exposed  for  about  two  months  to 
a  moist  atmosphere,  a  sub-salt  is  generated,  which  appears  in  crystalline 
blue  scales  and  needles  of  a  silky  lustre.  It  is  a  diacctate,  consisting  of  two 
equivalents  of  the  black  oxide  and  one  of  acetic  acid,  united  with  six  equiva. 

41* 


486  LACTIC  ACID. 

lents  of  water.  At  212°  it  loses  part  of  its  water  and  acquires  a  pretty  green 
tint.  When  freely  mixed  with  water  it  is  converted  into  the  soluble  neutral 
acetate,  and  into  an  insoluble  triacetate.  The  diacetate  is  the  principal  in- 
gredient  of  the  blue-coloured  varieties  of  verdigris. 

The  triacetate,  besides  being  formed  by  the  action  of  water  on  the  diace- 
tate,  is  obtained  as  a  light-green  powder  by  digesting  the  hydrated  oxide 
with  the  neutral  acetate.  It  is  also  generated  when  ammonia  is  cautiously 
added  to  a  solution  of  the  neutral  acetate :  in  a  cold  solution  the  precipitate 
is  uncrystalline  and  of  a  green  colour,  which  by  washing  passes  into  blue ; 
while  in  a  hot  solution  the  precipitate  is  granular,  and  of  a  dirty  grayish- 
green  tint.  By  the  continued  action  of  water,  freely  employed,  it  may  be 
resolved  into  oxide  and  neutral  acetate  of  copper.  It  consists  of  three  equiva- 
lents of  oxide,  one  of  acid,  and  one  and  a  half  of  water. 

Another  sub-salt,  composed  of  three  equivalents  of  oxide,  two  of  acid,  and 
six  of  water,  is  generated  by  adding  to  a  strong  boiling  solution  of  the  neu- 
tral acetate,  a  small  quantity  of  ammonia  insufficient  to  produce  a  perma- 
nent precipitate  of  the  triacetate.  The  sub-salt  in  question,  which  is 
sparingly  soluble  in  cold  water,  separates  on  cooling,  and  should  be  washed 
with  alcohol.  It  is  considered  by  Berzelius  as  the  principal  ingredient  of 
the  green  varieties  of  verdigris. 

The  pigment,  verdigris,  which  is  a  variable  mixture  of  the  subacetates,  is 
prepared  in  large  quantity  in  the  south  of  France,  by  covering  copper  with 
the  refuse  of  the  grape  after  the  juice  has  been  extracted  for  making  wine  : 
the  saccharine  matter  contained  in  the  husks  furnishes  acetic  acid  by  fer- 
mentation, and  in  four  or  six  weeks  the  plates  acquire  a  coating  of  the  ace- 
tate. A  purer  and  better  article  is  prepared  in  this  country  by  covering 
copper  plates  with  cloth  soaked  in  pyroligneous  acid. 

.  Acetate  of  Oxide  of  Zinc. — This  salt  may  be  prepared  by  way  of  double 
decomposition  by  mixing  sulphate  of  oxide  of  zinc  with  acetate  of  oxide  of 
lead  in  equivalent  proportions.  When  made  in  this  way,  it  is  very  apt  to 
retain  some  sulphate  of  oxide  of  lead  in  solution.  It  is  obtained  pure  by 
suspending  metallic  zinc  in  a  dilute  solution  of  acetate  of  oxide  of  lead, 
until  all  the  lead  is  removed,  or  by  dissolving  oxide  of  zinc  in  acetic  acid. 
This  salt  is  frequently  employed  as  an  astringent  collyrium. 

Acetate  of  Protoxide  of  Mercury. — The  only  interesting  compound  of 
mercury  and  acetic  acid  is  the  acetate  of  the  protoxide,  which  is  sometimes 
employed  in  the  practice  of  medicine.  It  is  prepared  by  mixing  crystallized 
protonitrate  of  mercury  with  neutral  acetate  of  potassa  in  the  ratio  of  one 
equivalent  of  each.  If  both  salts  are  dissolved  in  a  considerable  quantity  of 
hot  water,  the  solutions  retain  their  transparency  after  being  mixed ;  but  on 
cooling,  the  acetate  of  protoxide  of  mercury  is  deposited  in  white  scales  of 
a  silky  lustre.  It  is  easily  decomposed  ;  and  it  should  be  dried  by  a  very 
gentle  heat,  and  washed  with  cold  water  slightly  acidulated  with  acetic 
acid. 

LACTIC  ACID. 

Lactic  acid,  so  named  from  being  first  noticed  in  sour  milk,  was  disco- 
vered by  Scheele  in  1780.  It  has  been  detected  by  Berzelius  in  most  of  the 
animal  fluids,  and  in  the  beet-root  by  Braconnot,  who  termed  it  nanceic  acid. 
A  suspicion  has  long  existed  of  its  being  acetic  acid,  modified  in  its  charac- 
ter by  adhering  organic  matter ;  but  the  recent  experiments  of  J.  Gay-Lus- 
sac  and  Pelouze  have  finally  removed  all  doubt  about  the  existence  of  lactic 
acid.  (An.  de  Ch.  et  de  Ph.  lii.  410.) 

The  mode  of  preparation  employed  by  J.  Gay-Lussac  and  Pelouze,  was 
to  expose  a  large  quantity  of  the  juice  of  beet-root  to  a  temperature  of  80° 
for  several  days  in  order  to  establish  a  brisk  fermentation,  and  set  it  at  rest 
for  some  weeks  until  the  fermentation  has  ceased.  The  liquid  is  then  eva- 
porated to  the  consistence  of  syrup,  the  lactic  acid  taken  up  in  alcohol, 
which  separates  a  large  quantity  of  vegetable  matter,  and  the  alcoholic  ex- 


K1N1C  ACID.  487 

tract,  redissolved  in  water,  is  neutralized  by  carbonate  of  oxide  of  zinc,  by 
which  means  additional  impurities  are  precipitated.  The  soluble  lactate  of 
oxide  of  zinc  is  obtained  in  crystals  by  evaporation,  is  then  boiled  with  ani- 
mal charcoal  freed  from  phosphate  of  lime,  filtered  while  hot,  and  again 
crystallized.  The  salt  is  then  perfectly  white.  The  oxide  of  zinc  is  thrown 
down  by  pure  baryta,  and  the  lactate  of  baryta  decomposed  by  sulphuric 
acid.  If  any  portions  of  the  acid  are  not  quite  white,  they  may  be  converted 
into  lactate  of  lime,  purified  by  animal  charcoal,  crystallized,  dissolved  in 
alcohol,  and  lastly  decomposed  by  oxalic  acid.  A  similar  process  applied  to 
milk  after  long  fermentation  gives  pure  lactic  acid;  and  the  same  acid  has 
been  extracted  from  rice  and  from  nux  vomica. 

When  a  solution  of  lactic  acid  is  concentrated  in  vacuo  with  sulphuric 
acid,  it  acquires  the  consistence  of  syrup,  has  a  density  of  1-215,  is  colourless 
and  inodorous,  and  has  an  extremely  acid  taste.  It  attracts  moisture  on  ex- 
posute  to  the  air,  dissolves  in  all  proportions  in  water  and  alcohol,  and  is 
soluble  though  to  a  less  degree  in  ether.  When  mixed  with  a  strong  solu- 
tion of  acetate  of  potassa,  acetic  acid  is  disengaged,  and  with  a  strong  solu- 
tion of  the  acetates  of  magnesia  and  oxide  of  zinc,  the  lactates  of  those  bases 
subside.  It  yields  no  precipitate  with  baryta,  strontia,  or  lime. 

When  the  syrupy  lactic  acid  is  gradually  heated,  it  becomes  coloured  and 
yields  inflammable  gases,  acetic  acid,  a  white  crystalline  sublimate,  and  a 
residue  of  charcoal.  The  sublimed  matter,  freed  from  adhering  moisture  by 
bibulous  paper,  dissolves  freely  in  boiling  alcohol,  and  separates  on  cooling  in 
white  rhomboidal  tables.  These  crystals  fuse  at  225°,  and  the  liquid  boils  at 
472°,  yielding  an  inflammable  irritating  white  vapour,  which  crystallizes  as 
it  condenses :  it  may  be  volatilized  repeatedly  without  the  least  decomposi- 
tion. This  sublimed  acid,  as  stated  at  page  478,  differs  from  the  liquid  lactic 
acid  in  containing  two  eq.  less  of  water ;  and  though  when  first  put  into 
water  the  crystals  dissolve  slowly,  yet  when  once  in  solution  they  possess  all 
the  characters  of  the  liquid  acid. 

Lactic  acid  in  uniting  with  metallic  oxides  carries  into  the  salt  one  eq.  of 
water  or  its  elements,  which  cannot  be  expelled  without  decomposing  the 
salt  itself.  The  neutral  lactates  of  protoxides  in  their  dryest  state,  and  ex- 
clusive of  water  of  crystallization,  consist  of  one  eq.  of  the  oxide  and  81-72 
parts,jor  one  eq.  of  the  acid,  the  general  formula  being  M  +  C6H5O5  or 
M-f-L.  None  of  the  lactates  hitherto  examined  are  insoluble  in  water. 
The  lactates  of  baryta,  strontia,  potassa,  soda,  ammonia,  alumina,  and  oxide 
of  lead  are  very  soluble,  and  crystallize  with  difficulty.  That  of  oxide  of 
silver  is  white  and  crystallizes  in  needles.  The  salt  of  zinc  is  sparingly 
soluble  in  cold  water,  and  crystallizes  from  its  hot  solution  in  four-sided 
prisms,  which  are  insoluble  in  alcohol,  and  contain  four  eq.  of  water  of  crys- 
tallization. The  lactate  of  magnesia  also  crystallizes  readily,  and  also  with 
four  eq.  of  water. 

KINIC  ACID. 

This  acid,  noticed  in  1790  by  Hofmann,  and  studied  in  1806  by  Vau. 
quelin,  exists  in  cinchona  bark  in  combination  with  lime,  quinia,  and  cin- 
chonia.  On  evaporating  an  infusion  of  bark  to  the  consistence  of  an  ex- 
tract, and  treating  the  residue  with  alcohol,  a  viscid  matter  remains,  con- 
sisting of  kinate  of  lime  and  mucilaginous  matters.  On  dissolving  it  in 
water,  and  allowing  the  concentrated  solution  to  evaporate  spontaneously  in 
a  warm  place,  the  kinate  crystallizes  in  rhombic  prisms  with  dihedral 
summits,  and  sometimes  in  rhomboidal  plates.  From  a  solution  of  this  salt, 
exactly  decomposed  by  oxalic  acid,  kinic  acid  separates  in  foliated  crystals 
by  evaporation  in  a  warm  atmosphere  (An.  de  Ch.  lix.).  This  acid  and  its 
combinations  have  been  studied  by  Henry  and  Plisson,  Liebig,  and  Baup. 
(An.  de  Ch.  et  de  Ph.  xli.  325,  xlvii.  191,  and  li.  56).  Baup  recommends  that 
the  acid  should  be  prepared  from  kinate  of  lime  by  means  of  sulphuric 
acid. 


488  MALIC  ACID. 

Kinic  acid  possesses  strong  acidity,  dissolves  in  2£  times  its  weight  of 
water  at  48°,  and  is  also  soluble  in  alcohol,  but  appears  to  form  an  ethereal 
compound  with  it.  The  crystals  have  a  density  of  1-637,  and  consist  of 
181-8  parts  or  one  eq.  of  the  anhydrous  acid,  and  9  parts  or  one  eq.  of  water. 
When  strongly  heated  it  yields  a  volatile  acid  called  pyrokinic  acid. 

Kinic  acid  forms  very  soluble  compounds  with  all  the  alkalies,  alkaline 
earths,  and  oxides  of  mercury,  lead  and  silver.  These  neutral  kinates  are 
so  constituted  that  one  eq.  of  a  protoxide  is  united  wilh  181-8  parts  or  one 
eq.  of  kimc  acid,..the  general  formula  of  these  salts  being  M  +  C15H10O10 
or  M-J-K.  The  rhombic  crystals  of  kinate  of  lime  contain  ten  eq.  of  water. 
Kinate  of  soda  crystallizes  in  very  fine  six-sided  prisms  with  four  eq.  of 
water  ;  that  of  strontia  in  efflorescent  prisms  or  tables  with  ten  eq.  of  water; 
and  that  of  baryta  with  six  eq.  of  water.  Kinate  of  oxide  of  silver  yields 
by  evaporation  a  white  anhydrous  salt.  The  oxides  of  copper  and  lead 
form  with  it  neutral  and  sub-salts. 

MALIC  ACID. 

This  acid  is  contained  in  most  of  the  acidulous  fruits,  being  frequently 
associated  with  tartaric  and  citric  acids.  Grapes,  currants,  gooseberries, 
and  oranges  contain  it.  Vauquelin  found  it  in  the  tamarind  mixed  with  tar- 
taric  and  citric  acids,  and  in  the  house-leek  (sempervivum  tectorum^  com- 
bined  with  lime.  It  is  contained  in  considerable  quantity  in  apples,  a  cir- 
cumstance to  which  it  owes  its  name.  It  is  almost  the  sole  acidifying 
principle  of  the  berries  of  the  service-tree,  (sorbus  aucuparia),  in  which  it 
was  detected  by  Mr.  Donovan,  and  described  by  him  under  the  name  of 
sorbic  acid  in  the  Philosophical  Transactions  for  1815;  but  it  was  afterwards 
identified  with  the  malic  acid  by  Braconnot  and  Houton-Labillardiere.  (An. 
deCh.  et  dePh.viii.) 

Malic  acid  may  be  formed  by  digesting  sugar  with  three  times  its  weight 
of  nitric  acid  ;  but  the  best  mode  of  procuring  it  is  from  the  berries  of  the 
service-tree.  The  juice  of  the  unripe  berries  is  diluted  with  three  or  four 
parts  of  water,  filtered  and  heated;  and  while  boiling,  a  solution  of  acetate 
of  oxide  of  lead  is  added  as  long  as  any  turbidity  appears;  when  the  colour- 
ing matter  of  the  berry  is  precipitated,  while  the  malate  of  that  oxide  re- 
mains in  solution.  The  liquid,  while  at  a  boiling  temperature,  is  then  filtered. 
At  first  a  small  quantity  of  dark-coloured  salt  subsides ;  but  on  decanting 
the  hot  solution  into  another  vessel,  the  malate  of  oxide  of  lead  is  gradually 
deposited,  in  cooling,  in  groups  of  brilliant  white  crystals.  The  malate  is 
then  decomposed  by  a  quantity  of  dilute  sulphuric  acid,  insufficient  for  com- 
bining with  all  the  oxide  of  lead ;  by  which  means  a  solution  is  procured 
containing  malic  acid  together  with  a  little  lead.  The  latter  is  afterwards 
precipitated  by  hydrosulphuric  acid.  The  colouring  matter  is  more  easily 
separated  if  the  juice  is  allowed  to  ferment  for  a  few  days  before  being  used. 
Another  process  has  been  minutely  described  by  Liebig,  in  order  to  ensure 
the  absence  of  citric  and  tartaric  acids  wilh  which  it  is  sometimes  associated. 
(An.  de  Ch.  et  de  Ph.  Hi.  434.) 

Malic  acid  possesses  strong  acidity,  and  a  pleasant  flavour  when  diluted. 
It  crystallizes  with  difficulty,  attracts  moisture  from  the  air,  and  is  very  so- 
luble in  water  and  alcohol.  Its  aqueous  solution  is  decomposed  by  keeping, 
and  it  is  converted  into  the  oxalic  by  digestion  in  strong  nitric  acid.  Heated 
in  close  vessels  it  yields  a  volatile  acid  called  pyromatic,  the  properties  of 
which  are  not  yet  known.  From  the  late  analysis  of  Liebig  it  seems  that 
malic  and  citric  acids  are  isomeric. 

Most  of  the  salts  of  malic  acid  are  more  or  less  soluble  in  water.  The 
malates  of  soda  and  potassa  are  deliquescent.  The  bimalate  of  ammonia 
crystallizes  very  readily.  The  most  insoluble  of  the  malates  are  those  of 
baryta,  lime,  and  the  oxides  of  lead  and  silver  ;  but  these,  excepting  the  first, 
are  freely  soluble  in  boiling  water.  These  salts  are  composed  of  one  eq.  of 


CITRIC  ACID.  489 

base  and  5848  parts  or  one  eq.  of  acid,  the  general  formula  being  M-|- 
C4H2O4,  or  M+lVL  Pure  malate  of  oxide  of  lead  crystallizes  in  cooling 
from  its  hot  solution  in  small  brilliant  scales  of  extreme  whiteness.  The  sil- 
ver salt  also  crystallizes  from  its  solution  in  boiling  water ;  but  the  liquid 
darkens  from  the  reduction  of  oxide  of  silver. 

CITRIC  ACID. 

This  acid  is  contained  in  many  of  the  acidulous  fruits,  but  exists  in  large 
quantity  in  the  juice  of  the  lime  and  lemon,  from  which  it  is  procured  by  a 
process  very  similar  to  that  described  for  preparing  tartaric  acid.  To  any 
quantity  of  lime  or  lemon  juice,  finely  powdered  chalk  is  added  as  long  as 
effervescence  ensues ;  and  the  insoluble  citrate  of  lime,  after  being  well 
washed  with  water,  is  decomposed  by  digestion  in  dilute  sulphuric  acid. 
The  insoluble  sulphate  of  lime  is  separated  by  a  filter,  and  the  citric  acid 
obtained  in  crystals  by  evaporation.  They  are  rendered  quite  pure  by  being 
dissolved  in  water  and  recrystallized.  The  proportions  required  in  this  pro- 
cess are  86-98  parts  or  one  eq.  of  dry  citrate  of  lime,  and  49'1  parts  or  one 
eq.  of  strong  sulphuric  acid,  which  should  be  diluted  with  about  ten  parts  of 
water. 

Citric  acid  crystallizes  in  cooling  from  a  hot  saturated  solution  in  crystals 
which  consist  of  58-48  parts  or  one  eq.  of  the  anhydrous  acid,  and  9  parts 
or  one  eq.  of  water,  their  formula  being  H  +  C.  These  crystals  fuse  in  their 
water  at  a  heat  a  little  higher  than  212°,  but  without  loss  of  weight.  By 
spontaneous  evaporation  it  crystallizes  in  large  transparent  rhomboidal 
prisms,  which  differ  from  the  former  in  composition,  their  formula  being 
4H-J-3C  :  they  undergo  no  change  in  the  air  at  common  temperatures;  but 
at  82°  they  effloresce  and  part  with  exactly  half  their  water,  retaining  the 
remainder  until  the  heat  is  so  high  that  the  acid  itself  is  destroyed. 

Citric  acid  has  a  strong  sour  taste,  with  an  agreeable  flavour  when 
diluted,  reddens  litmus  paper,  and  neutralizes  alkalies.  In  a  dry  state  it  may 
be  preserved  for  any  length  of  time,  but  the  aqueous  solution  is  gradually 
decomposed  by  keeping.  The  crystals  are  soluble  in  an  equal  weight  of 
cold  and  in  half  their  weight  of  boiling  water,  and  are  also  dissolved  by  alco- 
hol. It  is  converted  into  the  oxalic  by  digestion  in  nitric  acid. 

Citric  acid  is  characterized  by  its  flavour,  by  the  form  of  its  crystals,  and 
by  forming  an  insoluble  salt  with  lime,  and  a  deliquescent  soluble  one  with 
potassa.  It  does  not  render  lime-water  turbid  unless  the  latter  is  in,  excess, 
and  fully  saturated  with  lime  in  the  cold. 

Citric  acid  is  employed  in  calico-printing,  and  in  medicinal  and  domestic 
purposes  instead  of  lemon  juice.  Tartaric  acid  is  often  substituted  for  it,  as 
being  similar  in  flavour,  and  less  expensive. 

Of  the  citrates,  those  of  potassa,  soda,  ammonia,  magnesia,  and  oxides  of 
iron  are  soluble  in  water ;  while  those  of  lime,  baryta,  strontia,  and  the 
oxides  of  lead,  mercury,  and  silver  are  very  sparingly  soluble  in  hot  water, 
though  dissolved  by  excess  of  their  own  acid.  They  are  decomposed  by  sul- 
phuric acid.  No  general  rule  can  be  stated  in  respect  of  their  constitution, 
since,  from  late  observations  of  Berzelius  (An.  de  Ch.  et  de  Ph.  liii.  424),  it 
appears  that  citric  acid  exhibits  very  unusual  modes  of  combination,  and  ia 
prone  to  form  sub-salts  of  a  complex  composition.  Thus,  on  mixing  neutral 
citrate  of  potassa  with  acetate  or  nitrate  of  oxide  of  lead,  it  is  impracticable 
to  procure  the  neutral  citrate,  Pb-f-C,  because  it  falls  in  mixture  with  an- 
other salt,  the  formula  of  which  is  Pb2CT34-2H,  and  which,  digested  with 
very  dilute  ammonia,  abandoned  its  water  and  half  of  its  acid,  forming  the 
salt  4rb-f-3C.  He  obtained  the  neutral  citrate  in  the  purest  state  by  adding 
an  alcoholic  solution  of  citric  acid  to  a  solution  of  acetate  of  oxide  of  lead, 
and  washing  the  precipitate  with  alcohol ;  for  water  deprives  it  of  acid,  and 
converts  it  into  a  sub-salt.  On  digesting  the  neutral  citrate  with  acetate  of 


490  TARTARIC  ACID. 

oxide  of  lead,  he  obtained  a  dicitrate,  of  which  the  formula  is  2Pb-|-C.  He 
found  it  very  difficult  to  obtain  neutral  citrates  of  lime  or  baryta,  as  they 
both  resolve  themselves  readily  into  acid  and  sub-salts  of  complex  composi- 
tion. The  most  uniform  of  the  citrates  is  that  of  oxide  of  silver,  the  neutral 
citrate,  Ag-f-C,  being  readily  obtained  by  double  decomposition. 

Pyrocitric  acid. — When  the  crystals  of  citric  acid  are  subjected  to  de- 
structive distillation,  three  volatile  products  are  obtained,  namely,  a  peculiar 
acid  called  pyrocitric,  water,  and  a  spirituous  matter  which  has  not  been  ex- 
amined. Pyrocitric  acid  forms  a  sparingly  soluble  salt  with  oxide  of  lead ; 
but  the  pyrocitrates  generally  have  not  yet  been  studied.  It  appears  to  form 
a  hydrate  with  one  equivalent  of  water. 

TARTARIC  ACID. 

This  acid  exists  in  the  juice  of  several  acidulous  fruits,  but  it  is  almost 
always  in  combination  with  lime  or  potassa.  It  is  prepared  by  mixing 
cream  of  tartar  and  chalk  in  the  ratio  of  their  equivalents,  189-11  to  50-62, 
and  boiling  them  in  10  times  their  weight  of  water  for  about  half  an  hour. 
The  carbonic  acid  of  the  chalk  is  displaced  with  effervescence,  one  eq.  of  in- 
soluble tartrate  of  lime  subsides,  and  one  eq.  of  neutral  tartrate  of  potassa  re- 
mains  in  solution.  On  washing  the  former,  and  then  digesting  it,  diffused 
through  a  moderate  portion  of  water,  with  one  equivalent  of  sulphuric  acid, 
the  tartaric  acid  is  set  free;  and  after  being  separated  from  the  sulphate  of 
lime  by  a  filter,  it  rnay  be  procured  by  evaporation  in  prismatic  crystals,  the 
primary  form  of  which  is  a  right  rhombic  prism. 

Tartaric  acid  has  a  sour  taste,  which  is  very  agreeable  when  diluted  with 
water.  It  reddens  litmus  paper  strongly,  arid  forms  with  alkalies  neutral 
salts,  to  which  the  name  o?  tartrates  is  applied.  It  requires  five  or  six  times 
its  weight  of  water  at  60°  for  solution,  and  is  much  more  soluble  in  boiling 
water.  It  is  dissolved  likewise,  though  less  freely,  in  alcohol.  The  aqueous 
solution  is  gradually  decomposed  by  keeping,  and  a  similar  change  is  expe- 
rienced, under  the  same  circumstances,  by  most  of  the  tartrates.  The  crys- 
tals may  be  exposed  to  the  air  without  change.  They  are  converted  into 
the  oxalic  by  digestion  in  nitric  acid. 

Tartaric  acid  cannot  be  deprived  of  its  water  of  crystallization,  except  by 
uniting  with  an  alkaline  base :  on  attempting  to  expel  it  by  heat,  the  acid 
fuses  and  is  decomposed,  yielding,  if  air  is  excluded,  the  usual  products  of 
destructive  distillation,  together  with  a  distinct  acid,  to  which  the  term  pyro- 
tartaric  acid  is  applied.  A  large  residue  of  charcoal  is  obtained. 

Tartaric  acid  is  distinguished  from  other  acids  by  forming  a  white  preci- 
pitate, bitartrate  of  potassa,  when  mixed  with  any  of  the  salts  of  that  alkali. 
This  acid,  therefore,  separates  potassa  from  other  acids.  It  occasions  with 
lime-water  a  white  precipitate,  which  is  very  soluble  in  an  excess  of  the 
acid. 

Tartaric  acid  is  remarkable  for  its  tendency  to  form  double  salts,  the  pro- 
perties of  which  are  often  more  interesting  than  the  simple  salts.  The  most 
important  of  these  double  salts  and  the  only  ones  which  have  been  much  stu- 
died, are  those  of  potassa  and  soda,  and  of  oxide  of  antimony  and  potassa. 
The  neutral  tartrates  of  the  alkalies,  of  magnesia,  and  protoxide  of  copper, 
are  soluble  in  water ;  but  most  of  the  tartrates  of  the  other  bases,  and  espe- 
cially those  of  lime,  baryta,  strontia,  and  oxide  of  lead,  are  insoluble.  All 
these  neutral  tartrates,  however,  which  are  insoluble  in  pure  water,  are  solu- 
ble in  an  excess  of  their  acid.  They  are  decomposed  by  digestion  in  carbonate 
of  potassa;  and  when  an  acid  is  added  in  excess,  the  bitartrate  of  potassa  is 
precipitated.  All  the  insoluble  tartrates  are  easily  procured  from  neutral  tar- 
trate of  potassa  by  way  of  double  decomposition.  The  neutral  tartrates  of 
protoxides  consist  of  66-48  parts  or  one  eq.  of  the  acid,  and  one  eq,  of  base, 
so  that  the  general  formula  is  M-J-C4HO5,  or  M-f-T". 

of  Potassa.— The  neutral  tartrate,  frequently  called  soluble  tar- 


TARTARIC  ACID.  491 

tar,  is  formed  by  neutralizing  a  solution  of  the  bitartrate  with  carbonate  of 
potassa :  and  it  is  a  product  of  the  operation  above  described  for  making  tar- 
taric  acid.  Its  primary  form  is  a  right  rhomboidal  prism  ;  but  it  often  occurs 
in  irregular  six-sided  prisms  with  dihedral  summits.  Its  crystals  are  very 
soluble  in  water,  and  attract  moisture  when  exposed  to  the  air.  They  con- 
sist of  113-63  parts  or  one  eq.  of  the  neutral  tartrate,  and  18  or  two  eq.  of 
water.  They  are  rendered  quite  anhydrous  by  a  temperature  not  exceeding 
248°  F. 

Of  the  Utartrate  an  impure  form,  commonly  known  by  the  name  of  tartar, 
is  found  encrusted  on  the  sides  and  bottom  of  wine  casks,  a  source  from 
which  all  the  tartar  of  commerce  is  derived.  This  salt  exists  in  the  juice  of 
the  grape,  and,  owing  to  its  insolubility  in  alcohol,  is  gradually  deposited 
during  the  vinous  fermentation.  In  its  crude  state  it  is  coloured  by  the  wine 
from  which  it  was  procured  ;  but  when  purified,  it  is  quite  white,  and  in  this 
state  constitutes  the  cream  of  tartar  of  the  shops. 

Bitartrate  of  potassa  is  very  sparingly  soluble  in  water,  requiring  60  parts 
of  cold  and  14  of  boiling  water  for  solution,  and  is  deposited  from  the  latter 
on  cooling  in  small  crystalline  grains.  Its  crystals  are  commonly  irregular 
six-sided  prisms,  terminated  at  each  extremity  by  six  surfaces ;  and  its  pri- 
mary form  is  either  a  right  rectangular,  or  a  right  rhombic  prism.  It  has  a 
sour  taste,  and  distinct  acid  reaction.  It  consists  of  47-15  parts  or  one  eq.  of 
potassa,  132-96  or  two  eq.  of  acid,  and  9  parts  or  one  equivalent  of  water.  Its 
water  of  crystallization  cannot  be  expelled  without  decomposing  the  salt 
itself. 

Bitartrate  of  potassa  is  employed  in  the  formation  of  tartaric  acid  and  all 
the  tarlrates.  It  is  likewise  used  in  preparing  pure  carbonate  of  potassa. 
When  exposed  to  a  strong  heat,  it  yields  an  acrid  empyreumatic  oil,  some 
pyrotartaric  acid,  together  with  water,  carburetted  hydrogen,  carbonic 
oxide,  and  carbonic  acid,  the  last  of  which  combines  with  the  potassa.  The 
fixed  products  are  carbonate  of  potassa  and  charcoal,  which  may  be  sepa- 
rated from  'each  other  by  solution  and  filtration.  When  deflagrated  with 
half  its  weight  of  nitre,  by  which  part  of  the  charcoal  is  consumed,  it  forms 
black  flux  ;  and  when  an  equal  weight  of  nitre  is  used,  so  as  to  oxidize  all 
the  carbon  of  the  tartaric  acid,  a  pure  carbonate  of  potassa,  called  white  flux 
is  procured. 

Tartrate  of  Potassa  and  Soda. — This  double  salt,  which  has  been  long 
employed  in  medicine  under  the  name  of  Seignette  or  Rochelle  salt,  is  pre- 
pared by  neutralizing  bitartrate  of  potassa  with  carbonate  of  soda.  By 
evaporation  it  yields  prismatic  csystals,  the  sides  of  which  often  amount  to 
ten  or  twelve  in  number ;  but  the  primary  form,  as  obtained  by  cleavage,  is 
a  right  rhombic  prism.  (Brooke.)  The  crystals  are  soluble  in  five  parts  of 
cold  and  in  a  smaller  quantity  of  boiling-  water,  and  are  composed  of  113-63 
parts  or  one  eq.  of  tartrate  of  potassa,  97-78  parts  or  one  eq.  of  tartrate  of 
soda,  and  72  or  eight  equivalents  of  water. 

Tartrate  of  Soda  is  frequently  used  as  an  effervescing  draught,  by  dis- 
solving equal  weights  of  tartaric  acid  and  bicarbonate  of  soda  in  separate 
portions  of  water,  and  then  mixing  the  solutions.  Soda  is  better  adapted 
for  this  purpose  than  potassa,  because  the  former  has  little  or  no  tendency 
to  form  an  insoluble  bitartrate. 

Tartrate  of  Oxide  of  Antimony  and  Potassa. — This  compound,  long  cele- 
brated as  a  medicinal  preparation  under  the  name  of  tartar  emetic,  is  made 
by  boiling  sesquioxide  of  antimony  with  a  solution  of  bitartrate  of  potassa. 
The  oxide  of  antimony  is  furnished  for  this  purpose  in  various  ways.  Some- 
times the  glass  or  crocus  of  that  metal  is  employed.  The  Edinburgh  col- 
lege  prepare  an  oxide  by  deflagrating  sulphuret  of  antimony  with  an  equal 
weight  of  nitre;  and  the  college  of  Dublin  employ  the  oxy-chloride.  Mr. 
Phillips  recommends  that  100  parts  of  metallic  antimony  in  fine  powder 
should  be  boiled  to  dryness  in  an  iron  vessel  with  200  of  sulphuric  acid, 
and  that  the  residual  subsulphate,  after  washing  with  water,  be  boiled  with 
an  equal  weight  of  cream  of  tartar.  The  solution  of  the  double  salt,  how- 


492  RACEMIC    ACID* 

ever  made,  should  be  concentrated  by  evaporation,  and  allowed  to  cool  in 
order  that  crystals  may  form. 

Tartar  emetic  yields  crystals,  which  are  transparent  when  first  formed, 
but  become  white  and  opaque  by  exposure  to  the  air.  Its  primary  form  has 
been  correctly  described  by  Mr.  Brooke  as  an  octohedron  with  a  rhombic 
base  (An.  of  Phil.  N.  S.  vi.  40.) ;  but  the  edges  of  the  base  are  frequently 
replaced  by  planes  which  communicate  a  prismatic  form,  and  its  summits 
are  generally  formed  with  an  edge  instead  of  a  solid  angle,  which  edge  is 
frequently  truncated,  presenting  a  narrow  rectangular  surface.  It  frequent- 
ly occurs  in  segments,  having  the  outline  of  a  triangular  prism,  a  form 
which  has  deceived  many  into  the  belief,  that  the  tetrahedron  or  regular 
octohedron  is  the  primary  form  of  tartar  emetic.  It  has  a  styptic  metallic 
taste,  reddens  litmus  paper  slightly,  and  is  soluble  in  15  parts  of  water  at 
60°,  and  in  3  of  boiling  water.  Its  aqueous  solution,  like  that  of  all  the 
tartrates,  undergoes  spontaneous  decomposition  by  keeping;  and,  therefore, 
if  kept  in  the  liquid  form,  alcohol  should  be  added  in  order  to  preserve  it. 
From  the  analysis  of  Thomson,  Phillips,  and  Wallquist,  it  may  be  considered 
a  compound  of 

1  eq.       1  eq. 

Base.      Acid.      Equiv.     Formulae. 

Tartrate  of  sesquioxide  of  antimony  153-2  4-66-48=219-68      Sb  +  T\ 

Tartrateofpotassa  .  .          47-15+66'48=113-63       K+Ti 

Water  of  crystallization,  2  eq.  .         .         .         =18 


351-31  )  (KT+SbT) 
(    4-2H7 

Tartar  emetic  is  decomposed  by  many  reagents.  Thus  alkaline  sub- 
stances,  from  their  superior  attraction  for  tartaric  acid,  separate  the  oxide  of 
antimony.  The  pure  alkalies,  indeed,  and  especially  potassa  and  soda,  pre- 
cipitate it  imperfectly,  owing  to  their  tendency  to  unite  with  and  dissolve 
the  oxide;  but  the  alkaline  carbonates  throw  down  the  oxide  much  more 
completely.  Lime-water  occasions  a  white  precipitate,  which  is  a  mixture 
of  oxide,  or  tartrate  of  the  oxide,  and  tartrate  of  lime.  The  stronger  acids, 
such  as  the  sulphuric,  nitric,  and  hydrochloric,  cause  a  white  precipitate, 
consisting  of  bitartrate  of  potassa  and  a  subsalt  of  the  oxide  of  antimony. 
Decomposition  is  likewise  effected  by  several  metallic  salts,  the  bases  of 
which  yield  insoluble  compounds  with  tartaric  acid.  Hydrosulphuric  acid 
throws  down  the  orange  sesquisulphuret  of  antimony.  It  is  precipitated  by 
many  vegetable  substances,  especially  by  an  infusion  of  gall-nuts,  and  other 
similar  astringent  solutions,  with  which  it  forms  a  dirty  white  precipitate, 
which  is  a  taunate  of  sesquioxide  of  antimony.  This  combination  is  inert, 
and,  therefore,  a  decoction  of  cinchona  bark  is  recommended  as  an  antidote 
to  tartar  emetic.  Heated  before  the  blowpipe,  metallic  antimony  is  readily 
brought  into  view ;  and  if  decomposed  by  heat  in  close  vessels,  a  very  in- 
flammable  pyrophorus  is  formed. 

RACEMIC  ACID. 

( Traubensaure,  or  Acid  of  Grapes  of  the  Germans.} 

This  acid  was  first  noticed  by  Mr.  Kestner,  chemical  manufacturer  at 
Thann  in  the  Upper  Rhine,  who  met  with  it  in  the  preparation  of  tartaric 
acid,  with  which  it  is  associated  in  the  juice  of  the  grape.  Kestner,  per- 
ceiving it  to  be  different  from  tartaric  acid,  considered  it  to  be  the  oxalic : 
John  in  1819  declared  it  to  be  distinct  from  both  of  those  acids,  and  termed 
it  acid  of  the  Vosges ;  and  in  1826  Gay-Lussac  and  Walchner,  receiving  a 


BENZOIC    ACID.  493 

supply  from  Kestner,  made  a  careful  examination  of  its  principal  characters. 
(Jour,  de  Ch.  Med.  ii.  335,  and  Gmelin's  Handbuch,  ii.  53.)  An  account  of 
its  properties  has  since  been  given  by  Berzelius,  who  has  suggested  for  it 
the  name  of  par atari a  ric  acid.  (An.  de  Ch.  et  de  Ph.  xlvi.  128.) 

Racemic  acid  is  associated  with  tartaric  acid,  apparently  as  a  biracemate 
of  potassa,  in  the  grape  of  the  Upper  Rhine,  and  subsides  during-  the  fer- 
mentation of  the  juice  along-  with  cream  of  tartar :  it  is  probably  contained 
in  the  juice  of  all  grapes.  It  is  readily  obtained  by  neutralizing  the  cream 
of  tartar  of  that  district  with  carbonate  of  soda,  separating  the  double  tar- 
trate  of  potassa  and  soda  by  crystallization,  throwing  down  the  racemic 
acid  by  a  salt  of  lime  or  oxide  of  lead,  and  decomposing  the  precipitate  by 
dilute  sulphuric  acid.  On  concentrating  the  solution,  the  racemic  acid 
crystallizes,  and  is  thus  completely  separable  from  any  remaining  tartaric 
acid,  the  latter  being  much  more  soluble  in  water  than  the  former. 

The  racemic  and  tartaric  acids,  besides  being  associated  in  nature,  afford 
a  most  interesting  instance  of  isornerism.  Gay-Lussac  showed  that  the 
equivalents  of  these  acids  are  represented  by  the  same  number;  and  Berze- 
lius has  not  only  confirmed  this  fact,  but  proved  that  their  composition  is 
likewise  identical.  There  is  also  a  close  analogy  in  their  chemical  rela- 
tions:— each  forms  insoluble  salts  with  the  same  bases,  as  with  lime,  baryta, 
and  oxide  of  lead ;  biracemate  of  potassa  is  a  sparingly  soluble  salt  analo- 
gous to  cream  of  tartar;  and  with  sesquioxide  of  antimony  the  biracemate 
of  potassa  yields  a  double  salt,  similar  in  many  respects  to  tartar  emetic, 
though  different  in  the  form  of  its  crystals.  Nevertheless,  the  two  acids  are 
essentially  distinct.  The  racemic  is  much  less  soluble  than  tartaric  acid; 
the  form  of  its  crystals  is  different,  being  an  oblique  rhombic  prism  ;  it  con- 
tains  two  equivalents  of  water  of  crystallization,  one  of  which  is  given  out 
at  212°,  and  the  other  when  it  unites  with  alkalies;  and  it  does  not  yield  a 
double  salt  with  potassa  and  soda.  The  racemate  of  lime,  too,  is  less  solu- 
ble than  the  tartrate,  and  is  but  sparingly  dissolved  by  excess  of  its  acid :  a 
solution  of  gypsum  is  not  affected  by  tartaric  acid,  whereas  a  little  racemic 
acid  after  an  interval  of  about  an  hour  causes  turbidity:  racemate  of  lime 
dissolved  in  dilute  hydrochloric  acid  is  almost  immediately  thrown  down  by 
the  addition  of  ammonia;  while  tartrate  of  lime  under  the  same  treatment 
does  not  subside  so  as  to  cause  turbidity,  but  after  a  time  slowly  separates 
in  octohedral  crystals  with  a  square  base,  which  are  found  adhering  to  the 
sides  of  the  glass.  It  thus  appears  that  racemic  and  tartaric  acids  have  the 
same  atomic  weight,  the  same  composition,  and  in  several  respects  the 
same  chemical  properties;  and  yet  on  closely  investigating  all  their  charac- 
ters, they  are  found  to  be  essentially  distinct.  Moreover,  the  different  ar- 
rangement of  the  atoms  in  these  two  acids  is  indicated  by  the  different  form 
of  similar  combinations. 

BENZOIC  ACID. 

Benzoic  acid  exists  in  gum  benzoin,  in  storax,  in  the  balsams  of  Peru  and 
Tolu,  and  in  several  other  vegetable  substances.  M.  Vogel  has  detected  it  in 
the  flowers  of  the  trifolium  melilotus  qfficinalis.  It  is  found  in  considerable 
quantity  in  the  urine  of  the  cow  and  other  herbivorous  animals,  and  is  per- 
haps derived  from  the  grasses  on  which  they  feed.  It  has  also  been  detected 
in  the  urine  of  children. 

This  acid  is  commonly  extracted  from  gum  benzoin.  One  method  con- 
sists in  heating  the  benzoin  in  an  earthen  pot,  over  which  is  placed  a  cone 
of  paper  to  receive  the  acid  as  it  sublimes ;  but  since  the  product  is  always 
impure,  owing  to  the  presence  of  empyreumatic  oil,  it  is  better  to  extract 
the  acid  by  means  of  an  alkali.  The  usual  process  consists  in  boiling  finely 
powdered  gum  benzoin  in  a  large  quantity  of  water  along  with  lime  or  car- 
bonate of  potassa,  by  which  means  a  benzoate  is  formed.  To  the  solution, 

42 


494  MECONIC   ACID. 

after  being  filtered  and  concentrated  by  evaporation,  hydrochloric  acid  is 
added,  which  unites  with  the  base,  and  throws  down  the  benzoic  acid.  It  is 
then  dried  by  a  gentle  heat,  and  purified  by  sublimation. 

Benzoic  acid  has  a  sweet  and  aromatic  rather  than  a  sour  taste;  but  it 
reddens  litmus  paper,  and  neutralizes  alkalies.  It  fuses  readily  by  heat,  and 
at  a  temperature  a  little  above  its  point  of  fusion,  it  is  converted  into  vapour, 
emitting  a  peculiar,  fragrant,  and  highly  characteristic  odour,  and  condens- 
ing on  cool  surfaces  without  change.  When  strongly  heated  it  takes  fire, 
and  burns  with  a  clear  yellow  flame.  It  undergoes  no  change  by  exposure 
to  the  air,  and  is  not  decomposed  by  the  action  even  of  nitric  acid.  It  re- 
quires about  24  parts  of  boiling  water  for  solution,  and  nearly  the  whole  of 
it  is  deposited  on  cooling  in  the  form  of  minute  acicular  crystals  of  a  silky 
lustre.  It  is  very  soluble  in  alcohol,  especially  by  the  aid  of  heat. 

Agreeably  to  the  late  admirable  researches  of  Liebig  and  Wohler  on  the 
oil  of  bitter  almonds,  benzoic  acid  must  be  regarded  as  the  oxide  of  a  com- 
pound inflammable  body  which  will  be  treated  of  in  the  third  section, 
and  to  which  they  have  applied  the  name  of  benzule,  composed  of  bcnz,  and 
V\H  matter  or  principle.  Benzule  is  composed  of  85*68  parts  or  fourteen  eq. 
of  carbon,  5  parts  or  five  eq.  of  hydrogen,  and  16  parts  or  two  eq.  of  oxygen, 
its  equivalent  being  106-68.  The  composition  of  benzoic  acid  may  be  thus 
stated,  an  equivalent  being  represented  by  Bz: — (An.  de  Ch.  et  de  Ph.  li. 
273.) 

Anhydrous  benzoic  acid.  Benzule  106'68-fOxygen  8=114-68  Bz-i-O  or  Bz. 
The  crystallized  acid  contains  one  eq.  of  water,  its  formula  being  Bz-f-H, 
and  it  cannot  be  deprived  of  its  water  by  heat.  Its  water  of  crystallization 
is  also  contained  in  benzoate  of  oxide  of  lead,  PbBz-f-H,  and  is  not  expelled 
by  heat  until  the  salt  ilself  is  decomposed.  Benzoate  of  oxide  of  silver  is  an- 
hydrous, its  formula  being  Ag-f-Bz :  it  falls  as  a  white  powder  when  nitrate 
of  oxide  of  silver  is  mixed  in  solution  with  benzoate  of  ammonia,  is  com- 
pletely dissolved  by  boiling  water,  and  is  deposited  on  cooling  in  brilliant 
foliated  crystals. 

The  composition  of  neutral  benzoates  of  protoxides  is  represented  by  the 
general  formula  M-f-Bz.  Most  of  these  are  soluble  in  water:  the  most  in- 
soluble are  the  benzoates  of  the  oxides  of  lead,  mercury,  and  silver,  and  sesqui- 
oxide  of  iron.  % 

MECONIC  ACID. 

This  acid,  which  derives  its  name  from  Mxxav,  poppy,  has  hitherto  been 
found  only  in  opium,  where  it  exists  in  combination  with  morphia  ;  and  it  is 
best  prepared  from  the  mixed  sulphate  and  rneconate  of  lime  obtained  in 
Gregory's  process  for  hydrochlorate  of  morphia.  The  impure  meconate  of 
lime  is  put  into  ten  times  its  weight  of  water  at  200°,  and  hydrochloric  acid 
is  added  until  the  meconale  is  dissolved  :  the  solution  is  then  filtered,  and 
on  cooling  deposites  bimeconate  of  lime  in  the  form  of  light  white  scaly  or 
acicular  crystals.  These  are  again  dissolved  by  hot  dilute  hydrochloric  acid 
as  before,  in  order  to  separate  the  remainder  of  the  lirne;  and  on  coding 
crystals  of  meconic  acid  subside.  If  they  leave  a  residue  after  calcination, 
they  should  be  again  dissolved  in  acid  and  re-crystallized.  To  procure  the 
acid  quite  white,  it  is  saturated  with  potassa  diluted  with  the  smallest  quan- 
tity of  water  required  by  the  aid  of  heat  to  dissolve  the  meconate,  and  when 
cold  the  fluid  part,  which  retains  the  colouring  matter,  is  separated  from  the 
crystals  by  filtration  and  pressure  in  cloth  or  bibulous  paper.  The  meconate 
of  potassa  is  then  decomposed  in  the  same  way  as  the  meconale  of  lime, 
when  meconic  acid  is  obtained  perfectly  white  and  in  transparent  micaceous 
scales. 

Meconic  acid  has  an  acid  taste  and  reaction,  and  is  soluble  both  in  alco- 
hol and  water,  requiring  only  four  times  its  weight  of  boiling  water  for  so- 


METAMECONIC  ACID. TANNIC  ACID.  495 

lutlon.  The  crystals  are  unchanged  in  the  air,  but  when  heated  to  212° 
they  become  quite  opaque  and  lose  21'5  per  cent,  of  water  crystallization, 
being  27  parts  or  three  eq.  to  100-84  parts  or  one  eq.  of  the  anhydrous  acid. 
They  still  continue  rneconic  acid  even  when  heated  to  248°  ;  but  if  boiled  in 
water,  carbonic  acid  gas  is  disengaged,  the  liquid  becomes  brown,  meconic 
acid  disappears,  and  metameconic  acid  is  generated. 

Meconic  acid  is  remarkable  for  forming  with  sesquisalts  of  iron  a  purple- 
red  colour,  which  affords  a  good  test  for  the  acid  whether  free  or  combined 
and  detects  meconic  acid  in  solutions  of  opium,  when  the  morphia  combined, 
with  it  could  not  be  discovered ;  the  colour  is  very  like  that  produced  by  hy- 
drosulphocyanic  acid.  Meconic  acid  forms  insoluble  white  salts  with  lime, 
baryta,  and  the  oxides  of  lead  and  silver,  which  are  soluble  in  nitric  acid.  It 
is  very  prone  to  form  bisalts,  as  the  bimeconate  of  potassa  and  lime,  which 
are  of  sparing  solubility.  The  meconate  of  oxide  of  silver  consists  of  116 
parts  or  one  eq.  of  that  base  and  100-84  parts  or  one  eq.  of  meconic  acid,  its 
formula  being  Ag-f-C7H2O7.  The  neutral  meconates  of  protoxides  are  ana- 
logous in  composition. 

METAMECONIC  ACID. 

Robiquet,  who  has  described  the  preparation  and  properties  of  meconic 
acid,  also  observed  its  conversion  into  metameconic  acid  by  boiling  its 
aqueous  solution  ;  and  Liebig,  by  his  skilful  analysis  of  both  acids,  has  proved 
(An.  de  Ch.  et  de  Ph.  li.  241  and  liv.  26)  that 

2  eq.  of  meconic  acid    )    •  n  J    1  eq.  of  metameconic  acid  12C4-4H  +  10O 
2(7C  +  2H-f-7O)       (  y        /    and  2  eq-  carbonic  acid        2(C  +  2O). 

The  brown  matter  formed  when  a  solution  of  meconic  acid  is  boiled,  and 
which  adheres  to  the  acid,  does  not  seem  essential  to  the  change,  since  it 
takes  place  in  a  very  slight  degree  when  a  meconate  is  boiled  with  hydro- 
chloric acid,  the  resulting  metameconic  acid  being  then  nearly  colourless. 

Metameconic  acid  is  soluble  in  16  times  its  weight  of  boiling  water,  and 
separates  on  cooling  in  anhydrous  hard  crystalline  grains  wholly  different 
from  meeonic  acid.  It  reddens  sesquisalts  of  iron,  but  its  other  properties 
have  not  yet  been  studied. 

When  anhydrous  meconic  acid  is  distilled,  it  yields  among  other  products 
a  crystalline  sublimate,  which  till  lately  was  regarded  as  pure  meconic  acid, 
though  in  reality  it  is  not  so.  It  reddens  sesquisalts  of  iron  ;  but  whether  it  is 
metameconic  acid,  or  some  other  compound,  has  not  been  determined. 

TANNIC  ACID  (TANNIN). 

This  substance  exists  in  an  impure  state  in  the  excrescences  of  several 
species  of  oak,  called  gall-nuts;  in  the  bark  of  most  trees;  in  some  inspis- 
sated juices,  such  as  kino  and  catechu  ;  in  the  leaves  of  the  tea-plant,  su- 
mach, and  whortleberry  (uva  ursa),  and  in  astringent  plants  generally,  be- 
ing the  chief  cause  of  the  astringency  of  vegetable  matter.  It>  is  frequently 
associated  with  gallic  acid,  as  in  gall.nuts,  in  most  kinds  of  bark,  and  in 
tea ;  but  in  kino,  catechu,  and  cinchona  bark,  little  or  no  gallic  acid  is 
present. 

Several  processes  are  recommended  for  the  preparation  of  tannic  acid. 
Thus,  it  may  be  precipitated  from  a  solution  of  gall-nuts  by  chloride  of  tin, 
and  the  precipitate  after  washing  be  decomposed  by  hydrosulphuric  acid  ;• 
or  it  may  be  thrown  down,  by  concentrated  sulphuric  acid  in  the  cold,  and 
the  precipitate*  when  dried  in  folds  of  bibulous  paper,  be  decomposed  by  di- 
gestion with  carbonate  of  oxide  of  lead.  But  in  these  and  similar  processes 
the  tannic  acid,  which  is  very  prone  to  change,  is  more  or  less  modified 
in  its  character  ;  and,  therefore,  the  process  with  ether  lately  recommended 
by  Pelouze  is  preferable.  (An.  de  Ch.  et  de  Ph,  liv.  337.)  The  lower  aper. 


496  TANNIC  ACID. 

ture  of  an  elongated  narrow  glass  vessel  is  loosely  closed  by  a  piece  of 
linen ;  on  this  is  laid  some  gall-nuts  in  fine  powder,  which  is  gently  pressed 
together,  and  then  sulphuric  ether  is  poured  upon  the  powder :  the  upper 
aperture  is  closed  hy  a  stopper  to  prevent  loss  of  ether  by  evaporation,  and 
the  apparatus  fixed  in  the  mouth  of  a  bottle,  which  receives  the  ether  as  it 
slowly  percolates  through  the  powder.  It  appears  that  the  small  quantity  of 
water  contained  in  ether  as  sold  in  the  shops,  combines  with  tannic  acid  to 
the  exclusion  of  the  other  ingredients  of  the  gall-nuts,  and  forms  a  saturated 
aqueous  solution,  which  collects  as  a  distinct  stratum  below  the  ether.  After 
exhausting  the  gall-nuts  by  repeated  portions  of  ether,  the  ethereal  part  is 
drawn  off  and  purified  by  distillation,  and  the  aqueous  solution  of  tannic 
acid,  after  being  washed  with  ether,  is  evaporated  to  dryness  at  a  very  gen- 
tle heat  or  in  vacuo  with  sulphuric  acid.  The  tannic  acid  is  left  as  a  uni- 
form spongy  mass,  not  crystallized,  either  quite  white  or  with  a  slightly 
yellow  tint.  Its  quantity  varies  from  35  to  40  per  cent,  of  the  gall-nuts  em- 
ployed. 

Pure  tannic  acid  is  colourless  and  inodorous,  has  a  purely  astringent 
taste  without  bitterness,  and  may  be  preserved  without  change  in  the  solid 
state.  It  is  very  soluble  in  water,  and  the  solution  reddens  litmus,  and  de- 
composes alkaline  carbonates  with  effervescence,  thus  leaving  no  doubt  of 
its  acidity.  Alcohol  and  ether  also  dissolve  tannic  acid,  but  more  sparingly 
than  water,  especially  when  anhydrous.  Solutions  of  tannic  acid  do  not 
affect  pure  protosalts  of  iron,  but  strike  a  deep  blue  precipitate  with  the 
sesquisalts  :  a  strong  solution  of  it  yields  a  copious  white  precipitate  with  the 
sulphuric,  nitric,  hydrochloric,  phosphoric  and  arsenic  acids,  but  none  with 
the  oxalic,  tartaric,  lactic,  acetic,  citric,  succinic,  and  selenious  acids.  It  is 
precipitated  also  by  the  carbonates  of  poipssa  and  ammonia,  by  the  alkaline 
earths,  alumina,  and  many  solutions  of  the  second  class  of  metals.  With 
cinchonia,  quinia,  brucia,  strychnia,  codeia,  narcotina,  arid  morphia,  it  yields 
white  tannates,  which  are  sparingly  soluble  in  pure  water,  but  are  dissolved 
readily  by  acetic  acid.  By  digestion  with  nitric  acid  it  yields  oxalic  acid. 

A  solution  of  tannic  acid  may  be  preserved  without  change,  provided  it 
be  excluded  from  oxygen  gas  ;  but  in  open  vessels  it  gradually  absorbs  oxy- 
gen, an  equal  volume  of  carbonic  acid  is  evolved,  it  becomes  turbid,  and  de- 
posites  a  crystalline  matter  of  a  gray  colour,  nearly  all  of  which  is  gallic  acid. 
After  digestion  with  a  little  animal  charcoal,  the  gallic  acid  is  perfectly  white 
and  pure.  There  is  no  doubt,  therefore,  of  the  conversion  of  tannic  into  gal- 
lic acid. 

Tannic  acid  is  distinguished  from  all  substances  except  gallic  acid,  by 
forming  a  deep  blue  precipitate  with  sesquisalts  of  iron,  which  is  the  basis  of 
writing-ink  and  the  black  dyes  ;  and  from  gallic  acid,  by  yielding  with  a 
solution  of  gelatin  a  white  flaky  precipitate,  which  is  soluble  in  a  solution  of 
gelatin,  but  insoluble  in  water  and  gallic  acid.  This  substance,  to  which  the 
name  of  tanno -gelatin  has  been  applied,  is  the  basis  of  leather,  being  always 
formed  when  skins  are  macerated  in  an  infusion  of  bark.  When  dried  it 
becomes  hard  and  tough,  and  resists  putrefaction.  Its  composition  is  apt  to 
vary,  according  to  the  relative  quantities  of  the  materials  used  in  its  for- 
mation;  but  if  the  gelatin  is  in  slight  excess  only,  the  resulting  compound 
contains  54  per  cent,  of  tannic  acid.  This  acid  cannot  be  so  wholly  separated 
by  gelatin,  that  the  remaining  solution  shall  not  be  affected  by  a  sesquisalt  of 
iron ;  but  Pelouze  finds  that  every  trace  of  it  is  removed  by  a  piece  of  skin 
previously  cleansed  by  lime  as  in  the  manufacture  of  leather,  leaving  any 
gallic  acid  which  may  have  been  present. 

From  the  experiments  of  Davy,  it  appears  that  the  inner  cortical  layers  of 
bark  are  the  richest  in  tannic  acid.  Its  quantity  is  greatest  in  early  spring, 
when  the  buds  begin  to  open,  and  smallest  during  winter.  Of  all  the  varie- 
ties of  bark  which  he  examined,  that  of  the  oak  contains  the  largest  quantity 
of  tannic  acid. 

Tannic  acid  dried  at  240°  is  anhydrous,  such  as  it  exists  in  the  white 
tannate  of  oxide  of  lead  when  dried  at  248°.  Pelouze  found  this  salt  to 


GALLIC  ACID.  497 

consist  of  111-6  parts  or  one  eq.  of  protoxide  of  lead,  and  215-16  parts  or 
one  eq.  of  tannic  acid,  its  formula  being  Pb-J-Tn.  The  other  tannates  of 
protoxides  have  most  probably  a  similar  composition.  The  white  tannate  of 
sesquioxide  of  antimony  and  the  blue  tannate  of  sesquoxide  of  iron  are  thus 
constituted : — 

Base.      Acid.      Equiv.      Formulae. 

Tannate  of  sesquiox.  of  antimony     153-2-J-645-48  =79868      Sb+3Tn. 
Tannate  of  sesquioxide  of  iron     .       80   4-645-48=725-48     Fe~f-3Tn. 

The  various  kinds  of  tannie  acid  obtained  from  cinchona  bark,  kino,  and 
other  sources,  correspond  in  most  respects  with  that  above  described  ;  but  at 
the  same  time  some  difference  is  observable,  some  kinds  striking  a  green  in- 
stead of  a  deep  blue  colour  with  the  sesquisalts  of  iron.  The  tannic  acid  from 
catechu  is  less  highly  oxidized  than  that  from  gall-nuts  (page  478). 

Artificial  Tannic  Acid. — This  substance  was  discovered  by  Mr.  Hatchett, 
and  is  best  prepared  by  the  action  of  nitric  acid  on  charcoal  (Phil.  Trans. 
]  805-6).  For  this  purpose  100  grains  of  charcoal  in  fine  powder  are  digested 
in  an  ounce  of  nitric  acid,  of  density  14,  diluted  with  two  ounces  of  water, 
with  a  gentle  heat  until  the  charcoal  is  dissolved.  The  reddish-brown  solu- 
tion is  then  evaporated  to  dryness,  in  order  to  expel  the  nitric  acid,  the  tern- 
perature  being  carefully  regulated  towards  the  close  of  the  process,  so  that 
the  product  may  not  be  decomposed. 

Artificial  tannic  acid  is  a  brown,  fusible  substance  of  a  resinous  fracture, 
astringent  taste,  and  acid  reaction.  It  is  soluble  even  in  cold  water  and  in 
alcohol.  With  a  salt  of  iron  and  solution  of  gelatin  it  acts  precisely  in  the 
same  manner  as  natural  tannic  acid.  It  differs,  however,  from  that  substance 
in  not  being  decomposed  by  the  action  of  strong  nitric  acid. 

Artificial  tannic  acid  may  be  prepared  in  several  ways.  Thus  it  is  gene- 
rated by  the  action  of  nitric  acid,  both  on  animal  or  vegetable  charcoal,  and 
on  pit-coal,  asphaltum,  jet,  indigo,  common  resin,  and  several  other  resinous 
substances.  It  is  also  procured  by. treating  common  resin,  elemi,  assafcetida, 
camphor,  balsams,  &c.,  first  with  sulphuric  acid,  and  then  with  alcohol. 

GALLIC  ACID. 

This  acid,  discovered  by  Scheele  in  1786,  exists  in  the  bark  of  many  trees, 
in  gall-nuts,  and  in  most  substances  which  contain  tannic  acid,  being  proba- 
bly developed  by  the  oxidation  of  that  acid.  The  best  process  for  preparing 
it  is  that  of  Scheele  as  modified  by  Braconnot  (An.  de  Ch.  et  de  Ph.  ix). 
Any  quantity  of  gall-nuts  reduced  to  powder,  is  infused  for  a  few  days  in 
four  times  its  weight  of  water,  and  the  infusion,  after  being  strained  through 
linen,  is  kept  for  two  months  in  an  open  vessel  and  a  moderately  warm  at- 
mosphere. During  this  period  the  surface  of  the  liquid  becomes  mouldy, 
and  tannic  acid  is  converted  by  the  oxygen  of  the  air  into  gallic  acid,  which 
subsides  as  a  yellowish  crystalline  matter,  mixed  with  ellagic  acid.  Qn  eva- 
porating the  solution  to  the  consistence  of  syrup,  an  additional  quantity  sub- 
sides on  cooling.  The  object  of  this  process  is  to  give  an  opportunity  for  the 
oxidation  of  tannic  acid,  which  disappears  more  or  less  completely,  and  is 
the  principal  source  of  the  gallic  acid,  since  the  latter  usually  exists  in  gall- 
nuts  in  very  small  quantity.  The  impure  gallic  is  separated  from  the  insoluble 
ellagic  acid  by  boiling  water;  and  it  is  rendered  white  by  digestion  with 
animal  charcoal  deprived  of  its  phosphate  of  lime  by  dilute  nitric  acid.  When 
the  colourless  solution  is  concentrated  by  evaporation,  the  gallic  acid  is  de- 
posited in  small  white  acicular  crystals  of  a  silky  lustre.  Some  crystals  pre- 
pared by  Mr.  Phillips,  and  examined  by  Mr.  Brooke,  were  in  the  form  of  an 
oblique  rhombic  prism. 

42* 


498  FYROGALLIC  ACID. 

Pure  gallic  acid  has  a  weak  acid  taste,  accompanied  with  slight  astrin- 
gency,  and  reddens  litmus.  In  boiling  water  it  is  freely  soluble,  but  it  re- 
quires 100  parts  of  cold  water  for  solution  ;  and  it  is  soluble  in  ether.  Its 
aqueous  solution  continues  unchanged  if  protected  from  oxygen  gas;  but  in 
open  vessels  it  is  gradually  decomposed,  acquires  a  yellow  tint,  and  deposites 
a  dark  brown  matter.  With  sulphate  of  the  protoxide  of  iron,  it  produces 
scarcely  any  change;  but  with  the  sesquisulphate  it  gives  a  dark  blue  precipi- 
tate, which  is  more  soluble  than  the  tannate  of  that  oxide,  and  slowly  dis- 
solves after  its  formation.  When  the  recent  precipitate  is  boiled  in  water, 
the  sulphuric  acid  gradually  reunites  with  the  iron,  which  is  reduced  to  the 
state  of  protoxide  at  the  expense  of  gallic  acid,  carbonic  acid  being  disen- 
gaged. The  same  action  ensues  slowly  in  the  cold,  and  the  tannate  of  the 
sesquioxide  is  liable  to  a  similar  change.  Both  the  lannate  and  gallate  of  the 
sesquioxide  exist  in  ink. 

Gallic  acid  does  not  precipitate  solutions  of  gelatin,  or  salts  of  the  vegeta- 
ble alkalies.  With  lime-water  it  gives  a  brownish-green  precipitate,  which 
is  redissolved  by  an  excess  of  the  alkali,  and  acquires  a  reddish  tint,  owing 
it  is  said  to  the  decomposing  agency  of  the  air. 

Crystallized  gallic  acid  loses  its  water  at  248°,  and  then  has  the  same 
composition  (page  478)  as  the  acid  when  united  with  oxide  of  lead.  This 
salt  falls  as  a  white  precipitate  when  gallic  acid  is  mixed  in  solution  with 
the  acetate  or  nitrate  of  oxide  of  lead  ;  and  Pelouze  states  that  when  dried 
at  248°  it  consists  of  11  1-6  parts  or  one  eq.  of  protoxide  of  lead,  and  85'84 
parts^or  one  eq.  of  gallic  acid;  whence  its  formula  is  Pb  +  C7H3O5,j>r 
Pb-|-G.  The  gallates  in  general  have  been  but  little  examined  ;  but  M-f-G 
may  be  taken  as  the  general  formula  of  the  constitution  of  neutral  gallates 
of  protoxides.  The  gallates  of  potassa,  soda,  and  ammonia  are  soluble  in 
water  ;  but  the  gallates  of  most  other  metallic  oxides  are  insoluble. 

PYROGALLIC  ACID. 

Braconnot  first  noticed  that  the  crystals  obtained  by  subliming  gallic  acid 
are  not,  as  was  thought,  gallic  acid,  but  an  acid  of  a  peculiar  kind  which  he 
has  termed  the  pyrogallic,  to  indicate  its  igneous  origin.  Pelouze  has  con- 
firmed this  observation,  and  finds  that  if  pure  anhydrous  gallic  acid  be  heat- 
ed in  a  dry  retort  plunged  in  oil  which  is  kept  at  a  temperature  varying 
from  410°  to  419°,  it  is  resolved  entirely  into  carbonic  acid  which  is  evolved 
as  gas,  and  pyrogallic  acid  which  condenses  in  the  upper  part  of  the  retort 
in  numerous  scaly  crystals  of  brilliant  whiteness.  The  decomposition  is 
such  that  (An.  de  Ch.  et  de  Ph.  xlvi.  206,  and  liv.  352.) 


1  .„.  gallic  acid  7C  +  3H+50  yields  ]  I 


Pyrogallie  acid  has  a  faintly  bitter  astringent  taste  without  acidity,  and 
barely  reddens  litmus  paper.  At  247°  it  fuses  and  at  410°  boils,  yielding  a 
colourless  vapour  of  a  faint  odour,  somewhat  resembling  that  of  benzoic  acid. 
At  480°  it  blackens,  and  is  resolved  into  metagallic  acid  and  water, 

Seq.pyrcgal-  >  9,fir  ,  oH  ,  o0s    •  ij:n_.  S  1  eq.  metagal.  acid  12C-f-3H+3O 
lie  acid!      I  2  (&C+3H+30)  yiel  ling  j  and  3  eq  of  water     3(H  +  Q) 

Pyrogallic  acid  dissolves  in  two  or  three  times  its  weight  of  cold  water, 
and  is  very  soluble  in  alcohol  and  ether.  Its  aqueous  solution,  at  first  co- 
lourless, becomes  brown  by  exposure  to  the  air,  and  in  a  few  days  is  de- 
composed. With  the  nitrates  of  the  oxides  of  silver  and  mercury  and  a 
sesquisalt  of  iron,  it  is  decomposed,  and  reduces  the  two  former  oxides  to  the 
metallic  state,  and  the  latter  to  the  state  of  protoxide,  the  iron  solution  ac- 
quiring a  brown  colour.  With  a  protosalt  of  iron  it  strikes  a  blackish-blue 
colour,  and  a  similar  tint  is  developed  with  a  sesquisalt  of  iron  and  a  pyro- 
gallate. 


METAGALLIC  ACID. — ELLAGIC  ACID. — SUCCINIC  ACID.  499 

METAGALLIC  ACID. 

If  instead  of  decomposing  gallic  acid  at  419°,  it  is  suddenly  heated  to 
480°,  carbonic  acid  and  water  are  disengaged,  and  instead  of  a  sublimate 
of  pyrogallic  acid,  a  black  shining  insoluble  matter  like  charcoal  remains 
in  the  retort,  to  which  Pelouze  has  given  the  name  of  metagallic  acid. 
Its  formation  obviously  depends  on  the  decomposition  of  pyrogallic  acid 
at  the  instant  of  its  formation,  agreeably  to  the  formula  above  given.  The 
same  products  are  obtained  by  distilling  tannic  acid  at  480°,  in  addition  to 
which  pyrogallic  acid  is  formed  if  the  distillation  is  conducted  at  410°. 

Metagallic  acid  is  dissolved  by  the  alkalies,  forming  neutral  metagal- 
lates,  from  which  it  is  precipitated  in  black  flakes  by  acids;  and  it  de- 
composes alkaline  carbonates  with  effervescence.  The  rnetagallate  of  po- 
tassa  gives  black  precipitates  with  soluble  salts  of  baryta,  strontia,  lime, 
magnesia,  and  the  oxides  of  iron,  zinc,  copper,  lead,  and  silver,  showing  that 
the  metagallates  of  those  bases  are  insoluble.  The  silver  salt  consists,  of  116 
parts  or  one  eq.  of  oxide  of  silver,  and  100-44  or  one  eq.  of  metagallic  acid, 
its  formula  being  Ag-|-C!sH3O3.  The  acid,  as  first  formed,  or  as  precipi- 
tated from  its  salts  by  acids,  is  a  hydrate  with  one  eq.  of  water,  of  which  the 
formula  is  H+ClaH303. 

ELLAGIC  ACID. 

This  acid,  called  ellagic  by  Braconnot,  from  the  word  galle  read  back- 
wards, is  left  in  the  process  for  gallic  acid  in  the  form  of  a  gray  powder,  in- 
soluble in  water,  but  soluble  in  a  solution  of  potassa,  and  precipitated  by 
acids  as  a  yellowish-gray  powder.-  Ellagic  acid,  when  dried  at  248°,  was 
found  by  Pelouze  to  have  the  same  composition  as  anhydrous  gallic  acid, 
minus  one  eq.  of  water ;  and  the  acid  before  being  so  dried  is  a  hydrate 
identical  in  its  ingredients  with  anhydrous  gallic  acid. 

SUCCINIC  ACID. 

This  acid  is  procured  by  heating  powdered  amber  in  a  retort  by  a  regu- 
lated temperature,  when  the  succinic  acid,  which  exists  ready  formed  in 
amber,  Basses  over  and  condenses  in  the  receiver.  As  first  obtained,  it  has 
a  yellow  colour  and  peculiar  odour,  owing  to  the  presence  of  some  cmpy- 
reumatic  oil;  but  it  is  rendered  quite  pure  and  white  by  being  dissolved  in 
nitric  acid,  and  then  evaporated  to  dryriess.  The  oil  is  decomposed,  and  the 
succinic  acid  is  left  unchanged. 

Succinic  acid  has  a  sour  taste,  and  reddens  litmus  paper.  It  is  soluble 
both  in  water  and  alcohol,  and  crystallizes  by  evaporation  in  anhydrous 
prisms.  When  briskly  heated,  it  fuses,  undergoes  decomposition,  and  in 
part  sublimes,  emitting  a  peculiar  and  very  characteristic  odour. 

The  salts  of  succinic  acid  have  been  little  examined.  The  succinates  of 
the  alkalies  are  soluble  in  water.  That  of  ammonia  is  frequently  employed 
for  separating  iron  from  manganese,  sesquisuccinate  of  iron  being  quite  inso- 
luble in  cold  water,  provided  the  solutions  are  neutral.  Succiiiale  of  prot- 
oxide of  manganese,  on  the  contrary,  is  soluble. 

By  reference  to  the  table  (page  478)  it  will  be  seen  that  succinic  acid  dif- 
fers in  composition  from  the  acetic,  only  in  containing  one  equivalent  less  of 
hydrogen. 

Mucic  or  Saccholactic  Acid  was  discovered  by  Scheele  in  1780.  It  is  ob- 
tained by  the  action  of  nitric  acid  on  certain  substances,  such  as  gum, 
manna,  and  sugar  of  milk.  The  readiest  and  cheapest  mode  of  forming  it  is 
by  digesting  gum  with  three  times  its  weight  of  nitric  acid.  On  applying 
heat,  effervescence  ensues,  and  three  acids — the  oxalic,  malic,  and  saccho- 


500  CAMPHORIC  ACID. VALERIAN1C  ACID. ROCtftLIC  ACID,  &C. 

lactic — are  the  products.  The  latter,  from  its  insolubility,  subsides  as  a 
white  powder,  and  may  be  separated  from  the  others  by  washing  with  cold 
water.  In  this  state  Dr.  Prout  says  it  is  very  impure.  To  purify  it  he  di- 
gests with  a  slight  excess  of  ammonia,  and  dissolves  the  resulting  salt  in 
boiling  water.  It  is  filtered  while  hot,  and  the  solution  evaporated  slowly 
almost  to  dryness.  The  saccholactate  of  ammonia  is  thus  obtained  in  crys- 
tals, which  are  to  be  washed  with  cold  distilled  water,  until  they  become 
quite  white.  They  are  then  dissolved  in  boiling  water,  and  the  saturated 
hot  solution  dropped  into  cold  diluted  nitric  acid. 

The  saceholactic  is  a  weak  acid,  which  is  insoluble  in  alcohol,  and  re- 
quires sixty  times  its  weight  of  boiling  water  for  solution.  When  heated 
in  a  retort  it  is  decomposed;  and  in  addition  to  the  usual  products,  yields  a 
volatile  white  substance,  to  which  the  name  of  pyrotnucic  acid  has  been 
applied. 

Camphoric  Acid. — This  compound  has  not  hitherto  been  found  in  any 
plant,  and  is  procured  only  by  digesting  camphor  for  a  considerable  time  in 
a  large  excess  of  nitric  acid.  As  the  solution  cools,  the  camphoric  acid  sepa- 
rates out  in  crystals;  but  it  appears  from  some  observations  of  Liebig  (An. 
de  Ch.  et  de  Ph.  xlvii.  95),  that  so  long  as  it  retains  the  odour  of  camphor, 
as  it  is  apt  to  do,  its  freedom  from  that  substance  is  incomplete,  and  it  re- 
quires renewed  digestion  with  nitric  acid.  It  is  sparingly  soluble  in  water, 
fuses  at  145°,  and  sublimes  at  a  temperature  by  no  means  elevated.  Its  taste 
is  rather  bitter,  and  when  quite  pure  has  probably  no  odour.  It  reddens  lit- 
mus paper,  and  combines  with  alkaline  bases,  forming  salts  which  are  called 
camphorates :  those  with  the  alkalies  are  very  soluble  and  even  deliquescent, 
but  with  oxide  of  lead  it  forms  an  insoluble  compound.  Camphoric  acid  is 
now  to  be  regarded  as  an  oxide  of  the  compound  radical,  camphene. 

Valerianic  Acid. — The  existence  of  this  acid  was  observed  by  M.  Grote, 
and  since  studied  by  Penz  and  TrommsdorfF  (An.  de  Ch.  et  de  Ph.  liv.  208.) 
This  acid  exists  in  the  root  of  valerian  (valeriana  officinalis}  and  passes  over 
along  with  an  essential  oil  when  that  root  is  distilled :  on  agitating  the  pro- 
duct with  carbonate  of  magnesia  and  water,  and  distilling,  the  essential  oil 
is  expelled,  and  valerianate  of  magnesia  is  left.  On  decomposing  this  salt 
by  dilute  sulphuric  acid,  the  valerianic  acid  may  be  obtained  by  distillation, 
partly  dissolved  in  the  water  which  passes  over  with  it,  and  partly  as  an 
oleaginous  matter  floating  on  its  surface. 

Pure  valerianic  acid  is  a  colourless  oleaginous  fluid,  of  density  0-944,  an 
odour  like  that  of  valerian,  and  a  strong,  acid,  disagreeable  taste.  It  boils  at 
270°,  but  distils  along  with  aqueous  vapour  at  a  much  lower  temperature : 
the  oily  stain  which  it  gives  to  paper  disappears  entirely  by  heat.  It  burns 
with  a  vivid  flame  without  residue.  It  dissolves  in  every  proportion  in  alco- 
hol, and  in  30  parts  of  cold  water.  It  has  a  strong  acid  reaction,  and  forms 
salts  with  alkaline  bases,  most  of  which  are  soluble  in  alcohol  and  water,  are 
fatty  to  the  touch,  and  when  decomposed  emit  the  peculiar  odour  of  the 
acid.  From  the  analysis  of  Ittner  (page  479)  the  general  formula  of  the 
neutral  valerianates  of  protoxides  is  M-f-C10H9O3,  and  the  oily  acid  is  a  hy- 
drate with  one  eq.  of  water. 

Rocellic  Acid.— This  aid  was  discovered  by  Heeren  in  the  rocella  tincto- 
ria,  and  is  separated  by  acting  on  the  lichen  with  a  solution  of  ammonia,  pre- 
cipitating with  chloride  of  calcium,  and  decomposing  the  rocellate  of  lime 
by  hydrochloric  acid,  when  rocellic  acid  subsides.  It  is  purified  by  solution 
in  ether,  and  is  deposited  by  evaporation  in  minute  white  crystals  of  a  silky 
lustre.  This  acid  fuses  at  266°,  is  very  soluble  in  alcohol  and  ether,  and  is 
insoluble  in  water. 

Moroxylic  Acid. — This  compound,  which  was  first  discovered  by  Klap- 
roth,  is  found  in  combination  with  lime  on  the  bark  of  the  morus  alba  or 
white  mulberry,  and  has  hence  received  the  appellation  of  moric  or  moroxylic 
acid.  It  is  obtained  by  decomposing  moroxylate  of  lime  by  acetate  of  oxile 
of  lead,  and  then  separating  that  oxide  by  means  of  sulphuric  acid. 


CHLOROXALIC  ACID, BOLETIC  ACID, — IGASURIC  ACID,  &C.  501 

Hydrocyanic  or  prussic  acid,  which  is  not  an  unfrequent  production  of 
plants,  has  already  been  described. 

The  sorbic,  as  already  mentioned,  has  been  shown  to  be  malic  acid. 

Rheumic  Acid. — This  name  was  applied  to  the  acid  principle  contained 
in  the  stem  of  the  garden  rhubarb;  but  M.  Lassaigne  has  shown  it  to  be 
oxalic  acid.  , 

Chloroxalic  Acid. — When  crystallizable  acetic  acid  is  put  into  a  glass  ves- 
sel full  of  dry  chlorine,  and  exposed  for  a  day  to  a  bright  sunshine,  hydro- 
chloric acid  gas  is  generated,  and  during  the  night  chloroxalic  acid  is  depo- 
sited in  dendritic  crystals  or  small  rhombic  scales.  In  order  to  obtain  it 
pure  the  chlorine  should  be  in  excess,  and  the  gases  subsequently  expelled 
from  the  flask  by  dry  air.  The  new  acid  is  very  volatile  and  deliques- 
cent, and  when  evaporated  in  vacua,  yields  rhombic  crystals.  Its  elements 
are  in  such  proportion  that  it  may  be  regarded  as  a  compound  of  one  equiva- 
lent of  hydrochloric  and  one  equivalent  of  oxalic  acid.  These  observations 
were  made  by  Dumas.  (Pog.  Annalen,  xx.  1G6.) 

Boletic  Acid  was  discovered  by  M.  Braconnot  in  the  juice  of  the  Boletus 
pseudo-igniarius.  As  it  is  a  compound  of  little  interest,  I  refer  the  reader 
to  the  original  paper  for  an  account  of  it.  (Annals  of  Phil.  vol.  ii.) 

Igasuric  Acid. — Pelletier  and  Caventou  have  proposed  this  name  for  the 
acid  which  occurs  in  combination  with  strychnia  in  the  mix  vomica  and  St. 
Ignatius's  bean.  It  may  be  conveniently  obtained  by  adding  acetate  of  oxide 
of  lead  to  the  aqueous  solution  of  nux  vomica  prepared  as  in  the  preparation 
of  strychnia,  when  the  igasurate  of  that  oxide  subsides:  the  precipitate,  after 
being  washed,  is  put  into  water  and  decomposed  by  a  current  of  hydrosul- 
phuric  acid  gas.  The  solution  of  igasuric  acid  is  then  separated  from  sul- 
phuret  of  lead  by  filtration,  and  may  be  purified  either  by  digestion  with 
animal  charcoal,  from  which  phosphate  of  lime  has  been  removed  by  an 
acid,  or  by  a  second  precipitation  with  acetate  of  oxide  of  lead.  On  concen- 
trating the  purified  solution  to  the  consistence  of  thin  syrup,  and  placing  it 
in  a  warm  situation,  the  acid  separates  in  crystals  which  are  commonly 
indistinct  in  their  form. 

Igasuric  acid  forms  soluble  salts  with  the  alkalies,  baryta,  and  the  oxides 
of  iron,  silver,  and  mercury.  With  oxide  of  lead,  lime,  and  magnesia,  it 
yields  sparingly  soluble  compounds;  but  the  the  two  latter  are  dissolved  by 
hot  water.  With  sulphate  of  oxide  of  copper  in  neutral  solutions,  it  occasions, 
either  immediately  or  after  a  short  interval,  a  light  green  precipitate,  which 
is  very  characteristic  of  igasuric  acid. 

Suberic  Acid  is  produced  by  the  action  of  nitric  acid  on  cork.  Its  acid 
properties  are  very  feeble.  It  is  very  soluble  in  boiling  water,  and  the 
greater  part  of  it  is  deposited  from  the  solution  in  cooling  in  the  form  of  a 
white  powder.  Its  salts,  which  have  been  little  examined,  are  known  by  the 
name  of  suberates. 

Zumic  Acid. — This  compound,  procured  by  Braconnot  from  several  vege- 
table substances  winch  had  undergone  the  acetous  fermentation,  appears 
from  the  observations  of  Vogel  to  be  lactic  acid.  (Annals  of  Philosophy, 
vol.  xii.) 

Pectic  Acid. — This  substance,  distinguished  by  its  remarkable  tendency 
to  gelatinize,  a  property  from  which  its  name  is  derived  (from  znjKT/?,  co- 
agulum),  was  originally  described  by  Braconnot;  and  it  has  since  been  ex- 
amined by  the  late  celebrated  Vauquelin.  (An.  de  Ch.  et  de  Ph.  xxviii.  173, 
and  xli.  46.)  Braconnot  believed  it  to  be  present  in  all  plants;  but  he  ex- 
tracted it  chiefly  from  the  carrot.  For  this  purpose  the  carrot  is  made  into 
a  pulp,  the  juice  is  expressed,  and  the  solid  part  well  washed  with  distilled 
water.  It  is  then  boiled  for  about  ten  minutes  with  a  very  dilute  solution  of 
pure  potassa,  or,  as  Vauquelin  advised,  with  bicarbonate  of  potassa  in  the 
ratio  of  5  parts  to  100  of  the  washed  pulp,  and  the  chloride  of  calcium  is 
added  to  the  filtered  liquor.  The  precipitate,  consisting-  of  pectic  acid  and 
lime,  is  well  washed,  and  the  lime  removed  by  water  acidulated  with  hydro 
chloric  acid. 


502  LACTUCIC  ACID. CRAMEIUC  ACID. CAINC1C  ACID,  &C. 

Pectic  acid,  as  thus  procured,  is  in  the  form  of  jelly.  It  is  insoluble  in  cold 
water  and  acids,  and  nearly  so  in  boiling  water.  It  has  a  slight  acid  reac- 
tion, and  a  feeble  neutralizing  power  with  alkalies,  with  which  it  forms  so- 
luble compounds.  The  earthy  pectates  are  very  insoluble,  and  on  this  ac- 
count, in  preparing  pectic  acid,  pare  water  must  be  used  ;  for  the  process 
always  fails,  when  water  containing  earthy  salts  is  employed. 

By  digestion  in  a  strong  solution  of  polassa,  pectic  acid  disappears,  the 
liquid  becomes  brown,  and  oxalate  of  potassa  is  obtained  by  evaporation. 
This  fact  excites  some  suspicion  that  pectic  acid  may  be  a  compound  of 
oxalic  acid  with  a  vegetable  principle  analogous  to  gum  ;  but  the  conversion 
of  organic  substances  in  general  into  oxalic  acid  by  the  action  of  potassa,  as 
already  noticed  at  pa^e  475,  diminishes  the  force  of  this  objection. 

Lactucic  Acid.—  This  acid  was  obtained  by  Pfaff  from  the  juice  of  the 
lactuca  virosa,  who  throws  down  the  acid  by  a  salt  of  copper  or  lead,  and 
then  separates  the  metallic  oxide  by  hydrosulphuric  acid.  It  is  said  to  differ 
from  oxalic  acid,  which  in  most  respects  it  resembles,  by  giving  a  green  pre- 
cipitate with  the  protosalts  of  iron,  and  a  brown  with  sulphate  of  protoxide 
of  copper;  but  its  properties  are  imperfectly  known. 

Crameric  Acid. — This  acid  was  discovered  by  M.  Peschier  of  Geneva  in 
the  extract  of  Rhatany  root,  Krameria  triandra.  After  separating  from  an 
aqueous  solution  of  the  extract  all  the  tannic  acid  by  means  of  gelatin,  and 
then  neutralizing  by  ammonia,  acetate  of  oxide  of  lead  is  added  as  long  as  it 
occasions  a  precipitate :  the  cramerate  of  that  oxide  is  decomposed  either  by 
sulphuric  acid  or  hydrosulphuric  acid;  and  the  solution  is  concentrated  in 
order  that  the  crameric  acid  may  crystallize.  This  acid  forms  a  sparingly 
soluble  salt  with  baryta;  and  it  is  singular  that  the  small  quantity  which  is 
dissolved,  is  not  precipitated  by  sulphuric  acid,  though  the  baryta  may  be 
thrown  down  by  an  alkaline  carbonate. 

Caincic  Acid. — This  acid,  discovered  by  MM.  Francois,  Caventou,  and 
Pelletier,  is  the  bitter  principle  of  the  bark  of  the  cainca  root,  a  Brazilian 
shrub  which  is  employed  for  the  cure  of  intermittent  fever.  (Journ.  de 
Pharm.  xvi.  465.)  It  crystallizes  in  delicate  white  needles  arranged  in  tufts 
like  hydrochlorate  of  morphia,  has  a  remarkably  bitter  taste,  arid  an  acid 
reaction.  It  is  sparingly  soluble  in  water  and  ether,  but  is  abundantly  dis- 
solved by  alcohol,  especially  when  heated.  It  unites  with  the  alkalies  form- 
ing soluble  salts  which  do  not  crystallize,  and  from  which  acids  throw  down 
caincic  acid.  It  forms  soluble  neutral  salts  with  baryta  and  lime,  but  the 
caincate  of  oxide  of  lead  and  the  subcaincate  of  lime  are  insoluble  in  water. 
It  is  decomposed  by  the  concentrated  mineral  acids-;  and  the  hydrochloric, 
even  in  the  cold,  converts  it  into  a  gelatinous  matter  which  is  nearly  in- 
sipid. Its  equivalent  has  not  yet  been  ascertained  ;  but  Liebig  finds  that  the 
crystallized  acid  loses  9  per  cent,  of  water  at  212°,  and  that  100  parts  of 
the  acid  thus  dried  contain  57-38  parts  of  carbon,  7'48  of  hydrogen,  and 
35'14  of  oxygen. 

Caincic  acid  is  prepared  by  exhausting  the  bark  with  hot  alcohol,  and 
evaporating  the  solution  to  the  consistence  of  an  extract,  which  is  then 
boiled  in  water,  and  the  hot  aqueous  solution,  after  filtration,  is  decomposed 
by  an  excess  of  lime.  The  precipitate  treated  with  oxalic  acid  yields  oxalate 
oiflime  and  free  caincic  acid,  which  are  both  insoluble  in  cold  water.  Hot 
alcohol  takes  up  the  latter,  which  is  decolourized  by  animal  charcoal. 

Indigotic  Acid. — This  acid  has  been  studied  by  Buff,  and  recently  ana- 
lyzed by  Dumas.  (An.  de  Ch.  et  de  Ph.  xxxvii.  160,  xxxix.  290,  li.  174,  and 
liii.  176.)  It  is  generated,  with  evolution  of  carbonic  acid  and  binoxide  of  ni- 
trogen gases  in  equal  measures,  but  without  the  production  of  any  carba- 
zotic  acid,  by  boiling  indigo  in  rather  dilute  nitric  acid,  formed  by  mixing 
nitric  acid  of  sp.  gr.  1-2  with  an  equal  weight  of  water.  To  the  solution, 
kept  boiling,  indigo  in  coarse  powder  is  gradually  added,  as  long  as  effer- 
vescence continues ;  and  hot  water  is  occasionally  added  to  supply  loss  by 
evaporation.  The  impure  incligotic  acid,  deposited  in  cooling,  is  boiled  with 
oxide  of  lead  and  filtered,  in  order  to  separate  resin ;  and  the  clear  yellow 


CARBAZOTIC    ACID.  503 

solution  is  decomposed  by  sulphuric  acid,  and  again  filtered  at  a  boiling 
temperature.  On  cooling1,  the  acid  crystallizes  in  yellowish-white  needles. 
In  order  to  purify  them  completely,  they  were  digested  in  water  with  carbo- 
nate of  baryta;  and  the  indigotate  of  baryta,  deposited  from  the  hot  filtered 
solution  in  cooling,  was  dissolved  in  hot  water,  and  decomposed  by  an  acid. 
Indigotic  acid  was  thus  obtained  in  acicular  crystals  of  snowy  whiteness, 
which  contracted  greatly  in  drying,  and  lost  their  crystalline  aspect ;  but 
the  dry  mass  was  dazzling  white,  and  had  a  silky  lustre. 

Indigotic  acid  decomposes  carbonates,  but  is  a  feeble  acid,  and  reddens 
litmus  faintly.  It  requires  1000  times  its  weight  of  cold  water  for  solution, 
but  is  soluble  to  any  extent  in  hot  water  and  alcohol.  Heated  in  a  tube  it 
fuses,  and  sublimes  without  decomposition;  and  the  fused  mass,  in  cooling, 
crystallizes  in  six-sided  plates.  When  heated  in  open  vessels,  it  is  inflamed, 
and  burns  with  much  smoke. 

Dumas  has  compared  together  the  constitution  of  indigogen,  indigo-blue, 
and  indigotic  acid,  and  finds  that  they  may  be  viewed  as  oxides  of  the  same 
compound  radical :  thus 

Carb.        Hyd.     Nitr.     Oxy.        Equiv.        For  mute. 
Indigogen        .        275-4  +15     +4245+  32     =364-85  045H15N3 
Indigo,  blue       .        275-4  +15     +42-45+  48     =380-85  C<5H15N3 

Do.  in  100  parts     72-8  +  4-04+10-8  +  12-36 
Indigotic  acid  275-4  +15     +42  45+240    =572-85  C<5HI5N3+30O. 

Do.  in  100  parts     48-23+  2-76+  7  73+  41-28 

The  equivalent  of  indigotic  acid  as  here  represented  has  not  been  proved 
by  the  composition  of  its  salts,  great  uncertainty  existing  as  yet  respecting 
the  composition  of  a -neutral  indigotate. 

Carbazotic  Acid. — This  name  has  been  applied  by  Liebig  to  a  peculiar 
acid  formed  by  the  action  of  nitric  acid  on  indigo.  It  was  first  noticed  by 
Hausmann,  and  subsequently  examined  by  Proust,  Fourcroy  and  Vauquelin, 
Chevreul,  and  Liebig.  It  is  made  by  dissolving  small  fragments  of  the  best 
indigo  in  8  or  10  times  their  weight  of  moderately  strong  nitric  acid,  and 
boiling  as  long  as  nitrous  acid  fumes  are  evolved.  During  the  action,  car- 
bonic, hydrocyanic,  and  nitrous  acids  are  evolved  ;  and  in  the  liquid,  besides 
carbazotic  acid,  is  found  a  resinous  matter,  artificial  tannin,  and  indigotic 
acid.  On  cooling',  carbazotic  acid  is  freely  deposited  in  transparent  yellow 
crystals;  and  on  evaporating  the  residual  liquid,  and  adding  cold  water,  an 
additional  quantity  of  the  acid  is  procured.  To  render  it  quite  pure,  it 
should  be  dissolved  in  hot  water,  and  neutralized  by  carbonate  of  potassa. 
As  the  liquid  cools,  carbazotate  of  potassa  crystallizes,  and  may  be  purified 
by  repeated  crystallization.  The  acid  may  be  precipitated  from  this  salt  by 
sulphuric  acid. 

Carbazotic  acid  is  sparingly  soluble  in  cold  water;  but  it  is  dissolved 
much  more  freely  by  the  aid  of  heat,  and  on  cooling  yields  brilliant  crystal- 
line plates  of  a  yellow  colour.  .Ether  and  alcohol  dissolve  it  readily.  It  is 
fused  and  volatilized  by  heat  without  decomposition  ;  but  when  suddenly 
exposed  to  a  strong  heat,  it  inflames  without  explosion,  and  burns  with  a 
yellow  flame,  with  a  residue  of  charcoal.  Its  solution  has  a  bright  yellow 
colour,  reddens  litmus  paper,  is  extremely  bitter,  and  acts  like  a  strong-  acid 
on  metallic  oxides.  It  is  said  to  be  poisonous.  (Journal  of  Science,  ii.  210, 
and  iii.  490.) 

The  salts  of  carbazotic  acid  are  for  the  most  part  crystallizable,  of  a  yel- 
low colour,  and  brilliant  lustre.  They  have  the  property,  when  rapidly 
heated,  either  of  detonating  like  fulminating  silver,  or  of  burning  rapidly 
with  scintillations.  The  sparing  solubility  of  carbazotate  of  potassa  is  the 
cause  of  carbazotic  acid  being  used  as  a  test  of  that  alkali. 

According  to  the  analysis  of  Liebig,  carbazotic  acid  contains  no  hydro- 
gen, and  its  ingredients  are  expressed  by  the  formula  C15N3O15,  its  equiva- 
lent being  254-25,  or  the  sum  of  the  equivalents  of  its  elements.  Buff  and 
Dumas  give  different  proportions,  and  the  latter  found  1-4  per  ceat.  of 


504  VEGETABLE  ALKALIES. 

hydrogen.  It  is  certain,  however,  that  it  is  a  highly  oxidized  body,  which 
accounts  for  the  detonating  property  of  its  salts.  Dumas  and  Liebig  concur 
in  representing  the  ratio  of  oxygen  and  nitrogen  to  be  the  same  as  in  nitric 
acid. 

Carbazotic  acid  is  generated  by  the  action  of  nitric  acid  on  many  sub- 
stances both  animal  and  vegetable,  especially  on  those  which  contain  nitro- 
gen.  The  bitter  principle,  formed  with  nitric  acid  and  silk  by  Welter,  and 
by  Braconnot  from  aloes,  is  carbazotic  acid.  It  is  also  formed  by  digesting 
indigotic  acid  in  nitric  acid,  with  formation  of  binoxide  of  nitrogen,  carbonic 
and  oxalic  acid,  and,  according  to  Dumas,  of  ammonia. 

The  substances  called  resin  and  artificial  tannin,  formed  during  the  pre- 
ceding process,  consist  of  a  brown  friable  matter  united  or  mixed  with  dif- 
ferent proportions  of  indigotic  and  nitric  acid.  It  is  insoluble  in  water  and 
alcohol ;  but  it  is  dissolved  by  the  pure  alkalies  and  their  carbonates,  and  is 
precipitated  from  the  solution  by  acids.  It  is  best  procured  by  boiling  1  part 
of  indigo  with  2  of  nitric  acid  diluted  with  15  or  20  of  water,  being  purified 
by  hot  water  from  indigotic  acid.  In  order  to  separate  it  from  unchanged 
indigo,  it  is  dissolved  by  carbonate  of  potassa,  and  precipitated  by  an  acid. 


SECTION   II. 

VEGETABLE  ALKALIES. 

UNDER  this  title  are  comprehended  those  proximate  vegetable  principles 
which  are  possessed  of  alkaline  properties.  The  honour  of  discovering  the 
existence  of  this  class  of  bodies  is  due  to  Sertuerner,  a  German  apothecary, 
who  published  an  account  of  morphia  so  long  ago  as  the  year  1803;  but  the 
subject  excited  no  notice  until  the  publication  of  his  second  essay  in  1816. 
The  chemists  who  have  since  cultivated  this  department  with  most  success 
are  M.  Robiquet,  arid  MM.  Pelletier  and  Caventou. 

All  the  vegetable  alkalies  which  have  been  analyzed  consist  of  carbon, 
hydrogen,  nitrogen,  and  oxygen  ;  and  it  is  remarked,  which  shows  a  close 
analogy  of  composition,  that  a  single  equivalent  of  each  alkali  contains  ex- 
actly one  equivalent  of  nitrogen.  They  are  decomposed  with  facility  by 
nitric  acid  and  by  heat,  and  ammonia  is  always  one  of  the  products  of  the 
destructive  distillation.  They  never  exist  in  an  insulated  state  in  the  plants 
which  contain  them ;  but  are  apparently  in  every  case  combined  with  an 
acid,  with  which  they  form  a  salt  more  or  less  soluble  in  water.  These 
alkalies  are  for  the  most  part  very  insoluble  in  water,  and  of  sparing  solubi- 
lity in  cold  alcohol  ;  but  Ihey  are  all  readily  dissolved  by  that  fluid  at  a 
boiling  temperature,  being  deposited  from  the  solution,  commonly  in  the 
form  of  crystals,  on  cooling.  Most  of  the  salts  are  far  more  soluble  in 
water  than  the  alkalies  themselves,  aud  several  of  them  are  remarkable  for 
their  solubility. 

Serullas  observed  that  iodic  acid  is  disposed  to  form  with  most  of  the  ve- 
getable alkalies  supersalts,  which  are  very  insoluble  in  alcohol,  and  he  pro- 
posed this  property  as  a  test  of  vegetable  alkalies.  It  suffices  to  dissolve  a 
vegetable  alkali,  especially  quinia  or  cinchonia,  or  any  of  their  salts,  in  alco- 
hol, and  to  add,  drop  by  drop  a  solution  of  iodic  acid,  so  that  it  may  be  in 
excess  :  a  supersalt  is  generated,  which,  though  in  very  minute  quantity,  is 
immediately  precipitated.  The  iodic  acid,  being  itself  insoluble  in  alcohol, 
should  be  so  far  diluted  with  water  until  it  ceases  to  give  a  precipitate  with 
strong  alcohol.  The  aqueous  solution  of  chloride  of  .iodine,  which  contains 
iodic  acid,  may  be  substituted  for  ihe  pure  acid.  (An.  de  Ch.  et  de  Ph.  xlv. 
68.)  It  should  be  remembered,  in  employing  this  test,  that  all  the  iodates 


MORPHIA.  505 

are  of  sparing  solubility; — that  a  little  potassa,  dissolved  in  alcohol,  would 
give  a  precipitate  on  the  addition  of  iodic  acid.  Care  should  be  taken  also 
in  drying  the  iodate  of  a  vegetable  alkali,  since  when  sharply  healed  they 
detonate  powerfully. 

As  the  vegetable  alkalies  agree  in  several  of  their  leading  chemical  pro- 
perties, the  mode  of  preparing  one  of  them  admits  of  being  applied  with 
slight  variation  to  all.  The  general  outline  of  the  method  is  as  follows  : — 
The  substance  containing  the  alkaline  principle  is  digested,  or  more  com- 
monly macerated,  in  a  large  quantity  of  water,  which  dissolves  the  salt,  the 
base  of  which  is  the  vegetable  alkali.  On  adding  some  more  powerful 
salifiable  base,  such  as  potassa  or  ammonia,  or  boiling  the  solution  for  a  few 
minutes  with  lime  or  pure  magnesia,  the  vegetable  alkali  is  separated  from 
its  acid,  and  being  in  that  state  insoluble  in  water,  may  be  collected  on  a 
filter  and  washed.  As  thus  procured,  however,  it  is  impure,  retaining  some 
of  the  other  principles,  such  as  the  oleaginous,  resinous,  or  colouring  mat- 
ters with  which  it  is  associated  in  the  plant.  To  purify  it  from  these  sub- 
stances, it  should  be  mixed  with  a  little  animal  charcoal,  and  dissolved  in 
boiling  alcohol.  The  alcoholic  solution,  which  is  to  be  filtered  while  hot, 
yields  the  pure  alkali,  either  on  cooling  or  by  evaporation  ;  and  if  not  quite 
colourless,  it  should  again  be  subjected  to  the  action  of  alcohol  and  animal 
charcoal.  In  order  to  avoid  the  necessity  of  employing  a  large  quantity  of 
alcohol,  the  following  modification  of  the  process  may  be  adopted.  The 
vegetable  alkali,  after  being  precipitated  and  collected  on  a  filter,  is  made  to 
unite  with  some  acid,  such  as  the  acetic,  sulphuric,  or  hydrochloric,  and  the 
solution  boiled  with  animal  charcoal,  until  the  colouring  matter  is  removed. 
The  alkali  is  then  precipitated  by  ammonia  or  some  other  salifiable  base. 

The  following  table,  formed  principally  from  analyses  by  Liebig  (An.  de 
Ch.  et  de  Ph.  xlvii.  199),  represents  the  composition  of  the  vegetable  alkalies 
in  their  anhydrous  state.  The  numeral  attached  to  each  symbol  indicate!? 
the  number  of  equivalents'of  that  element  in  one  equivalent  of  the  alkali. 
The  elements  of  those  whose  atomic  constitution  is  unknown,  are  given  in 
relation  to  100  parts. 


ALKALIES. 

Carb.      Hyd.      Nitrog.   Oxy.            Equiv. 

Formulas. 

Morphia    .     . 

208-08+18       +14-15-1-48      =     288-23 

C34H18N'O". 

Narcotlna 

65      +   5-5    +   2-51+26-99  in  100  parts. 

Codeia      .     . 

189-72  +  20       +14-15+40       =    263-87 

CS1H20N:0*. 

Narceia     .     . 

54-73+   6-52+   4-33+34-42  in  100  parts. 

Cinchonia 

122-4  +12       +1415+  8      =     156.55 

C^H^N'O1. 

Quinia      .     . 

122-4  +12       +14-15+16       =     164-55 

Cs°HiaNfO». 

Aricina    .     . 

122-4  +12       +1415+24       =     172-55 

C^H^NW. 

Strychnia 

183-6   +16       +1415+24       =    237-75 

C3°H16N'O8. 

Brucia    .,/"  v? 

195-84+18       +14-15+48       =    275-99 

C32H18N'O6. 

Veratria    .     . 

208-08  +  22       +14-15+48       =    292-23 

C84HaaN1O*. 

Emetia  ;'.  ':. 

64-57+   7-77  +   4-3  +22-95  in  100  parts. 

Delphia    .     . 

76-69+  8-89  +  5-93+  7-49  in  100  parts. 

MORPHIA. 

This  alkali  is  the  medicinal  agent  of  opium,  in  which  it  exists  combined 
with  meconic  and  sulphuric  acid,  and  associated  with  several  other  sub- 
stances, especially  with  narcotina,  codeia,  narceia,  meconin,  gummy,  re- 
sinous, and  extractive  colouring  matters,  lignin,  fixed  oil,  and  a  small 
quantity  of  caoutchouc.  The  first  step  in  its  preparation  consists  in  cutting 
a  given  quantity  of  opium  into  small  pieces,  pouring  on  it  distilled  water, 
and  macerating  for  two  or  three  days  at  a  temperature  not  exceeding  100°, 
aided  by  frequent  agitation ;  the  first  infusion  is  then  decanted,  and  a  second 
and  a  third  conducted  in  a  similar  manner,  so  that  the  soluble  parts  should 
be  completely  extracted.  A  highly  coloured  but  clear  solution  is  thus  ob- 
tained, which  has  the  peculiar  odour  of  opium,  is  distinctly  acid  to  test 

43 


506  MORPHIA. 

paper,  and  contains  all  the  meconate  and  sulphate  of  morphia,  together  with 
the  associated  alkalies,  contained  in  the  specimen.  To  obtain  pure  morphia 
from  the  solution,  one  of  two  modes  is  now  commonly  employed.  The  first 
consists  in  concentrating  the  aqueous  solution  of  opium,  and  adding-  a  slight 
excess  of  ammonia,  when  the  morphia  and  narcotina  are  precipitated.  The 
precipitate  is  digested  at  120°  or  130°  in  proof  spirit,  which  takes  up  most 
of  the  narcotina  and  colouring  matter  :  the  morphia  is  then  dissolved  in 
strong  hoiling  alcohol,  from  which  it  is  deposited  by  cooling  and  evapora- 
tion. The  object  of  the  second  is  to  obtain  the  morphia  in  the  form  of  a 
hydrochlorate,  by  which  means  its  separation  from  narcotina  is  more  fully 
accomplished  than  by  the  former  method;  and  the  following  process,  devised 
by  Drs.  Gregory  and  Robertson,  of  Edinburgh,  may  be  safely  employed, 
(Edin.  Med.  and  Surg.  Journal,  Nos.  107  and  111.)  The  aqueous  solution 
of  opium  is  concentrated  in  a  vessel  of  tinned  iron,  or  other  evaporator,  to 
the  consistence  of  a  thin  syrup,  when  a  slight  excess  of  chloride  of  calcium, 
neutral  and  quite  free  from  iron,  is  added  ;  the  mixture  is  boiled  for  a  few 
minutes,  and  then  poured  into  an  evaporating  basin.  When  cold,  the  hydro- 
chlorates  are  taken  up  in  water,  which  is  added  until  a  copious  separation 
of  resinous  flocks  ensues,  leaving  the  insoluble  meconate  and  sulphate  of 
lime  with  a  good  deal  of  colouring  matter.  The  clear  liquid  is  again  evapo- 
rated to  a  syrupy  consistence,  a  little  marble  being  added  to  ensure  perfect 
neutrality,  the  warm  fluid  is  poured  off  the  sediment  into  a  clean  capsule, 
and  is  well  stirred  during  crystallization.  The  mass  is  then  put  into  a  stout 
cloth,  and  the  liquid  part,  containing  chloride  of  calcium,  the  hydrochlorate 
of  narcotina,  and  colouring  matter,  is  pressed  out  from  the  crystallized 
hydrochlorate  of  morphia  :  this  impure  salt  is  redissolved  in  water  at  70°, 
filtered  through  cloth,  mixed  with  a  little  fresh  chloride  of  calcium,  crystal- 
lized, and  compressed  as  before.  It  is  taken  up  in  hot  water,  digested  for 
about  24  hours  with  animal  charcoal,  filtered,  evaporated,  crystallized,  and 
squeezed  in  cloth  as  on  former  occasions  ;  but  in  this  part  of  the  process  a 
little  free  hydrochloric-  acid  may  be  added  with  advantage,  as  it  holds  in 
solution  any  remaining  colouring  matter,  and  renders  the  crystallization  of 
the  hydrochlorate  of  morphia  more  perfect.  The  pure  salt  is  then  dried  at 
a  temperature  of  150°,  and  amounts  on  an  average  to  10  per  cent,  of  the 
opium  used,  corresponding  to  9*43  per  cent,  of  crystallized  morphia.  It 
contains  a  small  quantity  of  hydrochlorate  of  codeia,  which  is  left  in  solu- 
tion when  the  morphia  is  precipitated  by  ammonia.  The  absence  of  nar- 
cotina may  be  proved  by  the  following  character  : — If  dissolved  in  distilled 
water,  and  pure  potassa  be  added,  crystals  of  morphia  at  first  subside,  which 
are  completely  redissolved  by  an  excess  of  the  potassa;  but  when  narcotina 
is  present,  the  alkali  occasions  a  peculiar  milkiness,  and  by  heat  woolly 
flocks  are  separated. 

Pure  morphia  crystallizes  readily  when  its  alcoholic  solution  is  evapo- 
rated, and  yields  colourless  crystals  of  a  brilliant  lustre.  They  mostly  occur 
in  irregular  six-sided  prisms  with  dihedral  summits;  but  their  primary  form 
is  a  right  rhombic  prism,  of  which  the  lateral  planes  only  appear  in  the 
crystals  (Brooke).  According  to  Liebig,  they  consist  of  288-23  parts,  or 
one  eq.  of  anhydrous  morphia,  and  18  or  two  eq.  of  water,  which  ttiey  give 
out  at  248°,  the  loss  amounting  to  6  33  per  cent.  (An.  de  Ch.  et  de  Ph.  xlvii. 
198.)  Morphia  is  almost  wholly  insoluble  in  cold,  and  to  very  small  extent 
in  hot  water.  It  is  soluble  in  strong  alcohol  especially  by  the  aid  of  heat. 
In  its  pure  state  it  has  scarcely  any  taste  ;  but  when  rendered  soluble  by 
combining  with  an  acid  or  by  solution  in  alcohol,  it  is  intensely  bitter.  It 
has  an  alkaline  reaction,  and  combines  with  acids,  forming  neutral  salts, 
which  are  far  more  soluble  in  water  than  morphia  itself,  and  for  the  most 
part  are  capable  of  crystallizing.  Solutions  of  pure  potassa  and  soda  dissolve 
it,  as  in  some  measure  does  ammonia. 

Strong  nitric  acid  decomposes  morphia,  forming  a  red  solution,  which  by 
the  continued  action  of  the  acid  acquires  a  yellow  colour,  and  is  ultimately 


MORPHIA. NARCOTJNA.  507 

converted  into  oxalic  acid.  Nitric  acid  has  a  similar  effect  on  brucia.  With 
a  sesqviisalt  of  iron  morphia  strikes  a  blue  tint. 

Morphia  is  the  narcotic  principle  of  opium.  When  pure,  owing-  to  its  in. 
solubility,  it  is  almost  inert. ;  for  Orfila  gave  twelve  grains  of  it  to  a  dog 
without  its  being  followed  by  any  sensible  effect.  In  a  state  of  solution,  on 
the  contrary,  it  acts  on  the  animal  system  with  great  energy,  Sertuerner 
having  noticed  alarming  symptoms  from  so  small  a  quantity  as  half  a  grain. 
From  this  it  appears  to  follow  that  the  effects  of  an  oveivdose  of  a  salt  of 
morphia  may  be  prevented  or  diminished  by  giving  a  dilute  solution  of 
ammonia,  or  an  alkaline  carbonate,  so  as  to  precipitate  the  vegetable 
alkali. 

When  opium  is  administered  as  a  poison,  its  presence  is  rendered  obvious 
by  the  peculiar  odour  of  that  drug,  as  well  as  by  the  red  tint  given  to  sesqui. 
salts  of  iron  by  the  meeonie  acid  of  the  opium;  but  when  death  is  occa- 
sioned by  a  salt  of  morphia,  it  becomes  necessary  to  eliminate  the  morphia, 
a  practical  process  of  considerable  delicacy.  The  method  suggested  by 
Lassaigne  for  detecting  acetate  of  morphia,  may  be  applied  to  its  saline 
combinations  in  general  (An.  de  Ch.  et  de  Ph.  xxv.  102.)  The  suspected 
solution  is  evaporated  by  a  temperature  of  212°,  and  the  residue  treated 
with  alcohol,  by  which  the  salt  of  morphia,  together  with  osmazome  and 
some  salts,  is  dissolved.  The  alcohol  is  next  evaporated,  and  water  added 
to  separate  fatty  matter.  The  aqueous  solution  is  then  set  aside  for  sponta- 
neous evaporation,  during  which  the  salt  of  morphia  is  generally  deposited 
in  crystals.  From  an  aqueous  solution  of  the  salt,  ammonia  throws  down  a 
crystalline  precipitate,  which  may  be  recognised  as  morphia  by  the  combi- 
nation of  the  following  characters : — By  the  figure  of  its  crystals  ;  its  bitter 
taste;  solubility  in  alcohol;  alkalinity;  by  the  orange-red  tint  developed  by 
nitric  acid  ;  and  by  the  peculiar  action  of  iodic  acid.  The  last  character  is 
particularly  valuable  in  distinguishing  morphia  from  other  vegetable  alka- 
lies: the  latter  combine  with  iodic  acid  and  form  iodates;  but  morphia  de- 
composes iodic  acid,  and  sets  iodine  free,  which  may  then  be  detected  by 
starch.  A  grain  of  morphia  in  7000  grains  of  water  may  be  discovered  by 
this  test.  (Sertillas.) 

Salts  of  Morphia. — These  are  best  prepared  by  dissolving  pure  morphia 
in  dilute  acid,  and  evaporating  the  solution.  The  neutral  sulphate  crystal- 
lizes in  bunches  of  acicular  crystals,  which  consist  of  one  equivalent  of 
morphia,  one  equivalent  of  acid,  and  six  equivalents  of  water :  on  drying  at 
248°,  four  equivalents  of  water  are  expelled  ;  but  the  rest  of  the  water  can- 
not be  driven  off  without  decomposing  the  salt  itself,  and,  therefore,  seems 
essential  to  its  constitution.  The  water  lost  by  heat  is  absorbed  from  the 
atmosphere  as  the  sulphate  cools.  Morphia  also  forms  a  bisulphate. 

Hydrochlorate  of  morphia  may  be  generated  by  the  direct  action  of  hy- 
drochloric acid  gas  on  anhydrous  morphia  (Liebig),  by  dissolving  the 
alkali  in  dilute  hydrochloric  acid,  or  by  the  process  of  Gregory,  above  de- 
scribed. It  commonly  crystallizes  in  turfs  of  acicular  crystals,  which  are 
neutral,  are  anhydrous,  and  contain  an  equivalent  of  acid  and  of  base. 

Acetate  of  morphia,  though  till  lately  much  employed  in  medical  prac- 
tice, is  less  convenient  for  that  purpose  than  the  hydrochlorate,  being  varia- 
ble in  constitution.  To  procure  it  in  the  solid  state,  it  must  be  evaporated 
to  dryness,  and  in  this  process  some  of  its  acid  is  usually  expelled.  It  is 
deliquescent,  and  is  hence  with  difficulty  preserved  in  a  constant  state  of 
dryness:  and  when  neutral  it  is  decomposed  by  water,  whereby  part  of  the 
morphia  is  rendered  insoluble.  In  fact,  the  best  mode  of  employing  the 
acetate  is  to  dissolve  given  weights  of  morphia  in  dilute  acetic  acid,  and 
preserve  it  in  that  form,  taking  care  that  the  acid  is  in  excess.  The  basis 
of  Baltley's  sedative  liquor  is  supposed  to  be  acetate  of  morphia. 

Narcotina. — This  substance  was  described  in  1803  by  Dcrosne,  and  was 
long  called  the  salt  of  Derosne ;  Sertuerner  supposed  it  to  be  meconate  of 
morphia;  but  Robiquet  proved  that  it  is  an  independent  principle,  and  ap- 
plied to  it  the  name  of  narcotine.  It  is  easily  prepared  by  digesting  the 


508  CODEIA. 

aqueous  extract  of  opium,  or  the  precipitate  by  ammonia  from  the  aqueous 
infusion,  in  sulphuric  ether,  in  which  meconate  of  morphia  and  morphia 
are  insoluble,  but  which  takes  up  all  the  narcotina  and  deposites  it  in  regular 
crystals  by  evaporation.  It  may  be  further  purified  by  animal  charcoal 
arid  a  second  crystallization.  A  convenient  mode  of  separating"  it  from 
morphia  without  sulphuric  ether,  suggested  by  Dr.  Robertson  in  the  essay 
above  cited,  is  to  boil  the  impure  morphia  in  water,  and  add  successive  por- 
tions of  sal  ammoniac  as  long  as  ammonia  escapes:  the  morphia  at  a  boil- 
ing temperature  decomposes  that  salt,  and  the  resulting  hydrochlorate  of 
morphia  is  of  course  dissolved ;  while  all  the  narcotina  is  left  in  a  pulveru- 
lent form.  Other  salts  of  morphia  may  be  made  in  like  manner  by  employ- 
ing a  corresponding  salt  of  ammonia.  This  fact,  of  the  decomposition  of 
ammoniacal  salts  by  morphia,  is  due  to  M.  Buisson,  who  finds  that  most  of 
the  vegetable  alkalies  in  general  possess  the  same  property  at  a  high  tem- 
perature. 

Narcotina  is  insoluble  in  cold  and  very  slightly  soluble  in  hot  water.  It 
dissolves  in  oil,  ether,  and  alcohol;  the  latter,  though  diluted,  acting  as  a 
solvent  for  it  by  the  aid  of  heat.  It  is  not  alkaline  to  test  paper,  but  unites 
definitely  with  hydrochloric  acid,  forming  a  salt  extremely  soluble  in  water, 
which  crystallizes  in  needles  from  an  alcoholic  solution.  Robiquet  also  ob- 
tained the  crystallized  sulphate.  Its  presence  in  the  aqueous  infusion  of 
opium  is  due  to  a  free  acid,  and  yet  uncombined  narcotina  is  dissolved  from 
crude  opium  by  sulphuric  ether:  it  acts  so  feebly  as  a  base,  that  it  is  sepa- 
rated from  its  acid  either  by  the  ether,  or  probably  b}T  the  force  of  crystal- 
lization. A  similar  cause  may  account  for  the  variable  composition  of  its 
salts,  the  equivalent  of  narcotina  having  been  estimated  from  the  hydrochlo- 
rate at  319  by  Pelletier,  at  560  by  Liebig,  and  at  408  by  Robiquet  (An.  de 
Ch.  et  de  Ph.  li.  231). 

Narcotina  acts  much  less  energetically  on  the  animal  economy  than  mor- 
phia. The  stimulating  action  of  opium  is  partly  ascribed  to  narcotina ;  and 
the  opinion  is  supported  by  the  experience  of  medical  practitioners,  who 
find  that  pure  morphia  acts  more  agreeably  and  safely  than  when  narcotina 
is  present. 

CODEIA. 

This  alkali  was  discovered  in  1832  by  Robiquet  in  hydrochlorate  of  mor- 
phia, made  by  Gregory's  process  (An.  de  Ch.  et  de  Ph.  li.  259.)  It  appears 
that  hydrochlorate  of  codeia  crystallizes  along  with  the  salt  of  morphia,  and 
is  present  in  variable  quantity  :  in  hydrochlorate  of  morphia  from  East- 
India  opium,  Christison  obtained  l-12th  of  hydrochlorate  of  codeia,  and  Gre- 
gory l-30th  from  the  hydrochlorate  prepared  with  Turkey  opium.  On  dis- 
solving the  mixed  hydrochlorates  in  water,  and  precipitating  the  morphia 
by  ammonia,  the  codeia  remains  in  solution,  and  crystallizes  by  subsequent 
evaporation.  On  dissolving  in  hot  ether,  it  is  obtained  by  spontaneous  evapo- 
ration in  acicular  crystals  or  flat  prisms,  which,  when  pure,  are  quite  co- 
lourless and  transparent. 

Codeia  fuses  at  300°  without  decomposition,  arid  at  a  high  temperature 
burns  with  flame  without  residue.  Water  at  60°  dissolves  1-26  per  cent., 
3-7  at  110°,  and  5-9  at  212°.  When  more  of  it  is  present  than  boiling  wa- 
ter can  dissolve,  the  excess  fuses,  and  forms  a  stratum  of  an  oily  aspect  at 
the  bottom.  The  solution  is  distinctly  alkaline,  and  yields  neutral  salts  with 
alkalies,  some  of  which,  especially  the  nitrate,  crystallize  with  facility.  It  is 
distinguished  from  morphia  by  the  form  and  aspect  of  its  crystals,  greater 
solubility  in  water,  solubility  in  boiling  ether,  insolubility  in  solutions  of  the 
pure  alkalies,  by  yielding  a  copious  precipitate  with  tincture  of  gall-nuts, 
and  not  being  reddened  by  nitric  acid.  Its  crystals  consist  of  263-87  parts  or 
one  eq.  of  codeia  and  18  or  two  eq.  of  .water,  which  is  dissipated  at  212°. 


NARCEIA. — CINCHONIA.  509 

NARCEIA. 

This  alkali  was  discovered  by  Pelletier  in  1832  (An.  de  Ch.  et  de  Ph.  1. 
252),  and  is  contained  in  the  aqueous  infusion  of  opium,  probably  in  combi- 
nation with  meconic  acid.  After  precipitating  the  morphia  and  narcotina  by 
ammonia,  meconic  acid  by  pure  baryta,  and  the  excess  of  baryta  by  carbo- 
nate of  ammonia,  the  solution  is  boiled  to  expel  the  latter  salt,  and  then 
evaporated  to  the  consistence  of  syrup.  The  residue,  set  at  rest  for  some 
days  in  a  cool  place,  yields  crystals  which,  after  compression  in  linen  to  re- 
move  adhering  liquid,  should  be  dissolved  in  boiling  strong  alcohol,  and  re- 
crystallized  by  evaporation.  The  residue  consists  of  narccia,  together  with 
some  narcotina,  meconin,  and  fatty  matter:  the  three  last  are  taken  up  by 
digestion  in  sulphuric  ether,  in  which  the  narceia  is  insoluble.  It  is  puri- 
fied by  crystallization  from  alcohol  or  water,  to  which  a  little  animal  char- 
coal is  added. 

Pure  narceia  is  white,  and  crystallizes  in  needles  or  small  prisms.  It  is 
inodorous,  and  has  a  faint  bitter  taste,  with  slight  pungency.  It  fuses  at 
198°,  becomes  yellow  at  220°,  and  at  high  temperatures  is  decomposed, 
yielding  among  other  products  a  peculiar  volatile  acid.  It  is  soluble  in  375 
times  its  weight  of  cold  and  230  of  boiling  water,  and  dissolves  freely  in  hot 
alcohol,  but  it  is  insoluble  in  ether.  It  is  decomposed  by  the  stronger  acids, 
but  unites  with  them  when  diluted,  acting  as  a  feeble  alkali  which  neu- 
tralizes acids  imperfectly,  though  some  of  its  salts  are  crystallizable.  Its 
salts,  with  the  stronger  acids  especially,  have  the  peculiarity  of  being  blue 
in  a  certain  degree  of  concentration,  and  on  adding  successive  quantities  of 
water,  the  colour  changes  to  violet  and  rose-red,  and  lastly  disappears.  By 
this  character,  added  to  its  light  fusibility,  and  the  action  of  solvents,  it  is 
distinguished  from  the  other  principles  with  which  it  is  associated  in  opium. 
Its  equivalent  has  not  been  determined. 

CINCHONIA  AND  QUINIA. 

The  existence  of  a  distinct  vegetable  principle  in  cinchona  bark  was  in- 
ferred by  the  late  Dr.  Duncan  in  the  year  1803,  who  ascribed  to  it  the 
febrifuge  virtues  of  the  plant,  and  proposed  for  it  the  name  of  cinchonin 
(Nicholson's  Journal,  1803).  Dr.  Gomez  of  Lisbon,  whose  attention  was 
directed  to  the  subject  by  the  researches  of  Dr.  Duncan,  succeeded  in  pro- 
curing cinchonin  in  a  separate  state;  but  its  alkaline  nature  was  first  dis- 
eovered  in  1820  by  Pelletier  and  Caventou  (An.  de  Ch.  et  de  Ph.  xv.)  It 
has  been  fully  established  by  the  labours  of  those  chemists  that  the  febri- 
fuge property  of  bark  is  possessed  by  two  alkalies,  the  cinchnnia,  or  cin- 
chonin of  Dr.  Duncan,  and  quinia,  both  of  which  are  combined  with  kinic 
acid.  These  principles,  though  very  analogous,  are  distinctly  different, 
standing  in  the  same  relation  to  each  other  as  potassa  and  soda.  Cincho- 
nia  exists  in  the  Cinchona  condaminea,  or  pale  bark;  quinia,  oflen  with  a 
little  cinchonia,  is  present  in  C.  cordifolia,  or  yellow  bark;  and  they  are 
both  contained  in  C.  oblongifolia,  or  red  bark.  One  of  the  easiept  pro- 
cesses for  preparing  them,  is  to  take  up  the  soluble  parts  of  the  bark  by 
hot  water  acidulated  with  hydrochloric  acid,  concentrate  the  solution,  and 
then  digest  with  successively  added  portions  of  slaked  lime,  until  the  liquid 
is  distinctly  alkaline.  The  precipitate  is  carefully  collected,  and  the  vege- 
table alkali  separated  from  it  by  boiling  alcohol.  Slight  modifications  of 
the  method  have  been  proposed  by  Badollier  and  Voreton.  From  one  pound 
of  yellow  bark,  Voreton  procured  80  grains  of  quinia,  which  is  nearly  1-4 
per  cent.  (An.  dc  Ch.  et  de  Ph.  xvii) ;  but  the  quantity  obtained  from  differ- 
ent varieties  of  bark  is  very  variable. 

Cinchonia.— 'Pare  cinchonia  crystallizes  in  colourless  quadrilateral  prisms, 
which  are  anhydrous,  require  2500  times  their  weight  of  boiling  water  for 
solution,  and  are  insoluble  in  cold  water.  Its  proper  menstruum  is  boiling 

43* 


510 


QUINIA. 


alcohol;  but  it  is  dissolved  in  small  quantity  by  oils  and  ether.  Its  taste  is 
bitter,  though  slow  in  being  perceived,  on  account  of  its  insolubility;  but 
when  the  alkali  is  dissolved  by  alcohol  or  an  acid,  the  bitterness  is  very 
powerful,  and  accompanied  by  the  flavour  of  cinchona  bark.  Its  alkaline 
properties  are  exceedingly  well  marked,  since  it  neutralizes  the  strongest 
acids.  The  sulphate,  hydrochlorate,  nitrate,  and  acetate  of  cinchonia  are 
soluble  in  water,  and  the  sulphate  crystallizes  in  very  short  six-sided  prisms 
derived  from  an  oblique  rhomboidal  prism.  It  commonly  occurs  in  twin 
crystals;  and  is  composed  of  15655  parts  or  one  eq.  of  cinchonia,  401 
parts  or  one  eq.  of  sulphuric  acid,  and  36  parts  or  four  eq.  of  water.  It 
effloresces  in  a  dry  air,  and  gives  out  all  its  water  when  moderately  heated. 
Cinchonia  forms  a  disulphate,  which  is  much  less  soluble  than  the  neutral 
sulphate.  The  hydrochlorate  is  composed  of  single  equivalents  of  base  and 
acid,  fuses  at  212°,  is  readily  soluble  in  water  and  alcohol,  and  crystallizes 
in  shining  acicular  crystals.  The  neutral  tartrate,  oxalate,  and  gallate  of 
cinchonia  are  insoluble  in  cold,  but  soluble  in  hot  water,  as  well  as  in  al- 
cohol. 

Quinia  or  Quinine. — This  alkali  is  precipitated  from  its  solution  by  alka- 
lies in  white  flocks,  which  do  not  assume  a  crystalline  appearance  like  cin- 
chonia; and  it  crystallizes  imperfectly  even  from  an  alcoholic  solution.  It 
is  very  soluble  in  alcohol,  forming  a  solution  which  is  intensely  bitter,  and 
possesses  a  distinct  alkaline  reaction.  Ether  likewise  dissolves  it,  but  it 
is  almost  insoluble  in  water.  Its  febrifuge  virtues  are  more  powerful  than 
those  of  cinchonia,  and  it  is  now  extensively  employed  in  the  practice  of 
medicine. 

The  most  important  of  the  salts  of  quinia  is  the  disulphate,  which  is  made 
in  large  quantity  for  medical  purposes.  This  compound  crystallizes  in  deli- 
cate white  needles,  having  the  appearance  of  amianthus,  has  a  very  bitter 
taste,  and  is  less  soluble  in  water  than  sulphate  of  cinchonia.  It  is  freely 
dissolved  by  boiling  alcohol,  and  is  neutral  to  test  paper.  It  is  composed  of 
329'1  parts  or  two  eq.  of  quinia,  40  1  or  one  eq.  of  sulphuric  acid,  and  90  or 
ten  eq,  of  water :  when  dried  at  248°,  it  abandons  eight  equivalents  of  water, 
and  retains  the  remainder  until  the  salt  itself  is  decomposed. 

The  sulphate  of  neutral  composition  is  acid  to  test  paper,  and  crystallizes 
in  transparent  square  prisms,  which  effloresce  in  a  dry  air,  and  contain 
24'66  per  cent,  of  water,  corresponding  nearly  to  six  eq.  of  water/  This  salt 
is  much  more  soluble  than  the  disulphate.  The  neutral  gallate,  tartrate,  and 
oxalate  of  quinia,  like  the  analogous  salts  of  cinchonia,  are  insoluble  in  cold 
water. 

From  the  new  facts  which  have  been  ascertained  relative  to  the  consti- 
tuents of  bark,~the  action  of  chemical  tests  on  a  decoction  of  this  substance 
is  now  explicable.  According  to  the  analysis  of  Pelletier  and  Caventou,  the 
different  kinds  of  Peruvian  bark,  besides  the  kinate  of  cinchonia  or  quinia, 
Contain  the  following  substances: — a  greenish  fatty  matter;  a  red  insoluble 
matter;  a  red  soluble  principle,  which  is  a  variety  of  tanriic  acid;  a  yel- 
low colouring  matter;  kinate  of  lime;  gum,  starch,  and  lignin.  It  is  hence 
apparent  that  a  decoction  of  bark,  owing  to  the  tannic  acid  which  it  con- 
tains, may  precipitate  a  solution  of  tartar  emetic,  of  gelatin,  or  a  salt  of  iron, 
without  containing  a  trace  of  vegetable  alkali,  and  consequently  without 
possessing  any  febrifuge  virtues.  An  infusion  of  gall-nuts,  on  the  contrary, 
causes  a  precipitate  only  by  its  gallic  acid  uniting  with  cinchonia  or  quinia, 
and,  therefore,  affords  a  test  for  distinguishing  a  good  from  an  inert  variety 
of  bark. 

Sulphate  of  quinia,  from  its  commercial  value,  is  frequently  adulterated. 
The  substances  commonly  employed  for  the  purpose  are  water,  sugar,  gum, 
starch,  ammoniacal  salts,  and  earthy  salts,  such  as  sulphate  of  lime  and 
magnesia,  or  acetate  of  lime.  Pure  sulphate  of  quinia,  when  deprived  of  its 
water  of  crystallization  by  a  heat  of  212°,  should  lose  only  from  8  to  10  per 
cent,  of  water.  Sugar  may  be  detected  by  dissolving  the  suspected  salt  in 


ARICINA. STRYCHNIA.  511 

waler,  and  adding-  precisely  so  much  carbonate  of  potassa  as  will  precipitate 
the  quinia.  The  taste  of  the  sugar,  no  longer  obscured  by  the  intense  bitter 
of  the  quinia,  will  generally  be  perceived;  and  it  may  be  separated  from  the 
sulphate  of  potassa,  by  evaporating  gently  to  dryness,  and  dissolving  the  su- 
gar by  boiling  alcohol.  Gum  and  starch  are  left  when  the  impure  sulphate 
of  quinia  is  digested  in  strong  alcohol.  Ammoniacal  salts  are  discovered  by 
the  strong  odour  of  ammonia,  which  may  be  observed  when  the  sulphate  is 
put  into  a  warm  solution  of  potassa.  Earthy  salts  may  be  detected  by 
burning  a  portion  of  the  sulphate.  Several  of  the  preceding  directions  are 
taken  from  a  paper  on  the  subject  by  Mr.  Phillips.  (Phil.  Mag.  and  Ann.  iii. 
111.) 

Aricina. — This  alkali  was  observed  by  Pellelier  and  Corriol  in  1829  in  a 
sample  of  cinchona  bark  which  had  been  substituted  for  the  ordinary  kinds 
of  bark,  and  is  very  analogous  to  cinchonia  and  quinia  in  its  properties. 
By  reference  to  the  table  at  page  505,  it  will  be  seen  that  these  three  alka- 
lies have  such  an  analogy  of  composition,  that  they  may  be  viewed  as  oxides 
of  the  same  compound  radical,  the  formula  of  which  is  C80]!18]^1.  (An.  de 
Ch.  et  de  Ph.  li.  186.) 

STRYCHNIA  AND  BRUCIA. 

Strychnia. — Strychnia  was  discovered  in  1818  by  Pelletier  and  Caventou. 
in  the  fruit  of  the  Strychnos  ignatia  and  Strychnos  nux  vomica,  and  has 
since  been  extracted  by  the  same  chemists  from  the  Upas.  (An.  de  Ch.  et  de 
Ph.  x.  and  xxvi.) 

The  most  economical  process  for  preparing  this  alkali  is  that  recom- 
mended by  M.  Corriol.  (Journal  de  Pharmacie  for  October,  1825,  p.  492.) 
It  consists  in  treating  mix  vomica  with  successive  portions  of  cold  water, 
evaporating  the  solution  to  the  consistence  of  syrup,  and  precipitating  the 
gum  by  alcohol.  The  alcoholic  solution  is  then  evaporated  to  the  consist- 
ence of  an  extract  by  the  heat  of  a  water-bath.  The  extract,  which  consists 
almost  entirely  of  igasurate  of  strychnia,  is  dissolved  by  cold  water,  and  by 
this  means  deprived  of  a  little  fatty  matter,  which  had  originally  been  dis- 
solved, probably  through  the  medium  of  the  gum.  The  solution  is  next 
heated,  and  the  strychnia  precipitated  by  a  slight  excess  of  lime-water,  and 
then  dissolved  by  boiling  alcohol.  On  evaporating  the  spirit,  the  alkali  is 
obtained  pure,  except  in  containing  a  little  brucia  and  colouring  matter,  both 
of  which  are  effectually  removed  by  maceration  in  dilute  alcohol. 

Strychnia  is  very  soluble  in  boiling  alcohol,  and  is  procured  in  minute 
four-sided  prisms  by  allowing  the  solution  to  evaporate  spontaneously.  In 
this  state  it  is  anhydrous.  It  is  almost  insoluble  in  water,  requiring  more  than 
6000  parts  of  cold  and  2500  of  boiling  water  for  solution;  but  notwithstand- 
ing its  sparing  solubility,  it  excites  an  insupportable  bitterness  in  the  mouth. 
— Water  containing  only  l-600,OQOth  of  its  weight 'of  strychnia  has  a  bitter 
taste.  It  has  a  distinct  alkaline  reaction,  and  neutralizes  acids,  forming 
salts,  most  of  which  are  soluble  in  water.  It  is  united  in  the  nux  vomica 
and  St.  Ignatius's  bean  with  igasuric  acid  (page  501).  By  the  action  of 
strong  nitric  acid  it  yields  a  red  colour;  but  it  appears  from  some  observa- 
tions of  Pelletier  and  Caventou,  that  the  red  tint  is  owing  to  the  presence  of 
some  impurity,  which  is  probably  brucia. 

Strychnia  is  one  of  the  most  virulent  poisons  hitherto  discovered,  and  is 
the  poisonous  principle  of  the  substance  in  which  it  is  contained.  Its  energy 
is  so  great,  that  half  a  grain  blown  into  the  throat  of  a  rabbit  occasioned 
death  in  the  course  of  five  minutes.  Its  operation  is  always  accompanied 
with  symptoms  of  locked  jaw  and  other  tetanic  affections. 

Hydrpchlorate  of  strychnia  is  a  soluble  neutral  salt,  which  crystallizes 
readily  in  tufts  of  minute  quadrilateral  prisms  or  needles.  It  consists  of 
237-75  parts  or  one  eq.  of  base  and  36-42  or  one  eq.  of  acid.  The  neu- 
tral sulphate  crystallizes  in  small  transparent  cubes,  which  consist  of  single 
equivalents  of  base  and  acid,  united  with  three  eq.  of  water.  The  salt  when 


512  BRUC1A. — VERATRIA. — EMETIA. 

heated  fuses  in  its  water  of  crystallization,  and  is  rendered  anhydrous.     It 
requires  ten  times  its  weight  of  water  for  solution. 

Brucia. — This  alkali  was  discovered  in  the  Brucea  antidysenterica  by 
Pelletier  and  Caventou,  soon  after  tiicir  discovery  of  strychnia  (An  de  Ch. 
et  de  Ph.  xii.);  and  it  likewise  exists  in  small  quantity  in  the  St.  Ignatius's 
bean  and  nux  vomica.  In  its  bitter  taste  and  poisonous  qualities,  it  is  very 
similar  to  strychnia,  but  is  twelve  or  sixteen  times  less  energetic.  It  is  so- 
luble  both  in  hot  and  cold  alcohol,  especially  in  the  former;  arid  it  crystal- 
lizes when  its  solution  is  evaporated.  Its  crystals  dried  at  240°  lose  about 
19  per  cent,  of  water,  and  are  hence  composed  of  275*99  parts  or  one  eq.  of 
the  acid  to  72  parts  or  eight  eq.  of  water.  Even  dilute  alcohol  by  aid  of 
heat  dissolves  brucia,  and  on  this  property  is  founded  the  method  of  sepa- 
rating it  from  strychnia.  It  is  more  soluble  in  water  than  most  of  the  other 
vegetable  alkalies,  requiring  only  850  times  its  weight  of  cold,  and  500  of 
boiling  water  for  solution.  With  nitric  acid  it  acquires  a  deep  blood-red  co- 
lour, which  afterwards  passes  into  yellow  ;  and  when  either  of  these  changes 
has  taken  place,  the  addition  of  protochloride  of  tin  produces  a  pretty  violet 
tint,  and  a  precipitate  of  the  same  colour  subsides. 

VERATRIA,  EMETIA,  PICROTOXIA,  CORYDALIA,  SOLANIA,  &c. 

Veratria. — The  medicinal  properties  of  the  seeds  of  the  Veratrum  sala- 
dilla,  and  of  the  root  of  the  Veratrum  album,  or  white  hellebore,  and  Col- 
chicum  autumnale  or  meadow  saffron,  are  owing  to  the  peculiar  alkaline 
principle  veratria,  which  was  discovered  by  Pelletier  and  Caventou  in  1819 
(Journ.  de  Pharm.  vi.).  To  a  decoction  of  the  bruised  seeds  of  the  Veratrum 
sabadilla  add  acetate  of  oxide  of  lead  as  long  as  a  precipitate  falls,  by 
which  means  extractive  matter  is  thrown  down  :  the  filtered  solution  is  de- 
prived of  lead  by  hydrosulphuric  acid,  the  excess  of  the  gas  expelled  by 
heat,  and  the  solution  boiled  with  magnesia  or  slaked  lime  until  it  is  ren- 
dered alkaline.  The  precipitate  collected,  dried,  and  boiled  in  alcohol, 
yields  a  solution  of  veratria,  which  may  be  decolorized  by  digestion  with 
animal  charcoal,  and  be  obtained  by  evaporation.  It  may  be  procured  from 
the  roots  of  the  two  other  plants  by  a  similar  process.  This  alkali,  which 
appears  to  exist  in  those  plants  in  combination  with  gallic  acid,  is  white 
and  pulverulent,  has  not  been  obtained  in  crystals,  fuses  at  280°,  is  in* 
odorous,  and  of  an  acrid  taste.  It  requires  1000  times  its  weight  of  boiling, 
and  still  more  of  cold  water  for  solution.  It  is  very  soluble  in  alcohol,  and 
may  also  be  dissolved,  though  less  readily,  by  means  of  ether.  It  has  an 
alkaline  reaction,  and  neutralizes  acids  ;  but  it  is  a  weaker  base  than  mor- 
phia, quinia,  or  strychnia.  It  acts  with  singular  energy  on  the  membrane 
of  the  nose,  exciting  violent  sneezings  though  in  very  minute  quantity. 
When  taken  internally  in -very  small  doses,  it  produces  excessive  irritation  of 
the  mucous  coat  of  the  stomach  and  intestines ;  and  a  few  grains  were  found 
to  be  fatal  to  the  lower  animals. 

M.  Couerbe  has  prepared  the  sulphate  and  hydrochlorate  in  crystals,  and 
determined  the  probable  equivalent  of  veratria  as  given  at  page  505.  (An.  do 
Ch.  ct  de  Ph.  lii.  376.) 

Emetia. — Ipecacuanha  consists  of  an  oily  matter,  gum,  starch,  lignin, 
and  a  peculiar  principle,  which  was  discovered  in  1817  by  Pelletier,  and  to 
which  he  has  applied  the  name  of  emetine.  (Journal  de  Pharmacie,  iii.)  In 
order  to  extract  this  alkali,  the  oily  matter  is  first  removed  by  digesting 
the  powdered  root  in  ether,  and  the  ernelia  is  next  taken  up  by  boiling  alco- 
hol which  is  diluted  with  water,  and  the  spirit  expelled  by  distillation. 
Some  more  fatty  matter  is  thus  separated  :  the  emetia  is  then  thrown  down 
by  boiling  the  aqueous  solution  with  magnesia.  It  may  be  decolorized  by 
animal  charcoal  in  the  usual  manner.  Emetia,  of  which  ipecacuanha  con- 
tains 16  per  cent.,  appears  to  be  the  sole  cause  of  the  emetic  properties  of 
the  root. 

Emetia  is  a  white  pulverulent  substance,  of  a  rather  bitter  and  disagree- 


PICROTOXIA. — CORYDALIA, — SOLANIA. — CYNOPIA, — DELPHIA,  &C.  513 

able  taste,  sparingly  soluble  in  cold,  but  more  freely  in  hot  water,  and  in- 
soluble in  ether.  It  is  readily  dissolved  by  alcohol.  At  122°  it  fuses.  It 
has  a  distinct  alkaline  reaction,  and  neutralizes  acids ;  but  its  salts  are  little 
disposed  to  crystallize.  (An.  de  Ch.  et  de  Ph.  xxiv.  181.) 

Picrotoxia. — The  bitter  poisonous  principle  of  Cocculus  indicus  was  disco- 
vered  in  1819  by  M.  Boullay,  who  gave  it  the  name  of  picroloxine.  Its 
claim  to  the  title  of  a  vegetable  alkali,  among  which  class  of  bodies  it  was 
placed  by  its  discoverer,  has  been  called  in  question  by  M.  Cassaseca,  from 
whose  remarks  it  seems  that  picrotoxia  has  no  alkaline  reaction,  and  does 
not  neutralize  acidity.  It  combines,  however,  with  acids,  and  with  the  acetic 
and  nitric  acids  forms  crystallizable  compounds.  According  to  Oppermann 
100  parts  of  picrotoxia  contain  of  carbon  6lf434,  hydrogen  611,  and  oxygen 
32-456.  It  appears,  also,  that  the  menispermic  acid,  supposed  by  M.  Boullay 
to  be  united  in  Cocculus  indicus  with  picrotoxia,  is  merely  a  mixture  of  sul- 
phuric and  malic  acids.  (Edinburgh  »Tournal  of  Science,  v.) 

Corydalia. — This  alkali,  discovered  by  Dr.  Wackenroder,  is  contained  in 
the  root  of  the  fumitory,  (not  the  common  fumitory,  Fumaria  qfficinalis,  but) 
Fumaria  cava  and  Corydalis  tuberosa  .of  Decandolle.  It  exists  in  the  plant 
as  a  soluble  malate,  is  precipitated  from  its  aqueous  solution  by  magnesia, 
and  is  purified  by  alcohol. 

It  is  soluble  in  alcohol,  and  the  hot  saturated  solution  in  cooling  yields 
colourless  prismatic  crystals  of  a  line  in  length.  By  spontaneous  evapora- 
tion fine  laminae  are  formed.  It  is  likewise  soluble  in  ether,  but  very 
sparingly  in  water.  It  is  insipid  and  inodorous ;  but  when  dissolved  by 
acids  or  alcohol  it  is  very  bitter.  Its  solution  has  an  alkaline  reaction,  and 
it  neutralizes  acids.  Cold  dilute  nitric  acid  dissolves  it  and  yields  a  colour- 
less solution  ;  but  when  heated  it  acquires  a  red  tint,  and  becomes  blood-red 
when  concentrated.  Its  salts  are  precipitated  by  potassa,  pure  or  car- 
bonated, and  by  infusion  of  gall-nuts.  The  precipitate  is  white  when  the 
solution  is  dilute,  and  grayish-yellow  if  concentrated.  (Phil.  Mag.  and  An. 
iv.  153.) 

Solania. — The  active  principle  of  the  Solanum  dulcamara,  or  woody 
nightshade,  was  procured  in  a  pure  state  by  Des fosses ;  and  the  same  alkali 
exists  in  other  species  of  solarium.  Solania  is  combined  in  the  plant  with 
malic  acid,  and  is  thrown  down  of  a  gray  colour  by  ammonia  from  the  ex- 
pressed and  filtered  juice  of  the  ripe  berries.  After  being  well  washed  and 
dried,  it  is  purified  by  solution  in  hot  alcohol,  from  which  by  slow  evapora- 
tion it  is  deposited  as  a  white  powder  with  a  pearly  lustre.  It  is  insoluble 
in  cold  water,  and  requires  8000  times  its  weight  of  hot  water  for  solution. 
Alcohol  is  its  proper  menstruum  :  it  is  sparingly  dissolved  by  ether,  and  is 
insoluble  in  oil.  It  has  a  distinct  alkaline  reaction,  and  with  acids  forms 
neutral  salts,  which  have  a  bitter  taste.  (Journ.  de  Pharrn.  vi.  and  vii.) 

Cynopia. — Professor  Ficinus  of  Dresden  has  discovered  a  new  alkali  in 
the  jEfhusa  Cynapium,  or  lesser  hemlock,  to  which  he  has  given  the  name 
of  Cynopia.  It  is  crystallizable,  and  soluble  in  water  and  alcohol,  but  not 
in  ether.  The  crystals  are  in  the  form  of  a  rhombic  prism,  which  is  also 
that  of  the  crystals  of  the  sulphate. 

Delpliia. — This  substance  was  discovered  about  the  same  time  by  Fe- 
neuille  and  Lassaigne  in  France,  and  Brandes  in  Germany,  in  the  seeds  of 
the  Delphinium  Staphysagria  or  Stavesacre.  It  is  easily  prepared  by  digest- 
ing the  seeds  in  water  acidulated  with  sulphuric  acid,  and  precipitating  by 
magnesia  or  other  alkaline  substance.  It  is  then  purified  in  the  usual  man- 
ner  by  solution  in  alcohol  and  digestion  with  animal  charcoal.  It  is  left  by 
evaporation  as  a  white  crystalline  powder,  which  is  almost  insoluble  in 
water,  but  is  dissolved  by  alcohol,  ether,  and  the  oils.  It  has  a  feeble  alka- 
line reaction,  and  yields  neutral  salts  of  a  bitter  taste,  but  which  rarely 
crystallize.  (An.  de  Ch.  et  de  Ph.  xii.  and  lii.  364.) 

Althea  was  announced  by  M.  Bacon  of  Caen  as  a  new  vegetable  alkali, 
said  to  be  procured  from  the  root  of  the  marsh-mallow  (Althaea  OfKcinalis). 
According  to  M.  Plisson  this  alkali  has  no  existence,  and  what  was  thought 


514  NEUTRAL    SUBSTANCES. 

to  be  supermalate  of  althea  is  asparagin.  From  the  experiments  of  Witt- 
stock  it  appears  that  the  asparagin  found  by  Plisson  does  not  exist  in  the 
plant  itself:  the  aqueous  solution  of  the  marsh-mallow  contains  sugar,  a 
mucilaginous  matter,  and  a  peculiar  vegetable  acid  containing  nitrogen, 
which  is  united  with  magnesia ;  and  by  the  mutual  action  of  these  ingre- 
dients of  the  solution,  the  asparagin  or  althein  is  generated.  (Pog,  Annalen, 
xx.  346.) 

Sanguinaria  is  a  vegetable  alkali,  obtained  by  M.  Dana  from  the  San- 
guinaria Canadensis,  called  blood-root  in  America  from  the  red  colour  of 
its  juice.  The  powdered  root  is  digested  in  pure  alcohol,  and  the  red  solu- 
tion, mixed  with  a  little  ammonia,  is  poured  into  water,  when  a  brown  matter 
subsides.  After  washing  carefully,  and  removing  colouring  matter  by  ani- 
mal charcoal,  the  alkali  is  removed  by  hot  alcohol,  and  obtained  by  evapora- 
tion as  a  pearly  white  matter  of  an  acrid  taste  and  alkaline  reaction.  By 
exposure  to  air  it  becomes  yellow.  It  is  insoluble  in  water,  but  is  dissolved 
by  alcohol  and  ether.  Its  salts  have  a  red  colour.  (Phil.  Mag.  and  An. 
v.  151.) 

Nicotina. — This  alkali  was  extracted  by  MM.  Posselt  and  Reimann  from 
the  leaves  of  tobacco,  and  also  exists  in  the  seeds.  At  common  tempera- 
tures, and  even  at  21°,  it  is  a  liquid,  usually  of  a  yellow  tint,  but  colourless 
and  transparent  when  pure.  It  has  a  pungent  odour  like  that  of  tobacco, 
and  an  acrid  burning  taste  which  lasts  a  long  time.  It  is  highly  poisonous, 
a  single  drop  being  fatal  to  a  dog.  It  rises  in  vapour  at  212°,  and  boils  at 
475°,  but  is  decomposed  at  the  same  time.  Water  dissolves  it  in  all  propor- 
tions, and  it  is  very  soluble  in  ether,  which  withdraws  it  from  its  aqueous 
solution.  It  has  a  distinct  alkaline  reaction,  and  forms  with  acids  neutral 
salts,  several  of  which  are  crysiallizable. 

Besides,  the  vegetable  alkalies,  already  described,  it  has  been  rendered 
highly  probable,  chiefly  by  the  researches  of  M.  Brandes,  that  several  other 
plants,  such  as  the  Atropa  belladonna,  Conium  maculatum,  Hyoscyamus 
niger.  Datura  stramonium,  and  Digitalis,  owe  their  activity  to  the  presence 
of  an  alkali.  Vauquelin  rendered  it  probable  that  an  alkali  is  contained  in 
the  Daphne  mezereum,  to  which,  if  it  exist,  the  name  of  daphnia  may  be 
applied. 


SECTION  III. 

NEUTRAL  SUBSTANCES,   THE  OXYGEN  AND  HYDROGEN  OF 
WHICH  ARE  IN  THE  SAME  RATIO  AS  IN  WATER. 

THE  substances  contained  in  this  section  are  remarkable  for  a  close  re- 
semblance in  the  ratio  of  their  elements.  They  may  be  viewed,  like  several 
of  the  vegetable  acids  (page  478),  as  hydrates  of  carbon;  though  in  all 
probability  their  elements  are  combined  with  each  other  in  a  very  different 
order.  The  proportions  in  which  they  unite  with  other  bodies  is  so  imper- 
fectly known,  that  their  atomic  constitution  has  not  been  satisfactorily  de- 
termined. Their  composition,  stated  in  100  parts,  is  as  follows  : — 

Carbon.  Hydrogen.    Oxygen.                Analyzed  by 

Pure  cane  sugar  42-85  6-35  50-8  Prout. 

Mannite      .        38-7  6-8  54-5  Do. 

Wheat  starch      43-55  6-77  49-68  Gay-Lussac  and  Thenard. 

Potato  starch       44-25  6-67  49-08  Berzelius. 

Gum-arabic         42-23  6-93  50  84  Gay-Lussac  and  Thenard. 

Ljgnin        .        51-45  5-82  42-73  Gay-Lussac  and  Thenard. 


f, 


SUGAR.  515 


SUGAR. 

Sugar  is  an  abundant  vegetable  product,  existing  in  a  great  many  ripe 
fruits,  though  few  of  them  contain  it  in  sufficient  quantity  for  being  collect- 
ed.  The  juice  which  flows  from  incisions  made  in  the  trunk  of  the  Ameri- 
can maple  tree,  is  so  powerfully  saccharine  that  it  may  be  applied  to  useful 
purposes.  Sugar  was  prepared  in  France  and  Germany  during  the  late  war 
from  the  beet-root ;  and  this  manufacture  is  at  present  carried  on  in  France 
on  a  scale  of  considerable  magnitude.  Proust  extracted  it  in  Spain  from 
grapes.  But  most  of  the  sugar  at  present  used  in  Europe  is  obtained  from 
the  sugar-cane  (Arundo  sacchariferci),  which  contains  it  in  a  greater  quan- 
tity than  any  other  plant.  The  process,  as  practised  in  the  West  India 
Islands,  consists  in  evaporating  the  juice  of  the  ripe  cane  by  a  moderate 
and  cautious  ebullition,  until  it  has  attained  a  proper  degree  of  consistence 
for  crystallizing.  During  this  operation  lime-water  is  added,  partly  for  the 
purpose  of  neutralizing  free  acid,  and  partly  to  facilitate  the  separation  of 
extractive  and  other  vegetable  matters,  which  unite  with  the  lime  and  rise 
as  a  scum  to  the  surface.  When  the  syrup  is  sufficiently  concentrated,  it  is 
drawn  off  into  shallow  wooden  coolers,  where  it  becomes  a  soft  solid  com- 
posed of  loose  crystalline  grains.  It*  is  then  put  into  barrels  with  holes  in 
the  bottom,  through  which  a  black  ropv  juice,  called  molasses  or  treacle, 
;raduaJly  drops,  leaving  the  crystallized  sugar  comparatively  white  and  dry. 
n  this  state  it  constitutes  raw  or  muscovado  sugar. 

Raw  sugar  is  further  purified  by  boiling  a  solution  of  it  with  white  of 
eggs,  or  the  scrum  of  bullock's  blood,  lime-water  being  generally  employed 
at  the  same  time.  When  properly  concentrated,  the  clarified  juice  is  re- 
ceived in  conical  earthen  vessels,  the  apex  of  which  is  undermost,  in  order 
that  the  fluid  parts  may  collect  there,  and  bo  afterwards  drawn  off  by  the 
removal  of  a  plug.  In  this  state  it  is  loaf  or  refined  sugar.  In  the  process 
of  refining  sugar,  it  is  important  to  concentrate  the  syrup  at  a  low  tempera- 
ture;  and  on  this  account  a  very  great  improvement  was  introduced  some 
years  ago  by  conducting  the  operation  in  vacuo. 

Pure  sugar  is  solid,  white,  inodorous,  and  of  a  very  agreeable  taste.  It 
is  hard  and  brittle,  and  when  two  pieces  are  rubbed  against  each  other  in 
the  dark,  phosphorescence  is  observed.  It  crystallizes  in  the  form  of  four  or 
six-sided  prisms,  bevelled  at  the  extremities.  The  crystals  are  best  made  by 
fixing  threads  in  syrup,  which  is  allowed  to  evaporate  spontaneously  in  a 
warm  room ;  and  the  crystallization  is  promoted  by  adding  spirit  of  wine. 
In  this  state  it  is  known  by  the  name  of  sugar-candy. 

Sugar  undergoes  no  change  on  exposure  to  the  air ;  for  the  deliquescent 
property  of  raw  sugar  is  owing  to  impurities.  It  is  soluble  in  an  equal 
weight  of  cold,  and  to  almost  any  extent  in  hot  water.  It  is  soluble  in  about 
four  times  its  weight  of  boiling  alcohol,  and  the  saturated  solution,  by  cool- 
ing and  spontaneous  evaporation,  deposites  large  crystals.  When  the 
aqueous  solution  of  sugar  is  mixed  with  yeast,  it  undergoes  the  vinous  fer- 
mentation, the  theory  of  which  will  be  explained  in  a  subsequent  section. 

Sugar  unites  with  the  alkalies  and  alkaline  earths,  forming  compounds  in 
which  the  taste  of  the  sugar  is  greatly  injured  ;  but  it  may  be  obtained 
again  unchanged  by  neutralizing  with  sulphuric  acid,  and  dissolving  the 
sugar  in  alcohol.  When  boiled  with  oxide  of  lead,  it  forms  an  insoluble 
compound,  which  consists  of  58-26  parts  of  oxide  of  lead,  and  41-74  parts 
of  sugar  (Berzelius) ;  but  it  is  not  precipitated  by  acetate  or  subacetate  of 
oxide  of  lead. 

Sulphuric  acid  decomposes  sugar  with  deposition  of  charcoal  ;  and  nitric 
acid  causes  the  production  of  oxalic  acid,  as  already  described  in  a  former 
section.  The  vegetable  acids  diminish  the  tendency  of  sugar  to  crystallize. 

Sugar  is  very  easily  affected  by  heat,  acquiring  a  dark  colour  and  burnt 
flavour.  At  a  high  temperature  it  yields  the  usual  products  of  the  destruc- 


516  SUGAR. 

live  distillation  of  vegetable  matter,  together  with  a  considerable  quantity 
of  pyromucic  acid. 

Sugar  as  obtained  from  different  sources  varies  somewhat  in  composition. 
The  largest  quantity  of  carbon  was  found  by  Prout  in  cane  sugar  as  exem- 
plified in  sugar-candy  and  the  best  loaf-sugar,  dried  at  212°,  which  contain 
42-85  per  cent;  while  sugar  from  honey  contains  only  36*36  per  cent,  of 
carbon.  He  considers  the  sugar  from  starch,  diabetic  urine,  and  grapes,  to 
be  nearly  the  same  as  that  from  honey.  The  sugar  from  the  maple-tree  and 
the  beet-root  corresponds  with  cane  sugar  ;  but  the  quantity  of  carbon  in 
these  varieties  appears  to  vary  from  40  to  42-85  per  cent.  (Phil.  Trans.  1827.) 
If  sugar  with  40  per  cent,  of  carbon  be  taken  as  standard  sugar,  we  may 
consider  sugar  as  containing  carbon,  hydrogen,  and  oxygen  in  the  ratio  of 
their  equivalents. 

Molasses. — The  saccharine  principle  of  treacle  has  been  supposed  to  be 
different  from  cryslallizable  sugar  ;  but  it  chiefly  consists  of  common  sugar, 
which  is  prevented  from  crystallizing  by  the  presence  of  foreign  substances, 
such  as  saline,  acid,  and  other  vegetable  matters. 

Sugar jof  Grapes. — The  sugar  procured  from  the  grape  has  the  essential 
properties  of  cane  sugar,  though  not  quite  so  sweet;  and  it  contains  rather 
less  carbon.  The  saccharine  principle  of  the  acidulous  fruits  has  not  been 
particularly  examined.  It  is  obtained  with  difficulty  in  a  pure  state,  owing 
to  the  presence  of  vegetable  acids,  which  prevent  it  from  crystallizing. 

A  saccharine  substance  similar  to  that  from  grapes  may  be  procured  from 
several  vegetable  principles,  such  as  starch  and  the  ligneous  fibre,  by  the  ac- 
tion of  sulphuric  acid. 

Honey. — According  to  Prout,  honey  consists  of  two  kinds  of  saccharine 
matter,  one  of  which  crystallizes  readily  and  is  analogous  to  common  sugar, 
while  the  other  is  uncrystallizable.  They  may  be  separated  by  mixing 
honey  with  alcohol,  and  pressing  the  solution  through  a  piece  of  linen.  The 
liquid  sugar  is  removed,  and  the  crystallizable  portion  is  left  in  a  solid  state. 
Besides  sugar  it  contains  mucilaginous,  colouring,  and  odoriferous  matter, 
and  probably  a  vegetable  acid.  Diluted  with  water,  honey  is  susceptible  of 
the  vinous  fermentation  without  the  addition  of  yeast. 

The  natural  history  of  honey  is  as  yet  imperfect.  It  is  uncertain  whether 
honey  is  merely  collected  by  the  bee  from  the  nectaries  of  flowers,  and  then 
deposited  in  the  hive  unchanged,  or  whether  the  saccharine  matter  of  the 
flower  does  not  undergo  some  change  in  the  body  of  the  animal. 

Manna. — This  saccharine  matter  is  the  concrete  juice  of  several  species 
of  ash,  and  is  procured  in  particular  from  the  Fraximis  ornus.  The  sweet- 
ness of  manna  is  owing,  not  to  sugar,  but  to  a  distinct  principle,  called  man- 
nite, which  is  mixed  with  a  peculiar  vegetable  extractive  matter.  Manna  is 
soluble  both  in  water  and  boiling  alcohol,  and  the  latter,  on  cooling,  depo- 
sites  pure  mannite  in  the  form  of  minute  acicular  crystals,  which  are  often 
arranged  in  concentric  groups.  Mannite  differs  from  sugar,  in  not  ferment- 
ing  when  mixed  with  water  and  yeast. 

Sugar  of  Liquorice. — The  root  of  the  Glycyrrliiza  glabra,  as  also  the 
black  extract  of  the  root  well  known  under  the  name  of  liquorice^  contains  a 
saccharine  principle ;  but  it  is  quite  distinct  from  sugar.  It  may  be  pre- 
pared by  infusing  the  root  in  boiling  water,  filtering  when  cold,  and  gra- 
dually adding  sulphuric  acid  as  long  as  a  precipitate,  which  is  a  compound 
of  the  acid  and  saccharine  matter,  is  formed.  It  is  first  washed  with  water 
acidulated  with  sulphuric  acid,  and  then  with  pure  water ;  and  it  is  subse- 
quently dissolved  in  alcohol,  which  leaves  a  little  vegetable  albumen  and  mu- 
cilage. Solution  of  carbonate  of  potassa  is  then  added  very  gradually,  so  as 
exactly  to  neutralize  the  acid  ;  and  after  the  sulphate  of  potassa  has  subsided, 
the  alcoholic  solution  is  decanted  and  evaporated.  It  may  also  be  obtained 
in  a  similar  manner  from  the  extract,  except  that  the  solution,  when  first 
made,  must  be  purified  by  white  of  egg. 

Sugar  of  liquorice  is  thus  procured  in  the  form  of  a  yellow  transparent 
mass,  which  is  unchangeable  in  the  air,  and  soluble  in  water  and  alcohol.  It 


STARCH  OR  FECULA. — AMIDINE.  517 

is  characterised  by  its  tendency  to  form  sparingly  soluble  compounds  with 
acids,  which  accordingly  precipitate  it  from  its  solution  in  cold  water.  It 
unites  also  readily  with  alkaline  bases;  and  when  digested  in  water  con- 
taining carbonate  of  potassa,  baryta,  or  lime,  carbonic  acid  is  slowly  evolved, 
and  a  soluble  compound  of  the  base  with  the  saccharine  matter  is  generated. 
(Berzelius.) 

STARCH  OR  FECULA.— AMIDINE. 

Starch  exists  abundantly  in  the  vegetable  kingdom,  being  one  of  the  chief 
ingredients  of  most  varieties  of  grain,  of  some  roots,  such  as  the  potato,  and 
of  the  kernels  of  leguminous  plants.  It  is  easily  procured  by  letting  a  small 
current  of  water  fall  upon  the  dough  of  wheat-flour  enclosed  in  a  piece  of 
linen,  and  subjecting  it  at  the  same  time  to  pressure  between  the  fingers, 
until  the  liquid  passes  off  quite  clear.  The  gluten  of  the  flour  is  left  in  a 
pure  state,  the  saccharine  and  mucilaginous  matters  are  dissolved,  and  the 
starch  is  washed  away  mechanically,  being  deposited  from  the  water  on 
standing  in  the  form  of  a  white  powder.  The  starch  of  commerce  is  ob- 
tained by  an  analogous  process  from  the  grain  of  wheat  and  from  the  potato  ; 
but  in  the  preparation  of  wheat  starch,  the  water  containing  the  soluble  and 
insoluble  parts  of  the  grain  is  allowed  to  ferment,  whereby  acetic  acid  is 
generated,  which  dissolves  the  glutinous  portion,  and  thus  facilitates  its  se- 
paration from  the  starch.  The  microscopic  researches  of  Raspail  have 
proved  that  starch,  as  it  exists  in  plants,  occurs  as  white,  shining,  but  un- 
crystalline,  particles,  each  of  which  has  its  own  proper  envelope  of  an  amy- 
laceous nature,  but  more  insoluble  in  water  than  the  interior  particles. 

Starch  is  insipid  and  inodorous,  of  a  white  colour,  and  is  insoluble  in  al- 
cohol, ether,  and  cold  water.  It  does  not  crystallize  ;  but  it  is  commonly 
found  in  the  shops  in  six-sided  columns  of  considerable  regularity,  a  form 
occasioned  by  the  contraction  which  it  suffers  in  drying.  Boiling  water  acts 
upon  it  readily,  converting  it  into  a  tenacious  bulky  jelly,  which  is  employed 
for  stiffening  linen.  In  a  large  quantity  of  hot  water,  it  is  dissolved  com- 
pletely, and  is  not  deposited  on  cooling.  The  aqueous  solution  is  precipi- 
tated by  subacetate  of  oxide  of  lead  ;  but  the  best  test  of  starch,  by  which  it 
is  distinguished  from  all  other  substances,  is  iodine.  This  principle  forms 
with  starch,  whether  solid  or  in  solution,  a  blue  compound  which  is  insolu- 
ble in  cold  water  ;  with  hot  water  it  forms  a  colourless  solution,  which  depo- 
sites  the  blue  compound  as  it  cools ;  but  when  boiled  with  water,  iodine  acts 
upon  the  elements  of  the  starch,  hydriodic  acid  is  formed,  and  then  on  cool- 
ing the  blue  iodide  of  starch  is  not  reproduced. 

Starch  unites  with  the  alkalies,  forming  a  compound  which  is  soluble  in 
water,  and  from  which  the  starcli  is  thrown  down  by  acids.  On  mixing  so- 
lutions of  starch  with  baryta,  lime,  and  subacetate  of  oxide  of  lead,  white 
insoluble  compounds  are  obtained  ;  and  that  with  oxide  of  lead,  formed  at  a 
boiling  temperature  with  excess  of  the  sub-salt,  contains  72  parts  of  starch 
and  28  of  oxide  of  lead.  (Derzelius.)  Strong  sulphuric  acid  decomposes  it. 
Nitric  acid  in  the  cold  dissolves  starch  ;  but  converts  it  by  the  aid  of  heat 
into  oxalic  and  malic  acid. 

The  effects  of  heat  on  starch  are  peculiar,  and  have  been  examined  by 
Caventou.  (An.  de  Chim.  et  de  Ph.  xxxi.)  On  exposing  dry  starch  to  a  tem- 
perature a  little  above  212°  it  acquires  a  slightly  red  tint,  emits  an  odour  of 
baked  bread,  and  is  rendered  soluble  in  cold  water ;  and  a  similar  modifica- 
tion is  effected  by  the  action  of  hot  water.  Gelatinous  starch  is  generally 
supposed  to  be  a  hydrate  of  starch;  but  Caventou  maintains  that  the  jelly 
cannot  by  any  method  be  restored  to  its  original  state.  He  regards  this  mo, 
dified  starch  as  identical  with  the  substance  described  by  Saussure  under 
the  name  of  amidine.  Saussure  thought  it  was  generated  by  exposing  a 
paste  made  with  starch  arid  water  for  a  long  time  to  the  air;  but  according 
to  Caventou,  the  amidine  was  formed  by  the  action  of  the  hot  water  on 
starch  in  making  the  paste.  Its  essential  character  is  to  yield  a  blue  colour 

44 


518  GUM. 

with  iodine,  and  to  be  soluble  in  cold  water*  On  gently  evaporating-  the  so- 
lution to  dryness,  it  becomes  a  transparent  mass  like  horn,  which  retains  its 
solubility  in  cold  water. — To  terrified  starch,  that  is,  to  starch  thus  modified 
by  heat,  whether  in  the  dry  way  or  by  boiling  water,  the  term  amidine  may 
be  applied. 

When  starch  is  exposed  to  a  still  higher  temperature  than  is  sufficient  for 
its  conversion  into  amidine,  a  more  complete  change  is  effected.  It  then 
assumes  a  reddish-brown  colour,  swells  up  and  softens,  dissolves  with  much 
greater  facility  in  cold  water,  and  gives  with  iodine  either  a  purple  colour 
or  none  at  all.  In  this  state  it  is  very  analogous  to  gum,  and  is  employed 
by  calico-printers  under  the  name  of  British  gum  ;  but  it  differs  from  real 
guru  in  not  yielding  mucie  acid  by  digestion  with  nitric  acid.  A  similar 
change  may  be  produced  by  long-continued  ebullition. 

Starch  is  readily  convertible  into  sugar.  This  change  takes  place  in 
seeds  during  germination,  as  in  the  malting  of  barley  ;  and  a  similar  con- 
version appears  in  some  instances  as  an  effect  of  frost,  as  in  the  potato, 
apple,  and  parsnip.  Saccharine  matter  is  also  developed  when  gelatinous 
starch  is  kept  in  a  moist  state  for  a  long  time,  either  with  or  without  the 
access  of  air.  If  starch  is  boiled  for  a  considerable  time  in  water  acidu- 
lated with  l-12th  of  its  weight  of  sulphuric  acid,  it  is  wholly  converted  into 
a  saccharine  matter  similar  to  that  of  the  grape ;  and  this  change  takes 
place  much  more  rapidly  if  the  temperature  is  a  few  degrees  above  212°. 
This  fact  was  first  observed  by  Kirchoff,  and  has  since  been  particularly 
examined  by  Vogel,  De  la  Rive,  and  Saussure.  It  has  been  established  by 
Saussure  that  the  oxygen  of  the  air  exerts  no  influence  over  the  process, 
that  no  gas  is  disengaged,  that  the  quantity  of  acid  suffers  no  diminution, 
that  100  parts  of  starch  yield  110-14  of  sugar,  and  that  the  only  difference 
in  the  composition  of  starch  and  sugar  is,  that  the  latter  contains  more  of 
the  elements  of  water  than  the  former.  He  hence  inferred  that,  in  Kirchoff's 
process,  the  starch  is  converted  into  sugar  by  its  elements  combining  with 
a  certain  quantity  of  oxygen  and  hydrogen  in  the  proportion  to  form  water  ; 
and  that  the  acid  acts  only  by  increasing  the  fluidity  of  the  mass.  (Annals 
of  Philosophy,  vi.) 

The  researches  of  Caventou,  already  referred  to,  have  thrown  considera- 
ble light  on  the  chemical  nature  of  several  of  the  amylaceous  principles  of 
commerce.  The  Indian  arrow-root,  which  is  prepared  from  the  root  of  the 
Maranta  arundinacea,  has  all  the  characters  of  pure  starch.  Sago,  obtained 
from  the  cellular  substance  of  an  East-Indian  palm-tree.  (Sagus  farinifera}, 
and  tapioca  and  cassava  from  the  root  of  the  Jalropha  Manitiol,  are  chemi- 
cally the  same  substance.  They  both  exist  in  the  plants  from  which  they 
are  extracted  in  the  form  of  starch;  but  as  heat  is  employed  in  their  prepa- 
ration, the  starch  is  more  or  less  completely  converted  into  amidine.  It 
hence  follows  that  pure  potato  starch  may  be  used  instead  of  arrow-root;  and 
that  the  same  material,  modified  by  heat,  would  afford  a  good  substitute  for 
sago  and  tapioca.  Salep,  which  is  obtained  from  the  Orchis  mascula,  con- 
sists almost  entirely  of  the  substance  called  bassorin,  together  with  a  small 
quantity  of  gum  and  starch. 

When  starch  moistened  with  water  is  digested  with  an  equal  weight  of 
peroxide  of  manganese,  a  volatile  acid,  possessed  of  an  odour  similar  to  hy- 
drocyanic acid,  passes  over.  Its  discoverer,  M.  Tunnermann,  who  has  given 
it  the  name  of  amylic  acid,  considers  it  a  compound  of  three  equivalents  of 
oxygen  and  two  and  a  half  eq.  of  carbon;  but  it  requires  further  examina- 
tion before  being  enumerated  as  a  distinct  acid.  (Journal  of  Science,  N.  S. 
iv.  444.) 

GUM. 

Under  this  name  I  include  all  those  immediate  vegetable  principles  which 
form  with  water  a  clammy  adhesive  solution  called  mucilage,  and  which, 
when  boiled  with  about  four  limes  their  weight  of  nitric  acid,  yield  mucic 


GUM.  519 

acid.     The  nitric  acid  used  for  the  production  of  mucic  acid  should  have  a 
density  of  1-339  at  50°  F. 

The  properties  of  gum  are  best  studied  in  pure  specimens  of  gum-arabic, 
of  which  it  is  the  principal  ingredient.  It  is  colourless,  transparent,  in- 
odorous, and  insipid,  and  when  dry  it  is  very  brittle,  and  has  a  vitreous 
fracture.  When  put  into  water,  cither  hot  or  cold,  it  softens,  and  then  dis- 
solves, constituting  mucilage.  It  is  insoluble  in  ether  and  alcohol,  and  the 
former  precipitates  gum  from  its  solution  in  the  form  of  opaque  white 
flakes.  Its  solubility  is  increased  both  by  acids  and  alkalies.  Strong  sul- 
phuric acid  decomposes  it,  causing  the  formation  of  water  and  acetic  acid, 
with  deposition  of  charcoal.  Heated  with  a  quantity  of  nitric  acid  insuffi- 
cient for  the  production  of  mucic  acid,  it  yields  an  acid  resembling  the  malic. 
The  greatest  quantity  of  mucic  acid  which  can  be  procured  from  pure  gum 
is  16-88  per-cent.  (Guerin  in  An.  de  Ch.  et  de  Ph.  xlix.  248.) 

The  aqueous  solution  of  gum  may  be  preserved  a  considerable  time  with- 
out alteration;  but  at  length  it  becomes  sour,  and  exhales  an  odour  of  acetic 
acid,  a  .change  which  takes  place  without  exposure  to  the  air,  and  must, 
therefore,  be  owing  to  a  new  arrangement  of  its  own  elements. 

Gum  is  precipitated  from  its  solution  in  water  by  several  metallic  salts, 
and  especially  by  subacetate  of  oxide  of  lead,  which  occasions  a  curdy  pre- 
cipitate, consisting  of  38-25  parts  of  oxide  of  lead  and  61-75  parts  of  gum. 
(Berzelius).  It  is  also  thrown  down  by  a  solution  of  silicated  potassa,  but 
this  test  is  less  delicate  than  the  salt  of  lead. 

When  gum  is  heated  to  redness  in  close  vessels,  it  yields,  in  addition  to  the 
usual  products,  a  small  quantity  of  ammonia,  owing  to  some  impurity,  pro- 
bably gluten,  with  which  it  is  generally  associated. 

Gum-arabic. — This  substance  is  the  concrete  juice  of  several  species  of  the 
Mimosa  or  Acacia,  natives  of  Africa  and  Arabia.  It  occurs  in  small,  rounded, 
transparent,  friable  grains,  which  are  sometimes  colourless,  and  at  others 
yellow,  red,  or  brown.  Its  density  is  1  355.  Dried  at  250°  M.  Guerin  found 
it  to  lose  17-6  per  cent  of  water  :  the  remaining  82-4  when  burned  yielded  3 
parts  of  an  ash,  consisting  of  the  carbonates  of  lime  and  potassa,  a  little 
phosphate  of  lime,  chloride  of  potassium,  oxide  of  iron,  alumina,  silica,  and 
magnesia.  When  gum-arabic  is  dissolved  in  water,  a  small  quantity  of  inso- 
luble matter  containing  nitrogen  is  left,  and  a  portion  of  it  appears  to  be 
dissolved  in  the  mucilage.  The  solution  of  the  gum  contains  a  supermalate 
of  lime,  the  chlorides  of  calcium  and  potassium,  and  acetate  of  potassa. 
(Guerin.)  These  may  be  removed  by  digestion  in  alcohol. 

Gum-senegal,  the  juice  of  the  Acacia  Senegalensis,  contains  exactly  the 
same  principle  as  gum-arabic.  The  mucilage  of  linseed,  and  probably  of 
most  of  the  mucilaginous  seeds  and  plants,  possesses  the  essential  characters 
of  gum-arabic. 

Gum-tragacanih,  the  juice  of  the  Astragalus  gummifer>  differs  essentially 
from  the  pure  gums.  According  to  Guerin,  100  parts  contain  ll'l  of  water, 
2-5  of  ashes  left  when  the  gum  is  burned,  53-3  of  pure  gum  soluble  in  cold 
water,  and  identical  with  that  of  gum-arabic,  and  33-1  of  bassorin  and  starch, 
which  is  the  part  left  undissolved  by  cold  water. 

The  gum  which  issues  from  several  trees  of  the  genius  Prunus^  a«  from 
the  peach,  plum,  apricot,  and  cherry-tree  (P.  Cerasus},  was  found  by  Dr. 
Bostock  to  yield  mucic  acid  by  the  action  of  nitric  acid  (Nicholson's  Journal, 
xviii.).  M.  Guerin  finds  it  to  be  identical  in  composition  with  gum-arabic. 
It  differs,  however,  in  being  insoluble  in  cold  water;  but  when  boiled  in  that 
liquid,  it  is  dissolved,  and  the  solution  has  all  the  characters  of  pure  mucilage. 
In  fact  cherry-tree  gum,  which  Guerin  distinguishes  by  the  name  of  cerasin, 
seems  isomeric  with  the  standard  gum,  and  acquires  identity  of  character 
by  the  mere  influence  of  heat. 

The  gelatinous  principle  of  fruits,  such  as  is  derived  from  the  currant  or 
gooseberry,  appears  to  be  very  closely  allied  to  gum.  It  is  precipitated 
from  the  juice  by  free  admixture  with  alcohol,  forms  a  mucilaginous  solu- 
tion with  water,  though  less  adhesive  than  gum,  is  neutral  to  test  paper, 


520 


OLEAGINOUS,  RESINOUS,  AND  BITUMINOUS  SUBSTANCES. 


and  with  nitric  acid  yields  mucie  and  oxalic  acids.  It  is  distinguished  how- 
ever from  the  pure  gum  by  being  instantly  converted  into  pectic  acid  by  the 
presence  of  a  fixed  alkali  or  alkaline  earth :  on  adding  potassa,  and  then  an 
acid,  a  jelly  falls,  possessed  of  all  the  characters  of  pectic  acid  ;  and  when 
baryta  is  employed,  a  pectate  of  baryta  subsides.  The  jelly  of  fruits  is  thus 
distinct  from  gum,  and  Braconnot,  by  whom  these  facts  were  observed,  pro- 
poses  for  it  the  name  of  pectin.  (An.  de  Ch.  et  de  Ph.  xlvii.  266.) 

LIGNIN. 

Lignin^  or  woody  fibre  constitutes  the  fibrous  structure  of  vegetable  sub- 
stances, and  is  the  most  abundant  principle  in  plants.  The  different  kinds 
of  wood  contain  about  96  per  cent,  of  lignin.  It  is  prepared  by  digesting1 
the  sawings  of  any  kind  of  wood  successively  in  alcohol,  water,  and  dilute 
hydrochloric  acid,  until  all  the  substances  soluble  in  these  menstrua  are 
removed. 

Lignin  has  neither  taste  nor  odour,  undergoes  no  change  by  keeping,  and 
is  insoluble  in  alcohol,  water,  and  the  dilute  acids.  By  digestion  in  a  con- 
centrated solution  of  pure  potassa,  it  is  converted,  according  to  Braconnot, 
into  a  substance  similar  to  ulrnin.  Mixed  with  strong  sulphuric  acid  it 
suffers  decomposition,  and  is  changed  into  a  matter  resembling  gurn ;  and 
on  boiling  the  liquid  for  some  time  the  mucilage  disappears,  and  a  saccha- 
rine principle  like  the  sugar  of  grapes  is  generated.  Braconnot  finds  that 
several  other  substances  which  consist  chiefly  of  woody  fibre,  such  as  straw, 
bark,  or  linen,  yield  sugar  by  a  similar  treatment.  (An.  de  Ch.  et  de  Ph.  xii.) 
Digested  in  nitric  acid,  lignin  is  converted  into  the  oxalic,  malic,  and  acetic 
acids. 


SECTION   IV. 


OLEAGINOUS,  RESINOUS,  AND  BITUMINOUS  SUBSTANCES. 


THE  compounds  included  in  this  section,  besides  being  otherwise  allied, 
are.  remarkable  for  their  combustibility,  and  supply  the  materials  used  in  the 
arts  for  the  production  of  heat  and  light.  Most  of  them  contain  a  much 
larger  quantity  of  hydrogen  than  suffices  for  forming  water  with  their  oxy- 
gen. They  exert  in  general  but  a  very  feeble  affinity  for  other  bodies,  and 
consequently  their  combining  weights  and  atomic  constitution  have  in  few 
instances  been  determined.  Their  composition  will,  therefore,  be  best  stated 
in  reference  to  100  parts,  as  in  the  following  table  : — 


Substances. 
Olive  oil 

Essence  of  turpentine 
Oil  of  lemons 
Camphor 
Do.  from  oil  of  pepper- 

mint 

Do.  from  oil  of  anise 
Oil  of  cloves 
Caryophylline 
Oil  of  bitter  almonds 
Common  resin 
Caoutchouc 
Bees-wax 


Carbon.  Hyd.  Oxygen.  Analyzed  by 

77-213  13-36      9-427  Gay-Lussac  and  Thenard. 

85-5  11-5  Dumas. 

79-28  10-36     10-36    Dumas. 

77-3  12-6       10-1       Dumas. 

81-4  7-98    10.62     Dumas. 

70-02  7-42    22-56     Dumas. 

79-27  10-36     10-37     Dumas. 

79-56  5-56     14-88    Liebiff  and  Wohler. 

75  944  10-719  13-337  Gay-Lussac  and  Thenard. 

90  9.12       0-88    Ure. 

80-4  11-3        8-3      Urc. 


OLEAGINOUS    SUBSTANCES.  521 


OLEAGINOUS  SUBSTANCES. 

Oils  are  characterized  by  a  peculiar  unctuous  feel,  by  inflammability,  and 
by  insolubility  in  water.  They  are  divided  into  the  fixed  and  volatile  oils, 
the  former  of  which  are  comparatively  fixed  in  the  fire,  and,  therefore,  give 
a  permanently  greasy  stain  to  paper;  while  the  latter,  owing  to  their  vola- 
tility, produce  a  stain  which  disappears  by  gentle  h,eat, 

FIXED  OILS, 

The  fixed  oiis  are  usually  contained  in  the  seeds  of  plants,  as  for  exam- 
ple in  the  almond,  linseed,  rape-seed,  and  poppy -seed;  but  olive-oil  is  ex- 
tracted from  the  pulp  which  surrounds  the  stone.  They  are  procured  by 
bruising  the  seed,  ajid  subjecting"  the  pulpy  matter  to  pressure  in  hempen 
bags,  a  gentle  heat  being  generally  employed  at  the  same  time  to  render  the 
oil  more  limpid. 

Fixed  oils  are  nearly  inodorous,  have  little  taste,  and  are  lighter  than  wa- 
ter, their  density  in  general  varying  from  0*9  to  0  96.  Some,  such  as  cocoa- 
nut  and  pahn-oil,  are  fixed  at  50°  or  60°;  but  most  of  them  are  fluid  at 
common  temperatures,  and  they  all  become  limpid  in  becoming  warm.  They 
are  commonly  of  a  yellow  colour,  but  may  be  rendered  nearly  or  quite  co- 
lourless by  the  action  of  animal  charcoal.  At  or  near  600°  they  begin  to 
boil,  but  suffer  partial  decomposition  at  the  same  time,  an  inflammable  va- 
pour being  disengaged  even  below  500°.  When  heated  to  redness  in  close 
vessels,  a  large  quantity  of  the  combustible  compounds  of  carbon  and  hy- 
drogen is  formed,  together  with  the  other  products  of  the  destructive  distil- 
lation of  vegetable  substances ;  and  in  the  open  air  they  burn  with  a  clear 
white  light,  and  formation  of  water  and  carbonic  acid.  They  may  hence  be 
employed  for  the  purposes  of  artificial  illumination,  as  well  in  lamps,  as  for 
the  manufacture  of  gas. 

Fixed  oils  undergo  considerable  change  by  exposure  to  the  air,  a  change 
owing  to  the  action  of  oxygen,  and  which  has  been  examined  into  by  Saus- 
eure  (An.  de.  Ch.  et  de  Ph.  xlix.  225).  Olive-oil,  recently  expressed,  was  con- 
fined over  mercury  in  a  tube  full  of  oxygen  gas,  and  underwent  no  appre- 
ciable alteration  during  the  first  five  months,  absorbing  only  about  its  own 
volume  of  oxygen  :  the  absorption  then  became  very  rapid,  so  that  at  the 
end  of  the  first  year  it  had  absorbed  41  times  its  volume  of  oxygen,  and  be- 
came quite  colourless;  and  at  the  close  of  the  fourth  year,  when  the  action 
had  become  very  slight,  the  whole  absorption  of  oxygen  amounted  to  102 
times  its  volume.  The  oil  at  that  period  was  very  rancid,  and  less  limpid 
than  at  first.  During  these  changes  the  oil  gave  out  22  times  its  volume  of 
carbonic  acid  and  about  6  of  hydrogen,  together  with  a  trace  of  carbonic 
oxide.  The  rancidity  of  oils  is  commonly  ascribed  to  the  mucilaginous  mat- 
ters which  they  contain  becoming  acid,  and  probably  the  first  change  is  of 
this  nature ;  but  subsequently,  when  the  principal  absorption  takes  place,  the 
oil  itself  appears  to  be  modified. 

Similar  changes  occur  to  a  much  greater  extent  with  linseed-oil  and  other 
siccative  oils,  which  owe  their  property  of  drying  to  the  absorption  of  oxy- 
gen. The  oil  of  hemp-seed,  recently  expressed,  was  exposed  for  a  month  to 
oxygen  gas,  and  absorbed  of  it  less  than  its  own  volume  :  there  was  no  ab- 
sorption during  the  second  month;  but  subsequently  the  absorption  became 
rapid,  and  at  the  end  of  one  year  the  oil  had  taken  up  155  times  its  volume 
of  oxygen.  At  the  time  of  the  absorption  becoming  rapid,  the  oil  lost  its 
colour,  and  its  surface  acquired  a  mucilaginous  pellicle.  During  the  three 
following  years  it  still  continued  to  absorb  oxygen,  and  to  become  viscid  ; 
at  the  end  of  that  time  it  had  evolved  about  24  times  its  bulk  of  carbonic 
acid,  and  7  of  hydrogen,  with  a  little  carburetted  hydrogen.  The  oil  of  wal- 
nuts gave  similar  results.  This  property  of  drying,  for  which  linseed-oil  is 

44* 


522  VOLATILE  OILS. 

remarkable,  may  be  communicated  quickly  by  heating-  the  oil  in  an  open 
vessel.  Drying  oils  are  used  for  making  oil  paint,  and  mixed  with  lamp- 
black  they  constitute  printers'  ink. 

The  absorption  of  oxygen  by  fixed,  and  especially  by  drying  oils,  is  under 
some  circumstances  so  abundant  and  rapid,  and  accompanied  with  so  much 
heat,  that  light  porous  combustible  materials,  such  as  lampblack,  hemp,  or 
cotton. wool,  may  be  kindled  by  it.  Substances  of  this  kind,  moistened  with 
linseed-oil,  have  been  known  to  take  fire  during  the  space  of  24  hours,  a  cir- 
cumstance which  has  repeatedly  been  the  cause  of  extensive  fires  in  ware- 
houses and  in  cotton  manufactories. 

Fixed  oils  do  not  unite  with  water,  but  they  may  be  permanently  sus- 
pended in  that  fluid  by  means  of  mucilage  or  sugar,  so  as  to  constitute  an 
emulsion.  They  are  for  the  most  part  very  sparingly  soluble  in  alcohol  and 
ether.  Strong  sulphuric  acid  thickens  the  fixed  oils,  and  forms  with  them 
a  tenacious  matter  like  soap;  and  they  are  likewise  rendered  thick  and 
viscid  by  the  action  of  chlorine.  Concentrated  nitric  acid  acts  upon  them 
with  great  energy,  giving  rise  in  some  instances  to  the  production  of  flame. 

Alkaline  bases  have  a  remarkable  action  on  oils  and  fats.  With  ammonia 
oil  forms  a  soapy  liquid  to  which  the  name  of  volatile  liniment  is  applied:  it 
is  a  direct  compound  of  the  oil  and  alkali  suspended  in  water ;  but  by  keep, 
ing,  an  ammoniacal  soap  is  generated.  The  pure  fixed  alkalies  act  similarly 
in  the  cold ;  but  when  heated  with  oil,  the  latter  undergoes  an  entire  change 
of  constitution,  and  soap  is  generated.  A  similar  action  is  occasioned  by 
most  of  the  metallic  oxides. 

The  elaborate  researches  of  Chevreul  on  the  nature  of  oils  and  fats  have 
shown  that  these  bodies  are  not  pure  proximate  principles,  but  compounds  in 
variable  proportion  of  at  least  two  other  compounds,  one  of  which  is  solid 
at  common  temperatures,  while  the  other  is  fluid.  To  the  former  he  applied 
the  name  of  slearine,  from  o-<rt*£  suet,  and  to  the  latter  elaine  or  o/ezne,  from 
ehcttov  oil.  Oleine  is  the  fluid  principle  of  oils,  and  gives  fluidity  to  those  oils 
in  which  it  predominates.  It  requires  a  cold  of  20°  for  congelation,  and  is 
prepared  from  oils  by  exposing-  them  to  a  cold  of  about  25°,  and  pressing 
the  congealed  mass  between  folds  of  bibulous  paper;  when  the  oleine  is  ab- 
sorbed, and  may  be  separated  by  pressing  the  paper  under  water.*  Oleine  is 
well  adapted  for  lubricating  the  wheels  of  watches  or  other  delicate  ma- 
chinery, since  it  does  not  thicken  or  become  rancid  by  exposure  to  the  air. 
From  late  experiments  by  Lecanu,  it  appears  that  stearine,  though  con- 
tained  in  animal  fats,  is  rarely  present  in  those  of  vegetable  origin :  the 
solid  principle  present  in  the  latter  is  margarine,  a  substance  analogous  in 
its  properties  to  stearine.  The  nature  of  these  substances,  as  well  as  the 
changes  induced  in  them  during  the  formation  of  soap,  will  be  considered  in 
the  section  on  the  animal  fats. 

VOLATILE  OR  ESSENTIAL  OILS. 

Aromatic  plants  owe  their  flavour  to  the  presence  of  a  volatile  or  essential 
oil,  which  may  be  obtained  by  distillation,  water  being  put  into  the  still 
along  with  the  plant  in  order  to  prevent  the  latter  from  being  burned.  The 
oil  and  water  pass  over  into  the  recipient,  and  the  oil  collects  at  the  bottom 
or  the  surface  of  the  water  according  to  its  density. 

/  Essential  oils  have  a  penetrating  odour  and  acrid  taste,  which  are  often 
pleasant  when  sufficiently  diluted.  They  are  soluble  in  alcohol,  though  in 
different  proportions.  They  are  sparingly  dissolved  by  water,  and  hence 
water  acquires  the  odour  of  the  oil  with  which  it  is  distilled.  With  the  fixed 
oils  they  unite  in  every  proportion,  and  are  sometimes  adulterated  with 
them,  an  imposition  easily  detected  by  the  mixed  oil  causing  on  paper  a 
greasy  stain  which  is  not  removed  by  heat. 

Volatile  oils  burn  in  tho  open  air  with  a  clear  white  light,  and  the  sole 
products  of  the  combustion  are  water  and  carbonic  acid.  On  exposure  to  the 
atmosphere,  they  gradually  absorb  a  large  quantity  of  oxygen,  in  conse- 


VOLATILE   OILS.  523 

quence  of  which  they  become  thick,  acquire  a  deep  yellowish-brown  colour, 
and  are  at  length  converted  into  a  substance  resembling  resin.  Some  of 
them  deposite  during  this  action  crystalline  compounds  of  a  definite  nature. 
Saussure  lias  shown  that,  as  with  fixed  oils,  carbonic  acid  and  hydrogen 
gases  are  emitted  at  the  same  time.  This  change  is  rendered  more  rapid 
by  the  agency  of  light. 

Of  the  acids,  the  action  of  strong  nitric  acid  on  volatile  oils  is  the  most 
energetic,  being  often  attended  with  vivid  combustion, — an  effect  which  is 
rendered  more  certain  by  previously  adding  to  the  nitric  a  few  drops  of  sul- 
phuric acid. 

Volatile  oils  do  not  unite  readily  with  metallic  oxides,  and  are  attacked 
with  difficulty  even  by  the  alkalies.  The  substance  called  Starkey's  soap  is 
made  by  triturating  oil  of  turpentine  with  an  alkali. 

Volatile  oils  dissolve  sulphur  in  large  quantity,  forming  a  deep  brown- 
coloured  liquid,  called  balsam  of  sulphur.  The  solution  is  best  made  by 
boiling  flowers  of  sulphur  in  spirit  of  turpentine.  Phosphorus  may  likewise 
be  dissolved  by  the  same  menstruum. 

The  following  table  contains  a  list  of  the  principal  essential  oils: — 


Oils  of 

Colour. 

Density. 

Turpentine 

colourless             .             . 

0-87 

Lemons 

colourless  or  pale  yellow 

0-85 

Anise 

do.                       do. 

0-9857  at  80° 

Juniper 

do.              or  greenish-yellow 

0-911 

Chamomile 

deep  blue 

Car  raw  ay 

pale  yellow 

0-94 

Lavender 

yellow 

0-877  to  0-898 

Peppermint      '. 

colourless  or  pale  yellow 

0-92 

Rosemary 

colourless 

0-89  to  0-92 

Camphor- 

white 

0-988 

Cinnamon 

yellow      .             .             .    - 

1035 

Cloves  . 

colourless  or  pale  yellow 

1-061 

Sassafras 

yellow  or  red 

1-094 

Mustard 

yellow 

1-0387 

Bitter  alrnonds  . 

colourless 

1-043 

The  essential  oils  differ  in  constitution  from  the  fixed  oils,  and  are  divisi- 
ble into  three  groups.  The  first  consists  of  the  essence  of  turpentine  and  of 
lemons,  which  are  composed  solely  of  carbon  and  hydrogen ;  the  second, 
which  includes  oil  of  anise  and  the  ten  following  oils,  together  with  the  so- 
lid essence,  caYnphor,  contain  carbon,  hydrogen,  and  oxygen  ;  and  the  oils  of 
the  third  group,  as  oil  of  mustard  and  bitter  almonds,  contain  some  other 
element  in  addition  to  the  foregoing. 

Essence  of  Turpentine. — This  oil,  which  is  the  most  common  and  most 
generally  used  of  all  the  essential  oils,  is  procured  by  distillation  from  com- 
mon  turpentine,  and  is  a  limpid  colourless  fluid,  which  may  be  distilled 
without  residue,  and  yields  a  dense  white  light  in  burning.  It  is  sparingly 
soluble  in  alcohol.  In  its  purest  form  it  is  a  definite  compound  of  carbon, 
and  hydrogen.  Its  composition  has  already  been  given  in  the  table, 
page  248.  But  the  specimens  met  with  in  commerce  invariably  con- 
tain oxygen,  owing  to  the  absorption  of  that  gas  from  the  atmosphere, 
whereby  changes  in  the  constitution  of  the  essence  are  produced.  It  is  not 
improbable,  also,  that  the  essence  obtained  from  different  kinds  of  turpen- 
tine may  differ  in  original  constitution. 

Essence  of  turpentine  or  camphene  forms  an  interesting  compound  with 
hydrochloric  acid,  called  artificial  camphor,  consisting  of  two  eq.  of  camphene 
and  one  eq.  of  acid.  It  is  formed  by  transmitting  a  current  of  perfectly  dry 
hydrochloric  acid  gas  through  oil  of  turpentine,  which  has  been  recently 
and  carefully  distilled,  surrounded  by  a  mixture  of  snow  and  salt :  a  quan- 
tity of  gas  is  absorbed  equal  to  one-third  of  the  weight  of  the  oil;  the  liquid 
acquires  a  deep  brown  colour;  and  a  white  crystalline  volatile  substance, 


524  VOLATILE   OILS. 

very  similar  to  camphor,  is  slowly  generated.  The  liquid  parts  should  be 
removed  by  pressure  between  folds  of  bibulous  paper.  This  matter  was 
discovered  by  Kind,  and  has  since  been  studied  by  Trommsdorf,  Gchlen, 
Thenard,  and  Dumas.  When  carefully  separated  from  adhering-  acid  by 
washing-  with  water  containing  a  little  carbonate  of  soda,  it  is  quite  neutral, 
and  affords  an  instance  of  a  carburet  of  hydrogen  acting  as  a  base  to  u 
strong  acid. 

The  oil  of  lemons  has  the  same  composition  as  that  of  turpentine  (page 
520),  and  forms  with  hydrochloric  acid  an  artificial  camphor  analogous  to 
the  foregoing. 

Camphor. — This  substance  exists  ready  formed  in  the  Laurus  Camphora 
of  Japan,  and  is  obtained  from  its  trunk,  root,  arid  branches  by  sublimation. 
It  has  a  bitterish,  aromatic,  pungent  taste,  accompanied  with  a  sense  of  cool- 
ness. It  is  unctuous  to  the  touch,  and  rather  brittle,  though  possessing  a 
degree  of  toughness  which  prevents  it  from  being  pulverized  with  facility  ; 
but  it  is  easily  reduced  to  powder  by  trituration  with  a  few  drops  of  alcohol. 
Its  specific  gravity  is  0  988.  It  is  exceedingly  volatile,  being  gradually  dis- 
sipated in  vapour  if  kept  in  open  vessels.  At  288°  it  enters  into  fusion, 
and  boils  at  40l)°.  It  is  insoluble  in  water;  but  when  triturated  with  sugar, 
and  then  mixed  with  that  fluid,  a  portion  is  dissolved  sufficient  for  communi- 
cating its  flavour.  It  is  dissolved  freely  by  alcohol,  and  is  thrown  down  by 
the  addition  of  water.  It  is  likewise  soluble  in  the  fixed  and  volatile  oils, 
and  in  strong  acetic  acid.  Sulphuric  acid  decomposes  camphor,  converting 
it  into  a  substance  like  artificial  tannic  acid.  (Mr.  Hatchett.) 

The  researches  of  Durnas  have  shown  that  camphor  is  the  oxide 
of  carnphene,  and  that  the  same  inflammable  compound  by  the  action 
of  nitric  acid  is  still  further  oxidized,  and  then  constitutes  camphoric  acid. 
He  has  gone  far  to  prove  that  the  essential  oils  of  the  second  group  are  solu- 
tions in  variable  proportion  of  camphor  in  liquid  carburets  of  hydrogen.  The 
latter  seem  to  be  the  essential  and  original  material  of  the  oil,  which  by  a 
subsequent  process  of  oxidation  yields  more  or  less  camphor.  From  the  oil 
of  peppermint  exposed  to  a  cold  of  32°,  and  then  compressed  in  bibulous  pa- 
per to  separate  adhering  oil,  he  obtained  a  volatile  crystalline  solid  like  cam- 
phor, the  composition  of  which  is  reducible  to  the  formula  C10H10-f-O. 
A  similar  substance  was  procured  by  congelation  from  oil  of  anise,  the  for- 
mula of  which  is  C10H6-f*O.  Analogous  camphors  may  be  procured  from 
most  of  the  essential  oils,  if  kept  for  some  time  in  a  partially  closed  bottle. 
By  a  more  complete  oxidation,  the  same  compound  radicals  give  rise  to  resi- 
nous matter. 

Oil  of  Cloves. — Dumas  finds  that  the  dense  volatile  oils  are  more  highly 
oxidized  than  the  lighter  ones,  and  are  disposed  to  act  as  acids  in  relation  to 
alkaline  bases.  He  obtained  a  definite  crystalline  compound  of  the  oil  of 
cloves  with  ammonia,  composed  of  175'4  parts  or  one  eq.  of  the  oil,  and  17*15 
parts  or  one  eq.  of  the  alkali.  The  elements  of  the  oil  are  in  the  ratio  of 
122-4  parts  or  twenty  eq.  of  carbon,  13  parts  or  thirteen  eq.  of  hydrogen, 
and  40  parts  or  five  eq.  of  oxygen,  the  formula  being  C20H13-j-5O.  The 
crystalline  solid,  called  caryophylline^  deposited  from  this  oil  by  keeping,  has 
the  same  composition  as  camphor. 

Oil  of  Mustard. — This  oil  differs  from  the  foregoing  in  containing  sulphur 
and  nitrogen.  Dumas  and  Pelouze  found  100  parts  of  the  oil  to  consist  of 
sulphur  20-25,  nitrogen  14-45,  hydrogen  5-02,  carbon  49-98,  and  oxygen  10-3. 
The  carbon,  hydrogen,  and  nitrogen  form,  they  conceive,  a  distinct  compound 
radical,  which  then  combines  with  sulphur  and  oxygen ;  but  their  investiga- 
tion on  the  subject  is  not  yet  fully  reported.  (An.  de  Ch.  et  de  Ph.  liii.  184.) 

OIL  OF  BITTER  ALMONDS.— BENZULE. 

This  oil  differs  from  all  the  preceding  oils,  and  has  lately  led  to  impor. 
tant  discoveries.  When  the  bitter  almond  is  reduced  to  a  pulp  and  sub- 
jected to  compression,  a  pure  fixed  oil  is  obtained ;  but  when  distilled  along 


VOLATILE   OILS.  525 

with  water,  a  volatile  poisonous  oil  passes  over,  which  smells  strongly  of  hy- 
drocyanic acid,  and  contains  a  volatile  oil,  mixed  or  combined  with  that  acid. 
Neither  the  volatile  oil  nor  hydrocyanic  acid  pre-exist  in  the  almond,  but  are 
developed  in  it  by  the  action  of  water  during  the  distillation.  By  mixing  the 
impure  oil  with  a  solution  of  potassa  and  protochloride  of  iron,  agitating1 
strongly,  and  distilling  the  mixture,  the  oil  is  obtained  quite  free  from  hy- 
drocyanic acid  ;  and  by  a  second  distillation  from  pulverized  lime  it  is  de- 
prived of  adhering  moisture. 

The  oil  thus  purified  is  a  colourless  volatile  liquid,  which  retains  its  origi- 
nal odour,  has  a  burning  aromatic  taste,  and  a  density  of  1-043.  It  is  spa- 
ringly soluble  in  water,  but  freely  by  alcohol.  When  suddenly  and  strongly 
heated  in  open  vessels,  it  takes  fire  and  burns  with  flame;  but  it  may  be 
passed  alone  through  a  red-hot  glass  tube  without  decomposition.  In  ex- 
amining its  properties  and  composition,  Liebig  and  Wohler  have  proved  that 
it  may  be  regarded  as  a  compound  of  hydrogen  with  a  substance  called  ben- 
zule  (page  494),  which  consists  of  85-68  parts  or  fourteen  eq.  of  carbon,  5 
parts  or  five  eq.  of  hydrogen,  and  16  parts  or  two  eq.  of  oxygen.  The  for- 
mula of  benzule  is  C14H5O2,  and  its  symbol  is  Bz.  Benzule  has  not  yet 
been  obtained  in  an  uncombined  state;  but  it  is  readily  transferable  with- 
out decomposition  from  one  element  to  another  in  the  same  manner  as  cyan- 
ogen. The  several  compounds  examined  by  Liebig  and  Wohler  are  thus 
constituted  :—  (An  de  Ch.  et  de  Ph.  li.  273.) 
leq. 

Names.  Benzule.  Equiv.    Formulae. 


106-68+Hydrogen       1         1  eq.=107-68  Bz  +  H. 
}  106-68+Oxygen  8        1  eq.=114-68  Bz  +  O  or  Bz. 

\  106'68+Chlorine       35-42   1  eq.  =142-1     Bz  +  Cl. 

Bromide    do.  106-68+Bromme  78-4  1  eq.  =185-08  Bz  4.  Br. 

Iodide        do.  106-68+Iodine  126-3  1  eq.  =232-98  Bz  +  1. 

Sulphuret  do.  106-68  -f-Sulphur  16-1  1  eq.=122-78  Bz-f-S. 

Cyanuret   do.  106'68-r-Cyanogen  26'39  1  eq.  =133-07  Bz-fCy. 

The  purified  oil  is  a  hyduret  of  benzule.     When  heated  with  hydrate  of 
potassa,  the  oil  interchanges  elements  with  the  water,  so  that 

1  eq.  oil.  Bz-f-H  2   1  eq.  anhydrous  benzoic  acid          Bz  +  O 

and  1  eq.  water        H  +  O  -^  and  2  eq.  of  hydrogen  2H  ; 

the  hydrogen  is  evolved  and  benzoate  of  potassa  is  left.     When  exposed  to 
the  air  or  pure  oxygen  gas  the  reaction  is  such  that 

1  eq.  oil  Bz+H  2   1  eq.  anhydrous  benzoic  acid 

and  2  eq.  oxygen     2O        -^  and  1  eq.  water      .  . 


and  these  products  constitute  one  eq.  of  crystallized  benzoic  acid. 

Chloride  of  Benzule.  —  Hyduret  of  benzule  absorbs  chlorine  gas  with  heat, 
hydrochloric  acid  and  chloride  of  benzule  are  generated,  and  the  latter,  after 
being  heated  to  expel  any  excess  of  chlorine,  remains  as  a  limpid  liquid  like 
water.  It  has  a  density  of  M96,  a  peculiar  pungent  odour,  irritates  the 
eyes,  and  boils  at  an  elevated  temperature.  It  is  insoluble  in  water;  but  by 
long  ebullition  with  water,  it  yields  hydrochloric  and  benzoic  acids.  It  may 
be  distilled  from  anhydrous  lime  or  baryta  without  decomposition  ;  but  when 
heated  with  hydrate  of  potassa,  it  yields  chloride  of  potassium  and  benzoate 
of  potassa.  * 

Bromide  of  Benzule.  —  It  is  formed  by  the  action  of  bromine  on  hyduret 
of  benzule;  and  after  expelling  the  excess  of  -bromine  by  heat,  the  bromide 
is  left  as  a  soft  semi-fluid  mass,  consisting  of  large  foliated  crystals  of  a 
brown  colour.  It  is  soluble  without  change  in  alcohol  and  ether.  By  long 
boiling  with  water,  it  is  converted  into  hydrobrornic  and  benzoie  acids. 


526 


VOLATILE  OILS. 


The  iodide  of  benzule  is  obtained  as  a  brown  liquid  by  distilling-  a  mixture 
of  iodide  of  potassium  with  chloride  of  benzule,  and  on  cooling  becomes  a 
crystalline  solid  of  the  same  colour.  When  free  from  mixed  iodine  it  is 
colourless,  and  resembles  the  bromide  in  its  chemical  relations. 

Sulphur  et  of  Benzule.  —  It  is  formed  by  distilling  chloride  of  benzule  with 
sulphuret  of  lead  in  fine  powder,  and  passes  over  as  an  oil-like  fluid,  which 
on  cooling-  becomes  a  soft  crystalline  solid  of  a  yellow  colour.  Its  odour 
resembles  that  of  sulphur.  It  is  not  changed  by  the  action  of  water,  and  is 
but  slowly  resolved  by  a  boiling  solution  of  potassa  into  benzoate  of  potassa 
and  sulphuret  of  potassium. 

Cyanuret  of  Benzule.  —  It  is  obtained  by  distilling  the  chloride  of  benzule 
with  bicyanuret  of  mercury,  and  collects  in  the  recipient  as  an  oily  fluid  of 
a  yellow  colour.  By  distillation  it  is  rendered  colourless,  but  the  yellow 
colour  quickly  returns.  Its  vapour  has  a  strong  penetrating  odour,  and 
irritates  the  eyes.  By  water,  in  which  it  is  otherwise  insoluble,  it  is  speedi- 
ly converted  into  hydrocyanic  and  henzoic  acids. 

Benzamide.  —  Chloride  of  benzule  has  the  property  of  absorbing,  with 
mucli  heat,  dry  arnmoniacal  gas,  and  of  forming  a  white  solid,  which  after 
complete  saturation  with  ammonia,  consists  wholly  of  hydrochlorate  of  am- 
monia arid  benzamide.  By  cold  water  the  former  is  dissolved,  and  the 
latter  insulated.  It  derives  its  name  from  the  fact  that  it  bears  to  benzoate 
of  ammonia  the  same  relation  as  oxamide  to  oxalate  of  ammonia  (page  481.) 

Pure  benzamide  fuses  at  23.9°  into  a  limpid  liquid,  which  concretes  into  a 
foliated  mass  on  cooling.  When  strongly  heated  it  boils,  and  passes  over 
unchanged.  It  is  very  sparingly  dissolved  by  cold  water,  but  readily  and 
without  decomposition  in  boiling  water.  It  is  very  soluble  in  alcohol,  and 
is  dissolved  by  boiling  ether.  By  evaporation  from  its  solutions  it  crystal- 
lizes in  right  rhomboidal  prisms  of  a  pearly  Justre.  With  a  solution  of 
potassa  in  the  cold  it  is  not  changed,  and  emits  no  odour  of  ammonia;  but 
when  boiled  with  the  alkaline  solution,  ammonia  is  disengaged,  and  benzoate 
of  potassa.  is  found  in  solution.  The  same  change  is  effected  by  boiling  it 
in  a  solution  of  sulphuric  acid. 

In  the  action  of  ammonia  on  chloride  of  benzule 


1  eq.  chloride        C"H«O»  +  C1  2  j  l  e 

and  2  eq.  ammonia  2  (3H-J-N)    '>*    and  1  eq.  benzamide  C14H5O2-J-H3N. 

It  is  obvious  that 

1  eq.  benzamide  CI4H5O2-f.HQN  2  1  eq.  anhyd.  benzoic  acid  C14H5O2+O 
and  1  eq.  water  H-f-O  •£  and  1  eq.  ammonia  3H  +  N. 

I  have  theoretically  represented  benzamide  as  a  compound  of  benzule  with 
dinituret  of  hydrogen;  but  other  hypotheses  maybe  formed  respecting  its 
constitution,  as  in  the  case  of  oxamide. 

Benzoine.  —  The  oil  of  bitter  almonds,  like  several  other  essential  oils,  has 
been  observed  to  deposite  a  crystalline  matter,  which  is  formed  abundantly 
when  the  oil  is  left  for  a  few  weeks  in  a  corked  bottle  in  contact  with  a 
strong  solution  of  potassa.  It  has  at  first  a  yellow  tint;  but  by  solution  in 
boiling  alcohol,  and  digestion  with  animal  charcoal,  it  may  be  obtained  pure 
and  white.  It  crystallizes  from  its  alcoholic  solution  in  transparent  pris- 
matic crystals,  which  fuse  at  248°,  and  may  be  distilled  without  change. 
It  has  neither  taste  nor  odour.  Liebig  and  Wohler  found  its  elements  to 
coincide  exactly  with  those  of  the  original  oil  which  yielded  it,  though 
doubtless  their  arrangement  is  very  different. 

Coumarin.  —  This  name  was  first  applied  to  the  odoriferous  principle  of 
the  Tonka  bean  by  M.  Guibourt,  and  has  since  been  adopted  by  MM.  Boul- 
lay  and  Boutron-Charhrd.  (Journ.  de  Pharmacie,  1825.)  It  is  derived 
from  the  term  Coumarouna  odorata,  given  by  Aublet  to  the  plant  which 
yields  the  bean. 


RESINOUS  SUBSTANCES.  527 

Coumarin  is  white,  of  a  hot  pungent  taste,  and  distinct  aromatic  odour. 
It  crystallizes  sometimes  in  square  needles,  and  at  other  times  in  short 
prisms.  It  is  moderately  hard,  fracture  clean,  lustre  considerable,  and  den- 
sity greater  than  that  of  water.  It  fuses  at  a  moderate  temperature  into  a 
transparent  fluid,  which  yields  an  opaque  crystalline  mass  on  cooling. 
Heated  in  close  vessels,  it  is  sublimed  without  change.  It  is  sparingly 
soluble  in  water ;  but  is  readily  dissolved  by  ether  and  alcohol,  and  the  solu- 
tions crystallize  by  spontaneous  evaporation.  It  is  very  soluble  in  fixed  and 
volatile  oils, 

Vogel  mistook  coumarin  for  benzoic  acid  ;  Boullay  and  Boulron-Chalard 
maintain  that  it  has  neither  an  acid  nor  alkaline  reaction,  and  that  it  is  a 
peculiar  independent  principle,  nearly  allied  to  the  essential  oils.  These 
chemists  did  not  find  any  benzoic  acid  in  the  Tonka  bean,  and  consider 
coumarin  as  the  sole  cause  of  its  odour. 


RESINOUS  SUBSTANCES, 

Resins, — Resins  are  the  inspissated  juices  of  plants,  and  commonly  occur 
either  pure  or  in  combination  with  an  essential  oil.  They  are  solid  at  com- 
mon  temperatures,  brittle,  inodorous,  arid  insipid.  They  are  non-conductors 
of  electricity,  and  when  rubbed  become  negatively  electric.  They  are  gene* 
rally  of  a  yellow  colour,  and  semi-transparent. 

Resins  are  fused  by  the  application  of  heat,  and  by  a  still  higher  tempera* 
ture  are  decomposed.  In  close  vessels  they  yield  ernpyreumatic  oil,  and  a 
large  quantity  of  carburetted  hydrogen,  a  small  residue  of  charcoal  remain^ 
ing.  In  the  open  air  they  burn  with  a  yellow  flame  and  much  smoke,  being 
resolved  into  carbonic  acid  and  water. 

Resins  are  dissolved  by  alcohol,  ether,  and  the  essential  oils,  and  the  alco- 
holic and  ethereal  solutions  are  precipitated  by  water,  a  fluid  in  which  they 
are  quite  insoluble.  Their  best  solvent  is  pure  potassa  and  soda,  and  they 
are  also  soluble  in  the  alkaline  carbonates  by  the  aid  of  heat.  The  product 
is  in  each  case  a  soapy  compound,  which  is  decomposed  by  an  acid. 

Concentrated  sulphuric  acid  dissolves  resins ;  but  the  acid  and  the  resin 
mutually  decompose  each  other,  with  disengagement  of  sulphurous  acid, 
and  deposition  of  charcoal.  Nitric  acid  acts  upon  them  with  violence,  con- 
verting them  into  a  species  of  tannin,  which  was  discovered  by  Mr.  Hatchett. 
No  oxalic  acid  is  formed  during  the  action. 

The  uses  of  resin  are  various.  Melted  with  wax  and  oil,  resins  constitute 
ointments  and  plasters.  Combined  with  oil  or  alcohol,  they  form  different 
kinds  of  oil  and  spirit  varnish.  Sealing-wax  is  composed  of  lac,  Venice 
turpentine,  and  common  resin.  The  composition  is  coloured  black  by 
means  of  lampblack,  or  red  by  cinnabar  or  red  lead.  Lampblack  is  the  soot 
of  imperfectly  burned  resin. 

Of  the  different  resins  the  most  important  are  common  resin,  copal,  lac, 
sandarach,  mastich,  elemi,  and  dragon's  blood.  The  first  is  procured  by 
heating  turpentine,  which  consists  of  oil  of  turpentine  and  resin,  so  as  to 
expel  the  volatile  oil.  The  common  turpentine  obtained  by  incisions  made 
in  the  trunk  of  the  Scotch  fir-tree  (Pinus  sylvestri^  is  employed  for  this 
purpose;  but  the  other  kinds  of  turpentine,  such  as  Venice  turpentine,  that 
from  the  larch  (Pinus  larix},  Canadian  turpentine  from  the  Pinus  balsamea, 
or  the  Strasburgh  turpentine  from  the  Pinus  picea,  yield  resin  by  a  similar 
treatment. 

When  turpentine  is  extracted  from  the  wood  of  the  fir-tree  by  heat,  par- 
tial decomposition  ensures,  and  a  dark  substance,  consisting  of  resin,  empy- 
reumalic  oil,  and  acetic  acid  is  the  product.  This  constitutes  tar;  and  when 
inspissated  by  boiling,  it  forms  pitch.  Common  resin  fuses  at  276°,  is  com- 
pletely liquid  at  306°,  and  at  about  316°  bubbles  of  gaseous  matter  escape, 
giving  rise  to  the  appearance  of  ebullition.  By  distillation  it  yields  ernpy- 
reumatic oils:  in  the  first  part  of  the  process  a  limpid  oil  passes  over,  which 


528  RESINOUS  SUBSTANCES. 

rises  in  vapour  at  300°,  and  boils  at  360° ;  but  subsequently  the  product 
becomes  less  and  less  limpid,  till  towards  the  close  it  is  very  thick.  This 
matter  becomes  limpid  when  heat  is  applied,  and  boils  at  about  500°  F.  At 
a  red  heat  resin  is  entirely  decomposed,  yielding  a  large  quantity  of  com- 
bustible gas,  which  is  employed  for  the  purpose  of  artificial  illumination. 

Amber. — This  substance  is  brought  chiefly  from  the  southern  coast  of  the 
Baltic,  occurring  sometimes  in  beds  of  bituminous  wood,  and  at  others  on 
the  shore,  being  doubtless  washed  out  from  strata  of  brown  coal  by  the 
action  of  water.  Its  vegetable  origin  is  amply  attested  by  the  substances 
with  which  it  is  associated,  by  its  resinous  nature,  and  by  the  vegetable 
matters  which  it  frequently  envelopes.  It  is  commonly  met  with  in  trans- 
lucent pieces  of  various  shades  of  yellow  and  brown ;  but  it  is  sometimes 
transparent.  Its  specific  gravity  varies  from  1-065  to  1-07.  It  may  be  re- 
garded as  a  mixture  of  several  substances  ;  namely,  a  volatile  oil,  succinic 
acid,  separable  like  the  former  by  heat,  two  different  modifications  of  resin 
both  soluble  in  alcohol  and  ether,  and  a  peculiar  bituminous  matter,  which 
is  insoluble  in  alcohol  and  ether,  and  is  the  most  abundant  principle  in 
amber.  (Berzelius.) 

Balsams. — The  balsams  are  native  compounds  of  resin  and  benzoic  acid, 
and  issue  from  incisions  made  in  the  trees  which  contain  them,  in  the  same 
manner  as  turpentine  from  the  fir.  Some  of  them,  such  as  storax  and  ben- 
zoin, are  solid  ;  while  others,  of  which  the  balsams  of  Tolu  and  Peru  are 
examples,  are  viscid  fluids. 

Gum-resins. — The  substances  to  which  this  name  is  applied  are  the  con- 
crete juices  of  certain  plants,  and  consist  of  resin,  essential  oil,  gum,  and 
extractive  vegetable  matter.  The  two  former  principles  are  soluble  in  alco- 
hol and  the  two  latter  in  water.  Their  proper  solvent,  therefore,  is  proof 
spirit.  Under  the  class  of  gum-resins  are  comprehended  several  valuable 
medicines,  such  as  aloes,  ammoriiacum,  assafcetida,  euphorbiurn,  galbanum, 
gamboge,  myrrh, "scamrnony,  and  guaiacum. 

Caoutchouc,  commonly  called  elastic  gum  or  Indian  rubber,  is  the  con- 
crete juice  of  the  H&vea  caoutchouc  and  Jalropha  elastica,  natives  of  South 
America,  and  of  the  Ficus  Indica  and  Artocarpus  integrifolia,  which  grow 
in  the  East  Indies.  It  is  a  soft  yielding  solid,  of  a  whitish  colour  when  riot 
blackened  by  smoke,  possesses  considerable  tenacity,  and  is  particularly  re- 
markable for  its.  elasticity.  It  is  inflammable,  and  burns  with  a  bright 
flame.  It  is  insoluble  in  water  and  alcohol;  but  it  dissolves,  though  with 
some  difficulty,  in  pure  ether.  It  is  very  sparingly  dissolved  by  the  alkalies, 
but  its  elasticity  is  destroyed  by  their  action.  By  the  sulphuric  and  nitric 
acids  it  is  decomposed,  the  former  causing  deposition  of  charcoal,  and  the 
latter  formation  of  oxalic  acid. 

Caoutchouc  is  soluble  in  the  essential  oils,  ether,  naphtha,  cajuput  oil,  and 
in  the  volatile  liquid  obtained  by  distilling  caoutchouc;  and  from  all  these 
solvents,  except  the  essential  oils,  it  is  left  on  evaporation  without  loss  of  its 
elasticity.  Before  actually  dissolving,  the  caoutchouc  swells  up  remarkably, 
and  acquires  a  soft  gelatinous  aspect  and  consistency  :  in  this  state  it  is 
used  for  rendering  cloth  and  leather  impervious  to  water,  and,  as  suggested 
by  Dr.  Mitchell  of  Philadelphia,  may  be  cut  with  a  wet  knife  into  thin 
sheets  or  bottles,  and  be  extended  to  a  great  size.* 


*  Dr.  Mitchell  has  favoured  me  with  the  following  description  of  his  pe- 
culiar mode  of  preparing  bags  of  caoutchouc  of  large  size  : — "  Soak  the 
common  bags  in  sulphuric  ether,  sp.  gr.  0-753,  at  a  temperature  not  less 
than  50°  Fahr.  for  a  period  of  time  not  less  than  one  week  (the  longer  the 
better).  Empty  the  bag,  wipe  it  dry,  put  into  it  some  dry  powder,  such  as 
starch,  insert  a  tube  into  the  neck,  and  fasten  it  by  a  broad  soft  band  slightly 
applied,  and  then  commence  by  mouth  or  bellows  the  inflation.  If  the 
bag  be  unequal  in  thickness,  restrain  by  the  hand  the  bulging  of  the  thinner 


RESINOUS  SUBSTANCES.  529 

When  caoutchouc  is  cautiously  heated,  it  fuses  without  decomposition  ; 
but  at  a  higher  temperature  it  is  resolved  into  a  volatile  liquid  of  a  brown 
colour,  which  amounts  to  8-10ths  of  the  original  caoutchouc.  When  care- 
fully rectified,  a  very  volatile  liquid  of  sp.  gr.  0-64  is  obtained,  which  is  very 
combustible  and  burns  with  a  bright  flame,  mingles  with  alcohol,  and  dis- 
solves copal  and  other  resins.  It  is  manufactured  in  large  quantity  by 
Messrs.  Enderby,  of  London,  and  is  very  useful  as  a  solvent  for  caoutchouc 
and  for  the  preparation  of  varnishes. 

Wax. — This  substance,  which  partakes  of  the  nature  of  a  fixed  oil,  is  an 
abundant  vegetable  production,  entering  into  the  composition  of  the  pollen 
of  flowers,  covering  the  envelope  of  the  plum  and  other  fruit,  especially  the 
berries  of  the  Myrica  cm/era,  and  in  many  instances  forming  a  kind  of 
varnish  to  the  surface  of  leaves.  From  this  circumstance  it  was  long  sup- 
posed that  wax  is  solely  of  vegetable  origin,  and  that  the  wax  of  the  honey- 
comb is  derived  from  flowers  only  ;  but  it  appears  from  the  observations  of 
Huber  that  it  must  likewise  be  regarded  as  an  animal  product,  since  ho 
found  bees  to  deposite  wax,  though  fed  on  nothing  but  sugar.  Consistently 
with  this  remark  it  has  been  proved  by  Oppermann  that  pure  vegetable  wax 
differs  from  bees-wax  in  the  ratio  of  its  elements.  (An.  de  Ch.  et  de  Ph. 
xlix.  240.) 

Common  wax  is  always  more  or  less  coloured,  and  has  a  distinct  peculiar 
odour,  of  both  which  it  may  be  deprived  by  exposure  in  thin  slices  to  light, 
air,  and  moisture,  or  more  speedily  by  the  action  of  chlorine.  At  ordinary 
temperatures  it  is  solid,  and  somewhat  brittle ;  but  it  may  easily  be  cut 
with  a  knife,  and  the  fresh  surface  presents  a  characteristic  appearance,  to 
which  the  name  of  waxy  lustre  is  applied.  Its  specific  gravity  is  0'96.  At 
about  150°  it  enters  into  fusion,  and  boils  at  a  high  temperature.  Heated  to 
redness  in  close  vessels  it  suffers  complete  decomposition,  yielding  products 
very  similar  to  those  which  are  procured  under  the  same  circumstances 
from  oil.  As  it  burns  with  a  clear  white  light,  it  is  employed  for  forming 
candles. 

Wax  is  insoluble  in  water,  and  is  only  sparingly  dissolved  by  boiling 
alcohol  or  ether,  from  which  the  greater  part  is  deposited  on  cooling.  It  is 
readily  attacked  by  the  fixed  alkalies,  being  converted  into  a  soap  which  is 
soluble  in  hot  water ;  and  according  to  Pfaff,  the  action  is  attended,  as  in 
oils,  with  the  formation  of  an  acid,  to  which  the  name  of  eerie  acid  is  ap- 
plied. It  unites  by  the  aid  of  heat  in  every  proportion  with  the  fixed  and 
volatile  oils,  and  with  resin.  With  different  quantities  of  oil  it  constitutes 
the  simple  liniment,  ointment,  and  cerate  of  the  Pharmacopoeia. 

Wax,  according  to  the  observations  of  John,  consists  of  two  different 
principles,  one  of  which  is  soluble,  and  the  other  insoluble  in  alcohol.  To 
the  former  he  has  given  the  name  of  cerin,  and  to  the  latter  of  myricin.  It 
has  been  thought  that  these  principles  are  generated  in  the  wax  by  the  alcohol 
used  in  separating  them  ;  but  the  opinion  of  John  is  supported  by  a  fact  men- 
tioned to  me  by  Dr.Christison,  namely  that  the  suetty  matter  of  the  cinnamon 
berry  consists,  with  the  exception  of  a  little  oil,  entirely  of  cerin,  without  any 
myricin. 


parts,  until  the  thicker  have  been  made  to  give  way  a  little.  When  the  bag 
has  become  by  such  means  nearly  uniform,  inflate  a  little  more,  shake  up 
the  included  starch,  and  let  the  bag  collapse.  Repeat  the  inflation,  and 
carry  it  to  a  greater  extent,  again  permit  the  collapse,  again  inflate  still  more 
extensively,  and  so  on,  until  the  bag  is  sufficiently  distended.  Mere  gas 
holders  are  thus  easily  made,  but  it  requires  some  dexterity  and  experience 
to  make  them  thin  enough  for  balloons.  The  whole  experiment  should  not 
oocupy  more  than  from  five  to  twenty  minutes  of  time ;  and  the  prepared 
bag  should  be  closed  and  hung  up  to  dry  for  a  day  or  two." — Ed. 

45 


530  BITUMINOUS  SUBSTANCES. 


BITUMINOUS  SUBSTANCES. 

Under  this  title  are  included  several  inflammable  substances  which, 
though  of  vegetable  origin,  are  found  in  the  earth,  or  issue  from  its  surface. 
They  may  be  conveniently  arranged  under  the  two  heads  of  bitumen  and 
pit-coal.  The  first  comprehends  naphtha,  petroleum,  mineral  tar,  asphaltum , 
mineral  pitch,  and  retinasphaltum,  of  which  the  first  three  mentioned  are 
liquid,  and  the  others  solid.  The  second  comprises  brown  coal,  the  different 
varieties  of  common  or  black  coal,  and  glance  coal. 


BiTUMEtf. 

The  composition  of  naphtha,  the  purest  form  of  bitumen,  has  already 
been  given  (page  248). 

Petroleum  is  much  less  limpid  than  naphtha,  has  a  reddish-brown  colour, 
and  is  unctuous  to  the  touch.  It  is  found  in  several  parts  of  Britain  and  the 
continent  of  Europe,  in  the  West  Indies,  and  in  Persia.  It  occurs  particu- 
larly in  coal  districts. 

Mineral  tar  is  very  similar  to  petroleum,  but  is  more  viscid  and  of  a 
deeper  colour.  Both  these  species  become  thick  by  exposure  to  the  atmos- 
phere, arid  in  the  opinion  of  Mr.  Hatchett  pass  into  solid  bitumen. 

Asphaltum  is  a  solid  brittle  bitumen,  of  a  black  colour,  vitreous  lustre, 
and  conchoidal  fracture.  It  melts  easily,  and  is  very  inflammable.  It  emits 
a  bituminous  odour  when  rubbed,  and  by  distillation  yields  a  fluid  like 
naphtha.  It  is  soluble  in  about  five  times  its  weight  of  naphtha,  arid  the 
solution  forms  a  good  varnish.  It  is  rather  denser  than  water. 

Asphaltum  is  found  on  the  surface  and  on  the  banks  of  the  Dead  Sea, 
and  occurs  in  large  quantity  in  Barbadoes  and  Trinidad.  It  was  employed 
by  the  ancients  in  building,  and  is  said  to  have  been  used  by  the  Egyptians 
in  embalming. 

Mineral  Pitch  or  Maltha  is  likewise  a  solid  bitumen,  but  is  much  softer 
than  asphaltum.  Elastic  bitumen,  or  mineral  caoutchouc,  is  a  rare  variety 
of  mineral  pitch,  found  only  in  the  Odin  mine,  near  Castleton-in  Derby- 
shire. 

Relinasphaltum  is  a  peculiar  bituminous  substance,  found  associated 
with  the  brown  coal  of  Bovey  in  Devonshire  (Phil.  Trans.  1804).  It  con- 
sists partly  of  bitumen,  and  partly  of  resin,  a  composition  which  led  Mr. 
Hatchett  to  the  opinion  that  bitumens  are  chiefly  formed  from  the  resinous 
principle  of  plants. 

Inflammable  Principles  of  Tar. 

Among  the  products  of  the  destructive  distillation  of  vegetable  and  ani- 
mal substances  is  a  black  inflammable  liquid  called  tar,  which  in  aspect 
resembles  the  tar  from  fir  (page  527).  A  large  quantity  is  formed  during 
the  distillation  of  wood,  and  in  the  preparation  of  coal  gas.  The  tar  obtain- 
ed from  such  sources  has  been  the  subject  of  an  elaborate  inquiry  by  Dr. 
Reichenbach,  of  Blansko,  who  has  discovered  in  it  no  fewer  than  six  new 
principles  ;  namely,  paraffine,  eupione,  creosote,  picamar,  capnomor,  and 
pittacal.  The  original  essays  of  Reichenbach  appeared  in  Schweigger- 
Seidel's  Journal  for  1830  and  the  following  years. 

Cr€0£0/e.— This  substance  exists  in  solution  in  crude  pyroligneous  acid ; 
but  it  i^best  prepared  from  those  portions  of  the  oil  distilled  from  wood-tar, 
which  are  heavier  than  water.  The  oil  is  first  freed  from  adhering  acetic 
acid  by  carbonate  of  potassa,  and,  after  separation  from  the  acetate,  is  dis- 
tilled. A  little  phosphoric  acid  is  mixed  with  the  product  to  neutralize 
ammonia,  and  another  distillation  resorted  to.  It  is  next  mixed  with  a 


BITUMINOUS  SUBSTANCES.  531 

strong  solution  of  potassa,  which  combines  with  creosote,  allows  any 
eupione  which  may  be  present  to  collect  on  its  surface,  and  by  digestion 
decomposes  other  organic  matter :  the  alkaline  solution  is  then  neutralized 
by  sulphuric  acid,  and  the  oil  which  separates  is  collected  and  distilled. 
For  the  complete  purification  of  the  creosote,  this  treatment  with  potassa, 
followed  by  neutralization  and  distillation,  requires  to  be  frequently  re- 
peated. 

Creosote  is  a  colourless  transparent  liquid  of  an  oily  consistence,  which 
retains  its  fluidity  at  —17°,  has  a  sp.  gr.  of  1-037  at  68°,  boils  at  397°,  is 
a  non-conductor  of  electricity,  and  refracts  light  powerfully.  It  has  a  burn- 
ing taste  followed  by  sweetness,  and  its  odour  is  like  that  of  wood-smoke  or 
rather  of  smoked  meat.  It  is  highly  antiseptic  to  meat:  the  antiseptic  vir- 
tue of  tar,  smoke,  and  crude  pyroligneous  acid  seems  owing  to  the  presence 
of  creosote.  Its  name,  from  *gg*?  flesh,  and  <ra>£a>  I  save,  was  suggested  by 
this  property. 

Creosote  requires  about  80  parts  of  water  for  solution,  and  is  soluble  in 
every  proportion  in  alcohol,  ether,  sulphuret  of  carbon,  eupione,  and  naphtha. 
It  has  neither  an  acid  nor  alkaline  reaction  with  test-paper,  but  combines 
both  with  acids  and  alkalies.  With  potassa,  soda,  lime,  and  baryta  it  forms 
compounds  soluble  in  water ;  but  the  creosote  is  separated  even  by  feeble 
acids.  Of  the  acids,  it  unites  most  readily  with  the  acetic,  dissolving  in  every 
proportion :  by  strong  nitric  and  sulphuric  acid  it  is  decomposed,  Creosote 
unites  also  with  chlorine,  iodine,  bromine,  sulphur,  and  phosphorus. 

Creosote  acts  powerfully  in  coagulating  albumen,  this  effect  being  produced 
by  a  solution  of  one  drop  in  a  large  quantity  of  water.  It  acts  with  energy 
on  living  beings.  Insects  and  fish  thrown  into  the  aqueous  solution  of  cre- 
osote are  killed,  and  plants  die  when  watered  with  it.  It  appears  useful  in 
medicine  :  it  is  said  to  be  very  efficacious  as  a  topical  application  in  toothach, 
ulcers,  and  cutaneous  diseases ;  and  it  probably  admits  of  many  other  appli- 
cations. 

Creosote  is  a  compound  of  carbon,  hydrogen,  and  oxygen,  but  the  ratio  of 
its  elements  is  not  yet  known. 

Picamar. — This  substance  is  the  bitter  principle  of  tar,  whence  it  derives 
its  name  (in  pice  amarum}.  It  is  present  in  the  heaviest  portions  of  the  rec- 
tified oil  of  tar,  and  when  these  are  treated  by  potassa,  a  crystalline  com- 
pound of  the  alkali  and  picamar  is  formed:  this  compound,  when  purified  by 
repeated  solution  in  water  and  crystallization,  is  decomposed  by  phosphoric 
acid,  and  the  picamar  separated  by  distillation. 

Picamar  is  an  oily  colourless  liquid,  of  a  peculiar  odour  and  very  bitter 
taste.  Its  sp.  gr,  is  1-100,  and  it  boils  at  545°,  being  considerably  less  vola- 
tile than  creosote.  It  is  insoluble  in  eupione  and  sparingly  soluble  in  water  ; 
but  it  dissolves  without  limit  in  alcohol  and  ether.  It  has  no  action  on  test- 
paper  ;  but  it  unites  with  potassa  as  above  mentioned,  and  strong  sulphuric 
acid  dissolves  it  without  decomposition.  From  its  permanence  in  the  air,  its 
fixity  when  heated,  and  its  oily  nature,  it  is  well  adapted  for  greasing  machi- 
nery and  protecting  it  from  rust.  Its  composition  is  unknown. 

Capnomor. — This  substance  occurs  along  with  creosote,  picamar,  and  pit- 
tacal  in  the  heavy  oil  of  tar.  On  digesting  that  oil  with  solution  of  potassa, 
the  three  latter  principles  are  dissolved,  and  the  capnomor  collects  on  the 
surface,  combined  with  a  little  eupione.  The  capnomor  is  then  dissolved  by 
sulphuric  acid,  in  which  eupione  is  insoluble ;  and  from  the  solution,  on  being 
neutralized  with  carbonate  of  potassa,  capnomor  separates,  and  is  purified  by 
distillation.  Its  name  is  derived  from  HATTVOS  smoke,  and  ^oco/g*  part,  because 
it  is  one  of  the  ingredients  of  smoke. 

Capnomor  is  a  colourless  transparent  liquid,  of  a  pungent  taste  and  rather 
pleasant  odour,  has  a  sp.  gr.  of  0-975,  and  refracts  light  almost  as  power- 
fully as  creosote.  It  boils  at  365°.  It  is  insoluble  in  water  and  solution  of 
potassa,,  and  is  soluble  in  alcohol,  ether,  and  eupione.  It  has  the  property 
of  dissolving  caoutchouc,  especially  when  heated,  and  is  the  only  ingredient 
of  tar  which  does  so :  its  presence  in  coal  naphtha  is  the  cause  of  the  sol- 


532  BITUMINOUS  SUBSTANCES. 

vent  action  of  that  liquid  on  caoutchouc.  The  composition  of  capnomor 
has  not  been  ascertained,  though  doubtless  carbon  and  hydrogen  are  its 
principal  ingredients. 

Pittacal. — When  the  heavy  oil  of  tar  is  digested  with  a  solution  of  ba- 
ryta, a  fine  blue  colour  appears,  which  is  due  to  pittacal,  from  KITTA  pitch, 
and  **AAo?  ornament.  The  mode  of  preparing  it  has  not  been  described, 
It  is  a  solid  of  a  beautiful  blue  colour,  which  admits  of  being  fixed  as  a  dye* 
It  is  very  permanent,  contains  nitrogen  as  one  of  its  elements,  and  appears 
to  belong  to  the  same  class  of  bodies  as  indigo, 

PIT-COAL. 

p 

Brown  Coal  is  characterized  by  burning  with  a  peculiar  bituminous  odour, 
like  that  of  peat.  It  is  sometimes  earthy,  but  the  fibrous  structure  of  the 
wood  from  which  it  is  derived  is  generally  more  or  less  distinct,  and  hence 
this  variety  is  called  bituminous  wood.  Pitch  coal  or  jet,  which  is  employed 
for  forming  ear-rings  and  other  trinkets,  is  intermediate  between  brown 
and  black  coal,  but  is  perhaps  more  closely  allied  to  the  former  than  the 
latter. 

Brown  coal  is  found  at  Bovey  in  Devonshire  (Bovey  coal),  in  Iceland, 
where  it  is  called  surturbrand,  and  in  several  parts  of  the  continent,  espe- 
cially at  the  Meissner  in  Hessia,  in  Saxony,  Prussia,  and  Styria. 

Common  or  Black  Coal. — Of  the  common  or  black  coal  there  are  several 
varieties,  which  differ  from  each  other,  not  only  in  the  quantity  of  foreign 
matters,  such  as  sulphuret  of  iron  and  earthy  substances,  which  they  con- 
tain, but  also  in  the  proportion  of  what  may  be  regarded  as  essential  consti- 
tuents. Thus  some  kinds  of  coal  consist  almost  entirely  of  carbonaceous 
matters,  and,  therefore,  form  little  flame  in  burning ;  while  others,  of  which 
canriel  coal  is  an  example,  yield  a  large  quantity  of  inflammable  gases  by 
heat,  and  consequently  burn  with  a  large  flame.  Dr.  Thomson  has  arranged 
the  different  kinds  of  coal  which  are  met  with  in  Britain  into  four  subdivi- 
sions. (An.  of  Phil,  xiv.)  The  first  is  caking  coal,  beciause  its  particles  are 
softened  by  heat  and  adhere  together,  forming  a  compact  mass.  The  coal 
found  at  Newcastle,  around  Manchester,  and  many  other  parts  of  England, 
is  of  this  kind.  The  second  is  termed  splint  coal,  from  the  splintery  appear- 
ance of  its  fracture.  The  cherry  coal  occurs  in  Staffordshire,  and  in  the 
neighbourhood  of  Glasgow.  Its  structure  is  slaty,  and  it  is  more  easily 
broken  than  splint  coal,  which  is  much  harder.  It  easily  takes  fire,  and  is 
consumed  rapidly,  burning  with  a  clear  yellow  flarne.  The  fourth  kind  is 
cannel  coal,  which  is  found  of  peculiar  purity  at  Wigan  in  Lancashire.  In 
Scotland  it  is  known  by  the  name  of  parrot  coal.  From  the  brilliancy  of  the 
light  which  it  emits  while  burning,  it  is  sometimes  used  as  a  substitute  for 
candles,  a  practice  which  is  said  to  have  led  to  the  name  of  cannel  coal.  It 
has  a  very  compact  structure,  does  not  soil  the  fingers  when  handled,  and 
admits  of  being  polished.  Snuff-boxes  and  other  ornaments  are  made  with 
this  coal;  and  it  is  peculiarly  well  fitted  for  forming  coal  gas.  According  to 
the  experiments  of  Thomson,  these  varieties  of  coal  are  thus  constituted : — 

Caking  Coal.  Splint  Coal.  Cherry  Coal.  Cannel  Coal. 
Carbon             75-28                   75-00                     74-45  64-72 

Hydrogen         4-18  6-25  12-40  21-56 

Nitrogen         15-96  6-25  10-22  13-72 

Oxygen  4-58  12-50  2-93  0-00 

100-00  100-00  100-00  100-00 

Judging  from  the  quantity  of  oxidized  products  (water,  carbonic  acid,  and 
carbonic  oxide)  which  are  procured  during  the  distillation  of  coal,  Henry  in- 
fers that  coal  contains  more  oxygen,than  was  found  by  Thomson.  (Elements, 
lllh  Edit.  ii.  p.  348.)  This  opinion  is  supported  by  the  analysis  of  Ure,  who 
found  26*66  per  cent,  of  oxygen  in  splint,  and  21'9  in  cannel  coal.  When 


SPIRITUOUS  AND  ETHEREAL  SUBSTANCES.  533 

coal  is  heated  to  redness  in  close  vessels,  a  great  quantity  of  volatile  matter 
is  dissipated,  and  a  carbonaceous  residue,  called  coke,  remains  in  the  retort. 
The  volatile  substances  are  coal  tar,  acetic  acid,  water,  hydrosulphuric  acid, 
and  hydrosulphate  and  carbonate  of  ammonia,  together  with  the  several 
gases  formerly  enumerated.  The  greater  part  of  these  substances,  even 
most  of  the  bituminous  principles,  are  real  products,  that  is,  are  generated 
during  the  distillation. 

Glance  Coal.—' Glance  coal,  or  anthracite,  differs  from  common  coal,  which 
it  frequently  accompanies,  in  containing-  no  bituminous  substances,  and  in 
not  yielding  inflammable  gases  by  distillation.  Its  sole  combustible  ingre- 
dient is  carbon,  and  consequently  it  burns  without  flame.  It  commonly 
occurs  in  the  immediate  vicinity  of  basalt,  under  circumstances  which  lead 
to  the  suspicion  that  it  is  coal  from  which  the  volatile  ingredients  have  been, 
expelled  by  subterranean  heat.  At  the  Meissner,  in  Hessia,  it  is  found  be* 
tween  a  bed  of  brown  coal  and  basalt.  Kilkenny  coal  appears  to  be  a  variety 
of  glance  coal.  (Thomson,  An.  of  Phil.  vol.  xv.) 


SECTION    V. 

SPIRITUOUS  AND  ETHEREAL  SUBSTANCES. 

ALCOHOL. 

ALCOHOL  is  the  intoxicating  ingredient  of  all  spirituous  and  vinous  liquors. 
It  does  not  exist  ready  formed  in  plants,  but  is  a  product  of  the  vinous  fer- 
mentation, the  theory  of  which  will  be  stated  in  a  subsequent  section. 

Common  alcohol  or  spirit  of  wine  is  prepared  by  distilling  whisky  or 
some  ardent  spirit,  and  the  rectified  spirit  of  wine  is  procured  by  a  second 
distillation.  The  former  has  a  specific  gravity  of  about  0  867,  and  the  lat- 
ter of  0-835  or  0-84.  In  this  state  it  contains  a  quantity  of  water,  from 
which  it  may  be  freed  by  the  action  of  substances  which  have  a  strong 
affinity  for  that  liquid.  Thus,  when  carbonate  of  potassa  heated  to  300°  is 
mixed  with  spirit  of  wine,  the  alkali  unites  with  the  water,  forming  a  dense 
solution,  which,  on  standing,  separates  from  the  alcohol,  so  that  the  latter 
may  be  removed  by  decantation.  To  the  alcohol,  thus  deprived  of  part  of 
its  water,  fresh  portions  of  the  dry  carbonate  are  successively  added,  until  it 
fills  through  the  spirit  without  being  moistened.  Other  substances,  which 
have  a  powerful  attraction  for  water,  may  be  substituted  for  carbonate  of  po- 
tassa. Gay-Lussac  recommends  the  use  of  pure  lime  and  baryta  (An.  de 
Ch.  Ixxxvi.);  and  dry  alumina  may  also  be  employed.  A  very  convenient 
process  is  to  mix  the  alcohol  with  chloride  of  calcium  in  powder,  or  with 
quicklime,  and  draw  off  the  stronger  portions  by  distillation.  Another  pro- 
cess, which  has  been  recommended  for  depriving  alcohol  of  water,  is  to  put 
it  into  the  bladder  of  an  ox,  and  suspend  it  over  a  sand-bath.  The  water 
gradually  passes  through  the  coats  of  the  bladder,  while  the  pure  alcohol  is 
retained;  but  though  this  method  answers  well  for  strengthening  weak 
spirit,  its  power  of  purifying  strong  alcohol  is  very  questionable.  CJournal  of 
Science,  xviii.)  The  strongest  alcohol  which  can  be  procured  by  any  of 
these  processes  has  a  specific  gravity  of  0-796  at  60°  F.  This  is  called  abso- 
lute alcohol,  to  denote  its  entire  freedom  from  water. 

An  elegant  and  easy  process  for  procuring  absolute  alcohol  has  been  pro- 
posed by  Mr.  Graham.  (Eclin.  Philos.  Trans.  1828.)  A  large  shallow  basin 
is  covered  to  a  small  depth  with  quicklime  in  coarse  powder,  and  a  smaller 
oiie  containing  three  or  four  ounces  of  commercial  alcohol  is  supported  just 

45* 


534  ALCOHOL. 

above  it.  The  whole  is  placed  upon  the  plate  of  an  air-pump,  covered  by  a 
low  receiver,  and  the  air  withdrawn  until  the  alcohol  evinces  signs  of  ebul- 
lition. Of  the  mingled  vapours  of  water  and  alcohol  which  fill  the  receiver, 
the  former  alone  is  absorbed  by  the  quicklime,  while  the  latter  is  unaffected. 
Now  it  is  found  that  water  cannot  remain  in  alcohol,  unless  covered  by  an 
atmosphere  of  its  own  vapour ;  and  consequently  the  water  continues  to 
evaporate  without  interruption,  while  the  evaporation  of  the  alcohol  is  en- 
tirely arrested  by  the  pressure  of  the  vapour  of  alcohol  on  its  surface.  Com- 
mon alcohol  is  in  this  way  entirely  deprived  of  water  in  the  course  of  about 
five  days.  The  temperature  should  be  preserved  as  uniform  as  possible 
during  the  process.  Sulphuric  acid  cannot  be  substituted  for  quicklime, 
since  both  vapours  are  absorbed  by  this  liquid. 

Alcohol  is  a  colourless  limpid  fluid,  of  a  penetrating  odour,  and  burning 
taste.  It  is  highly  volatile,  boiling,  when  its  density  is  0-820,  at  the  tempe- 
rature of  176°  F.  The  sp.  gravity  of  its  vapour,  according  to  Gay-Lussac, 
is  1-613.  Like  volatile  liquids  in  general,  it  produces  a  considerable  degree 
of  cold  during  evaporation.  It  has  hitherto  retained  its  fluidity  under  every 
degree  of  cold  to  which  it  has  been  exposed. 

Alcohol  is  highly  inflammable,  and  burns  with  a  lambent  yellowish-blue 
flame.  Its  colour  varies  considerably  with  the  strength  of  the  alcohol,  the 
blue  tint  prenominating  when  it  is  strong,  and  the  yellow  when  it  is  diluted. 
Its  combustion  is  not  attended  with  the  least  degree  of  smoke,  and  the  sole 
products  are  water  and  carbonic  acid.  When  transmitted  through  a  red- 
hot  tube  of  porcelain,  it  is  resolved  into  carburetted  hydrogen,  carbonic 
oxide,  and  water,  and  the  tube  is  lined  with  a  small  quantity  of  charcoal. 

Alcohol  unites  with  water  in  every  proportion.  The  act  of  combining  is 
usually  attended  with  diminution  of  volume,  so  that  a  mixture  of  50  mea- 
sures of  alcohol  and  50  of  water  occupies  less  than  100  measures.  Owing  to 
this  circumstance,  the  action  is  accompanied  with  increase  of  temperature. 
Since  the  density  of  the  mixture  increases  as  the  water  predominates,  the 
strength  of  the  spirit  may  be  estimated  by  its  sp.  gravity.  Equal  weights 
of  absolute  alcohol  and  water  constitute  proof  spirit,  the  density  of  which  is 
0'917;  but  the  proof  spirit  employed  by  the  colleges  for  tinctures  has  a  sp. 
gravity  of  0-930,  or  0-935. 

Of  the  salifiable  bases  alcohol  can  alone  dissolve  potassa,  soda,  lithia,  am- 
monia, and  the  vegetable  alkalies.  None  of  the  earths  or  other  metallic 
oxides  are  dissolved  by  it.  Most  of  the  acids  attack  it  by  the  aid  of  heat, 
giving  rise  to  a  class  of  bodies  to  which  the  name  of  ether  is  applied.  All  the 
salts  which  are  either  insoluble,  or  sparingly  soluble  in  water,  are  insoluble 
in  alcohol.  The  efflorescent  salts  are,  likewise,  for  the  most  part  insoluble 
in  this  menstruum ;  but,  on  the  contrary,  it  is  capable  of  dissolving  nearly 
all  the  deliquescent  salts,  except  carbonate  of  potassa.  Many  of  the  vegeta- 
ble principles,  such  as  sugar,  manna,  camphor,  resins,  balsams,  and  the  es- 
sential oils,  are  soluble  in  alcohol. 

The  solubility  of  certain  substances  in  alcohol  appears  owing  to  the  for- 
mation of  definite  compounds,  which  are  soluble  in  that  liquid.  This  has 
been  proved  of  the  chlorides  of  calcium,  manganese,  and  zinc,  and  of  the 
nitrates  of  lime  and  magnesia,  by  Mr.  Graham  in  the  essay  above  cited.  It 
appears  from  his  experiments  that  all  these  bodies  unite  with  alcohol  in  de- 
finite proportion,  and  yield  crystalline  compounds,  which  are  deliquescent 
and  soluble  both  in  water  and  alcohol.  From  their  analogy  to  hydrates, 
Mr.  Graham  has  applied  to  them  the  name  of  alcoates.  These  are  formed 
by  dissolving  the  substances  in  absolute  alcohol  by  means  of  heat,  when  on 
cooling  a  group  of  crystals  more  or  less  irregular  is  deposited.  The  salt  and 
alcohol  employed  for  the  purpose  should  be  quite  anhydrous ;  for  the  crys- 
tallization is  prevented  by  a  very  small  quantity  of  water.  Estimating  the 
combining  proportion  of  alcohol  at  23  24,  the  alcoate  of  chloride  of  calcium 
is  composed  of  one  equivalent  of  chloride  of  calcium,  and  three  equivalents 
and  a  half  of  alcohol.  Nitrate  of  magnesia  crystallizes  with  nine  equivalents 
of  alcohol ;  nitrate  of  lime  with  two  and  a  half  equivalents ;  protochloride  of 


ETHER.  535 

manganese  with  three  equivalents;  and  chloride  of  zinc  with  half  an  equiva- 
lent of  alcohol. 

The  following  statement  of  the  components  of  alcohol  is  drawn  from  an 
analysis  by  Saussure  (An.  de  Ch.  Ixxxix.) : — 

Carbon  52-17  12-24  2C       or        24-48  4C 

Hydrogen        13-04  3  3H  6  6H 

Oxygen  34-79  8  O  16  2O 

100-00  23-24        CaH3O  4648        C4H6Oa. 

Chemists  are  not  agreed  about  the  equivalent  of  alcohol.  It  is  usually  con- 
sidered as  23-24  or  23,  an  opinion  supported  by  the  composition  of  the  al- 
coates  above  mentioned  ;  but  some  circumstances  favour  the  adoption  of  twice 
that  number,  agreeably  to  the  second  of  the  preceding  formulae.  Admitting 
23-24  as  its  equivalent,  100  measures  of  the  vapour  of  alcohol  may  be  viewed 
as  consisting  of  100  measures  of  olefiant  gas  and  100  of  aqueous  vapour; 
since  0-9808  (sp.  gr.  of  olefiant  gas)+0-6202  (sp.  gr,  of  aqueous  vapour) 
=1-6009,  which  closely  coincides  with  the  observed  sp.  gravity  of  the  vapour 
of  alcohol.  The  formula  of  alcohol  will  in  this  case  be  H2CS-J-H;  and  alco- 
hol is  really  resolved  into  olefiant  gas  and  water  by  the  action  of  galvanism 
(Ritchie).  Adopting  46-48  as  the  equivalent  of  alcohol,  then  it  may  be  viewed 
as  a  compound  of  etherine  (page  248)  and  aqueous  vapour,  H4C4-|-2H ;  or  as 
a  hydrate  of  ether  formed  of  equal  volumes  of  the  vapours  of  ether  and  wa- 
ter, united  without  condensation.  On  both  hypotheses,  the  calculated  density 
of  the  vapour  of  alcohol  agrees  with  observation. 

Alcohol  exists  ready  formed  in  wine  and  spirituous  liquors,  and  may  be 
collected  without  heat.  Mr.  Brande  (Phil.  Trans.  1811  and  1813)  procured 
it  from  wine  by  precipitating  the  acid  and  extractive  colouring  matters  by 
subacetate  of  lead,  and  then  depriving  the  alcohol  of  water  by  dry  carbonate 
of  potassa :  the  pure  alcohol  may  then  be  measured  in  a  graduated  tube. 
Gay-Lussac  obtained  alcohol  from  wine  by  distilling  it  in  vacuo  at  the  tem- 
perature of  60°  F.  He  also  succeeded  in  separating  the  alcohol  by  the  me- 
thod of  Mr.  Brande ;  but  he  suggests  the  employment  of  litharge  in  fine 
powder,  instead  of  subacetate  of  lead,  for  precipitating  the  colouring  matter. 
(Mem.  d'Arcueil,  vol.  iii.) 

The  preceding  researches  of  Mr.  Brande  led  him  to  examine  the  quantity 
of  alcohol  contained  in  spirituous  and  fermented  liquors.  According  to  his 
experiments,  brandy,  rurn,  gin,  and  whisky,  contain  from  51  to  54  per  cent, 
of  alcohol,  of  specific  gravity  0-825.  The  stronger  wines,  such  as  Lissa, 
Raisin  wine,  Marsala,  Port,  Madeira,  Sherry,  Teneriffe,  Conslantia,  Malaga, 
Bucellas,  Calcavella,  and  Vidonia,  contain  from  between  18  or  19  to  25  per 
cent,  of  alcohol.  In  Claret,  Sauterne,  Burgundy,  Hock,  Champagne,  Her- 
mitage, and  Gooseberry  wine,  the  quantity  is  from  12  to  17  per  cent.  In 
cider,  perry,  ale,  and  porter,  the  quantity  varies  from  4  to  near  10  per  cent 
In  all  spirits,  such  as  brandy  or  whisky,  the  alcohol  is  simply  combined 
with  water;  whereas  in  wine  it  is  in  combination  with  mucilaginous,  sac- 
charine, and  other  vegetable  principles,  a  condition  which  tends  to  diminish 
the  action  of  the  alcohol  upon  the  system.  This  may,  perhaps,  account  for 
the  fact  that  brandy,  which  contains  little  more  than  twice  as  much  real  al- 
cohol as  good  port  wine,  has  an  intoxicating  power  which  is  considerably 
more  than  double. 

ETHER. 

Most  of  the  stronger  acids,  when  heated  with  alcohol,  give  rise  to  the 
formation  of  a  volatile  inflammable  liquid  called  ether,  the  different  kinds  of 
which  are  further  distinguished  by  the  name  of  the  acid  with  which  they 
were  prepared.  Thus  by  sulphuric,  hydrochloric,  and  oxalic  ether  are 
meant  the  ethers  formed  by  means  of  sulphuric,  hydrochloric,  and  oxalic 
acid.  Most  of  these  ethers  actually  contain  the  acid,  or  the  elements  of  the 


536  ETHER. 

acid,  employed  in  their  production,  and,  therefore,  differ  essentially  from  each 
other ;  but  that  which  is  formed  by  means  of  sulphuric  and  phosphoric  acid 
is  a  definite  compound  of  carbon,  hydrogen,  and  oxygen,  and  is  altogether 
free  from  acid.  It  is  to  this  compound  the  generic  term  ether  will  always 
be  applied. 

In  the  usual  process  for  preparing  ether,  strong  sulphuric  acid  is  gently 
poured  upon  an  equal  weight  of  rectified  spirit  of  wine  contained  in  a  thin 
glass  retort,  and  after  mixing  the  fluids  together  by  agitation,  which  occa- 
sions a  sudden  rise  of  temperature,  the  mixture  is  heated  as  rapidly  as  pos- 
sible until  ebullition  commences.  At  the  beginning  of  the  process  nothing 
but  alcohol  passes  over  ;  but  as  soon  as  the  liquid  boils,  ether  is  generated, 
and  condenses  in  the  recipient,  which  is  purposely  kept  cool  by  the  applica- 
tion of  ice  or  moist  cloths.  When  a  quantity  of  ether  is  collected,  equal  in 
general  to  about  half  of  the  alcohol  employed,  white  furnes  begin  to  appear 
in  the  retort.  At  this  period,  the  process  should  be  discontinued,  or  the  re- 
ceiver  changed ;  for  although  ether  does  not  cease  to  be  generated,  its  quan- 
tity is  less  considerable,  and  several  other  products  make  their  appearance  : 
thus  on  continuing  the  operation,  sulphurous  acid  is  disengaged,  and  a  yel- 
lowish liquid,  commonly  called  ethereal  oi/,  or  oil  of  wine,  passes  over  into  the 
receiver.  If  the  heat  be  still  continued,  a  large  quantity  of  olefiant  gas  is 
disengaged,  and  all  the  phenomena  ensue  which  were  mentioned  in  the  de- 
scription of  that  compound.  (Page  251.) 

Ether,  thus  formed,  is  always  mixed  with  alcohol,  and  generally  with  some 
sulphurous  acid.  To  separate  these  impurities  the  ether  should  be  agitated 
with  a  strong  solution  of  potassa,  which  neutralizes  the  acid,  while  the 
water  unites  with  the  alcohol.  The  ether  is  then  distilled  by  a  very  gentle 
heat,  and  may  be  rendered  still  stronger  by  distillation  from  chloride  of 
calcium. 

Pure  ether  is  a  colourless  limpid  liquid,  of  a  hot  pungent  taste,  and  fra- 
grant odour.  Its  sp.  gr.  is  0-700,  or  0-632  according  to  Lovitz;  but  that  of 
the  shops  is  074,  or  even  greater,  owing  to  the  presence  of  some  alcohol 
and  water.  Its  volatility  is  very  great :  under  the  atmospheric  pressure, 
ether  of  sp.  gr.  0-720  boils  at  96°  or  98°,  and  at  —40°  in  a  vacuum.  Its 
evaporation,  from  the  rapidity  with  which  it  occurs,  occasions  intense  cold, 
sufficient  in  a  cool  atmosphere  for  freezing  mercury.  The  sp.  gr.  of  its  va- 
pour was  found  by  Gay-Lussac  to  be  2-586.  At  — 46°  it  is  congealed. 

Ether  combines  with  alcohol  in  every  proportion,  but  is  very  sparingly  so- 
luble in  water.  When  agitated  with  water,  the  greater  part  separates  on 
standing,  a  small  quantity  being  retained,  which  imparts  an  ethereal  odour  to 
the  water.  The  ether  so  washed  is  very  free  from  alcohol,  which  combines 
by  preference  with  the  water. 

Ether  is  highly  inflammable,  burning  with  a  yellow  flame,  and  formation 
of  water  and  carbonic  acid.  With  oxygen  gas  its  vapour  forms  a  mixture, 
which  explodes  violently  on  the  approach  of  flame,  or  by  the  electric  spark. 
On  being  transmitted  through  a  red-hot  porcelain  tube  it  undergoes  decom- 
position, and  yields  the  same  products  as  alcohol. 

When  a  coil  of  platinum  wire  is  heated  to  redness,  and  then  suspended 
above  the  surface  of  ether  contained  in  an  open  vessel,  the  wire  instantly  be- 
gins to  glow,  and  continues  in  that  state  until  all  the  ether  is  consumed. 
During  this  slow  combustion,  pungent  acrid  fumes  are  emitted,  which,  if 
received  in  a  separate  veesel,  condense  into  a  colourless  liquid  possessed  of 
acid  properties.  Professor  Daniell,  who  prepared  a  large  quantity  of  it,  was 
at  first  inclined  to  regard  it  as  a  new  acid,  which  he  described  under  the 
name  oflampic  acid ;  but  he  has  since  ascertained  that  its  acidity  is  owing 
to  acetic  acid,  which  is  combined  with  some  compound  of  carbon  and  hy- 
drogen different  both  from  ether  and  alcohol.  (Journal  of  Science,  vi.  and 
xii.)  Alcohol,  when  similarly  burned,  likewise  yields  acetic  acid. 

If  ether  is  exposed  to  light  in  a  vessel  partially  filled,  and  which  is  fre- 
quently  opened,  it  gradually  absorbs  oxygen,  and  a  portion  of  acetic  acid  is 
generated.  This  change  was  first  noticed  by  M,  Planche,  and  has  been 


ETHER, 


537 


confirmed  by  Gay-Lussac.  (An.  de  Ch.  et  de  Ph.  ii.  98  and  213.)    M.  Henry 

of  Paris  attributes  its  developement  to  acetic  ether,  which  he  believes  to  be 

always  contained  in  sulphuric  ether. 

The  solvent  properties  of  ether  are  less  extensive  than  those  of  alcohol.    It 

dissolves  the  essential  oils,  resins,  and  most  of  the  fatty  principles.     Some  of 

the  vegetable  alkalies  are  soluble  in  it,  and  it  dissolves  ammonia ;  but  the 

fixed  alkalies  are  insoluble  in  ether. 

From  the  analyses  of  Saussure,  and  Dumas  and  Boullay,  the  composition 

of  pure  ether  is  admitted  to  be  as  follows  : — 

Carbon        .        .        64-96  24-48        4  eq.  4C 

Hydrogen  .        13-47  5  5  eq.  5H 

Oxygen       .        .        21-57  8  1  eq.  O 


100-00 


37-48 


leq. 


C4H5O 


On  comparing  the  composition  of  ether  with  that  of  alcohol,  it  will  be 
obvious  that  these  compounds  may  be  regarded  as  hydrates  of  etherine : 
— thus 

Alcohol.  Ether. 

Etherine    .        .        28-48        H4C4  28-48      H4C4 


Water 


18 


2H 


H 


46-48        H4C4-f-2H       37-48      H4C4+H. 


Recent  discoveries  in  organic  chemistry  have  induced  Berzelius  to  regard 
ether  as  the  oxide  of  a  compound  inflammable  body  called  ethule  or  ethyle 
(from  ether  and  V\H  principle) ;  and  his  opinion  has  been  ably  supported  by 
Liebig  (An  de  Ch.  et  de  Ph.  Iv.  113).  On  this  supposition  ethule  consists  of 
four  eq.  of  carbon  and  five  eq.  of  hydrogen,  H5C4,  so  that  the  formula  of  ether 
is  H5C4+O,  a  constitution  analogous  to  that  of  camphor.  It  may  be  urged 
against  this  view  that  ethule  has  not  been  obtained  in  a  separate  form,  and 
that  the  sp.  gr.  of  the  vapours  of  alcohol  and  ether  is  exactly  such  as  would 
be  expected  from  hydrates  of  etherine  ;  but  as  a  theory  it  applies  at  least  as 
well  as  the  former  theory.  This  will  appear  from  the  following  comparative 
view,  which  represents  the  composition  of  the  principal  compounds  described 
in  this  section,  agreeably  to  both  theories.  Etherine  is  expressed  symbolically 
by  En,  and  ethule  by  El : 


Alcohol 
Ether 

Sulpho-vinic  acid 
Ethero-sulphuric  acid 


orEnH3 
En + H  or  EnH 
EnHa+2S 
EnH-r-2S 


Ethero-phosphoric  acid       EnH  +  P 


El+HorElH. 
El +O  or  El. 
E1H+2S. 
E1+2S. 
El-i-P.' 


Oil  of  wine 
Hydrochloric  ether 
Hydriodic  ether 
Hydrobromic  ether 

Nitrous  ether 
Oxalic  ether 


2En  +  2S 
En  +  HCl 
En  +  HI 
En  +  HBr 

EnH+N 
EnH-f-Ox 


E1  +  C1. 
El  +  I. 
El  +  Br. 

El-f-N. 
El-fOx. 


538 


Benzoic  ether     .  .  EnH-J-B  El+B. 

Acetic  ether       .  .  EnH+A  El-fA. 

Tartaric  ether    .  .  EnH-f-T  E1-|-"T. 

Pyroxylic  spirit  .  En-J-H  E1+2O. 

Sulpho-vinic  Acid. — This  acid  was  first  noticed  in  the  year  1800  by  M. 
Dabit,  and  has  since  hcen  studied  by  Sertuerner,  Vogel,  and  Gay-Lussac. 
and  more  lately  by  Serullas,  Hennell,  Wohler  and  Liebig,  and  Magnus. 
(An.  de  Ch.  et  do  Ph.  xlvii.  421  ;  Phil.  Trans.  1826  and  1828 ;  and  Pog. 
Annalen,  xxvii.  367.)  It  is  formed  by  the  action  of  strong  sulphuric  acid 
on  alcohol,  and  plays  an  essential  part  in  the  formation  of  ether.  When 
the  ingredients  for  forming"  ether  are  intermixed,  and  before  heat  is  applied, 
nearly  half  of  the  acid  exists  in  the  state  of  sulpho-vinic  acid,  and  may  be 
separated  from  sulphuric  acid  by  neutralizing  the  mixture  with  carbonate  of 
baryta,  when  an  insoluble  sulphate  and  a  soluble  sulpho-vinate  of  baryta  are 
generated,  the  latter  of  which  by  evaporation  may  be  obtained  in  crystals. 
Soluble  sulpho-vinates  of  lime  and  oxide  of  lead  may  be  obtained  in  the  same 
manner ;  and  by  decomposing  a  solution  of  these  salts  by  carbonate  of  po- 
tassa  or  soda,  a  sulpho-vinate  of  these  alkalies  is  formed. 

f  Sulpho-vinic  acid  may  be  procured  in  solution  by  exactly  decomposing 
sulpho-vinate  of  baryta  with  sulphuric  acid;  but  it  has  not  been  obtained  in 
a  dry  state  except  when  combined  with  a  base.  Hennell  considers  the  acid 
to  be  a  compound  of  sulphuric  acid  with  olefiant  gas  or  ethcrine;  but  the 
analyses  of  sulpho-vinate  of  baryta  by  Wohler,  Liebig,  and  Magnus  indicate 
that  it  consists  of  sulphuric  acid  and  alcohol.  The  crystals  of  this  salt 
consist  of 


Probable  Formula. 


Sulphuric  acid  .  .        80-2    2S 

Baryta        .  .  .        76-7     Ba 

Alcohol       .  .  .        46-48  Enlia 

Water         .  ...  .  "      9      H 

On  heating  the  crystals  to  122°.  one  equivalent  of  water  of  crystallization 
is  expelled,  and  the  anhydrous  sulpho-vinate  remains ;  but  on  raising  the 
heat,  alcohol  is  evolved,  and  sulphate  of  baryta  generated.  The  salt  cannot 
exist  as  a  sulpho-vinate  without  possessing  sufficient  water  to  convert  all  its 
etherine  into  alcohol.  Sulpho-vinic  acid  may  be  viewed  as  a  bisulphate  of 
alcohol,  and  sulpho-vinate  of  baryta  as  a  double  sulphate  of  baryta  and  alco- 
hol, in  which  one  half  of  the  acid  is  neutralized  by  alcohol  and  the  other  half 
by  baryta. 

Theory  of  the  Fvrmalion  of  Ether. — It  was  formerly  thought,  as  first  sug- 
gested by  Fourcroy  and  Vauquelin,  that  the  sole  principle  concerned  in  the 
formation  of  ether  was  the  attraction  of  sulphuric  acid  for  water,  by  which 
the  alcohol  was  directly  converted  into  ether.  It  is  apparently  in  this  way 
that  certain  substances  which  are  very  greedy  of  water,  such  as  the  arsenic 
and  fluoboric  acids,  and  the  chlorides  of  tin  and  arsenic,  effect  the  conver- 
sion of  alcohol  into  ether;  but  it  is  now  obvious  that  the  ordinary  process  of 
forming  ether  by  sulphuric  acid,  is  of  a  more  complex  nature.  It  consists 
of  two  distinct  parts  ;  namely,  the  formation  of  sulpho-vinic  acid,  and  the 
subsequent  decomposition  of  that  acid  under  the  joint  agency  of  heat  and 
sulphric  acid.  The  affinities  which  determine  the  formation  of  sulpho- 
vinic  acid  are  the  attraction  of  sulphuric  acid  for  water  and  for  alcohol. 
The  anhydrous  acid  is  divided  between  the  water  and  alcohol  in  such  a 
manner  that 


539 


4  cq.protohydrate  of  sulphuric  acid    4(II+S)  ^   (En-}-2H)-f  2S 

.    "3 
and  1  eq.  of  alcohol  .        .        En  +  2H  '^  and 


The  actual  composition  of  the  hydrated  acid  varies  with  the  strength  of 
the  acid  and  alcohol  which  are  used  :  the  diagram  is  only  intended  to  indi- 
cate that  one-half  of  the  acid  yields  its  water  to  the  other  half,  and  com- 
bines with  alcohol.  Any  excess  of  alcohol  remains  uncombined  in  the 
mixture,  or  rises  in  vapour.  If  the  materials  are  kept  cool,  no  ether  is 
generated;  but  as  soon  as,  on  applying  heat,  the  temperature  rises  to  about 
260°,  the  sulpho-vinic  acid  is  resolved  into  hydrated  sulphuric  acid  arid  ether. 
The  sulpho-vinic  acid  gradually  disappears,  and  all  the  sulphuric  acid  returns 
to  its  original  state  of  a  hydrate,  except  that  it  is  rather  more  diluted  than  at 
first.  The  same,  acid  may  be  employed  to  convert  successive  portions  of 
alcohol  into  ether,  until  it  becomes  too  dilute  to  form  sulphovinic  acid.  Con- 
sistently with  the  foregoing  explanation,  Mr.  liennell  obtained  ether  by  heat- 
ing sulpho-vinate  of  potassa  along  with  strong  sulphuric  acid.  On  distilling 
sulpho-vinate  of  potassa  with  sulphuric  acid,  not  concentrated,  but  diluted 
with  half  its  weight  of  water,  he  procured  alcohol  instead  of  ether.  Hence 
it  seems  that  the  first  effect  of  heat  on  sulpho-vinic  acid  is  to  expel  alcohol, 
which,  if  too  much  water  is  not  present,  is  converted  into  ether  in  the  act  of 
separation. 

Et  hero-sulphuric  Acid.  —  When  the  vapour  of  anhydrous  sulphuric  acid 
is  introduced  into  absolute  alcohol  preserved  at  a  low  temperature,  a  yellow- 
ish oily  liquid  is  formed,  which  consists  of  hydrated  sulphuric  and  ethero- 
sulphuric  acid,  the  latter  consisting  of  sulphuric  acid  and  ether,  in  the  ratio 

indicated  by  the  foruula  EnH-J-2S.  Its  production  is  owing  to  the  water 
and  ether,  which  constitutes  alcohol,  uniting  with  separate  portions  of  anhy- 
drous sulphuric  acid.  On  diluting  the  mixed  acids  with  water,  and  neu- 
tralizing with  carbonate  of  baryta,  an  insoluble  sulphate  and  soluble  ethero- 
sulphate  of  baryta  are  obtained.  The  latter  salt  does  not  crystallize,  and  is 
insoluble  in  alcohol,  in  which  respects  it  differs  from  sulpho-vinate  of  baryta. 
The  ethero-sulphate  ef  baryta,  when  dried  in  vacuo  along  with  sulphuric 
acid,  is  anhydrous,  and  consists  of  one  eq.  of  baryta,  and  one  eq.  of  ethcro- 

sulphuric  acid.     Its  formula  is  Ba-f-(EnH-r-2S). 

Magnus,  who  discovered  this  acid  (Pog,  Annalen,  xxvii.  378),  also  formed 
it  by  the  action  of  anhydrous  sulphuric  acid  on  ether  ;  but  in  this  case  some 
oil  of  wine  was  generated  at  the  same  time,  indicating  the  separation  of  a 
portion  of  ether  into  etherine  and  water.  He  likewise  obtained,  by  partially 
decomposing  ethero-sulphuric  acid  by  heat,  another  acid  of  a  similar  compo- 
sition, the  nature  of  which  is  not  yet  determined. 

Ethero-phosphoric  Acid.  —  It  has  been  known  for  years  that  ether,  identi- 
cal with  that  above  described,  mny  be  formed  by  heating  alcohol  with  con- 
centrated phosphoric  acid  ;  and  Pelouzc  has  lately'  proved  that  its  formation 
is  preceded  by  the  production  of  an  acid  similar  to  the  foregoing.  (An.  de 
Ch.  et  de  Ph.  lii.  37.)  Phosphoric  acid  of  a  sp.  gr.  less  than  1-2  has  no 
effect  on  alcohol  ;  and  if  in  a  state  of  great  concentration,  phosphoric  acid 
decomposes  the  alcohol  entirely,  olefiant  gas  is  disengaged,  a  liquid  like  oil 
of  wine  passes  over,  and  charcoal  is  set  free,  —  phenomena  similar  to  those 
produced  by  an  excess  of  strong  sulphuric  acid,  and  referable  to  the  strong 
affinity  of  those  acids  for  water.  To  prepare  ethero-phosphoric  acid,  mix 
equal  weights  of  absolute  alcohol  and  phosphoric  acid  in  the  state  of  syrup, 
heat  the  mixture  for  a  few  minutes  to  160°,  set  aside  for  twenty-four  hours, 
and  then  dilute  with  seven  parts  of  water  :  the,  solution,  neutralized  by  car- 
bonate of  baryta,  boiled  to  expel  free  alcohol,  and  filtered,  yields  on  cooling 
a  white  ethero-nhosphate  of  baryta  in  hexagonal  larninsB.  A  solution  of 
this  salt,  exactly  decomposed  by  sulphuric  acid,  yields  clliero-phosphoric 
acid. 


540  ETHER. 

Ethero-phosphoric  acid  forms  soluble  salts  with  soda,  potassa,  ammonia, 
baryta,  and  magnesia,  and  insoluble  ones  with  lime,  and  the  oxides  of  lead, 
mercury,  and  silver.  A  moderately  dilute  solution  suffers  very  partial  de- 
composition when  boiled,  which  explains  why  phosphoric  acid  and  alcohol 
yield  but  a  small  portion  of  ether ;  but  if  the  concentrated  acid  is  boiled, 
then  ether,  traces  of  an  oily  matter  like  oil  of  wine,  and  olefiant  gas  are 
evolved,  leaving  at  length  phosphoric  acid  and  charcoal. 

Pelouze  considered  ethero-phosphoric  acid  as  a  compound  of  phosphoric 
acid  and  alcohol,  analogous  to  sulpho-vinic  acid;  but  from  a  subsequent 
analysis  by  Liebig,  it  appears  that  it  is  a  compound  of  phosphoric  acid  and 
ether  (page  537).  The  ethero-phosphate  of  baryta  in  crystals  contains 
twelve  eq.  of  water  of  crystallization,  which  may  be  expelled  by  heat,  leav- 
ing one  eq.  of  acid  and  two  eq.  of  baryta,  2Ba  -f-  (Enll+P).  If  the  ether 
and  baryta  were  regarded  as  two  bases  united  with  phosphoric  acid,  the 

resulting  salt,  (2Ba+EnH)-|-Pi  would  be  analogous  in  composition  to  the 
anhydrous  rhombic  phosphate  of  soda  (page  440). 

Oil  of  Wine. — In  the  process  above  given  for  preparing  ether,  the  quantity 
of  alcohol  perpetually  diminishes,  and  that  of  free  sulphuric  acid  augments, 
the  temperature  of  the  mixture  rises,  and  at  length  the  same  changes  ensue 
as  in  the  preparation  of  olefiant  gas  (page  251).  The  energetic  affinity  for 
water  exerted  by  the  sulphuric  acid  decomposes  the  ether  which  would 
otherwise  be  formed,  olefiant  gas  is  evolved,  and  the  oil  of  wine  collects 
in  the  receiver  in  form  of  a  yellowish  fluid.  It  may  be  obtained  in  greater 
quantity  by  distilling  alcohol  with  an  equal  measure  of  sulphuric  acid. 
The  oil  of  wine  should  be  purified  from  adhering  sulphurous  acid  and  ether 
by  washing  with  water,  and  be  then  dried  in  vacuo  along  with  sulphuric 
acid  and  fused  potassa.  Oil  of  wine  is  also  formed  when  sulpho-vinic  acid 
or  a  sulpho-vinate  is  distilled,  some  alcohol  and  ether  being  first  disen- 
gaged. 

The  oil  of  wine  has  an  oily  consistence,  an  aromatic  odour,  and  a  bitter, 
ish  pungent  taste.  Its  sp.'gr.  is  1-133.  It  is  neutral  to  test  paper,  is 
sparingly  soluble  in  water,  but  more  freely  in  alcohol  and  ether,  from  which 
it  may  be  recovered  by  evaporation.  It  is  said  by  Hennell  to  consist  of 
sulphuric  acid,  united  with  twice  as  much  carbon  and  hydrogen  as  in 
sulpho-vinic  acid,  and  may  be  hence  regarded  as  a  sulphate  of  etherine,  the 

formula  of  which  is  En-|-S  or  2En+2S.  According  to  Serullas  it  also 
contains  half  as  much  water  as  is  associated  in  ether  with  etherine,  its  for- 
mula being  (2En-|-H)-r-2S.  When  evaporated  with  an  alkali,  or  simply 
boiled  along  with  a  little  water,  it  is  converted  into  olefiant  gas  and  sulpho- 
vinic  acid. 

In  the  preparation  of  ether,  the  last  portions  of  that  fluid  contain  oil  of 
wine  in  solution.  On  distilling  such  ether  from  lime,  the  oil  of  wine  is 
changed  into  sulpho-vinic  acid,  which  unites  with  the  lime,  and  another 
oily  matter  is  left,  which  is  lighter  than  water  and  contains  no  sulphuric 
acid.  The  source  and  nature  of  this  oil  have  not  been  determined. 

Hydrochloric  Ether. — This  compound  is  generated  by  the  action  of  hydro- 
chloric acid  on  alcohol,  and  may  be  prepared  by  several  processes  : — by  dis- 
tilling alcohol  previously  saturated  with  hydrochloric  acid  gas,  or  mixed 
with  an  equal  volume  of  strong  hydrochloric  acid;  by  heating  a  mixture 
of  5  parts  of  alcohol,  5  of  strong  sulphuric  acid,  and  12  of  fused  sea-salt  in 
fine  powder ;  or  by  distilling  alcohol  with  the  chlorides  of-tin,  bismuth, 
antimony,  or  arsenic.  The  products  are  transmitted  through  tepid  water, 
by  which  free  alcohol  and  acid  are  absorbed,  and  the  pure  hydrochloric  ether 
is  then  received  in  a  vessel  surrounded  by  ice  or  a  freezing  mixture. 

Hydrochloric  ether  is  a  colourless  liquid,  of  a  penetrating,  somewhat  allia- 
ceous ethereal  odour,  and  a  strong  rather  sweet  taste.  Its  sp.  gr.  at  41°  is 


v** 

!l«=. 

0-774,  and  it  is  so  volatile  that  it  boils  at  about  54°.  It  is  neutral  to  lest 
paper.  When  inflamed,  as  it  issues  from  a  small  aperture,  it  burns  with  an 
emerald-green  flame  without  smoke,  yielding  abundant  vapours  of  hydro- 
chloric acid.  The  elements  of  this  ether  are  in  such  a  ratio  that  it  may  be 
viewed  either  as  a  hydrochlorate  of  etherine  or  a  chloride  of  ethule  (page 
537). 

Hydriodic  Ether. — This  ether,  analogous  in  composition  to  the  foregoing, 
is  most  conveniently  generated  by  distilling  at  a  gentle  heat  2£  parts  of 
iodide  of  phosphorus  with  1  part  of  alcohol  of  sp.  gr.  0*845.  The  product 
is  washed  with  water,  and  then  distilled  from  chloride  of  calcium.  This 
ether  is  colourless,  and  has  a  strong  ethereal  odour,  has  a  sp.gr.  of  1-9206  at 
72°,  and  boils  at  148°. 

Hydrobromic  Ether. — This  ether  is  analogous  to  the  preceding,  and  is 
prepared  by  introducing  into  a  retort  40  parts  of  alcohol  of  sp.  gr.  0-84,  and 
1  of  phosphorus,  to  which  is  added  drop  by  drop  7  or  8  parts  of  bromine, 
and  then  distilling.  By  the  reaction  of  the  phosphorus  and  bromine,  phos- 
phorous and  hydrobromic  acids  are  generated ;  and  the  latter  in  the  nascent 
state  unites  with  etherine.  The  product  should  be  washed  with  water,  to 
which  a  little  potassa  is  added,  in  order  to  separate  adhering  acid  and  al- 
cohol. 

Nitrous  Ether. — The  three  foregoing  etherial  fluids  may  be  viewed  as 
compounds  of  a  hydracid  with  etherine;  but  the  ether  now  to  be  described 
consists  of  an  acid  in  combination  with  sulphuric  ether.  Nitrous  ether  is 
prepared  by  distilling  a  mixture  of  concentrated  nitric  acid  with  an  equal 
weight  of  alcohol;  but  as  the  reaction  is  apt  to  be  exceedingly  violent,  the 
process  should  be  conducted  with  extreme  care.  The  safest  method  is  to 
add  the  acid  to  the  alcohol  by  small  quantities  at  a  time,  allowing  the  mix- 
ture to  cool  after  each  addition  before  more  acid  is  added.  The  distilla- 
tion is  then  conducted  at  a  very  gentle  temperature,  and  the  ether  collected 
in  Woulfe's  apparatus.  During  the  process  there  is  a  disengagement  of 
nitrogen,  protoxide  and  binoxide  of  nitrogen,  and  carbonic  acid  gases,  from 
which  it  is  apparent  that  nitric  acid  is  deoxidized  at  the  expense  of  the  alco- 
hol. According  to  the  researches  of  Dumas  and  Boullay,  its  elements  are 
in  such  proportion  that  it  may  be  viewed  as  a  compound  of  37*48  parts  or 
one  eq.  of  ether,  and  38-15  or  one  eq.  of  hyponitrous  acid  (An.  de  Ch.  et  de 
Ph.  xxxii.  26.) 

The  nitrous  agrees  with  sulphuric  ether  in  its  leading  properties;  but  it  is 
still  more  volatile.  When  recently  distilled  from  quicklime  by  a  gentle  heat, 
it  is  quite  neutral ;  but  it  soon  becomes  acid  by  keeping.  The  products  of 
its  spontaneous  decomposition  are  alcohol,  nitrous  acid,  and  a  little  acetic 
acid.  A  similar  change  is  instantly  effected  by  mixing  the  ether  with  water, 
or  distilling  it  at  a  high  temperature.  It  is  also  decomposed  by  potassa,  and, 
on  evaporation,  crystals  of  the  nitrite  or  hyponitrite  of  that  alkali  are  depo- 
sited (Memoires  d'Arcueil,  i.). 

Oxalic  Ether. — This  ether  is  generated  by  the  action  of  oxalic  acid  on 
common  ether  in- its  nascent  state,  and  is  conveniently  prepared  by  distilling 
1  part  of  alcohol,  and  1  of  binoxalate  of  potassa,  with  2  parts  of  sulphuric 
acid.  At  first  alcohol  and  then  ether  pass  over,  and  lastly  the  oxalic  ether 
collects  as  an  oily  liquid  at  the  bottom  of  the  recipient.  The  alcohol  which 
collects  is  repeatedly  returned  to  the  retort  and  redistilled.  The  oxalic  ether 
is  quickly  washed  with  water,  and  boiled  along  with  litharge  in  fine  powder 
until  the  boiling  print  of  the  liquid  descends  to  362°.  Adhering  water  and 
alcohol  are  thus  dissipated,  and  free  oxalic  acid  combines  with  oxide  of  lead: 
the  oxalic  ether  is  then  decanted  and  distilled.  It  is  apt  to  contain  a  small 
quantity  of  oil  of  wine. 

Oxalic  ether  is  a  colourless  fluid  of  an  oily  aspect,  of  an  aromatic  allia- 
ceous odour,  and  a  sp.  gr.  of  1-0929  at  45°.  It  boils  at  362°.  It  is  neutral 
to  test  paper  when  pure,  is  sparingly  soluble  in  water,  and  dissolves  in  every 
proportion  in  alcohol.  When  kept  for  some  time  it  is  decomposed,  and 
oxalic  acid  separates  in  crystals ;  and  with  alkalies  it  readily  yields  alcohol 

46 


542  ETHER* 

and  oxalic  acid.  According-  to  the  analysis  of  Dumas  and  Boullay,  it  is 
composed  of  36-24  parts  or  one  eq.  of  oxalic  acid,  and  37-48  parts  or  one  eq. 
of  ether. 

When  oxalic  ether  is  hriskly  agitated  with  an  aqueous  solution  of  pure 
ammonia,  a  white  precipitate  is  formed,  which,  after  being-  washed  succes- 
sively with  water  and  alcohol,  was  found  by  Liebig  to  be  pure  oxamide 
(page  481).  Alcohol  is  generated  at  the  same  time,  the  interchange  of  ele- 
ments being  such,  that 

1  eq.  oxalic  ether  (En+H)+(2C-f  3O)  2  1  eq.  oxamide  2C+N-f-2H  +  2O 
and  1  eq.  of  ammonia  3H-f-N.  '£,  and  1  eq.  alcohol  En  +  2H 

When  oxalic  ether  is  agitated  with  alcohol  saturated  with  ammonia,  no 
oxamide  is  formed,  and  the  solution  on  evaporation  yields  crystals,  which 
consist  of  one  eq.  of  oxalic  ether  and  one  eq.  of  oxalate  of  ammonia.  This 
compound  may  be  viewed  as  an  ether-oxalate  of  ammonia,  ether-oxalic  acid 
consisting  of  two  eq.  of  oxalic  acid  and  one  eq.  of  ether,  a  constitution  similar 
to  ethero-sulphuric  acid.  This  compound  and  oxamide  are  both  generated 
when  dry  ammohiacal  gas  is  transmitted  over  oxalic  ether. 

Acetic  Ether. — This  compound  may  be  formed  by  distilling  strong  acetic 
acid  with  an  equal  weight  of  alcohol,  but  it  is  more  readily  produced  by  dis- 
tilling to  dry  ness  3  parts  of  acetate  of  potassa  and  3  of  alcohol  with  2  parts 
of  sulphuric  acid.  In  each  case  a  considerable  quantity  of  free  acetic  acid 
and  alcohol  are  commonly  present,  and  hence  the  product  should  be  re- 
peatedly returned  into  the  retort  and  redistilled.  Fragments  of  chloride  of 
calcium  are  then  introduced,  which  gradually  combines  with  free  alcohol, 
forming,  if  in  quantity,  a  dense  stratum,  from  which  the  acetic  ether  may 
be  removed  by  a  syphon.  If  acetic  acid  is  present,  it  should  be  neutralized 
by  potassa,  and  the  acetic  ether  again  distilled. 

Acetic  ether  is  a  colourless  liquid,  of  an  agreeable  but  burning  taste,  and 
a  very  fragrant  odour.  Its  density  is  0-882  at  65°,  and  it  boils  at  165°.  It 
is  soluble  in  7  or  8  times  its  weight  of  water  at  60°,  and  in  all  proportions 
in  alcohol.  It  may  be  preserved  without  change;  but  if  distilled  with  pure 
potassa  or  lime,  an  acetate  is  formed,  and  alcohol  passes  over.  It  consists  of 
one  eq.  of  acetic  acid  and  one  eq.  of  ether.  Formic  acid,  like  the  acetic, 
forms  an  ether  with  alcohol  without  the  aid  of  any  other  acid. 

Tartaric,  Citric,  and  Malic  Ether,  Sfc. — These  ethereal  fluids  may  be  ob- 
tained by  distilling  their  respective  acids  with  sulphuric  acid  and  alcohol, 
and  in  composition  are  analogous  to  oxalic  and  acetic  ethers.  Kiriic  and 
benzoic  ethers  have  also  been  formed,  and  the  former  is  solid  at  common 
temperatures. 

Cyanuric  Ether.-*-This  ether  was  formed  by  Wohler  by  mixing  the  va- 
pours  of  anhydrous  cyannric  acid  and  alcohol,  and  collects  as  a  white  pow- 
der, nearly  insoluble  in  cold  alcohol.  It  is  soluble  by  aid  of  heat  in  a  mix- 
ture of  alcohol  and  ether,  and  crystallizes  in  colourless  prisms  by  evapora- 
tion. When  heated  in  open  vessels,  it  fuses  and  then  passes  off  in  vapour. 
In  addition  to  cyanuric  acid  and  ether,  it  contains  the  eleme.nts  of  water;  so 
that  it  is  not  analogous  to  the  ethers  previously  described. 

Sulphocyanic  Ether. — The  substance  so  termed,  Liebig  discovered  by  dis- 
tilling  a  mixture  of  1  part  of  sulphocyanuret  of  potassium,  2  of  sulphuric 
acid,  and  3  of  strong  alcohol.  He  believes  it  to  be  a  compound  of  sulphuret 
of  cyanogen  and  a  carburet  of  hydrogen.  (An.  de  Ch.  et  de  Ph.  xli.  202.) 

Chloric  Ether. — This  name  is  sometimes  applied  to  the  compound  of  ole- 
fiant  gas  and  chlorine  (page  252),  and  sometimes  to  an  oily  liquid  prepared 
either  by  distilling  a  mixture  of  sulphuric  acid,  peroxide  of  manganese,  sea- 
salt,  and  alcohol,  or  by  directly  transmitting  chlorine  gas  into  cold  alcohol. 
It  is  probable,  from  the  mode  of  preparation,  that  the  liquid  obtained  from 
chlorine  and  alcohol  is  identical  with  chloral.* 

*  Besides  those  mentioned  in  the  text,  there  is  still  another  variety  of 
chloric  ether,  formed  by  the  reciprocal  action  of  alcohol  and  chloride  of 


ETHER.  543 

Oxidized  Ether. — This  name  has  been  applied  by  Doberciner  to  a  sub- 
stance obtained  by  distilling  alcohol  with  sulphuric  acid  and  peroxide  of 
manganese;  and  a  similar  compound  is  formed  by  placing  alcohol  in  a  dish 
covered  with  an  open  jar,  and  setting  just  over  the  surface  of  the  spirit  some 
moist  spongy  platinum  contained  in  watch-glasses.  The  substance  obtained 
by  the  latter  process  has  been  termed  acetal  by  Liebig  (Pog.  Ann.  xxvii. 
605);  but  the  nature  and  properties  of  these  products  have  not  yet  been  de- 
termined, nor  is  it  certain  that  they  are  definite  compounds. 

Pyroacetic  Spirit. — This  compound  is  generated  by  distilling  the  salts  of 
acetic  acid,  and  is  one  of  the  ingredients  of  wood  tar.  It  was  obtained  by 
Derosne  from  acetate  of  copper,  and  was  called  by  him  pyroacetic  ether. 
Mr.  Chevenix  formed  it  by  distilling  the  acetates  of  manganese,  zinc,  and 
lead.  It  is  purified  from  acetic  acid  and  ernpyreumatic  oil,  xvhich  pass  over 
at  the  same  time,  by  admixture  with  a  solution  of  potassa,  and  redistillation; 
and  it  is  subsequently  rendered  anhydrous  by  distillation  from  dry  carbo- 
nate of  potassa  or  chloride  of  calcium.  It  has  been  examined  by  Macaire 
and  Marcet  (An.  of  Phil.  N.  S.  viiL  69),  and  its  constitution  has  been  deter- 
mined by  Liebig  and  Dumas  (An.  de  Ch.  et  de  Ph.  xlix). 

Pyroacetic  spirit,  when  carefully  purified  from  water,  acid,  and  oil,  is  a 
colourless  limpid  liquid,  highly  volatile  and  inflammable,  of  a  peculiar  pene- 
trating odour  different  from  both  alcohol  and  ether,  and  has  a  density  of 
0-7921  at  64°.  It  boils  at  132°,  and  the  density  of  its  vapour  is  2-019.  It 
unites  with  water,  alcohol,  ether,  and  oil  of  turpentine  in  every  proportion. 
It  may  be  exposed  for  months  to  the  air  without  change,  and  be  distilled 
from  the  alkalies  without  decomposition;  but  it  is  entirely  decomposed  by 
sulphuric  acid  without  the  formation  of  ether. 

When  pyroacetic  spirit  is  distilled  from  a  solution  of  chloride  of  lime,  a 
chloride  of  carbon  is  formed,  consisting  of  five  eq.  of  chlorine  and  four  eq.  of 
carbon.  By  the  action  of  chlorine  gas  hydrochloric  acid  is  formed,  together 
with  a  peculiar  oily  fluid,  which  has  a  density  of  1-331,  and  of  which  100 
parts  contain  52-6  of  chlorine,  28  of  carbon,  2-8  of  hydrogen,  and  16-6  of 
oxygen.  (Liebig.) 

According  to  the  analysis  of  Liebig,  which  is  confirmed  by  Dumas,  pyro- 
acetic spirit  is  composed  of  three  eq.  of  carbon,  three  eq.  of  hydrogen,  and 
one  eq.  of  oxygen.  These  quantities  are  such  that  one  equivalent  of  acetic 
acid,  4C-r-3Fi-|-3O,  exactly  corresponds  to  one  equivalent  of  pyroacetic 
spirit,  3C-f-3[i-|-O,  and  one  equivalent  of  carbonic  acid,  C^j-20.  Accord- 
ingly both  Liebig  and  Dumas  have  observed  that  dry  acetate  of  baryta  is 
converted  by  heat  into  pyroacetic  spirit  and  carbonate  of  baryta. 

Pyroxylic  Spirit. — When  wood  is  heated  in  close  vessels,  it  yields  a  large 
quantity  of  impure  acetic  acid  (pyroligneous  acid),  and  charcoal  of  great 

lirne.  It  was  discovered  by  Mr.  Samuel  Guthrie,  of  the  state  of  New  York, 
who  prepares  it  by  distilling  a  gallon  from  a  mixture  of  three  pounds  of 
chloride  of  lime  and  two  gallons  of  alcohol  of  sp.  gr.  0-844,  and  rectifying 
the  product  by  redistillations,  first  from  a  great  excess  of  chloride  of  lime, 
and  afterwards  from  strong  sulphuric  acid.  About  the  same  time  that 
Guthrie  was  making  his  researches  in  this  country,  the  same  ether  was  dis- 
covered by  Soubeiran  in  France,  who  obtained  it  from  the  same  materials 
which  had  been  employed  by  Guthrie. 

This  ether,  as  obtained  by  Mr.  Guthrie's  process,  is  an  extremely  volatile 
liquid,  of  a  sweetish,  ethereal  odour,  and  hot,  aromatic,  peculiar  taste.  It 
boils  at  166°,  and  has  the  sp.  gr.  of  1-486.  It  is  not  acted  on  by  the  mineral 
acids,  is  slightly  soluble  in  water,  and  soluble  in  all  proportions  in  alcohol. 
When  sufficiently  diluted  with  water,  it  forms  an  aromatic  and  saccharine 
liquid,  very  grateful  to  the  taste,  and  acting  as  a  diffusible  stimulus,  appli- 
cable to  several  states  of  disease.  According  to  Soubeiran,  it  consists  of  two 
eq.  of  chlorine  70-84,  and  one  eq.  of  light  carburctted  hydrogen  8-12=78-96. 
As  this  ether  does  not  contain  chloric  crcirf,  I  have  elsewhere  proposed  for  it 
the  name  of  chlorine  ether,  as  being  more  appropriate. — Ed. 


544  COLOURING   MATTERS. 

purity  remains  in  the  retort.  During  this  process  a  peculiar  spirituous 
liquid  is  formed,  which  was  discovered  in  1812  by  Mr.  P.  Taylor,*  and  soon 
afterwards  examined  by  Macaire  and  Marcet,t  who  proposed  for  it  the  name 
of  pyroxylic  spirit.  This  liquid  is  similar  to  alcohol  in  several  of  its  proper- 
ties, and  may  be  substituted  for  it  in  spirit-lamps,  and  frequently  as  a  sol- 
vent  for  chemical  compounds;  but  it  differs  essentially  from  alcohol  in  not 
yielding  ether  by  the  action  of  sulphuric  acid.  It  has  a  strong  penetrating 
ethereal  odour,  with  a  flavour  like  the  oil  of  peppermint,  and  u  pungent  pepper- 
like  taste.  Its  sp.  gr.  at  65°  is  0-804,  and  it  boils  at  150°.  It  burns  with  a 
blue  flame,  without  residue.  . 

According  to  Liebig,  pyroxylic  spirit  contains  exactly  one  more  equiva- 
lent of  oxygen  than  ether  (page  537);  but  Reichenbach  has  raised  a  doubt 
about  the  existence  of  pyroxylic  spirit  as  a  definite  compound,  maintaining 
it  to  be  a  mixture  of  alcohol  and  pyroacetic  spirit. 


SECTION   VI. 


COLOURING  MATTERS. 

INFINITE  diversity  exists  in  the  colour  of  vegetable  substances ;  but  the 
prevailing  tints  are  red,  yellow,  blue,  and  green,  or  mixtures  of  these  co- 
lours. Colouring  matter  rarely  or  never  occurs  in  an  insulated  state,  but  is 
always  attached  to  some  other  proximate  principle,  such  as  mucilaginous, 
extractive,  farinaceous,  or  resinous  substances,  by  which  some  of  its  proper- 
ties, and  particularly  that  of  solubility,  is  greatly  influenced.  Nearly  all 
kinds  of  vegetable  colouring  matter  are  decomposed  by  the  combined  agency 
of  the  sun's  rays  and  a  moist  atmosphere;  and  they  are  all,  without  excep- 
tion, destroyed  by  chlorine  (page  213).  Heat,  likewise,  has  a  similar  effect, 
even  without  being  very  intense ;  for  a  temperature  between  300°  or  400°, 
aided  by  moist  air,  destroys  the  colouring  ingredient.  Acids  and  alkalies 
commonly  change  the  tint  of  vegetable  colours,  entering  into  combination 
with  them,  so  as  to  form  new  compounds. 

Several  of  the  metallic  oxides,  and  especially  alumina  and  the  oxides  of 
iron  and  tin,  form  with  colouring  matter  insoluble  compounds,  to  which  the 
name  of  lakes  is  applied.  Lakes  are  commonly  obtained  by  mixing  alum  or 
pure  chloride  of  tin  with  a  coloured  solution,  and  then  by  means  of  an  al- 
kali precipitating  the  oxide,  which  unites  with  the  colour  at  the  moment  of 
separation.  On  this  property  are  founded  many  of  the  processes  in  dyeing 
and  calico-printing.  The  art  of  the  dyer  consists  in  giving  a  uniform  and 
permanent  colour  to  cloth.  This  is  sometimes  effected  merely  by  immers- 
ing the  cloth  in  the  coloured  solution;  whereas  in  other  instances  the  affinity 
between  the  colour  and  the  fibre  of  the  cloth  is  so  slight,  that  it  only  re- 
ceives a  stain  which  is  removed  by  washing  with  water.  In  this  case  some 
third  substance  is  requisite,  which  has  an  affinity  both  for  the  cloth  and  co- 
louring matter,  and  which,  by  combining  at  the  same  time  with  each,  may 
cause  the  dye  to  be  permanent.  A  substance  of  this  kind  was  formerly 
called  a  mordant;  but  the  term  basis,  introduced  by  the  late  Mr.  Henry  of 
Manchester,  is  now  more  generally  employed.  The  most  important  bases, 
and  indeed  the  only  ones  in  common  use,  are  alumina,  oxide  of  iron,  and 
oxide  of  tin.  The  two  former  are  exhibited  in  combination  either  with  the 
sulphuric  or  acetic  acid,  and  the  latter  most  commonly  as  the  chloride, 

*  Quarterly  Journal,  xiv.  436.  t  An.  of  Phil.  N.  a  viii.  69. 


COLOURING   MATTERS.  545 

Those  colouring  substances  that  adhere  to  the  cloth  without  a  basis  are  called 
substantive  colours,  and  those  which  require  a  basis,  adjective  colours. 

Various  as  are  the  tints  observable  in  dyed  stuffs,  they  may  all  be  produced 
by  the  four  simple  ones,  blue,  red,  yellow,  and  black;  and  hence  it  will  be 
convenient  to  treat  of  colouring-  matters  in  that  order. 

Blue  Dyes. — Indigo  is  chiefly  obtained  from  an  American  and  Asiatic 
plant,  the  Indigofera,  several  species  of  which  are  cultivated  for  the  purpose. 
It  is  likewise  extracted  from  the  Nerium  tinctorium ;  and  an  inferior  sort  is 
prepared  from  the  Isatis  tinctoria  or  woad^  a  native  of  Europe.  Two  differ- 
ent methods  are  employed  for  its  extraction.  In  one,  the  recent  plant,  cut 
a  short  time  before  its  flowering,  is  placed  in  bundles  in  a  steeping  vat, 
where  it  is  kept  down  with  cross  bars  of  wood,  and  covered  to  the  depth  of 
an  inch  or  two  with  water.  In  a  short  time  fermentation  sets  in,  carbonic 
acid  gas  is  freely  disengaged,  and  a  yellow  solution  is  formed.  In  the 
course  of  ten  or  twelve  hours,  when  its  surface  begins  to  look  green  from 
the  mixture  of  blue  indigo  with  the  yellow  solution,  it  is  drawn  off  into  the 
beating  vat,  where  it  is  agitated  with  paddles,  until  all  the  colouring  matter 
is  oxidized  by  absorbing  oxygen  from  the  atmosphere,  and  is  deposited  in 
the  form  of  blue  insoluble  indigo.  The  other  method  consists  in  drying  ths 
leaves  like  hay,  removing  the  leaf  from  its  stalk  by  threshing,  and  grinding 
the  former  into  powder,  in  which  state  it  is  preserved  for  use.  The  dye  is 
then  extracted  either  by  maceration  in  water  at  the  temperature  of  the  air, 
and  fermentation;  or  by  digestion  in  water  at  150°  or  180°,  without  being 
fermented.  In  either  ease  it  is  beaten  with  paddles  as  before.  (Ure  in 
Journ.  of  Science,  N.  S.  vi.  259,)  The  process  of  fermentation,  by  some 
thought  essential,  may  be  dispensed  with.'  According  to  Mr.  Weston,  how- 
ever, the  dye,  as  contained  in  the  plant,  is  insoluble  in  cold  water;  but  by 
exposure  to  the  air  it  undergoes  a  change,  in  which  oxygen  acts  a  part,  and 
by  which  it  is  rendered  soluble  in  water.  (Journ  of  Science,  N.  S.  v.  296.) 

The  indigo  of  commerce,  which  occurs  in  cakes  of  a  deep  blue  colour 
and  earthy  aspect,  is  a  mixed  substance,  containing,  in  addition  to  salts  of 
magnesia  and  lime,  the  four  following  ingredients: — 1.  a  glutinous  matter  ; 
2.  indigo-brown;  3.  indigo-red ;  4.  indigo-blue.  (Berzelius  in  Lehrbuch, 
iii.  679.) 

1.  The  gluten  is  obtained  by  digesting  finely  pulverized  indigo  in  dilute 
sulphuric  acid,  neutralizing  with  chalk,  and  evaporating  the  filtered  solution 
to  dryness.     The  gluten   is  then  taken  up  by  alcohol,  and  on  evaporation  is 
left   with    the    appearance    of  a   yellow    or    yellowish-brown,  transparent, 
shining  varnish.     Its  odour  is  similar  to  that  of  broth,  and  it  contains  nitro- 
gen as  one  of  its  elements.     It  differs,  however,  from  common  gluten  in  its 
free  solubility  both  in  alcohol  and  water. 

2.  Indigo-brown  has  not  been  obtained  in  a  perfectly  pure  state,  owing  to 
its  tendency  to  unite  both  with   acids    and    alkalies.     With  the  former  it 
yields  in  general  sparingly  soluble,  and  with  the  latter  very  soluble  com- 
pounds, which  have  a  deep  brown   colour.     From  indigo,  freed  from  gluten 
by  dilute  acid,  it  is  separated  by  a  strong  solution  of  potassa  aided  by  gentle 
heat;  arid  after  dilution  with  water,  without  which  it  passes  with  difficulty 
through  paper,  the  liquid  is  filtered.     The  solution  has  a  green  tint,  owing- 
to  some  indigo-blue  being  dissolved,  and  with  sulphuric  acid  yields  a  bulky 
eemi-gelatinous  precipitate  of  a  blackish  colour.     By  dissolving  it  in  solution 
of  carbonate  of  ammonia,  evaporating-  to  dryness,  and  removing  the  soluble 
parts  by  a  small  quantity  of  water,  the  brown  matter  is  freed  from  indigo- 
blue  and   sulphuric  acid.     It  still,  however,  contains  ammonia,  and  though 
this  alkali  may  be  expelled  by  means  of  hydrated  lirne  or  baryta,  the  indigo- 
brown  is  still  impure,  since  it  retains  some  lime  or  baryta  in  combination, 
Like  indigo-gluten  it  contains  a  considerable  quantity  of  nitrogen  as  one  of 
its  elements.     The  indigo-green  of  Chevreul  is  probably  a  mixture  of  this 
substance  with  indigo-blue. 

3.  Indigo-red  is  obtained  by  boiling  indigo,  previously  purified  by  potassa, 
in  successive  portions  of  strong  alcohol  as  long  as  a  red  solution  is  obtained, 

46* 


546  COLOURING  MATTERS. 

The  alcoholic  solutions  are  then  concentrated  by  evaporation,  during  which 
the  indigo-red  is  deposited  as  a  blackish-brown  powder.  The  concentrated 
solution,  of  a  deep  red  colour,  yields  by  evaporation  a  compound  of  indigo- 
red  and  indigo-brown  with  alkali,  which  is  soluble  in  water. 

Indigo-red  is  insoluble  in  water  arid  alkalies ;  but  it  is  soluble,  though 
sparingly,  in  hot  alcohol,  and  rather  more  freely  in  ether.  It  dissolves  in 
strong  sulphuric  acid,  and  forms  a  dark  yellow  liquid  ;  and  with  nitric  acid 
it  yields  a  beautiful  purple  solution,  which  speedily  becomes  yellow  by  de- 
composition. When  heated  in  vacua,  it  yields  a  gray  crystalline  sublimate, 
which,  when  purified  by  a  second  sublimation,  is  obtained  in  minute  trans- 
parent needles,  shining  and  white.  This  substance,  in  its  relation  to  re- 
agents, resembles  indigo-red;  and  especially  by  yielding  with  nitric  acid  a 
similar  purple-red  solution,  which  subsequently  becomes  yellow. 

4.  Indigo  blue. — This  term  is  applied  to  the  real  colouring  matter  of  in- 
digo, which  is  left,  though  not  quite  pure,  after  acting  on  common  indigo 
with  dilute  acid,  potassa,  and  alcohol.  It  is  conveniently  prepared  from  the 
greenish-yellow  solution,  which  dyers  make  by  mixing  indigo  with  green 
vitriol,  hydrate  of  lime,  and  water ;  when  the  indigo  is  deoxidized  by  the 
protoxide  of  iron,  and  yields  a  soluble  compound  with  lime.  On  pouring 
this  solution  into  an  excess  of  hydrochloric  acid,  while  freely  exposed  to 
the  air,  oxygen  gas  is  absorbed,  and  the  indigo  is  obtained  in  the  form  of  a 
blue  powder.  It  may  also  be  procured  in  a  state  of  great  purity  by  subli- 
mation ;  but  this  process  is  one  of  delicacy,  from  the  circumstance  that  the 
subliming  and  decomposing  points  of  indigo  are  very  near  each  other;  and 
minute  directions  have  been  given  by  Mr.  Crum  for  conducting  it  with  suc- 
cess. (An.  of  Phil.  N.  S.  v.)  To  be  sure  of  obtaining  it  quite  pure  by  either 
process,  the  indigo  should  first  be  purified  by  the  action  of  dilute  acid,  potassa, 
and  alcohol. 

Pure  indigo  sublimes  at  550°,  forming  a  violet  vapour  with  a  tint  of  red, 
and  condensing  into  long  flat  acicular  crystals,  which  appear  red  by  reflect- 
ed, and  blue  by  transmitted  light.  It  has  neither  taste  nor  odour,  arid  it  is 
insoluble  in  water,  alkalies,  and  ether.  Boiling  alcohol  takes  up  a  trace  of 
it,  and  acquires  a  blue  tint;  but  it  is  generally  deposited  again  on  standing. 
Nitric  acid  produces  a  change  which  has  already  been  described  (page  502). 
Concentrated  sulphuric  acid,  especially  that  of  Nordhausen,  dissolves  it 
readily,  forming  an  intensely  deep  blue  solution,  commonly  termed  sulphate 
of  indigo,  which  is  employed  by  dyers  for  giving  the  Saxon  blue.  The  in- 
digo during  solution  undergoes  a  change,  and  in  this  modified  state  it  has 
received  the  name  of  cerulin  from  Mr.  Crum,  who  regards  it  as  a  compound 
of  one  equivalent  of  indigo  and  four  of  water.  According  to  Berzelius  the 
solution  is  of  a  more  complicated  nature,  and  contains  the  three  following 
substances:  1.  indigo  -pur pie ;  2.  sulphate  of  indigo;  3.  hyposulphate  of 
indigo. 

Indigo-purple  is  chiefly  formed  when  indigo  is  dissolved  in  English  oil  of 
vitriol,  and  subsides  when  the  solution  is  diluted  with  from  30  to  50  times  its 
weight  of  water.  It  was  first  described  under  the  name  of  phenecin,  from 
qoivt%,  purple,  by  Mr.  Crum,  who  considers  it  a  hydrate  of  indigo  with  two 
equivalents  of  water.  Into  the  dilute  solution,  after  phenecin  is  separated, 
Berzelius  inserts  fragments  of  carefully  washed  flannel,  until  all  the  colour 
is  withdrawn  from  the  liquid.  The  dyed  flannel,  after  the  adhering  acid  is 
entirely  removed,  is  digested  in  water,  with  a  little  carbonate  of  ammonia, 
by  which  means  a  blue  solution  is  obtained,  consisting  of  ammonia  in  com- 
bination with  sulphate  and  hyposulphate  of  indigo.  The  solution  is  evaporated 
to  dryness  at  140C,  and  to  the  residue  is  added  alcohol  of  0-833,  which  dis- 
solves only  the  hyposulphate. 

The  compounds  of  indigo  with  sulphuric  and  hyposulphuric  acid  are 
considered  by  Berzelius,  not  as  salts  in  which  indigo  acts  as  a  base,  but  as 
distinct  acids  of  which  indigo  is  an  essential  ingredient.  Indigo-sulphuric 
acid,  as  sulphate  of  indigo  may,  therefore,  be  called,  is  prepared  by  mixing 
indigo-sulphate  of  ammonia  with  acetate  of  oxide  of  lead,  when  indigo- 


COLOURING  MATTERS.  547 

sulphate  of  that  oxide  subsides.  This  salt  is  suspended  in  water,  and  de- 
composed by  hydrosulphurio  acid :  the  sulphuret  of  lead  is  collected  on  a 
filter;  and  the  filtered  solution,  at  first  colourless  or  nearly  so,  owing  to  de- 
oxidation  of  indigo  by  hydrosulphuric  acid,  but  which  soon  becomes  blue  by 
the  action  of  the  air,  is  evaporated  at  a  temperature  not  exceeding  122°  F. 
The  acid  is  left  as  a  dark  blue  solid,  of  a  sour  astringent  taste,  soluble  in 
water  and  alcohol,  and  capable  of  forming  a  distinct  group  of  salts  with  alka- 
lies. Indigo  -hypo  sulphur  ic  acid  may  be  prepared  by  a  similar  process. 

One  of  the  most  remarkable  characters  of  indigo-blue  is  its  susceptibility 
of  being  deoxidized,  and  thus  returning  to  the  state  in  which  it  appears  to 
exist  in  the  plant,  and  of  again  recovering  its  blue  tint  by  subsequent  oxida- 
tion. The  change  is  effected  by  various  deoxidizing  agents,  such  as  hydro- 
sulphuric  acid,  hydrosulphate  of  amonia,  hydrated  protoxide  of  iron,  or  solu- 
tion of  orpiment  in  potassa.  In  the  deoxidized  state  it  readily  unites  with 
alkaline  substances,  such  as  potassa  or  lime,  and  forms  compounds  which  are 
very  soluble  in  water.  The  method  by  which  dyers  prepare  their  blue  vat 
is  founded  on  these  properties.  A  portion  of  indigo  is  put  into  a  tub  with 
about  three  times  its  weight  of  green  vitriol  and  an  equal  quantity  of  slaked 
lime,  and  water  is  added.  The  protoxide  of  iron,  precipitated  by  lime,  gra- 
dually deoxidizes  the  indigo,  and  in  the  course  of  a  day  or  two  a  yellow  solu- 
tion is  obtained.  When  cotton  cloth  is  moistened  with  this  liquid  and 
exposed  to  the  air,  it  speedily  becomes  green  from  the  mixture  of  colours, 
and  then  blue  ;  and  as  the  blue  indigo  is  insoluble,  and  unites  chemically 
with  the  fibre  of  the  cloth,  the  dye  is  permanent. 

Deoxidized  indigo  has  been  obtained  in  a  separate  state  by  Liebig.  A 
mixture  is  made  with  1*5  parts  of  indigo,  2  of  green  vitriol,  2'5  of  hydrate  of 
lime,  and  50  or  60  of  water  ;  and  after  an  interval  of  24  hours  the  yellow 
solution  is  carefully  drawn  off  by  a  syphon,  and  mixed  with  dilute  hydro- 
chloric acid.  A  thick  white  precipitate  falls,  which  remains  without  change 
if  carefully  excluded  from  oxygen,  and  may  even  be  exposed  to  the  air  when 
quite  dry;  but  it  rapidly  becomes  blue  by  exposure  to  the  atmosphere  while 
moist,  or  by  being  covered  with  aerated  water.  To  this  substance  Liebig 
has  applied  the  name  of  indigogen;  and  he  has  ascertained  that,  in  passing 
into  blue  indigo,  it  absorbs  115  per  cent,  of  oxygen.  The  necessity  for  per- 
fectly excluding  every  source  of  oxygen  renders  the  preparation  of  indigogen 
difficult.  All  the  vessels  employed  in  the  process  should  be  filled  with  hydro- 
gen gas,  the  water  be  freed  from  air  by  boiling,  and  as  a  further  protection  a 
little  sulphate  of  ammonia  is  added  both  to  the  acid  by  which  the  precipitate 
is  made,  and  to  the  water  with  which  it  is  washed. 

The  composition  of  indigogen  and  indigo-blue  will  be  found  at  page  503. 

Red  Dyes. — The  chief  substances  which  are  employed  for  the  red  dye  are 
cochineal,  lac,  archil,  madder,  Brazil  wood,  logwood,  and  safflowcr,  all  of 
which  are  adjective  colours.  The  cochineal  is  obtained  from  an  insect  which 
feeds  upon  the  leaves  of  several  species  of  the  Cactus,  and  which  is  supposed 
to  derive  this  colouring  matter  from  its  food.  It  is  very  soluble  in  water,  and 
is  fixed  on  cloth  by  means  of  alumina  or  oxide  of  tin.  Its  natural  colour  is 
crimson;  but  when  bitartrate  of  potassa  is  added  to  the  solution,  it  yields  a 
rich  scarlet  dye.  The  beautiful  pigment  called  carmine  is  a  lake  made  of 
cochineal  and  alumina,  or  oxide  of  tin. 

The  dye  called  archil  is  obtained  from  a  peculiar  kind  of  lichen,  (Lichen 
roccella)  which  grows  chiefly  in  the  Canary  Islands,  and  is  employed  by  the 
Dutch  in  forming  the  blue  pigment  called  litmus  or  turnsol.  The  colouring 
ingredient  of  litmus  is  a  compound  of  the  red  colouring  matter  of  the  lichen 
and  an  alkali;  and  hence,  on  the  addition  of  an  acid,  the  colouring  matter  is 
get  free,  and  the  red  tint  of  the  plant  is  restored.  Litmus  is  not  only  used  as 
a  dye,  but  is  employed  by  chemists  for  detecting  the  presence  of  a  free 
acid. 

The  colouring  principle  of  logwood  has  been  procured  in  a  separate  state 
by  Chevreul,  who  has  applied  to  it  the  name  ofhematin.  (An  de  Ch.  Ixxxi.) 


548  COLOURING    MATTERS. 

It  is  obtained  in  crystals  by  digesting  the  aqueous  extract  of  logwood  in 
alcohol,  and  allowing  the  alcoholic  solution  to  evaporate  spontaneously. 

Safflovver  is  the  dried  flowers  of  the  Carthamus  tinctorius,  which  is  culti- 
vated in  Egypt,  Spain,  and  in  some  parts  of  the  Levant.  The  pigment 
called  rouge  is  prepared  from  this  dye. 

Madder,  extensively  employed  in  dyeing  the  Turkey  red,  is  the  root  of 
the  Rubia  linctorum.  A  red  substance,  supposed  to  be  the  chief  colouring 
principle  of  the  plant,  has  been  obtained  in  an  insulated  state  by  Robiquet 
and  Colin,  who  have  termed  it  alizarine,  from  Ali-zari,  the  commercial 
name  by  which  madder  is  known  in  the  Levant.  Their  process  has  received 
the  following  modification  by  Zen  neck.  Ten  parts  of  madder  are  digested 
in  four  of  ether,  the  solution  is  evaporated  to  the  consistence  of  syrup,  and 
then  allowed  to  become  dry  by  spontaneous  evaporation.  The  residue  is 
pulverized,  and  sublimed  by  a  gentle  heat  from  a  watch  glass.  The  sub- 
limate,  which  is  collected  by  covering  the  watch  glass  with  a  cone  of  paper, 
is  deposited  in  the  form  of  yellowish-red,  brilliant,  diaphanous,  acicular 
crystals,  which  are  soft,  flexible,  and  heavier  than  water.  They  soften 
when  heated,  and  sublime  at  a  temperature  between  500  and  600°,  causing 
an  aromatic  odour.  They  are  nearly  insoluble  in  cold  and  very  sparingly 
soluble  in  hot  water.  They  require  for  solution  210  times  their  weight  of 
alcohol,  and  1GO  of  ether  at  60°.  According  to  Zenneck  the  acidity  of 
alizarine  is  very  decisive,  both  in  its  sour  taste,  and  its  power  of  neutralizing 
alkalies.  Jt  consists,  in  100  parts,  of  18  of  carbon,  20  of  hydrogen,  and  62 
of  oxygen.  (Journal  of  Science,  N.  S.  v.  198.) 

Yellow  Dyes. — The  chief  yellow  dyes  are  quercitron  bark,  turmeric,  wild 
American  hiccory,  fustic,  and  saffron ;  all  of  which  are  adjective  colours. 
Quercitron  bark,  which  is  one  of  the  most  important  of  the  yellow  dyes, 
was  introduced  into  notice  by  Dr.  Bancroft.  With  a  basis  of  alumina,  the 
decoction  of  this  bark  gives  a  bright  yellow  dye.  With  oxide  of  tin  it  com. 
municates  a  variety  of  tints,  which  may  be  made  to  vary  from  a  pale  lemon 
colour  to  deep  orange.  With  oxide  of  iron  it  gives  a  drab  colour. 

Turmeric  is  the  root  of  the  Curcuma  longa,  a  native  of  the  East  Indies. 
Paper  stained  with  a  decoction  of  this  substance  constitutes  the  turmeric  or 
curcuma  paper  employed  by  chemists  as  a  test  of  free  alkali,  by  the  action 
of  which  it  receives  a  brown  stain. 

The  colouring  ingredient  of  saffron  (Crocus  sativus]  is  soluble  in  water 
and  alcohol,  has  a  bright  yellow  colour,  is  rendered  blue  and  then  lilac  by 
sulphuric  acid,  and  receives  a  green  tint  on  the  addition  of  nitric  acid. 
From  the  great  diversity  of  colours  which  it  is  capable  of  assuming  under 
different  circumstances,  Bouillon  Lagrange  and  Vogel  have  proposed  for  it 
the  name  polychroite.  (An.  de  Ch.  Ixxx.) 

Black  Dyes. — The  black  dye  is  made  of  the  same  ingredients  as  writing 
ink,  and,  therefore,  consists  essentially  of  a  compound  of  oxide  of  iron  with 
gallic  acid  and  tannin.  From  the  addition  of  logwood  and  acetate  of  copper, 
the  black  receives  a  shade  of  blue. 

By  the  dextrous  combination  of  the  four  leading  colours,  blue,  red,  yel- 
low, and  blackball  other  shades  of  colour  may  be  procured.  Thus  green  is 
communicated  by  forming  a  blue  ground  with  indigo,  and  then  adding  a 
yellow  by  means  of  quercitron  bark. 

The  reader  who  is  desirous  of  studying  the  details  of  dyeing  and  calico- 
printing,  a  subject  which  does  not  fall  within  the  plan  of  this  work,  may 
consult  Berthollet's  Elemens  de  VArt  de  la  Teinture;  the  treatise  of  Dr. 
Bancroft  on  Permanent  Colours;  a  paper  by  Mr.  Henry  in  the  third  volume 
of  the  Manchester  Memoirs;  and  the  Essay  of  Thenard  and  Roard  in  the 
74th  volume  of  the  Annales  de  Chimie, 


VEGETABLE  ALBUMEN. — GLUTEN.  549 


SECTION   VII. 

SUBSTANCES  WHICH,  SO  FAR  AS  IS  KNOWN,  DO  NOT  BELONG 
TO  EITHER  OF  THE  PRECEDING  SECTIONS. 

Vegetable  Albumen. — Under  this  name  is  distinguished  a  vegetable  prin- 
ciple which  has  a  close  resemblance  to  animal  albumen,  especially  in  the  cha- 
racteristic property  of  being-  coagulable  by  heat.  This  substance  was  found 
by  Vogel  in  the  bitter  almond,  and  in  the  sweet  almond  by  Boullay ;  it  ap- 
pears to  be  an  ingredient  of  emulsive  seeds  generally  ;  and  it  exists  in  the 
sap  of  many  plants.  Einhof  detected  it  in  wheat,  rye,  barley,  peas,  and  beans. 
Vegetable  albumen  is  soluble  in  cold  water,  but  by  a  boiling  temperature  it 
is  coagulated,  and  thus  completely  deprived  of  its  solubility.  It  is  insoluble 
in  alcohol,  and  very  sparingly  soluble  in  acids.  Alkalies  dissolve  it  readily, 
and  it  may  be  precipitated  from  them  by  acids ;  but  the  albumen  falls  in 
combination  with  a  portion  of  the  acid.  Ferrocyanate  of  potassa  arid  corro- 
sive sublimate  act  upon  it  as  on  solutions  of  animal  albumen. 

Vegetable  albumen  contains  nitrogen  as  one  of  its  elements,  and  is  very 
prone,  when  kept  in  the  moist  state,  to  undergo  the  putrefactive  fermenta- 
tion, emitting  an  offensive  odour,  with  disengagement  of  ammonia  and  for- 
mation of  acetate  of  ammonia.  Durinjr  a  certain  period  of  putrefaction  it 
has  the  odour  of  old  cheese.  (Berzelius.)^ 

Gluten. — In  the  separation  of  starch  from  wheat  flour,  as  already  de- 
scribed (page  517),  a  gray  viscid  substance  remains,  fibrous  in  its  texture, 
and  elastic.  Beccaria,  who  first  carefully  examined  its  properties,  was 
struck  with  its  analogy  to  glue,  both  in  its  viscidity  as  well  as  its  tendency 
to  putrefy  like  animal  matter,  and  gave  it  the  name  of  vegetable  gluten. 
Einhof  has  since  shown  that  this  gluten  is  a  mixed  substance,  containing 
gluten  and  vegetable  albumen. 

Pure  gluten  is  obtained  by  washing  dough  in  water  until  the  starch  and 
soluble  parts  arc  removed,  and  treating  the  residue  with  boiling  alcohol.  On 
mixing  the  alcoholic  solution  with  water,  and  distilling  off  the  spirit,  the 
gluten  is  deposited  in  large  coherent  flakes.  As  thus  obtained  it  has  a  pale 
yellow  colour,  and  a  peculiar  odour,  but  no  taste,  adheres  tenaciously  to  the 
fingers  when  handled,  and  has  considerable  elasticity.  It  is  insoluble  in 
water  and  ether,  but  dissolves  readily  in  hot  alcohol,  apparently  without  any 
change  of  property;  but  if  the  alcoholic  solution  is  evaporated  to  dryness, 
the  gluten  is  left  as  a  transparent  varnish.  It  swells  up  and  softens  with 
acetic  acid,  forming-  a  compound  which  is  soluble  in  water.  It  unites  also 
with  the  mineral  acids;  and  these  compounds,  excepting  that  with  sulphuric 
acid,  dissolve  readily  in  pure  water,  but  are  insoluble  when  there  is  an  ex- 
cess of  acid.  It  is  dissolved  by  a  dilute  solution  of  potassa,  apparently  with- 
out  being  decomposed;  for  the  gluten,  after  being  thrown  down  by  the  min- 
eral acids,  retains  its  viscidity.  In  this  state,  however,  it  is  combined  with 
some  of  the  acid.  (Berzelius.) 

When  gluten  is  kept  in  a  warm  moist  situation  it  ferments,  and  an  acid 
is  formed;  but  in  a  few  days  putrefaction  ensues,  and  an  offensive  odour, 
like  that  of  putrefying  animal  matter,  is  emitted.  According  to  Proust,  who 
made  these  spontaneous  changes  a  particular  object  of  study,  the  process  is 
divisible  into  two  distinct  periods.  In  the  first,  carbonic  acid  and  hydrogen 
gases  are  evolved ;  and  in  the  second,  besides  acetic  and  phosphoric  acids 
and  ammonia,  two  new  compounds  are  generated,  for  which  he  proposed  the 
names  of  caseic  acid  and  caseous  oxide.  These  are  the  same  principles  which 
are  generated  during-  the  fermentation  of  the  curd  of  milk,  and  their  real 
nature  will  be  considered  in  the  section  on  milk.  It  is  apparent  from  these 
circumstances  that  gluten  contains  nitrogen  as  one  of  its  elements,  and  that 


550  YEAST. — ASPARAGIN. 

it  approaches  closely  to  the  nature  of  animal  substances.     It  has  hence  been 
called  a  vegeto-animal  principle. 

If  gluten  is  dried  by  a  gentle  heat,  it  contracts  in  volume,  becomes  hard 
and  brittle,  and  may  in  this  state  be  preserved  without  change.  Exposed  to 
a  strong  heat,  it  yields,  in  addition  to  the  usual  inflammable  gases,  a  thick 
fetid  oil  and  carbonate  of  ammonia... 

Gluten  is  present  in  most  kinds  of  grain,  such  as  wheat,  barley,  rye,  oats, 
peas,  and  beans;  but  the  first  contains  it  in  by  far  the  largest  proportion. 
This  is  the  reason  that  wheaten  bread  is  more  nutritious  than  that  made 
with  other  kinds  of  flour  ;  for  of  all  vegetable  substances  gluten  appears  to 
be  the  most  nutritive.  It  is  to  the  presence  of  gluten  that  wheat  flour  owes 
its  property  of  forming  a  tenacious  paste  with  water.  To  the  same  cause  is 
owing  the  formation  of  light  spongy  bread;  the  carbonic  acid  which  is  dis- 
engaged during"  the  fermentation  of  dough,  being  detained  by  the  viscid  glu- 
ten, distends  the  whole  mass,  and  thus  produces  the  rising  of  the  dough. 
From  the  experiments  of  Davy,  it  appears  that  good  wheat  flour  contains 
from  19  to  24  per  cent,  of  gluten.  The  wheat  grown  in  the  south  of  Europe 
is  richer  in  gluten  than  that  of  colder  climates. 

M.  Taddei,  an  Italian  chemist,  has  given  an  account  of  two  principles  se- 
parable from  the  gluten  of  Beccaria  by  means  of  boiling  alcohol.  To  the 
substance  soluble  in  alcohol  he  has  applied  the  name  of  gliadine,  yxix,  glu- 
ten ;  and  to  the  other  that  of  zymome,  from  ^y^H,  a  ferment.  (An.  of  Phil, 
xv.)  For  the  latter  he  has  discovered  a  delicate  test  in  the  powder  of  guaia- 
cum,  which,  when  rubbed  in  a  rnortar  with  moist  zymome,  instantly  strikes 
a  beautiful  blue  colour;  and  the  same  tint  appears,  though  less  rapidly, 
when  it  is  kneaded  with  gluten  or  dough  made  with  good  wheat  flour.  But 
with  bad  flour,  the  gluten  of  which  has  suffered  spontaneous  decomposition, 
the  blue  tint  is  scarcely  visible;  and  accordingly  M.  Taddei  conceives  that 
useful  inferences  as  to  the  quality  of  flour  may  be  drawn  from  the  action  of 
guaiacum. 

These  views  have  been  criticised  by  Berzelius,  who  declares  that  the  sub- 
stances described  by  Taddei  are  nothing  else  than  the  gluten  and  vegetable 
albumen  already  described;  and  the  habitual  accuracy  of  Berzelius  leaves 
little  chance  of  error  in  his  statement.  The  blue  tint,  above  alluded  to,  must 
have  arisen  from  the  action  of  guaiacum  either  on  vegetable  albumen  itself, 
or  on  some  substance  by  which  it  is  accompanied  in  wheat.  (An.  of  Phil.  iv. 
69.  or  Lehrbuch,  iii.  362.) 

Yeast. — This  substance  is  always  generated  during  the  vinous  fermenta- 
tion of  vegetable  juices  and  decoctions,  rising  to  the  surface  in  the  form  of  a 
frothy,  flocculent,  somewhat  viscid  matter,  the  nature  and  composition  of 
which  are  unknown.  It  is  insoluble  in  water  and  alcohol,  and  in  a  warm, 
moist  atmosphere  gradually  putrefies,  a  sufficient  proof  that  nitrogen  is  one 
of  its  elements.  Submitted  to  a  moderate  heat,  it  becomes  dry  and  hard,  and 
may  in  this  state  be  preserved  without  change.  Heated  to  redness  in  close 
vessels,  it  yields  products  similar  to  those  procured  under  the  same  circum- 
stances from  gluten.  To  this  substance,  indeed,  yeast  is  supposed  by  some 
chemists  to  be  very  closely  allied. 

The  most  remarkable  property  of  yeast  is  that  of  exciting  fermentation. 
By  exposure  for  a  few  minutes  to  the  heat  of  boiling  water,  it  loses  this  pro- 
perty, but  after  some  time  again  acquires  it.  Nothing  conclusive  is  known 
concerning  either  the  nature  of  these  changes,  or  the  mode  in  which  yeast 
operates  in  establishing  the  fermentative  process. 

Asparagin. — This  principle  was  discovered  by  Vauquelin  and  Robiquet  in 
the  juice  of  the  asparagus,  from  which  it  is  deposited  in  crystals  by  evapora- 
tion. It  is  also  contained  in  the  root  of  the  marsh-mallow  and  liquorice. 
Robiquet,  who  first  procured  it  from  the  juice  of  the  recent  liquorice  root, 
doubted  its  identity  with  asparagin,  and  gave  it  the  name  of  agedoite  ;  but 
the  mistake  has  been  corrected  by  M.  Plisson. 

Asparagin  crystallizes  in  the  form  of  a  rectangular  octohedron,  six-sided 
prism,  or  right  rhombic  prism,  is  inodorous,  and  has  a  cool  slightly  nauseous 


BASSORIN. — CAFFEIN.  551 

taste.  In  ether  and  pure  alcohol  it  is  insoluble,  and  requires  for  solution  58 
parts  of  cold  water,  but  is  more  freely  dissolved  by  the  aid  of  heat.  It  has 
neither  an  acid  nor  alkaline  reaction  with  test-paper.  Plisson  has  noticed  that 
when  boiled  for  some  time  with  hydrated  oxide  of  lead  or  magnesia,  it  is  re- 
solved into  ammonia,  and  a  new  acid,  called  the  aspartic.  The  possibility  of 
such  a  change  is  intelligible  from  the  late  analysis  of  asparagin  arid  aspartic 
acid  by  Liebig,  as  subjoined : — (An.  de  Ch.  et  de  Ph.  liii.  416.) 

Anhydrous  Asparagin.  Anhydrous  Aspartic  Acid. 

Carbon        3674        48-96        8C  42-16        48-96         8C 

Hydrogen      5-94          8             8H  4-37          5              5H 

Nitrogen     21-27         28-3           2N  12-20         14-15           N 

Oxygen       36-05        48             6(X  41-27        48              6O 

100-00      133-26   C8H8NSO6      100-00      116-11  C8H5NO°. 

It  is  obvious  that  one  eq.  of  anhydrous  asparagin  contains  one  eq.  of  aspar- 
tic acid  and  one  eq.  of  ammonia.  And  yet  asparagin  is  not  aspartate  of 
ammonia,  since  acids  do  not  eliminate  aspartic  acid,  nor  alkalies  ammonia 
with  the  facility  which  would  be  expected  on  that  supposition.  The  crys- 
tals of  asparagin  lose  12-133  per  cent,  of  water  when  heated,  or  consist  of 
133'26  parts  of  one  eq.  of  anhydrous  asparagin  and  18  or  two  eq.  of  water. 
Aspartic  acid  is  prepared  by  decomposing  the  asparlate  of  oxide  of  lead  by 
hydrosulphuric  acid,  and  evaporating  the  filtered  solution,  when  the  acid  is 
obtained  as  a  colourless  powder  composed  of  minute  prismatic  crystals, 
which,  like  asparagin,  contain  two  eq.  of  water  of  crystallization.  It  has 
little  taste,  is  sparingly  soluble  in  cold  water,  arid  still  less  so  in  alcohol.  Its 
aqueous  solution  is  not  precipitated  by  the  soluble  salts  of  baryta,  lime,  lead, 
magnesia,  copper,  mercury,  or  silver.  The  aspartates,  when  the  taste  of  the 
base  does  not  interfere,  have  the  taste  of  the  juice  of  meat.  It  yields  am- 
monia when  decomposed  by  heat.  (An.  de  Ch.  et  de  Ph.  xxxv.  175,  and  xl. 
309.)  - 

Bassorin  was  first  noticed  in  gum  Bassora  by  Vauquelin.  It  is  an  ingre- 
dient of  gum-tragacanth  (page  519),  and  probably  occurs  in  other  gums. 
Salep,  from  the  experiments  of  Caventou,  appears  to  consist  almost  totally  of 
bassorin. 

Bassorin  is  characterized  by  forming  with  cold  water  a  bulky  jelly,  which 
is  insoluble  in  that  menstruum,  as  well  as  in  alcohol  and  ether.  Boiling 
water  does  not  dissolve  it  except  by  long-continued  ebullition,  when  the  bas- 
sorin at  length  disappears,  and  is  converted  into  a  substance  similar  to  gum- 
arabic. 

Caffein  was  discovered  in  coffee  by  Robiquet  in  the  year  1821,  and  was 
soon  after  obtained  from  the  same  source  by  Pelletier  and  Caventou,  with- 
out a  knowledge  of  the  discovery  of  Robiquet.  (An.  of  Phil.  N.  S.  xii.)  It  is 
best  prepared  by  making  an  aqueous  decoction  of  bruised  raw  coffee,  add- 
ing subacetate  of  oxide  of  lead  as  long  as  a  precipitate  falls,  by  which  means 
a  large  quantity  of  extractive  and  colouring  matter  is  thrown  down,  and 
then  precipitating  the  excess  of  oxide  of  lead  by  hydrosulphuric- acid.  The 
cafFein,  which  is  left  in  solution,  is  ultimately  obtained  in  crystals  by  evapo- 
ration. Pfaff  and  Liebig  recommend  that  it  should  be  decolorized  by 
digestion  with  animal  charcoal  together  with  some  moist  hydrated  oxide  of 
lead. 

Caffein  is  a  white  crystalline  volatile  matter,  sparingly  soluble  in  cold  wa- 
ter, but  very  soluble  in  boiling  water  and  alcohol,  and  is  deposited  from  these 
solutions  as  they  cool,  in  the  form  of  silky  filaments  like  amianthus.  Pelle- 
tier, contrary  to  the  opinion  of  Robiquet,  at  first  regarded  it  as  an  alkaline 
base:  but  he  now  admits  that  it  does  not  affect  the  vegetable  blue  colours, 
nor  combine  with  acids.  From  a  late  analysis  by  Pfaff  and  Liebig,  made 
with  a  purer  specimen  than  that  analyzed  by  Pelletier  and  Dumas,  cafFein 
is  composed  of  48-96  parts  or  eight  eq.  of  carbon,  5  parts  or  five  eq.  of  hy- 
drogen, 28-3  or  two  eq.  of  nitrogen,  and  16  or  two  eq.  of  oxygen.  (An.  de 


552  CATHARTIN. FUNGIN. — SUBERIN. — ULMIN. — LUPULIN,  &,C. 

Ch.  et  de  Ph.  xlix.  303.)  Though  it  contains  more  nitrogen  than  most  ani- 
mal substances,  it  does  not,  under  any  circumstances,  undergo  the  putrefac- 
tive fermentation. 

In  the  precipitate  caused  in  a  decoction  of  coffee  by  acetate  of  oxide  of 
lead,  tannic  acid  is  present,  together  with  another  acid  supposed  to  be  pecu- 
liar to  coffee,  and  termed  by  Pfaff  caffeic  acid. 

Cathartin. — This  name  has  been  applied  by  Lassaigne  and  Feneulle  to 
the  active  principle  of  senna.  (An.  de  Ch.  et  de  Ph.  vol.  xvi.)  A  similar  bit- 
ter purgative  principle,  called  Cytisin,  has  been  prepared  from  the  Cytisus 
Alpinus. 

Fungin. — This  name  is  applied  by  Braconnot  to  the  fleshy  substance  of 
the  mushroom,  purified  by  digestion  in  hot  water,  to  which  a  little  alkali  is 
added.  Fungin  is  nutritious  in  a  high  degree,  and  in  composition  is  very 
analogous  to  animal  substances.  Like  flesh  it  yields  nitrogen  gas  when  di- 
gested in  dilute  nitric  acid. 

Suberin. — This  name  has  been  applied  by  Chevreul  to  the  cellular  tissue 
of  the  common  cork,  the  outer  bark  of  the  cork-oak,  (quercus  suiter},  after 
the  astringent,  oily,  resinous,  and  other  soluble  matters  have  been  removed 
by  the  action  of  water  and  alcohol.  Suberin  differs  from  all  other  vegetable 
principles  by  yielding  the  suberic  when  treated  by  nitric  acid. 

Ulmin^  discovered  by  Klaproth,  is  a  substance  which  exudes  sponta* 
neously  from  the  elm,  oak,  chesnut,  and  other  trees;  and  according  to  Ber- 
zelius  is  a  constituent  of  most  kinds  of  bark.  It  may  be  prepared  by  acting 
upon  elm-bark  by  hot  alcohol  and  cold  water,  and  then  digesting  the  residue 
in  water,  which  contains  an  alkaline  carbonate  in  solution.  On  neutralizing 
the  alkali  with  an  acid,  the  ulmin  is  precipitated. 

Ulrnin  is  a  dark  brown,  nearly  black  substance,  is  insipid  and  inodorous, 
and  is  very  sparingly  soluble  in  water  and  alcohol.  It  dissolves  freely,  on 
the  contrary,  in  the  solution  of  an  alkaline  carbonate,  and  is  thrown  down 
by  an  acid.  Ulmin  is  regarded  as  an  acid  by  M.  P.  Boullay,  who  has  pro- 
posed for  it  the  name  of  ulrnic  acid.  He  found  that  100  parts  of  it  contain 
56*7  of  carbon,  and  43-3  of  oxygen  and  hydrogen,  in  the  ratio  to  form  wa- 
ter. According  to  him  it  is  an  ingredient  of  vegetable  mould  and  turf,  and 
contributes  much  to  the  growth  of  plants.  The  black  matter  deposited 
during  the  decomposition  of  prussic  acid,  supposed  by  Gay-Lussac  to  be  a 
carburet  of  nitrogen,  is  an  acid  very  similar  to  the  ulrnic,  and  to  which  he 
has  given  the  name  ofazulmic  acid.  (An.  de  Ch.  et  de  Ph.  xliii.  273.) 

Lupulin  is  the  name  applied  by  Dr.  Ives  to  the  active  principle  of  the  hop, 
but  which  has  not  yet  been  obtained  in  a  state  of  purity. 

Inulin  is  a  white  powder  like  starch,  which  is  spontaneously  deposited 
from  a  decoction  of  the  roots  of  the  Inula  helenium  or  elecampane.  This 
substance  is  insoluble  in  cold,  and  soluble  in  hot  water,  and  is  deposited  from 
the  latter  as  it  cools,  a  character  which  distinguishes  it  from  starch.  With 
iodine  it  forms  a  greenish-yellow  compound  of  a  perishable  nature.  Its  so- 
lution is  somewhat  mucilaginous;  but  inulin  is  distinguished  from  gum  by 
insolubility  in  cold  water,  and  in  not  yielding  the  saccholactic  when  digested 
in  nitric  acid. 

Medullin. — This  namo  was  applied  by  John  to  the  pith  of  the  sunflower, 
but  its  existence  as  an  independent  principle  is  somewhat  dubious?.  The  term 
pollenin  has  been  given  by  the  same  chemist  to  the  pollen  of  tulips. 

Piperin  is  the  name  which  is  applied  to  a  white  crystalline  substance  ex- 
tracted from  black  or  white  pepper.  It  is  tasteless,  and  is  quite  free  from 
pungency,  the  stimulating  property  of  the  pepper  being  found  to  reside  in  a 
fixed  oil.  (Pelletier,  in  An.  de  Ch.  et  de  Ph.  vol.  xvi.)  Dr.  A.  T.  Thomson 
has  extracted  it  from  chamornile  flowers. 

A  process  recommended  for  its  preparation  by  Vogel  consists  in  digest- 
ing for  two  days  16  ounces  of  black  pepper  in  coarse  powder  in  twice  its 
weight  of  water,  five  times  in  succession  ;  and  digesting  the  insoluble  parts, 
previously  well  pressed  and  dried,  for  three  days  in  24  ounces  of  alcohol. 
The  solution  is  pressed  through  linen  cloth,  filtered,  and  evaporated  to  the 


OLIVILE. SARCOCOLL. — RIIUBARBARIN. — RHEIN,  &C.  553 

consistence  of  syrup;  and  the  impure  crystals  of  piperin,  deposited  by  cool- 
ing-, are  freed  from  adhering  resinous  matter  by  ether,  and  further  purified 
by  animal  charcoal,  re-solution  in  alcohol,  and  a  second  crystallization. 

Piperin  crystallizes  in  four-sided  prisms,  which  have  commonly  a  yellow 
colour,  owing  to  adhering1  oil  or  resin.  It  is  insoluble  in  cold,  and  sparingly 
soluble  in  hot  water;  but  it  is  very  soluble  in  alcohol,  and  less  so  in  ether, 
Acetic  acid  also  dissolves  it,  and  leaves  it  by  evaporation  in  feathery  crys- 
tals. It  fuses  at  212°,  and  according-  to  Gobel  consists  of  80-95  parts  of  car- 
bon, 8-13  of  hydrogen,  and  10-92  of  oxygen. 

OZivi/e.— When  the  gum  of  the  olive-tree  is  dissolved  in  alcohol,  and  the 
solution  is  allowed  to  evaporate  spontaneously,  a  peculiar  substance,  appa- 
rently different  from  the  other  proximate  principles  hitherto  examined,  is 
deposited  either  in  flattened  needles  or  as  a  brilliant  amylaceous  powder. 
To  this  Pelletier,  its  discoverer,  has  given  the  name  of  Olivile.  (An.  of 
Phil,  xii.) 

Sarcocoll  is  the  concrete  juice  of  the  Pen&a  sarcocolla,  a  plant  which 
grows  in  the  northern  parts  of  Africa.  It  is  imported  in  the  form  of  small 
grains  of  a  yellowish  or  reddish  colour  like  gum-arabic,  to  which  its  proper- 
ties are  similar.  It  has  a  sweetish  taste,  dissolves  in  the  mouth  like  gum, 
and  forms  a  mucilage  with  water.  It  is  distinguished  from  gum,  however, 
by  its  solubility  in  alcohol,  and  by  its  aqueous  solution  being  precipitated  by 
tannin.  Dr.  Thomson,  who  has  given  a  full  account  of  sarcocoll  in  his 
System  of  Chemistry,  considers  it  closely  allied  to  the  saccharine  matter  of 
liquorice. 

Rhubarbarin  is  the  name  employed  by  PfafT  to  designate  the  principle  in 
which  the  purgative  property  of  the  rhubarb  resides.  M.  Nani  of  Milan  re- 
gards the  active  principle  of  this  plant  as  a  vegetable  alkali;  but  he  has  not 
given  any  proof  of  its  alkaline  nature.  (Journal  of  Science,  xvi.  172.) 

Rhein. — M.  Vaudin  has  applied  this  name  to  a  substance  which  he  obtained 
by  gently  heating  rhubarb  in  powder  with  eight  times  its  weight  of  nitric 
acid  of  1'375,  evaporating  to  the  consistence  of  syrup,  and  diluting  with  cold 
water.  Rhein,  which  is  then  deposited,  is  inodorous,  has  a  slightly  bitter 
taste,  and  an  orange  colour.  It  is  sparingly  soluble  in  cold  water;  but  it 
dissolves  in  alcohol,  ether,  and  hot  water,  and  its  solutions  are  rendered  pale 
yellow  by  acids,  and  rose-red  by  alkalies.  It  may  be  extracted  from  rhubarb 
by  ether,  a  fact  which  proves  that  it  exists  ready  formed  in  the  plant;  and 
its  mode  of  preparation  shows  that  it  possesses  unusual  permanence,  power- 
fully resisting  the  action  of  nitric  acid. 

Rhaponticin. — This  substance  was  obtained  by  Hornemann  from  the 
Rheum  Rhaponticum,  It  was  obtained  in  the  form  of  yellow  scales,  which 
are  tasteless  and  inodorous,  insoluble  in  cold  water  and  ether,  and  requires 
for  solution  24  times  its  weight  of  boiling  water,  and  only  twice  its  weight 
of  anhydrous  alcohol. 

Colocyntin. — This  name  was  applied  by  Vauquelin  to  a  bitter  resinous 
matter  extracted  from  colocynth  by  the  action  of  alcohol,  and  left  by  evapo-  » 
ration  as  a  brittle  substance  of  a  golden-yellow  colour.     It  is  slightly  soluble 
in  water,  is  freely  dissolved  by  alcohol  and  alkalies,  and  possesses  the  purga- 
tive properties  of  colocynth.  (Journal  of  Science,  xviii.  400.) 

Berberin. — This  is  a  yellow  bitter  principle  contained  in  the  alcoholic  ex- 
tract of  the  root  of  the  barberry. 

Bryonin. — This  is  a  bitter,  rather  poisonous  principle,  obtained  first  by 
Vauquelin  and  afterwards  by  Brandos  from  the  root  of  the  Brionia  alba. 

Gentianin  is  the  name  applied  to  the  bitter  principle  of  the  root  of  the 
gentian. 

Zanthopicrin  is  a  bitter  principle  obtained  from  the  bark  of  the  Zantlwxy- 
lum  caribaum  by  Chevallier  and  Pelletan.  It  is  of  sparing  solubility  in 
water,  insoluble  in  ether,  very  soluble  in  alcohol,  from  which  it  crystallizes 
by  evaporation  in  yellow  acicular  crystals  of  a  silky  lustre. 

Cetrarin  is  the  name  applied  by  Herberger  to  the  bitter  principle  of  Ice- 
land  moss. 

47 


554  SCILLITIN.  —  SENEGIN.  —  SAPONIN.  —  ARTHANATIN, 


Scillitin  is  the  name  applied  by  Vogel  to  the  bitter  medicinal  principle  of 
squills  (Scilla  maratima).  It  is  prepared  by  evaporating  the  juice  expressed 
from  the  fresh  root  of  squills  to  the  consistence  of  an  extract,  forming1  a  solu- 
tion of  it  in  alcohol,  which  is  then  evaporated  to  dryness,  and  the  soluble 
parts  taken  up  by  water.  The  solution  contains  scillitin  associated  with 
tannic  iicid  and  saccharine  matter;  the  former  is  separated.  by  means  of 
subacetate  of  oxide  of  lead;  and  the  latter  by  forming  an  alcoholic  solution 
of  the  sciljitin  and  sugar,  freed  from  tanriic  acid,  and  adding  ether,  which 
throws  down  the  sugar,  leaving  most  of  the  scillitin  in  solution.  13y  evapo- 
ration the  scillitin  remains  in  the  form  of  a  white  friable  mass  of  a  resinous 
fracture. 

Sencgin  is  the  name  given  by  Gehlen  to  the  bitter  acrid  principle  coiv 
lained  in  the  root  of  the  Polygala  Senega. 

Saponin.  —  This  substance  is  contained  in  the  root  of  the  Saponaria  offici- 
nalis,  and  is  the  cause  of  the  lather  which  that  root  forms  when  agitated 
with  water.  It  is  prepared  by  evaporating  to  dryness  an  aqueous  solution 
of  the  alcoholic  extract  of  the  root,  or  an  alcoholic  solution  of  the  aqueous 
extract.  Both  solvents  are  requisite,  in  order  to  separate  the  saponin  from 
resinous  and  gummy  matter  with  which  it  is  associated  in  the  root 

Arthanutin.  —  This  name  was  applied  by  Saladin  to  a  colourless  crystalline 
matter,  which  is  extracted  by  alcohol  from  the  root  of  the  Cyclamen  Eu- 
ropium. 

Extractive  Matter.  —  This  expression,  if  applied  to  one  determinate  princi- 
ple supposed  to  be  the  same  in  different  plants,  is  quite  inapplicable.  It  is 
indeed  true  that  most  plants  yield  to  water  a  substance  which  differs  from 
gum,  sugar,  or  any"  proximate  principle  of  vegetables,  which,  therefore,  con* 
stitutes  a  part  of  what  is  called  an  extract  in  pharmacy,  and  which,  for  want 
of  a  more  precise  term,  may  be  expressed  by  the  name  of  extractive.  It 
must  be  remembered,  however,  that  this  matter  is  always  mixed  with 
other  proximate  principles,  and  that  there  is  no  proof  whatever  of  its  being 
identical  in  different  plants.  The  solution  of  saffron  in  hot  water,  said  to 
afford  pure  extractive  matter  by  evaporation,  contains  the  colouring  matter 
of  the  plant,  together  with  all  the  other  vegetable  principles  of  saffron,  which 
happen  to  be  soluble  in  the  menstruum  employed. 

Plumbagin,  extracted  by  Dulong  from  the  root  of  the  Plumbago  Europcea^ 
is  soluble  in  water,  alcohol,  arid  ether,  and  crystallizes  from  its  solutions  in 
acicular  crystals  of  a  yellow  colour.  Its  aqueous  solution  is  made  cherry- 
red  by  alkalies,  subacetate  of  oxide  of  lead,  and  perchloride  of  iron  ;  but  acids 
restore  the  yellow  tint,  and  the  plumbagin  is  found  unaltered.  Its  taste  is 
at  first  sweet,  but  is  subsequently  sharp  and  acrid,  extending  to  the  throat. 
(Journal  of  Science,  N.  S.  vi.  191.) 

Chlorophyle.  —  This  name  has  been  applied  by  Pelletier  and  Caventou  to 
the  green  colouring  matter  of  leaves.  It  is  prepared  by  bruising  green  leaves 
into  a  pulp  with  water,  pressing  out  all  the  liquid,  and  boiling  the  pulp  in 
alcohol.  The  solution  is  mixed  with  water,  and  the  spirit  driven  off  by  dis- 
tillation, when  the  chlorophyle  is  left  floating  on  the  surface  of  the  water. 
As  thus  obtained,  it  appears  to  be  wax  stained  with  the  green  colour  of  the 
leaves;  and  from  some  late  observations  of  Macaire  Prinsep,  the  wax  may 
be  removed  by  ether,  and  the  colouring  matter  left  in  a  pure  state.  The  red 
autumnal  tint  of  the  leaves,  according  to  the  same  observer,  is  the"  effect  of 
an  acid  generated  in  the  leaf.  The  green  tint  may  be  restored  by  the  action 
of  an  alkali. 

Amygdalin.  —  This  substance  was  extracted  in  1830  by  Robiquet  and 
Boutron-Charlard  from  the  bitter  almond.  (An.  de  Ch.  et  de  Ph.  xliv.  352.) 
The  almond,  reduced  to  a  pulp,  is  digested  with  ether  in  order  to  separate  its 
fixed  oil,  after  which  it  is  boiled  in  3  or  4  successive  portions  of  alcohol,  and 
the  alcoholic  solution  is  distilled  in  a  water  bath  to  the  consistence  of  syrup. 
This  residue  is  then  briskly  agitated  with  ether,  and  set  at  rest  in  a  tube 
placed  perpendicularly,  when  three  distinct  strata  are  gradually  formed  :  the 
•upper  one  is  nearly  pure  ether,  the  lower  is  viscid  and  consists  of  saccharine 


SALICIN. — POPULIN. — MECONiN.  555 

matter,  and   the   intermediate  stratum,  white  and  semi-solid,  contains  the 
axnygdalin. 

Amygdalin,  insoluble  in  water,  dissolves  freely  in  hot  alcohol,  and  crystal- 
lizes as  the  solution  cools  in  white  needles,  which  are  not  volatile,  and  remain 
unchanged  in  the  open  air.  Its  taste  is  sweet  followed  by  a  bitter  flavour, 


.rogen  as  one  of  its  elements,  and  emits  a  strong  < 
tnonia  when  it  is  boiled  in  a  solution  of  potassa.  Heated  with  nitric  acid  it 
yields  benzoic  acid.  It  certainly  has  a  close  relation  to  benzule,  but  the  na- 
ture of  that  connexion  has  not  yet  been  traced. 

Salicin. — This  principle  was  discovered  in  1830  in  the  bark  of  the  willow 
(Salix  helix)  by  M.  Leroux,  who  announced  it,  along  with  attestations  of  its 
virtues  from  Majendie  and  other  medical  authorities,  as  a  cure  for  intermit- 
tent fever  of  sufficient  power  to  become  a  substitute  for  quinia ;  and  obser- 
vations on  its  preparation  and  properties  have  since  been  made  by  Braconnot, 
Pelouze  and  J.  Gay-Lussac,  and  Peschier.  (An.  de  Ch.  et  de  Ph.  xliii.  440, 
and  xliv.  220,  296,  and  418.)  It  exists  in  several  species  of  the  willow,  and 
Braconnot  has  met  .with  it  in  the  bark  of  the  poplar,  especially  of  the  Popu- 
lus  tremula.  The  most  approved  method  of  preparation  consists  in  forming 
an  aqueous  decoction  of  the  willow  bark,  adding  subacetate  of  oxide  of  lead 
as  long  as  a  precipitate  falls,  in  order  to  remove  colouring  matter,  boiling 
with  chalk  to  throw  down  the  excess  of  oxide  of  lead,  and  evaporating  the 
solution.  The  salicin  is  deposited  in  crystals,  which  may  be  purified  by 
solution  in  alcohol  and  digestion  with  animal  charcoal. 

Pure  salicin  is  perfectly  white,  crystallizes  in  delicate  prisms  or  needles, 
and  has  a  very  bitter  taste.  In  cold  water  it  is  sparingly  soluble;  but  it  is 
freely  taken  up  both  by  water  and  alcohol  at  a  boiling  temperature,  and  is 
insoluble  in  ether.  By  strong  sulphuric  acid  in  the  cold  it  is  decomposed, 
and  the  acid  acquires  a  purple  tint.  Heated  with  sulphuric  acid  somewhat 
diluted.,  or  with  strong  hydrochloric  acid,  it  is  converted  into  a  white  insolu- 
ble matter  of  the  nature  of  resin.  When  digested  with  eight  times  its  weight 
of  nitric  acid,  salicin  yields  a  large  quantity  of  carbazotic  acid. 

Salicin  has  neither  acid  nor  alkaline  properties,  and  according  to  Pelouze 
and  J.  Gay-Lussac  consists  of  carbon,  hydrogen,  and  oxygen,  in  the  ratio  of 
two  equivalents  of  the  first  element,  two  equivalents  of  the  second,  and  one 
equivalent  of  the  third. 

Populin. — A  substance,  described  under  this  name,  was  found  by  Bra- 
connot in  the  bark  of  the  Populus  tremula  during  his  search  for  salicin. 
It  exists  still  more  plentifully  in  the  leaves  of  the  same  tree,  and  is  obtained 
by  throwing  down  the  colouring  and  extractive  matter  of  an  aqueous  decoc- 
tion of  the  leaves  by  subacetate  of  lead,  as  in  the  process  for  salicin,  and 
then  evaporating  to  the  consistence  of  thin  syrup  :  the  impure  crystals  are 
pressed  within  linen,  mixed  with  a  little  animal  charcoal,  and  dissolved  in 
160  times  their  weight  of  boiling  water.  The  filtered  solution  depositee,  in 
cooling,  white,  silky,  acicular  crystals  of  populin. 

Populin  requires  2000  times  its  weight  of  cold,  and  70  of  boiling  water 
for  solution ;  but  it  is  much  more  soluble^in  hot  alcohol.  Acids  act  upon  it 
exactly  in  the  same  manner  as  on  salicin,  showing  that  these  two  sub- 
stances, if  essentially  distinct,  are  very  analogous  in  properties  and  com- 
position. 

Meconin. — This  principle  was  discovered  separately  by  M.  Couerbe  in 
1830,  and  before  that  period  by  M.  Dublanc;  but  we  are  indebted  to  the 
former  for  a  knowledge  of  its  composition  and  properties  (An.  de  Ch.  et  de 
Ph.  1.  337).  At  common  temperatures  it  is  a  white  solid,  inodorous,  and  of 
a  rather  acrid  taste  after  some  time,  though  tasteless  at  first.  It  begins  to 
liquefy  at  190°,  and  is  a  limpid  liquid  at  195°,  and  may  be  kept  fluid  till 
the  temperature  falls  to  167°.  At  311°  it  sublimes,  and  condenses  on  cool- 
ing into  a  white  matter  like  fat.  It  requires  266  parts  of  cold,  and  18-5  of 
water  for  solution,  and  is  very  soluble  in  alcohol,  ether,  and  the  ei- 


556  COLUMBIN. — ELATIN. — SINAPISIN. 

sential  oils.  It  crystallizes  from  these  solutions  in  six-sided  prisms,  two 
parallel  faces  of  the  prism  being  larger  than  the  rest,  and  forming  a  dihedral 
summit.  When  a  crystal  is  put  into  water  which  is  then  heated,  the  crystal 
becomes  softer,  then  forms  a  liquid  globule  like  oil  at  the  bottom  of  the 
flask,  and  then,  as  the  water  boils,  it  soon  disappears  entirely. 

Meconin  has  neither  acid  nor  alkaline  properties.  The  sulphuric  and 
nitric  acids  and  chlorine  decompose  it,  and  produce  compounds  of  a  charac- 
teristic nature.  In  sulphuric  acid  diluted  with  a  quarter  or  half  its  weight 
of  water  it  forms  in  the  cold  a  colourless  solution  ;  but  on  concentrating  to  a 
certain  point,  the  solution  acquires  a  deep  blue  tint :  in  this  state  the  me- 
conin  is  wholly  decomposed,  and  on  dilution  with  water  a  chestnut  matter 
falls,  which  is  soluble  in  warm  strong  sulphuric  acid,  alkalies,  alcohol,  and 
ether,  reproducing  the  green  solution  with  tine  first,  and  a  rose-red  with  the 
two  last.  Digested  in  nitric  acid  it  yields  a  yellow  solution,  which  yields  by 
evaporation  elongated  crystals  of  the  same.colour.  Chlorine,  transmitted  over 
fused  meconin,  gives  rise  to  a  fused  mass  of  a  reddish-yellow  colour,  consist- 
ing principally  of  chlorine  in  union  with  a  new  acid,  which  Couerbe  has 
termed  mechloic  acid. 

Meconin  is  a  constituent  of  opium,  and  is  procured  in  the  process  for 
preparing  narceia  already  described  (page  509).  By  ether  narceia  is  puri- 
fied in  that  process  from  narcotina,  fat,  and  meconin  ;  and  on  treating  the 
ethereal  extract  with  hot  water  the  meconin  is  separated  from  narcotina  and 
fat.  It  should  be  purified  by  a  second  crystallization,  a  little  animnl  char- 
coal  being  added.  Some  meconin  is  likewise  present  in  the  impure  mass  of 
morphia  when  precipitated  by  ammonia  (page  506),  and  is  taken  up  by  the 
alcohol  used  in  its  purification.  Meconin  is  present  in  very  small  quantity 
in  opium,  one  pound  containing  about  2^  grains ;  so  that  it  is  hopeless  to 
search  for  it  except  in  large  manufacturing  operations. 

According  to  Couerbe,  100  parts  of  meconin  contain  60-247  of  carbon, 
4-756  of  hydrogen,  and  34*997  of  oxygen. 

Columbin. — This  is  a  bitter  crystalline  principle,  obtained  by  M.  Witt- 
stock  from  an  alcoholic  deeociion  of  columbo  root:  the  solution  is  concen- 
trated to  about  a  third  of  its  volume,  and  is  then  left  in  a  warm  place,  when 
yellowish-brown  crystals  are  gradually  deposited.  It  is  purified  in  the 
usual  manner  by  animal  charcoal  and  solution  in  hot  alcohol,  from  which  it 
is  afterwards  obtained  in  colourless  prismatic  crystals.  (Royal  Inst,  Jour- 
nal, N.  S.  i.  630.) 

Elatin. — This  matter  has  been  described  by  Mr.  Hennell  (R.  Inst.  Jour- 
nal, N.  S.  i.  532),  and  is  prepared  by  forming  an  alcoholic  decoction  of 
elaterium,  distilling  off  most  of  the  alcohol,  and  setting  aside  the  remainder 
for  spontaneous  evaporation.  The  residual  mass  consists  of  a  green  resin, 
in  which  the  medical  qualities  of  elaterium  appear  to  reside,  and  a  crystal- 
line matter :  the  former  is  readily  taken  up  by  sulphuric  ether,  and  the  lat- 
ter left  in  a  nearly  pure  state.  It  is  deposited  in  colourless  acicular  tufts 
when  its  solution  in  hot  alcohol  is  allowed  to  cool.  In  water  it  is  nearly  in- 
soluble, and  is  very  slightly  dissolved  by  ether.  In  has  neither  acid  nor 
alkaline  properties,  fuses  at  a  heat  between  300°  and  400°,  and  has  a  bitter 
taste.  According  rto  the  analysis  of  Hennell,  46  parts  contain  17  of  carbon, 
11  of  hydrogen,  and  18  of  oxygen.  Elaterium  contains  40  per  cent,  of 
elatin,  and  21  per  cent,  of  the  green  resin,  the  remainder  being  ligneous 
fibre,  earthy  matter,  and  starch. 

Sinapisin, — A  peculiar  principle,  called  sulpho-sinapisin,  sinapisin,  or 
sinapin,  has  been  extracted  from  mustard  seed  (sinapis  alba)  by  MM.  Henry, 
jun.,  and  Garot,  who  at  first  supposed  it  to  be  an  acid,  but  have  since  cor- 
rected their  mistake  (Phil.  Mag.  and  An.  ix.  390).  They  believe  it  to  con- 
tain the  elements  of  sulphuret  of  cyanogen  united  with  a  peculiar  organic 
matter  from  which  the  volatile  oil  of  mustard  may  be  developed.  It  is  ob- 
tained by  forming-  an  aqueous  decoction  of  mustard  seed,  adding  subacetate 
of  oxide  of  lead  as  long  as  a  precipitate  falls,  removing  the  excess  of  that 


SACCHARINE  FERMENTATION.  557 

oxide  by  hydrosulphuric  acid,  and  concentrating  the  filtered  solution.  The 
first  crop  of  crystals  is  purified  by  a  second  crystallization. 

Pure  sinapisin  is  white  and  inodorous,  has  a  bitter  taste,  accompanied 
with  a  flavour  of  mustard,  is  more  soluble  in  hot  water  or  alcohol  than  when 
they  are  cold,  and  crystallizes  in  pearly  needles  or  small  prisms  arranged  in 
tufts.  Heated  with  hydrochloric  acid  it  is  decomposed,  emitting  an  odour  of 
hydrocyanic  acid;  and  when  distilled  with  sulphuric  or  phosphoric  acid,  sui- 
phocyanic  acid  is  generated.  By  the  fixed  alkalies  it  is  also  decomposed : 
evaporated  with  potassa,  the  sulphocyanuret  of  potassium  is  generated,  and  a 
strong  odour  of  the  volatile  oil  of  mustard  may  be  perceived.  With  sesqui- 
salts  of  iron  a  solution  of  sinapisin  strikes  a  deep  red  colour. 

The  ultimate  elements  contained  in  100  parts  of  sinapisin  are  50-504  car- 
bon, 7-795  hydrogen,  4'94  nitrogen,  9-657  sulphur,  and  27*104  oxygen. 


SECTION    VIII. 

SPONTANEOUS  CHANGES  OF  VEGETABLE  MATTER. 

VEGETABLE  substances,  for  reasons  already  explained  in  the  remarks  in- 
troductory to  the  study  of  organic  chemistry,  are  very  liable  to  spontaneous 
decomposition.  So  long,  indeed,  as  they  remain  in  connexion  with  the  living 
plant  by  which  they  were  produced,  the  tendency  of  their  elements  to  form 
new  combinations  is  controlled ;  but  as  soon  as  the  vital  principle  is  extinct, 
of  whose  agency  no  satisfactory  explanation  can  at  present  be  afforded,  they 
become  subject  to  the  unrestrained  influence  of  chemical  affinity.  To  the 
spontaneous  changes  which  they  then  experience  from  the  operation  of  this 
power,  the  term  fermentation  is  applied. 

As  might  be  expected  from  the  difference  in  the  constitution  of  different 
vegetable  compounds,  they  are  not  all  equally  prone  to  fermentation ;  nor  is 
the  nature  of  the  change  the  same  in  aril.  Thus  alcohol,  the  oxalic,  acetic, 
and  benzoic  acids,  and  probably  the  vegetable  alkalies,  may  be  kept  for 
years  without  change,  and  some  of  them  appear  unalterable ;  while  others, 
such  as  gluten,  sugar,  starch,  and  mucilaginous  substances,  are  very  liable 
to  decomposition.  In  like  manner,  the  spontaneous  change  sometimes  ter- 
minates in  the  formation  of  sugar,  at  another  time  in  that  of  alcohol,  at  a 
third  in  that  of  acetic  acid,  and  at  a  fourth  in  the  total  dissolution  of  the  sub- 
stance. This  has  led  to  the  division  of  the  fermentative  processes  into  four 
distinct  kinds,  namely,  the  saccharine,  vinous,  acetous,  and  putrefactive  fer- 
mentation. 

SACCHARINE  FERMENTATION. 

The  only  substance  known  to  be  subject  to  the  first  kind  of  fermentation 
is  starch.  When  gelatinous  starch,  or  amidine,  is  kept  in  a  moist  state  for  3 
considerable  length  of  time,  a  change  gradually  ensues,  and  a  quantity  of 
sugar,  equal  to  .about  half  the  weight  of  the  starch  employed,  is  generated. 
Exposure  to  the  atmosphere  is  not  necessary  to  this  change,  but  the  quantity 
of  sugar  is  increased  by  access  of  air. 

The  germination  of  seeds,  as  exemplified  in  the  malting  of  barley,  is  like- 
wise an  instance  of  the  saccharine  fermentation  ;  but  as  it  differs  in  some 
respects  from  the  process  above  mentioned,  being  probably  modified  by  the 
vitality  of  the  germ,  it  may  with  greater  propriety  be  discussed  in  the  follow* 
ing  section. 

47* 


558  VINOUS  FERMENTATION. 

The  ripening  of  fruit  has  also  been  regarded  as  an  example  of  the  saccha- 
rine fermentation,  especially  since  many  fruits,  of  which  the  pear  and  apple 
are  examples,  if  gathered  before  their  maturity,  ripen  by  keeping;  and  this 
view  is  contended  for  by  M.  Couverchel  as  an  inference  from  his  experi- 
mental inquiry  on  the  maturation  of  fruits.  (An.  de  Ch.  et  de  Ph.  xlvi.  147.) 
Proust,  who  examined  the  unripe  grape  in  its  different  stages  towards  matu- 
rity, found  that  the  green  fruit  contains  a  large  quantity  of  free  acid,  chiefly 
the  citric,  which  gradually  disappears  as  the  grape  ripens,  while  its  place  is 
occupied  by  sugar.  Couverchel  examined  the  grape,  peach,  apricot,  and 
pear.  He  found  that  the  acid  and  mucilaginous  matters  of  the  fruit  are 
diminished,  while  carbonic  acid,  water,  and  sugar  are  generated  :  these 
changes  he  found  to  be  independent  of  the  oxygen  of  the  air,  and  to  occur 
whether  the  fruit  is  on  the  tree  or  removed  from  it :  they  arise  from  reaction 
among  the  ingredients  of  the  fruit,  rendered  operative  by  heat,  but  indepen- 
dent of  vitality.  He  considers  the  developement  of  sugar  and  disapperance 
of  acid,  which  occur  during  the  process  of  ripening,  to  be  a  change  purely 
chemical. 

VINOUS  FERMENTATION. 

The  conditions  which  are  required  for  establishing  the  vinous  fermentation 
are  four  in  number ;  namely,  the  presence  of  sugar,  water,  yeast,  or  some 
ferment,  and  a  certain  temperature.     The  best  mode  of  studying  this  pro- 
cess, so  as  to  observe  the  phenomena  and  determine  the  nature  of  the  change, 
is  to  place  five  parts  of  sugar  with  about  twenty  of  water  in  a  glass  flask 
furnished  with  a  bent  tube,  the  extremity  of  which  opens  under  an  inverted 
jar  full  of  water  or  mercury ;  arid  after  adding  a  little  yeast,  to  expose  the 
mixture  to  a  temperature  of  about  60°  or  70°.     In  a  short  time  bubbles  of 
gas  begin  to  collect  in  the  vicinity  of  the  yeast,  and  the  liquid  is  soon  put 
into  brisk  motion,  in  consequence  of  the  formation  and  disengagement  of  a 
large  quantity  of  gaseous  matter;  the  solution  becomes  turbid,  its  tempera- 
ture rises,  and  froth  collects  upon  its  surface.     After  continuing  for  a  few 
days,  the  evolution  of  gas  begins  to  abate,  and  at  length  ceases  altogether ; 
the  impurities  gradually  subside,  and  leave  the  liquor  clear  and  transparent. 
The  only  appreciable  changes  which  are  found  to  have  occurred  during 
the  process  are  the  disappearance  of  the  sugar,  and  the  formation  of  alcohol, 
which  remains  in  the  flask,  and  of  carbonic  acid  gas,  which  is  collected  in 
the  pneumatic  apparatus.     A  small  portion  of  yeast  is  indeed  decomposed; 
but  the  quantity  is  so  minute  that  it  may  without  inconvenience  be  left  out 
of  consideration.  -The  yeast  indeed  appears  to  operate  only  in  exciting  the 
fermentation,  without  further  contributing  to  the  products.  The  atmospheric 
air,  it  is  obvious,  has  no  share  in  the  phenomena,  since  it  may  be  altogether 
excluded  without  affecting  the  result.     The  theory  of  the  process  is  founded 
on  the  fact  that  the  sugar,  which  disappears,  is  almost  precisely  equal  to  the 
united  weights  of  the  alcohol  and  carbonic  acid ;  and  hence  the  former  is 
supposed  to  be  resolved  into  the  two  latter.    The  mode  in  which  this  change 
is  conceived  to  take  place  has  been  ably  explained  by  Gay-Lussac,  an  expla- 
nation which  will  easily  be   understood  by  comparing  the  composition  of 
sugar  with  that  of  alcohol.     The  elements  of  sugar,  which  consist  of  car- 
bon, hydrogen,  and  oxygen,  in  the  ratio  of  one  equivalent  of  each  (page  516), 
are  multiplied  by  six,  in  order  to  equalize  the  quantity  of  hydrogen  contained 
in  the  two  compounds.     (An.  de  Ch.  xcv.  317.) 

Sugar.  Alcohol.  Carbonic  acid. 

Carbon     .     .    36-72      6  eq.  24-48      4  eq.  1224      2  eq. 

Hydrogen    .6          6  eq.  6          6  eq. 

Oxygen        .48          6  eq.  16          2  eq.  32          4  eq. 

90-72  46-48      1  eq.  44-24     2  cq. 

Tt  hence  appears  that  90-72  parts  of  sugar  are  capable  of  supplying  46-48 


VINOUS  FERMENTATION.  559 

of  alcohol,  and  44-24  of  carbonic  acid,  nearly  equal  weights,  without  any 
other  products. 

It  admits  of  doubt  whether  any  substance  besides  sugar  is  capable  of  un- 
dergoing1 the  vinous  fermentation.  The  only  other  principle  which  is  sup- 
posed to  possess  this  property  is  starch,  and  this  opinion  chiefly  rests  on  the 
two  following  facts.  First,  it  is  well  known  that  potatoes,  which  contain 
but  little  sugar,  yield  a  large  quantity  of  alcohol  by  fermentation,  during 
which  the  starch  disappears.  And,  secondly,  M.  Clement  procured  the  same 
quantity  of  alcohol  from  equal  weights  of  malted  and  unrnalted  barley.  (An. 
de  Ch.  et  de  Ph.  v.  422.)  Nothing  conclusive  can  be  inferred,  however,  from 
these  data  ;  for,  from  the  facility  with  which  starch  is  converted  into  sugar, 
it  is  probable  thai  the  saccharine  may  precede  the  vinous  fermentation.  This 
view  is,  indeed,  justified  by  the  practice  of  distillers,  who  do  not  ferment 
with  unmalted  barley  only,  but  are  obliged  to  mix  with  it  a  certain  proportion 
of  malt,  which  appears  to  act  as  a  ferment  to  the  unmalted  grain. 

Though  a  solution  of  pure  sugar  is  not  susceptible  of  the  vinous  fermen- 
tation without  being  mixed  with  yeast,  or  some  such  ferment,  yet  the  sac- 
charine juices  of  plants  do  not  require  the  addition  of  that  substance;  or  in 
other  words,  they  contain  some  principle  which,  like  yeast,  excites  the  fer- 
mentative process.  Thus,  must  or  the  juice  of  the  grape  ferments  sponta- 
neously;  but  Gay-Lussac  has  observed  that  these  juices  cannot  begin  to 
ferment  unless  they  are  exposed  to  the  air.  By  heating  must  to  212°,  and 
then  corking  it  carefully,  the  juice  may  be  preserved  without  change;  but  if 
it  be  exposed  to  the  air  for  a  few  seconds  only,  it  absorbs  oxygen,  and  fer- 
mentation takes  place.  From  this  it  would  appear  that  the  must  contains  a 
principle  which  is  convertible  into  yeast,  or  at  least  acquires  the  character- 
istic property  of  that  substance,  by  absorbing  oxygen. 

It  appears  from  the  experiments  of  M.  Colin,  that  various  substances  are 
capable  of  acting  as  a  ferment.  This  property  is  possessed  by  gluten  and 
vegetable  albumen,  caseous  matter,  albumen,  fibrin,  gelatin,  blood,  and  urine. 
In  general  they  act  most  efficaciously  after  the  commencement  of  putrefac- 
tion;  and  indeed  exposure  to  oxygen  gas  seems  equally  necessary  for  ena- 
bling these  substances  to  act  as  ferments,  as  to  the  principle  contained  in 
the  juice  of  fruit. 

The  various  kinds  of  stimulating  fluids,  prepared  by  means  of  the  vinous 
fermentation,  are  divisible  into  wines  which  are  formed  from  the  juices  of 
saccharine  fruits,  and  the  various  kinds  of  ale  and  beer  produced  from  a 
decoction  of  the  nutritive  grains  previously  malted. 

The  juice  of  the  grape  is  superior,  for  the  purpose  of  making  wine,  to  that 
of  all  other  fruits,  not  merely  in  containing  a  larger  portion  of  saccharine 
matter,  since  this  deficiency  may  be  supplied  artificially,  but  in  the  nature  of 
its  acid.  The  chief  or  only  acidulous  principle  of  the  mature  grape,  ripened 
in  a  warm  climate,  such  as  Spain,  Portugal,  or  Madeira,  is  bitartrate  of  po- 
tassa.  As  this  salt  is  insoluble  in  alcohol,  the  greater  part  of  it  is  deposited 
during  the  vinous  fermentation ;  and  an  additional  quantity  subsides,  con- 
stituting the  crusty  during  the  progress  of  wine  towards  its  point  of  highest 
perfection.  The  juices  of  other  fruits,  on  the  contrary,  such  as  the  goose- 
berry or  currant,  contain  malic  and  citric  acids,  which  are  soluble  both  in 
water  and  alcohol,  and  of  which  therefore  they  can  never  be  deprived.  Con- 
sequently these  wines  are  only  rendered  palatable  by  the  presence  of  free' 
sugar,  which  conceals  the  taste  of  the  acid:  and  hence  it  is  necessary  to 
arrest  the  progress  of  fermentation  long  before  the  whole  of  the  saccharine 
matter  is  consumed.  For  the  same  reason,  these  wines,  unless  made  very 
sweet,  do  not  admit  of  being  long  kept;  for  as  soon  as  the  free  sugar  is  con- 
verted into  alcohol  by  the  slow  fermentative  process,  which  may  be  retarded 
by  the  addition  of  brandy,  but  cannot  be  prevented,  the  wine  acquires  a 
strong  sour  taste. 

Ale  and  beer  differ  from  wine  in  containing  a  large  quantity  of  mucilagi- 
nous and  extractive  matters  derived  from  the  malt  with  which  they  are  made. 
From  the  presence  of  these  substances  they  always  contain  a  free  acid,  and 


560  ACETOUS  FERMENTATION. 

are  greatly  disposed  to  pass  into  the  acetous  fermentation.  The  sour  taste 
is  concealed  partly  by  free  sugar,  and  partly  by  the  bitter  flavour  of  the  hoj>, 
the  presence  of  which  diminishes  the  tendency  to  the  formation  of  an  acid. 

The  fermentative  process  which  takes  place  in  dough  mixed  with  yeast, 
and  on  which  depends  the  formation  of  good  bread,  has  been  supposed  to  be 
of  a  peculiar  kind,  and  is  sometimes  designated  by  the  name  of  panary  fer- 
mentation. The  ingenious  researches  of  Dr.  Colquhoun,  however,  leave  no 
doubt  that  the  phenomena  are  to  be  ascribed  to  the  saccharine  matter  of  the 
flour  undergoing  the  vinous  fermentation,  by  which  it  is  resolved  into  alcohol 
and  carbonic  acid,  (Brewster's  Journal,  vi.)  Mr.  Graham  first  procured 
alcohol  by  distillation  from  fermented  dough,  and  a  Company  was  formed  in 
London  for  collecting  the  spirit  emitted  by  dough  in  the  process  of  baking. 

ACETOUS  FERMENTATION. 

When  any  liquid  which  has  undergone  the  vinous  fermentation,  or  even 
pure  alcohol  diluted  with  water,  is  mixed  with  yeast,  and  exposed  in  a  warm 
place  to  the  open  air,  an  intestine  movement  speedily  commences,  heat  is 
developed,  the  fluid  becomes  turbid  from  the  deposition  of  a  peculiar  fila- 
mentous matter,  and  in  general  carbonic  acid  is  disengaged.  Oxygen  is 
absorbed  from  the  atmosphere.  These  changes,  after  continuing  a  certain 
time,  cease  spontaneously;  the  liquor  becomes  clear,  and  instead  of  alcohol, 
it  is  now  found  to  contain  acetic  acid.  This  process  is  called  the  acetous 
fermentation. 

The  vinous  may  easily  be  made -to  terminate  in  the  acetous  fermenta- 
tion ;  nay,  the  transition  takes  place  so  easily,  that  in  many  instances,  in 
which  it  is  important  to  prevent  it,  this  is  with  difficulty  effected.  It  is 
the  uniform  result,  if  the  fermenting  liquid  be  exposed  to  a  warm  tempera- 
ture and  to  the  open  air ;  and  the  means  by  which  it  is  avoided  is  by  ex- 
cluding the  atmosphere,  or  by  exposure  to  cold. 

For  the  acetous  fermentation  a  certain  degree  of  warmth  is  indispensable. 
It  takes  place  tardily  below  60°  F. ;  at  50°  it  is  very  sluggish ;  and  at  32°, 
or  not  quite  so  low,  it  is  wholly  arrested.  It  proceeds  with  vigour,  on  the 
contrary,  when  the  thermometer  ranges  between  60°  and  80°,  and  is  even 
promoted  by  a  temperature  somewhat  higher.  The  presence  of  water  is 
likewise  essential ;  and  a  portion  of  yeast,  or  some  analogous  substance,  by 
which  the  process  may  be  established,  must  also  be  present. 

The  information  contained  in  chemical  works  relative  to  the  substances 
susceptible  of  the  acetous  fermentation  is  somewhat  confused,  a  circum- 
stance which  appears  to  have  arisen  from  phenomena  of  a  totally  different 
nature  being  included  under  the  same  name.  It  seems  necessary  to  dis- 
tinguish between  the  mere  formation  of  acetic  acid,  and  the  acetous  fer- 
mentation. Several  or  perhaps  most  vegetable  substances  yield  acetic  acid 
when  they  undergo  spontaneous  decomposition.  Mucilaginous  substances 
in  particular,  though  excluded  from  the  air,  gradually  become  sour ;  and 
consistently  with  this  fact,  inferior  kinds  of  ale  and  beer  are  known  to 
acquire  acidity  in  a  short  time,  even  when  confined  in  well-corked  bottles. 
In  like  manner,  a  solution  of  sugar,  mixed  with  water,  in  which  the  gluten  of 
wheat  has  fermented,  and  kept  in  close  vessels,  was  found  by  Fourcroy  and 
Vauquelin  to  yield  acetic  acid.  All  these  processes,  however,  appear  essen- 
tially different  from  the  proper  acetous  fermentation  above  described,  being 
unattended  with  visible  movement  in  the  liquid,  with  absorption  of  oxygen, 
or  disengagement  of  carbonic  acid. 

The  acetous  fermentation,  in  this  limited  sense,  consists  in  the  conver- 
sion of  alcohol  into  acetic  acid.  That  this  change  does  really  take  place 
is  inferred,  not  only  from  the  disappearance  of  alcohol,  and  the  simulta- 
neous production  of  acetic  acid,  but  also  from  the  quantity  of  the  latter  be- 
ing precisely  proportional  to  that  of  the  former.  The  nature  of  the  chemi- 
cal action  requires  to  be  elucidated  by  future  researches.  The  production 
of  carbonic  acid  was  long  considered  as  an  essential  part  of  the  change;  but 


PUTREFACTIVE  FERMENTATION.  561 

as  it  is  now  known  that  the  acetificalion  of  pure  alcohol  may  occur  with- 
out  the  formation  of  carbonic  acid,  it  is  probable  that  the  appearance  of  that 
gas  during-  the  acetous  fermentation  of  vinous  liquors  is  referable  to  the 
simultaneous  evolution  of  alcohol  from  sugar  contained  in  the  solution. 
Looking  to  the  composition  of  alcohol  and  acetic  acid,  and  to  the  fact  that 
alcohol  may  be  acetified  by  atmospheric  oxygen  without  any  carbonic  acid 
being  formed,  the  most  feasible  theory  is,  that  a  certain  portion  of  alcohol 
and  oxygen  is  resolved  into  water  and  acetic  acid,  the  proportions  being 
such  that 

1  eq.  of  alcohol  4C-f-6H-J-2O  2    1  eq.  of  acetic  acid     4C  +  3H-f-3O 

and  4  eq.  of  oxygen     .         .         4O  '^  and  3  eq.  of  water  3(H-f-O). 

Tiiis  requires,  however,  a  more  direct  experimental  proof  than  it  has 
hitherto  received. 

The  acetous  fermentation  is  conducted  on  a  large  scale  for  yielding  the 
common  vinegar  of  commerce.  In  France  it  is  prepared  by  exposing  weak 
wines  to  the  air  during  warm  weather ;  and  in  this  country  it  is  made  from 
a  solution  of  brown  sugar  or  molasses,  or  an  infusion  of  malt.  The  vinegar 
thus  obtained  always  contains  a  large  quantity  of  mucilaginous  and  other 
vegetable  matters,  the  presence  of  which  renders  it  liable  to  several  ulterior 
changes. 

PUTREFACTIVE  FERMENTATION. 

By  this  term  is  implied  a  process  which  is  not  attended  with  the  pheno- 
mena of  the  saccharine,  vinous,  or  acetous  fermentation,  but  during  which 
the  vegetable  matter  is  completely  decomposed.  All  proximate  principles 
are  not  equally  liable  to  this  kind  of  dissolution.  Those  in  which  charcoal 
end  hydrogen  prevail,  such  as  the  oils,  resins,  and  alcohol,  do  not  undergo 
the  putrefactive  fermentation;  nor  do  acids,  which  contain  a  considerable 
excess  of  oxygen,  manifest  a  tendency  to  suffer  this  change.  Those  sub- 
stances alone  are  disposed  to  putrefy,  the  oxygen  and  hydrogen  of  which 
are  in  proportion  to  form  water ;  and  such,  in  particular,  as  contain  nitro- 
gen. Among  these,  however,  a  singular  difference  is  observable.  Caffein 
evinces  no  tendency  to  spontaneous  decomposition ;  while  gluten,  which 
certainly  must  contain  a  smaller  proportional  quantity  of  nitrogen,  putre- 
fies with  great  facility.  It  is  difficult  to  assign  the  precise  cause  of  this 
difference;  but  it  most  probably  depends  partly  upon  the  mode  in  which 
the  ultimate  elements  of  bodies  are  arranged,  and  partly  on  their  cohesive 
power; — those  substances,  the  texture  of  which  is  the  most  loose  and  soft, 
being,  c&teris  paribus,  the  most  liable  to  spontaneous  decomposition. 

The  conditions  which  are  required  for  enabling  the  putrefactive  process 
to  take  place,  are  moisture,  air,  aud  a  certain  temperature. 

The  presence  of  a  certain  degree  of  moisture  is  absolutely  necessary  ; 
and  hence  vegetable  substances,  which  are  disposed  to  putrefy  under  favour- 
able circumstances,  may  be  preserved  for  an  indefinite  period  if  carefully 
dried,  and  protected  from  humidity.  Water  acts  apparently  by  softening1 
the  texture,  and  thus  counteracting  the  agency  of  cohesion ;  and  a  part  of 
the  effect  may  also  be  owing  to  its  affinity  for  some  of  the  products  of  putre- 
faction. It  is  not  likely  that  this  liquid  is  actually  decomposed,  since  water 
appears  to  be  a  uniform  product. 

The  air  cannot  be  regarded  as  absolutely  necessary,  since  putrefaction  is 
found  to  be  produced  by  the  concurrence  of  the  two  other  conditions  only; 
but  the  process  is  without  doubt  materially  promoted  by  free  exposure  to 
the  atmosphere.  Its  operation  is  of  course  attributable  to  the  oxygen  com- 
bining  with  the  carbon  and  hydrogen  of  the  decaying  substance. 

The  temperature  most  favourable  to  the  putrefactive  process  is  between 
60°  and  100°.  A  strong  heat  is  unfavourable,  by  expelling  moisture;  and 
a  cold  of  32°,  at  which  water  congeals,  arrests  its  progress  altogether,  Tho 


562  GERMINATION'. 

mode  in  which  caloric  acts  is  the  same  as  in  all  similar  cases,  namely,  by 
tending  to  separate  elements  from  one  another  which  are  already  combined. 

The  products  of  the  putrefactive  fermentation  may  be  divided  into  the 
solid,  liquid,  and  gaseous.  The  liquid  are  chiefly  water,  together  with  a 
little  acetic  acid,  and  probably  oil.  The  gaseous  products  are  light  car- 
buretted  hydrogen,  carbonic  acid,  and,  when  nitrogen  is  present,  ammonia. 
Pure  hydrogen,  and  probably  nitrogen,  are  sometimes  disengaged.  Thus 
hydrogen  and  carbonic  acid,  according  to  Proust,  are  evolved  from  putrefy- 
ing gluten;  and  Saussure  obtained  the  same  gases  from  the  putrefaction 
of  wood  in  close  vessels.  Under  ordinary  circumstances,  however,  the 
chief  gaseous  product  of  decaying  plants  is  light  carburetted  hydrogen, 
which  is  generated  in  great  quantity  at  the  bottom  of  stagnant  pools  during 
summer  and  autumn  (page  248).  Another  elastic  principle,  supposed  to 
arise  from  putrefying  vegetable  remains,  is  the  noxious  rniasm  of  marshes. 
The  origin  of  these  miasms,  however,  is  exceedingly  obscure.  Every  at- 
tempt to  obtain  them  in  an  insulated  state  has  hitherto  proved  abortive ; 
and,  therefore,  if  they  are  really  a  distinct  species  of  matter,  they  must  be 
regarded,  like  the  effluvia  of  contagious  fevers,  as  of  too  subtle  a  nature  for 
being  subjected  to  chemical  analysis. 

When  the  decay  of  leaves  or  other  parts  of  plants  has  proceeded  so  far 
that  all  trace  of  organization  is  effaced,  a  dark  pulverulent  substance  re- 
mains, consisting  of  charcoal  combined  with  a  little  oxygen  and  hydrogen. 
This  compound  is  vegetable  mould,  which,  when  mixed  with  a  proper 
quantity  of  earth,  constitutes  the  soil  necessary  to  the  growth  of  plants. 
Saussure,  in  his  excellent  Recherches  Chimiques  sur  la  Vegetation,  has  de- 
ecribed  vegetable  mould  as  a  substance  of  uniform  composition  ;  and  on 
heating  it  to  redness  in  close  vessels,  he  procured  carburetted  hydrogen  and 
carbonic  acid  gases",  water  holding  acetate  or  carbonate  of  ammonia  in  solu- 
tion, a  minute  quantity  of  ernpyreumatic  oil,  and  a  large  residue  of  charcoal 
mixed  with  saline  and  earthy  ingredients.  On  exposing  vegetable  mould  to 
the  action  of  light,  air,  and  moisure,  a  chemical  change  ensues,  the  effect 
of  which  is  to  render  a  portion  of  it  soluble  in  water,  and  thus  applicable  to 
the  nutrition  and  growth  of  plants. 


SECTION    IX. 


CHEMICAL  PHENOMENA  OF  GERMINATION  AND 
VEGETATION. 

Germination. 

GERMINATION  is  the  process  by  which  a  new  plant  originates  from  seed. 
A  seed  consists  essentially  of  two  parts,  the  germ  of  the  future  plant,  en- 
dowed with  a  principle  of  vitality,  and  the  cotyledons  or  seed-lobes,  both  of 
which  are  enveloped  in  a  common  covering  of  cuticle.  In  the  germ  two 
parts,  the  radicle  and  plumula,  may  be  distinguished,  the  former  of  which  is 
destined  to  descend  into  the  earth  and  constitute  the  root,  the  latter  to  rise 
into  the  air  and  form  the  stem  of  the  plant.  The  office  of  the  seed-lobes  is 
to  afford  nourishment  to  the  young  plant,  until  its  organization  is  so  far  ad- 
vanced, that  it  may  draw  materials  for  its  growth  from  extraneous  sources. 
For  this  reason  seeds  are  composed  of  highly  nutritious  ingredients.  The 
chief  constituent  of  most  of  them  is  starch,  in  addition  to  which  they  fre- 
quently contain  gluten,  gum,  vegetable  albumen  or  curd,  and  sugar. 

The  conditions  necessary  to  germination  are  three-fold  ;  namely,  moisture, 


GERMINATION.  563 

a  certain  temperature,  and  the  presence  of  oxygen  gas.  The  necessity  of 
moisture  to  this  process  has  been  proved  by  extensive  observation.  It  is 
well  known  that  the  concurrence  of  other  conditions  cannot  enable  seeds  to 
germinate,  provided  they  are  kept  quite  dry. 

A  certain  degree  of  warmth  is  not  less  essential  than  moisture.  Germi- 
nation cannot  take  place  at  32° ;  and  a  strong  heat,  such  as  that  of  boiling 
water,  prevents  it  altogether,  by  depriving  the  germ  of  the  vital  principle. 
The  most  favourable  temperature  ranges  from  60°  to  80°,  the  precise  degree 
varying  with  the  nature  of  the  plant,  a  circumstance  that  accounts  for  tho 
difference  in  the  season  of  the  year  at  which  different  seeds  begin  to  ger- 
minate. 

That  the  presence  of  air  is  necessary  to  germination  was  demonstrated 
by  several  philosophers,  such  as  Ray,  Boyle,  Muschenbroeck  and  Boerhaave, 
before  the  chemical  nature  of  the  atmosphere  was  discovered  ;  and  Scheele, 
soon  after  the  discovery  of  oxygen,  proved  that  beans  do  not  germinate 
without  exposure  to  that  gas.  Achard  afterwards  demonstrated  the  same 
fact  with  respect  to  seeds  in  general,  and  his  experiments  have  been  fully 
confirmed  by  subsequent  observers.  It  has  even  been  shown  by  Humboldt, 
that  a  dilute  solution  of  chlorine,  owing  to  the  tendency  of  that  gas  to  de- 
compose water  and  set  oxygen  at  liberty,  promotes  the  germination  of  seeds. 
These  circumstances  account  for  the  fact  that  seeds,  when  buried  deep  in 
the  earth,  are  unable  to  germinate. 

It  is  remarkable  that  the  influence  of  light,  which  is  so  favourable  to  all 
the  subsequent  stages  of  vegetation,  is  injurious  to  the  process  of  germina- 
tion, Ingenhousz  and  Sennebier  have  proved  that  a  seed  germinates  more 
rapidly  in  the  shade  than  in  light,  and  in  diffused  daylight  quicker  than 
when  exposed  to  the  direct  solar  rays. 

From  the  preceding  remarks  it  is  apparent  that  when  a  seed  is  placed  an 
inch  or  two  under  the  surface  of  the  ground  in  spring,  and  is  loosely  cover- 
ed with  earth,  it  is  in  a  state  every  way  conducive  to  germination.  The 
ground  is  warmed  by  absorbing  tho  solar  rays,  and  is  moistened  by  occa- 
sional showers  ;  the  earth  at  the  same  time  protects  the  seed  from  light,  but 
by  its  porosity  gives  free  access  to  the  air. 

The  operation  of  malting  barley,  in  which  the  grain  is  made  to  germi- 
nate by  exposure  to  warmth,  air,  and  humidity,  affords  the  best  means  of 
studying  the  phenomena  of  germination.  In  preparing  malt,  the  grain 
passes  through  four  distinct  stages,  called  steeping,  couching,  flooring,  and 
kiln-drying.  In  the  first  it  is  steeped  in  water  for  about  two  days,  when  it 
absorbs  moisture,  softens,  and  swells  considerably.  It  is  then  removed  to 
the  couch-frame,  where  it  is  laid  in  heaps  30  inches  in  depth  for  from  26  to 
30  hours.  In  this  situation  the  grain  becomes  warm,  and  acquires  a  dispo- 
sition to  germinate  ;  but  as  the  temperature,  in  such  large  heaps,  would 
rise  very  unequally,  and  germination  consequently  be  rapid  in  some  portions 
and  slow  in  others,  the  process  of  flooring  is  employed.  This  consists  in 
laying  the  grain  in  strata  a  few  inches  thick  on  large  airy  but  shaded  floors, 
where  it  remains  for  about  12  or  14  days  until  germination  has  advanced  to 
the  extent  desired  by  the  malstcr.  During  this  interval  the  grain  is  fre- 
quently turned,  in  order  that  the  temperature  of  the  whole  mass  should  be 
uniform,  that  each  grain  should  be  duly  exposed  to  the  air,  and  that  the 
radicles  of  contiguous  grains  should  not  become  entangled  with  each  other. 
As  soon  as  saccharine  matter  is  freely  developed,  germination  must  be  ar- 
rested ;  since  otherwise,  being  taken  up  as  nutriment  by  the  young  plant,  it 
would  speedily  disappear.  Accordingly,  the  grain  is  removed  to  the  kiln, 
where  it  is  exposed  to  a  temperature  gradually  rising  from  100°  to  160°,  or 
rather  higher ;  the  object  being,  first,  to  dry  the  grain  completely,  and  then 
to  provide  against  any  recurrence  of  germination  by  destroying  the  vitality 
of  the  plant.  The  most  convenient  mode  of  applying  the  heat  is  to  place 
the  grain  on  a  metallic  net-work,  through  which  passes  hot  air  issuing  from 
a  fire  made  with  good  coke.  The  process  of  malting  is  not  conducted 
during  summer,  because  in  hot  weather  the  grain  is  apt  to  become  mouldy. 


564  GROWTH  OF  PLANTS. 

The  difference  between  malted  and  un malted  barley  is  readily  perceived 
by  the  taste;  but  it  will  be  more  correctly  appreciated  by  inspecting  the  re* 
suit  of  Proust's  comparative  analysis  of  malted  and  unmalted  barley.  (An. 
de  Ch.  et  de  Ph.  v.) 

In  100  In  100 
parts  of  barley.                         parts  of  malt. 

Resin          ....           1  ....  1 

Gum            ....           4  ....  15 

Sugar          ....          5  ....  15 

Gluten        ....          3  ....  1 

Starch          ....         32  ....  56 

Hordein       ....        55  ....  12 

It  is  hence  apparent  that,  during  germination,  the  hordein  is  converted 
into  starch,  gum,  and  sugar;  so  that,  from  an  insoluble  material,  which 
could  not  in  that  state  be  applied  to  the  uses  of  the  young  plant,  two  soluble 
and  highly  nutritive  principles  result,  which  by  being  dissolved  in  water  are 
readily  absorbed  by  the  radicle. 

The  chemical  changes  which  take  place  during  germination  have  been 
ably  investigated  by  Suussure,  whose  experiments  are  detailed  in  the  work 
to  which  I  have  already  referred.  The  leading  facts  which  he  determined 
are  the  following: — that  oxygen  gas  is  consumed,  that  carbonic  acid  is 
evolved,  and  that  the  volume  of  the  latter  is  precisely  equal  to  that  of  the 
former.  Now  since  carbonic  acid  gas  contains  its  own  volume  of  oxygen, 
it  follows  that  this  gas  must  have  united  exclusively  with  carbon.  It  is 
likewise  obvious  that  the  grain  must  weigh  less  after  than  before  germina- 
tion, provided  it  is  brought  to  the  same  state  of  dryness  in  both  instances. 
Saussure  indeed  found  that  the  loss  is  greater  than  can  be  accounted  for  by 
the  carbon  of  the  carbonic  acid  which  is  evolved;  and  hence  he  concluded 
that  a  portion  of  water,  generated  at  the  expense  of  the  grain  itself,  is  dis- 
sipated in  drying.  According-  to  Proust,  the  diminution  in  weight  is  about 
a  third;  but  Dr.  Thomson  affirms  that  in  fifty  processes,  conducted  on  a 
large  scale  under  his  inspection,  the  average  loss  did  not  exceed  one-fifth. 

Growth  of  Plants. 

While  a  plant  differs  from  an  animal  in  exhibiting  no  signs  of  perception 
or  voluntary  motion,  and  in  possessing  no  stomach  to  serve  as  a  receptacle 
for  its  food,  there  exists  between  them  a  close  analogy  both  of  parts  and 
functions,  which,  though  not  discerned  at  first,  becomes  striking  on  a  near 
examination.  The  stem  and  branches  act  as  a  frame-work  or  skeleton  for 
the_  support  and  protection  of  the  parts  necessary  to  the  life  of  the  individual. 
The  root  serves  the  purpose  of  a  stomach  by  imbibing  nutritious  juices 
from  the  soil,  and  thus  supplying  the  plant  with  materials  for  its  growth. 
The  sap  or  circulating  fluid,  composed  of  water  holding  in  solution  saline, 
extractive,  mucilaginous,  saccharine,  and  other  soluble  substances,  rises  up- 
wards through  the  wood  in  a  distinct  system  of  tubes  called  the  common 
vessels,  which  correspond  in  their  office  to  the  lacteals  and  pulmonary  arte- 
ries of  animals,  and  are  distributed  in  minute  ramifications  over  the  surface 
of  the  leaves.  In  its  passage  through  this  organ,  which  may  be  termed  the 
lungs  of  a  plant,  the  sap  is  fully  exposed  to  the  agency  of  light  and  air,  ex- 
periences a  change  by  which  it  is  more  completely  adapted  to  the  wants  of 
the  vegetable  economy,  and  then  descends  through  the  inner  layer  of  the 
bark  in  another  system  of  tubes  called  the  proper  vessels,  yielding  in  its 
course  all  the  juices  and  principles  peculiar  to  the  plant. 

The  chemical  changes  which  take  place  during  the  circulation  of  the  sap 
are  in  general  of  such  a  complicated  nature,  and  so  much  under  the  control 
of  the  vital  principle,  as  to  elude  the  sagacity  of  the  chemist.  One  part  of 
the  subject,  however,  namely,  the  reciprocal  agency  of  the  atmosphere  and 


GROWTH  OF  PLANTS.  565 

growing  vegetables  on  each  other,  falls  within  the  reach  of  chemical  inquiry, 
and  has  accordingly  been  investigated  by  several  philosophers. 

For  the  leading  facts  relative  to  what  is  called  the  respiration  of  plants 
or  the  chemical  changes  which  the  leaves  of  growing  vegetables  produce  on 
the  atmosphere,  we  are  indebted  to  Priestley  and  Ingenhousz,  the  former  of 
whom  discovered  that  plants  absorb  carbonic  acid  from  the  air  under  certain 
circumstances,  and  emit  oxygen  in  return;  and  the  latter  ascertained  that 
this  change  occurs  only  during  exposure  to  the  direct  rays  of  the  sun. 
When  a  healthy  plant,  the  roots  of  which  are  supplied  with  proper  nourish- 
ment, is  exposed  to  the  direct  solar  beams  in  a  given  quantity  of  atmo- 
spheric air,  the  carbonic  acid  after  a  certain  interval  is  removed,  and  an 
equal  volume  of  oxygen  is  substituted  for  it.  If  a  fresh  portion  of  carbonic 
acid  is  supplied,  the  same  result  will  ensue.  In  like  manner,  Sermebier  and 
Woodhouse  observed,  that  when  the  leaves  of  a  plant  are  immersed  in  water, 
arid  exposed  to  the  rays  of  the  sun,  oxygen  gas  is  disengaged.  That  the 
evolution  of  oxygen  in  this  experiment  is  accompanied  with  a  proportional 
absorption  of  carbonic  acid,  is  proved  by  employing  water  deprived  of  car- 
bonic acid  by  boiling,  in  which  case  little  or  no  oxygen  is  procured. 

Such  are  the  changes  induced  by  plants  when  exposed  to  sunshine;  but 
in  the  dark  an  opposite  effect  ensues.  Carbonic  acid  gas  is  not  absorbed 
under  these  circumstances,  nor  is  oxygen  gas  evolved ;  but,  on  the  contrary, 
oxygen  disappears,  and  carbonic  acid  gas  is  evolved.  In  the  dark,  therefore, 
vegetables  deteriorate  rather  than  purify  the  air,  producing  the  same  effect  as 
the  respiration  of  animals. 

The  cause  of  these  opposite  effects  has  been  lately  discussed  by  Professor 
Burnet,  who  has  offered  an  ingenious  explanation,  supported  by  experi- 
ments which  appear  to  rne  satisfactory.  (R.  Inst.  Journ.  N.  S.  i.  83.)  He 
considers  that  the  influence  of  vegetation  on  the  atmosphere  is  owing  not  to 
one  but  to  two  functions,  digestion  and  respiration :  the  latter  is  believed  to 
proceed  at  all  times  as  in  animals  without  intermission,  and  its  uniform 
effect  is  the  production  of  carbonic  acid  ;  while  the  former  takes  place  only 
under  the  influence  of  light,  and  gives  rise  to  evolution  of  oxygen  gas,  and 
the  abstraction  of  carbonic  acid.  A  plant,  exposed  to  sunshine,  purifies  the 
air,  by  absorbing  carbonic  acid  from  the  atmosphere,  as  well  as  that  emitted 
by  its  own  respiration,  and  emits  oxygen  gas  in  return.  In  the  dark,  diges- 
tion is  at  a  stand,  and  respiration  continuing  without  intermission,  carbonic 
acid  accumulates. 

From  several  of  the  preceding  facts,  it  is  supposed  that  the  oxygen  emit- 
ted by  plants  while  under  the  influence  of  light  is  derived  from  the  carbonic 
acid  which  they  absorb,  and  that  the  carbon  of  that  gas  is  applied  to  the 
purposes  of  nutrition.  Consistently  with  this  view  it  has  been  observed  that 
plants  do  not  thrive  when  kept  in  an  atmosphere  of  pure  oxygen  ;  and  it 
was  found  by  Dr.  Percival  and  Mr.  Henry,  that  the  presence  of  a  little  car- 
bonic acid  is  even  favourable  to  their  growth.  Saussure,  who  examined  this 
subject  minutely,  ascertained  that  plants  grow  better  in  an  atmosphere 
which  contains  about  one-twelfth  of  carbonic  acid  than  in  common  air,  pro- 
vided they  arc  exposed  to  sunshine;  but  if  that  gas  be  present  in  a  greater 
proportion,  its  influence  is  prejudicial.  In  an  atmosphere  consisting  of  one- 
half  of  its  volume  of  carbonic  acid,  the  plants  perished  in  seven  days;  and 
they  did  not  vegetate  at  all  when  that  gas  was  in  the  proportion  of  two- 
thirds.  In  the  shade,  the  presence  of  carbonic  acid  is  always  detrimental. 
He  likewise  observed  that  the  presence  of  oxygen  is  necessary,  in  order  that 
a  plant  should  derive  benefit  from  admixture  with  carbonic  acid. 

Saussure  is  of  opinion  that  plants  derive  a  large  quantity  of  their  carbon 
from  the  carbonic  acid  of  the  atmosphere,  an  opinion  which  receives  great 
weight  from  the  two  following  comparative  experiments.  On  causing  a 
plant  to  vegetate  in  pure  water,  supplied  with  common  air  and  exposed  to 
light,  the  carbon  of  the  plant  increased  in  quantity;  but  when  supplied  with 
common  air  in  a  dark  situation,  it  even  lost  a  portion  of  the  carbon  which  it 
had  previously  possessed. 

48 


566  FOOD    OF   PLANTS. 

Light  is  necessary  to  the  colour  of  plants.  The  experiments  of  Sennebier 
and  Mr.  Gough  have  shown  that  the  green  colour  of  the  leaves  is  not  de- 
veloped, except  when  they  are  in  a  situation  to  absorb  oxygen  and  give  out 
carbonic  acid. 

Though  the  experiments  of  different  philosophers  agree  as  to  the  in- 
fluence of  vegetation  on  the  air  in  sunshine  and  during  the  night,  very  dif- 
ferent opinions  have  been  expressed  both  as  to  the  phenomena  occasioned 
by  diffused  daylight,  and  concerning  the  total  effect  produced  by  plants  on 
the  constitution  of  the  atmosphere.  Priestley  found  that  air,  vitiated  by 
combustion  or  the  respiration  of  animals,  and  left  in  contact  for  several 
days  and  nights  with  a  sprig  of  mint,  was  gradually  restored  to  its  original 
purity  ;  and  hence  he  inferred  that  the  oxygen  gas,  consumed  during  these 
and  various  other  processes,  is  restored  to  the  mass  of  the  atmosphere  by 
the  agency  of  growing  vegetables.  This  doctrine  was  confirmed  by  the  re- 
searches of  Ingenhousz  and  Saussure,  who  found  that  the  quantity  of  oxy- 
gen evolved  from  plants  by  day  exceeds  that  of  carbonic  acid  emitted  during 
the  night;  and  Davy  arrived  at  the  same  conclusions  as  Priestley.  But  an 
opposite  opinion  has  been  supported  by  Mr.  Ellis,  who,  from  an  extensive 
series  of  experiments,  contrived  with  much  sagacity,  inferred  that  growing 
plants  give  out  oxygen  only  in  direct  sunshine,  while  at  other  times  they 
absorb  it;  that  when  exposed  to  the  ordinary  vicissitudes  of  sunshine  and 
shade,  light  and  darkness,  they  form  more  carbonic  acid  in  the  period  of  a 
day  and  night  than  they  destroy ;  and,  consequently,  that  the  general  effect 
of  vegetation  on  the  atmosphere  is  the  same  as  that  produced  by  animals. 
(Ellis's  Researches  and  Farther  Inquiries  on  Vegetation,  &c.) 

The  recent  experiments  of  Dr.  Daubeny  appear  decisive  of  this  question. 
He  has  convinced  himself  that  in  fine  weather  a  plant  consisting  chiefly  of 
leaves  and  stems,  if  confined  in  the  same  portion  of  air  night  and  day,  and 
duly  supplied  with  carbonic  acid  gas  during  the  sunshine,  will  go  on  adding 
to  the  proportion  of  oxygen  present,  so  long  as  it  continues  healthy,  at  least 
up  to  a  certain  point;  the  slight  diminution  of  oxygen  and  increase  of  car- 
bonic acid  which  takes  place  during  the  night,  bearing  no  considerable  ratio 
to  the  degree  in  which  the  opposite  effect  occurs  by  day.  He  accounts  for 
the  discordance  between  his  own  results  and  those  of  Mr.  Ellis,  by  his  hav- 
ing carefully  removed  the  plants  from  the  experimenting  jar  as  soon  as 
they  began  to  suffer  from  the  heat  or  confinement,  and  conducted  the  expe- 
riments on  a  larger  and  more  suitable  scale.  (Reports  of  the  British  Asso- 
ciation for  1834,  436.) 

Food  of  Plants. 

The  chief  source  from  which  plants  derive  the  materials  for  their  growth 
is  the  soil.  However  various  the  composition  of  the  soil,  it  consists  essen- 
tially of  two  parts,  so  far  as  its  solid  constituents  are  concerned.  One  is  a 
certain  quantity  of  earthy  matters,  such  as  siliceous  earth,  clay,  lime,  and 
sometimes  magnesia ;  and  the  other  is  formed  from  the  remains  of  animal 
and  vegetable  substances,  which,  when  mixed  with  the  former,  constitute 
common  mould.  A  mixture  of  this  kind,  moistened  by  rain,  affords  the 
proper  nourishment  of  plants.  The  water,  percolating  through  the  mould, 
dissolves  the  soluble  salts  with  which  it  comes  in  contact,  together  with  the 
gaseous,  extractive,  and  other  matters  which  are  formed  during  the  decom- 
position of  the  animal  and  vegetable  remains.  In  this  state  it  is  readily  ab- 
sorbed by  the  roots,  and  conveyed  as  sap  to  the  leaves,  where  it  undergoes 
a  process  of  assimilation. 

But  though  this  is  the  natural  process  by  which  plants  obtain  the  greater 
part  of  their  nourishment,  and  without  which  they  do  not  arrive  at  perfect 
maturity,  they  may  live,  grow,  and  even  increase  in  weight,  when  wholly 
deprived  of  nutrition  from  this  source.  Thus  in  the  experiment  of  Saussure, 
already  described,  sprigs  of  peppermint  were  found  to  vegetate  in  distilled 
water ;  and  it  is  well  known  that  many  plants  grow  when  merely  suspended 


FOOD   OF   PLANTS.  567 

in  the  air.  In  the  hot-houses  of  the  botanical  garden  of  Edinburgh,  for  ex- 
ample, there  are  two  plants,  species  of  the  fig-tree,  the  Ficus  australis  and 
Ficus  elastica,  the  latter  of  which,  as  Dr.  Graham  informs  me,  has  been 
suspended  for  ten,  and  the  former  for  nearly  sixteen  years,  during  which 
time  they  have  continued  to  send  out  shoots  and  leaves. 

Before  scientific  men  had  learned  to  appreciate  the  influence  of  atmo- 
spheric air  on  vegetation,  the  increase  of  carbonaceous  matter,  which  occurs 
in  some  of  these  instances,  was  supposed  to  be  derived  from  water,  an 
opinion  naturally  suggested  by  the  important  offices  performed  by  this  fluid 
in  the  vegetable  economy.  Without  water  plants  speedily  wither  and  die. 
It  gives  the  soft  parts  that  degree  of  succulence  necessary  for  the  perform- 
ance of  their  functions; — it  affords  two  elements,  oxygen  and  hydrogen, 
which  either  as  water,  or  under  some  other  form,  are  contained  in  all  vege- 
table products; — and,  lastly,  the  roots  absorb  from  the  soil  those  substances 
only,  which  are  dissolved  or  suspended  in  water.  So  carefully,  indeed,  has 
nature  provided  against  the  chance  of  deficient  moisture,  that  the  leaves  are 
endowed  with  a  property  both  of  absorbing  aqueous  vapour  directly  from 
the  atmosphere,  and  of  lowering  their  temperature  during  the  night  by  ra- 
diation so  as  to  cause  a  deposition  of  dew  upon  their  surface,  in  conse- 
quence of  which,  during  the  driest  seasons  and  in  the  warmest  climates, 
they  frequently  continue  to  convey  this  fluid  to  the  plant,  when  it  can  no 
longer  be  obtained  in  sufficient  quantity  from  the  soil.  But  necessary  as 
water  is  to  vegetable  life,  it  cannot  yield  to  plants  a  principle  which  it  does 
not  possess.  The  carbonaceous  matter  which  accumulates  in  plants,  under 
the  circumstances  above  mentioned,  may,  with  every  appearance  of  justice, 
be  referred  to  the  atmosphere;  since  we  know  that  carbonic  acid  exists 
there,  and  that  growing  vegetables  have  the  property  of  taking  carbon  from 
that  gas. 

When  plants  are  incinerated,  their  ashes  are  found  to  contain  saline  and 
earthy  matters,  the  elements  of  which,  if  not  the  compounds  themselves,  are 
supposed  to  be  derived  from  the  soil.  Such  at  least  is  the  view  deducible 
from  the  researches  of  Saussure,  and  which  might  have  been  anticipated  by 
reasoning  on  chemical  principles.  The  experiments  of  M.  Schrader,  how- 
ever,  lead  to  a  different  conclusion.  He  sowed  several  kinds  of  grain,  such 
as  barley,  wheat,  rye,  and  oats,  in  pure  flowers  of  sulphur,  and  supplied  the 
shoots  as  they  grew  with  nothing  but  air,  light,  and  distilled  water.  On  in- 
cinerating the  plants,  thus  treated,  they  yielded  a  greater  quantity  of  saline 
&nd  earthy  matters  than  were  originally  present  in  the  seeds. 

These  results,  supposing  them  accurate,  may  be  accounted  for  in  two 
ways.  It  may  be  supposed,  in  the  first  place,  that  the  foreign  matters  were 
introduced  accidentally  from  extraneous  sources,  as  by  fine  particles  of  dust 
floating  in  the  atmosphere;  or,  secondly,  it  may  be  conceived,  that  they  were 
derived  from  the  sulphur,  air,  and  water,  with  which  the  plants  were  sup- 
plied. If  the  latter  opinion  be  adopted,  we  must  infer  either  that  the  vital 
principle,  which  certainly  controls  chemical  affinity  in  a  surprising  manner, 
and  directs  this  power  in  the  production  of  new  compounds  from  elementary 
bodies,  may  likewise  convert  one  element  into  another ;  or  that  some  of  the 
substances,  supposed  by  chemists  to  be  simple,  such  as  oxygen  and  hydro- 
gen, are  compounds,  not  of  two,  but  of  a  variety  of  different  principles.  As 
these  conjectures  are  without  foundation,  and  are  utterly  at  variance  with 
the  facts  and  principles  of  the  science,  I  do  not  hesitate  in  adopting  the  more 
probable  opinion,  that  the  experiments  of  M.  Schrader  were  influenced  by 
some  source  of  error  which  escaped  detection, 


568 


ANIMAL  CHEMISTRY. 

ALL  distinct  compounds,  which  are  derived  from  the  bodies  of  animals, 
are  called  proximate  animal  principles.  They  are  distinguished  from  inor- 
ganic matter  by  the  characters  stated  in  the  introduction  to  organic  chemis- 
try. The  circumstances  which  serve  to  distinguish  them  from  vegetable 
matter  are,  the  presence  of  nitrogen,  their  strong  tendency  to  putrefy,  and 
the  highly  offensive  products  to  which  their  spontaneous  decomposition  gives 
rise.  It  should  be  remembered,  however,  that  nitrogen  is  likewise  a  consti- 
tuent of  many  vegetable  substances;  though  few  of  these,  the  vegeto-animal 
principles  excepted  (page  549),  are  prone  to  suffer  the  putrefactive  fermenta- 
tion. It  is  likewise  remarkable  that  some  compounds  of  animal  origin,  such 
as  cholesterine  and  the  oils,  do  not  contain  nitrogen  as  one  of  their  elements, 
and  are  not  disposed  to  putrefy. 

The  essential  constituents  of  animal  compounds  are  carbon,  hydrogen, 
oxygen,  and  nitrogen,  besides  which  some  of  them  contain  phosphorus,  sul- 
phur, iron,  and  earthy  and  saline  matters  in  small  quantity.  Owing  to  the 
presence  of  sulphur  and  phosphorus,  the  process  of  putrefaction,  which  will 
be  particularly  described  hereafter,  is  frequently  attended  with  the  disen- 
gagement of  hydrosulphuric  acid  and  phosphuretted  hydrogen  gases.  When 
heated  in  close  vessels,  they  yield  water,  carbonic  oxide,  carburetted  hydro- 
gen, probably  free  nitrogen  and  hydrogen,  carbonate  and  hydrocyanate  of 
ammonia,  and  a  peculiarly  fetid  thick  oil.  The  carbonaceous  matter  left  in 
the  retort  is  less  easily  burned,  and  is  more  effectual  as  a  decolorizing  agent, 
than  charcoal  derived  from  vegetable  matter. 

The  principle  of  the  method  of  analyzing  animal  substances  has  already 
been  mentioned  (page  476). 

In  describing  the  proximate  animal  principles,  the  number  of  which  is  far 
less  considerable  than  that  of  vegetable  compounds,  the  arrangement  sug- 
gested by  Gay-Lussac  and  Thenard  in  their  Recherches  Physico-Chimiques^ 
and  followed  by  Thenard  in  his  System  of  Chemistry  has  been  adopted. 
The  animal  compounds  are  accordingly  arranged  in  three  sections.  The 
first  contains  substances  which  are  neither  acid  nor  oleaginous;  the  second 
comprehends  the  animal  acids;  and  the  third  includes  the  animal  oils  and 
fats.  Several  of  the  principles  belonging  to  the  first  division,  such  as  fibrin, 
albumen,  gelatin,  caseous  matter,  and  urea,  were  shown  by  Gay-Lussac  and 
Thenard  to  have  several  points  of  similarity  in  their  composition.  They  all 
contain,  for  example,  a  large  quantity  of  carbon,  and  their  hydrogen  is  in 
such  proportion  as  to  convert  all  their  oxygen  into  water,  and  their  nitrogen 
into  ammonia.  No  general  laws  have  been  established  relative  to  the  con- 
stitution of  the  compounds  comprised  in  the  other  sections. 

PROXIMATE  ANIMAL  SUBSTANCES. 

SECTION    I. 
SUBSTANCES  WHICH  ARE  NEITHER  ACID  NOR  OLEAGINOUS. 

Fibrin. 

FIBRIN  enters  largely  into  the  composition  of  the  blood,  and  is  the  basis  of 
the  muscles;  it  may  be  regarded,  therefore,  as  one  of  the  most  abundant  of 
the  animal  principles.  It  is  most  conveniently  procured  by  stirring  recently 
drawn  blood  with  a  stick  during  its  coagulation,  and  then  washing  the 


FIBRIN.  -  ALBUMEN.  569 

adhering  fibres  with  water  until  they  are  perfectly  white.  It  may  also  be 
obtained  from  lean  beef  cut  into  small  slices,  the  soluble  parts  being  removed 
by  digestion  in  several  successive  portions  of  water. 

Fibrin  is  solid,  white,  insipid,  and  inodorous.  When  moist  it  is  somewhat 
elastic,  but,  on  drying,  it  becomes  hard,  brittle,  and  semi-transparent.  In  a 
moist,  warm  situation  it  readily  putrefies.  It  is  insoluble  in  water  at  com- 
mon  temperatures,  and  is  dissolved  in  very  minute  quantity  by  the  continued 
action  of  boiling  water.  Alcohol,  of  specific  gravity  0-81,  converts  it  into  a 
fatty  adipocirous  matter,  which  is  soluble  in  alcohol  and  ether,  but  is  preci- 
pitated by  water. 

The  action  of  acids  on  fibrin  has  been  particularly  described  by  Berzelius. 
(Medico-Chir.  Trans,  iii.  201  )  Digested  in  concentrated  acetic  acid,  fibrin 
swells  and  becomes  a  bulky  tremulous  jelly,  which  dissolves  completely, 
with  disengagement  of  a  little  nitrogen,  in  a  considerable  quantity  of  hot 
water. 

By  the  action  of  nitric  acid  of  specific  gravity  1-25,  aided  by  heat,  on 
fibrin,  a  yellow  solution  is  formed  with  disengagement  of  a  large  quantity  of 
nearly  pure  nitrogen,  in  which  Berzelius  could  not  detect  the  least  trace  of 
binoxide  of  nitrogen.  After  digestion  for  24  hours,  a  pale  yellow  pulverulent 
substance  is  deposited,  which  Fourcroy  and  Vauquelin  described  as  a  new 
acid  under  the  name  of  yellow  acid.  According  to  Berzelius,  however,  it  is 
a  compound  of  modified  fibrin  and  nitric  acid,  together  with  some  malic  and 
nitrous  acids.  It  likewise  contains  some  fatty  matter,  which  may  be  re- 
moved by  alcohol.  The  origin  of  the  nitrogen  which  is  disengaged  in  the 
beginning  of  the  process  is  somewat  obscure.  From  the  total  absence  of 
binoxide  of  nitrogen,  it  is  probable  that  in  the  early  stages  very  little,  if  any, 
of  the  nitric  acid  is  decomposed,  and  that  the  nitrogen  gas  is  solely  or  chiefly 
derived  from  the  fibrin. 

Dilute  hydrochloric  acid  hardens  without  dissolving  fibrin,  and  the  strong 
acid  decomposes  it.  The  action  of  sulphuric  acid,  according  to  Braconnot, 
is  very  peculiar.  When  fibrin  is  mixed  with  its  own  weight  of  concentrated 
sulphuric  acid,  a  perfect  solution  ensues,  without  change  of  colour,  or  disen- 
gagement of  sulphurous  acid.  On  diluting  with  water,'  boiling  for  nine 
hours,  and  separating  the  acid  by  means  of  chalk,  the  filtered  solution  was 
found  to  contain  a  peculiar  white  matter,  to  which  Braconnot  has  applied 
the  name  of  leucine.  (An.  de  Ch.  et  de  Ph.  xiii.)  Digested  in  strong  sul- 
phuric'acid,  a  dark  reddish-brown,  nearly  black,  solution  is  formed,  and  the 
fibrin  is  carbonized  and  decomposed. 

Fibrin  is  dissolved  by  pure  potassa,  and  is  thrown  down  when  the  solution 
is  neutralized.  The  fibrin  thus  precipitated,  however,  is  partially  changed, 
since  it  is  no  longer  soluble  in  acetic  acid.  It  is  soluble  likewise  in  am- 
monia. 

The  following  is  a  tabular  view  of  the  composition  in  100  parts  of  fibrin, 
albumen,  gelatin,  and  urea  :  —  • 

Carbon.     Hydrog.    Nitrogen.    Oxygen, 
Fibrin      .     .    53-36          7-02  19-934         19-685  Gay-L.  and  Thenard. 

Albumen       5    52'883         7'54  15>705         23<872  Ditto- 

Albumen 


Gelatin    .     .    47  881         7-914         16-998        27-207  Gay-L.  and  Thenard. 
Urea   .    .    .    19-99          6-66          46-66          26-66    Prout. 

Albumen. 

Albumen  enters  largely  into  the  composition  both  of  animal  fluids  and 
solids.  Dissolved  in  water  it  forms  an  essential  constituent  of  the  serum  of 
the  blood,  the  liquor  of  the  serous  cavities,  and  the  fluid  of  dropsy;  and  in  a 
solid  state  it  is  contained  in  several  of  the  textures  of  the  body,  such  as  the 
cellular  membrane,  the  skin,  glands,  and  vessels.  From  this  it  appears  that 
albumen  exists  under  two  forms,  liquid  and  solid, 

48* 


570  ALBUMEN. 

Liquid  albumen  is  best  procured  from  the  white  of  eggs,  which  consists 
almost  solely  of  this  principle,  united  with  water  and  free  soda,  and  mixed 
with  a  small  quantity  of  saline  matter.  In  this  state  it  is  a  thick  glairy 
fluid,  insipid,  inodorous,  and  easily  miscible  with  cold  water,  in  a  sufficient 
quantity  of  which  it  is  completely  dissolved.  When  exposed  in  thin  layers 
to  a  current  of  air  it  dries,  and  becomes  a  solid  and  transparent  substance, 
which  retains  its  solubility  in  water,  and  may  be  preserved  for  any  length  of 
time  without  change;  but  if  kept  in  its  fluid  condition  it  readily  putrefies. 
From  the  free  soda  which  they  contain,  albuminous  liquids  have  always  an 
alkaline  reaction. 

Liquid  albumen  is  coagulated  by  heat,  alcohol,  and  the  stronger  acids. 
Undiluted  albumen  is  coagulated  by  a  temperature  of  160°,  and  when 
diluted  with  water  at  212°  F.  Water  which  contains  only  l-1000lh  of  its 
weight  of  albumen  is  rendered  opaque  by  boiling.  (Bostock.)  On  this  pro- 
perty is  founded  the  method  of  clarifying  by  means  of  albuminous  sola- 
tions;  for  the  albumen  being  coagulated  by  heat,  entangles  in  its  substance 
all  the  foreign  particles  which  are  not  actually  dissolved,  and  carries  them 
with  it  to  the  surface  of  the  liquid.  The  character  of  being  coagulated  by 
hot  water  distinguishes  albumen  from  all  other  animal  fluids. 

The  acids  differ  in  their  action  on  albumen.  The  sulphuric,  hydrochlo- 
ric, nitric,  and  tannic  acids  coagulate  it;  and  in  each  case,  some  of  the  acid 
is  retained  by  the  albumen.  It  is  precipitated  also  by  metaphosphoric  acid, 
but  not  by  the  phosphoric  or  pyrophosphoric  (page  204).  The  solution  of 
albumen  is  not  precipitated  at  all  by  acetic  acid.  By  maceration  in  dilute 
nitric  acid  for  a  month,  it  is  converted,  according  to  Mr.  Hatchett,  into  a 
substance  soluble  in  hot  water,  and  possessed  of  the  leading  properties  of 
gelatin.  Digested  in  strong  sulphuric  acid,  the  coagulum  is  dissolved,  and 
a  dark  solution  is  formed  similar  to  that  produced  by  the  same  acid  on 
fibrin ;  but  if  the  heat  be  applied  very  cautiously,  the  liquid  assumes  a  beau- 
tiful red  colour.  This  property  was  discovered  some  years  ago  by  Dr.  Hope, 
who  informs  me  that  the  experiment  does  not  always  succeed,  the  result 
being  influenced  by  very  slight  causes. 

Albumen  is  precipitated  by  several  reagents,  especially  by  metallic  salts. 
Of  these  the  most  delicate  as  a  test  is  corrosive  sublimate,  which  causes  a 
railkiness  when  the  albumen  is  diluted  with  2000  parts  of  water.  The  pre- 
cipitate, as  stated  at  page  381,  is  generally  considered  as  a  compound  of 
calomel  and  albumen ;  but  a  late  analysis  by  Rose  has  proved  that  it  con- 
sists of  oxide  of  mercury  and  albumen  (Pog.  Ann.  xxviii.  ]32.)  Other 
metallic  solutions,  such  as  the  chlorides  of  tin  and  iron,  subacetate  of  oxide 
of  lead,  and  the  sulphates  of  alumina  and  oxide  of  copper,  also  precipitate 
albumen ;  the  precipitate  in  every  case  consists,  according  to  Rose,  of  a 
metallic  oxide  united  with  albumen.  All  these  precipitates,  not  excepting 
that  from  corrosive  sublimate,  dissolve  in  an  excess  of  albumen,  and  most 
of  them  are  soluble  in  an  excess  of  the  metallic  salt.  Ferrocyanuret  of 
potassium  is  a  test  for  albumen  equally  delicate  as  corrosive  sublimate,  if 
not  more  so,  provided  acetic  acid  is  previously  added  to  neutralize  the 
alkali. 

When  an  albuminous  liquid  is  exposed  to  the  agency  of  galvanism,  pure 
soda  makes  its  appearance  at  the  negative  wire,  and  the  albumen  coagulates 
around  that  which  is  in  connexion  with  the  positive  pole  of  the  battery. 
Mr.  Brande,*  who  first  observed  this  phenomenon,  ascribes  it  to  the  separa- 
tion of  free  soda,  upon  which  he  supposes  the  solubility  of  albumen  in 
water  to  depend  ;  but  Lassaignet  attributes  it  to  the  decomposition  of  chlo- 
ride of  sodium  and  the  developement  of  acid,  which  coagulates  the  albumen. 
However  this  may  be,  galvanism  is  one  of  the  most  elegant  and  delicate 
tests  which  we  possess  of  the  presence  of  albumen  in  animal  fluids. 

Chemists  are  not  agreed  as  to  the  cause  of  the  coagulation  of  albumen  by 

*  Philosophical  Transactions  for  1809.       f  An  de  Ch.  et  de  Ph.  vol.  xx. 


GELATIN.  571 

alcohol  and  heat.  The  explanation  usually  given  is  that  proposed  by  Dr. 
Thomson,  who  ascribes  the  solubility  of  albumen  to  the  presence  of  free 
soda,  and  its  coagulation  to  the  removal  of  tiie  alkali.  To  this  hypothesis 
Dr.  Bostock  objects,  and  with  justice,  that  albuminous  liquids  do  not  contain 
a  sufficient  quantify  of  free  alkali  for  the  purpose  (Medico-Chir.  Trans,  ii. 
175).  Were  I  to  hazard  an  opinion  on  this  subject,  it  would  be  the  follow- 
ing : — that  albumen  combines  directly  with  water  at  the  moment  of  being 
secreted,  at  a  time  when  its  particles  are  in  a  state  of  minute  division ;  but 
as  its  affinity  for  that  liquid  is  very  feeble,  the  compound  is  decomposed  by 
slight  causes,  arid  the  albumen  thereby  rendered  quite  insoluble.  Silicic  acid 
affords  an  instance  of  a  similar  phenomenon.  (Page  207.) 

Albumen  coagulates  without  appearing  to  undergo  any  change  of  compo- 
sition, but  is  quite  insoluble  in  water,  and  is  less  liable  to  putrefy  than  in 
its  liquid  state.  It  is  dissolved  by  alkalies  with  disengagement  of  ammo- 
nia, and  is  precipitated  from  its  solution  by  acids.  In  the  coagulated  state 
it  bears  a  very  close  resemblance  to  fibrin,  and  is  with  difficulty  distinguished 
from  it.  Alcohol,  ether,  acids,  and  alkalies,  according  to  Berzelius,  act 
upon  each  in  the  same  manner.  He  observes,  however,  that  acetic  acid  and 
ammonia  dissolve  fibrin  more  easily  than  coagulated  albumen.  According 
to  Thenard,  they  are  readily  distinguished  by  means  of  binoxide  of  hydro- 
gen, from  which  fibrin  causes  evolution  of  oxygen,  while  albumen  has  no 
action  upon  it. 

Gelatin. 

Gelatin  exists  abundantly  in  many  of  the  solid  parts  of  the  body,  espe- 
cially in  the  skin,  cartilages,  tendons,  membranes,  and  bones.  According 
to  Berzelius,  it  is  not  contained  in  any  of  the  healthy  animal  fluids;  and 
Dr.  Bostock,  with  respect  to  the  blood,  has  demonstrated  the  accuracy  of  this 
statement.  (Medico-Chir.  Trans,  vol.  i,  and  ii.) 

Gelatin  is  distinguished  from  all  animul  principles  by  its  ready  solubility 
in  boiling  water,  and  by  the  solution  forming  a  bulky,  semitransparenr, 
tremulous  jelly  as  it  cools.  Its  tendency  to  gelatinize  is  such,  that  one  part 
of  gelatin,  dissolved  in  100  parts  of  water,  becomes  solid  in  cooling.  This 
jelly  is  a  hydrate  of  gelatin,  and  contains  so  much  water,  that  it  readily 
liquefies  when  warmed.  On  expelling  the  water  by  a  gentle  heat,  a  brittle 
mass  is  left,  which  retains  its  solubility  in  hot  water,  and  may  be  preserved 
for  any  length  of  time  without  change.  Jelly,  on  the  contrary,  soon  be- 
comes acid  by  keeping,  and  then  putrefies. 

The  common  gelatin  of  commerce  is  the  well-known  cement  called  glue, 
which  is  prepared  by  boiling  cuttings  of  parchment,  or  the  skins,  ears,  and 
hoofs  of  animals,  arid  evaporating  the  solution:  it  may  also  be  prepared 
from  bones.  Isinglass,  which  is  the  purest  variety  of  gelatin,  is  prepared 
from  the  sounds  of  fish  of  the  genus  acipenser,  especially  from  the  sturgeon. 
The  animal  jelly  of  the  confectioners  is  made  from  the  feet  of  calves,  the 
tendinous  and  ligameiitous  parts  of  which  yield  a  large  quantity  of  gelatin. 

Gelatin  is  insoluble  in  alcohol,  but  is  dissolved  readily  by  most  of  the 
diluted  acids,  which  form  an  excellent  solvent  for  it.  Mixed  with  twice  its 
weight  of  concentrated  sulphuric  acid,  it  dissolves  without  being  charred; 
and  on  diluting  the  solution  with  water,  boiling  for  several  hours,  separating 
the  acid  by  means  of  chalk,  and  evaporating  the  filtered  liquid,  a  peculiar 
saccharine  principle  is  deposited  in  crystals.  This  substance  has  a  sweet 
taste,  somewhat  like  that  of  the  sugar  of  grapes,  is  soluble  in  water,  though 
less  so  than  common  sugar,  and  is  insoluble  in  alcohol.  When  heated  to 
redness,  it  yields  ammonia  as  one  of  the  products,  a  circumstance  which 
shows  that  it  contains  nitrogen.  Mixed  with  yeast,  its  solution  does  not  un- 
dergo the  vinous  fermentation  ;  and  it  combines  directly  with  nitric  acid.  It 
is  hence  apparent  that,  though  possessed  of  a  sweet  taste,  it  differs  entirely 
from  sugar.  This  substance  was  discovered  by  Braconnot.  (An.  de  Ch.  et 
de  Ph.  vol.  xiii.) 


572  UREA. 

Gelatin  is  dissolved  by  the  liquid  alkalies,  and  the  solution  is  not  precipi- 
tated by  acids. 

Gelatin  manifests  little  tendency  to  unite  with  metallic  oxides.  Corrosive 
sublimate  and  subacetate  of  oxide  of  lead  do  not  occasion  any  precipitate  in 
a  solution  of  gelatin,  and  the  salts  of  tin  and  silver  affect  it  very  slightly. 
The  best  precipitant  for  it  is  tannic  acid.  By  means  of  an  infusion  of  gall- 
nuts,  Dr.  Bostock  detected  the  presence  of  gelatin  when  mixed  with  51)00 
times  its  weight  of  water;  and  its  quantity  may  even  be  estimated  approxi- 
mately by  this  reagent  (page  496).  But  since  other  animal  substances,  as 
for  example  albumen,  are  precipitated  by  tannic  acid,  it  cannot  be  relied  on 
as  a  test  of  gelatin.  The  best  character  for  this  substance  is  that  of  solu- 
bility in  hot  water,  and  of  forming  a  jelly  as  it  cools. 

Urea. 

Urea  is  procured  by  evaporating  fresh  urine  to  the  consistence  of  a  syrup, 
and  then  gradually  adding  to  it,  when  quite  cold,  pure  concentrated  nitric 
acid,  which  should  be  free  from  nitrous  acid,  till  the  whole  becomes  a  dark- 
coloured  crystallized  mass,  which  is  to  be  repeatedly  washed  with  ice-cold 
water,  and  then  dried  by  pressure  between  folds  of  bibulous  paper.  To  the 
nitrate  of  urea,  thus  procured,  a  pretty  strong  solution  of  carbonate  of 
potassa  is  added,  until  the  acid  is  neutralized ;  and  the  solution  is  afterwards 
concentrated  by  evaporation,  and  set  aside,  in  order  that  the  nitre  may  sepa- 
rate in  crystals.  Dr.  Prout  recommends  that  the  residual  liquid,  which  is 
an  impure  solution  of  urea,  should  be  made  up  into  a  thin  paste  with  animal 
charcoal,  and  be  allowed  to  remain  in  that  state  for  a  few  hours.  The  paste 
is  then  mixed  with  cold  water,  which  takes  up  the  urea,  while  the  colouring 
matter  is  retained  by  the  charcoal;  and  the  colourless  solution  is  evaporated 
to  dryness  at  a  low  temperature.  The  residue  is  then  boiled  in  pure  alco- 
hol, by  which  the  urea  is  dissolved,  and  from  which  it  is  deposited  in  crys- 
tals on  cooling.  (Medico-Chir.  Trans,  viii.  529.)  In  order  to  obtain  them 
quite  colourless,  it  is  necessary  to  redissolve  in  alcohol,  and  crystallize  a 
second  or  even  a  third  time. 

The  crystals  of  pure  urea  are  transparent  and  colourless,  of  a  slight 
pearly  lustre,  and  have  commonly  the  form  of  a  four-sided  prism.  It  leaves 
a  sensation  of  coldness  on  the  tongue  like  nitre,  and  its  smell  is  faint  and 
peculiar,  but  not  urinous.  Its  specific  gravity  is  about  1-35.  It  docs  not  affect 
the  colour  of  litmus  or  turmeric  paper.  In  a  moist  atmosphere  it  deliquesces 
slightly  ;  but  otherwise  it  undergoes  no  change  on  exposure  to  the  air. 
(Prout.)  It  is  fused  at  248°,  and  at  a  rather  higher  temperature  it  is  de- 
composed, being  resolved  chiefly  into  carbonate  of  ammonia  and  cyanuric 
acid,  the  latter  of  which,  if  the  heat  be  not  incautiously  raised,  is  left  in  the 
retort.  (Page  273 ) 

Water  at  60°  dissolves  more  than  its  own  weight  of  urea,  and  boiling  wa- 
ter takes  up  an  unlimited  quantity.  It  requires  for  solution  about  five  times 
its  weight  of  alcohol  of  specific  gravity  0816  at  60°,  and  rather  less  than 
its  own  weight  at  a  boiling  temperature.  The  aqueous  solution  of  pure 
urea  may  be  exposed  to  the  atmosphere  for  several  months,  or  be  heated  to 
the  boiling  point,  without  change;  but,  on  the  contrary,  if  the  other  con- 
stituents of  urine  are  present,  it  putrefies  with  rapidity,  and  is  decomposed 
by  a  temperature  of  212°,  being  almost  entirely  resolved  into  carbonate  of 
ammonia  by  continued  ebullition. 

The  pure  fixed  alkalies  and  alkaline  earths  decompose  urea,  especially  by 
the  aid  of  heat,  carbonate  of  ammonia  being  the  chief  product. 

Though  urea  has  not  any  distinct  alkaline  properties,  it  unites  with  the 
nitric  and  oxalic  acids,  forming  sparingly  soluble  compounds,  which  crys- 
tallize in  scales  of  a  pearly  lustre.  This  property  affords  an  excellent  test 
of  the  presence  of  urea.  Both  compounds  have  an  acid  reaction,  and  the 
nitrate  consists  of  54-15  parts  or  one  equivalent  of  nitric  acid,  and  60-54  parts 
or  one  equivalent  of  urea. 


SUGAR  OF  MILK. SUGAR  OF  DIABETES.  573 

Urea  has  been  carefully  analyzed  by  Dr.  Prout,  and  the  accuracy  of  his 
analysis  is  amply  attested  by  the  late  researches  of  Liebig  and  Wohler.  Its 
equivalent  is  60-54;  and  its  elements  are  in  precisely  the  same  ratio  as  in  the 
hydrated  cyanate  of  ammonia. 

A  singular  instance  of  the  artificial  production  of  urea  has  been  noticed 
by  Wohler.  It  is  formed  by  the  action  of  ammonia  on  cyanogen,  as  also 
by  direct  contact  of  cyanic  acid  and  ammonia;  but  the  best  mode  of  pre- 
paring it  is  by  decomposing  cyanate  of  oxide  of  silver  with  hydrochlorate 
of  ammonia,  or  cyanate  of  oxide  of  lead  with  ammonia,  the  action  being 
promoted  by  a  gentle  heat.  In  the  last  case,  oxide  of  lead  is  set  free,  and 
the  only  other  product  appears  in  colourless,  transparent,  four-sided,  rect- 
angular crystals.  These  crystals,  judging  by  the  mode  of  preparation,  must 
be  cyanate  of  ammonia;  but  yet  no  ammonia  is  evolved  from  them  by  the 
action  of  potassa :  the  stronger  acids  do  not,  as  with  other  cyanates,  cause 
an  evolution  of  carbonic  and  cyanic  acids;  nor  do  they  yield  precipitates 
with  salts  of  lead  and  silver.  In  fact,  though  procured  by  the  mutual  ac- 
tion of  cyanic  acid  and  ammonia,  and  containing  the  very  same  elements, 
the  characters  above  mentioned  do  not  indicate  the  presence  of  either ; 
but  on  the  contrary  the  crystals  agree  with  urea  obtained  from  urine  in 
composition,  and  in  all  their  chemical  properties.  (Journal  of  Science, 
N.  S.  iii.  491.)  The  cyanic  acid  above  referred  to  is  that  discovered  by 
Wohler. 

Sugar  of  Milk  and  Sugar  of  Diabetes. 

Sugyr  of  Milk. — The  saccharine  principle  of  milk  is  obtained  from  whey 
by  evaporating  that  liquid  to  the  consistence  of  syrup,  and  allowing  it  to 
cool.  It  is  afterwards  purified  by  means  of  albumen  and  a  second  crystal- 
lization. 

The  sugar  of  milk  has  a  sweet  taste,  though  less  so  than  the  sugar  of  the 
cane,  from  which  it  differs  essentially  in  several  other  respects.  Thus  it  re- 
quires seven  parts  of  cold  and  four  of  boiling  water  for  solution,  and  is  in- 
soluble in  alcohol.  It  is  not  susceptible  of  undergoing  the  vinous  fermenta- 
tion ;  and  when  digested  with  nitric  acid  it  yields  saccholactic  acid,  a 
property  first  noticed  by  Scheele,  and  which  distinguishes  the  saccharine 
principle  of  milk  from  every  other  species  of  sugar.  Like  starch,  it  is  con- 
vertible into  real  sugar  by  being  boiled  in  water  acidulated  with  sulphuric 
acid. 

Sugar  of  milk  contains  no  nitrogen,  and,  according  to  the  analysis  of  Gay- 
Lussac  and  Thenard,  is  very  analogous  to  common  sugar  in  the  proportion 
of  its  elements. 

Sugar  of  Diabetes. — In  the  disease  called  diabetes  the  urine  contains  a  pe- 
culiar saccharine  matter,  which,  when  properly  purified,  appears  identical 
both  in  properties  and  composition  with  vegetable  sugar,  approaching  nearer 
to  the  sugar  of  grapes  than  that  from  the  sugar-cane.  This  kind  of  sugar 
is  obtained  in  an  irregularly  crystalline  mass  by  evaporating  diabetic  urine 
to  the  consistence  of  syrup,  and  keeping  it  in  a  warm  place  for  several  days. 
It  is  purified  by  washing  the  mass  with  alcohol,  either  cold  or  at  most  gen- 
tly heated,  till  that  liquid  comes  off  colourless,  and  then  dissolving  it  in  hot 
alcohol.  By  repeated  crystallization  it  is  thus  rendered  quite  pure.  (Prout.) 
*  A  few  other  principles  yet  remain  to  be  considered,  such  as  the  colouring 
principle  of  the  blood,  caseous  matter,  and  mucus;  but  these  will  be  more 
conveniently  studied  in  subsequent  sections. 


574  ANIMAL  ACIDS. 


SECTION  II. 


ANIMAL  ACIDS. 

IN  animal  bodies  several  acids  ore  found,  such  as  sulphuric,  hydrochloric, 
phosphoric,  acetic,  &c.  which  belong-  equally  to  the  mineral  or  vegetable 
kingdom,  and  which  have  consequently  been  described  in  other  parts  of  the 
work.  In  this  section  are  included  those  acids  only  which  are  believed  to  be 
peculiar  to  animal  bodies. 

Uric  or  Lilkic  Acid, — This  acid  is  a  common  constituent  of  urinary  and 
gouty  concretions,  and  is  always  present  in  healthy  urine,  combined  with 
ammonia  or  some  other  alkali.  The  urine  of  birds  of  prey,  such  as  the  , 
eagle,  and  of  the  boa  constrictor  and  other  serpents,  consists  almost  solely  of 
urate  of  ammonia,  from  which  pure  uric  acid  may  be  procured  by  a  very 
simple  process.  For  this  purpose  the  'solid  urine  of  the  boa  constrictor  is 
reduced  to  a  fine  powder,  and  digested  in  a  solution  of  pure  potassa,  in 
which  it  is  readily  dissolved  with  disengagement  of  ammonia.  The  urate 
of  potassa  is  then  decomposed  by  adding  acetic,  hydrochloric,  or  sulphuric 
acid  in  slight  excess,  when  the  uric  acid  is  thrown  down,  and,  after  being 
washed,  is  collected  on  a  filter.  On  its  first  separation  from  the  alkali  it  is 
in  the  form  of  a  gelatinous  hydrate,  but  in  a  short  time  this  compound  is 
decomposed  spontaneously,  and  the  uric  acid  subsides  in  small  crystals. 

Pure  uric  acid  is  white,  tasteless,  and  inodorous.  It  is  insoluble  in  alco- 
hol, and  is  dissolved  very  sparingly  by  cold  or  hot  water,  requiring  about 
10,000  times  its  weight  of  that  fluid  at  60°  F.  for  solution.  (Prout.)  It  red: 
dens  litmus  paper,  and  unites  with  alkalies,  forming  salts  which  are  called 
urates  or  lithates.  The  uric  acid  does  not  effervesce  with  alkaline  carbo- 
nates;  but  Dr.  Thomson  affirms  that  when  boiled  for  some  time  with  carbo- 
nate of  soda,  the  whole  of  the  carbonic  acid  is  expelled.  A  current  of  car- 
bonic acid,  on  the  contrary,  throws  down  the  uric  acid  when  dissolved  by 
potassa.  This  acid  undergoes  no  change  by  exposure  to  the  air. 

Of  the  acids  none  exert  any  peculiar  action  on  the  uric  excepting  nitric 
acid.  When  a  few  drops  of  nitric  acid,  slightly  diluted,  are  mixed  on  a 
watch-glass  with  uric  acid,  and  the  liquid  is  evaporated  to  dryness,  a  beauti- 
ful purple  colour  comes  into  view,  the  tint  of  which  is  improved  by  the  ad- 
dition of  water.  This  character  affords  an  unequivocal  test  of  the  presence 
of  uric  acid.  The  nature  of  the  change  will  be  considered  immediately. 

Uric  acid  is  decomposed  by  chlorine.  Liebig  has  observed,  that  when  dry 
uric  acid  is  heated  with  dry  chlorine,  an  enormous  quantity  of  cyanic  and 
muriatic  acid  is  generated.  If  the  uric  acid  is  moist,  chlorine  then  gives 
rise  to  the  disengagement  of  carbonic  and  cyanic  acids ;  while  in  solution 
there  remain  hydrochloric  acid,  ammonia,  and  much  oxalic  acid. 

According  to  a  late  analysis  by  Liebig,  uric  acid  is  thus  constituted  :— 
(An.  de  Ch.  et  de  Ph,  Iv.  58.) 

Carbon  .  .  .  36-11  30-6  or         5  eq. 

Hydrogen  .  .  .  2-34  2  2  eq. 

Nitrogen  .  .  ,    .  33-36  28-3  2  eq. 

Oxygen  ,  .  .  28-19  24  3  eq. 

100-00  84-9  1  eq. 

Liebig  has  given  strong  evidence  to  prove  that  the  foregoing  constitution 
is  more  correct  than  that  of  Prout,  who  found  six  eq.  of  carbon  instead  of 
five.  Crystallized  uric  acid  is  considered  by  most  chemists  to  be  anhy- 
drous ;  but  Dr.  Thomson  maintains  that  at  400°  it  loses  precisely  two  equi- 
valents of  water. 


ANIMAL  ACIDS.  575 

The  salts  of  uric  acid  have  been  described  by  Henry  (Manchester  Me- 
moirs, vol.  ii.  N.  S.)  The  principal  ones  yet  examined  are  the  urates  of  am- 
monia,  potassa,  and  soda.  Urate  of  ammonia  is  soluble  to  a  considerable 
extent  in  boiling,  but  more  sparingly  in  cold  water.  The  urates  of  soda  and 
potassa,  if  neutral,  are  of  a  very  sparing  solubility ;  but  an  excess  of  either 
alkali  takes  up  a  large  quantity  of  the  acid.  The  former  was  found  by  Wol- 
laston  to  be  the  chief  constituent  of  gouty  concretions. 

When  uric  acid  is  heated  in  a  retort,  carbonate  arid  liydrocyanate  of  am- 
monia  are  generated,  and  a  volatile  acid  sublimes,  called  pyro-uric  acid, 
which  was  formerly  described  by  Henry,  and  has  since  been  studied  by  Che- 
vallier  and  Lassaigne,  Liebig,  and  Wohler.  The  two  latter  chemists  have 
noticed,  that  pyro-uric  is  identical  with  cyanuric  acid  ;  and  Wohler  finds  that 
urea,  as  well  as  cyanuric  acid,  is  an  essential  product  of  the  destructive 
distillation  of  uric  acid. 

Purpuric  Acid. — This  compound  was  first  recognized  as  a  distinct  acid  by 
Prout,  and  was  described  by  him  in  the  Philosophical  Transactions  for  1818. 
Though  colourless  itself,  it  has  a  remarkable  tendency  to  form  red  or  purple- 
coloured  salts  with  alkaline  bases,  a  character  by  which  it  is  distinguished 
from  all  other  substances,  and  to  which  it  owes  the  name  of  purpuric  acid, 
suggested  by  Wollaston.  Thus  the  purple  residue  above  mentioned,  as  indi- 
cative of  the  presence  of  uric  acid,  is  purpurateof  ammonia,  which  is  always 
generated  when  the  uric  is  decomposed  by  nitric  acid. 

Purpuric  acid  may  be  prepared  by  the  following  process,  for  the  outline  of 
which  I  am  indebted  to  directions  kindly  given  me  by  Prout.  Let  200  grains 
of  uric  acid,  prepared  from  the  urine  of  the  boa  constrictor,  be  dissolved  in 
300  grains  of  pure  nitric  acid  diluted  with  an  equal  weight  of  water,  the 
uric  acid  being  added  gradually  in  order  that  the  heat  may  not  be  excessive. 
Effervescence  ensues  after  each  addition,  nitrous  acid  fumes  appear,  heat  is 
evolved,  and  a  colourless  solution  is  formed,  which,  on  standing  in  a  eoor* 
place  for  some  hours,  yields  colourless  crystals,  which  have  the  outline  of  an 
oblique  rhornboidal  prism.  By  gentle  evaporation  an  additional  quantity 
may  be  obtained.  They  contain  nitric  and  purpuric  acid,  and  ammonia, 
should  be  dissolved  in  water,  and  be  exactly  neutralized  by  pure  ammonia; 
and  the  liquid  is  then  digested  in  a  solution  of  potassa,  until  the  ammonia  is 
wholly  expelled.  On  pouring  this  solution  into  dilute  sulphuric  acid,  pur- 
puric acid  is  set  free,  which,  being  insoluble  in  water,  subsides  as  a  granular 
powder,  of  a  white  colour  if  pure,  but  commonly  of  a  yellowish-white  tint. 

Considerable  uncertainty  prevails  as  to  the  nature  of  purpuric  acid.  Vau- 
quelin  denied  thai  its  salts  have  a  purple  colour,  attributing  that  tint  to  some 
impurity,  and  Lassaigne  is  inclined  to  the  same  opinion  (An.  de  Ch.  et  de 
Ph.  xxii.  334) ;  but  from  the  intense  colour  given  even  by  a  very  minute 
quantity  of  purpuric  acid,  the  opinion  of  Dr.  Prout  appears  to  me  the  more 
probable.  The  composition  of  the  acid  is,  likewise  unsettled;  for  Prout 
has  expressd  a  doubt  of  the  accuracy  of  the  analysis  which  he  formerly 
published. 

The  name  of  erythric  acid  (from  ggvSgam/v,  to  redden}  was  applied  by 
Brugnatella  to  a  substance  which  he  procured  by  the  action  of  nitric  on  uric 
acid.  It  obviously  contains  purpuric  acid,  and  Prout  thinks  it  probable  that 
it  is  a  supersalt,  consisting  of  purpuric  and  nitric  acids,  and  ammonia,  being 
probably  identical  with  the  crystals  above  mentioned. 

Rosacic  Acid. — This  name  was  applied  by  Proust  to  a  peculiar  acid  sup- 
posed to  exist  in  the  red  matter,  commonly  called  by  medical  practitioners 
the  lateritious  sediment,  which  is  deposited  from  the  urine  in  some  stages  of 
fever.  From  the  experiments  of  Vogel  it  appears  to  be  uric  acid,  either 
combined  with  an  alkali,  or  modified  by  the  presence  of  animal  matter. 
Prout  is  of  opinion  that  it  contains  some  purpurate  of  ammonia;  and,  as  he 
has  detected  the  presence  of  nitric  acid  in  the  urine  from  which  such  sedi- 
ments were  deposited,  he  thinks  it  probable  that  the  purpurate  may  be  gene- 
rated by  the  reaction  of  the  uric  and  nitric  acids  on  each  other  in  the  uri- 
nary passages. 


576  ANIMAL  ACIDS. 

Hippuric  Acid. — Under  this  name,  derived  from  /TTTTOC  a  horse,  and  cyg« 
urine,  Liebig  has  described  a  peculiar  compound,  which  is  deposited  from 
the  urine  of  the  horse  when  it  is  mixed  with  hydrochloric  acid  in  excess. 
The  deposite,  which  is  crystalline  and  of  a  yellowish-brown  tint,  is  boiled 
with  milk  of  lime,  to  which  small  quantities  of  chloride  of  lime  are  added, 
until  the  urinous  odour  ceases.  It  is  then  digested  with  animal  charcoal; 
and  on  mixing  the  hot  filtered  solution  with  a  large  excess  of  hydrochloric 
acid,  hippuric  acid  is  deposited  in  cooling  in  rather  large  prisms,  two  or 
three  inches  in  length,  and  beautifully  white.  It  exists  in  the  urine  of  most 
herbivorous  animals  united  with  soda.  (An.  de  Ch.  et  de  Ph.  xliii.  188.) 

Hippuric  acid  is  analogous  in  its  characters  to  benzoic  acid,  and  was  at 
first  supposed  to  be  that  acid  modified  by  the  presence  of  animal  matter; 
but  Liebig  contends  that  it  is  clearly  distinguished  from  benzoic  acid  by  the 
character  of  its  salts,  in  being  less  soluble  in  water,  and  in  containing  nitro- 
gen. It  is  composed  of 

Carbon.         Hydrogen.     Nitrogen.         Oxygen. 
In  100  parts.      60-76  4-92  7-82  26-5 

In  equivalents.  122-4  or  20  eq.+9  or  9  eq.+14-15  or  1  eq.+48  or  6  eq.=193-55. 

Formic  Acid. — A  sour  liquor  exists  in  ants,  which  they  eject  when  irri- 
tated, and  which  may  be  obtained  in  solution  by  bruising  these  insects  into 
a  pulp  with  water :  the  liquor  was  supposed  by  Fourcroy  and  Vauquelin  to 
contain  acetic  and  malic  acids;  but  the  experiments  of  Suersen,  Gehlen,  Ber- 
zelius,  and  Dobereiner  have  proved  that  it  is  a  mixture  of  the  malic  with  a 
peculiar  volatile  acid,  distinct  from  acetic  acid,  and  easily  separable  by  dis- 
tillation. The  peculiar  origin  of  this  compound  has  suggested  for  it  the 
name  of  formic  acid.  Dobereiner  has  shown  that  it  is  readily  generated 
artificially  by  distilling  a  mixture  of  1  part  of  tartaric  acid,  1£  of  peroxide 
of  manganese,  and  1£  of  sulphuric  acid  diluted  with  about  2£  parts  of  water  : 
a  capacious  retort  should  be  used,  as  the  materials  froth  up  during  the  pro- 
cess. The  tartaric  acid  receives  oxygen  from  the  manganese,  and  is  resolved 
into  water,  carbonic  acid,  and  formic  acid.  (An.  of  Phil.  N.  S.  iv.  311.) 
Liebig  and  Gmelin  have  found  that  several  other  substances,  such  as  sugar, 
starch,  sugar  of  milk,  and  ligneous  fibre,  may  be  substituted  for  tartaric 
acid  ;  but  the  formic  acid  is  then  accompanied  by  some  foreign  matter,  which 
may  be  removed  by  neutralizing  with  an  alkali,  and  decomposing  the  formate 
by  sulphuric  acid.  Even  alcohol  may  be  used;  but  it  must  be  employed  in 
a  dilute  state,  in  order  to  prevent  the  production  of  sulphuric  or  formic  ether. 
Formic  acid,  indeed,  appears  to  be  a  frequent  result  of  chemical  changes,  and 
hence  it  is  important  to  be  well  acquainted  with  its  composition. 

By  these  processes  formic  acid  is  procured  in  a  very  dilute  state :  it  is 
obtained  with  less  water  by  distilling  a  mixture  of  one  part  of  water,  two  of 
strong  sulphuric  acid,  and  three  of  dry  formate  of  potassa.  But  the  free  acid 
in  its  most  concentrated  form  has  not  less  than  19-6  per  cent,  of  water,  and 
a  density  of  1-1168.  Formic  acid  is  a  feeble  acid,  has  a  sour  taste  and  reac- 
tion, and  its  odour  resembles  that  of  acetic  acid,  but  is  attended  with  a  pecu- 
liar pungency.  With  bases  it  forms  crystallizable  salts,  by  the  form  of 
which,  especially  of  the  formates  of  baryta,  stronlia,  lime,  and  oxide  of  zinc, 
it  is  completely  distinguished  from  acetic  acid. 

According  to  the  analysis  of  formate  of  oxide  of  lead  by  Bcrzelius,  the 
equivalent  of  this  acid  is  inferred  to  be  37-24;  and  it  is  composed  of  12-24 
parts  or  two  equivalents  of  carbon,  1  part  or  one  equivalent  of  hydrogen, 
and  24  parts  or  three  equivalents  of  oxygen.  From  the  ratio  of  these  ele- 
ments, it  is  manifest  that  formic  acid  may  be  considered  a  compound  of  two 
equivalents  of  carbonic  oxide  and  one  equivalent  of  water,  as  expressed  by 
the  formula  2(0+0) -J-(  H-|-O) ;  and  it  is  actually  resolved  into  these  com- 
pounds by  being  gently  heated  with  strong  sulphuric  acid,  carbonic  oxide 
gas  being  disengaged.  Warmed  with  peroxide  of  mercury  it  takes  oxygen 
from  the  metal,  and  is  resolved  into  water  and  carbonic  acid,  the  latter  of 


ANIMAL  OILS  AND  FATS.  577 

which  escapes  with  effervescence.  By  these  characters  formic  acid  is  dis- 
tinguished from  other  acids. 

Allantoic  acid. — This  compound,  described  by  Buniva  and  Vauquelin  un- 
der the  name  of  amniotic  acid,  and  said  to  exist  in  the  liquor  amnii  of  the 
cow,  was  found  by  Dzondi  to  be  present  solely  in  the  liquor  of  the  allantois, 
and  to  be  in  fact  the  urine  of  the  fo3tus.  The  mistake  of  the  discoverers  has 
also  been  corrected  by  Lassaigne.  (An.  de  Ch.  et  de  Ph.  xxxiii.  279.) 

The  allantoic  acid  is  obtained  by  gently  evaporating  the  liquid  of  the 
allantois  of  the  fetal  calf,  when  the  acid  is  deposited  in  the  form  of  white 
acicular  crystals.  It  is  very  sparingly  soluble  in  water,  but  yields  with  the 
alkalies  soluble  compounds  which  are  decomposed  by  most  of  the  acids. 
According  to  the  analysis  of  Liebig,  its  elements  are  in  the  ratio  of  five 
equivalents  of  carbon,  four  of  hydrogen,  two  of  nitrogen,  and  four  of  oxygen. 

Several  other  animal  acids,  such  as  the  stearic,  oleic,  margaric,  and  others, 
should  also  be  mentioned  here ;  but  as  they  are  closely  allied  to  the  fatty 
principles  from  which  they  are  derived,  they  will  be  more  conveniently 
described  in  the  following  section. 


SECTION   III. 

ANIMAL  OILS  AND  FATS. 

THE  fatty  principles  derived  from  the  bodies  of  animals  are  very  analo- 
gous in  composition  and  properties  to  the  vegetable  fixed  oils;  and  in  Britain, 
where  the  latter  are  comparatively  expensive,  the  former  are  employed,  both 
for  the  purpose  of  giving  light,  and  for  the  manufacture  of  soap.  Their 
ultimate  elements  are  carbon,  hydrogen,  and  oxygen ;  and  most  of  them, 
like  the  fixed  oils,  consist  of  two  or  more  definite  compounds,  such  as  stea- 
rine,  margarine,  and  oleine,  in  a  state  of  combination. 

From  a  curious  experiment  of  Berard  it  appears  that  a  substance  very 
analogous  to  fat  may  be  made  artificially.  On  mixing  together  one  measure 
of  carbonic  acid,  ten  measures  of  carburetted  hydrogen,  and  twenty  of  hydro- 
gen,  and  transmitting  the  mixture  through  a  red-hot  tube,  several  white 
crystals  were  obtained,  which  were  insoluble  in  water,  soluble  in  alcohol, 
and  fusible  by  heat  into  an  oily  fluid.  (An.  of  Ph.  xii.  41.)  Dobereiner  pre- 
pared an  analogous  substance  from  a  mixture  of  coal  gas  and  aqueous 
vapour. 

The  annexed  table  shows  the  composition  of  several  animal  fats,  and  of 
their  products  when  formed  into  soap.  The  analyses  are  by  Chevreul, 
excepting  that  of  stearine  by  Lecanu,  of  spermaceti  by  Berard,  and  of  am- 
breine  by  Pelletier. 

Garb.       Hyd.        Oxy.  Formulae. 

Human  fat  79-000+11  416+  9-584=100 

Oleine  of  human  £    78.566+11.4474_  9.987=100 

Hogslard  .        79-098+1 H46+  9-756=100 

01lard   °f  h°gS"  1    79'03  +H-422+  9-548=100 
Mutton  suet  78-996+11-700+  9-304=100 

Stearine  of  mut-  >    78-02  +12-2     4-  9-78  =100       (  C78H7°O7  or 
ton  suet  $  446-76  +70       +56       =572-76  { C7°H87O5+C8H303 

79-354+11-09  +  9-556=100 
49 


578 


ANIMAL  OILS  AND  FATS. 


Garb.        Hyd.         Oxy. 
Stearic  acid  (an-  (    80-1 45+1 2478 -f-   7-377=100 

hydrous)  £  4284    +67        +40        =535-4 

Margaric      acid)    79-053+12-01    +   8-937=100 

(anhydrous)     )  4284    +65        +48        =5414 
Oleic   acid    (an-)    80942+11-359+   7-699=100 
$428-4    +58        +40        =5264 


hydrous) 
Glycerine 

Celine 
Spermaceti 

Ethal 


Formula?. 
\  C7°H°7OC 

C70H65OG 

C70H58O5 

C8H4O3  or  . 
C3H3O2 


;  CI6H17O  or 


Phocenic  acid 

Cholesterine 
Ambreine 


C10H7O3 


40-071+  8-925  +  51-004=100 
18-36  +  4        +24       =  46-36 
81-660+12-862+  4578=  99-1 
79-5    +11-6     +  89     =100 
79-766+13-945+  6289  =  100       j 
97-92  +17        +8        =122-92) 
6500  +  8-25+26-75  =100       )t 
61-2    +7        +24        =  92-2    C( 
85-095+11 88  +  3-025=100 
83-37  +1332  +  3-31   =100 

Train  Oil. — Train  oil  is  obtained  by  means  of  heat  from  the  blubber  of 
the  whale,  and  is  employed  extensively  in  making  oil  gas,  and  for  burning 
in  common  lamps.  It  is  generally  of  a  reddish  or  yellow  colour,  emits  a 
strong  unpleasant  odour,  and  has  a  considerable  degree  of  viscidity,  proper- 
ties which  render  it  unfit  for  being  burned  in  Argand  lamps,  and  which  are 
owing  partly  to  the  heat  employed  in  its  extraction,  and  partly  to  the  pre- 
sence of  impurities.  By  purification,  indeed,  it  may  be  rendered  more  lim- 
pid, and  its  odour  less  offensive ;  but  it  is  always  inferior  to  spermaceti  oil. 

Spermaceti  Oil  is  obtained  from  an  oily  matter  lodged  in  a  bony  cavity  in 
the  head  of  the  Physeter  macrocephalus,  or  spermaceti  whale.  On  subject- 
ing this  substance  to  pressure  in  bags,  a  quantity  of  pure  limpid  oil  is  ex- 
pressed;  and  the  residue,  after  being  melted,  strained,  and  boiled  with  a 
solution  of  potassa,  is  sold  under  the  name  of  spermaceti.  This  principle  is 
probably  modified  in  the  process  by  which  it  is  purified. 

Animal  Oil  of  Dippel, — This  name  is  applied  to  a  limpid  volatile  oil, 
which  is  entirely  different  from  the  oils  above  mentioned,  and  is  a  product 
of  the  destructive  distillation  of  animal  matter,  especially  of  albuminous 
and  gelatinous  substances.  When  purified  by  distillation,  it  is  clear  and 
transparent.  It  was  formerly  much  used  in  medicine,  but  is  now  no  longer 
employed. 

Human  Fat. — This  variety  of  fat  has  a  yellowish  colour,  is  inodorous, 
fuses  at  a  very  gentle  heat,  and  retains  its  fluidity  at  59°:  that  of  the  loins 
begins  to  solidify  at  77°  and  it  is  quite  solid  at  63°.  It  requires  for  solu- 
tion 40  parts  of  hot  alcohol,  which  in  cooling  deposites  stearine  of  a  peculiar 
kind,  leaving  oleine  in  solution.  When  saponified  it  yields  margaric  and 
oleic  acids  and  glycerine,  but  no  stearic  acid. 

Hogslard. — This  fat  is  of  a  nearly  white  colour,  and  the  fusing  point  of 
different  varieties  between  79°  and  88°.  It  probably  contains  both  the 
stearine  and  margarine  besides  oleine.  When  saponified,  it  yields  marga- 
ric, stearic,  and  oleic  acids,  and  glycerine. 

Suet. — This  term  is  applied  to  the  fat  situated  about  the  loins  and  kidneys, 
which  is  less  fusible  than  the  fat  from  other  parts  of  the  same  animal.  The 
suet  from  the  ox  and  sheep  is  principally  used :  when  separated  by  fusion 
from  the  membrane  in  which  it  occurs,  it  is  called  tallow,  and  is  extensively 
employed  in  the  manufacture  of  soap  and  candles.  Beef  and  mutton  suet 
resemble  hogslard  in  their  constituents  and  in  the  products  of  saponification. 
Beef  suet,  when  fused,  congeals  at  102°,  and  mutton  suet  at  98°  or  a  few 
decrees  higher. 

Stearine. — This  compound  is  a  constituent  of  several  animal  fats,  espe- 
cially of  hogslard  and  suet,  the  latter  of  which  contains  one-fifth  of  stea- 
rine. It  is  prepared  by  fusing  mutton  suet  in  a  flask,  agitating-  with  ils 
own  weight  of  ether,  and  when  the  whole  is  cold  separating  the  soluble 


[ANIMAL  OILS  AND  FATS.  579 

parts  by  pressure  in  a  cloth  and  in  bibulous  paper.  This  process  is  repeated 
until  the  parts  soluble  in  cold  ether  are  removed.  The  insoluble  part  is 
stearine.  It  may  also  be  prepared  by  mixing  essence  of  turpentine  with 
fused  mutton  suet,  and  when  the  mass  has  cooled  pressing-  out  the  fluid 
parts  by  bibulous  paper :  the  solid  part  left  after  repeated  fusion  with  tur- 
pentine is  stearine,  which  should  be  purified  by  solution  in  hot  ether  to  re- 
move adhering-  turpentine. 

Pure  stearine,  as  separated  from  its  ethereal  solution,  and  dried  by  com- 
pression in  bibulous  paper,  occurs  in  small  white  brilliant  lamina?,  and  fuses 
at  129°  into  a  mass  like  wax,  but  so  friable  that  it  may  be  reduced  to  pow- 
der. It  dissolves  in  boiling-  strong  alcohol,  but  separates  on  cooling  in  snow- 
white  flakes.  Boiling  ether  dissolves  it  in  large  proportion,  but  when  cold 
retains  an  l-225th  of  its  weight.  When  sharply  heated,  it  is  decomposed, 
and  among  other  products  it  yields  stearic  acid.  When  digested  in  pure  po- 
tassa,  it  is  entirely  resolved  into  stearic  acid  and  glycerine,  both  regarded  as 
anhydrous.  This  will  be  obvious  by  the  formulae^  of  pages  577  and  578. 
Stearine*  may  be  regarded  as  a  compound  of  stearie  acid  and  glycerine,  and 
its  conversion  into  soap  as  the  mere  separation  of  glycerine,  which,  in  the 
act  of  quitting  the  stearic  acid,  combines  with  one  eq.  of  water.  The  fore- 
going facts  are  drawn  from  a  late  essay  by  Lecanu,  (An.  de  Ch.  et  de  Ph. 
Iv.  192.) 

Margarine. — After  the  stearine  in  the  foregoing  process  has  been  depo- 
sited, another  solid  fatty  principle,  which  Lecanu  terms  margarine,  may  be 
obtained  by  allowing  the  ethereal  solution  to  evaporate  spontaneously.  To 
free  it  from  adhering  ether  and  oleine,  it  should  be  pressed  between  folds 
of  bibulous  paper.  Margarine  is  very  similar  in  its  properties  to  stearine, 
but  is  distinguished  from  it  by  its  greater  fusibility,  its  point  of  fusion  being 
117^°,  and  by  its  ready  solubility  in  cold  ether.  With  an  alkali  it  yields 
slearic  acid  and  glycerine. 

The  solid  matter  of  vegetable  oils  is  not  identical  with  the  stearine  of 
suet,  as  was  thought  by  Chevreul,  but  appears  from  the  late  experiments  of 
Lecanu  to  be  more  closely  allied  to  the  margarine  of  suet.  It  differs,  how- 
ever, from  both  by  yielding  margttric  and  oleic,  and  not  stearic  acid  when 
converted  into  soap. 

Oleine. — The  liquid  matter  of  animal  fats,  obtained  by  compression  in 
bibulous  paper,  is  very  similar  to  the  oleine  obtained  in  a  similar  manner 
from  frozen  vegetable  oils. 

Margaric  and  Oleic  Acids. — When  the  fats  above  mentioned,  or  the  fixed 
vegetable  oils,  are  boiled  with  a  solution  of  potassa  or  soda,  the  elements  of 
the  fat  or  oil  undergo  a  new  arrangement,  whereby,  without  losing  any 
gaseous  substance  or  absorbing  any  from  the  air,  they  are  converted  into  one 
or  more  fatty  acids  and  glycerine.  To  this  change  the  elements  of  water 
contribute.  The  new  acids  combine  with  the  alkali  and  constitute  soap, 
which  after  due  evaporation  collects  on  the  surface  of  the  water,  while  the 
glycerine  remains  in  solution.  The  acids  which,  in  ordinary  soap,  are  united 
with  potassa  or  soda  as  compounds  soluble  in  water,  form  insoluble  com- 
pounds with  most  other  metallic  oxides ;  and  hence  it  is  that  solutions  of 
soap  are  precipitated  by  salts  of  lime,  oxide  of  lead,  and  similar  metallic  so- 
lutions. These  insoluble  soaps  may  be  formed  directly  by  digesting  oleagi- 
nous substances  with  water  and  metallic  oxides. 

The  margaric  and  oleic  acids  are  best  prepared  from  soap  made  with  po- 
tassa and  fluid  vegetable  oil.  This  soap,  after  being  well  dried,  is  treated 
by  successive  portions  of  cold  alcohol  of  sp.  gr.  0-821,  in  which  the  oleate  of 
potassa  is  soluble  and  the  margarate  insoluble.  The  two  salts,  thus  sepa- 
rated, are  decomposed  by  means  of  an  acid. 

Margaric  acid,  so  named  from  its  pearly  lustre  (from  /uA^ya^tT^  a,  pearl) 
is  insoluble  in  water,  and  is  hence  precipitated  by  acids  from  the  solution  of 
its  salts.  It  is  abundantly  dissolved  by  hot  alcohol,  and  is  deposited  from 
the  saturated  solution,  on  cooling,  in  a  crystalline  mass  of  a  pearly  lustre. 
At  140°  it  is  fused,  and  shoots  into  brilliant  white  acicular  crystals  as  it 


580  ANIMAL  OILS  AND  FATS. 

cools,  It  has  an  acid  reaction,  and  its  salts,  those  of  the  alkalies  excepted, 
are  very  sparingly  soluble  in  water.  The  crystallized  acid  contains  3'4  per 
cent,  of  water,  corresponding  to  two  eq.  of  water,  from  which  it  can  only  be 
separated  by  combining  with  an  alkaline  base. 

Oleic  acid  is  best  prepared  from  soap  made  with  linseed  oil  and  potassa, 
since  the  greater  part  of  it  consists  of  the  oleate  of  that  alkali.  This  salt  is 
first  separated  from  margarate  of  potassa  by  cold  alcohol,  and  the  oleic  acid 
then  precipitated  from  an  aqueous  solution  of  the  oleate  by  means  of  an 
acid.  At  the  mean  temperature  oleic  acid  is  a  colourless  oily  fluid,  which 
congeals  when  it  is  cooled  to  near  zero.  It  has  a  slightly  rancid  odour  and 
taste,  and  reddens  litmus  paper.  Its  specific  gravity  is  0-898.  It  is  insolu- 
ble in  water,  but  is  dissolved  in  every  proportion  by  alcohol.  Of  the  neutral 
oleates  hitherto  examined,  those  of  soda  and  potassa  are  alone  soluble  in 
water. 

In  its  free  state  it  contains  3-8  per  cent.,  corresponding  to  one  equivalent 
of  water,  which  it  loses  in  uniting  with  most  metallic  oxides. 

Stearic  Acid. — This  acid  is  best  prepared  by  converting  pure  stearine  into 
soap,  and  decomposing  the  resulting  stearate  with  an  acid.  It  is  very  simi- 
lar in  its  appearance  and  properties  to  margaric  acid,  the  principal  distinc- 
tion being  a  difference  of  fusibility,  the  fusing  point  of  stearic  acid  being 
158°.  The  crystallized  acid  consists  of  one  eq.  of  anhydrous  stearic  acid 
and  one  eq.  of  water. 

Sebacic  Acid. — Thenard  has  applied  this  name  to  an  acid  which  is  obtain- 
ed by  the  distillation  of  hogslard  or  suet,  and  is  found  in  the  recipient  mixed 
with  acetic  acid  and  fat,  partially  decomposed.  It  is  separated  from  the 
latter  by  means  of  boiling  water,  and  from  the  former  by  acetate  of  oxide  of 
lead.  The  sebacate  of  that  oxide,  which  subsides,  is  subsequently  decomposed 
by  sulphuric  acid. 

Sebacic  acid  reddens  litmus  paper,  dissolves  freely  in  alcohol,  and  is  more 
soluble  in  hot  than  in  cold  water.  It  melts  like  fat  when  heated,  and  crys- 
tallizes in  small  white  needles  in  cooling.  It  is  not  applied  to  any  use. 

Butyrine. — Butter  differs  from  the  common  animal  fats  in  containing  a  pe- 
culiar oleaginous  matter,  which  is  quite  fluid  at  70°,  and  to  which  Chevreul 
has  applied  the  name  of  butyrine.  When  converted  into  soap,  it  yields,  in 
addition  to  the  usual  products,  three  volatile  odoriferous  compounds,  namely, 
the  butyric,  caproic>  and  capric  acids. 

Phocenine  is  a  peculiar  fatty  substance  contained  in  the  oil  of  the  porpoise 
(Delphinus  phoccena)  mixed  with  oleine.  When  converted  into  soap,  it  yields 
a  volatile  odoriferous  acid,  called  the  phocenic  acid.  (Chevreul.) 

Hircine  is  contained  in  the  fat  of  the  goat  and  sheep,  and  yields  the  kircic 
acid  when  converted  into  soap.  (Chevreul.) 

Other  acids,  more  or  less  analogous  to  those  above  described,  are  formed 
during  ths  conversion  of  other  oleaginous  substances  into  soap.  Thus, 
castor  oil  yields  three  acids,  to  which  Bussy  and  Lecanu  have  applied  the 
names  of  margaritic,  ricinicYand  elaiodic  acid.  The  cevadic  acid  was  pre- 
pared in  a  similar  manner  by  Pelletier  and  Caventou  from  oil  derived  from 
the  seeds  of  the  Veratrum  sabadilla  ;  and  the  same  chemists  have  given 
the  name  of  jatrophic  acid  (more  properly  crotanic)  to  the  acid  of  the  soap 
made  from  croton  oil.  This  oil  is  derived  from  the  seeds  of  the  Craton 
tiglium. 

Glycerine. — The  sweet  principle  of  oils,  glycerine  of  Chevreul,  was  dis- 
covered by  Seheele.  It  was  originally  obtained  in  the  formation  of  common 
plaster  by  boiling  oil  with  oxide  of  lead  and  a  little  water ;  and  Chevreul 
found  that  it  is  produced  during  the  saponification  of  fatty  substances  in 
general.  In  preparing  soap  by  means  of  potassa,  the  glycerine  is  left  in  the 
mother  liquor;  and  on  neutralizing  the  free  alkali  with  sulphuric  acid, 
evaporating  to  the  consistence  of  syrup,  and  treating  the  residue  with  alco- 
hol, it  is  dissolved.  The  alcoholic  solution,  when  eraporated,  yields  glyce- 
rine in  the  form  of  an  uncrystallized  syrup.  It  is  soluble  in  water  and 


ANIMAL  GILS  AND  FATS.  581 

alcohol,  and  has  a  sweet  taste,  but  is  not  susceptible  either  of  the  vinous  or 
acetous  fermentation. 

Spermaceti. — This  inflammable  substance,  which  is  prepared  from  the 
spermaceti  whale,  as  above  mentioned,  commonly  occurs  in  crystalline 
plates  of  a  white  colour  and  silvery  lustre.  It  is  brittle,  and  feels  soft  and 
slightly  unctuous  to  the  touch.  It  has  no  taste,  and  scarcely  any  odour.  It 
is  insoluble  in  water,  but  dissolves  in  about  thirteen  times  its  weight  of  boil- 
ing  alcohol,  from  which  the  greater  part  is  deposited  on  cooling  in  the  form 
of  brilliant  scales.  It  is  still  more  soluble  in  ether.  It  is  exceedingly  fusible, 
liquefying  at  a  temperature  which  is  distinctly  below  212°. 

The  spermaceti  of  commerce  always  contains  some  fluid  oil,  from  which 
it  may  be  purified  by  solution  in  boiling  alcohol.  To  the  white  crystalline 
scales  deposited  from  the  spirit  as  it  cools,  and  which  is  spermaceti  in  a 
state  of  perfect  purity,  Chevreul  has  given  the  name  of  cetine. 

Ethal. — When  cetine  is  boiled  with  alkalies  it  is  slowly  and  incompletely 
saponified,  since,  in  addition  to  margaric  and  oleic  acid,  a  solid  fatty  princi- 
ple is  generated,  amounting  to  40-64  per  cent,  of  the  cetine  used.  Chevreul 
gives  it  the  name  of  etkal,  from  the  first  syllable  of  the  words  ether  and  alco- 
hol, because  of  its  analogy  to  those  liquids  in  point  of  composition  (page  578.) 
Ethal  congeals  after  fusion  at  86°,  and  at  124°  under  water.  It  is  soluble 
in  every  proportion  in  strong  alcohol  at  130°,  and  may  be  distilled  without 
change. 

Adipocire. — When  a  piece  of  fresh  muscle  is  exposed  for  some  time  to 
the  action  of  water,  or  is  kept  in  moist  earth,  the  fibrin  entirely  disappears, 
and  a  fatty  matter  called  adipocire  remains,  which  has  some  resemblance  to 
spermaceti.  The  fibrin  was  formerly  thought  to  be  really  converted  into 
adipocire  ;  but  Gay  Lussac*  and  Chevreul  maintain  that  this  substance  pro- 
ceeds entirely  from  the  fat  originally  present  in  the  muscle,  and  that  the 
fibrin  is  merely  destroyed  by  putrefaction.  Dr.  Thomson  maintains,  how- 
ever, that  the  conversion  of  fibrin  into  fat  does  occur  in  some  instances,  and 
has  related  a  remarkable  case  in  proof  of  his  opinion.  (An.  of  Phil.  vol.  xii. 
p.  41.)  According  to  M.  Chevreul,  the  adipocire  is  not  a  pure  fatty  principle, 
but  a  species  of  soap,  chiefly  consisting  of  margaric  acid  in  combination 
with  ammonia  generated  during  the  decomposition  of  the  fibrin. 

Cholesterine.] — This  name  is  applied  by  Chevreul  to  the  crystalline  mat- 
ter which  constitutes  the  basis  of  most  of  the  biliary  concretions  formed  in 
the  human  subject.  Fourcroy,  regarding  it  as  identical  with  spermaceti  and 
the  fatty  matter  just  described,  comprehended  all  these  circumstances  under 
the  general  appellation  of  adipocire  ;  but  Chevreul  has  shown  that  it  is  an 
independent  principle,  wholly  different  from  spermaceti. 

Cholesterine  is  a  white  brittle  solid  of  a  crystalline  lamellated  structure 
and  brilliant  lustre,  very  much  resembling  spermaceti;  but  it  is  distinguished 
from  that:  substance  by  requiring  a  temperature  of  278°  for  fusion,  and 
by  not  being  convertible  into  soap  when  digested  in  a  solution  of  potassa. 
It  is  free  from  taste  and  odour,  and  is  insoluble  in  water.  It  dissolves  freely 
in  boiling  alcohol,  from  which  it  is  deposited  on  cooling  in  white  pearly 
scales. 

When  heated  with  its  own  weight  of  concentrated  nitric  acid,  cholesterine 
is  dissolved  with  disengagement  of  nitric  oxide  gas  ;  and  in  cooling  a  yellow 
matter  subsides,  an  additional  quantity  of  which  may  be  obtained  by  dilution 
with  water.  This  substance  possesses  the  properties  of  acidity,  and  is  called 
cholesteric  acid.  It  is  insoluble  in  water,  but  dissolves  freely  in  alcohol, 
especially  with  the  aid  of  heat.  Its  taste  is  slightly  styptic,  and  its  odour 
somewhat  like  that  of  butter;  it  is  lighter  than  water,  and  fusible  at  136J°  F. 
In  mass  it  is  of  an  orange-yellow  tint;  but  when  the  alcoholic  solution  is 
evaporated  spontaneously,  it  is  deposited  in  acicular  crystals  of  a  white 
colour.  It  reddens  litmus  paper,  and  neutralizes  alkaline  bases.  The 

*  An  de  Ch.  et  de  Ph.  vol.  iv.  t  From  £o\>f  6i/c,  and  o-ngioc  solid. 

49* 


582  BLOOD. 

cholesterates  of  potassa  and  soda  are  deliquescent  and  very  soluble  in  water, 
but  insoluble  in  alcohol  and  ether.  The  cholesterates  of  the  earths  and 
other  metallic  oxides  are  either  sparingly  dissolved  by  water  or  altogether 
insoluble.  Its  salts  are  precipitated  by  the  mineral  and  most  of  the  vegeta- 
ble acids ;  but  are  not  decomposed  by  carbonic  acid.  For  these  facts  re- 
specting the  formation  and  properties  of  cholesteric  acid,  we  are  indebted 
to  the  experiments  of  Pelletier  and  Caventou.  (Journal  de  Pharmacie, 
iii.  292.) 

Cholesterine  has  been  detected  in  the  bile  of  man,  and  of  several  of  the 
lower  animals,  such  as  the  ox,  dog,  pig,  and  bear.  This  interesting  disco- 
very was  made  about  the  same  time  by  Chevreul  in  Paris,  and  by  Tiede- 
mann  and  Gmelin  in  Heidelberg.  Lassaigne  has  likewise  found  it  in  the 
biliary  calculus  of  a  pig.  (An.  de  Ch.  et  de  Ph.  xxxi.)  It  is  frequently 
formed  in  parts  of  the  body  quite  unconnected  with  the  hepatic  circulation, 
and  appears  to  be  a  common  product  of  deranged  vascular  action.  Caventou, 
in  the  Journal  de  Pharmacie  for  October  1825,  states  that  the  contents  of  an 
abscess,  formed  under  the  jaw,  apparently  in  consequence  of  a  carious  tooth, 
were  found  by  him  to  consist  almost  entirely  of  cholesterine.  In  the  article 
Calcul  of  the  Nouveau  Dictionnaire  de  Medecine,  M.  Breschet  observes  that 
cholesterine  has  been  found  in  cancer  of  the  intestines,  and  in  the  fluid  of 
hydrocele  and  ascites  in  the  human  subject ;  and  he  adds  that  M.  Barruel 
procured  it  in  large  quantity  from  an  ovarian  cyst  in  a  mare,  and  in  the 
fluid  drawn  off  from  the  ovary  of  a  woman,  and  scrotum  of  a  man.  Breschet 
has  found  it  also  in  a  tumour  under  the  tongue.  Dr.  Christison  found  it  in 
the  fluid  of  hydrocele,  taken  from  a  patient  in  the  Royal  Infirmary  of  Edin- 
burgh by  the  late  Dr.  William  Cullen ;  in  an  osseous  cyst,  into  which  the 
kidneys  of  another  patient  were  converted ;  and  in  the  membranes  of  the 
brain  of  an  epileptic  patient.  Reichenbach  has  detected  it  in  animal  tar, 
whence  it  would  seem  to  be  a  product  of  the  destructive  distillation  of  ani- 
mal matter. 

The  best  method  of  preparing  pure  cholesterine  is  to  treat  human  biliary 
concretions,  reduced  to  powder,  with  boiling  alcohol,  and  to  filter  the  hot 
solution  as  rapidly  as  possible.  As  the  liquid  cools,  the  greater  part  of  the 
cholesterine  subsides.  In  this  way  it  is  freed  from  the  colouring  matter 
with  which  it  is  commonly  associated  in  the  gall-stone. 

Ambergris. — This  substance  is  found  floating  on  the  surface  of  the  sea 
near  the  coasts  of  India,  Africa,  and  Brazil,  and  is  supposed  to  be  a  concre- 
tion formed  in  the  stomach  of  the  spermaceti  whale.  It  has  commonly  been 
regarded  as  a  resinous  principle ;  but  its  chief  constituent  is  a  substance 
very  analogous  to  cholesterine,  and  to  which  Pelletier  and  Caventou  have 
given  the  name  of  ambreine.  By  digestion  in  nitric  acid,  ambreine  is  con- 
verted into  a  peculiar  acid  called  the  ainbreic  acid.  (An.  of  Phil.  vol.  xvi.) 


MORE  COMPLEX  ANIMAL  SUBSTANCES,  AND  SOME 
FUNCTIONS  OF  ANIMAL  BODIES. 

SECTION   I. 
BLOOD,  RESPIRATION,  AND  ANIMAL  HEAT. 

Blood. 

THE  blood  is  distinguished  from  other  animal  fluids  by  its  colour,  which 
is  a  florid  red  in  the  arteries  and  of  a  dark  purple  tint  in  the  veins.  Its  taste 
is  slightly  saline,  its  odour  peculiar,  and  to  the  touch  it  seems  somewhat 
unctuous.  Its  specific  gravity  is  variable,  but  most  commonly  it  is  near 
1-05;  and  in  man  its  temperature  is  about  98°  or  100°  F.  While  flowing 


BLOOD.  583 

in  its  vessels,  or  when  recently  drawn,  it  appears  to  the  naked  eye  as  a  uni- 
form homogeneous  liquid ;  but  if  examined  with  a  microscope  of  sufficient 
power,  numerous  red  particles  of  a  globular  form  are  seen  floating  in  a  nearly 
colourless  fluid.  Henoe  the  blood,  while  circulating,  is  mechanically  distin- 
guishable into  two  parts,  one  essentially  liquid,  which  may  be  called  liquor 
sanguinis,  and  the  other  essentially  solid,  which  is  merely  suspended  in  the 
former,  and  imparts  its  red  colour  to  the  mixture. 

Both  of  these  constituents  of  the  blood  are  complex  substances.  The  red 
globules,  discovered  by  Leuwenhoeck  and  carefully  examined  by  Hewson, 
were  observed  by  the  late  Dr.  Young  to  consist  of  two  parts,  a  colourless 
globule  insoluble  in  water,  and  a  red  colouring  matter  soluble  in  that  men- 
struum. The  observations  of  Mr.  Bauer,  coinciding  with  those  of  Young, 
led  to  the  belief  that  the  entire  red  globule  consists  of  a  central  smaller  glo- 
bule of  fibrin,  which  is  surrounded  with  a  pellicle  or  film  of  colouring  mat- 
ter :  the  coloured  globules  manifest  no  tendency  to  cohere ;  but  the  nuclei  of 
fibrin,  when  deprived  of  their  colouring  envelope,  which  they  soon  lose  after 
the  blood  is  drawn,  adhere  together  with  great  facility.  (Phil.  Trans.  1818, 
p.  172.)  These  remarks  have  been  corroborated  by  Prevost  and  Dumas,  who 
extended  their  researches  to  the  blood  of  various  animals ;  and  they  further 
observed  that  in  birds  and  the  cold-blooded  tribes  the  globules  are  elliptical, 
while  they  are  spherical  in  the  mammiferous  animals. 

The  liquor  sanguinis,  considered  by  some  as  serum,  has  been  shown  by 
Dr.  Benjamin  Babington,  in  a  short  essay  replete  with  sound  observation,  to 
be  very  similar  to  chyle,  and  to  consist  of  fibrin,  held  in  solution,  along  with 
albuminous,  oleaginous,  and  saline  matter,  by  the  water  of  the  blood.  When 
set  at  rest  the  liquor  sanguinis  coagulates,  yielding  a  uniform  jelly  of  pre- 
cisely the  same  volume  as  when  it  was  liquid,  and  possessing  the  exact  figure 
of  the  containing  vessel;  and  in  a  short  time,  by  the  contraction  of  the  mass 
of  coagulated  fibrin,  a  yellowish  liquid  appears,  which  is  the  serum  of  the 
blood.  The  microscopical  observations  of  Mr.  Bauer,  cited  by  the  late  Sir 
E.  Home  in  the  Croonian  lecture  for  1818  (Phil.  Trans.  1819,  p.  i.),  prove 
that,  during  this  process,  numerous  globules,  smaller  than  the  colourless 
nuclei  of  the  red  globules,  are  generated,  and  give  rise  to  coagulation  by 
mutual  adhesion.  Though  the  production  of  these  globules  is  most  abun- 
dant soon  after  the  blood  is  drawn,  yet  their  developement  continues  for 
several  days ;  Mr.  Bauer  observed  them  to  appear  in  the  clear  serum  of  a 
sheep  8  or  10  days  after  removal  from  the  animal ;  and  Mr.  Faraday  made 
the  same  observation  with  the  serum  of  human  blood. 

It  is  the  liquor  sanguinis,  thus  shown  to  be  spontaneously  separable  into 
fibrin  and  serum,  which  forms  a  yellowish  liquid  stratum  at  the  surface  of 
blood  recently  drawn  from  persons  in  acute  rheumatism  or  other  inflamma- 
tory fevers.  In  such  affections  the  liquor  sanguinis,  from  causes  not  at  all 
understood,  generally  coagulates  with  unusual  slowness,  so  that  the  heavier 
red  globules  have  time  to  subside  to  an  appreciable  extent,  leaving  an  upper 
stratum  of  nearly  colourless  fluid,  which  by  the  cautious  use  of  a  spoon  may 
be  removed  and  collected  in  a  separate  vessel.  The  buffy  coat  of  such  blood 
is  the  pure  fibrin  separated  by  coagulation  from  the  liquor  sanguinis.  The 
coagulable  lymph  of  Surgeons,  which  is  thrown  out  on  cut  surfaces,  appears 
to  be  the  liquor  sanguinis ;  and  this  fluid  is  also  not  unfrequently  exhaled  in 
dropsies,  when  the  fibrin  either  constitutes  a  gelatinous  deposite,  or  appears 
as  white  flakes  floating  in  the  serous  fluid.  It  is  poured  out  by  the  intes- 
tines during  an  attack  of  cholera,  the  rice-water  fluid  characteristic  of  that 
disease  consisting  of  a  saline  and  albuminous  solution,  in  which  numerous 
shreds  of  fibrin  are  suspended. 

When  blood  drawn  from  a  healthy  person  is  set  at  rest,  it  speedily  coagu- 
lates, and  is  found  after  a  few  hours  to  have  separated  itself  into  two  parts, 
one  the  serum  identical  with  that  obtained  from  the  liquor  sanguinis,  and  the 
other  a  uniformly  red  coagulum  called  the  clot,  cruor,  or  crassamentum. 
The  uniform  redness  of  the  clot  is  owing  to  the  fibrin  coagulating  before  the 
red  globules  have  had  time  to  subside.  It  contains  the  colouring  matter  of 


584  BLOOD. 

the  blood,  together  with  all  the  fibrin,  except  traces  held  in  solution  in  the 
serum,  as  well  that  which  had  formed  part  of  the  liquor  sanguinis,  as  the 
fibrinous  nuclei  of  the  red  globules.  The  ratio  of  the  clot  and  serum  is  very 
variable,  and  by  no  means  represents  the  quantity  of  fibrin  or  colouring  mat- 
ter contained  in  the  blood.  Dr.  B.  Babirigton  has  shown,  in  the  essay  already 
referred  to,  that  the  ratio  materially  depends  on  the  figure  of  the  containing 
vessel: — two  portions  of  blood  were  drawn  from  the  same  person,  one  being 
received  and  allowed  to  coagulate  in  a  pear-shaped  bottle,  and  the  other  in  a 
pint  basin  ;  and  the  ratio  of  serum  to  clot  was  as  1000  to  1292  in  the  former, 
and  as  1000  to  1717  in  the  latter.  In  fact,  when  a  mass  of  coagulating  blood 
is  contained  in  a  spherical  vessel,  the  particles  of  fibrin  being  little  removed 
from  a  common  centre  are  more  powerfully  attracted  towards  each  other, 
yield  a  denser  clot,  and  squeeze  out  more  serum,  than  when  the  coagulation 
takes  place  in  a  shallow  wide  basin,  where  the  particles  are  spread  over  a 
large  surface.  The  clot  of  the  former  is  compact  and  small;  while  that  of 
thr  latter,  being  spongy,  and  hence  retaining  much  serum  within  it,  is  large 
and  abundant,  though  the  actual  quantity  of  solid  matter  is  the  same  in  both. 
The  following  table  exhibits  the  results  of  two  careful  analyses  of  the  blood 
by  Lecanu :-— (An.  de  Ch.  et  de  Ph.  xlviii.  308.) 

Water            .....  780-145  785-590 

Fibrin 2-100  3-565 

Colouring  matter       ....  133-000  119-626 

Albumen        .             .             .             .             .  65-090  69-415 

Crystalline  fatty  matter         .             .             .  2-430  4-300 

Oily  matter                ....  1-310  2-270 

Extractive  matter  soluble  in  water  and  alcohol      1-790  1-920 

Albumen  combined  with  soda            .        p    *  /  1*265  2010 
Chloride  of  sodium    . 


potassium 
i     # 


Carbonates  f  >          8-370  7-304 

Phosphates  >  of  potassa  and  soda 

Sulphates     ^ 

Carbonates  of  lime  and  magnesia 

Phosphates  of  lime,  magnesia,  and  iron      S  2-100  1-414 

Sesquioxide  of  iron  ) 

Loss  ....        2-400  2-586 


1000-000       1000-000 

The  earthy  salts  were  obtained  by  incinerating  the  albumen,  and  the 
trace  of  iron  was  obviously  derived  from  a  little  colouring  matter  of  the 
blood.  Fatty  matter  appears  to  be  always  present  in  serum,  having  been 
found  by  Dr.  B.  Babington  as  well  as  by  Lecanu:  the  former  obtained  it  by 
agitating  serum  repeatedly  but  gently  with  ether,  which  took  up  the  fattv 
substance,  and  left  it  by  evaporation ;  while  the  latter  mixed  the  serum  with 
alcohol,  and  dissolved  the  fatty  principles  from  the  alcoholic  extract  by 
means  of  ether.  The  oily  matter  of  the  serum  is  very  soluble  in  ether  and 
cold  alcohol,  is  liquid  at  common  temperatures,  and  is  readily  converted  into 
soap  by  potassa.  The  crystalline  fatty  matter  is  similar  in  appearance  to 
cholesterine,  resists  the  action  of  potassa,  and  is  soluble  in  ether  and  boiling 
alcohol:  it  appears  to  contain  nitrogen  as  one  of  its  elements. 

The  relative  proportion  of  the  ingredients  of  the  blood  must  necessarily 
vary,  independent  of  disease,  even  in  the  same  individual,  according  as  the 
nutrition  is  scanty  or  abundant.  According  to  Lecanu  slight  variations  arise 
from  difference  of  age  and  sex,  and  the  following  comparative  view  is  the 
mean  of  his  analysis  made  with  blood  drawn  from  ten  women  and  from 
ten  men. 


585 


Female.  Male. 

Water 804-37  .  789-32 

Albumen 69-72  .  67-50 

Saline  and  extractive  matter          .            9-95  .  10-69 

Red  globules         ....        115-96  .  132-49 


100000  1000-00 

In  addition  to  the  constituents  of  the  blood  already  enumerated,  M.  Bar- 
ruel  declares  that  this  fluid  contains  a  volatile  principle,  peculiar  to  each 
species  of  animal.  This  principle  has  an  odour  resembling  that  of  the  cu- 
taneous or  pulmonary  exhalation  of  the  animal,  and  serves  as  a  distinctive 
character  by  which  the  blood  of  different  animals  may  be  recognized.  It  is 
dissolved  in  the  blood,  and  its  odour  may  be  perceived  when  the  blood  or  its 
serum  is  mixed  with  strong  sulphuric  acid.  The  odour  is  commonly 
stronger  in  the  male  than  in  the  female.  In  man  it  resembles  the  human 
perspiration ;  in  the  ox,  it  smells  like  oxen  or  a  cow-house ;  and  the  odour 
from  horses'  blood  is  similar  to  that  of  their  perspiration.  (Journ.  of  Science, 
vi.  N.  S.  187.)  Should  the  accuracy  of  these  observations  be  confirmed,  they 
may  be  advantageously  applied  in  some  cases  of  legal  medicine. 

Minute  portions  of  alumina,  silica,  and  manganese  have  been  detected  in 
the  blood,  and  Dr.  O'Shaughnessy  confirms  the  statement  of  M.  Sarzeau 
that  a  trace  of  copper  may  likewise  be  found  ;  but  the  extremely  minute 
quantity  in  which  these  substances  occur,  renders  it  doubtful  whether  they 
really  exist  in  the  blood,  or  are  casually  introduced  in  the  course  of  ana- 
lysis.  Dr.  Clanny  reports  the  existence  of  a  large  quantity  of  free  carbon 
in  the  blood ;  but  I  am  not  aware  that  the  statement  is  borne  out  by  experi- 
ment, and  it  is  entirely  opposed  to  the  observation  of  other  chemists.  Of 
the  presence  of  free  carbonic  acid  in  the  blood,  I  shall  have  occasion  to 
speak  while  discussing  the  subject  of  respiration, 

Serum  of  the  Blood. — This  liquid,  which  separates  during  the  coagulation 
of  the  blood,  has  a  yellowish  colour,  is  transparent  when  carefully  collected, 
has  a  slightly  saline  taste,  and  is  somewhat  unctuous  to  the  touch.  Its 
average  specific  gravity  is  about  1-029.  It  "has  a  slight  alkaline  reaction 
with  test  paper,  owing  to  the  presence  of  soda,  which  some  chemists  believe 
to  be  combined  with  carbonic  acid,  and  others  with  albumen :  the  last 
opinion  is  the  more  probable ;  since  serum,  when  agitated  with  carbonic  acid, 
absorbs  that  gas  in  considerable  quantity.  Like  other  albuminous  liquids, 
it  is  coagulated  by  heat,  acids,  alcohol,  and  all  other  substances  which 
coagulate  albumen.  On  subjecting  the  coagulum  prepared  by  heat  to  gentle 
pressure,  a  small  quantity  of  a  colourless  limpid  fluid,  called  the  serosity, 
oozes  out,  which  contains,  according  to  Dr.  Bostoek,  about  l-50th  of  its 
weight  of  animal  matter,  together  with  a  little  chloride  of  sodium.  Of  this 
animal  matter  a  portion  is  albumen,  whicli  may  easily  be  coagulated  by 
means  of  galvanism ;  but  a  small  quantity  of  some  other  principle  is  present, 
which  differs  both  from  albumen  and  gelatin.  (Medico-Chir.  Trans,  ii.  166.) 

The  composition  of  the  serum,  according  to  the  late  analysis  of  Lecanu, 
may  be  seen  from  his  analysis  of  the  blood,  abstracting  the  colouring  mat- 
ter  and  fibrin  which  are  foreign  to  it  (page  584).  The  late  Dr.  Marcet 
found  that  1000  parts  of  the  serum  of  human  blood  are  composed  of  water 
900  parts,  albumen  86-8,  muriate  of  potassa  and  soda  6-6,  muco-extractive 
matter  4,  carbonate  of  soda  1-65,  sulphate  of  potassa  0-35,  and  of  earthy 
phosphates  0-60.  This  result  agrees  very  nearly  with  that  obtained  by  Ber- 
zelius,  who  states,  that  the  extractive  matter  of  Marcet  is  lactate  of  soda 
united  with  animal  matter.  (Medico-Chir.  Trans,  iii.  231.) 

Colouring  Matter  of  the  Blood. — This  substance,  to  which  the  term  Jiema- 
tosine  is  now  applied,  is  so  analogous  in  most  of  its  chemical  relations  to 
albumen,  that  its  complete  separation  from  it  is  attended  with  great  difficulty. 
It  is  obtained  nearly  pure  by  cutting  the  clot  of  blood  into  very  thin  slices 
with  a  sharp  knife,  as  advised  by  Berzelius,  soaking  them  repeatedly  in  dis- 


586  BLOOD. 

tilled  water,  and  letting  them  drain  on  bibulous  paper  after  each  immersion : 
the  slices  are  then  broken  up  in  distilled  water  with  a  stick,  briskly  stirring 
in  order  to  dissolve  the  colouring  matter;  and  the  filtered  solution  is  evapo- 
rated to  dryness  in  shallow  capsules  or  dishes  at  a  temperature  of  80°  or 
100°  F.  As  thus  prepared,  the  colouring  matter,  or  hematosine,  is  soluble 
and  possessed  of  all  its  characters ;  but  it  retains  a  little  serum.  It  may  be 
still  further  purified  by  the  method  of  Engelhart,  which  is  founded  on  the 
fact  that  hematosine  is  more  coagulable  by  heat  than  albumen :  serum  di- 
luted with  ten  parts  of  water  does  not  coagulate  at  160°;  whereas  hema- 
tosine, dissolved  in  fifty  parts  of  water,  begins  to  coagulate  at  149°,  and  is 
thrown  down  in  insoluble  flocks  of  a  brown  colour.  Unfortunately,  how- 
ever, its  characters  are  changed  by  this  operation,  uncoagulated  and  coagu- 
lated hematosine  bearing  the  same  relation  to  each  other  as  soluble  and 
insoluble  albumen.  For  the  purpose  of  ultimate  analysis  the  pure  insoluble 
hematosine  should  be  employed;  but  for  examining  the  properties  of  hema- 
tosine, its  less  pure  but  soluble  state  is  preferable. 

Soluble  hematosine,  when  quite  dry,  is  black,  with  a  lustre  like  jet  in 
mass,  and  red  in  powder  or  in  thin  layers,  is  insipid  to  the  taste,  and  inodo- 
rous. In  cold  water  it  readily  dissolves,  forming  a  red  liquid,  which  may  be 
preserved  without  change  for  months.  Its  solution,  like  that  of  albumen, 
may  be  coagulated  by  heat  as  already  mentioned ;  but  when  quite  dry  it 
may  be  heated  to  212°  without  being  rendered  insoluble.  Alcohol  and  acids 
likewise  precipitate  it :  the  latter  deepen  its  tint,  and  fall  in  combination 
with  it;  but  the  compounds  of  hematosine  with  the  muriatic,  sulphuric,  and 
acetic  acid  may  be  dissolved  in  water  by  means  of  an  excess  of  their  acid. 
The  alkalies  do  not  precipitate  the  aqueous  solution  of  hematosine ;  but  its 
solution  in  hydrochloric  acid  yields  red  flocks  on  the  addition  of  ammonia. 
With  some  of  the  metallic  oxides  it  forms  insoluble  compounds,  especially 
with  the  oxides  of  tin  and  mercury;  and  hence  the  salts  of  these  metals 
precipitate  hematosine.  In  most  of  these  properties,  colour  excepted,  it  re- 
sembles albumen  ;  but  Lecanu  has  indicated  two  pointed  differences  : — 1.  a 
solution  of  hematosine  is  not  precipitated  by  the  acetate  or  subacetate  of 
oxide  of  lead,  while  both  of  these  salts  throw  down  albumen ;  2.  the  preci- 
pitate occasioned  by  hydrochloric  acid,  when  pressed  between  folds  of  linen 
to  remove  adhering  acid  and  well  dried,  is  soluble  in  strong  boiling  alcohol, 
whereas  the  corresponding  compound  of  albumen  and  hydrochloric  acid  is 
quite  insoluble.  By  this  character  Lecanu  found  that  hematosine,  carefully 
prepared  from  human  blood,  contains  very  little  albumen ;  but  that  the  co- 
louring matter  of  blood  from  the  ox  and  sheep  appears  to  be"  a  compound,  in 
nearly  equal  parts,  of  hematosine  and  albumen.  (An.  de  Ch.  et  de  Ph.  xlv.  5.) 

Hematosine,  according  to  the  analysis  of  Michaelis,  consists  of  carbon, 
hydrogen,  nitrogen,  and  oxygen,  very  nearly  in  the  same  ratio  as  in  fibrin 
and  albumen ;  but  it  differs  from  both  in  containing  iron.  This  was  an- 
nounced in  1806  by  Berzelius  in  his  comparative  examination  of  the  ingre- 
dients of  the  blood  (Medico-Chir.  Trans,  iii.  213) :  from  the  albumen  and 
fibrin  he  could  obtain  no  iron;  but  100  parts  of  hematosine,  when  burned  in 
the  open  air,  left  1*25  of  ashes,  containing  0-625  of  oxide  of  iron,  and  0-625 
of  a  mixture  of  carbonate  and  phosphate  of  lime,  phosphate  of  magnesia, 
and  subphosphate  of  oxide  of  iron.  He  was  unable  to  detect  the  presence  of 
iron  by  any  of  the  liquid  tests.  These  facts,  though  questioned  by  other 
chemists,  were  fully  established  by  Dr.  Engelhart,  who  gained  the  prize 
offered  in  the  year  1825  by  the  Medical  Faculty  of  Gottin^en  for  the  best 
Essay  on  the  nature  of  the  colouring  matter  of  the  blood  (Edinb.  Med.  and 
Surg.  Journ.  for  January,  1827).  He  demonstrated  that  the  fibrin  and  albu- 
men of  the  blood,  when  carefully  separated  from  colouring  particles,  do  not 
contain  a  trace  of  iron ;  and,  on  the  contrary,  he  procured  iron  from  the  red 
globules  by  incineration.  But  he  likewise  succeeded  in  proving  the  exist- 
ence of  iron  in  the  colouring  matter  of  the  blood  by  the  liquid  tests;  for,  on 
transmitting  a  current  of  chlorine  gas  through  a  solution  of  the  red  glo- 
bules, the  colour  entirely  disappeared,  white  flocks  were  thrown  down,  and  a 


BLOOD.  587 

transparent  solution  remained,  in  which  sesquioxide  of  iron  was  discovered  by 
all  the  usual  reagents.  The  results  obtained  by  Dr.  Engclhart,  relative  to 
the  quantity  of  the  iron,  correspond  with  those  of  Berzelius.  These  facts 
have  been  since  confirmed  by  Rose,  who  has  accounted  in  a  satisfactory 
manner  for  the  failure  of  former  chemists  in  detecting  iron  in  the  blood 
while  in  a  fluid  state.  He  finds  that  oxide  of  iron  cannot  be  precipitated  by 
the  alkalies,  hydrosulphuret  of  ammonia,  or  infusion  of  galls,  if  it  is  dissolved 
in  a  solution  which  contains  albumen  or  other  soluble  organic  principles. 

From  the  presence  of  iron  in  hematosine,  and  its  total  absence  in  the  other 
principles  of  the  blood,  chemists  were  induced  to  suspect  that  its  peculiar 
colour  was  in  some  way  or  other  produced  by  that  metal,  an  idea  which  re- 
ceived additional  support  from  the  known  tendency  of  sesquioxide  of  iron  to 
form  salts  of  a  red  colour.  But  this  view,  though  plausible  on  these  grounds, 
is  in  other  respects  improbable.  The  real  state  in  which  iron  exists  in  the 
blood  is  quite  unknown,  and  its  minute  proportion  seems  unequal  to  produce 
so  intense  a  colour  as  that  of  the  blood.  The  only  probable  mode  of  explain- 
ing the  diversity  of  tints  which  agents  of  different  kinds  produce  in  the 
blood,  is  to  adopt  the  opinion  ably  maintained  by  Mr.  Brande,  who  supposes 
that  the  tint  of  hematosine  is  owing  to  a  peculiar  animal  colouring  principle, 
capable  like  cochineal  or  madder  of  acting  as  a  dye,  and  of  combining  with 
metallic  oxides.  He  succeeded  in  obtaining  a  compound  with  hematosine 
and  oxide  of  tin;  but  it  yields  the  finest  lakes  with  nitrate  of  peroxide  of 
mercury  and  corrosive  sublimate.  Woollen  cloths,  impregnated  with  either 
of  these  compounds,  and  immersed  in  an  aqueous  solution  of  hematosine, 
acquired  a  permanent  red  dye,  unchangeable  by  washing  with  soap.  (Phil. 
Trans.  1812.) 

Fibrin  of  the  Blood. — Fibrin  appears  to  exist  in  the  blood  in  two  states,  as 
already  mentioned  ; — as  the  central  nuclei  of  the  red  globules,  and  in  solu- 
tion in  the  serum.  The  fibrin  from  both  sources  is  obtained  by  beating  up 
the  clot  of  blood  with  successive  portions  of  water,  so  as  to  dissolve  all  the 
serum  and  colouring  matter,  leaving  the  insoluble  fibrin  quite  white;  but 
the  best  mode  of  separation  is  to  stir  recently  drawn  blood  with  a  stick 
during  coagulation,  when  the  fibrin  adheres  to  it  in  strings,  which  are  easily 
rendered  colourless  by  washing. 

Coagulation  of  the  Blood. — This  phenomenon  is  occasioned  by  the  agglu- 
tination of  the  fibrin  of  the  blood, — both  of  the  nuclei  of  the  red  globules, 
after  they  have  lost  their  colouring  envelope,  and  of  that  part  which  is  in 
solution.  The  time  required  for  coagulation  is  influenced  by  temperature, 
being  promoted  by  heat,  and  retarded  by  cold.  Sir  C.  Scudamore  finds  that 
blood  which  begins  to  coagulate  in  four  minutes  and  a  half  in  an  atmosphere 
of  53°,  undergoes  the  same  change  in  two  minutes  and  a  half  at  98° ;  and 
that  which  coagulates  in  four  minutes  at  98°  will  become  solid  in  one  minute 
at  120°.  On  the  contrary,  blood  which  coagulates  firmly  in  five  minutes  at 
60°  will  remain  quite  fluid  for  twenty  minutes  at  the  temperature  of  40°, 
and  requires  upwards  of  an  hour  for  complete  coagulation.  (Scudamore  on 
the  Blood.) 

The  process  of  coagulation  is  influenced  by  exposure  to  the  air.  If  atmo- 
spheric air  be  excluded,  as  by  filling  a  bottle  completely  with  recently  drawn 
blood,  and  closing  the  orifice  with  a  good  stopper,  coagulation  is  retarded. 
It  is  singular,  however,  that  if  blood  be  confined  within  the  exhausted  re- 
ceiver of  an  air-pump,  the  coagulation  is  accelerated.  (Scudamore.) 

Recently  drawn  blood,  owing  doubtless  to  its  temperature,  is  known  to 
give  off  a  portion  of  aqueous  vapour,  which  has  a  peculiar  odour,  indicative 
of  the  presence  of  some  peculiar  principle,  but  in  which  nothing  but  water 
can  be  detected.  Physiologists  are  not  agreed  upon  the  question  whether 
the  act  of  coagulation  is  or  is  not  accompanied  with  disengagement  of  gase- 
ous matter.  In  the  experiments  of  Vogel,  Brande,  and  Scudamore,  blood 
coagulating  in  the  vacuum  of  an  air-pump  was  found  to  emit  carbonic  acid, 
and  Scudamore  even  inferred  that  the  evolution  of  this  gas  constitutes  an 
essential  part  of  the  process.  Other  experimentalists,  however,  have  obtained 


588  BLOOD. 

a  different  result.  Dr.  John  Davy  and  the  late  Dr.  Duncan,  jun.,  failed  in 
their  attempts  to  procure  carbonic  acid  from  blood  during  coagulation ;  and 
Dr.  Christison,  in  an  experiment  which  I  witnessed,  was  not  more  success*, 
ful.  This  evidence  seems  positive  against  the  notion  that  the  evolution  of 
carbonic  acid  gas  is  an  essential  part  of  coagulation.  The  existence  of  car- 
bonic acid  in  venous  blood,  is  a  different  question,  and  this  point  will  be  dis- 
cussed under  the  head  of  respiration. 

Coagulation  is  influenced  by  the  rapidity  with  which  the  blood  is  removed 
from  the  body.  Sir  C.  Scudamore  observed,  that  blood  slowly  drawn  from  a 
vein  coagulates  more  rapidly  than  when  taken  in  a  full  stream. 

Experiments  are  still  wanting  to  show  the  influence  of  different  gases  on 
coagulation.  Oxygen  gas  accelerates  coagulation,  and  carbonic  acid  retards 
but  cannot  prevent  it. 

He<it  is  evolved  during  the  coagulation  of  the  blood.  The  late  Dr.  Gordon 
estimated  the  rise  of  the  thermometer  at  six  degrees  ;  and  Dr.  Davy,  on  the 
other  hand,  regards  the  increase  of  temperature  from  this  cause  as  very 
slight.  Sir  C.  Scudamore  finds  that  the  rate  at  which  blood  cools  is  distinctly 
slower  than  it  would  be  were  no  caloric  disengaged,  and  he  observed  tho 
thermometer  to  rise  one  degree  at  the  commencement  of  coagulation. 

Some  substances  prevent  the  coagulation  of  the  blood.  This  effect  is  pro- 
duced by  a  saturated  solution  of  chloride  of  sodium,  hydrochlorate  of  am- 
monia, nitre,  and  a  solution  of  potassa.  The  coagulation,  on  the  contrary, 
is  promoted  by  alum  and  the  sulphates  of  the  oxides  of  zinc  and  copper. 
The  blood  of  persons  who  have  died  a  sudden  violent  death,  by  some  kinds 
of  poison,  or  from  mental  emotion,  is  usually  found  in  a  fluid  state.  Light- 
ning is  said  to  have  a  similar  effect;  but  Sir  C.  Scudamore  declares  this  to 
be  an  error.  Blood,  through  which  electric  discharges  were  transmitted, 
coagulated  as  quickly  as  that  which  was  not  electrified  ;  and  in  animals  killed 
by  the  discharge  of  a  powerful  galvanic  battery,  the  blood  in  the  veins  was 
always  found  in  a  solid  state. 

The  cause  of  the  coagulation  of  the  blood  has  been  the  subject  of  much 
speculation  to  physiologists.  The  tendency  of  this  fluid  to  preserve  the 
liquid  form  while  contained  in  a  living  animal,  cannot  be  ascribed  to  the 
motion  to  which  it  is  continually  subject  within  the  vessels.  It  is  a  familiar 
fact  that  blood,  though  continually  stirred  out  of  the  body,  is  not  prevented 
from  coagulating ;  and  it  has  been  noticed,  that  the  coagulation  of  blood 
which  is  set  at  rest  within  its  proper  vessels  by  the  application  of  ligatures, 
or  which  has  been  accidentally  extravasated  within  the  body,  is  materially 
retarded.  It  has,  indeed,  been  hitherto  found  impossible  to  account  in  a 
satisfactory  manner  for  the  blood  retaining  fluidity  by  reference  to  motion, 
temperature,  or  the  operation  of  any  physical  or  chemical  laws ;  and,  conse- 
quently, it  is  generally  ascribed  to  the  agency  of  the  vital  principle.  The 
blood  is  supposed  either  to  be  endowed  with  a  principle  of  vitality,  or  to  re- 
ceive from  the  living  parts  with  which  it  is  in  contact  a  certain  vital  impres- 
sion, which,  together  with  constant  motion,  counteracts  its  tendency  to 
coagulate. 

Blood  in  Disease. — The  blood  may  be  diseased  either  by  the  excess  or  de- 
ficiency of  one  or  more  of  its  proper  constituents,  or  from  the  presence  of 
substances  which  are  foreign  to  it.  One  familiar  instance  of  diseased  blood 
is  jaundice,  when  bile  enters  the  circulation  and  is  distributed  to  every  or- 
ganized part  of  the  body.  Though  the  presence  of  bile  in  the  blood  during 
jaundice  has  been  detected,  yet  its  passage  into  the  circulating  mass  appears 
so  rapidly  succeeded  by  its  exit,  that  its  detection  in  the  blood  itself  is  gene- 
rally difficult.  Urea  has  also  been  detected,  sometimes  in  very  large  quan- 
tity :  it  appears  to  be  constantly  present  in  the  blood,  whenever  the  secretion 
of  urine  is  suppressed.  Prevost  and  Dumas  wholly  arrested  tho  secretion  of 
urine  in  a  dog  by  tying  the  renal  vessels  and  excising  the  kidneys,  and  two 
days  after  the  operation  they  obtained  20  grains  of  urea  from  5  ounces  of  his 
blood.  (An.  de  Ch.  et  de  Ph.  xxxiii.  90.)  Dr.  Christison  found  urea  in  the 
blood  of  persons  suffering  under  renal  disease,  as  will  be  mentioned  in  the 


BLOOD. 

section  on  the  urine;  and  Dr.  Prout  appears  also  to  have  made  a  similar 
observation.  The  serum  of  the  blood  in  this  affection  has  Usually  a  lower 
sp.  gr.  than  healthy  serum,  the  average  of  several  cases  being  1-021  (Gre- 
gory) ;  and  the  albumen  is  in  smaller  proportion  than  natural.  Urea  has  been 
detected  by  Dr.  O'Shaughnessy  in  the  blood  of  persons  labouring  under  cho- 
lera, in  which  disease  the  action  of  the  kidneys  is  generally  very  much  dis- 
turbed. The  sp.  gr.  of  the  serum  of  diabetic  blood  is  usually  above  the 
natural  standard,  being  so  high  as  1-0354.  (Marcet). 

The  serum  of  blood,  instead  of  being  transparent,  as  it  commonly  is,  has 
sometimes  a  cloudy  appearance  like  whey,  and  in  some  more  rare  instances 
is  perfectly  opaque  and  white,  as  if  it  had  been  mixed  with  milk.  The  cause 
of  the  opacity  has  been  experimentally  examined  by  Drs.  Traill  and  Chris- 
tison,  who  have  traced  it  to  the  presence  of  oleaginous  matter,  which  the 
latter  has  shown  to  contain  both  stearine  and  elaine,  and  to  be  very  similar  to 
human  fat.  The  milkiness  may,  therefore,  be  ascribed  to  fat  being  mecha- 
nically diffused  through  the  serum  like  oil  in  an  emulsion.  It  may  be  easily 
separated  by  agitating  the  serum  in  a  tube  with  half  its  bulk  of  sulphuric 
ether,  when  the  adipose  matter  is  instantly  dissolved;  the  opacity  in  conse- 
quence disappears,  and  on  evaporating  the  clear  ethereal  solution,  which  rises 
to  the  surface  of  the  mixture,  the  fat  is  obtained  in  a  separate  state.  By  this 
means  he  procured  on  one  occasion  five  per  cent,  of  fat  from  milky  serum, 
and  one  per  cent,  from  serum  which  had  the  aspect  of  whey.  (Edinb.  Med. 
and  Surg.  Journal,  April,  1830.) 

The  most  remarkable  kind  of  diseased  blood  which  has  yet  been  studied 
by  chemists  is  that  which  occurs  in  cholera.  During  the  progress  of  that 
disease  an  enormous  discharge  takes  place  of  a  whitish-coloured  fluid  simi- 
lar to  a  mixture  of  boiled  rice  with  water,  an  appearance  occasioned  by  a 
white  flaky  matter  floating  in  a  nearly  colourless  liquid.  The  insoluble 
part  has  the  character  of  fibrin :  while  the  liquid  portion  is  a  weak  solution 
of  albumen,  is  faintly  alkaline,  and  contains  the  same  kind  of  salts  as  exist 
in  the  blood.  On  examining  the  blood  itself,  it  is  found  to  contain  less 
water  and  more  albumen  and  hematosine  than  healthy  blood.  The  density  of 
the  serum  is  consequently  greater  than  usual;  its  colour  is  remarkably  black 
even  in  the  arteries.  In  some  cases  it  is  semi-fluid  and  incapable  of  coagu- 
lating1, having  the  appearance  of  tar;  and  the  salts  of  the  blood  are  often  in 
unusually  small  quantity,  being  sometimes  almost  entirely  wanting.  On 
comparing  the  condition  of  the  blood  with  that  of  the  discharges,  it  is  mani- 
fest that  the  latter  contain  all  the  ingredients  of  the  blood  except  the  red 
globules ;  but  that  the  aqueous  arid  saline  parts  pass  out  of  the  circulation 
more  rapidly  than  the  albuminous. 

The  cause  of  the  dark  colour  of  the  blood  in  cholora  is  a  point  by  no 
means  decided.  Dr.  Thomson  states  that  the  blood  in  cholera  is  not  ren- 
dered florid  by  exposure  to  atmospheric  air,  and  hence  argues  that  the  dark 
colour  is  owing  to  some  diseased  condition  of  the  blood  which  unfits  it  for 
being  duly  arterialized ;  but  this  view  is  opposed  to  the  statement  of  Dr. 
O'Shaughnessy,  who  declares  that  the  dark  blood  in  cholera  is  susceptible 
of  arterialization, — that,  at  least,  on  being  agitated  with  air,  it  is  rendered 
florid,  absorbs  oxygen,  and  emits  carbonic  acid  gas.  Dr.  Stevens,  in  his 
treatise  on  the  blood,  maintains  that  the  black  colour  is  primarily  owing  to 
the  contagion  of  cholera,  which  throws  the  circulating  fluids  into  a  morbid 
state;  and  that  the  effect  of  the  poison  is  increased  by  the  diminished 
quantity  of  saline  matter,  an  opinion  intimately  connected  with  his  theory 
of  arterialization,  which  will  shortly  be  explained.  He  has  observed  the 
blood  of  persons  living  in  a  cholera  hospital  to  be  preternaturally  dark, 
though  they  were  not  affected  with  the  disease.  Perhaps  the  most  correct 
opinion  is,  that  the  blood  of  persons  in  cholera,  in  consequence  of  deranged 
arterial  action,  circulates  sluggishly,  arid  is  hence  imperfectly  arterialized : 
from  this  cause  the  dark  colour  may  arise  without  any  diminution  of  saline 
matter;  and  it  may  disappear,  from  an  improved  circulation,  without  the 
administration  of  salt.  But  there  is  no  doubt  that  loss  of  saline  matter  in- 

50 


590  RESPIRATION. 

creases  the  dark  tint  of  the  blood,  and  prevents  it  from  acquiring  the  arterial 
colour. 

The  substance  known  under  the  name  of  black  vomit,  ejected  by  the 
stomach  during  the  last  stages  of  yellow  fever,  appears  from  the  observations 
of  Dr.  Stevens  to  be  blood  blackened  and  partially  coagulated  by  a  free  acid. 
The  acidity  is  suspected  by  Dr.  Prout  to  arise  from  the  secretion  of  acetic 
acid  ;  and  the  presence  of  hydrochloric  acid  is  also  probable. 

Respiration. 

When  venous  blood  is  brought  into  contact  with  atmospheric  air,  its  sur- 
face passes  from  a  dark  purple  to  a  florid-red  colour,  oxygen  gas  disappears, 
and  carbonic  acid  gas  is  emitted.  The  change  takes  place  more  speedily 
when  air  is  agitated  with  blood ;  it  is  still  more  rapid  when  pure  oxygen  is 
substituted  for  atmospheric  air;  and  it  does  not  occur  at  all  when  oxygen 
is  entirely  excluded.  These  facts,  which  were  long  con.sidered  indisputable, 
have  been  questioned  by  Dr.  Davy ;  hut  they  are  nevertheless  perfectly  true, 
and  have  been  fully  established  by  Dr.  Christison.  (Edin.  Med.  and  Surg. 
Journal,  Jan.  1831.)  The  quantity  of  carbonic  acid  developed  very  exactly 
corresponds  with  the  oxygen  which  disappears;  but  when  the  blood  and  air 
are  agitated  together,  part  of  the  carbonic  acid  which  would  otherwise  be 
found  as  gas,  is  absorbed  by  the  serum.  It  appears  certain,  from  the  expe- 
riments of  Dr.  Christison,  that  the  colouring  matter  is  the  part  of  the  blood 
essentially  concerned  in  the  phenomenon;  an  inference  which  is  drawn, 
not  frotn  the  mere  change  of  tint,  but  from  the  effect  of  the  blood  on  the  air 
varying  with  the  quantity  and  condition  of  the  colouring  matter.  In  some 
fevers,  as  acute  rheumatism,  in  which  the  circulation  is  rapid  and  the  respi- 
ration free,  the  venous  blood  is  found  to  be  very  florid,  and  to  withdraw  very 
little  oxygen  from  air;  and  a  similar  scanty  abstraction  of  oxygen  is  ob- 
served in  dark  venous  blood,  when  its  usual  proportion  of  colouring  matter 
is  deficient. 

The  conversion  of  the  dark  purple  colour  of  venous  blood  into  the  florid  tint 
of  that  contained  in  the  arteries,  is  familiarly  expressed  by  the  term  arteria- 
lization;  or,  more  strictly,  this  name  is  applied  to  a  change  in  the  constitu- 
tion of  the  blood,  which  is  accompanied  and  indicated  by  change  of  colour, 
evolution  of  carbonic  acid,  and  abstraction  of  oxygen  from  the  air. 

Chemists  have  differed  about  the  origin  of  thc^carbonic  acid.  Some  sup- 
pose that  the  blood,  in  circulating  through  the  body,  becomes  charged  with 
carbon  in  some  unknown  mode  of  combination,  which  causes  the  venous 
character;  and  that  when  such  blood  is  exposed  to  the  air,  its  redundant 
carbon,  by  a  process  of  oxidation,  unites  directly  with  atmospheric  oxygen, 
the  carbonic  acid  so  generated  is  set  free,  and  the  blood,  unloaded  of  carbon, 
recovers  the  arterial  character.  By  others,  venous  blood  is  thought  to  owe 
its  colour  to  the  presence  of  carbonic  acid  ready  formed  within  it:  they 
maintain  that  oxygen  gas  is  directly  absorbed  into  the  blood,  and  displaces 
the  pre-existing  carbonic  acid.  The  near  coincidence  between  the  quantity 
of  evolved  carbonic  acid  and  absorbed  oxygen,  which  has  been  urged  in 
favour  of  the  former  theory,  is  scarcely  an  argument  either  way  ;  for  though 
true,  on  the  one  hand,  that  carbonic  acid  contains  its  own  volume  of  oxygen, 
it  is  also  true,  on  the  other,  that  if  one  gas  displaces  another  from  a  liquid, 
the  volumes  of  evolved  and  absorbed  gas  usually  correspond.  The  strongest 
evidence  is  in  favour  of  the  latter  theory.  Carbonic  acid  has  been  proved  to 
be  capable  when  absorbed  by  arterial  blood  of  causing  the  venous  character; 
and  Mr.  Hoffman  has  shown  that  when  venous  blood  is  received  from  a  vein 
into  a  vessel  of  full  hydrogen  gas,  without  exposure  to  the  atmosphere,  and  is 
then  agitated  with  the  hydrogen,  carbonic  acid  gas  is  evolved.  (Medical 
Gazette,  March  30,  1833.) 

But  arterialization  does  not  alone  depend,  as  was  thought  till  lately,  on  the 
influence  of  the  atmosphere.  Dr.  Stevens,  in  his  treatise  on  the  blood,  has 
the  merit  of  proving  the  saline  matter  of  the  scrum  to  be  essential  to  the 


RESPIRATION.  591 

phenomenon.  Various  salts,  such  as  nitre,  chlorate  of  potassa,  sea-salt,  and 
bicarbonate  of  soda,  have  the  property  of  giving  to  hematosine,  or  the  colour- 
ing principle  of  the  blood,  a  bright  red  tint,  far  more  florid,  when  a  strong 
saline  solution  is  used,  than  arterial  blood.  A  saline  solution  of  the  requisite 
strength  gives  to  venous  blood  the  arterial  tint,  without  exposure  to  the  air; 
but  the  serum  contains  so  small  a  quantity  of  salt  that  its  effect  becomes 
visible  only  when  aided  by  the  agency  of  the  atmosphere.  A  clot  of  venous 
blood,  when  carefully  separated  from  its  serum,  is  not  brightened  by  oxygen 
gas;  and  arterial  blood,  when  its  serum  is  displaced  by  pure  water,  becomes 
as  dark  as  venous  blood.  Hence  it  may  be  inferred  that  the  change  from 
venous  to  arterial  blood  consists  of  two  parts  which  are  essentially  distinct: 
one  is  attended  with  the  direct  absorption  of  oxygen,  and  the  evolution  of 
carbonic  acid  pre-existing  in  venous  blood,  an  action  essential  to  life;  and  the 
other,  the  most  conspicuous  but  probably  least  essential,  is  the  effect  of  the 
saline  parts  of  the  serum,  which  impart  a  florid  tint  to  the  colouring  matter 
after  the  former  change  has  occurred.  By  what  means  the  absorption  of 
oxygen  gives  rise  to  the  evolution  of  carbonic  acid,  is  a  question  which,  like 
others  that  will  occur  to  the  attentive  reader,  has  not  been  sufficiently  ex- 
plained, and  invites  further  investigation. 

The  same  changes  which  occur  in  blood  out  of  the  body  are  continually 
taking  place  within  it.  During  respiration,  venous  blood  is  exposed  in  the 
lungs  to  the  agency  of  the  air  and  is  arterialized,  oxygen  gas  disappears,  and 
carbonic  acid  is  evolved ;  and  it  is  remarkable  that  these  phenomena  ensue 
not  only  during  life,  but  even  after  death,  provided  the  respiratory  process  be 
preserved  artificially.  Since,  therefore,  all  the  characteristic  phenomena  of 
arterialization  are  the  same  in  a  living  and  in  a  dead  animal,  and  whether 
the  blood  is  or  is  not  contained  in  the  body,  it  seems  legitimate  to  infer,  that 
this  process  is  not  necessarily  dependent  on  the  vital  principle,  but  is  solely 
determined  by  the  laws  of  chemical  action. 

In  studying  the  subject  of  respiration,  the  first  object  is  to  determine  the 
precise  change  produced  in  the  constitution  of  the  air  which  is  inhaled. 
Dr.  Black  was  the  first  to  notice  that  the  air  exhaled  from  the  lungs  contains 
a  considerable  quantity  of  carbonic  acid,  which  may  be  detected  by  trans- 
mission through  lime-water.  Priestley,  some  years  after,  observed  that  air 
is  rendered  unfit  for  supporting  flame  or  animal  life  by  the  process  of  respi- 
ration; from  which  it  was  probable  that  oxygen  is  consumed;  and  Lavoisier 
subsequently  established  the  fact,  that  during  respiration  oxygen  gas  disap- 
pears, and  carbonic  acid  is  disengaged.  The  chief  experimentalists  who  have 
since  cultivated  this  department  of  chemical  physiology  are,  Priestley, 
Scheele,  Lavoisier,  Seguin,  Crawford,  Goodwin,  Davy,  Ellis,  Allen  and 
Pepys,  Edwards,  and  Despretz.  Of  these,  the  results  obtained  by  Messrs. 
Allen  and  Pepys  (Phil.  Trans.  1808),  and  Dr.  Edwards,*  are  the  most  con- 
clusive and  satisfactory  :  their  researches  having  been  conducted  with  great 
care,  and  aided  by  all  the  resources  of  modern  chemistry. 

One  of  the  chief  objects  of  Allen  and  Pepys,  in  their  experiments,  was  to 
ascertain  if  any  uniform  relation  exists  between  the  oxygen  consumed  and 
the  carbonic  acid  evolved.  They  found  in  general  that  the  quantity  of  the 
former  exceeds  that  of  the  latter ;  but  as  the  difference  was  very  trifling, 
they  inferred  that  the  carbonic  acid  of  the  expired  air  is  exactly  equal  to  the 
oxygen  which  disappears.  The  experiments  of  Dr.  Edwards  were  attended 
with  a  remarkable  result,  which  accounts  very  happily  for  some  of  the  dis- 
cordant statements  of  preceding  inquirers.  He  found  the  ratio  between  the 
gases  to  vary  with  the  animal.  In  some  animals  it  might  be  regarded  as 
nearly  equal ;  while  in  others  the  loss  of  oxygen  considerably  exceeded  the 
gain  of  carbonic  acid,  so  that  the  respired  air  suffered  a  material  diminution 
in  volume.  With  respect  to  the  human  subject,  the  statement  of  Allen  and 
Pepys  seems  very  near  the  truth. 

*  De  PInfluence  des  Agens  Physiques  sur  la  Vie,  1824. 


592  RESPIRATION. 

The  quantity  of  oxygen  withdrawn  from  the  atmosphere,  and  of  carbonic 
acH  disengaged,  is  variable  in  different  individuals,  and  in  the  same  indivi- 
dual at  different  times.  It  is  estimated  by  Allen  and  Pepys,  that  in  every 
minute  during-  the  cairn  respiration  of  a  healthy  man  of  ordinary  stature, 
26*6  cubic  inches  of  carbonic  acid  of  the  temperature  of  50°  are  emitted, 
and  an  equal  volume  of  oxygen  withdrawn  from  the  atmosphere.  From 
these  data  it  has  been  calculated,  that  in  an  interval  of  twenty-four  hours, 
not  less  than  eleven  ounces  of  carbon  are  given  off  from  the  lungs  alone, — 
an  estimate  which  must  surely  be  inaccurate,  the  quantity  being  so  great  as 
sometimes  to  exceed  the  weight  of  carbon  contained  in  the  food.  The  same 
observers  have  lately  found  the  production  of  carbonic  acid  in  a  pigeon, 
breathing  freely  in  atmospheric  air,  to  be  such  that,  supposing  the  same  rate 
to  continue,  the  bird  must  have  thrown  off  96  grains  of  carbon  in  the  space 
of  24  hours.  From  the  observations  of  Dr.  Prout,  it  appears  that  the  quan- 
tity of  carbonic  acid  emitted  from  the  lungs  is  variable  at  particular  periods 
of  the  day,  and  in  particular  states  of  the  system.  It  is  more  abundant 
during  the  day  than  the  night;  about  daybreak  it  begins  to  increase,  con- 
tinues to  do  so  till  about  noon,  and  then  decreases  until  sunset.  During  the 
night  it  seems  to  remain  uniformly  at  a  minimum;  and  the  maximum 
quantity  given  off  at  noon  exceeds  the  minimum  by  about  one-fifth  of  the 
whole.  The  quantity  of  carbonic  acid  is  diminished  by  any  debilitating 
causes,  such  as  low  diet,  depressing  passions,  and  the  like.  (An.  of  Phil.  xiii. 
269.)  The  experiments  of  Dr.  Fyfe,  published  in  his  Inaugural  Disserta- 
tion, are  confirmatory  of  those  above  mentioned. 

Messrs.  Allen  and  Pepys  observed  that  atmospheric  air,  when  drawn  into 
the  lungs,  returns  charged,  in  the  succeeding  expiration,  with  from  8  to  6  per 
cent,  of  carbonic  acid  gas;  but  this  estimate  is  probably  too  high,  since  in 
some  recent  observations  of  Dr.  Apjohn  of  Dublin,  air,  once  respired,  con- 
tained only  3-6  per  cent,  of  carbonic  acid.  When  an  animal  is  confined  in 
the  same  quantity  of  air,  death  ensues  before  all  the  oxygen  is  consumed  : 
when  the  same  portion  of  air  is  repeatedly  respired  until  it  can  no  longer 
support  life,  it  then  contains  10  per  cent,  of  carbonic  acid  according  to  Allen 
and  Pepys,  and  barely  8  per  cent,  according  to  Dr.  Apjohn.  (Edin.  Med.  and 
Surg.  Journal,  Jan.  1831.) 

Although  in  respiration,  the  arterialization  of  the  blood  by  means  of  free 
oxygen  is  the  essential  change,  without  the  due  performance  of  which  the 
life  of  warm-blooded  animals  cannot  be  preserved  beyond  a  few  minutes,  and 
which  is  likewise  necessary  to  the  lowest  of  the  insect  tribe,  it  is  important 
to  determine  whether  the  nitrogen  of  the  atmosphere  has  any  influence  in 
the  function.  The  results  of  different  inquirers  differ  considerably.  In  the 
experiments  of  Priestley,  Davy,  Humboldt,  Henderson,  and  Pfaff,  there 
appeared  to  be  absorption  of  nitrogen,  a  less  quantity  of  that  gas  being  ex- 
haled than  was  inspired.  Nysten,  Berthollet,  and  Despretz,  on  the  contrary, 
remarked  an  increase  in  the  bulk  of  the  nitrogen;  and  from  the  researches 
of  Seguin  and  Lavoisier,  Vauquelin,  Ellis,  Dalton,  and  Spallanzani,  it  was 
inferred  that  there  is  neither  absorption  nor  exhalation  of  nitrogen,  the 
quantity  of  that  gas  undergoing  no  change  during  its  passage  through  the 
air-cells  of  the  lungs.  Allen  and  Pepys  arrived  at  a  similar  conclusion ;  and 
since  the  appearance  of  their  Essay,  the  opinion  has  prevailed  very  generally 
among  physiologists,  that  in  respiration  the  nitrogen  of  the  air  is  altogether 
passive. 

The  facts  ascertained  by  Edwards  relative  to  this  subject  are  novel  and 
of  peculiar  interest.  This  acute  physiologist  has  reconciled  the  discordant 
results  of  preceding  experimenters  by  showing  that,  during  the  respiration 
even  of  the  same  animal,  the  quantity  of  nitrogen  may  one  while  be  in- 
creased, at  another  time  diminished,  and  at  a  third  wholly  unchanged.  He 
has  traced  these  phenomena  to  the  influence  of  the  seasons ;  and  he  sus- 
pects, as  indeed  is  most  probable,  that  other  causes,  independently  of  season, 
have  a  share  in  their  production.  In  nearly  all  the  lower  animals  which 
were  made  the  subject  of  experiment,  an  augmentation  of  nitrogen  was  ob- 


RESPIRATION.  593 

servable  during  summer.  Sometimes,  indeed,  it  was  so  slight,  that  it  might 
be  disregarded.  But  in  many  other  instances,  it  was  so  great  as  to  place 
the  fact  beyond  the  possibility  of  doubt;  and  on  some  occasions  it  almost 
equalled  the  whole  bulk  of  the  animal.  Such  continued  to  be  the  result  of 
his  inquiries  until  the  close  of  October,  when  he  observed  a  sensible  diminu- 
tion of  nitrogen,  and  the  same  continued  throughout  the  whole  of  winter  and 
the  beginning  of  spring. 

There  are  two  modes  of  accounting  for  these  phenomena.  According  to 
one  view,  the  nitrogen  which  disappears  is  ascribed  to  the  absorption  of 
what  was  inhaled,  arid  its  increase  to  direct  exhalation,  the  opposite  pro- 
cesses of  absorption  and  exhalation  being  supposed  not  to  occur  at  the  same 
moment.  According  to  the  other  view,  both  these  processes  are  always  going 
on  at  the  same  time,  and  the  result  depends  on  the  preponderance  of  one 
over  the  other.  When  absorption  prevails,  a  smaller  quantity  of  nitrogen  is 
exhaled  than  was  inspired ;  when  exhalation  exceeds  absorption,  increase  of 
nitrogen  takes  place ;  but  when  absorption  and  exhalation  are  equal,  the 
bulk  of  the  inspired  air,  so  far  as  concerns  nitrogen,  is  unchanged.  The  lat- 
ter opinion,  which  is  adopted  by  Edwards,  is  supported  by  two  decisive  ex- 
periments performed  by  Allen  and  Pepys,  in  one  of  which  a  guinea-pig  was 
confined  in  a  vessel  of  oxygen  gas,  and  in  the  other  in  an  atmosphere  com. 
posed  of  21  measures  of  oxygen  and  79  of  hydrogen.  In  both  cases  the  re- 
sidual air  contained  a  quantity  of  nitrogen  greater  tharu,the  bulk  of  the  ani- 
mal itself;  and  in  the  latter  a  portion  of  hydrogen  had  disappeared.  Hence 
it  follows  that  nitrogen  may  be  exhaled  from  the  lungs,  and  that  hydrogen 
may  be  absorbed. 

An  account  of  some  interesting  researches  on  the  respiration  of  birds, 
bearing  directly  on  this  subject,  was  published  in  1829  by  Allen  and  Pepys. 
(Phil.  Trans.)  The  subject  of  inquiry  was  the  pigeon,  and  the  phenomena 
attending  its  respiration  were  observed  under  three  different  circumstances, 
namely,  in  atmospheric  air,  in  oxygen  gas,  and  in  a  mixture  of  oxygen  and 
hydrogen,  in  which  the  former  amounted,  as  in  the  atmosphere,  to  20  per 
cent.  In  each  case  the  bulk  of  the  gaseous  mixture  remained  without 
change.  In  the  experiments  with  atmospheric  air,  the  oxygen  which  disap- 
peared was  equal  to  the  carbonic  acid  evolved ;  the  nitrogen  was  unaffected, 
except  on  one  occasion  when  the  bird  appeared  uneasy,  and  then  there  was 
a  slight  loss  of  nitrogen.  In  oxygen  gas  the  production  of  carbonic  acid 
was  about  half  the  quantity  emitted  when  the  pigeon  breathed  common  air ; 
and  the  decrease  in  oxygen  was  exactly  equal  to  the  united  volumes  of  the 
carbonic  acid  and  nitrogen  which  were  disengaged.  When  the  pigeon  was 
placed  in  mixed  oxygen  and  hydrogen  gases,  the  production  of  carbonic  acid 
was  rather  more  abundant  than  in  atmospheric  air,  and  its  volume  equalled 
exactly  the  loss  in  oxygen }  nitrogen,  as  before,  was  given  out  with  con- 
siderable freedom,  and  its  bulk  precisely  corresponded  to  the  decrease  in 
hydrogen.  In  the  two  latter  series  of  experiments,  especially  in  the  last,  the 
respiration  of  the  pigeon  was  at  times  laborious.  The  experiments,  how- 
ever, are  decisive  of  the  fact,  that  carbonic  acid  and  nitrogen  gases  may  be 
thrown  off  from  the  lungs,  and  that  oxygen  and  hydrogen  gases  may  bo 
absorbed. 

Two  theories  similar  to  those  of  arterialization  (page  590)  have  been  pro. 
posed  to  explain  the  phenomena  of  respiration.  According  to  one  theory, 
the  carbonic  acid  found  in  the  respired  air  is  actually  generated  in  the  lungs 
themselves;  while,  according  to  the  other,  this  gas  is  thought  to  exist  ready 
formed  in  the  blood,  and  to  be  merely  thrown  off  from  that  liquid  during  its 
distribution  through  the  lungs.  The  former  theory,  which  appears  to  have 
originated  with  Priestley,  has  received  several  modifications.  Priestley 
imagined  that  the  phenomena  of  respiration  are  owing  to  the  disengagement 
of  phlogiston  from  the  blood,  and  its  combination  with  the  air.  Dr.  Craw- 
ford modified  this  doctrine  in  the  following  manner.  (Crawford  on  Animal 
Heat.)  He  was  of  opinion  that  venous  blood  contains  a  peculiar  compound 
of  carbon  and  hydrogen,  termed  hydro-carbon,  the  elements  of  which  unite  in 

50* 


534  RESPIRATION. 

the  lungs  with  the  oxygen  of  the  air,  forming  water  with  the  one,  and  car- 
bonic acid  with  the  other;  and  that  the  blood,  thus  purified,  regains  its  florid 
hue,  and  becomes  fit  for  the  purposes  of  the  animal  economy. 

The  hypothesis  of  Crawford,  however,  is  not  merely  liable  to  the  objection 
that  the  supposed  hydro-carbon,  as  respects  the  blood,  is  quite  imaginary  ; 
but  it  was  found  at  variance  with  the  leading  facts  established  by  Allen  and 
Pepys.  By  the  elaborate  researches  of  these  chemists  it  was  established, 
that  carbonic  acid  gas  contains  its  own  volume  of  oxygen;  and  they  also 
concluded  that  air,  inhaled  into  the  lungs,  returns  charged  with  a  quantity 
of  carbonic  acid,  almost  exactly  equal  in  bulk  to  the  oxygen  which  disap- 
pears— an  inference  which,  as  applied  to  man  and  some  of  the  lower  ani- 
mals, seems  very  near  the  truth.  A  review  of  these  circumstances  induced 
them  to  adopt  the  opinion,  that  the  oxygen  of  the  air  combines  in  the  lungs 
exclusively  with  carbon  ;  and  that  the  watery  vapour,  which  is  always  con- 
tained in  the  breath,  is  an  exhalation  from  minute  pulmonary  vessels. 
They  conceived  that  the  fine  animal  membrane  interposed  between  the 
blood  and  the  air  does  not  prevent  chemical  action  from  taking  place  be- 
tween them. 

This  view  has  been  further  modified  by  Mr.  Ellis,  who  supposes  that  the 
carbon  is  separated  from  the  venous  blood  by  a  process  of  secretion,  and 
that  then,  coming  into  direct  contact  with  oxygen,  it  is  converted  into  car- 
bonic acid.  (Inquiry,  &c.  Parts  i.  and  ii.)  The  circumstance  which  led 
Mr.  Ellis  to  this  opinion,  was  a  disbelief  in  the  possibility  of  oxygen  acting 
upon  the  blood  through  the  animal  membrane  in  which  it  is  confined.  This 
difficulty,  as  will  immediately  appear,  no  longer  exists ;  and  the  free  per- 
meability of  membranes  by  gases  is  now  completely  established. 

According  to  the  second  theory,  which  was  supported  by  Le  Grange  and 
Hassenfralz,  and  has  lately  been  adopted  by  Edwards,  carbonic  acid  gene- 
rated during  the  course  of  the  circulation  is  given  off  from  venous  blood  in 
the  lungs,  and  oxygen  gas  is  absorbed.  This  doctrine,  though  generally 
regarded  hitherto  as  less  probable  than  the  preceding,  is  supported  by  very 
powerful  arguments.  The  experiments  and  observations  of  Dr.  Edwards 
seem  to  leave  no  doubt  that  the  blood,  while  circulating  through  the  lungs, 
is  capable  of  absorbing  hydrogen,  nitrogen,  and  oxygen  gases,  and  of 
emitting  nitrogen  ;  and  he  has  gone  very  far  towards  proving  that  the  car- 
bonic acid  is  derived  from  the  same  source.  On  confining  frogs  and  snails 
for  some  time  in  an  atmosphere  of  hydrogen,  the  residual  air  was  found  to 
contain  a  quantity  of  carbonic  acid,  which  was  in  some  instances  even 
greater  than  the  bulk  of  the  animal ;  and  a  similar  result  was  obtained  with 
young  kittens. 

These  facts,  in  proving  the  possibility  of  gaseous  inhalation  and  exhala- 
tion, as  well  as  the  evolution  of  carbonic  acid  independently  of  atmospheric 
air,  entitle  the  theory  of  Edwards  to  a  preference;  and  they  will  go  far, 
when  attested  by  more  extensive  observation,  especially  should  the  constant 
presence  of  carbonic  acid  in  venous  blood  be  established,  to  the  rejection  of 
the  former  theory. 

The  difficulty  which  formerly  stood  in  the  way  of  both  theories  of  respi- 
ration, arising  from  the  supposed  impermeability  of  animal  membranes  by 
gases,  has  been  entirely  removed  by  the  researches  of  Drs.  Faust  and  Mit- 
chell. (American  Journal  of  the  Medical  Sciences,  No.  13.)  It  fully  ap- 
pears from  their  experiments,  and  of  the  accuracy  of  their  principal  results 
I  am  satisfied  from  personal  observation,  that  animal  membranes  both  in 
the  living  and  dead  subject,  both  in  and  out  of  the  body,  are  freely  penetra- 
ble by  gaseous  matter; — that  the  phenomena  of  endosrnose  and  exosmose, 
observed  in  liquids  by  Dutrochet,  are  likewise  exhibited  by  gases.  If  a 
glass  full  of  carbonic  acid  be  closed  by  an  animal  membrane,  such  as  the 
coecum  of  a  fowl,  or  the  bladder  of  a  sheep,  and  be  then  exposed  to  the  at- 
mosphere, a  portion  of  air  will  pass  into  the  glass  and  some  of  the  confined 
gas  escape  from  it :  and  if  the  experiment  be  reversed  by  confining  air  in 
the  glass,  which  is  then  placed  in  an  atmosphere  of  carbonic  acid,  the  latter 


RESPIRATION.  595 

passes  in  and  the  former  out  of  the  glass.  Similar  phenomena  ensue  with 
other  gases;  so  that  when  any  two  gases  are  separated  by  a  membrane, 
both  of  them  pass  through  the  partition.  The  permeability  of  a  membrane 
is  greater  in  a  living  than  in  a  dead  animal;  but  the  property  is  by  no  means 
peculiar  to  organized  matter,  since  a  thin  lamina  of  any  substance  of  organic 
origin,  such  as  a  sheet  of  caoutchouc,  is  freely  permeable.  Water  and  other 
liquids  transmit  gases  apparently  on  the  same  principle  as  membranes;  and 
porous  solid  bodies  of  the  mineral  kingdom  will  doubtless  be  found  to  pos- 
sess a  similar  property. 

But  though  all  gases  pass  through  membranous  septa,  they  differ  remark- 
ably  in  the  relative  rapidity  of  transmission.  Thus  Dr.  Mitchell  found  that 
the  time  required  for  the  passage  of  equal  volumes  of  different  gases 
through  the  same  membrane,  was  1  minute  with  ammonia,  2^  minutes  with 
sulphuretted  hydrogen,  3^  with  cyanogen,  5£  with  carbonic  acid,  6^  with 
protoxide  of  nitrogen,  27£  with  arseriiu retted  hydrogen,  28  with  olefiant  gas, 
37£  with  hydrogen,  113  with  oxygen,  160  with  carbonic  oxide,  and  a  much 
greater  time  with  nitrogen.  Hence,  when  a  bladder  full  of  air  is  surrounded 
with  carbonic  acid,  the  latter  enters  faster  than  the  former  escapes,  and  the 
bladder  bursts;  but  on  reversing  the  conditions  of  the  experiment,  the  blad- 
der becomes  flaccid,  because  the  carbonic  acid  within  passes  out  more 
rapidly  than  the  exterior  air  enters.  The  transmission  of  gases  in  some  of 
these  experiments  takes  place  in  opposition  to  a  pressure  equal  to  several  at- 
mospheres. 

It  would  perhaps  be  premature  to  speculate  on  the  cause  of  this  singular 
property  of  gases,  nor  is  it  material  for  my  present  purpose  to  do  so ;  but 
as  the  reader  will  naturally  desire  some  explanation,  the  following,  which  is 
nearly  that  of  Dr.  Mitchell,  may  be  given  as  most  consistent  with  the 
known  properties  of  matter. — The  passage  of  a  gas  through  a  membrane 
or  other  substance  containing  within  it  very  fine  pores,  appears  to  depend  in 
the  first  place  on  the  power  of  the  porous  body  to  absorb  the  gas  into  its 
substance.  This  action  is  apparently  of  the  same  kind  as  that  exerted  on 
gases  by  charcoal,  and  seems  to  depend  on  the  attraction  which  all  bodies 
similar  or  dissimilar  exert  upon  each  other,  such  as  is  exemplified  by  the 
tendency  of  contiguous  floating  bodies  to  approach  one  another,  by  the  ad- 
hesion of  water  to  the  surface  of  glass,  and  the  ascent  of  liquids  in  capillary 
tubes.  The  absorbent  power  of  such  bodies,  which  may  thus  be  regarded 
as  aggregates  of  capillary  tubes,  will  vary  with  the  size  and  number  of  the 
pores.  The  entrance  of  a  gas  into  such  pores  will  be  promoted  by  its  elas. 
ticity ;  but  the  same  force  will  oppose  its  retention  within  the  pores,  will  re- 
sist its  return  into  the  mass  of  the  same  particles,  and  urge  it  to  escape 
where  there  is  no  such  resistance.  Hence,  when  two  gases  are  separated 
by  a  membrane,  each  passes  through,  and  mixes  with  the  other :  the  pene- 
tration of  each  is  arrested  as  soon  as  its  individual  elasticity  is  the  same  on 
both  sides  of  the  partition,  and  therefore  that  gas  which  penetrates  the 
membrane  the  more  rapidly,  is  the  first  to  be  stationary.  The  relative 
velocity  of  transmission  is.  doubtless  a  complex  phenomenon,  referable  to  the 
natural  elasticity  of  each  gas,  to  its  diffusiveness,  to  its  affinity  for  water, 
and  to  the  size  of  its  atom  should  that  differ  in  different  gases.  The  power 
of  different  liquids  to  absorb  gases  with  which  they  have  no  chemical 
action,  is  explicable  on  the  same  principles.  A  gas  may  be  absorbed  by 
such  a  liquid,  entering  between  its  particles  as  into  the  pores  of  a  mem- 
brane:  on  exposure  to  a  different  atmosphere,  a  portion  of  the  absorbed  gas 
escapes,  and  about  an  equal  volume  of  the  other  enters  the  space  which  the 
former  had  occupied.  But  whatever  may  be  thought  of  these  speculations, 
the  facts  which  they  are  designed  to  explain  are  obviously  applicable  to  the 
phenomena  of  respiration.  It  is  clear  that  ox v gen  has  free  ingress  to  the 
blood  through  the  fine  membrane  of  the  lungs;  and  carbonic  acid,  whether 
pre-existing  in  venous  blood  or  generated  during  its  flow  through  the  lungs, 
has  a  free  passage  outwards.  This  is  a  sufficiently  direct  inference  from 
what  has  already  been  mentioned ;  but  it  may  be  added,  as  additional  evi- 


596  ANIMAL  HEAT. 

dence,  that  an  aqueous  solution  of  carbonic  acid  confined  in  a  bladder  gives 
out  that  gas  to  the  surrounding  atmosphere,  and  that  venous  blood  exposed 
in  a  bladder  to  the  air,  absorbs  oxygen,  emits  carbonic  acid,  and  acquires 
the  arterial  character. 

It  appears  from  the  essays  of  Drs.  Faust  and  Mitchell  that  their  attention 
was  awakened  to  the  permeability  of  membranes  to  gases  by  the  endosmose 
and  exosmose  of  liquids  described  by  Dutrochet,  by  an  insulated  example  of 
a  similar  phenomenon  in  gases  observed  by  Mr.  Graham,  and  by  some  facts 
of  a  like  kind  noticed  long  ago  by  Priestley.  Dr.  Stevens  also,  as  stated  at 
page  96  of  his  treatise  on  the  blood,  was  aware  that  carbonic  acid  passes 
readily  through  animal  membranes  when  air  is  on  the  other  side,  applied 
that  fact  to  the  theory  of  respiration,  and  brought  the  subject  under  the 
notice  of  several  men  of  science  in  New  York  shortly  before  the  publication 
of  Drs.  Faust  and  Mitchell.  But  the  views  of  Dr.  Stevens,  though  well  cal- 
culated to  elicit  inquiry,  were  vague  and  partial ;  and  the  American  philoso- 
phers are  entitled  to  the  merit  of  advancing  from  the  detached  facts  of  others 
to  the  establishment  of  a  principle. 

The  conversion  of  venous  into  arterial  blood  appears  not  to  be  confined  to 
the  lungs.  The  disengagement  of  carbonic  acid  from  the  surface  of  the 
skin,  and  the  corresponding  disappearance  of  oxygen  gas,  was  demonstrated 
by  the  experiments  of  Jurine  and  Abernethy ;  and  although  the  accuracy  of 
their  results  has  been  doubted  by  some  persons,  it  has  been  confirmed  by 
others.  However  this  may  be  in  the  human  subject,  the  fact  with  respect 
to  many  of  the  lower  animals  is  unquestionable.  Spallanzani  proved  that 
some  animals  possessed  of  lungs,  such  as  serpents,  lizards,  and  frogs,  pro- 
duce the  same  changes  on  the  air  by  means  of  their  skin,  as  by  their  proper 
respiratory  organs ;  and  Dr.  Edwards,  in  a  series  of  masterly  experiments, 
has  shown  that  this  function  compensates  so  fully  for  the  want  of  respiration 
by  the  lungs,  as  to  enable  these  animals,  in  the  winter  season,  to  live  for  an 
almost  unlimited  period  under  the  surface  of  water, 

Animal  Heat. 

The  striking  analogy  between  the  processes  of  combustion  and  respiration, 
in  both  of  which  oxygen  gas  disappears,  and  an  oxidized  body  is  substituted 
for  it,  led  Dr.  Black  to  infer  that  the  heat  generated  in  the  animal  system, 
by  means  of  which  the  more  perfect  animals  preserve  their  temperature 
above  that  of  the  surrounding  medium  is  derived  from  the  changes  going 
forward  in  the  lungs.  But  this  opinion  is  not  founded  on  analogy  alone; 
many  circumstances  conspire  to  show  that  the  developement  of  animal  heat 
is  dependent  on  the  function  of  respiration,  although  the  mode  by  which  the 
effect  is  produced  has  not  hitherto  been  satisfactorily  determined.  Thus,  in 
all  animals  whose  respiratory  organs  are  small  and  imperfect,  and  which, 
therefore,  consume  but  a  comparatively  minute  quantity  of  oxygen,  and 
generate  little  carbonic  acid,  the  temperature  of  the  blood  varies  with  that  of 
the  medium  in  which  they  live.  In  warm-blooded  animals,  on  the  contrary, 
in  which  the  respiratory  apparatus  is  larger,  and  the  chemical  changes  more 
complicated,  the  temperature  is  almost  uniform;  and  those  have  the  highest 
temperature  whose  lungs,  in  proportion  to  the  size  of  their  bodies,  are  largest, 
and  which  consume  the  greatest  quantity  of  oxygen.  The  temperature  of 
the  same  animal  at  different  times  is  connected  with  the  state  of  the  respi- 
ration.  When  the  blood  circulates  sluggishly,  and  the  temperature  is  low, 
the  quantity  of  oxygen  consumed  is  comparatively  small;  but,  on  the  con- 
trary, a  large  quantity  of  that  gas  disappears  when  the  circulation  is  brisk, 
and  the  power  of  generating  heat  energetic.  It  has  also  been  observed, 
especially  by  Crawford  and  De  Laroche,  that  when  an  animal  is  placed  in  a 
very  warm  atmosphere,  so  as  to  require  little  heat  to  be  generated  within 
his  own  body,  the  consumption  of  oxygen  is  unusually  small,  and  the  blood 
within  the  veins  retains  the  arterial  character. 

The  connexion  between  the  power  of  generating  heat,  and  respiration  has 


ANIMAL  HEAT.  597 

been  illustrated  in  a  very  pointed  manner  by  Dr.  Edwards.  Some  young 
animals,  such  as  puppies  and  kittens,  require  so  small  a  quantity  of  oxygen 
for  supporting  life,  that  they  may  be  deprived  of  that  gas  altogether  for 
twenty  minutes  without  material  injury;  and  it  is  remarkable  that  so  long 
as  they  possess  this  property,  the  temperature  of  their  bodies  sinks  rapidly 
by  free  exposure  to  the  air.  But  as  they  grow  older  they  become  able  to 
maintain  their  own  temperature,  and  at  the  same  time  their  power  to  endure 
the  privation  of  oxygen  ceases.  The  same  observation  applies  to  young 
sparrows,  and  other  birds  which  are  naked  when  hatched;  while  young  par- 
tridges, which  are  both  fledged  and  able  to  retain  their  own  temperature  at 
the  period  of  quitting  the  shell,  die,  when  deprived  of  oxygen,  as  rapidly  as 
an  adult  bird. 

The  first  consistent  theory  of  the  production  of  animal  heat  was  proposed 
by  Dr.  Crawford.  This  theory  was  founded  on  the  assumption  that  the  car- 
bonic acid  contained  in  the  breath  is  generated  in  the  lungs,  and  that  its  for- 
mation is  accompanied  with  disengagement  of  caloric.  But  since  the  tem- 
perature of  the  lungs  is  not  higher  than  that  of  other  internal  organs,  and 
arterial  very  little  if  at  all  warmer  than  venous  blood,  it  follows  that  the 
greater  part  of  the  caloric,  instead  of  becoming  free,  must  in  some  way  or 
other  be  rendered  insensible.  Accordingly,  on  comparing  the  specific  caloric 
of  arterial  and  venous  blood,  Dr.  Crawford  found  the  capacity  of  the  former 
to  exceed  that  of  the  latter  in  the  ratio  of  1030  to  892.  He,  therefore,  inferred 
that  the  dark  blood  within  the  veins,  at  the  moment  of  being  arterialized, 
acquires  an  increase  of  insensible  caloric;  and  that  while  circulating  through 
the  body,  and  gradually  resuming  the  venous  character,  it  suffers  a  diminu- 
tion of  capacity,  and  evolves  a  proportional  degree  of  heat. 

Unfortunately  for  the  hypothesis  of  Crawford,  one  of  the  leading  facts  on 
which  it  is  founded  has  been  called  in  question ;  Dr.  Davy  maintaining,  on 
the  authority  of  his  own  experiments,  that  there  is  little  or  no  difference  be- 
tween the  capacity  of  venous  and  arterial  blood.  (Philos.  Trans,  for  1814.) 
If  this  be  true,  the  hypothesis  itself  necessarily  falls  to  the  ground.  One 
part  of  the  doctrine  of  Crawford  may,  however,  in  a  modified  form,  be  ap- 
plied to  the  theory  of  respiration  advocated  by  Dr.  Edwards.  For  if  oxygen 
be  absorbed  by  the  blood  in  its  passage  through  the  lungs,  and  carbonic  acid, 
ready  formed,  be  emitted  in  return,  it  follows  that  this  gas  must  be  gene- 
rated during  the  course  of  the  circulation ;  and  it  may  be  inferred  that  the 
heat  developed  in  consequence  of  this  chemical  change  is  at  once  communi- 
cated  to  the  adjacent  organs.  In  this  way  the  question  concerning  the 
capacity  of  the  blood  for  caloric  may  be  entirely  disregarded. 

While  some  physiologists  have  been  disposed  to  refer  the  source  of  animal 
heat  entirely  to  the  alternate  changes  of  venous  to  arterial,  and  of  arterial  to 
venous  blood,  others  have  denied  its  agency  altogether,  ascribing  the  evolu- 
tion of  caloric  solely  to  the  influence  of  the  nervous  system.  The  chief 
foundation  for  this  opinion  is  in  the  experiments  of  Mr.  Brodie,  who  inflated 
the  lungs  of  animals  recently  killed  by  narcotic  poisons  or  division  of  the 
spinal  marrow.  (Phil.  Trans,  for  1811  and  3812.)  In  an  animal  so  treated, 
the  blood  continued  to  circulate,  oxygen  gas  disappeared,  carbonic  acid  was 
evolved,  and  the  usual  changes  of  colour  took  place  with  regularity ;  but 
notwithstanding  the  concurrence  of  all  these  circumstances,  the  temperature 
fell  with  equal  if  not  greater  rapidity  than  in  any  other  animal  killed  at  the 
same  time,  but  in  which  artificial  respiration  was  not  performed. 

Were  these  experiments  rigidly  exact,  they  would  lead  to  the  opinion  that 
no  caloric  is  evolved  by  the  mere  process  of  arterialization.  This  inference, 
however,  cannot  be  admitted  for  two  reasons: — first,  because  other  physiolo- 
gists, in  repeating  the  experiments  of  Brodie,  have  found  that  the  process  of 
cooling  is  retarded  by  artificial  respiration  ;  and,  secondly,  because  it  is  diffi- 
cult to  conceive  why  the  formation  of  carbonic  acid,  which  uniformly  gives 
rise  to  increase  of  temperature  in  other  cases,  should  not  be  attended  within 
the  animal  body  with  a  similar  effect.  It  may  hence  be  inferred,  that  this 
is  one  of  the  sources  of  animal  heat.  It  is  certain,  however,  that  the  heat 


598  SALIVA. 

of  animals  cannot  be  maintained  by  the  sole  process  of  arterialization.  Con- 
sistently with  this  fact,  the  researches  of  Dulong  and  Despretz  agree  in  prov- 
ing, in  opposition  to  the  resnlts  obtained  by  Lavoisier  and  Crawford,  that  a 
healthy  animal  imparts  to  surrounding  bodies  a  quantity  of  heat  considerably 
greater  than  can  be  accounted  for  by  the  combustion  of  the  carbon  thrown 
off  during- the  same  interval  from  the  lungs  in  the  form  of  carbonic  acid. 
(An.  de  Ch.  et  de  Ph.  xxvi.) 

Though  the  influence  of  the  nervous  system  over  the  developement  of 
animal  heat  is  no  longer  doubtful,  physiologists  are  not  agreed  as  to  the 
mode  by  which  it  operates.  Its  action  may  either  be  direct  or  indirect;  that 
is,  the  nerves  may  possess  some  specific  power  of  generating  heat,  or  they 
may  excite  certain  operations  by  which  the  same  effect  is  occasioned.  It  is 
far  from  improbable,  that  the  nerves  act  more  by  the  latter  than  the  former 
mode;  that  the  infinite  number  of  chemical  phenomena  going  on  in  the  mi- 
nute arterial  branches  during  the  processes  of  secretion  and  nutrition,  pro- 
cesses which  are  entirely  dependent  on  the  nervous  system,  are  attended 
with  disengagement  of  caloric.  This  view  has,  at  least,  been  ably  defended 
by  Dr.  Williams  in  an  essay  published  in  the  Medico-Chir.  Trans,  of  Edin- 
burgh.  (Vol.  ii.) 


SECTION  II. 

SECRETED  FLUIDS  SUBSERVIENT  TO  DIGESTION. 

Saliva* 

THE  saliva  is  a  slightly  viscid  liquor,  secreted  by  the  salivary  glands. 
When  mixed  with  distilled  water,  a  flaky  matter  subsides,  which  is  mucus, 
derived  apparently  from  the  lining  membrane  of  the  mouth.  The  clear  so- 
lution, when  exposed  to  the  agency  of  galvanism,  yields  a  coagulum,  and  is 
hence  inferred  by  Mr.  Brande  to  contain  albumen ;  but  the  quantity  of  this 
principle  is  so  very  small  that  its  presence  cannot  be  demonstrated  by  any 
other  reagent.  The  greater  part  of  the  animal  matter  remaining  in  the 
liquid  is  peculiar  to  the  saliva,  and  may  be  termed  salivary  matter.  It  is 
soluble  in  water,  insoluble  in  alcohol,  and,  when  freed  from  the  accompany- 
ing salts,  is  not  precipitated  by  subacetate  of  lead,  corrosive  sublimate,  or 
infusion  of  gall-nuts.  The  saliva  likewise  contains  a  small  quantity  of  ani- 
mal matter,  which  is  soluble  both  in  alcohol  and  water,  and  which  is  sup- 
posed by  Tiedemann  and  Gmelin  to  be  osmazome. 

The  solid  contents  of  the  saliva,  according  to  Berzelius,  do  not  exceed 
seven  in  1000  parts,  the  rest  being  water.  From  the  analysis  of  Tiedemann 
and  Gmelin,  the  chief  saline  constituent  is  chloride  of  potassium  ;  but  seve- 
ral other  salts,  such  as  the  sulphate,  phosphate,  acetate,  and  carbonate  of 
potassa,  are  likewise  present  in  small  quantity.  The  saliva  of  the  human 
subject,  according  to  the  same  authority,  contains  very  little  soda.  The  pro- 
perty which  the  saliva  possesses  of  striking  a  red  colour  with  a  sesquisalt  of 
iron  is  owing  to  sulpho-cyanuret  of  potassium.  The  salt  exists  also  in  the 
saliva  of  the  sheep ;  but  it  has  not  been  found  in  that  of  the  dog.  The  sa- 
liva of  the  sheep  contains  so  much  carbonate  of  soda,  that  it  effervesces 
with  acids. 

The  only  known  use  of  the  saliva  is  to  form  a  soft  pulpy  mass  with  the 
food  during  mastication,  so  as  to  reduce  it  into  a  state  fit  for  being  swal- 
lowed with  facility,  and  for  being  more  readily  acted  on  by  the  juices  of  the 
stomach. 

Concretions  are  sometimes  found  in  the  salivary  glands  and  ducts.  A  stone 
contained  in  the  salivary  gland  of  an  ass  was  found  by  M.  Caventou  to  con- 


PANCREATIC  AND  GASTRIC  JUICE.  599 

tain  91-6  parts  of  carbonate  of  lime,  4-8  of  phosphate  of  lime,  and  3-6  of  ani- 
mal matter.  A  salivary  concretion  of  a  horse  was  found  by  M.  Henry,  jun. 
to  consist  of  carbonate  of  lime  85-52,  carbonate  of  magnesia  7-56,  phosphate 
of  lime  4-40,  and  2-48  of  animal  matter.  Carbonate  of  lime  is  the  chief  in- 
gredient  of  salivary  concretions. 

Pancreatic  Juice. 

This  fluid  is  commonly  supposed  to  be  analogous  to  the  saliva,  but  it  ap- 
pears from  the  analysis  of  Tiedernann  and  Gmelin  that  it  is  essentially  dif- 
ferent. The  chief  animal  matters  are  albumen,  and  a  substance  like  curd ; 
but  it  also  contains  a  small  quantity  of  salivary  matter  and  osmazome.  It 
reddens  litmus  paper,  owing  to  the  presence  of  free  acid,  which  is  supposed 
to  be  the  acetic.  Its  salts  are  nearly  the  same  as  those  contained  in  the  sa- 
liva, except  that  sulphocyanic  acid  is  wanting.  The  uses  of  this  fluid  are 
entirely  unknown. 

Gastric  Juice. 

The  gastric  juice,  collected  from  the  stomach  of  an  animal  killed  while 
fasting,  is  a  transparent  fluid  which  has  a  saline  taste,  and  has  neither  an 
acid  nor  alkaline  reaction.  During  the  process  of  digestion,  on  the  contrary, 
it  is  found  to  be  distinctly  acid.  Thus  free  hydrochloric  acid  was  detected 
under  these  circumstances  by  Dr.  Prout  in  the  stomach  of  the  rabbit,  hare, 
horse,  calf,  and  dog  (Phil.  Trans.  1824);  and  he  has  discovered  the  same 
acid  in  the  sour  matter  ejected  from  the  stomach  of  persons  labouring  under 
indigestion,  a  fact  which  has  since  been  confirmed  by  Mr.  Children.  Tiedo 
mann  and  Gmelin  observed  that  the  secretion  of  acid  commences  as  soon  as 
the  stomach  receives  the  stimulus  of  food  or  any  foreign  body.  This  effect 
is  occasioned,  for  example,  by  the  presence  of  flint  stones  or  other  indigesti- 
ble matter ;  but  it  is  produced  in  a  still  greater  degree  by  a  substance  of  a 
stimulating  nature.  According  to  their  observations  the  acidity  is  owing  to 
the  secretion  of  free  hydrochloric  and  acetic  acids. 

The  gastric  juice  coagulates  milk,  apparently  in  consequence  of  the  acid 
secreted  during  digestion.  According  to  the  experiments  of  Spallanzani  and 
Stevens  it  is  highly  antiseptic,  not  only  preventing  putrefaction,  but  render- 
ing meat  fresh  after  it  is  tainted.  But  of  all  the  properties  of  the  gastric 
juice,  its  solvent  virtue  is  the  most  remarkable,  being  that  on  which  depends 
the  first  stage  of  the  process  of  digestion.  When  the  food  is  introduced  into 
the  stomach,  it  is  there  intimately  mixed  with  the  gastric  juice,  by  the 
agency  of  which  it  is  dissolved,  and  converted  into  a  semifluid  matter  called 
chyme.  That  this  change  is  really  owing  to  the  solvent  power  of  the  gastric 
juice  fully  appears  from  the  researches  of  Spallanzani,  Reaumur,  and  Stevens. 
In  the  experiments  of  Dr.  Stevens,  described  in  his  Inaugural  Dissertation, 
the  common  articles  of  food  were  enclosed  in  hollow  silver  spheres  perfo- 
rated with  holes,  and  after  remaining  for  some  time  within  the  stomach, 
complete!}7  protected  from  pressure  and  trituration,  the  alimentary  sub- 
stances were  found  to  have  been  entirely  dissolved.  A  similar  effect  takes 
place  when  nutritious  matters,  out  of  the  body,  are  mixed  with  the  gastric 
fluid,  and  the  mixture  is  exposed  to  a  temperature  of  100°.  So  great,  in- 
deed, is  the  solvent  power  of  this  fluid,  that  it  has  been  known  to  dissolve 
the  coats  of  the  stomach  itself;  at  least  the  corrosions  of  this  organ,  some- 
times witnessed  in  persons  who  have  died  suddenly  while  fasting,  and  in 
good  health,  were  ascribed  by  the  celebrated  physiologist,  John  Hunter,  to 
this  cause.  That  the  agent  here  assigned  is  adequate  to  produce  such  an 
effect,  has  been  fully  proved  by  my  colleague,  Dr.  Carswell.  (Edin.  Med. 
and  Surg.  Journal,  October,  1830.)  Rabbits  were  killed  by  a  blow  on  the 
head  during  digestion,  and  then  suspended  for  some  hours  by  the  hinder 
legs.  The  most  dependent  parts  of  the  stomach,  to  which  the  fluids  had 
gravitated,  were  invariably  more  or  less  dissolved ;  in  some  cases  the  lex- 


600  BILE. 

tures  were  thin,  white,  soft,  and  pulpy;  and  in  others,  complete  perforations 
existed,  arid  the  contiguous  viscera  were  attacked.  The  blood  in  the  vessels 
of  the  corroded  part  was  black  and  more  or  less  coagulated,  an  effect  analo- 
gous to  that  produced  by  an  acid.  The  corroding  fluid,  as  during  healthy 
digestion,  was  strongly  acid ;  and  this  acid  liquor,  taken  from  the  stomach 
of  one  rabbit  and  introduced  into  that  of  another  previously  killed,  produced 
corrosion. 

Great  diversity  of  opinion  has  prevailed  respecting  the  cause  of  the  sol- 
vent  property  of  the  gastric  fluid.  It  was  formerly  ascribed  to  some  specific 
power,  and  was  thought  to  be  inexplicable  on  any  known  chemical  princi- 
ples ;  but  the  more  precise  observation  of  recent  experimentalists  has  re- 
moved one  great  part  of  the  mystery.  Tiedernann  and  Gmelin  directly 
ascribe  the  solvent  action  of  the  gastric  juice  to  the  acid  which  it  contains: 
they  found  healthy  digestion  to  be  invariably  attended  with  the  secretion  of 
hydrochloric  and  acetic  acids,  and  ascertained  that  these  acids,  at  the  tem- 
perature of  the  body,  are  capable  of  dissolving  all  the  digestible  substances 
employed  as  food.  Similar  remarks  on  the  invariable  connexion  between 
the  acidity  and  solvent  power  of  the  gastric  fluids  have  been  made  by  Dr. 
Carsvvell,  who  informs  me  of  the  additional  decisive  fact,  that  on  neutralizing 
the  gastric  juice  with  magnesia,  its  solvent  property  was  destroyed.  It 
would  thus  seem  that  the  stimulus  of  food  causes  the  neutral  salts  of  the 
blood  circulating  in  the  stomach  to  be  decomposed,  either  by  a  purely  vital 
process,  or,  as  Dr.  Prout  suggests,  by  a  galvanic  operation  (Bridgewater 
Treatise);  that  the  alkali  remains  in  the  blood,  causing  the  alkalinity  of  tbat 
liquid ;  and  that  the  acids,  passing  into  the  stomach,  dissolve  the  food. 

Bile. 

The  bile  is  a  yellow  or  greenish-yellow  coloured  fluid,  of  a  peculiar  sick- 
ening odour,  and  of  a  taste  at  first  sweet  and  then  bitter,  but  exceedingly 
nauseous.  Its  consistence  is  variable,  being  sometimes  limpid,  but  more 
commonly  viscid  and  ropy.  It  is  rather  denser  than  water,  and  may  be 
mixed  with  that  liquid  in  every  proportion.  It  contains  a  minute  quantity  of 
free  soda,  and  is,  therefore,  slightly  alkaline ;  but  owing  to  the  colour  of  the 
bile  itself,  its  action  on  test  paper-is  scarcely  visible. 

Of  the  chemists  who  have  of  late  years  investigated  the  composition  of  the 
bile,  Thenard,  Berzelius,  Tiedemann,  and  Grnelin  deserve  particular  men- 
tion. In  an  elaborate  essay  published  in  the  Memoires  d'Arcueil,  vol.  L 
Thenard  endeavoured  to  show  that  the  bile  of  the  ox  consists  of  three  dis- 
tinct animal  principles,  a  yellow  colouring  matter,  a  species  of  resin,  and  a 
peculiar  substance,  to  which,  from  its  sweetish  bitter  taste,  he  applied  the 
name  of  picromel.  According  to  his  analysis,  800  parts  of  bile  consist  of 
water  700  parts,  resin  15,  picromel  69,  yellow  matter  about  4,  soda  4,  phos- 
phate of  soda  2,  muriates  of  soda  and  potassa  35,  sulphate  of  soda  0-8,  phos- 
phate of  lime  and  perhaps  magnesia  1-2,  and  a  trace  of  oxide  of  iron.  He 
supposed  the  resin  to  be  combined  with  the  picromel  and  soda,  and  ascribes 
its  solubility  in  water  to  this  cause. 

Berzelius  takes  a  totally  different  view  of  the  constitution  of  the  bile.  He 
denies  that  its  fluid  contains  any  resinous  principle,  and  regards  the  yel- 
low matter,  resin,  and  picromel  of  Thenard,  as  one  and  the  same  substance, 
to  which  he  applied  the  name  of  biliary  matter.  (Medico-Chir.  Trans,  iii.) 
Tiedemann  and  Gmelin,  however,  in  their  recent  work  on  Digestion,  admit 
the  existence  of  picromel  and  resin  as  the  chief  constituents  of  bile  ;  although 
it  appears  from  their  experiments  that  the  substance  described  by  Thenard 
as  picromel  was  not  pure,  but  contained  a  portion  of  resin.  According  to 
the  analysis  of  these  chemists,  the  bile  of  the  ox  is  a  very  complex  fluid, 
consisting  of  the  following  ingredients: — water  to  the  extent  of  91'5  per 
cent.;  a  volatile  odoriferous  principle;  cholesterine;  resin;  asparagin;  pi- 
cromel; yellow  colouring  matter;  a  peculiar  azotized  substance  soluble  in 
water  and  alcohol ;  a  substance  which  is  soluble  in  hot  alcohol,  but  insolu- 


BILIARY   CONCRETIONS.  601 

ble  in  water,  supposed  to  be  gluten ;  osmazome  ;  a  principle  which  emits  a 
uririous  odour  when  heated ;  a  substance  analogous  to  albumen  or  caseous 
matter;  and  mucus.  The  salts  of  the  bile  are  the  margarate,  oleate,  acetate, 
cholate,  bicarbonate,  phosphate,  sulphate,  and  hydrochlorate  of  soda,  together 
with  a  little  phosphate  of  lime.  The  cholic  is  a  peculiar  animal  acid,  which 
crystallizes  in  needles,  reddens  litmus  paper,  and  is  distinguished  from 
analogous  compounds  by  having  a  sweet  taste. 

The  flaky  precipitate  which  is  occasioned  by  adding  acids  to  bile  from  the 
ox,  consists  of  several  substances.  At  first  the  caseous  and  colouring  mat- 
ters,  along  with  mucus,  are  thrown  down ;  and,  afterwards,  the  margaric 
acid  and  a  compound  of  picromel  and  resin  with  the  acid  employed  are  pre- 
cipitated. When  acetate  of  lead  is  mixed  with  this  fluid,  a  white  precipi- 
tate falls,  which  consists  of  oxide  of  lead  combined  with  the  phosphoric,  sul- 
phuric, and  several  other  acids,  together  with  a  small  quantity  of  the 
compound  of  picromel  and  resin.  On  adding  subacetate  of  lead  to  the  clear 
liquid,  a  copious  precipitate  ensues,  consisting  chiefly  of  picromel,  resin,  and 
oxide  of  lead.  If  this  compound  be  suspended  in  water,  through  which  a 
current  of  hydrosulphuric  acid  gas  is  transmitted,  sulphuret  of  lead  and  the 
resin  subside,  while  the  picromel  remains  in  solution.  By  collecting  and 
drying  the  precipitate,  and  digesting  it  in  alcohol,  the  resin  is  dissolved,  and 
may  be  obtained  by  evaporation.  The  aqueous  solution,  when  evaporated, 
yields  the  picromel  of  Thenard ;  but  according  to  Tiedemann  and  Gmelin, 
it  still  contains  a  portion  of  resin.  The  chief  difficulty,  indeed,  of  preparing 
pure  picromel  arises  from  its  tendency  to  dissolve  the  resin ;  and  the  only 
mode  of  separation  is  by  throwing  them  down  repeatedly  by  means  of  sub- 
acetate  of  lead.  By  this  process  the  affinity  of  the  picromel  and  resin  for 
each  other  is  gradually  lessened,  until  at  length  the  separation  is  rendered 
complete. 

Pure  picromel  occurs  in  opaque,  rounded,  crystalline  particles,  is  soluble 
in  water  and  alcohol,  but  is  insoluble  in  ether.  Its  taste  is  sweet  without 
any  bitterness ;  but  it  cannot  be  regarded  as  a  species  of  sugar,  because  a 
large  quantity  of  nitrogen  enters  into  its  composition.  Its  aqueous  solution 
is  not  precipitated  by  acids,  nor  by  acetate  and  subacetate  of  lead.  When 
digested  with  the  resin  of  bile,  a  portion  of  the  latter  is  dissolved,  and  a 
solution  is  obtained,  which  has  both  a  bitter  and  sweet  taste,  and  yields  a 
precipitate  with  subacetate  of  lead  and  the  stronger  acids.  This  is  the  com- 
pound which  causes  the  peculiar  taste  of  the  bile. 

The  bile  of  the  human  subject  has  not  been  studied  so  minutely  as  that  of 
the  ox.  According  to  Thenard  it  consists,  besides  salts,  of  water,  colouring 
matter,  albumen,  and  a  species  of  resin.  Chevallier  has  since  detected  picro- 
mel, and  Chevreul  cholesterine,  in  human  bile;  and  both  these  discoveries 
have  been  confirmed  by  the  observations  of  Tiedemann  and  Gmelin. 

The  derangement  which  takes  place  in  the  system  when  the  secretion  of 
bile  or  its  passage  into  the  intestines  is  arrested,  is  a  sufficient  indication  of 
the  importance  of  this  fluid.  It  acts  as  a  stimulus  to  the  intestinal  canal 
generally,  and  produces  on  the  chyme  some  peculiar  change,  which  is  essen- 
tial to  its  conversion  into  chyle, 

Biliary  Concretions. 

THE  concretions  which  are  sometimes  formed  in  the  human  gall-bladder 
have  been  particularly  examined  by  Fourcroy,  Thenard,  and  Chevreul.  Four- 
croy  found  that  they  consist  chiefly  of  a  peculiar  fatty  matter,  resembling 
spermaceti,  which  he  included  under  the  name  ofadipocire  (page  581);  and 
the  experiments  of  Thenard  tended  to  confirm  this  view.  According  to 
Chevreul,  however,  biliary  concretions  in  general  are  composed  of  the  yellow 
colouring  matter  of  the  bile  and  cholesterine,  the  latter  predominating,  and 
being  sometimes  in  a  state  of  purity ;  and  I  have  had  frequent  opportunities 
of  satisfying  myself  of  the  accuracy  of  this  observation.  These  substances 
may  easily  be  separated  from  each  other  by  boiling  alcohol,  which  dissolves 

51 


602  CHYLE. 

the  cholesterine,  and  leaves  the  colouring  matter ;  or  by  digestion  in  dilute 
potassa,  in  which  the  colouring  matter  is  dissolved,  while  the  cholesterine  is 
insoluble. 

Gall-stones  sometimes  contain  a  portion  of  inspissated  bile ;  and  in  some 
rare  instances  the  cholesterine  is  entirely  wanting. 

The  concretions  found  in  the  gall-bladder  of  the  ox  consist  almost  entirely 
of  the  yellow  biliary  colouring  matter,  which,  from  the  beauty  and  perma- 
nence of  its  tint,  is  much  valued  by  painters.  This  substance  is  readily  dis- 
tinguished by  its  yellow  or  brown  colour,  by  insolubility  in  water  and  alco- 
hol, and  by  being  readily  dissolved  by  a  solution  of  potassa.  The  solution 
has  at  first  a  yellowish-brown  colour,  which  gradually  acquires  a  green 
tint,  and  is  precipitated  in  green  flocks  by  hydrochloric  acid,  According  to 
the  observations  of  Tiedemann  and  Gmelin,  the  colouring  matter  is  influ- 
enced by  the  presence  of  oxygen  gas.  The  yellowish  precipitate,  occasioned 
by  adding  hydrochloric  acid  to  bile,  absorbs  oxygen  by  exposure  to  the  air, 
and  its  colour  changes  to  green.  The  action  of  nitric  acid  is  still  more 
remarkable.  By  successive  additions  of  this  acid,  the  tint  of  the  colouring 
matter  may  be  converted  into  green,  blue,  violet,  and  red,  in  the  course  of  a 
few  seconds. 

Erythrogen.~-This  substance  was  discovered  in  1821  by  M.  Bizio  of  Venice 
in  a  peculiar  fluid,  quite  different  from  bile,  which  was  found  in  the  gall- 
bladder of  a  person  who  had  died  of  jaundice.  It  is  of  a  green  colour,  trans- 
parent, tasteless,  and  of  the  odour  of  putrid  fish.  It  is  unctuous  to  the  toueht 
may  be  scratched  or  cut  with  facility,  and  has  a  specific  gravity  of  1-57. 
It  does  not  affect  the  colour  of  litmus  or  turmeric  paper.  At  110°  it  fuses, 
having  the  appearance  of  oil,  and  crystallizes  when  slowly  cooled ;  and  at 
122°  it  rises  in  the  form  of  vapour.  It  is  insoluble  in  water  and  ether,  but 
is  dissolved  readily  by  hot  alcohol ;  and  the  solution,  by  partial  evaporation 
and  cooling,  yields  crystals  in  the  form  of  rhomboidal  parallelopipedons. 

When  erythrogen  is  put  into  nitric  acid  of  the  temperature  of  about  120 
or  140°  its  green  tint  disappears,  effervescence,  owing  to  the  escape  of  oxy- 
gen gas,  ensues,  and  the  solution  acquires  a  deep  purple  colour.  A  similar 
phenomenon  takes  place,  with  disengagement  of  hydrogen  gas,  when  erythro- 
gen is  digested  in  a  solution  of  ammonia ;  and  when  volatilized  in  the  open 
air,  it  yields  a  purple-coloured  vapour.  M.  Bizio  is  of  opinion  that  the  ery- 
throgen, under  all  these  circumstances,  unites  with  nitrogen,  and  that  the 
product  is  identical  with  the  colouring  matter  of  the  blood.  The  production 
of  the  red  compound  is  characteristic  of  erythrogen,  and  suggested  the  name 
by  which  this  substance  is  designated.  (Egyflgof,  ruber}.  (Journal  of  Sci- 
ence, vol.  xvi.) 

Erythrogen  has  not  been  discovered  either  in  bile  or  in  any  of  the  animal 
fluids. 


SECTION    III. 

CHYLE,  MILK,  AND  EGGS. 

Chyle. — The  fluid  absorbed  by  the  lacteal  vessels  from  the  small  intes* 
tines  during  the  process  of  digestion  is  known  by  the  name  of  chyle.  Its 
appearance  varies  in  different  animals  5  but  as  collected  from  the  thoracic 
duct  of  a  mammiferous  animal  three  or  four  hours  after  a  meal,  it  is  a  white 
opaque  fluid  like  milk,  having  a  sweetish  and  slightly  saline  taste.  In  a  few 
minutes  after  removal  from  the  duct  it  becomes  solid,  and  in  the  course  of 
twenty-four  hours  separates  into  a  firm  coagulum,  and  a  limpid  liquid,  which 
may  be  called  the  serum  of  the  chyle.  The  coagulum  is  an  opaque  white 
substance,  of  a  slightly  pink  hue,  insoluble  in  water,  but  soluble  easily  in 


MILE.  603 

the  alkalies  and  alkaline  carbonates.  Vauquelin*  regards  it  as  a  fibrin  in  an 
imperfect  state,  or  as  intermediate  between  that  principle  and  albumen;  but 
Mr.  Brandet  considers  it  more  closely  allied  to  the  caseous  matter  of  milk 
than  to  fibrin. 

The  serum  of  chyle  is  rendered  turbid  by  heat,  and  a  few  flakes  of  albu- 
men are  deposited ;  but  when  boiled  after  being  mixed  with  acetic  acid,  a 
copious  precipitation  ensues.  To  this  substance,  which  thus  differs  slightly 
from  albumen,  Dr.  Prout  has  applied  the  name  of  incipient  albumen.  The 
same  chemist  has  made  a  comparative  analysis  of  the  chyle  of  two  dogs,  one 
of  which  was  fed  on  animal  and  the  other  on  vegetable  substances,  and  the 
result  of  his  inquiry  is  as  follows  : — (Aanals  of  Philos.  vol.  xiii.  p.  25.) 

Vegetable  Animal 

Food.  Food. 

Water 93-6  89-2 

Fibrin       ......      0-6  0-8 

Incipient  albumen  ?                                                        4-6  4-7 

Albumen  with  a  little  red  colouring  matter          .       0-4  4-6 
Sugar  of  milk?     ,             .             .             .             a  trace 

Oily  matters         ....             a  trace  a  trace 

Saline  matters      .            .            .            .            .0-8  0-7 

100-0          100-0 

Milk. — This  well-known  fluid,  secreted  by  the  females  of  the  class  mam- 
malia for  the  nourishment  of  their  young,  consists  of  three  distinct  parts, 
the  cream,  curd,  and  whey,  into  which  by  repose  it  spontaneously  separates. 
The  cream,  which  collects  upon  its  surface,  is  an  unctuous  yellowish-white 
opaque  fluid,  of  agreeable  flavour.  According  to  Berzelius  100  parts  of 
cream,  of  specific  gravity  1-0244,  consists  of  butter  4-5,  caseous  matter  3-5, 
and  whey  92.  By  agitation,  as  in  the  process  of  churning,,  the  butter  as- 
sumes  the  solid  form,  and  is  thus  obtained  in  a  separate  state.  During  the 
operation  there  is  an  increase  of  temperature  amounting  to  about  three  or 
four  degrees,  oxygen  gas  is  absorbed,  and  an  acid  is  generated  ;  but  the  ab- 
sorption of  oxygen  cannot  be  an  essential  part  of  the  process,  since  butter 
may  be  obtained  by  churning,  even  when  atmospheric  air  is  entirely  ex- 
cluded. 

After  the  cream  has  separated  spontaneously,  the  milk  soon  becomes  sour, 
and  gradually  separates  into  a  solid  coagulurn  called  curd,  and  a  limpid  fluid 
•which  is  whey.  This  coagulation  is  occasioned  by  free  acetic  acid,  and  it 
may  be  produced  at  pleasure  either  by  adding  a  free  acid,  or  by  means  of 
the  fluid  known  by  the  name  of  rennet,  which  is  made  by  infusing  the  inner 
coat  of  a  calf's  stomach  in  hot  water.  When  an  acid  is  employed,  the  curd 
is  found  to  contain  some  of  it  in  combination,  and  may,  therefore,  be  re- 
garded as  an  insoluble  compound  of  an  acid  with  the  caseous  matter  of  milk. 
The  action  of  rennet  requires  further  examination :  it  confessedly  acts  by 
means  of  the  gastric  fluid  which  it  contains,  and  hence  its  coagulating 
power,  consistently  with  the  facts  stated  in  trhe  last  section,  is  referable  to  the 
acidity  of  that  juice. 

The  curd  of  skim  milk,  made  by  means  of  rennet,  and  separated  from 
the  whey  by  washing  with  water,  is  generally  considered  to  be  caseous  mat- 
ter, or  the  basis  of  cheese  in  a  state  of  purity.  In  this  state  it  is  a  white, 
insipid,  inodorous  substance,  insoluble  in  water,  but  readily  soluble  in  the 
alkalies,  especially  in  ammonia.  By  alcohol  it  is  converted,  like  albumen 
and  fibrin,  into  an  adipocirous  substance  of  a  fetid  odour ;  and,  like  the 
same  substance,  it  may  be  dissolved  by  a  sufficient  quantity  of  acetic  acid. 

*  An.  de  Ch.  vol.  xxxi. 
t  Philos.  Trans,  for  1812. 


604  MILK. 

Braconnot  maintains  that  caseum,  in  its  coagulated  state,  is  always  com- 
bined with  some  foreign  substance,  generally  an  earthy  salt  or  an  acid,  on 
which  its  insolubility  depends;  and  that  when  pure,  it  is  soluble  both  in  hot 
and  cold  water,  is  not  coagulated  either  by  heat  or  air,  and  when  concen- 
trated becomes  viscid  like  mucilage,  being  so  highly  adhesive  that  it  may 
be  usefully  employed  as  a  cement.  Soluble  caseum  may  be  obtained  from 
curd,  spontaneously  formed  in  milk  as  it  becomes  sour,  in  which  state  it  is 
combined  with  acetic  acid,  by  washing  the  curd,  and  digesting  it  with 
water,  to  which  so  much  carbonate  of  potassa  is  added  as  is  sufficient  to 
unite  with  the  acetic  acid.  Acetate  of  potassa  is  generated  with  disengage- 
ment of  carbonic  acid,  and  the  caseum  is  dissolved.  In  order  to  separate  it 
from  the  accompanying  acetate,  the  solution,  after  separating  the  cream 
which  collects  on  its  surface  by  repose,  is  mixed  with  a  little  sulphuric  acid, 
and  the  precipitated  sulphate  of  caseum,  carefully  washed,  is  dissolved  in 
water  by  means  of  the  smallest  possible  quantity  of  carbonate  of  potassa. 
If  alcohol  is  then  freely  employed,  the  caseum  itself  is  thrown  down ;  but  if 
the  solution  is  mixed  with  about  its  own  volume  of  alcohol,  a  deposite  of 
sulphate  of  potassa  with  some  curd  and  cream  takes  place,  and  the  filtered 
liquor  contains  caseum  in  a  state  of  great  purity. 

Caseum,  as  thus  prepared,  still  contains  a  little  potassa;  but  Braconnot 
considers  its  solubility  as  not  dependent  on  the  presence  of  the  alkali. 
When  evaporated  to  dryness  it  forms  a  diaphanous  mass  which  strongly  re- 
sembles gum-arabic,  may  be  long  preserved  without  change,  and  still  retains 
its  solubility  in  water.  It  has  an  acid  reaction,  and  combines  readily  with 
the  alkalies,  forming  very  soluble  compounds.  With  other  metallic  oxides, 
as  well  as  with  their  salts,  it  forms  sparingly  soluble  compounds.  Its  affi- 
nity for  acids  is  equally  marked,  and  it  is  precipitated  by  all  the  mineral 
acids,  except  the  phosphoric.  Braconnot  conceives  that  soluble  caseum  may 
be  advantageously  employed  in  a  commercial  point  of  view,  Its  adhesive- 
ness fits  it  as  a  cement  for  glass,  porcelain,  wood,  and  paper.  Its  solution, 
flavoured  with  sugar  and  aromatics,  may  be  serviceable  to  convalescents  as 
an  article  of  food.  It  may  be  taken  in  its  dry  state  in  long  voyages,  form- 
ing together  with  water,  butter,  and  sugar,  an  excellent  substitute  for  milk. 
(An.  de  Ch.  et  de  Ph.  xliii.  337.) 

Caseum  is  commonly  considered  to  have  a  close  resemblance  to  animal 
albumen,  and  the  analogy  is  supported  by  its  being  coagulated  by  acids.  In 
other  respects,  if  the  remarks  of  Braconnot  prove  correct,  it  resembles  gum 
rather  than  albumen.  It  differs  from  both,  however,  in  the  nature  of  the 
spontaneous  changes  to  which  it  is  subject ;  for  when  kept  in  a  moist  state, 
it  undergoes  a  species  of  fermentation  precisely  analogous  to  that  expe- 
rienced by  gluten  under  the  same  circumstances  (page  549).  The  accuracy 
of  the  remarks  made  by  Proust  on  this  subject  has  been  questioned  by  Bra- 
connot (Brewster's  Journal,  viii.  369).  The  latter  states  that,  in  his  experi- 
ments, the  curd  from  spontaneously  coagulated  skim  milk,  covered  with 
water,  and  kept  at  a  temperature  of  about  75°,  undewent  complete  putre- 
faction in  the  space  of  a  month.  The  soluble  parts  were  then  filtered,  and 
by  evaporation  yielded  a  product  of  a  very  fetid  odour,  acetate  of  ammonia, 
and  acetic  acid.  The  residue,  after  being  reduced  to  the  consistence  of 
syrup,  concreted  on  cooling  into  a  granulated  reddish  mass  like  honey,  but 
of  a  saline  bitter  tasto,  and  was  separated  by  the  action  of  alcohol  into  two 
parts,  one  soluble  and  the  other  insoluble.  The  former  is  the  caseate  of 
ammonia  of  Proust,  and  the  latter  is  his  caseous  oxide. 

In  order  to  obtain  caseous  oxide  quite  pure,  it  must  be  washed  carefully 
with  alcohol,  treated  with  animal  charcoal,  and  dissolved  repeatedly  in  boil- 
ing water,  from  which  it  is  separated  by  evaporation.  In  this  state  it  is  a 
beautiful  white  powder,  inodorous,  and  of  a  slightly  bitter  taste.  It  is 
heavier  than  water,  and  soluble  in  14  parts  of  that  fluid  at  72°.  ^  On  allow- 
ing the  solution  to  evaporate  spontaneously,  it  crystallizes  either  in  the  form 
of  elegant  dendritic  ramifications,  or  in  rings  composed  of  delicate  acicular 
crystals  of  a  silky  lustre, 


EGGS.  605 

Caseous  oxide  is  almost  entirely  insoluble  even  in  boiling  alcohol.  Its 
aqueous  solution  yields  a  white  flaky  precipitate  with  infusion  of  gall-nuts, 
soluble  in  excess  of  the  precipitant;  and  subacetate  of  lead  likewise  throws 
down  a  white  precipitate,  The  crystals,  if  suddenly  heated,  volatilize  with? 
out  change;  but  if  the  heat  is  gradually  raised,  decomposition  ensues,  and 
a  large  quantity  of  carbonate  and  hydrosulphate  of  ammonia  is  generated. 
When  strongly  heated  in  open  vessels  it  takes  fire,  and  burns  with  flame 
without  residue. 

The  composition  of  caseous  oxide  has  not  been  determined,  but  from  the 
facility  with  which  its  aqueuus  solution  putrefies,  Braconnot  regards  it  as  a 
highly  azotized  animal  principle.  It  contains  sulphur  also.  He  believes  it 
to  be  a  product  of  the  putrefaction  of  all  animal  substances,  and  proposes  for 
it  the  name  of  aposepedine,  from  ATTO  and  <rv7n3a>Vi  result  of  putrefaction,  as 
more  appropriate  than  caseous  oxide. 

Braconnot  denies  the  existence  of  caseous  acid.  Proust's  caseate  of  am- 
monia consists  of  various  substances,  such  as  free  acetic  acid,  aposepedine, 
animal  matter,  resin,  several  salts,  and  a  yellow  pungent  oil,  which  is  the 
chief  cause  of  the  pungency  of  old  cheese. 

From  750  parts  of  curd,  completely  putrefied,  were  obtained  36  of  dry 
matter  insoluble  in  water.  These  consisted  of  14-92  parts  of  margarate  of 
lime,  2-57  of  margaric  acid,  and  18-51  of  oleic  acid,  retaining  margaric  acid 
and  a  brown  animal  matter. 

According  to  the  analysis  of  Gay-Lussac  and  Thenard,  100  parts  of  the 
caseous  matter  are  composed  of  carbon  59*781,  hydrogen  7429,  oxygen 
11-409,  and  nitrogen  21-381.  It  yields  by  incineration  a  white  ash  amount- 
ing to  6-5  per  cent,  of  its  weight,  the  greater  part  of  which  is  phosphate  of 
lime,  a  circumstance  which  renders  caseous  matter  an  article  of  food  pecu- 
liarly proper  for  young  animals. 

Milk  carefully  deprived  of  its  cream  has  a  specific  gravity  of  about  T033 ; 
and  1000  parts  of  it,  according  to  Berzelius,  are  thus  constituted : — water 
928*75,  caseous  matter  with  a  trace  of  butter  28;  sugar  of  milk  35;  muriate 
and  phosphate  of  potassa  1'95 ;  lactic  acid,  acetate  of  potassa,  and  a-  trace 
of  lactate  of  iron  6,  and  earthy  phosphates  0-3.  Subtracting  the  caseous 
matter,  the  remaining  substances  constitute  whey. 

Eggs. — The  composition  of  the  recent  egg,  and  the  changes  which  it  un- 
dergoes during  the  process  of  incubation,  have  been  ably  investigated  by 
Dr.  Prout  (Phil.  Trans,  for  1822).  New-laid  eggs  are  rather  heavier  than 
water ;  but  they  become  lighter  after  a  time,  in  consequence  of  water  evapo- 
rating through  the  pores  of  the  shell,  and  air  being  substituted  for  it.  An 
egg  of  ordinary  size  yields  to  boiling  water  about  three-tenths  of  a  grain  of 
saline  matter,  consisting  of  the  sulphates,  carbonates,  and  phosphates  of 
linse  and  magnesia,  together  with  animal  matter  and  a  little  free  alkali. 

Of  an  egg  which  weighs  1000  grains,  the  shell  constitutes  106-9,  the 
white  604-2,  and  the  yelk  288-9  grains.  The  shell  contains  about  two  per 
cent,  of  animal  matter,  one  per  cent,  of  tho  phosphates  of  lime  and  mag? 
ncsia,  and  the  residue  is  carbonate  of  lime  with  a  little  carbonate  of  magv 
nesia. 

When  the  yelk  of  a  hard-boiled  egg  is  repeatedly  digested  in  alcohol  of 
specific  gravity  0-807,  until  that  fluid  comes  off  colourless,  there  remains  a 
white  pulverulent  residuum,  possessed  of  many  of  the  properties  of  albumen, 
but  distinguished  from  that  principle  by  containing  a  large  quantity  of 
phosphorus  in  some  unknown  state  of  combination.  The  alcoholic  solution 
is  of  a  deep  yellow  colour,  and  on  cooling  deposites  crystals  of  a  sebaceous 
matter,  and  a  portion  of  yellow  semi-fluid  oil.  On  distilling  off  the  alcohol, 
the  oil  is  left  in  a  separate  state.  When  the  yelk  is  dried  and  burned,  the 
phosphorus  is  converted  into  phosphoric  acid,  which,  melting  into  a  glass 
upon  the  surface  of  the  charcoal,  protects  it  from  complete  combustion. 
In  the  white  of  the  egg,  which  consists  chiefly  of  albumen,  sulphur  is 
present. 

The  obvious  use  of  the  phosphorus  contained  in  the  yelk  is  to  supply 


606  LIQUIDS  OF  SEROUS  AND  MUCOUS  SURFACES,  &C. 

phosphoric  acid  for  forming  the  bones  of  the  chick ;  but  Dr.  Prout  was  un- 
able to  discover  any  source  of  the  lime  with  which  that  acid  unites  to  form 
the  earthy  part  of  bone.  It  cannot  be  discovered  in  the  soft  parts  of  the 
egg ;  and  hitherto  no  vascular  connexion  has  been  traced  between  the  chick 
and  its  shell, 


SECTION    IV. 

LIQUIDS  OF  SEROUS  AND  MUCOUS  SURFACES,  &c. 

THE  surface  of  the  cellular  membrane  is  moistened  with  a  peculiar  limpid 
transparent  fluid  called  lymph,  which  is  in  very  small  quantity 'during  health, 
but  collects  abundantly  in  some  dropsical  affections.  Mr.  Brande  collected 
it  from  the  thoracic  duct  of  an  animal  which  had  been  kept  without  food  for 
twenty-four  hours.  Its  chief  constituent  is  water,  besides  which  it  contains 
muriate  of  soda  and  albumen,  the  latter  being  in  such  minute  quantity  that 
it  is  coagulated  only  by  the  action  of  galvanism.  Lymph  does  not  affect  the 
colour  of  test-paper;  but  when  evaporated  to  dryness,  the  residue  gives  a 
green  tint  to  the  syrup  of  violets. 

The  fluid  secreted  by  serous  membranes  in  general,  such  as  the  pericar- 
dium, pleura,  and  peritoneum,  is  very  similar  to  lymph.  According  to  Dr. 
Bostock,  100  parts  of  the  liquid  of  the  pericardium  consist  of  water  92  parts, 
albumen  5-5,  mucus  2,  and  muriate  of  soda  0'5.  The  serous  fluid  exhaled 
within  the  ventricles  of  the  brain  in  hydrocephalus  internus  is  composed,  in 
1000  parts,  of  water  988-3,  albumen  1-66,  muriate  of  potassa  and  soda  7-09, 
lactate  of  soda  and  its  animal  matter  2-32,  soda  0-28,  and  animal  matter  so- 
luble only  in  water,  with  a  trace  of  phosphates,  0-35.  (Berzelius,  in  Medico- 
Chir.  Trans,  vol.  iii.  p.  252.) 

The  liquor  of  the  amnios,  or  the  fluid  contained  in  the  membrane  which 
surrounds  the  foetus  in  utero,  differs  in  different  animals.  That  of  the  hu- 
man female  was  found  by  Vauquelin  and  Buniva  to  contain  a  small  quantity 
of  albumen,  soda,  muriate  of  soda,  phosphate  and  carbonate  of  lime,  and  a 
matter  like  curd  which  gives  it  a  milky  appearance.  That  of  the  cow  was 
said  by  the  same  chemists  to  contain  a  peculiar  acid,  which  has  since  been 
recognized  as  belonging  to  the  allantois  (page  577;.  Dr.  Prout  found  some 
sugar  of  milk  in  the  amnios  of  a  woman.  (An.  of  Phil.  v.  417.) 

Humours  of  the  Eye. — The  aqueous  and  vitreous  humours  of  the  eye  con- 
tain  rather  more  than  80  per  cent,  of  water.  The  other  constituents  are  a 
small  quantity  of  albumen,  muriate  and  acetate  of  soda,  pure  soda,  though 
scarcely  sufficient  to  affect  the  colour  of  test-paper,  and  animal  matter  solu- 
ble only  in  water,  but  which  is  not  gelatin.  (Berzelius.)  The  crystalline  lens, 
besides  the  usual  salts,  contains  36  per  cent,  of  a  peculiar  animal  matter, 
very  analogous  to  albumen  if  not  identical  with  it.  In  cold  water  it  is  so- 
luble, but  is  coagulated  by  boiling.  The  coagulum,  according  to  Berzelius, 
has  all  the  properties  of  the  colouring  matter  of  the  blood  excepting  its 
colour. 

The  tears  are  limpid  and  of  a  saline  taste,  dissolve  freely  in  water,  and, 
owing  to  the  presence  of  free  soda,  communicate  a  green  tint  to  the  blue  in- 
fusion of  violets.  Their  chief  salts  are  chloride  of  sodium  and  phosphate  of 
soda.  According  to  Fourcroy  and  Vauquelin  the  animal  matter  of  the  tears 
is  mucus ;  but  it  is  more  probably  either  albumen,  or  some  analogous  prin- 
ciple. Its  precise  nature  has  not  however  been  satisfactorily  determined. 

Mucus. — The  term  mucus  has  been  employed  in  very  different  significa- 
tions. Dr.  Bostock  applies  it  to  a  peculiar  animal  matter  which  is  soluble 
both  in  hot  and  cold  water,  is  not  precipitated  by  corrosive  sublimate  or  so- 


LIQUIDS  OF  SEROUS  AND  MUCOUS  SURFACES,  &C.  607 

lution  of  tannin,  is  not  capable  of  forming  a  jelly,  and  which  yields  a  preci- 
pitate with  subacetate  of  lead.  The  existence  of  this  principle  has  not,  how- 
ever, been  fully  established ;  for  the  presence  of  muriatic  and  phosphoric 
acids,  the  latter  of  which  is  frequently  contained  in  animal  fluids,  and  the 
former  scarcely  ever  absent,  sufficiently  accounts  for  the  precipitates  occa- 
sioned in  them  by  the  salts  of  lead  or  silver.  But  even  supposing  the  opinion 
of  Dr.  Bostock  to  be  correct,  it  would  be  advisable  to  give  some  new  name 
to  his  principle,  and  apply  the  term  mucus  solely  to  the  fluid  secreted  by 
mucous  surfaces. 

The  properties  of  mucus  vary  somewhat  according  to  the  source  from 
which  it  is  derived;  but  its  leading  characters  are  in  all  cases  the  same, 
and  are  best  exemplified  in  mucus  from  the  nostrils.  Nasal  mucus,  accord- 
ing to  Berzelius,  has  the  following  properties.  Immersed  in  water,  it  im- 
bibes so  much  of  that  fluid  as  to  become  transparent,  with  the  exception  of 
a  few  particles  which  remain  opaque.  When  dried  on  blotting-paper,  it 
loses  its  transparency,  but  again  acquires  it  when  moistened.  It  is  not  co- 
agulated or  rendered  horny  by  being  boiled  in  water ;  but  as  soon  as  the 
ebullition  has  ceased,  it  collects  unchanged  at  the  bottom  of  the  vessel.  It 
is  dissolved  by  dilute  sulphuric  acid.  Nitric  acid  at  first  coagulates  it ;  but 
by  continued  digestion,  the  mucus  gradually  softens  and  is  finally  dissolved, 
forming  a  clear  yellow  liquid.  Acetic  acid  hardens  mucus,  and  does  not  dis- 
solve it  even  at  a  boiling  temperature.  Pure  potassa  at  first  renders  it  more 
viscid,  but  afterwards  dissolves  it.  By  tannic  acid  mucus  is  coagulated,  both 
when  softened  by  the  absorption  of  water,  and  when  dissolved  either  in  an 
acid  or  an  alkali. 

Pus.- — Purulent  matter  is  the  fluid  secreted  by  an  inflamed  and  ulcerated 
surface.  Its  properties  vary  according  to  the  nature  of  the  sore  from  which 
it  is  discharged.  The  purulent  matter  formed  by  an  ill-conditioned  ulcer  is 
a  thin,  transparent,  acrid,  fetid  ichor;  whereas  a  healing  sore  in  a  sound 
constitution  yields  a  yellowish-white  coloured  liquid,  of  the  consistence  of 
cream,  which  is  described  as  bland,  opaque,  and  inodorous.  This  is  termed 
healthy  pus,  and  is  possessed  of  the  following  properties.  Though  it  ap- 
pears homogeneous  to  the  naked  eye,  when  examined  with  the  microscope 
it  is  found  to  consist  of  minute  globules  floating  in  a  transparent  liquid.  Its 
specific  gravity  is  about  1'03.  It  is  insoluble  in  water,  and  it  is  thickened, 
but  not  dissolved,  by  alcohol.  When  recent,  it  does  not  affect  the  colour  of 
test-paper ;  but  by  exposure  to  the  air  it  becomes  acid.  The  dilute  acids 
have  little  effect  upon  it;  but  strong  sulphuric,  nitric,  and  muriatic  acids 
dissolve  it,  and  the  pus  is  thrown  down  by  dilution  with  water.  Ammonia 
reduces  it  to  a  transparent  jelly,  and  gradually  dissolves  a  considerable  por- 
tion of  it.  With  the  fixed  alkalies  it  forms  a  whitish  ropy  fluid,  which  is 
decomposed  by  water. 

The  composition  of  pus  has  not  been  ascertained  with  precision  ;  but  its 
characteristic  ingredient  is  more  closely  allied  to  albumen  than  the  other 
animal  principles. 

Several  attempts  have  been  made  to  discover  a  chemical  test  for  distin- 
guishing pus  from  mucus.  When  these  fluids  are  in  their  natural  state,  the 
appearance  of  each  is  so  characteristic  that  the  distinction  cannot  be  at- 
tended with  any  difficulty ;  but,  on  the  contrary,  when  a  mucous  surface  is 
inflamed,  its  secretion  becomes  opaque,  and,  as  sometimes  happens  in  some 
pulmonary  diseases,  acquires  more  or  less  of  the  aspect  of  pus.  Mr.  Charles 
Darwin,  who  examined  this  subject,  pointed  out  three  grounds  of  distinc- 
tion between  them.  1.  When  the  solution  of  these  liquids  in  sulphuric 
acid  is  diluted,  the  pus  subsides  to  the  bottom,  and  the  mucus  remains  sus- 
pended in  the  water.  2.  When  pus  and  catarrhal  mucus  are  diffused  through 
water,  the  former  sinks,  and  the  latter  floats.  3.  Pus  is  precipitated  from 
its  solution  in  potassa  by  water,  while  the  solution  of  mucus  is  not  decom- 
posed by  similar  treatment.  Dr.  Thomson,  in  his  System  of  Chemistry,  has 
given  the  following  test  on  the  authority  of  Grasmeyer.  The  substance  to 
be  examined,  after  being  triturated  with  its  own  weight  of  water,  is  mixed 


608  URINE. 

with  an  equal  quantity  of  a  saturated  solution  of  carbonate  of  potassa.  If  it 
contain  pus,  a  transparent  jelly  forms  in  a  few  hours  ;»but  this  does  not  hap- 
pen  if  mucus  only  is  present.  Dr.  Young-,  in  his  work  on  Consumptive 
Diseases,  has  given  a  very  elegant  character  for  distinguishing  pus,  founded 
on  its  optical  properties.  But  the  practical  utility  of  tests  of  any  kind  is 
rendered  very  questionable  by  the  fact  that  inflamed  mucous  membranes 
may  secrete  genuine  pus  without  breach  of  surface,  and  that  the  natural 
passes  into  purulent  secretion  by  insensible  shades. 

Sweat. — Watery  vapour  is  continually  passing  off  by  the  skin  in  the  form 
of  insensible  perspiration ;  but  when  the  external  heat  is  considerable,  or 
violent  bodily  exercise  is  taken,  drops  of  fluid  collect  upon  the  surface,  and 
constitute  what  is  called  sweat.  This  fluid  consists  chiefly  of  water;  but  it 
contains  some  muriate  of  soda  and  free  acetic  acid,  in  consequence  of  which 
it  has  a  saline  taste  and  an  acid  reaction, 


SECTION   V. 

URINE  AND  URINARY  CONCRETIONS. 

Urine. 

THE  urine  differs  from  most  of  the  animal  fluids  which  have  been  de- 
scribed by  not  serving  any  ulterior  purpose  in  the  animal  economy.  It  is 
merely  an  excretion  designed  for  ejecting  from  the  system  substances, 
which,  by  their  accumulation  within  the  body,  would  speedily  prove  fatal  to 
health  and  life.  The  sole  office  of  the  kidneys,  indeed,  appears  to  consist  in 
separating  from  the  blood  the  superfluous  matters  that  are  not  required  or 
adapted  for  nutrition,  or  which  have  already  formed  part  of  the  body,  and 
been  removed  by  absorption.  The  substances  which  in  particular  pass  off 
by  this  organ  are  nitrogen,  in  the  form  of  highly  azolized  products,  and 
various  saline  and  earthy  compounds.  This  sufficiently  accounts  for  the 
great  diversity  of  different  substances  contained  in  urine. 

The  quantity  of  the  urine  is  affected  by  various  causes,  especially  by  the 
nature  and  quantity  of  the  liquids  received  into  the  stomach  ;  but  on  an  ave- 
rage, a  healthy  person  voids  between  thirty  and  forty  ounces  daily.  The 
quality  of  this  fluid  is  likewise  influenced  by  the  same  circumstances,  being 
sometimes  in  a  very  dilute  state,  and  at  others  highly  concentrated.  The 
urine  voided  in  the  morning  by  a  person  who  has  fed  heartily,  and  taken  no 
more  fluids  than  is  sufficient  for  satisfying  thirst,  may  be  regarded  as  afford- 
ing  the  best  specimen  of  natural  healthy  urine. 

The  urine  in  this  state  is  a  transparent  limpid  fluid  of  an  amber  colour, 
having  a  saline  taste,  and  while  warm  emitting  an  odour  which  is  slightly 
aromatic,  and  not  at  all  disagreeable.  The  average  sp.  gr.  of  the  urine  of 
fifty  healthy  men,  observed  by  the  late  Dr.  Gregory  in  autumn  at  mid-day, 
is  1*02246.  It  gives  a  red  tint  to  litmus  paper,  a  circumstance  which  indi- 
cates the  presence  either  of  a  free  acid  or  of  a  supersalt.  Though  at  first 
quite  transparent,  an  insoluble  matter  is  deposited  on  standing ;  so  that  urine, 
voided  at  night,  is  found  to  have  a  light  cloud  floating  in  it  by  the  following 
morning.  This  substance  consists  in  part  of  mucus  from  the  urinary  pas- 
sages, and  partly  of  superurate  of  ammonia,  which  is  much  more  soluble  in 
warm  than  in  cold  water. 

The  urine  is  very  prone  to  spontaneous  decomposition.  When  kept  for 
two  or  three  days  it  acquires  a  strong  urinous  smell ;  and  as  the  putrefaction 
proceeds,  the  disagreeable  odour  increases,  until  at  length  it  becomes  exceed- 


URINE.  609 

ingly  offensive.  As  soon  as  these  changes  commence,  the  urine  ceases  to 
have  an  acid  reaction,  and  the  earthy  phosphates  are  deposited.  In  a  short 
time,  a  free  alkali  makes  its  appearance,  and  a  large  quantity  of  carbonate 
of  ammonia  is  gradually  generated.  Similar  changes  may  be  produced  in 
recent  urine  by  continued  boiling.  In  both  cases  the  phenomena  are  owing 
to  the  decomposition  of  urea,  which  is  almost  entirely  resolved  into  carbo- 
nate of  ammonia. 

The  composition  of  the  urine  has  been  studied  by  several  chemists,  but 
the  most  recent  and  elaborate  analysis  of  this  fluid  is  by  Berzelius.  Ac- 
cording to  the  researches  of  this  indefatigable  chemist,  1000  parts  of  urine 
are  composed  of 

Water 933-00 

Urea 30-10 

Uric  acid    .            .            .            .             .            .            .  1-00 

Free  lactic  acid,  lactate  of  ammonia,  and  animal  matter 

not  separable  from  them          ....  17-14 

Mucus  of  the  bladder          .            .            .                         .  0-32 

Sulphate  of  potassa              .....  3-71 

Sulphate  of  soda     .  .  .  .  .  ,3-16 

Phosphate  of  soda  .             .....  2-94 

Phosphate  of  ammonia        .             .             .             .             .  1-65 

Muriate  of  soda      .             .             .             .             .             .  4-45 

Muriate  of  ammonia           .....  1-50 

Earthy  matters,  with  a  trace  of  fluate  of  lime         .  .          .  1-00 

Siliceous  earth        ......  0-03 

Besides  the  ingredients  included  in  the  preceding  list,  the  urine  contains 
several  other  substances  in  small  quantity.  From  the  property  this  fluid 
possesses  of  blackening  silver  vessels  in  which  it  is  evaporated,  owing  to  the 
formation  of  sulphuret  of  silver,  Proust  inferred  the  presence  of  uwoxidized 
sulphur  ;  and  Dr.  Prout,  from  the  odour  of  phosphuretted  hydrogen,  which 
he  thinks  he  has  perceived  in  putrefying  urine,  suspects  that  phosphorus  is 
likewise  present.  The  urine  also  contains  a  peculiar  yellow  colouring  mat- 
ter which  has  not  hitherto  been  obtained  in  a  separate  state.  From  the  pre- 
cipitate occasioned  in  urine  by  the  infusion  of  gall-nuts,  the  presence  of 
gelatin  has  been  inferred;  but  this  effect  appears  owing  to  the  presence  not 
o(  gelatin  but  of  a  small  portion  of  albumen. 

According  to  Scheele,  the  urine  of  infants  sometimes  contains  benzoic 
acid,  a  compound  which,  when  present,  may  be  easily  procured  by  evapora- 
ting the  urine  nearly  to  the  consistence  of  syrup,  and  adding  hydrochloric 
acid.  The  precipitate,  consisting  of  uric  and  benzoic  acids,  is  digested  in 
alcohol,  which  dissolves  the  benzoic  acid. 

Notwithstanding  the  high  authority  of  Berzelius,  it  is  very  doubtful  if  any 
free  acid  be  present  in  healthy  urine.  Dr.  Prout,  with  every  appearance  of 
reason,  maintains  that  the  acidity  of  recent  urine  is  occasioned  by  super- 
salts,  and  not  by  uncombined  acid.  He  is  of  opinion  that  the  acid  reaction 
is  chiefly,  if  not  wholly,  to  be  ascribed  to  the  superphosphate  of  lime  and 
superurate  of  ammonia,  salts  which  he  finds  may  co-exist  in  a  liquid  without 
mutual  decomposition.  A  very  strong  argument,  which  to  me  indeed  ap- 
pears conclusive,  in  favour  of  this  view,  is  derived  from  the  fact,  that  on 
adding  hydrochloric  acid  to  recent  urine,  minute  crystals  of  uric  acid  are 
gradually  deposited,  as  always  happens  when  this  acid  subsides  slowly  from 
a  state  of  solution :  but,  on  the  contrary,  if  no  free  acid  is  added,  an  amor- 
phous sediment,  which  Dr.  Prout  regards  as  superurate  of  ammonia  is 
obtained. 

Such  is  the  general  view  of  the  composition  of  human  urine  in  its  natural 
healthy  state.  But  this  fluid  is  subject  to  a  great  variety  of  morbid  condi- 
tions, which  arise  either  from  the  deficiency  or  excess  of  certain  principles 
which  it  ought  to  contain,  or  from  the  presence  of  others  wholly  foreign  to 
its  composition.  As  the  study  of  these  affections  affords  an  interesting  ex- 


610  URINE. 

ample  of  the  application  of  chemistry  to  pathology  and  the  practice  of  me- 
dicine, I  shall  briefly  mention  some  of  the  most  important  morbid  states  of 
this  fluid,  referring  for  more  ample  details  to  the  excellent  treatise  of 
Dr.  Prout.* 

Of  the  substances  which,  though  naturally  wanting1,  are  sometimes  con- 
tained  in  the  urine,  the  most  remarkable  is  sugar,  which  is  secreted  by  the 
kidneys  in  diabetes  (page  573).  Diabetic  urine  has  a  sweet  taste,  and  yields 
a  syrup  by  evaporation,  is  almost  always  of  a  pale  straw  colour,  and  in  gene- 
ral has  a  greater  specific  gravity  than  ordinary  urine.  A.  specimen  of  dia- 
betic urine,  the  sp.  gr.  of  which  was  1-03626,  was  found  by  Mr.  Kane  to 
contain  in  1000  parts,  913  of  water,  60  of  sugar,  6-5  of  urea,  and  20  of  salts 
(Dublin  Journal  of  Science,  i.  20).  Owing  to  the  large  quantity  of  sugar 
and  the  dilute  state  of  the  urea,  diabetic  urine  has  little  tendency  to  putrefy, 
and  is  susceptible  of  undergoing  the  vinous  fermentation. 

The  acidifying  process  which  is  constantly  going  forward  in  the  kidneys, 
as  evinced  by  the  formation  of  sulphuric,  phosphoric,  and  uric  acids,  some- 
times proceeds  to  a  morbid  extent,  in  consequence  of  which  two  acids,  the 
oxalic  and  nitric,  are  generated,  neither  of  which  exists  in  healthy  urine. 
The  former,  by  uniting  with  lime,  gives  rise  to  one  of  the  worst  kinds  of 
urinary  concretions ;  and  the  latter,  in  the  opinion  of  Dr.  Prout,  leads  to  the 
production  of  purpurate  of  ammonia,  by  reacting  on  uric  acid. 

In  severe  cases  of  jaundice,  the  bile  passes  from  the  blood  into  the  kid- 
neys, and  communicetes  a  yellow  colour  to  the  urine.  The  most  delicate 
test  of  its  presence  is  hydrochloric  acid,  which  causes  a  green  tint. 

Though  albumen  is  contained  in  very  minute  quantity  in  healthy  urine, 
in  some  diseases  it  is  present  in  large  proportion,  According  to  Dr.  Black- 
all  it  is  characteristic  of  certain  kinds  of  dropsy,  accompanied  with  an  in- 
flammatory diathesis,  as  in  that  which  supervenes  in  scarlet  fever;  and 
Dr.  Prout  has  described  two  cases  of  albuminous  urine,  in  which,  without 
any  febrile  symptoms,  albumen  existed  in  such  quantity  that  spontaneous 
coagulation  took  place  within  the  bladder.  Dr.  Bright,  in  his  Medical 
Reports,  has  shown  that  dropsical  effusions  with  albuminous  urine  are  often 
associated  with  disease  of  the  kidney,  and  his  observations  have  been  con- 
firmed by  the  experience  of  Dr.  Christison  and  the  late  Dr.  Gregory  (Edin. 
Med.  and  Surg.  Journal  for  Oct,  1829,  Oct.  1831,  and  Jan.  1832).  In  this 
affection  the  urine  is  scanty,  and  its  sp.  gravity,  from  deficient  quantity  of 
saline  matter  and  urea,  is  lower  than  natural,  being  in  the  average  of 
50  cases  1-01318,  and  is  rarely  so  high  as  T02:  this  is  so  constant,  that 
scanty  albuminous  urine  of  a  low  sp.  gravity  was  considered  by  Dr.  Gregory 
as  nearly  a  sure  indication  of  renal  disease.  The  albumen  is  readily  de- 
tected by  the  coagulating  effect  of  heat  or  by  ferrocyanuret  of  potassium 
(page  570),  the  urine  if  not  acid,  which  it  frequently  is,  being  always  pre- 
viously acidulated  by  acetic  acid.  In  the  blood  of  patients  suffering  under 
renal  disease  with  albuminous  urine,  Dr.  Bostock  detected  a  crystalline  sub- 
stance resembling  urea,  and  Dr.  Christison,  pursuing  the  inquiry,  obtained 
urea,  with  all  its  characteristic  properties. 

Urea  is  secreted  less  abundantly  than  usual  during  inflammatory  affec- 
tions of  the  liver,  whether  acute  or  chronic,  in  ihe  renal  disease  just  men- 
tioned, and  during  the  hysteric  paroxysm,  in  which  latter  affection  the  saline 
ingredients  of  the  urine  are  secreted  in  unusual  quantity.  Urea  is  said  to 
be  wanting  in  diabetic  urine,  an  error  caused  by  the  presence  of  sugar  dimi- 
nishing the  tendency  of  nitrate  of  urea  to  crystallize.  Dr.  Henry  has  shown 
that  urea,  when  mixed  with  a  considerable  proportion  of  sugar,  cannot  be 
discovered  by  the  usual  test  of  nitric  acid  ;  and,  consequently,  though  present 
in  diabetic  urine,  it  may  easily  be  overlooked.  He  has  succeeded  in  detect- 
ing it  in  such  cases  by  distillation,  urea  being  the  only  known  animal  priYi- 
ciple  which  is  converted  into  carbonate  of  ammonia  at  a  boiling  temperature. 

*  Inquiry  into  the  Nature  and  Treatment  of  Gravel,  Calculus,  &c. 


URINE.  611 

Mr.  Kane  has  succeeded  in  separating  the  nitrate  of  urea  in  crystals  by  em- 
ploying  as  the  test  nitric  acid  diluted  with  an  equal  weight  of  water,  and 
plunging  the  mass  into  a  freezing  mixture  of  salt  and  ice.  He  has  thus 
been  able  to  prove  that  diabetic  patients  void  in  the  course  of  24  hours  as 
much  urea  as  healthy  persons. 

The  mode  by  which  Dr.  Prout  estimates  the  proportion  of  this  principle 
is  by  putting  the  urine  into  a  watch-glass,  and  carefully  adding  to  it  nearly 
an  equal  quantity  of  nitric  acid,  in  such  a  manner  that  the  acid  may  collect 
at  the  bottom.  If  spontaneous  crystallization  ensue,  an  excess  of  urea  is 
indicated;  and  the  degree  of  excess  may  be  inferred  approximately  by 
marking  the  time  which  elapses  before  the  effect  takes  place.  Undiluted 
healthy  urine  yields  crystals  only  after  an  interval  of  half  an  hour;  but  the 
nitrate  crystallizes  within  that  interval  when  the  urea  is  in  excess. 

An  unusually  abundant  secretion  of  uric  acid  is  a  circumstance  by  no 
means  uncommon.  In  some  instances  this  acid  makes  it  appearance  in  a 
free  state :  but  happily  it  generally  occurs  in  combination  with  an  alkali, 
especially  with  soda  or  ammonia.  As  the  urates  are  much  more  soluble  in 
warm  than  in  cold  water,  the  urine  in  which  they  abound  is  quite  clear  at 
the  moment  of  being  voided,  but  deposites  a  copious  sediment  in  cooling. 
The  undue  secretion  of  these  salts,  if  temporary,  occasions  scarcely  any  in- 
convenience, and  arises  from  such  slight  causes,  that  it  frequently  takes 
place  without  being  noticed.  This  affection  is  generally  produced  by  errors 
in  diet,  whether  as  to  quantity  or  quality,  and  by  all  causes  which  inter- 
rupt the  digestive  process  in  any  of  its  stages,  or  render  it  imperfect. 
Dr.  Prout  specifies  unfermented  heavy  bread,  and  hard  boiled  puddings  or 
dumplings,  as  in  particular  disposing  to  the  formation  of  the  urates.  These 
sediments  have  commonly  a  yellowish  tint,  which  is  communicated  by  the 
colouring  matter  of  the  urine;  or  when  they  are  deposited  in  fevers,  forming- 
the  lateritious  sediment,  they  are  red,  in  consequence  of  the  colouring  mat- 
ter of  the  urine  being  then  more  abundant.  In  fevers  of  an  irritable  nature, 
as  in  hectic,  the  sediment  has  often  a  pink  colour,  and  is  considered  by 
Prout  to  consist  of  urate  of  ammonia,  coloured  by  purpurate  of  ammonia; 
but  Messrs.  Brett  and  Bird  have  examined  several  pink  sediments,  in  all  of 
which  the  colouring  ingredient  was  a  substance  soluble  in  alcohol  and  not 
purpuric  acid.  (Medical  Gazette,,  August  23,  1834.) 

So  long  as  uric  acid  remains  in  combination  with  a  base,  it  never  yields 
a  crystalline  deposite ;  but  when  this  acid  is  in  excess  and  in  a  free  state,  its 
very  sparing  solubility  causes  it  to  separate  in  minute  crystals,  even  within 
the  bladder,  giving  rise  to  two  of  the  most  distressing  complaints  to  which 
human  nature  is  subject, — to  gravel  when  the  crystals  are  detached  from 
one  another,  and  when  agglutinated  by  animal  matter  into  concrete  masses, 
to  the  disease  called  the  stone.  These  diseases  may  arise  either  from  uric 
acid  being  directly  secreted  by  the  kidneys,  or,  as  Dr.  Prout  suspects,  from 
the  formation  of  some  other  acid,  by  which  the  urate  of  ammonia  is  de- 
composed. The  tendency  of  urine  to  contain  free  acid  occurs  most  fre- 
quently in  dyspeptic  persons  of  a  gouty  habit,  and  is  familiarly  known  by 
the  name  of  the  uric  or  lithic  acid  diathesis.  In  these  individuals  the  dispo- 
sition to  undue  acidity  of  the  urine  is  superadded  to  that  state  of  the  system 
which  leads  to  an  unusual  supply  of  the  urates. 

A  deficiency  of  acid  in  urine  is  not  less  injurious  than  its  excess.  As 
phosphate  of  lime  in  its  neutral  state  is  insoluble  in  water,  this  salt  cannot 
be  dissolved  in  urine  except  by  being  in  the  form  of  a  superphosphate. 
Hence  it  happens  that  healthy  urine  yields  a  precipitate,  when  it  is  neu- 
tralized by  an  alkali;  and  if,  by  the  indiscriminate  employment  of  alkaline 
medicines,  or  from  any  other  cause,  the  urine,  while  yet  within  the  bladder, 
is  rendered  neutral,  the  earthy  phosphates  are  necessarily  deposited,  and  an 
opportunity  afforded  for  the  formation  of  a  stone. 


612  URINARY  CONCRETIONS. 


Urinary  Concretions. 

The  first  step  towards  a  knowledge  of  urinary  calculi  was  made  in  the 
year  1776  by  Scheele,  who  showed  that  many  of  the  concretions  formed  in 
the  bladder  consist  of  uric  or  lithic  acid.  The  subject  was  afterwards  suc- 
cessfully investigated  by  Wollaston  and  Pearson  in  this  country,  and  by 
Fourcroy  and  Vauquelin  in  France  ;  but  the  merit  of  having  first  ascertained 
the  composition  and  chemical  characters  of  most  of  the  species  of  urinary 
calculi  at  present  known,  belongs  to  Dr.  Wollaston.  (Phil.  Trans,  for  1797.) 
The  chemists  who  have  since  materially  contributed  to  advance  our  know- 
ledge of  this  department  of  science,  are  Henry,  Brande,  Prout,  and  the  late 
Dr.  Marcet,  to  whose  "  Essay  on  the  Chemical  History  and  Medical  Treat- 
ment of  Calculous  Disorders,"  I  may  refer  the  reader  who  is  desirous  of 
studying-  this  important  subject. 

The  most  common  kind  of  urinary  concretions  may  be  conveniently 
divided  into  six  species  :  1.  The  uric  acid  calculus ;  2.  The  bone-earth  cal- 
culus, principally  consisting  of  phosphate  of  lime;  3.  The  ammoniaco- 
magnesian  phosphate;  4.  The  fusible  calculus,  being  a  mixture  of  the  two 
preceding  species;  5.  The  mulberry  calculus,  composed  of  oxalate  of  lime; 
and,  lastly,  the  cystic  oxide  calculus.  (Marcet.) 

1.  The  uric  acid  forms  a  hard  inodorous  concretion,  commonly  of  an  oval 
form,   of  a  brownish  or  fawn   colour,  and  smooth  surface.     These  calculi 
consist  of  layers  arranged    concentrically  around  a   central  nucleus,  the 
laminse  being  distinguished  from  each  other  by  a  slight  difference  in  colour, 
and  sometimes  by  the  interposition  of  some  other  substance. 

This  species  is  readily  distinguished  by  the  following  characters.  It  is 
very  sparingly  soluble  in  water  and  muriatic  acid.  Digested  in  pure 
potassa  it  quickly  disappears,  and  on  adding  an  acid  to  the  solution,  the  uric 
acid  is  precipitated.  It  is  dissolved  with  effervescence  by  nitric  acid,  and 
the  solution  yields  purpurate  of  ammonia  when  evaporated.  Before  the 
blowpipe  it  becomes  black,  emits  a  peculiar  animal  odour,  and  is  gradu- 
ally consumed,  leaving  a  trace  of  white  ash,  which  has  an  alkaline  re- 
action. 

As  a  variety  of  this  species  may  be  mentioned  urate  of  ammonia,  a  rare 
kind  of  calculus  first  noticed  by  Fourcroy.  Brande  and  Marcet  expressed 
a  doubt  of  its  ever  forming  an  independent  concretion ;  but  its  existence,  as 
such,  has  been  established  by  Prout.  The  calculus  of  urate  of  ammonia 
has  the  same  general  chemical  characters  as  that  composed  of  uric  acid, 
from  which  it  is  distinguished  by  its  solubility  in  boiling  water,  when  re- 
duced to  powder,  and  by  its  solution  in  potassa  being  attended  with  the  dis- 
engagement of  ammonia.  It  deflagrates  remarkably  before  the  blowpipe. 
(Medico-Chir.  Trans,  x.  389.) 

2.  The  bone-earth  calculus,  first  correctly  analyzed  by  Wollaston,  consists 
of  phosphate  of  lime.     The  surface  of  these  calculi  is  of  a  pale  brown  co- 
lour, and   quite  smooth  as  if  it  had  been  polished.     When  sawed  through 
the  middle,  they  are  found  to  be  laminated   in  a  very  regular  manner,  and 
the  layers  in  general  adhere  so  slightly  that  they  may  be  separated  with 
ease  into  concentric  crusts.    Dr.  Yellovvly,  in  several  bone-earth  concretions, 
has  detected   small  quantities  of  carbonate  of  lime,  which  appears  to  have 
been  overlooked  by  others. 

This  calculus,  when  reduced  to  powder,  dissolves  with  facility  in  dilute 
nitric  or  muriatic  acid,  but  is  insoluble  in  potassa.  Before  the  blowpipe  it 
first  assumes  a  black  colour,  from  the  decomposition  of  a  little  animal  mat- 
er, and  then  becomes  quite  white,  undergoing  no  further  change  unless  the 
heat  be  very  intense,  when  it  is  fused. 

3.  Phosphate  of  ammonia  and  magnesia  was  first  described  as  a  consti- 
tuent of  urinary  calculi  by  Wollaston.     It  rarely  exists  quite  alone,  because 
the  same  state  of  the   urine  which   leads  to  the  formation  of  this  species, 
favours  the  deposition  of  phosphate  of  lime ;  but  it  is  frequently  the  pre- 


URINARY  CONCRETIONS.  613 

vailing  ingredient.  It  often  appears  in  the  form  of  minute  sparkling  crys* 
tals,  diffused  over  the  surface  or  between  the  interstices  of  other  calculous 
laminae. 

Calculi,  in  which  this  salt  prevails,  are  generally  white,  and  less  compact 
than  the  foregoing  species.  When  reduced  to  powder  they  are  dissolved  by 
cold  acetic  acid,  and  still  more  easily  by  the  stronger  acids,  the  salt  being 
thrown  down  unchanged  by  ammonia.  Digested  in  pure  potassa,  it  emits 
an  ammoniacal  odour,  but  is  not  dissolved.  Before  the  blowpipe,  a  smell 
of  ammonia  is  given  out,  it  diminishes  in  size,  and  melts  into  a  white  pearl 
with  rather  more  facility  than  phosphate  of  lime. 

4.  The  fusible  calculus,  the  nature  of  which  was  first  determined  by  Wol- 
laston,  is  a  mixture  of  the  two  preceding  species.     It  is  commonly  of  a 
white  colour,  and  its  fracture  is  usually  ragged  and  uneven.     It  is  more 
friable  than  any  of  the  other  kinds  of  calculus,  separates  easily  into  layers, 
and  leaves  a  white  dust  on  the  fingers.     These  concretions  are  very  com- 
mon, and  sometimes  attain  a  large  size. 

The  fusible  calculus  is  characterized  by  the  facility  with  which  it  melts 
into  a  pearly  globule,  which  is  sometimes  quite  transparent.  When  reduced 
to  powder,  and  put  into  cold  acetic  acid,  the  phosphate  of  ammonia  and 
magnesia  is  dissolved,  and  the  phosphate  of  lime,  almost  the  whole  of  which 
is  left,  dissolves  readily  in  hydrochloric  acid. 

5.  The  mulberry  calculus,  so  named  from  its  resemblance  to  the  fruit  of 
the  mulberry,  was  first  proved  to   consist  of  oxalate  of  lime  by  Wollaston. 
This  concretion  is  sufficiently  characterized  by  its  dark-coloured  tubercu- 
lated  surface,  and  by  being  very  hard  and  compact ;  but  it  may  also  be  dis- 
tinguished chemically  by  the  following  properties.     Heated  before  the  blow- 
pipe, the  oxalic  acid  is  decomposed,  and  pure  lime  remains,  which  gives  a 
strong   brown  stain  to   moistened  turmeric  paper.     It  is  insoluble  in  the 
alkalies ;  but  by  digestion  in  carbonate  of  potassa,  it  is  decomposed,  and  the 
insoluble  carbonate  of  lime  is  left.     When  reduced  to  powder  and  digested 
in  hydrochloric  or  nitric  acid,  a  perfect  solution  is  effected.     It  is  not  dis- 
solved by  acetic  acid,  a  circumstance  which  distinguishes  it  from  the  am- 
moniaco-magnesian  phosphate ;  and  it  is  distinguished  from  phosphate  of 
lime  by  being  insoluble  in  phosphoric  acid. 

6.  The  cystic  oxide  was  described  by  its  discoverer  Wollaston  in  the  Phi- 
losophical Transactions  for  1810.     This  concretion  is   not  laminated,  but 
appears  as  one  uniform  mass,  confusedly  crystallized  through  its  whole  sub- 
stance, having  somewhat  the  appearance  of  the  ammoniaco-magnesian  phos- 
phate, though  more  compact.   Before  the  blowpipe  it  emits  a  peculiarly  fetid 
smell,  quite  distinct  from  that  of  uric  acid,  and  is  consumed.     It  is  charac- 
terized by  the  great  variety  of  reagents  in  which  it  is  soluble.  It  is  dissolved 
abundantly  by  the  hydrochloric,  nitric,  sulphuric,  and  oxalic  acids ;  by  po- 
tassa, soda,  ammonia,  and   lime-water;  and  even  by  the  neutral  carbonates 
of  soda  and  potassa.     It  is  insoluble  in  water,  alcohol,  bicarbonate  of  am- 
monia, and  in  the  tartaric,  citric,  and  acetic  acids. 

From  the  similarity  which  this  substance  bears  to  certain  oxides  in 
uniting  both  with  acids  and  alkalies,  Dr.  Wollaston  termed  it  an  oxide,  and 
gave  it  the  name  of  cystic,  on  the  supposition  of  its  being  peculiar  to  the 
bladder.  Dr.  Marcet,  however,  has  found  it  in  the  kidney. 

Cystic  oxide  is  a  rare  species  of  calculus.  In  this  country  seven  speci- 
mens only  have  been  found ; — two  by  Wollaston,  two  by  Dr.  Henry,  and 
three  by  Dr«  Marcet :  Professor  Stromeyer  has  met  with  two  instances  of 
it  in  one  family,  and  in  one  of  the  cases,  the  cystic  oxide  was  also  detected 
in  the  urine,  M.  Lassaigne  has  likewise  found  it  in  a  stone  taken  from  the 
bladder  of  a  dog.  From  the  analysis  of  this  chemist,  100  parts  of  cystic 
oxide  are  composed  of  carbon  36-2,  hydrogen  12-8,  oxygen  17,  and  nitro- 
gen 34. 

Dr.  Prout  found  the  urine,  during  the  formation  of  cystic  oxide  calculus, 
to  have  a  density  varying  from  1-020  to  1-022,  to  be  rather  abundant,  faintly 
acid,  of  a  yellowish-green  colour  and  peculiar  odour,  and  to  contain  very 

52 


614 


SOLID  PARTS  OF  ANIMALS. 


little  uric  acid  and  urea.  A  greasy-looking  film  of  cystic  oxide  collected  on 
its  surface,  and  a  copious  pale  precipitate  was  thrown  down  by  bicarbonate 
of  ammonia,  consisting  of  cystic  oxide  and  the  ammoniaco-magnesian  phos- 
phate. The  cystic  oxide  was  also  precipitated  by  acetic  acid.  Dr.  Venables 
has  examined  the  urine  in  a  similar  state,  and  made  similar  remarks. 
(Edin.  Med.  and  Surg.  Journal,  Oct.  1830.) 

It  is  remarkable  that  cystic  oxide  is  never  accompanied  with  the  matter 
of  any  other  concretion ;  whereas  the  other  species  are  frequently  met  with 
in  the  same  stone.  They  are  sometimes  so  intimately  mixed  that  they  can 
be  separated  from  one  another  only  by  chemical  analysis,  forming  what  is 
called  a  compound  calculus ;  but  more  frequently  the  concretion  consists  of 
two  or  more  different  species  arranged  in  distinct  alternate  layers.  This  is 
termed  the  alternating  calculus. 

Besides  the  calculus  just  mentioned,  a  few  other  species  have  been  noticed. 
Two  were  described  by  Dr.  Marcet  under  the  names  of  xanthic  oxide  and 
fibrinous  calculus,  both  of  which  are  exceedingly  rare.  Xanthic  oxide  is  of 
a  reddish  or  yellow  colour,  is  soluble  both  in  acids  and  alkalies,  and  its  so- 
lution  in  nitric  acid,  when  evaporated,  assumes  a  bright  lemon-yellow  tint, 
a  property  to  which  it  owes  its  name,  and  by  which  it  is  characterized. 
(|atv9oc  yellow.}  The  fibrinous  calculus  derives  its  name  from  fibrin,  to 
which  its  properties  are  closely  analogous.  The  third  species  consists  chiefly 
of  carbonate  of  lime,  and  is  likewise  of  rare  occurrence.  It  is  probable  that 
in  some  very  uncommon  cases,  silica  forms  the  principal  ingredient  of  a 
stone ;  at  least  silicious  matter  was  found  by  Dr.  Venables  to  be  voided  in 
one  if  not  in  two  cases  of  gravel.  (Journal  of  Science,  N.  S.  vi.  234).  He 
has  since  met  with  it  in  other  cases. 

From  the  solubility  of  urinary  concretions  in  chemical  menstrua,  hopes 
were  once  entertained  that  reagents  might  be  introduced  into  the  urine 
through  the  medium  of  the  blood,  or  be  at  once  injected  into  the  bladder,  so 
as  to  dissolve  urinary  calculi,  and  thus  supersede  the  necessity  of  a  painful 
and  dangerous  operation,  It  has  been  found,  however,  that,  for  this  pur- 
pose, it  would  be  necessary  to  employ  acid  or  alkaline  solutions  of  greater 
strength  than  may  safely  be  introduced  into  the  bladder  ;  and  consequently  all 
attempts  of  the  kind  have  been  abandoned.  The  last  suggestion  of  this  na- 
ture was  made  by  Prevost  and  Dumas,  who  proposed  to  disunite  the  elements 
of  calculi  by  means  of  galvanism.  This  agent,  however,  though  it  may  pro- 
duce this  effect  out  of  the  body,  will  scarcely,  I  conceive,  be  found  admissible 
in  practice. 


SECTION  VI. 


SOLID   PARTS  OF  ANIMALS. 

Bones  consist  of  earthy  salts  and  animal  matter  intimately  blended ;  the 
former  of  which  are  designed  for  giving  solidity  and  hardness,  and  the  lat* 
ter  for  agglutinating  the  earthy  particles.  The  animal  substances  are  chiefly 
cartilage,  gelatin,  and  a  peculiar  fatty  matter  called  marrow.  On  reducing 
bones  to  powder,  and  digesting  them  in  water,  the  fat  rises  aad  swims  upon 
its  surface,  while  the  gelatin  is  dissolved.  By  digesting  bones  in  dilute  hy- 
drochloric acid,  the  earthy  salts  are  dissolved,  and  a  flexible  mass  remains, 
which  retains  the  original  figure  of  the  bone,  and  consists  of  gelatin  and  car- 
tilage :  the  former  is  by  far  the  most  abundant,  since  nearly  the  whole  may 
be  dissolved  in  boiling  water,  and  yields  a  solution  possessed  of  all  the  pro. 
perties  of  gelatin.  The  residual  cartilage  appears  identical  with  coagulated 


SOLID  PARTS  OF  ANIMALS.  615 

albumen.  The  animal  matter  of  bones  is  formed  before  the  earthy  matter, 
and  constitutes  the  nidus  in  which  the  latter  is  deposited. 

When  bones  are  heated  in  close  vessels,  a  large  quantity  of  carbonate  of 
ammonia,  some  fetid  empyreumatic  oil,  and  the  usual  inflammable  gases 
pass  over  into  the  recipient;  while  a  mixture  of  charcoal  and  earthy  matter, 
called  animal  charcoal,  remains  in  the  retort.  If,  on  the  contrary,  they  are 
heated  to  redness  in  an  open  fire,  the  charcoal  is  consumed,  and  a  pure  white 
friable  earth  is  the  sole  residue. 

According  to  the  analysis  of  Berzelius,  100  parts  of  dry  human  bones  con- 
sist of  animal  matters  33-3,  phosphate  of  lime  51-04,  carbonate  of  lime  11-3, 
fluate  of  lime  2,  phosphate  of  magnesia  1'16,  and  soda,  muriate  of  soda,  and 
water  1-2.  Mr.  Hatchelt  found,  also,  a  small  quantity  of  sulphate  of  lime ; 
and  Fourcroy  and  Vauquelin  discovered  traces  of  alumina,  silica,  and  the 
oxides  of  iron  and  manganese. 

Teeth  are  composed  of  the  same  materials  as  bone ;  but  the  enamel  dis- 
solves completely  in  dilute  nitric  acid,  and,  therefore,  is  free  from  cartilage. 
From  the  analysis  of  Mr.  Pepys,  the  enamel  contains  78  per  cent,  of  phos. 
phate  and  6  of  carbonate  of  lime,  the  residue  being  probably  gelatin.  The 
composition  of  ivory  is  similar  to  that  of  the  bony  matter  of  teeth  in  general. 

The  shells  of  eggs  and  the  covering  of  crustaceous  animals,  such  as  lob. 
sters,  crabs,  and  the  starfish,  consist  of  carbonate  and  a  little  phosphate  of 
lime  and  animal  matter.  The  shells  of  oysters,  muscles,  and  other  mollus- 
cous animals  consist  almost  entirely  of  carbonate  of  lime  and  animal  mat- 
ter, and  the  composition  of  pearl  and  mother  of  pearl  is  similar. 

Horn  differs  from  bone  in  containing  only  a  trace  of  earth.  It  consists 
chiefly  of  gelatin  and  a  cartilaginous  substance  like  coagulated  albumen. 
The  composition  of  the  nails  and  hoofs  of  animals  is  similar  to  that  of  horn; 
and  the  cuticle  belongs  to  the  same  class  of  substances. 

Tendons  appear  to  be  composed  almost  entirely  of  gelatin ;  for  they  are 
soluble  in  boiling  water,  and  the  solution  yields  an  abundant  jelly  on  cool- 
ing. The  composition  of  the  true  skin  is  nearly  the  same  as  that  of  ten- 
dons. Membranes  and  ligaments  are  composed  chiefly  of  gelatin,  but 
they  also  contain  some  substance  which  is  insoluble  in  water,  and  is  similar 
to  coagulated  albumen. 

According  to  the  analysis  of  Vauquelin,  the  principal  ingredient  of  hair 
is  a  peculiar  animal  substance,  insoluble  in  water  at  212°  F.  but  which  may 
be  dissolved  in  that  liquid  by  means  of  Papin's  digester,  and  is  soluble  in 
a  solution  of  potassa.  Besides  this  substance  hair  contains  oil,  sulphur, 
silica,  iron,  manganese,  and  carbonate  and  phosphate  of  lime.  The  colour 
of  the  hair  depends  on  that  of  its  oil ;  and  the  effect  of  metallic  solutions, 
such  as  nitrate  of  oxide  of  silver,  in  staining  the  hair,  is  owing  to  the  pre- 
sence of  sulphur. 

The  composition  of  wool  and  feathers  appears  analogous  to  that  of  hair. 
The  quill  part  of  the  feather  was  found  by  Mr.  Hatchett  to  consist  of  co- 
agulated albumen. 

Silk  is  covered  with  a  peculiar  varnish  which  is  soluble  in  boiling  water 
and  in  alkaline  solutions,  and  amounts  to  about  23  per  cent,  of  the  raw  ma- 
terial. By  digestion  in  alcohol  it  is  also  deprived  of  a  portion  of  wax.  The 
remaining  fibrous  structure  has  been  examined  in  a  very  imperfect  manner, 
By  the  action  of  nitric  acid  it  is  converted  into  carbazotic  acid. 

The  flesh  of  animals,  or  muscle,  consists  essentially  of  fibrin ;  but  inde- 
pendently of  this  principle,  it  contains  several  other  ingredients,  such  as  al- 
bumen, gelatin,  a  peculiar  extractive  matter  called  osmazome,  fat,  and  salts, 
substances  which  are  chiefly  derived  from  the  blood,  vessels,  and  cellular 
membrane,  dispersed  through  the  muscles.  On  macerating  flesh,  cut  into 
small  fragments,  in  successive  portions  of  cold  water,  the  albumen,  osma- 
zome,  and  salts  are  dissolved ;  and  on  boiling  the  solution,  the  albumen  is 
coagulated.  From  the  remaining  liquid,  the  osmazome  may  be  procured  in 
a  separate  state  by  evaporating  to  the  consistence  of  an  extract,  and  treating- 


61 G  PUTREFACTION. 

it  with  cold  alcohol.  By  the  action  of  boiling  water,  the  gelatin  of  the 
muscle  is  dissolved,  the  fat  melts  and  rises  to  the  surface  of  the  water,  and 
pure  fibrin  remains. 

The  characteristic  odour  and  taste  of  soup  are  owing-  to  the  osmazome. 
This  substance  is  of  a  yellowish-brown  colour,  and  is  distinguished  from  the 
other  animal  principles  by  solubility  in  water  and  alcohol,  whether  cold  or  at 
a  boiling  temperature,  and  by  not  forming  a  jelly  when  its  solution  is  con- 
centrated by  evaporation.  Like  gelatin  and  albumen  it  yields  a  precipitate 
with  infusion  of  gall-nuts. 

The  substance  of  the  brain,  nerves,  and  spinal  marrow  differs  from  that  of 
all  other  animal  textures.  The  most  elaborate  analysis  of  cerebral  matter  is 
by  Vauquelin,  who  found  that  100  parts  of  it  consist  of  water  SO,  albumen  7, 
white  fatty  matter  4-53,  red  fatty  matter  0-7,  osmazome  1'12,  phosphorus  1-5, 
and  acids,  salts,  and  sulphur  5-15.  (Annals  of  Phil,  i.) 

M.  Couerbe  has  discovered  in  the  brain  a  large  quantity  of  cholcsterine. 
He  also  states  that  the  brain  of  persons  of  sound  intellect  usually  contains 
from  2  to  2£  per  cent,  of  phosphorus :  in  the  brain  of  idiots  the  phosphorus 
is  about  1  or  1£  per  cent.,  and  in  maniacs  it  amounts  to  3,  4,  and  4£  per  cent, 

The  presence  of  albumen  accounts  for  the  partial  solubility  of  the  brain 
in  cold  water,  and  for  the  solution  being  coagulated  by  heat,  acids,  alcohol, 
and  by  the  metallic  salts  which  coagulate  other  albuminous  fluids.  By  act- 
ing upon  cerebral  matter  with  boiling  alcohol,  the  fatty  principles  and  osma- 
zome are  dissolved,  and  the  solution  in  cooling  deposites  the  white  fatty 
matter  in  the  form  of  crystalline  plates.  On  expelling  the  alcohol  by  evapo- 
ration, and  treating  the  residue  with  cold  alcohol,  the  osmazome  is  taken  up, 
and  a  fixed  oil  remains  of  a  reddish-brown  colour,  and  an  odour  like  that  of 
the  brain  itself,  though  much  stronger.  These  two  species  of  fat  differ  little 
from  each  other,  and  both  yield  phosphoric  acid  when  deflagrated  with  nitre. 


SECTION    VIL 


PUTREFACTION. 

WHEN  dead  animal  matter  is  exposed  to  air,  moisture,  and  a  moderate 
temperature,  it  speedily  runs  into  putrefaction,  during  which  every  trace  of 
its  original  texture  disappears,  and  products  of  a  very  offensive  nature  are 
generated.  The  most  favourable  temperature  is  from  60°  to  80°  or  90°  F. 
Below  50°  the  process  takes  place  tardily,  and  at  32°  it  is  wholly  arrested ; — 
a  fact,  which  is  clearly  evinced  by  the  circumstance  that  the  bodies  of  ani- 
mals, which  have  been  buried  in  snow  or  ice,  are  found  unchanged  after  a 
long  series  of  years.  The  necessity  of  a  certain  degree  of  moisture  is  shown 
by  the  facility  with  which  the  most  perishable  substances  may  be  preserved 
when  quite  dry.  The  preservation  of  smoked  meat  is  chiefly  owing  to  this 
cause;  and,  for  a  like  reason,  animals  buried  in  the  dry  sand  of  Arabia  and 
Egypt  have  remained  for  years  without  change. 

It  is  probable  that  when  moisture  and  warmth  concur,  putrefaction  in 
animal  matter  which  has  not  been  heated  to  212°  will  take  place  indepen- 
dently of  atmospheric  influence.  But  when  animal  matter  has  been  boiled, 
and  is  then,  without  subsequent  exposure,  completely  protected  from  air,  it 
may  be  preserved  for  years,  even  though  moist  and  in  a  temperature  favour- 
able to  putrefaction.  The  practice  of  preserving  every  kind  of  food,  both 
animal  and  vegetable,  now  a  subject  of  extensive  commercial  enterprise,  af- 
fords ample  demonstration  of  this  statement.  The  mode  generally  adopted 
is  the  following.  Into  a  tin  vessel  is  placed  any  kind  of  food,  such  as  joints 
of  meat,  fish,  game,  and  vegetables,  dressed  for  the  table;  and  into  the  inter- 


PUTREFACTION.  61 T 

slices  is  poured  a  rich  gravy,  care  being  taken  to  have  the  vessel  completely 
full.  A  tin  cover,  with  a  small  aperture,  is  then  carefully  fixed  by  solder; 
and  while  the  whole  vessel  is  perfectly  full,  and  at  the  temperature  of  2J2°, 
the  remaining  aperture  is  closed.  As  the  ingredients  within  cool  and  con- 
tract, a  vacuum  is  formed  if  the  operation  has  been  skilfully  conducted,  and 
the  sides  of  the  vessel  are  in  consequence  slightly  pressed  in  by  the  weight 
of  the  atmosphere.  In  this  state  the  vessel  may  be  sent  to  tropical  climates 
without  fear  of  putrefaction ;  and  the  most  delicate  food  of  one  country  be 
thus  eaten  in  its  original  perfection,  in  a  distant  region,  many  months  or 
even  years  after  its  preparation. 

For  reasons  formerly  mentioned,  animal  matters  commonly  undergo  pu- 
trefaction more  rapidly  than  those  which  are  derived  from  the  vegetable 
kingdom  (page  475) ;  but  they  are  not  all  equally  disposed  to  putrefy.  The 
acid  and  fatty  principles  are  less  liable  to  this  change  than  urea,  fibrin,  and 
other  analogous  substances.  The  chief  products  to  which  their  dissolution 
gives  rise  are  water,  ammonia,  carbonic  acid,  and  sulphuretted,  phosphuretf 
ted,  and  carburetted  hydrogen  gases. 


52* 


PART   IV. 

ANALYTICAL  CHEMISTRY. 


THE  object  of  this  Fourth  Part  of  the  volume  is  to  serve  as  a  guide  to 
those  who  purpose  merely  to  skim  the  surface  of  analytical  chemistry.  To 
render  it  a  complete  manual  was  never  intended:  to  do  so  would  be  foreign 
to  the  plan  of  these  Elements,  and  would  encroach  on  space  which  is  devoted 
to  another  purpose.  This  part  is,  therefore,  left  without  addition ;  and  this 
is  done  the  more  willingly,  because  I  hope  at  some  future  period  to  embody 
the  results  of  my  own  experience  in  analytical  chemistry  in  a  separate  vo- 
lume. To  those  who  are  much  occupied  in  the  laboratory  I  would  recom- 
mend the  following  works : — The  Analytical  Chemistry  of  Rose,  either  in 
the  original  German  or  the  translation  by  Griffith,  for  processes  of  analysis  ; 
— Faraday's  work  on  Chemical  Manipulation,  for  the  delicate  operations  of 
research  ; — and  Reid's  Elements  of  Practical  Chemistry,  for  experiments  of 
demonstration.  The  few  following  directions  are  thrown  into  three  sec- 
tions, which  treat  of  the  analysis  of  mixed  gases,  of  minerals,  and  of  mine- 
ral waters. 


SECTION   I. 

ANALYSIS  OF  MIXED  GASES. 

Analysis  of  Air  or  of  Gaseous  Mixtures  containing  Oxygen. — Of  the  various 
processes  by  which  oxygen  gas  may  be  withdrawn  from  gaseous  mixtures, 
and  its  quantity  determined,  none  are  so  convenient  and  precise  as  the  me- 
thod by  means  of  hydrogen  gas.     In  performing  this  analysis,  a  portion  of 
atmospheric  air  is  carefully  measured  in  a  graduated  tube,  and  mixed  with 
a  quantity  of  hydrogen  gas  which  is  rather  more  than  sufficient  for  uniting 
with  all  the  oxygen  present.  The  mixture  is  then  introduced 
into  a  strong  glass  tube,  A,  called  Volta's  eudiometer,  shown 
in  the  annexed  wood-cut,  and  an  electric  spark  is  passed 
through  it  by  means  of  the  conducting  wires  B,  B,  fixed  into 
the  tube.    The  aperture  is  closed  by  the  thumb  at  the  mo- 
ment  of  detonation,  in  order  to  prevent  any  of  the  mixture 
from  escaping.     The  total  diminution  in  volume,  divided  by 
three,  indicates  the  quantity  of  oxygen  originally  contained 
in  the  mixture.    This   operation  may  be  performed  in  a  ______ 

trough  either  of  water  or  mercury. 

Instead  of  electricity,  spongy  platinum  may  be  employed  for  causing  the 
union  of  oxygen  and  hydrogen  gases;  and  while  its  indications  are  very 
precise,  it  has  the  advantage  of  producing  the  effect  gradually  and  without 
detonation.  The  most  convenient  mode  of  employing  it  with  this  intention 
is  the  following.  A  mixture  of  spongy  platinum  and  pipe-clay,  in  the  pro- 
portion of  about  three  parts  of  the  former  to  one  of  the  latter,  is  made  into 
a  paste  with  water,  and  then  rolled  between  the  fingers  into  a  globular  form. 


ANALYSIS  OF  MIXED  GASES. 


619 


In  order  to  preserve  the  spongy  texture  of  the  platinum,  a  little  hydrochlo- 
rate  of  ammonia  is  mixed  with  the  paste  ;  and  when  the  ball  has  become 
dry,  it  is  cautiously  ignited  at  the  flame  of  a  spirit-lamp.  The  sal  ammo- 
niac,  escaping  from  all  parts  of  the  mass,  gives  it  a  degree  of  porosity  which 
is  peculiarly  favourable  to  its  action.  The  ball,  thus  prepared,  should  be 
protected  from  dust,  and  be  heated  to  redness  just  before  being  used.  To 
insure  accuracy,  the  hydrogen  employed  should  be  kept  over  mercury  for  a 
few  hours  in  contact  with  a  platinum  ball  and  a  piece  of  caustic  potassa. 
The  first  deprives  it  of  traces  of  oxygen  which  it  commonly  contains,  and 
the  second  of  moisture  and  hydrosulphuric  acid.  The  analysis  must  be  per- 
formed in  a  mercurial  trough.  The  time  required  for  completely  removing 
the  oxygen  depends  on  the  diameter  of  the  tube.  If  the  mixture  is  contained 
in  a  very  narrow  tube,  the  diminution  does  not  arrive  at  its  full  extent  in  less 
than  twenty  minutes  or  half  an  hour;  while  in  a  vessel  of  an  inch  in  diame- 
ter, the  effect  is  complete  in  the  course  of  five  minutes. 

Mode  of  determining  the  Quantity  of  Nitrogen  in  Gaseous  Mixtures. — 
As  atmospheric  air,  which  has  been  deprived  of  moisture  and  carbonic  acid, 
consists  of  oxygen  and  nitrogen  only,  the  proportion  of  the  latter  is  of 
course  known  as  soon  as  that  of  the  former  is  determined.  The  only 
method,  indeed,  by  which  chemists  are  enabled  to  estimate  the  quantity  of 
this  gas,  is  by  withdrawing  the  other  gaseous  substances  with  which  it  is 
mixed. 

Mode  of  determining  the  Quantity  of  Carbonic  Acid  in  Gaseous  Mixtures. 
— When  carbonic  acid  is  the  only  acid  gas  which  is  present,  as  in  analyzing 
atmospheric  airt  in  the  ultimate  analysis  of  organic  compounds,  and  in  most 
other  analogous  researches,  the  process  for  determining  its  quantity  is  ex- 
ceedingly simple;  for  it  consists  merely  in  absorbing  that  gas  by  lime-water 
or  a  solution  of  caustic  potassa.  This  is  easily  done  in  the  course  of  a  few 
minutes  in  an  ordinary  graduated  tube ;  or  it  may  be  effected 
almost  instantaneously  by  agitating  the  gaseous  mixture  with 
the  alkaline  solution  in  Hopes's  eudiometer.  This  apparatus,  as 
represented  in  the  figure,  is  formed  of  two  parts: — of  the  bot- 
tie  A,  capable  of  containing  about  twenty  drachms  of  fluid,  and 
furnished  with  a  well  ground  stopper  C ;  and  of  the  tube  B,  of 
the  capacity  of  one  cubic  inch,  divided  into  100  equal  parts, 
and  accurately  fitted  by  grinding  to  the  neck  of  the  bottle. 
The  tu.be,  full  of  gas,  is  fixed  into  the  bottle  previously  filled 
with  lime-water,  and  its  contents  are  briskly  agitated.  The 
stopper  C  is  then  withdrawn  under  water,  when  a  portion  of 
liquid  rushes  into  the  tube,  supplying  the  place  of  the  gas 
which  has  disappeared;  and  the  process  is  afterwards  repeated, 
as  long  as  any  absorption  ensues. 

The  eudiometer  of  Dr.  Hope  was  originally  designed  for  ana- 
lyzing air  or  other  similar  mixtures,  the  bottle  being  filled  with  a 
solution  of  hydrosulphuret  of  potassa  or  lime,  or  some  liquid  capa- 
ble of  absorbing  oxygen.  To  the  employment  of  this  apparatus 
it  has  been  objected,  that  the  absorption  is  rendered  slow  by  the 
partial  vacuum  which  is  continually  taking  place  within  it,  an 
inconvenience  particularly  felt  towards  the  close  of  the  process, 
in  consequence  of  the  eudiometric  liquor  being  diluted  by  the 
admission  of  water.  To  remedy  this  defect,  Dr.  Henry  has 
substituted  a  bottle  of  elastic  gum  for  that  of  glass,  as  in  the 
annexed  wood-cut,  by  which  contrivance  no  vacuum  can  occur. 
From  the  improved  method  of  analyzing  air,  however,  this 
instrument  is  now  rarely  employed  in  eudiometry ;  but  it  may 
be  used  with  advantage  for  absorbing  carbonic  acid  or  simi- 
lar gases,  and  is  particularly  useful  for  the  purpose  of  demon- 
stration. 


620  ANALYSIS   OF   MINERALS. 

Mode  of  Analyzing  Mixtures  of  Hydrogen  and  other  Inflammable  Gases.—- 
When  hydrogen  is  mixed  with  nitrogen,  oxygen,  or  atmospheric  air,  its 
quantity  is  easily  ascertained  by  causing  it  to  combine  with  oxygen  either 
by  means  of  platinum  or  the  electric  spark.  If,  instead  of  hydrogen,  any 
other  combustible  substance,  such  as  carbonic  oxide,  light  carburetted  hy- 
drogen, or  olefiant  giis,  be  mixed  with  nitrogen,  the  analysis  is  easily  effect- 
ed by  adding  a  sufficient  quantity  of  oxygen,  and  detonating  the  mixture  by 
electricity.  ,The  diminution  in  volume  indicates  the  quantity  of  hydrogen 
contained  in  the  gas,  and  from  the  carbonic  acid,  which  may  then  be  re- 
moved by  an  alkali,  the  quantity  of  carbon  is  inferred. 

An  elegant  mode  of  converting  carbonic  oxide  into  carbonic  acid  gas, 
suggested  by  Dr.  Henry,  is  to  mix  it  with  rather  more  than  its  own  volume 
of  nitrous  oxide  gas,  and  fire  the  mixture  by  the  electric  spark.  The  two 
gases  mutually  decompose  each  other,  and  give  rise  to  nitrogen  and  car- 
bonic acid  gases.  For  each  measure  of  carbonic  oxide  one  of  carbonic  acid 
is  produced,  one  measure  of  nitrous  oxide  is  decomposed,  and  one  of  nitro- 
gen evolved.  By  employing  a  slight  excess  of  pure  carbonic  oxide,  the 
composition  of  nitrous  oxide  may  be  ascertained.  The  mixed  gases  occupy 
the  same  space  after  deflagration  as  before  it;  and  the  carbonic  acid  gas 
occupies  the  same  space  as  the  nitrous  oxide  which  had  been  present.  (An? 
nals  of  Philosophy,  xxiv.  301.) 

When  olefiant  gas  is  mixed  with  other  inflammable  gases,  its  quantity  is 
easily  determined  by  an  elegant  and  simple  process  proposed  by  Dr.  Henry. 
It  consists  in  mixing  100  measures,  or  any  convenient  quantity  of  the 
gaseous  mixture,  with  an  equal  volume  of  chlorine  in  a  vessel  covered 
with  a  piece  of  cloth  or  paper,  so  as  to  protect  it  from  light ;  and  after 
an  interval  of  about  ten  minutes,  the  excess  of  chlorine  is  removed  by  a 
solution  of  lime  or  potassa.  The  loss  experienced  by  the  gas  to  be  analyzed, 
indicates  the  exact  quantity  of  olefiant  gas  which  it  had  contained. 

This  method  is  not  correct  when  the  vapours  of  the  dense  hydrocarburets 
are  present.  Thus  when  oil  gas  is  mixed  with  chlorine,  the  diminution  in 
volume  arises  from  the  removal  of  the  combustible  vapours  as  well  as  of 
olefiant  gas ;  for  the  former  are  equally  disposed  as  the  latter  to  unite  with 
chlorine. 

In  mixtures  of  hydrogen,  carburetted  hydrogen,  and  carbonic  oxide,  the 
analytic  process  is  exceedingly  difficult  and  complicated,  and  requires  all 
the  resources  of  the  most  refined  chemical  knowledge,  and  all  the  address  of 
an  experienced  analyst.  The  most  recent  information  on  this  subject  will 
be  found  in  Dr.  Henry's  Essay  in  the  Philosophical  Transactions  for  1824. 


SECTION   II. 


ANALYSIS  OF  MINERALS. 

As  the  very  extensive  nature  of  this  department  of  analytical  chemistry 
renders  a  selection  necessary,  I  shall  confine  my  remarks  solely  to  the  ana- 
lysis of  those  earthy  minerals  with  which  the  beginner  usually  commences 
his  labours.  The  most  common  constituents  of  these  compounds  are  silica, 
alumina,  iron,  manganese,  lime,  magnesia,  potassa,  soda,  and  carbonic  and 
sulphuric  acids ;  and  I  shall,  therefore,  endeavour  to  give  short  directions 
for  determining  the  quantity  of  each  of  these  substances. 

In  attempting  to  separate  two  or  more  fixed  principles  from  each  other, 
the  first  object  of  the  analytical  chemist  is  to  bring  them  into  a  state  of 
solution.  If  they  are  soluble  in  water,  this  fluid  is  preferred  to  every  other 
menstruum  ;  but  if  not,  an  acid  or  any  convenient  solvent  may  be  employed, 


ANALYSIS   OF   MINERALS.  621 

In  many  instances,  however,  the  substance  to  be  analyzed  resists  the  action 
even  of  the  acids,  and  in  that  case  the  following  method  is  adopted: — The 
compound  is  first  crushed  by  means  of  a  hammer  or  steel  mortar,  and  is 
afterwards  reduced  to  an  impalpable  powder  in  a  mortar  of  agate :  it  is 
then  intimately  mixed  with  three,  four,  or  more  times  its  weight  of  potassa, 
soda,  baryta,  or  their  carbonates ;  and,  lastly,  the  mixture  is  exposed  in  a 
crucible  of  silver  or  platinum  to  a  strong  heat.  During  the  operation,  the 
alkali  combines  with  one  or  more  of  the  constituents  of  the  mineral;  and, 
consequently,  its  elements  being  disunited,  it  no  longer  resists  the  action  of 
the  acids. 

Analysis  of  Marble  or  Carbonate  of  Lime. — This  analysis  is  easily  made 
by  exposing  a  known  quantity  of  marble  for  about  half  an  hour  to  a  full 
white  heat,  by  which  means  the  carbonic  acid  gas  is  entirely  expelled,  so 
that  by  the  loss  in  weight,  the  quantity  of  each  ingredient,  supposing  the 
marble  to  have  been  pure,  is  at  once  determined.  In  order  to  ascertain  that 
the  whole  loss  is  owing  to  the  escape  of  carbonic  acid,  the  quantity  of  this 
gas  may  be  determined  by  a  comparative  analysis.  Into  a  small  flask  con- 
taining hydrochloric  acid  diluted  with  two  or  three  parts  of  water,  a  known 
quantity  of  marble  is  gradually  added,  the  flask  being  inclined  to  one  side 
in  order  to  prevent  the  fluid  from  being  flung  out  of  the  vessel  during  the 
effervescence.  The  diminution  in  weight  experienced  by  the  flask  and  its 
contents,  indicates  the  quantity  of  carbonic  acid  which  has  been  expelled. 

Should  the  carbonate  suffer  a  greater  loss  in  the  fire  than  when  decom- 
posed by  an  acid,  it  will  most  probably  be  found  to  contain  water.  This 
may  be  ascertained  by  heating  a  piece  of  it  to  redness  in  a  glass  tube,  the 
sides  of  which  will  be  bedewed  with  moisture,  if  water  is  present.  Its 
quantity  may  be  determined  by  causing  the  watery  vapour  to  pass  through 
a  weighed  tube  filled  with  fragments  of  the  chloride  of  calcium,  by  which 
the  moisture  is  absorbed. 

Separation  of  Lime,  and  Magnesia. — The  more  common  kinds  of  carbonate 
of  lime  frequently  contain  traces  of  silicious  and  aluminous  earths,  in  con- 
sequence of  which  they  are  not  completely  dissolved  in  dilute  hydrochloric 
acid.  A  very  frequent  source  of  impurity  is  carbonate  of  magnesia,  which 
is  often  present  in  such  quantity  that  it  forms  a  peculiar  compound  called 
magnesian  limestone.  The  analysis  of  this  substance,  so  far  as  respects 
carbonic  acid,  is  the  same  as  that  of  marble.  The  separation  of  the  two 
earths  may  be  conveniently  effected  in  the  following  manner.  The  solution 
of  the  mineral  in  muriatic  acid  is  evaporated  to  perfect  dryness  in  a  flat 
dish  or  capsule  of  porcelain,  and  after  redissolving  the  residuum  in  a  mode- 
rate quantity  of  distilled  water,  a  solution  of  oxalate  of  ammonia  is  added 
as  long  as  a  precipitate  ensues.  The  oxalate  of  lime  is  then  allowed  to  sub- 
side, collected  on  a  filter,  converted  into  quicklime  by  a  white  heat,  and 
weighed ;  or  the  oxalate  may  be  decomposed  by  a  red  heat,  and  after  moist- 
ening the  resulting  carbonate  with  a  strong  solution  of  carbonate  of  ammo- 
nia, in  order  to  supply  any  particles  of  quicklime  with  carbonic  acid,  it 
should  be  dried,  heated  to  low  redness,  and  regarded  as  pure  carbonate  of 
lime.  To  the  filtered  liquid,  containing  the  magnesia,  a  mixture  of  pure 
ammonia  and  phosphate  of  soda  is  added,  when  the  magnesia  in  the  form 
of  the  ammoniaco-phosphate  is  precipitated.  Of  this  precipitate,  heated  to 
redness,  100  parts,  according  to  Stromeyer,  correspond  to  37  of  pure  mag- 
nesia. 

The  precipitation  of  magnesia  by  means  of  phosphoric  acid  and  am- 
monia, though  extremely  accurate  when  properly  performed,  requires  several 
precautions.  The  liquid  should  be  cold,  and  either  neutral  or  alkaline. 
The  precipitate  is  dissolved  with  great  ease  by  most  of  the  acids;  and 
Stromeyer  has  remarked  that  some  of  it  is  held  in  solution  by  carbonic 
acid  whether  free  or  in  union  with  an  alkali.  The  absence  of  carbonic  acid 
should,  therefore,  always  be  insured,  prior  to  the  precipitation,  by  heating 
the  solution  to  212°,  acidulating  at  the  same  time  by  hydrochloric  acid, 
should  an  alkaline  carbonate  be  present.  Berzelius  has  also  observed,  that 


622  ANALYSIS  OF  MINERALS. 

in  washing  the  ammoniaco-magnesian  phosphate  on  a  filter,  a  portion  of  the 
salt  is  dissolved  as  soon  as  the  saline  matter  of  the  solution  is  nearly  all  re- 
moved ;  that  is  to  say,  it  is  dissolved  by  pure  water.  Hence  the  edulcoration 
should  be  completed  by  water,  which  is  rendered  slightly  saline  by  hydro- 
chlorate  of  ammonia. 

Earthy  Sulphates. — The  most  abundant  of  the  earthy  sulphates  is  that  of 
lime,  the  analysis  of  which  is  easily  effected.  By  boiling  it  for  fifteen  or 
twenty  minutes  with  a  solution  of  twice  its  weight  of  carbonate  of  soda, 
double  decomposition  ensues;  and  the  carbonate  of  lime,  after  being  col- 
lected on  a  filter  and  washed  with  hot  water,  is  either  heated  to  low  redness 
to  expel  the  water,  and  weighed,  or  at  once  reduced  to  quicklime  by  a  white 
heat.  Of  the  dry  carbonate,  50  parts  correspond  to  28  of  lime.  The  alka- 
line solution  is  acidulated  with  hydrochloric  acid,  and  the  sulphuric  acid 
thrown  down  by  chloride  of  barium.  From  the  sulphate  of  baryta,  collected 
and  dried  at  a  red  heat,  the  quantity  of  acid  may  easily  be  estimated. 

The  method  of  analyzing  the  sulphate  of  strontia  and  baryta  is  some- 
what different.  "As  these  salts  are  difficult  of  decomposition  in  the  moist 
way,  the  following  process  is  adopted.  The  sulphate,  in  fine  powder,  is 
mixed  with  three  times  its  weight  of  carbonate  of  soda,  and  the  mixture  is 
heated  to  redness  in  a  platinum  crucible  for  the  space  of  an  hour.  The 
ignited  mass  is  then  digested  in  hot  water,  and  the  insoluble  earthy  carbo- 
nate collected  on  a  filter.  The  other  parts  of  the  process  are  the  same  as 
the  foregoing. 

Mode  of  analyzing  Compounds  of  Silica,  Alumina,  and  Iron. — Minerals, 
thus  constituted,  are  decomposed  by  an  alkaline  carbonate  at  a  red  heat,  in 
the  same  manner  as  sulphate  of  baryta.  The  mixture  is  afterwards  digested 
in  dilute  hydrochloric  acid,  by  which  means  all  the  ingredients  of  the  mine- 
ral, if  the  decomposition  is  complete,  are  dissolved.  The  solution  is  next 
evaporated  to  dryness,  the  heat  being  carefully  regulated  towards  the  close 
of  the  process,  in  order  to  prevent  any  of  the  chloride  of  iron,  the  volatility 
of  which  is  considerable,  from  being  dissipated  in  vapour.  By  this  operation, 
the  silica,  though  previously  held  in  solution  by  the  acid,  is  entirely  deprived 
of  its  solubility ;  so  that  on  digesting  the  dry  mass  in  water  acidulated  with 
hydrochloric  acid,  the  alumina  and  iron  are  taken  up,  and  the  silica  is  left 
in  a  state  of  purity.  The  silicious  earth,  after  subsiding,  is  collected  on  a 
filter,  carefully  edulcorated,  heated  to  redness,  and  weighed. 

To  the  clear  liquid,  containing  sesquioxide  of  iron  and  alumina,  a  solution 
of  pure  potassa  is  added  in  moderate  excess ;  so  as  not  only  to  throw  down 
those  oxides,  but  to  dissolve  the  alumina.  The  sesquioxide'  of  iron  is  then  col- 
lected on  a  filter,  edulcorated  carefully  until  the  washings  cease  to  have  an 
alkaline  reaction,  and  is  well  dried  on  a  sand-bath.  Of  this  hydrated  sesqui- 
oxide, 49  parts  contain  40  of  anhydrous  sesquioxide  of  iron.  But  the  most 
accurate  mode  of  determining  its  quantity  is  by  expelling  the  water  by  a  red 
heat.  This  operation,  however,  should  be  done  with  care ;  since  any  ad- 
hering particles  of  paper,  or  other  combustible  matter,  would  bring  the  iron 
into  the  state  of  black  oxide,  a  change  which  is  known  to  have  occurred  by 
the  iron  being  attracted  by  a  magnet. 

To  procure  the  alumina,  the  liquid  in  which  it  is  dissolved  is  boiled  with 
hydrochlorate  of  ammonia,  when  chloride  of  potassium  is  formed,  the  vola- 
tile alkali  is  dissipated  in  vapour,  and  the  alumina  subsides.  As  soon  as 
the  solution  is  thus  rendered  neutral,  the  hydrous  alumina  is  collected  on  a 
filter,  dried  by  exposure  to  a  white  heat,  and  quickly  weighed  after  removal 
from  the  fire. 

Separation  of  Iron  and  Manganese. — A  compound  of  these  metals  or  their 
oxides  may  be  dissolved  in  hydrochloric  acid.  If  the  iron  is  in  a  large  pro- 
portion compared  with  the  manganese,  the  following  process  may  be  adopted 
with  advantage.  To  the  cold  solution  considerably  diluted  with  water,  and 
acidulated  with  hydrochloric  acid,  carbonate  of  soda  is  gradually  added,  and 
the  liquid  is  briskly  stirred  with  a  glass  rod  during  the  effervescence,  in  order 
that  it  may  become  highly  charged  with  carbonic  acid.  By  neutralizing  the 


ANALYSIS  OF  MINERALS.  623 

solution  in  this  manner,  it  at  lengh  attains  a  point  at  which  the  sesquioxide 
of  iron  is  entirely  deposited,  leaving  the  liquid  colourless;  while  the  manga- 
nese, by  aid  of  the  free  carbonic  acid,  is  kept  in  solution.  The  iron,  after 
subsiding,  is  collecting  on  a  filter,  and  its  quantity  determined  in  the  usual 
manner.  The  filtered  liquid  is  then  boiled  with  an  excess  of  carbonate  of 
soda ;  and  the  precipitated  carbonate  of  manganese  is  collected,  heated  to 
full  redness  in  an  open  crncible,  by  which  it  is  converted  into  the  red  oxide, 
and  weighed.  This  method  is  one  of  some  delicacy  ;  but  in  skilful  hands  it 
affords  a  very  accurate  result.  It  may  also  be  employed  for  separating  iron 
from  magnesia  and  lime  as  well  as  from  manganese. 

But  if  the  proportion  of  iron  is  small  compared  with  that  of  manganese, 
the  best  mode  of  separating  it  is  by  succinate  of  ammonia  or  soda,  prepared 
by  neutralizing  a  solution  of  succinic  acid  with  either  of  those  alkalies. 
That  this  process  should  succeed,  it  is  necessary  that  the  iron  be  wholly  in 
the  state  of  sesquioxide,  that  the  solution  be  exactly  neutral,  which  may  easily 
be  insured  by  the  cautious  use  of  ammonia,  and  that  the  reddish-brown 
coloured  succinate  of  sesquioxide  of  iron  be  washed  with  cold  water.  Of  this 
succinate,  well  dried  at  a  temperature  of  212°,  90  parts  correspond  to  40  of 
the  sesquioxide.  From  the  filtered  liquid  the  manganese  may  be  precipitated 
at  a  boiling  temperature  by  carbonate  of  soda,  and  its  quantity  determined 
in  the  way  above  mentioned.  The  benzoate  may  be  substituted  for  succinate 
of  ammonia  in  the  preceding  process. 

It  may  be  stated  as  a  general  rule,  that  whenever  it  is  intended  to  preci- 
pitate iron  by  means  of  the  alkalies,  the  succinates,  or  benzoates,  it  is  essen- 
tial that  this  metal  be  in  the  maximum  of  oxidation.  It  is  easily  brought 
into  this  state  by  digestion  with  a  little  nitric  acid. 

Separation  of  Manganese  from  Lime  and  Magnesia. — If  the  quantity  of 
the  former  be  proportionally  small,  it  is  precipitated  as  a  sulphuret  by  hy. 
drosulphate  of  ammonia  or  sulphuret  of  potassium.  The  sulphuret  is  then 
dissolved  in  hydrochloric  acid,  and  the  manganese  thrown  down  as  usual 
by  means  of  an  alkali.  But  if  the  manganese  be  the  chief  ingredient,  the 
best  method  is  to  precipitate  it  at  once,  together  with  the  two  earths,  by  a 
fixed  alkaline  carbonate  at  a  boiling  temperature.  The  precipitate,  after 
being  exposed  to  a  low  red  heat  and  weighed,  is  put  into  cold  water  acidu- 
lated with  a  drop  or  two  of  nitric  acid,  when  the  lime  and  magnesia  will 
be  slowly  dissolved  with  effervescence.  Should  a  trace  of  the  manganese 
be  likewise  taken  up,  it  may  easily  be  thrown  down  by  hydrosulphate  of 
ammonia. 

Stromeyer  has  recommended  a  very  elegant  and  still  better  process  for  re- 
moving small  quantities  of  manganese  from  lime  and  magnesia.  The  solu- 
tion is  acidulated  with  nitric  or  hydrochloric  acid,  bicarbonate  of  soda  is  gra- 
dually added  in  very  slight  excess,  stirring  after  each  addition,  that  the  liquid 
may  be  charged  with  carbonic  acid,  and  a  solution  of  chlorine,  or  a  current 
of  the  gas,  is  introduced.  The  protoxide  of  manganese  is  converted  by  the 
chlorine  into  the  insoluble  hydrated  peroxide,  while  any  traces  of  lime  or 
magnesia,  which  might  otherwise  fall,  are  retained  in  solution  by  means  of 
carbonic  acid.  A  solution  of  chloride  of  soda  or  lime  is  in  fact  our  most 
delicate  test  for  small  quantities  of  manganese. 

Mode  of  analyzing  an  Earthy  Mineral  containing  Silica,  Iron,  Alumina, 
Manganese,  Lime,  and  Magnesia. — The  mineral,  reduced  to  fine  powder,  is 
ignited  with  three  or  four  times  its  weight  of  carbonate  of  potassa  or  soda, 
the  mass  is  taken  up  in  dilute  hydrochloric  acid,  and  the  silica  separated  in 
the  way  already  described.  To  the  solution,  thus  freed  from  silica  and  duly 
acidulated,  carbonate  of  soda,  or  still  better  the  bicarbonate,  is  gradually 
added,  so  as  to  charge  the  liquid  with  carbonic  acid,  as  in  the  analysis  of 
iron  and  manganese.  In  this  manner  the  iron  and  alumina  are  alone  pre- 
cipitated, substances  which  may  be  separated  from  each  other  by  means  of 
pure  potassa  (page  622).  The  manganese,  lime,  and  magnesia  may  then  be 
determined  by  the  processes  above  described. 

Analysis  of  Minerals  containing  a  Fixed  Alkali. — When  the  object  is  to 


624  ANALYSIS  OF  MINERALS. 

determine  the  quantity  of  fixed  alkali,  such  as  potassa  or  soda,  it  is  of  course 
necessary  to  abstain  from  the  employment  of  these  reagents  in  the  analysis 
itself;  and  the  beginner  will  do  well  to  devote  his  attention  to  the  alkaline 
ingredients  only.  On  this  supposition,  he  will  proceed  in  the  following  man- 
ner. The  mineral  is  reduced  to  a  very  fine  powder,  mixed  intimately  with 
six  times  its  weight  of  artificial  carbonate  of  baryta,  and  exposed  for  an  hour 
to  a  white  heat.  The  ignited  mass  is  dissolved  in  dilute  hydrochloric  acid, 
and  the  solution  evaporated  to  perfect  dryness.  The  soluble  parts  are  taken 
up  in  hot  water  ;  an  excess  of  carbonate  of  ammonia  is  added ;  and  the  in- 
soluble matters,  consisting  of  silica,  carbonate  of  baryta,  and  all  the  consti- 
tuents of  the  mineral,  excepting  the  fixed  alkali,  are  collected  on  a  filter. 
The  clear  solution  is  evaporated  to  dryness  in  a  porcelain  capsule,  and  the 
dry  mass  is  heated  to  redness  in  a  crucible  of  platinum,  in  order  to  expel  the 
salts  of  ammonia.  The  residue  is  chloride  of  potassium  or  sodium. 

In  this  analysis,  it  generally  happens  that  traces  of  manganese,  and  some- 
times of  iron,  escape  precipitation  in  the  first  part  of  the  process;  and,  in 
that  case,  they  should  be  thrown  down  by  hydrosulphate  of  ammonia.  If 
neither  lime  nor  magnesia  is  present,  the  alumina,  iron,  and  manganese  may 
be  separated  by  pure  ammonia,  and  the  baryta  subsequently  removed  by  the 
carbonate  of  that  alkali.  By  this  method  the  carbonate  of  baryta  is  reco- 
vered in  a  pure  state,  and  may  be  reserved  for  another  analysis.  The  baryta 
may  also  be  thrown  down  as  a  sulphate  by  sulphuric  acid,  in  which  case  the 
soda  or  potassa  is  procured  in  combination  with  that  acid ;  but  this  mode  is 
objectionable,  because  the  sulphate  of  baryta  is  very  apt  to  retain  small 
quantities  of  sulphate  of  potassa. 

The  analysis  is  attended  with  considerable  inconvenience  when  magnesia 
happens  to  be  present;  because  this  earth  is  not  completely  precipitated  either 
by  ammonia  or  its  carbonate,  and,  therefore,  some  of  it  remains  with  the 
fixed  alkali.  The  best  mode  with  which  I  am  acquainted,  is  to  precipitate 
the  magnesia  by  phosphate  of  ammonia;  subsequently  separating  from  the 
filtered  solution  the  excess  of  phosphoric  acid  by  acetate  of  lead,  and  that  of 
lead  by  hydrosulphuric  acid.  The  acetate  of  the  alkali  is  then  brought  to 
dryness,  ignited,  and  by  the  addition  of  sulphate  of  ammonia  converted  into 
a  sulphate. 

In  the  preceding  account,  several  operations  have  been  alluded  to,  which, 
from  their  importance,  deserve  more  particular  mention.  The  process  of 
filtering,  for  example,  is  one  on  which  the  success  of  analysis 
materially  depends.  Filtration  is  effected  by  means  of  a  glass 
funnel  B,  into  which  a  filter  C,  of  nearly  the  same  size  and  form, 
made  of  white  bibulous  paper,  is  inserted.  For  researches  of  de- 
licacy, the  filter,  before  being  used,  is  macerated  for  a  day  or  two 
in  water  acidulated  with  nitric  acid,  in  order  to  dissolve  lime  and 
other  substances  contained  in  common  paper,  and  it  is  afterwards 
washed  with  hot  water  till  every  trace  of  acid  is  removed.  It  is 
next  dried  at  212°,  or  any  fixed  temperature  insufficient  to  de- 
compose it,  and  then  carefully  weighed,  the  weight  being  marked  upon  it 
with  a  pencil.  As  dry  paper  absorbs  hygrometric  moisture  rapidly  from  the 
atmosphere,  the  filter,  while  being  weighed,  should  be  inclosed  in  a  light  box 
made  for  the  purpose.  When  a  precipitate  is  collected  on  a  filter,  it  is  wash- 
ed with  pure  water  until  every  trace  of  the  original  liquid  is  removed.  It  is 
subsequently  dried  and  weighed  as  before,  and  the  weight  of  the  paper  sub- 
tracted from  the  combined  weight  of  the  filter  and  precipitate.  The  trouble 
of  weighing  the  filter  may  sometimes  be  dispensed  with.  Some  substances, 
such  as  silica,  alumina,  and  lime,  which  are  not  decomposed  when  heated 
with  combustible  matter,  may  be  put  into  a  crucible  while  yet  contained  in 
the  filter,  the  paper  being  set  on  fire  before  it  is  placed  in  the  furnace.  In 
these  instances,  the  ash  from  the  paper,  the  average  weight  of  which  is  de- 
termined by  previous  experiments,  must  be  subtracted  from  the  weight  of 
the  heated  mass. 

The  tests  commonly  employed  in  ascertaining  the  acidity  or  alkalinity  of 


ANALYSIS  OF  MINERAL  WATERS.  625 

liquids  are  litmus  and  turmeric  paper.  The  former  is  made  by  digesting  lit- 
mus, reduced  to  a  fine  powder,  in  a  small  quantity  of  water,  and  painting 
with  it  white  paper  which  is  free  from  alum.  Turmeric  paper  is  made  in  a 
similar  manner;  but  the  most  convenient  test  of  alkalinity  is  litmus  paper 
reddened  by  a  dilute  acid. 


SECTION   III. 

ANALYSIS  OF  MINERAL  WATERS. 

RAIN  water  collected  in  clean  vessels  in  the  country,  or  freshly  fallen  snow 
when  melted,  affords  the  purest  kind  of  water  which  can  be  procured  with- 
out having  recourse  to  distillation.  The  water  obtained  from  these  sources, 
however,  is  not  absolutely  pure,  but  contains  a  portion  of  carbonic  acid  and 
air,  absorbed  from  the  atmosphere.  It  is  remarkable  that  this  air  is  very 
rich  in  oxygen.  That  procured  from  snow  water  by  boiling  was  found  by 
Gay-Lussac  and  Humboldt  to  contain  34-8,  and  that  from  rain  water  32  per 
cent,  of  oxygen  gas.  From  the  powerfully  solvent  properties  of  water,  this 
fluid  no  sooner  reaches  the  ground  arid  percolates  through  the  soil,  than  it 
dissolves  some  of  the  substances  which  it  meets  with  in  its  passage.  Under 
common  circumstances  it  takes  up  so  small  a  quantity  of  foreign  matter,  that 
its  sensible  properties  are  not  materially  affected ;  and  in  this  state  it  gives 
rise  to  spring,  well,  and  river  water.  Sometimes,  on  the  contrary,  it  be- 
comes so  strongly  impregnated  with  saline  and  other  substances,  that  it  ac- 
quires a  peculiar  flavour,  and  is  thus  rendered  unfit  for  domestic  uses.  It  is 
then  know  by  the  name  of  mineral  water. 

The  composition  of  spring  water  is  dependent  on  the  nature  of  the  soil 
through  which  it  flows.  If  it  has  filtered  through  primitive  strata,  such  as 
quartz  rock,  granite,  and  the  like,  it  is  in  general  very  pure ;  but  if  it  meets 
with  limestone  or  gypsum  in  its  passage,  a  portion  of  these  salts  is  dissolved, 
and  communicates  the  property  called  hardness.  Hard  water  is  character- 
ized by  decomposing  soap,  the  lime  of  the  former  yielding  an  insoluble  com- 
pound with  the  margaric  and  oleic  acid  of  the  latter.  If  this  defect  is  owing 
to  the  presence  of  carbonate  of  lime,  it  is  easily  remedied  by  boiling,  when 
free  carbonic  acid  is  expelled,  and  the  insoluble  carbonate  of  lime  subsides. 
If  sulphate  of  lime  is  present,  the  addition  of  a  little  carbonate  of  soda,  by 
precipitating  the  lime,  converts  the  hard  into  soft  water.  Besides  these  in- 
gredients, the  chlorides  of  calcium  and  sodium  are  frequently  contained  in 
spring  water. 

Spring  water,  in  consequence  of  its  saline  impregnation,  is  frequently  unfit 
for  chemical  purposes,  and  on  these  occasions  distilled  water  is  employed. 
Distillation  may  be  performed  on  a  small  scale  by  means  of  a  retort,  in  the 
body  of  which  water  is  made  to  boil,  while  the  condensed  vapour  is  received 
in  a  glass  flask,  called  a  recipient,  which  is  adapted  to  its  beak  or  open  ex- 
tremity. This  process  is  more  conveniently  conducted,  however,  by  means 
of  a  still. 

The  different  kinds  of  mineral  water  may  be  conveniently  arranged  for 
the  purpose  of  description  in  the  six  divisions  of  acidulous >  alkaline,  chalybe- 
ate, sulphuretted,  saline,  and  silicious  spring's. 

1.  Acidulous  springs,  of  which  those  of  Seltzer,  Spa,  Pyrmont,  and  Carls- 
bad are  the  most  celebrated,  commonly  owe  their  acidity  to  the  presence  of 
free  carbonic  acid,  in  consequence  of  the  escape  of  which  they  sparkle  when 
poured  from  one  vessel  into  another.  Such  carbonated  waters  communicate 
a  red  tint  to  litmus  paper  before,  but  not  after  being  boiled,  and  the  redness 
disappears  on  exposure  to  the  air.  Mixed  with  a  sufficient  quantity  of  lime- 
water,  they  become  turbid  from  the  deposition  of  carbonate  of  lime.  They 

53 


626  ANALYSIS  OF  MINERAL  WATERS. 

frequently  contain  the  carbonates  of  lime,  magnesia,  and  protoxide  of  iron, 
in  consequence  of  the  facility  with  which  these  salts  are  dissolved  by  water 
charged  with  carbonic  acid. 

The  best  mode  of  determining  the  quantity  of  carbonic  acid  is 
by  heating  a  portion  of  the  water  in  a  flask,  as  in  the  annexed 
figure,  and  receiving  the  carbonic  acid,  by  means  of  a  bent  tube, 
in  a  graduated  jar  filled  with  mercury. 

2.  Alkaline  waters  are  such  as  contain  a  free   or  carbonated 
alkali,  and,  consequently,  either  in  their  natural  state  or  when 
concentrated  by  evaporation,  possess  an  alkaline  reaction. 

These  springs  are  rare.  The  best  instance  I  have  met  with  is 
in  water  collected  at  the  Furnas,  St.  Michael's,  Azores,  and  sent  to  the  Royal 
Society  of  Edinburgh  by  Lord  Napier.  These  springs  contain  carbonate  of 
soda  and  carbonic  acid,  and  are  almost  entirely  free  from  earthy  substances. 
Of  five  different  kinds  of  these  waters  which  I  examined,  the  greater  part 
also  contained  protoxide  of  iron,  hydrosulphuric  acid,  and  chloride  of  sodium. 

3.  Chalybeate  waters  are  characterized  by  a  strong  styptic,  inky  taste,  and 
by  striking  a  black  colour  with  the  infusion  of  gall-nuts.     The  iron  is  some- 
times combined  with  hydrochloric  or  sulphuric  acid;  but  most  frequently  it 
is  in  the  form  of  protocarbonate,  held  in  solution  by  free  carbonic  acid.     On 
exposure  to  the  air,  the  protoxide  is  oxidized,  arid  the  hj'drated  sesquioxide  sub- 
sides, causing  the  ochreous  deposite  so  commonly  observed  in  the  vicinity  of 
chalybeate  springs. 

To  ascertain  the  quantity  of  iron  contained  in  a  mineral  water,  a  known 
weight  of  it  is  concentrated  by  evaporation,  and  the  iron  is  brought  to  the 
state  of  sesquioxide  by  means  of  nitric  acid.  The  sesquioxide  is  then  precipi- 
tated by  an  alkali  and  weighed  ;  and  if  lime  and  magnesia  are  present,  it 
may  be  separated  from  those  earths  by  the  process  described  in  the  last 
section. 

Chalybeate  waters  are  by  no  means  uncommon ;  but  the  most  noted  in 
Britain  are  those  of  Tunbridge,  Cheltenham,  and  Brighton.  The  Bath  water 
also  contains  a  small  quantity  of  iron. 

4.  Sulphuretted  waters,  of  which  the  springs  of  Aix-la-Chapelle,  Harrow- 
gate,  and  MofFat  afford  examples,  contain  hydrosulphuric  acid,  and  are  easily 
recognized  by  their  odour,  and  by  causing  a  brown  precipitate  with  a  salt  of 
lead  or  silver.     The  gas  is  readily  expelled  by  boiling,  and  its  quantity  may 
be  inferred  by  transmitting  it  through  a  solution  of  acetate  of  oxide  of  lead, 
and  weighing  the  sulphuret  which  is  generated. 

5.  Those  mineral  springs  are  called    saline,  the    character  of  which  is 
caused  by  saline  compounds.     The   salts  which  are   most  frequently  con- 
tained in  these  waters  are  the  sulphates  and  carbonates  of  lime,  magnesia, 
and  soda,  and  the  chlorides  of  calcium,  magnesium,  and  sodium.     Potassa 
sometimes  exists  in  them,  and  Berzelius  has  found  lithia  in  the  spring  of 
Carlsbad.     It  has  lately  been  discovered  that  the  presence  of  hydriodic  acid 
in  small  quantity  is  not  unfrequent.*     As  examples  of  saline  water   may  be 
enumerated  the  springs  of  Epsom,  Cheltenham,  Bath,  Bristol,  Bareges,  Bux- 
ton,  Pitcaithly,  and  Toeplitz. 

The  first  object  in  examining  a  saline  spring  is  to  determine  the  nature  of 
its  ingredients.  Hydrochloric  acid  is  detected  by  nitrate  of  oxide  of  silver, 
and  sulphuric  acid  by  chloride  of  barium ;  and  if  an  alkaline  carbonate  be 
present,  the  precipitate  occasioned  by  either  of  these  tests  will  contain  a  car- 
bonate of  oxide  of  silver  or  baryta.  The  presence  of  lime  and  magnesia  may 
be  discovered,  the  former  by  oxalate  of  ammonia,  and  the  latter  by  phos- 
phate of  ammonia.  Potassa  is  known  by  the  action  of  chloride  of  platinum 
(page  280).  To  detect  soda,  the  water  should  be  evaporated  to  dryness,  the 
deliquescent  salts  removed  by  alcohol,  and  tiie  matter  insoluble  in  that  men- 

*  The  salt  spring  at  Theodorshalle,  in  Germany,  contains  a  considerable 
quantity  of  bromine.  See  note,  page  235. — Ed. 


ANALYSIS  OF  MINERAL  WATERS.  627 

struum  taken  up  by  a  small  quantity  of  water,  and  allowed  to  crystallize  by 
spontaneous  evaporation.  The  salt  of  soda  may  then  be  recognized  by  the 
rich  yellow  colour  which  it  communicates  to  flame  (page  284).  If  the  pre- 
sence of  hydriodic  acid  be  suspected,  the  solution  is  brought  to  dryness,  the 
soluble  parts  dissolved  in  two  or  three  drachms  of  a  cold  solution  of  starch, 
and  strong  sulphuric  acid  gradually  added  (page  231). 

Having  thus  ascertained  the  nature  of  the  saline  ingredients,  their  quan- 
tity may  be  determined  by  evaporating  a  pint  of  water  to  dryness,  heating 
to  low  redness,  and  weighing  the  residue.  In  order  to  make  an  exact  ana- 
lysis, a  given  quantity  of  the  mineral  water  is  concentrated  in  an  evaporating 
basin  as  far  as  can  be  done  without  causing  either  precipitation  or  crystal- 
lization, and  the  residual  liquid  is  divided  into  two  equal  parts.  Frond  one 
portion  the  sulphuric  and  carbonic  acids  are  thrown  down  by  nitrate  of  ba- 
ryta, and  after  collecting  the  precipitate  on  a  filter,  the  hydrochloric  acid  is 
precipitated  by  nitrate  of  oxide  of  silver.  The  mixed  sulphate  and  carbo- 
nate is  exposed  to  a  low  red  heat,  and  weighed ;  and  the  latter  is  then  dis- 
solved by  dilute  hydrochloric  acid,  and  its  quantity  determined  by  weighing 
the  sulphate.  The  chloride  of  silver,  of  which  143-42  parts  correspond  to 
36-42  of  hydrochloric  acid,  is  fused  in  a  platinum  spoon  or  crucible,  in  order 
to  render  it  quite  free  from  moisture.  To  the  other  half  of  the  concentrated 
mineral  water,  oxalate  of  ammonia  is  added  for  the  purpose  of  precipitating 
the  lime;  and  the  magnesia  is  afterwards  thrown  down  as  the  ammoniaco- 
phosphute,  by  means  of  ammonia  and  phosphoric  acid.  Having  thus  deter- 
mined the  weight  of  each  of  the  fixed  ingredients  excepting  the  soda,  the 
loss  of  course  gives  the  quantity  of  that  alkali ;  or  it  may  be  procured  in  a 
separate  state  by  the  process  described  in  the  foregoing  section. 

The  individual  constituents  of  the  water  being  known,  it  remains  to  de- 
termine the  state  in  which  they  were  originally  combined.  In  a  mineral 
water  containing  sulphuric  and  hydrochloric  acids,  lime,  and  soda,  it  is  ob- 
vious that  three  cases  are  possible.  The  liquid  may  contain  sulphate  of  lime 
and  chloride  of  sodium,  or  chloride  of  calcium  and  sulphate  of  soda;  or  each 
acid  may  be  distributed  between  both  the  bases.  It  was  at  one  time  sup- 
posed that  the  lime  must  be  in  combination  with  sulphuric  acid,  because  the 
sulphate  of  that  earth  is  left  when  the  water  is  evaporated  to  dryness.  This, 
however,  by  no  means  follows.  In  whatever  state  the  lime  may  exist  in  the 
original  spring,  gypsum  will  be  generated  as  soon  as  the  concentration 
reaches  that  degree  at  which  sulphate  of  lime  cannot  be  held  in  solution. 
The  late  Dr.  Murray,  who  treated  this  question  with  much  sagacity,  ob- 
serves that  some  mineral  waters,  which  contain  the  four  principles  above 
mentioned,  possess  higher  medicinal  virtues  than  cakn  be  justly  ascribed  to 
the  presence  of  sulphate  of  lime.  He  advances  the  opinion  that  alkaline 
bases  are  united  in  mineral  waters  with  those  acids  with  which  they  form 
the  most  soluble  compounds,  and  that  the  insoluble  salts  obtained  by  evapo- 
ration are  merely  products.  He,  therefore,  proposes  to  arrange  the  sub- 
stances determined  by  analysis  according  to  this  supposition.  (Edin.  Phil. 
Trans,  vii.)  To  this  practice  there  is  no  objection ;  but  it  is  probable  that 
each  acid  is  rather  distributed  between  several  bases  than  combined  exclu- 
sively with  either,  (page  129). 

Sea-water  may  be  regarded  as  one  of  the  saline  mineral  waters.  Its  taste 
is  disagreeably  bitter  and  saline,  and  its  fixed  constituents  amount  to  about 
three  per  cent.  Its  specific  gravity  varies  from  1-0269  to  1-0285.;  and  it 
freezes  at  about  28-5°  F.  According  to  the  analysis  of  Dr.  Murray,  10,000 
parts  of  water  from  the  Frith  of  Forth  contain  220-01  parts  of  common  salt, 
33-16  of  sulphate  of  soda,  42-08  of  muriate  of  magnesia,  and  7-84  of  muriate 
of  lime.  Wollaston  detected  potassa  in  sea-water,  which  likewise  contains 
small  quantities  of  hydriodic  and  hydrobromic  acids. 

The  water  of  the  Dead  Sea  has  a  far  stronger  saline  impregnation  than 
sea-water,  containing  one-fourth  of  its  weight  of  solid  matter.  It  has  a  pe- 
culiarly bitter,  saline,  and  pungent  taste,  and  its  specific  gravity  is  V211. 
According  to  the  analysis  of  Marcet,  100  parts  of  it  are  composed  Qf  mu.i 


628  ANALYSIS  OF  MINERAL  WATERS. 

riate  of  magnesia  10-246,  muriate  of  soda  10-36,  muriate  of  lime  3-92,  and 
sulphate  of  lime  0-054.  In  the  river  Jordan,  which  flows  into  the  Dead  Sea, 
Marcet  discovered  the  same  principles  as  in  the  lake  itself. 

6.  Silicious  waters  are  very  rare,  and  in  those  hitherto  discovered,  the 
silica  appears  to  have  been  dissolved  by  means  of  soda.  The  most  remark- 
able of  these  are  the  boiling  springs  of  the  Geyser  and  Rykum  in  Iceland,  a 
gallon  of  which,  according  to  the  analysis  of  Black,  contains  the  following 
substances  :  (Edinburgh  Philos.  Trans,  iii.  95.) 

Geyser.  Rykum. 

Soda    .            .            .        556  .  3 

Alumina           .            .2-8  .  0-29 

Silica  .            .             .       31-5  .  21-83 

Muriate  of  soda            .       14-42  .  16-96 

Sulphate  of  soda          .        8-57  .  7-53 

The  hot  springs  of  Pinnarkoon  and  Loorgootha  in  India  are  analogous  to 
the  foregoing.  A  gallon  of  the  water  yields  about  24  grains  of  solid  matter ; 
and  the  saline  contents,  sent  to  Dr.  Brewster  by  Mr.  P.  Breton,  I  found  to 
contain  21-5  per  cent,  of  silica,  19  of  chloride  of  sodium,  19  of  sulphate  of 
soda,  19  of  carbonate  of  soda,  pure  soda  5,  and  15-5  of  water.  (Edinburgh 
Journal  of  Science,  No.  xvii.  p.  97.) 

It  is  remarkable  that  nitrogen  gas  very  generally  occurs  in  hot  springs.  It 
was  found  by  Longchamp  in  various  hot  springs  of  France,  and  a  similar 
observation  has  been  made  by  Dr.  Daubeny.  Its  probable  source  is  clearly 
referable  to  atmospheric  air  contained  in  water,  which  air  has  been  deprived 
of  its  oxygen  by  chemical  changes  in  the  interior  of  the  earth, 


COMPOSITION   OF  MINERAL  WATERS, 


629 


TABLE, 

Showing  the  Composition  of  several  of  the  Principal  Mineral  Wafers. 
(From  Dr.  Henry's  Elements.) 

[N.  B.     The  temperature,  when  not  expressed,  is  to  be  understood  to  be 
49°  or  50°  Fahrenheit.] 

I.  CARBONATED  WATERS. 


SELTZER.     Bergmann. 
In  each  wine  pint. 
Carbonic  acid     .     .     .    .  *17  cub.  in. 

SPA.     Bergmann,. 
Specific  gravity  1-0010 
In  each  wine  pint. 
Carbonic  acid                       13  cub  in 

Specific  gravity  1-0027. 
Carbonate  of  soda    ....      4  grs. 
•  of  magnesia     .     .      5 
•  —of  lime    ....      3 
Chloride  of  sodium  .     ...    17 

29 

Carbonate  of  soda    .     .     .     1-5  grs. 
of  magnesia     .     4-5 
oflirne    ...     1-5 
Chloride  of  sodium  .     .     .     0'2 
Oxide  of  iron.    ....     0-6 

IK* 

CARLSBAD.     (Temperature  165°  F.) 
Berzelius. 
In  a  wine  pint. 
Carbonic  acid      .    .  '  t-  .     5  cub.  in. 

PYRMONT.     Bergmann. 
Specif  c  gravity  1-IOJ4. 
In  each  wine  pint. 

In  1000  parts  by  weight 

Sulphate  of  soda      .     .     2-58714  grs. 
Carbonate  of  soda    .          1-25200 

Carbonate  of  magnesia     .  10     grs. 

Chloride  of  sodium  .     .     1-04893 
Carbonate  of  lime             0-31219 

Sulphate  of  magnesia  .     .    5-5 

()f  limC                                                        g.£J 

Fluateofdo  0-00331 
Phosphate  of  do.      .     .    0-00039 
Carbonate  of  strontia  .     0-00097 
—  —  —  of  magnesia    0-18221 
Phosphate  of  alumina  .     0-00034 
Carbonate  of  iron    .     .     0-00424 
of  manganese,  a  trace 
Silica    .    .    .                  0-07504 

Chloride  of  sodium.     .     .     1-5 
Oxide  of  iron      ....    0*6 

30-6 
POUGES.     Hassenfratz. 

5-46656 

Carbonic  acid     ....  30  cub.  in. 

Carbonate  of  soda    .     .     .10    grs. 
*—  -  of  magnesia     .     1*2 
of  lime    .     .     .12 
Chloride  of  sodium  .     .     .    2-2 
Oxide  of  iron  2-5 

28-4 

53* 


630 


COMPOSITION  OF  MINERAL  WATERS. 


AIX-LA.CHAPELLE.     Bergmann. 

Temperature  143°. 

In  each  wine  pint. 


II.  SULPHURETTED  WATERS. 

MOFFAT.    Garnet. 


Nitrogen 0-5  cub.  in. 

Carbonic  acid  ....      0-6 


Sulphuretted  hydrogen   .   5-5  cub.  in.  Sulphuretted  hydrogen  .      1-2 


Carbonate  of  soda 
'  —  of  lime 

Muriate  of  soda  . 


12      grs.  Muriate  of  soda 
4-75 
5 


4-5 


21-75 


HARROWGATE  WATER. 
New  Well,  at  the  Crown  Inn. 


CHELTENHAM,  Sulphur  Spring. 
Brande  and  Parkes. 
Specific  gravity  1-0085. 
In  each  wine  pint. 

(West.  Quart.  Journ.  xv.  82.) 
Specific  gravity  1-01286  at  69°. 
One  wine  gallon  contains 
Sulphuretted  hydrogen  .  6'4    cub.  in. 
Carbonic  acid  ....  5-25 

Carbonic  acid  ....     1-5  cub.  in. 
Sulphuretted  hydrogen  .    25 

Carburetted  hydrogen   .  4'65 

Sulphate  of  soda  ....    23-5  grs. 
of  magnesia    .    .      5 
_  of  lime                        1*° 

22-8 
Also, 
Muriate  of  soda    ...     735      grs. 

Muriate  of  soda   ....     35 

of  lime    .     .     .       71-5 
—  —  —     —  ofmannesia            43 

65 

Bicarbonate  of  soda  .    .      14*75 
864-25 

f\i  j  Tir-7/ 

LEAMINGTON,  Sulphur  Water. 

Scudamore. 

Specific  gravity  1*0042. 
Sulphuretted  hydrogen,  quantity  not 
ascertained. 

In  each  pint. 
Muriate  of  soda     .         .     15       grs, 

of  lime    ';  .... 

-of  magnesia 


Sulphate  of  soda 
Oxide  of  iron 


7-96 
3-30 
11-60 
a  trace 


37-86 


Sp.  gr.  1-01324  at  60°. 
Sulphuretted  hydrogen   14      cub.  in. 
Carbonic  acid    .     .     .       4*25 
Azotic  gas    ....       8 
Carburetted  hydrogen       4-15 

30-4 

,  752      grs. 
.      6575 
.      29-2 
.      12-8 

859-75 


Also, 
Muriate  of  soda    .     . 

of  lime     .     . 

of  magnesia 

Bicarbonate  of  soda  . 


III.  SALINE  WATERS. 


SEIDLITZ.     Bergmann 

Specific  gravity  1-0060. 

In  a  pint. 

Carbonate  of  magnesia 

of  lime  .     . 

Sulphate  of  magnesia . 

. of  lime     .     . 

Muriate  of  magnesia  . 


in. 
)60. 

2-5  grs. 
0-8 
180 
5 
4-5 

192-8 

CHELTENHAM,  pure  saline. 
Parkes  and  Brande. 
In  each  pint. 
Sulphate  of  soda  ....    15    grs. 

of  lime    ....      4-5 
Muriate  of  soda    ....    50 

80-5 

COMPOSITION  OF  MINERAL  WATERS. 


631 


LEMINGTON,  saline.    Scudamore. 
Specific  gravity  1-0119. 
In  a  pint. 
Muriate  of  soda     .     .          53-75  grs. 

/->riirvnr»                                               Oft«fi/l 

BATH.    Solid  conte 
Scudamore. 

Muriate  of  lime     ... 

nts. 

1*2  grs. 
1-6 
95 
0-9 
0-2 
0-01985 
0-58015 

14~~ 

Sulphate  of  lime    .     .     . 
of  soda    .    •/5/l«^ 
Silica  .     .     .-..>>,  'j/»- 

Sulphate  of  soda     .     .             7-83 
Oxide  of  iron    ,    •  V.          a  trace 

110-38 

Oxide  of  iron    .... 
Loss,  partly  carb.  of  soda 

LEAMINGTON,  Lord  Aylesford's  Spring. 

Scudamore. 

Specific  gravity  1-0093. 
In  a  pint. 


Mr.  Cuff  has  found  both  potassa  and 
iodine  in  the  Bath  waters. 


Muriate  of  soda     .    .           12-25  grs. 
of  lime     .     .          28-24 
of  magnesia              5-22 
Sulphate  of  soda    .     .           32-96 
Oxide  of  iron     ...          a  trace 

BUXTON.    Scudamore. 
Sp.  gr.  at  60°  1-0006.    Temp.  82°. 
In  a  wine  gallon. 
Carbonic  acid     .     .         1*5     cub.  in, 

78-67 

Nitrogen  ....         4*64 

BRISTOL.    Carrick. 
Temp.  74°.    Sp.  gravity  1-00077. 
In  each  pint. 

Muriate  of  magnesia        .     0-58  grs. 
of  soda      .         .     2-40 
Sulphate  of  lime     .         .      0-60 
Carbonate  of  lirne  .          .    10-40 
Extractive  and  vegetable  7  Q.,-Q 
matter   3 

Carbonic  acid                      3'5  cub  in 

Loss      0-52 

Carbonate  of  lime       .               1-5  grs. 
Sulphate  of  soda    .     .               1-5 
—  of  lime    .    .               1-5 
Muriate  of  soda     .     .               0-5 
—  of  mairnesia 

15 

Or,  according  to  Dr.  Murray's  views. 
Sulphate  of  soda    .               0*63  grs. 

Muriate  of  lime      .               0-57 
of  soda                     1*80 

of  magnesia             0*58 

T^ATTT           TMl  lllinc 

Extract  and  loss     .                1-02 

Temp.  109°  to  117°.    Sp.  gr.  1-002. 
In  each  pint. 
Carbonic  acid  ....    1-2  cub.  in. 

15 

Carbonate  of  lime  ....     0-8  grs. 
Sulphate  of  soda     ....     1-4 
,.,..  .  of  lime                        9-3 

MATLOCK  BATH.    Scudamore. 
Temp.  68U.    Sp.  gr.  1-0003. 

Muriate  of  soda     ....    3-4 
Silica             0-2 

Free  carbonic  acid. 
Muriates  and    )  magnesia,  lime,  and 

Oxide  of  iron    .....    a  trace 

sulphates  off              soda? 

15-1 


in  very  minute  quantities  not  yet  as- 
certained. 


632 


COMPOSITION  OF  MINERAL  WATERS. 


IV.  CHALYBEATE  WATERS. 


TUNBRIDGE.    Scudamore. 
Specific  gravity  1-0007. 

In  each  gallon. 
Muriate  of  soda     . 

of  lime 

of  magnesia 


Sulphate  of  lime 
Carbonate  of  lime 
Oxide  of  iron    . 
Traces  of  manganese,  vege- 

table  fibre,  silica,  &c. 
Loss 


2-46  grs. 

0-39 

0-29 

1-41 

0-27 

2-22 

0-44 
0-13 

7-61 


CHELTENHAM.    Brande  and  Parkes. 
Specific  gravity  1.0092. 

In  a  pint. 
Carbonic  acid    .   "^  w .  - 

Carbonate  of  soda  .     . 
Sulphate  of  soda    •  ' . 

of  magnesia 

of  lime     !«    ^  7 

Muriate  of  soda      .     . 
Oxide  of  iron    .    .'    . 


BRIGHTON.    Marcet. 

Specific  gravity  1-00108. 

Carbonic  acid  gas    .     .     .  2^  cub.  in. 


Sulphate  of  iron  ....  1-80  grs. 

of  lime  ....  4-09 

Muriate  of  soda   ....  1-53 

of  magnesia    .     .  0'75 

Silica 0-14 

Loss 019 

8-5 


HARROWGATE,  Oddie's  Chalybeate. 

Scudamore. 
Specific  gravity  1  0053. 


.  2-5  cub.  in. 

All  BBVB  go. 

Muriate  of  soda     ^./ 

IWI 

. 

300-4 
99 

0'5  grs. 

iSpf 

9.9 

6 
2-5 
41-3 

Sulphate  of  lime     . 
Carbonate  of  do.     »  T 
of  magnesi 

a 

1-86 
6-7 
0-8 
2-4 

0-8 

73»3 

Residue,  chiefly  silica 

•4 
344-4fi 

APPENDIX. 


I  AM  indebted  to  Mr.  Graham  for  the  following  interesting  communication 
on  certain  hydrated  salts  and  peroxides,  and  on  phosphuretted  hydrogen. 

Various  classes  of  salts,  besides  the  arseniates  and  phosphates,  contain 
water  which  is  essential  to  their  constitution,  of  which  the  sulphates  of  mag- 
nesia, and  the  protoxides  of  zinc,  manganese,  iron,  copper,  nickel,  and  cobalt 
are  examples.  These  salts  crystallize  from  their  aqueous  solution  either  with 
seven  or  five  equivalents  of  water  (page  421),  one  of  which  is  in  a  state  of 
much  more  intimate  union  than  the  other  six  or  four.  Thus,  crystallized 
sulphate  of  oxide  of  zinc  loses  six  eq.  of  water  at  a  temperature  not  exceed- 
ing 65°  when  placed  over  sulphuric  acid  in  vacuo,  but  retains  one  eq.  of 
water  at  410°,  and  all  inferior  temperatures.  The  salt  may  be  viewed  as  a 
sulphate  of  oxide  of  zinc  and  water,  with  six  eq.  of  water  of  crystallization : 

a  constitution  which  may  be  expressed  as  follows,  HZnS^J-GH.  This  sul- 
phate of  zinc  may  be  made  anhydrous,  but  when  moistened  always  regains 
one  eq.  of  water,  slaking  with  the  evolution  of  heat.  This  last  equivalent  of 
water  appears  to  discharge  a  basic  function  in  the  constitution  of  the  salt, 
and  affords  a  clue  to  the  disposition  of  this  sulphate  to  form  double  sulphates. 
Sulphate  of  oxide  of  zinc  combines  with  sulphate  of  potassa,  and  forms  a 
well-known  double  salt  (page  428),  in  which  the  basic  water  of  the  sulphate 
of  zinc  is  replaced  by  sulphate  of  potassa  without  any  farther  change.  The 

formula  of  the  double  sulphate  is  (KS)ZnS  +  6H.  In  the  double  salt,  the 
whole  six  cq.  of  water  are  retained  with  somewhat  greater  force  than  in  the 
simple  sulphate,  but  even  the  double  salt  becomes  anhydrous  below  212°  in 
vacuo. 

The  sulphates  of  the  other  metallic  oxides  mentioned  are  quite  analogous 
to  sulphate  of  oxide  of  zinc  in  their  habitudes  with  water,  although  the 
particular  temperature  at  which  they  part  with  their  water  of  crystallization 
is  different  in  each.  The  analogy  holds  also  in  the  double  sulphates  of  those 
oxides. 

Of  hydrous  sulphate  of  lime  or  gypsum,  the  two  eq.  of  water  which  it 
contains  appear  to  be  essential,  and  are  retained  at  212°.  At  a  temperature 
not  exceeding  270°,  this  salt  becomes  anhydrous,  but  retains  the  power  of 
recombining  with  two  eq.  of  water  or  setting.  The  salt  is  then  in  a  peculiar 
condition.  Heated  above  300°  the  salt  becomes  properly  sulphate  of  lime, 
and  has  lost  the  disposition  to  combine  with  water. 

Berzelius  found  the  peroxide  of  tin  formed  by  the  action  of  nitric  acid  on 
metallic  tin  to  differ  in  certain  properties  from  the  same  compound  precipi- 
tated from  a  persalt  of  tin  by  an  alkali,  and  distinguished  the  first  under  the 
name  of  the  nitric  acid  peroxide  of  tin.  Both  peroxides  combine  with  hydro- 
chloric acid,  but  the  hydrochlorate  of  the  nitric  acid  peroxide  is  peculiar  in 
being  insoluble  in  water  strongly  acidulated  with  hydrochloric  acid.  The 
precipitated  peroxide  of  tin  assumes  all  the  properties  of  the  other  modifica- 
tion when  kept  for  some  time  in  boiling  water,  or  even  when  strongly  dried 
over  sulphuric  acid  in  vacuo  at  the  ordinary  temperature  of  the  atmosphere. 


634  APPENDIX. 

The  two  modifications  are  merely  different  hydrates  of  the  peroxide  of  tin, 
but  it  is  difficult  to  ascertain  what  proportion  of  water  is  essential  to  each. 
The  hydrates  combine  with  acids  and  form  two  sets  of  compounds;  but  ab- 
solute peroxide  of  tin  itself  (which  is  obtained  by  heating  the  hydrated  per- 
oxide to  redness)  has  no  disposition  to  combine  with  acids. 

Rose  has  shown  that  the  two  kinds  of  phosphuretted  hydrogen,  one  of 
which  is  spontaneously  inflammable  in  air,  and  the  other  not  so,  are  of  the 
same  composition  and  specific  gravity.  To  account  for  their  possessing  dif- 
ferent properties  recourse  is  had  to  the  doctrine  of  isomerism.  But  the  ob- 
servations of  Graham  indicate  the  existence  of  a  peculiar  principle  in  the 
spontaneously  inflammable  species,  which  principle  may  be  withdrawn,  and 
leaves  the  gas  not  spontaneously  inflammable. 

1.  The  peculiar  principle  is  withdrawn  by  charcoal,  which  has  been  heated 
to  redness  and  cooled  under  mercury,  in  the  proportion  of  l-500dth  part  of 
the  volume  of  the  gas,  with  a  contraction  of  not  more  than  1  per  cent.,  the 
greater  part  of  which  is  due  to  the  absorption  of  a  portion  of  the  gas  itself 
by  the  charcoal.     Baked  clay  has  a  similar  effect  upon  the  gas.     The  pecu- 
liar principle  appears  to  be  present  in  a  small,  almost  infinitesimal  propor- 
tion, and  cannot  be  separated  again  from  the  porous  absorbent  by  which  it 
has  been  taken  up. 

2.  The  vapours  of  essential  oils,  of  naphtha,   and  of  ether,  olefiant  gas, 
and  the  other  carburets  of  hydrogen,  destroy  the  peculiar  principle  in  a  short 
time,  or  prevent  its  action. 

3.  Concentrated  phosphorous  and  phosphoric  acids  withdraw  the  peculiar 
principle;  so  does  arsenic  acid,  but  the  last  quickly  reacts  on  the  phosphu- 
retted hydrogen  itself.     A  little  air  destroys  the  inflammability  of  a  large 
quantity  of  gas,  probably  from  the  phosphoric  acid  which  is  produced. 

4.  A  most  minute  quantity  of  potassium  or  of  the  amalgam  of  potassium 
.destroys  the  spontaneous  inflammability  without  occasioning  any  reduction 

of  volume  that  could  be  measured.     Caustic  potassa  has  not  this  effect. 

The  property  of  taking  fire  spontaneously  in  air  may  be  communicated  to 
phosphuretted  hydrogen,  which  does  not  possess  it,  by  a  very  slight  impreg- 
nation of  nitrous  acid  vapour.  The  quantity  of  nitrous  acid  vapour  should 
not  much  exceed  1  measure  to  1000  measures  of  the  gas:  when  the  propor- 
tion of  nitrous  acid  is  greater,  the  mixture  is  not  spontaneously  inflammable, 
but  becomes  so  on  diluting  it  with  phosphuretted  hydrogen.  The  gas  con- 
tinues spontaneously  inflammable  for  24  or  48  hours  over  water,  but  for  a 
shorter  period  when  kept  over  mercury.  Pure  nitric  oxide  impedes  the  oxi- 
dation of  phosphuretted  hydrogen,  and  cannot  be  substituted  for  the  nitrous 
acid.  The  addition  of  nitrous  acid  to  the  phosphuretted  hydrogen  may  be 
made  in  various  ways.  Commercial  sulphuric  acid,  diluted  with  three 
volumes  of  water  and  cooled,  contains  nitrous  acid,  which  it  imparts  to 
phosphuretted  hydrogen  agitated  in  a  phial  along  with  it.  Hence,  too,  the 
hydrogen  gas  evolved  at  the  beginning  of  the  action  of  sulphuric  acid  upon 
zinc,  often  suffices  for  making  phosphuretted  hydrogen  inflammable,  when 
added  to  the  extent  of  half  a  volume.  The  nitrous  acid  of  Dulong  may  be 
added  directly  to  phosphuretted  hydrogen  over  mercury  by  passing  it  up  in 
a  glass  spherule.  The  most  convenient  process,  however,  is  to  impregnate 
hydrogen  gas  first  with  nitrous  acid.  For  that  purpose,  to  a  three-ounce 
phial  add  a  drachm  of  nitric  acid  with  a  few  drops  of  the  nitrous  acid  of 
Dulong.  Fill  up  the  phial  with  water,  and  make  use  of  it  as  a  receiver  to 
collect  hydrogen  gas.  The  addition  to  phosphuretted  hydrogen  of  ^th  or  ^th 
of  its  volume  of  this  nitrous  hydrogen,  does  not  disturb  the  transparency  of 
that  gas,  but  renders  it  highly  inflammable.  A  greater  proportion  of  the 
nitrous  hydrogen  is  generally  injurious. 

Now,  phosphuretted  hydrogen,  made  inflammable  in  this  way,  has  a  great 
analogy  to  the  gas  procured  at  first  in  a  spontaneously  inflammable  state  by 
the  common  processes.  The  factitious  gas  is  deprived  of  its  spontaneous 
inflammability  by  porous  absorbents,  by  carburets  of  hydrogen,  by  amalgam 


APPENDIX.  635 

of  potassium,  but  not  by  phosphoric  acid.  Neither  gas  can  be  kept  over 
mercury  for  a  long-  period  without  losing  'its  spontaneous  inflammability. 

It  seems  probable,  from  the  action  of  potassium  and  the  carburets  of 
hydrogen  on  the  ordinary  spontaneously  inflammable  gas,  that  its  peculiar 
principle  is  an  oxygenated  body.  It  cannot  be  nitrous  acid,  but  it  may  be  a 

compound  of  phosphorus  and  oxygen,  P,  analogous  to  nitrous  acid.     In  all 

the  reactions  by  which  the  spontaneously  inflammable  phosphuretted  hydro- 
gen is  produced,  we  have  the  formation  of  compounds  of  phosphorus  and 

oxygen,  such  as  hypophosphorous  and  phosphoric  acids.  The  compound  P 
is  hypothetic,  however,  and  has  not  been  formed  directly,  although  the  com- 
plete  analogy  between  phosphuretted  hydrogen  and  ammonia  affords  a  pre- 
sumptive argument  of  its  possible  existence. 

Nitrous,  or  rather  hyponitrous,  acid  has  a  disposition  to  unite  with  other 
acids.  It  may,  therefore,  promote  the  oxidability  of  phosphuretted  hydrogen 
in  air,  by  uniting  with  the  resulting  acid  compound  of  phosphorus  and  oxy. 
gen ;  but  this  is  a  mere  conjecture. 


636 


TABLE  I. 

TABLE  of  the  elastic  Force  of  Aqueous  Vapour  at  different  Temperatures, 
expressed  in  Inches  of  Mercury. 


TEMP. 
Fahr. 

rorce  of  Vapour. 

TEMP. 
Fahr. 

Force  of  Vapour. 

TEMP. 
Fahr. 

Force  of  Vapour. 

Walton. 

Ure. 

Dalton. 

Ure. 

Dalton. 

Ure. 

32^ 

0200 

0-200 

79° 

0-971 

126° 

3-89 

33 

0207 

80 

1-00 

1-010 

127 

4-00 

34 

0-214 

81 

1-04 

128 

411 

35 

0-221 

82 

1-07 

129 

4-22 

36 

0-229 

83 

1-10 

130 

4-34 

4-366 

37 

0237 

84 

1-14 

131 

4-47 

38 

0-245 

85 

1-17 

1-170 

132 

4-60 

39 

0-254 

86 

1-21 

133 

4-73 

40 

0.263 

0-250 

87 

1-24 

134 

4-86 

41 

0273 

88 

1-28 

135 

500 

5-070 

42 

0-283 

89 

1-32 

136 

5-14- 

43 

0-294 

90 

1-36 

1-360 

137 

5-29 

44 

0-305 

91 

1-40 

138 

5-44 

45 

0-316 

92 

1-44 

139 

5-59 

46 

0-328 

93 

1-48 

140 

5-74 

5-770 

47 

0-339 

94 

1-53 

141 

5-90 

48 

0-351 

95 

1-58 

1-640 

142 

605 

49 

0-363 

96 

1-63 

143 

6-21 

50 

0-375 

0-360 

97 

1-08 

144 

6-37 

51 

0-388 

98 

1-74 

145 

6-53 

6-600 

52 

0-401 

99 

1-80 

146 

6-70 

53 

0-415 

100 

1-86 

1-860 

147 

6-87 

54 

0-429 

101 

1-92 

148 

7-05 

55 

0-443 

0-416 

102 

1-98 

149 

723 

56 

0-458 

103 

2-04 

150 

7-42 

7-530 

57 

0-474 

104 

2-11 

151 

7-61 

58 

0-490 

105 

2-18 

2-100 

152 

7-81 

59 

0-507 

106 

2-25 

153 

8-01 

60 

0-524 

0-516 

107 

2-32 

154 

8-20 

61 

0-542 

108 

2-39 

155 

840 

8-500 

62 

0-560 

109 

2-46 

156 

8-60 

63 

0578 

110 

2-53 

2-456 

157 

8-81 

£4 

0-597 

111 

2-60 

158 

9-02 

65 

0616 

0-630 

112 

2-68 

159 

9-24 

66 

0-635 

113 

2-76 

160 

9-46 

9.600 

67 

0-655 

114 

2-84 

161 

9-68 

68 

0-676 

115 

2-92 

2-820 

162 

9-91 

69 

0-698 

116 

3-00 

163 

10-15 

70 

0-721 

0-726 

117 

3-08 

164 

10-41 

71 

0-745 

118 

3-16 

165 

1068 

10-800 

72 

0-770 

119 

3-25 

166 

1096 

73 

0-796 

120 

3-33 

2-300 

167 

11-25 

74 

0-823 

121 

342 

168 

11-54 

75 

0851 

0-860 

122 

3-.50 

169 

1183 

76 

0-880 

123 

3-59 

170 

12-13 

12-050 

77 

0-910 

124 

3-69 

171 

12-43 

78 

0-940 

125 

3-79 

3-830 

172 

1273 

Table  1.  continued. 


637 


TEMP. 
Fahr. 

Force  of  Vapour 

TE31P. 

Fahr. 

Force  of  Vapour 

TEMP 
Fahr. 

Force  of  V^0"1"' 

Dalton 

Ure. 

Dalton. 

Ure. 

Dalton. 

Ure. 

173° 

13-02 

2240 

37-53 

275o 

83-13 

93-480 

174 

1332 

225 

38-20 

39-110 

276 

84-35 

175 

13-62 

13-550 

226 

38-89 

40-100 

277 

85-47 

97-800 

176 

13-92 

227 

39-59 

278 

86-50 

177 

14-22 

228 

40-30 

279 

87-63 

101-600 

178 

14-52 

229 

41-02 

280 

88-75 

101-900 

179 

14-83 

230 

41-75 

43-100 

!  281 

89-87 

104-400 

180 

1515 

15-160 

231 

42-49 

282 

90-99 

181 

15-50 

232 

43-24 

283 

92-11 

107-700 

182 

15-86 

233 

44-00 

284 

93-23 

183 

16-23 

234 

44-78 

46-800 

285 

94-35 

112-200 

184 

16-61 

235 

45-58 

47-220 

286 

95-48 

185 

17-00 

16-900 

236 

46-39 

287 

96-64 

114800 

186 

17-40 

237 

47-20 

288 

97-80 

187 

17-80 

238 

48-02 

50-300 

289 

98-96 

118-200 

188 

1820 

239 

48-84 

290 

100-12 

120-150 

189 

18-60 

240 

49-67 

51-700 

291 

101-28 

190 

19-00 

19-000 

241 

5050 

292 

102-45 

123-100 

191 

19-42 

242 

51-34 

53-600 

293 

103-63 

192 

19-86 

1  243 

52-18 

294 

104-80 

126-700 

193 

20-32 

244 

53-03 

295 

105-97 

129-000 

194 

20-77 

245 

53-88 

56-340 

296 

107-14 

195 

21-22 

21-100 

246 

54-68 

297 

108-31 

133-900 

196 

21-68 

247 

55-54 

298 

109-48 

137-400 

197 

22-13 

248 

56-42 

60-400 

299 

110-64 

198 

22-69 

249 

57-31 

300 

111-81 

139-700 

199 

23-16 

250 

58-21 

61-900 

301 

112-98 

200 

23-64 

23-600 

251 

59-12 

63-500 

302 

114-15 

144-300 

201 

24-12 

252 

60-05 

303 

115-32 

147-700 

202 

24-61 

253 

61-00 

304 

116-50 

203 

25-10 

254 

61-92 

66-700 

305 

117-68 

150-560 

204 

25-61 

1  255 

62-85  6725 

306 

118-86 

154-400 

205 

26-13 

25-900 

i  256 

63-76 

307 

120-03 

206 

26-66 

1  257 

64-82  69-800 

308 

121-20 

157-700 

207 

27-20 

258 

65-78 

309 

122-37 

208 

27-74 

259 

66-75 

310 

123-53 

161-300 

209 

28-29 

260 

67  73  72-300 

311 

12469 

164-800 

210 

28-84 

28-880 

261 

68-72 

312 

125-85  . 

167-000 

211 

2941 

262 

69-72 

75-900 

313 

127-00 

212 

30-00 

30-000 

263 

70-73 

314 

128-15 

213 

30-60 

264 

71-74 

77-900 

315 

129-29 

214 

31-21 

265 

72-76 

78-040 

316 

130-43 

215 

31-83 

266 

73-77 

317 

131-57 

216 

32-46 

33-400 

267 

74-79 

81-900 

318 

132-72 

217 

33-09 

268 

75-80 

319 

133-86 

218 

33-72 

269 

76-82 

S4-900 

320 

13500 

219 

34-35 

270 

77-85 

86-300 

321 

136-14 

220 

34-99 

35-540 

271 

77-89 

88-000 

322 

137-28 

221 

35-63 

36-700 

272 

79-94 

323 

138-42 

222 

36-25 

273 

80-98 

91-200 

324 

139-56 

223 

36-88 

274 

82-01 

325 

140-70 

54 


638 


APPENDIX. 


TABLE  II. 

•.  Z/re's  TABLE,  showing  the  elastic  Force  of  the  Vapours  of  Alcohol 
Ether,  Oil  of  Turpentine,  and  Petroleum  or  Naphtha,  at  different 
Temperatures,  expressed  in  Inches  of  Mercury. 


Ether. 

Alcohol  sp.gr.  0-813. 

Alcohol  sp.gr.  0813. 

Petroleum. 

Temp. 

Force  of 
Vapour. 

Temp 

Force  of 
Vapour. 

Temp. 

Force  of 
Vapour. 

Temp. 

Force  of 
Vapour. 

34° 

6-20 

32° 

0-40 

206° 

60-10 

316° 

30-00 

44 

8-10 

40 

0-56 

210 

65-00 

320 

31-70 

54 

10-30 

45 

0-70 

214 

69-30 

325 

34-00 

64 

10-00 

50 

0-86 

216 

7220 

330 

36-40 

74 

16-10 

55 

1-00 

220 

78-50 

335 

38-90 

84 

20-00 

60 

1-23 

225 

87-50 

340 

41-60 

94 

2470 

65 

1-49 

230 

94-10 

345 

44-10 

104 

3000 

70 

1-76 

232 

97-10 

350 

46-86 

105 

30-00 

75 

2-10 

236 

103-60 

355 

50-20 

110 

3254 

80 

2-45 

238 

106-90 

360 

53-30 

115 

35-90 

85 

2-93 

240 

111-24 

365 

56-90 

120 

39-47 

90 

3-40 

244 

118-20 

370 

60-70 

125 

43-24 

95 

3-90 

247 

122-10 

372 

61-90 

130 

47-14 

100 

4-50 

248 

126-10 

375 

64-00 

135 

51-90 

105 

5-20 

249-7 

131-40 

140 

56-90 

110 

6-00 

250 

132-30 

Oil  of  Turpentine. 

145 

62-10 

115 

7-10 

252 

138-60 

150 

67-60 

120 

8-10 

254-3 

143-70 

Force  of 

155 

73-60 

125 

9-25 

258-6 

151-60 

Temp. 

Vapour. 

1fift 

80-30 

130 

in.cn 

9RO 

1  ^^-9(1 

luu 

165 

86-40 

JLOU 

135 

1  U  DU 

12-15 

«6UU 

262 

1OO  £\J 

16140 

304° 

30-00 

170 

92-80 

140 

13-90 

264 

166-10 

307-6 

32-60 

175 

99-10 

145 

15-95 

310 

33-50 

180 

108-30 

150 

18-00 

315 

35-20 

185 

116-10 

155 

20-30 

320 

37-06 

190 

124-80 

160 

2260 

322 

37-80 

195 

133-70 

165 

25-40 

326 

40-20 

200 

142-80 

170 

28-30 

330 

42-10 

205 

151-30 

173 

30-00 

336 

45-00 

210 

166-00 

178-3 

33-50 

340 

4730 

180 

34-73 

343 

49-40 

182-3 

36-40 

347 

51-70 

185-3 

39-90 

350 

53-80 

190 

43-20 

354 

56-60 

193-3 

46-60 

357 

58-70 

196-3 

50-10 

360 

60-80 

200 

53-00 

362 

62-40 

APPENDIX. 


639 


TABLE  III. 

Dr.  Ure's  TABLE  of  the  Quantity  of  Oil  of  Vitriol,  of  sp.  gr,  1-8485,  and 
of  Anhydrous  Acid,  in  100  Parts  of  dilute  Sulphuric  Acid,  at  different 
Densities. 


liiquid. 

Sp.  Gr. 

Dry. 

^iquid. 

Sp.  Gr. 

Dry. 

Liquid. 

Sp.  Gr. 

Dry. 

100 

1-8485 

81-54 

66 

1-5503 

53-82 

32 

1-2334 

2609 

99 

1-8475 

80-72 

65 

1-5390 

53-00 

31 

1-2260 

25-28 

98 

1.8460 

7990 

64 

1-5280 

52-18 

30 

1-2184 

24-46 

97 

1-8439 

79-09 

63 

1-5170 

51-37 

29 

1-2108 

23-65 

96 

1-8410 

78-28 

62 

1-5066 

50-55 

28 

1-2032 

22-83 

95 

1-8376 

77-46 

61 

1-4960 

4974 

27 

1-1956 

22-01 

94 

1-8336 

76-65 

60 

1-4860 

48-92 

26 

1-1876 

21-20 

93 

1-8290 

75-83 

59 

1-4760 

48-11 

25 

1-1792 

2038 

92 

1-8233 

75-02 

58 

1-4660 

47-29 

24 

1-1706 

19-57 

91 

1-8179 

74-20 

57 

1-4560 

46-48 

23 

1-1626 

18-75 

90 

1-8115 

73-39 

56 

1-4460 

45-66 

22 

1-1549 

17-94 

89 

1-8043 

72-57 

55 

1-4360 

44-85 

21 

1-1480 

17-12 

88 

1-7962 

7175 

54 

1-4265 

44-03 

20 

1-1410 

16-31 

87 

1-7870 

7094 

53 

1-4170 

43-22 

19 

1-1330 

15-49 

86 

1-7774 

70-12 

52 

1-4073 

42-40 

18 

1-1246 

14-68 

85 

1-7673 

69-31 

51 

1-3977 

41-58 

ir 

1-1165 

13-86 

84 

1-7570 

68-49 

50 

1-3884 

40-77 

16 

1-1090 

13-05 

83 

1-7465 

67-68 

49 

1-3788 

3995 

15 

1-1019 

12  23 

82. 

1  7360 

6686 

48 

1-3697 

39-14 

14 

1-0953 

11-41 

81 

1-7245 

66-05 

47 

1-3612 

38-32 

13 

1-0887 

10-60 

80 

1-7120 

65-23 

46 

1-3530 

37-51 

12 

1-0809 

9-78 

79 

1-6993 

64-42 

45 

1-3440 

3669 

11 

1-0743 

8-97 

78 

1-6870 

63-60 

44 

1-3345 

3588 

10 

1-0682 

8-15 

77 

1  '6750 

6278 

43 

1-3255 

3506 

9 

1-0614 

7-34 

76 

1-6630 

61-97 

42 

1-3165 

34-25 

8 

1-0544 

6-52 

75 

1-6520 

61-15 

41 

1-3080 

33-43 

7 

1  -0477 

5-71 

74 

1-6415 

60-34 

40 

1-2999 

32-61 

6 

1  -0405 

4-89 

73 

1-6321 

59-52 

39 

1-2913 

31-80 

5 

1-0336 

4-08 

72 

1-6204 

5871 

38 

1-2826 

30-98 

4 

1-0268 

3-26 

71 

1-6090 

57-89 

37 

1-2740 

30-17 

3 

1-0206 

2-446 

70 

1-5975 

57-08 

36 

1-2654 

2935 

2 

1-0140 

1-63 

69 

1-5868 

56-26 

35 

1-2572 

38-54 

1 

1-0074 

0-8154 

68 

1-5760 

55-45 

34 

1-2490 

27'72 

67 

1-5648 

54-63 

33 

1-2409 

26-91 

640 


TABLE  IV. 

Dr.  Ure's  TABLE  of  the  Quantity  of  Real  or  Anhydrous  Nitric  Acid  in 
100  Parts  of  Liquid  Acid,  at  different  Densities. 


Specific 
Gravity. 

Real  Acid 
in  100  parts 
of  the  liquid. 

Specific 
Gravity. 

Real  Acid 
in  ]00  parts 
of  the  liquid. 

Specific 
Gravity. 

Real  Acid 
in  100  parts 
of  the  liquid. 

1-5000 

79700 

1-3783 

52-602 

1-1895 

26-301 

1-4980 

78903 

1-3732 

51-805 

1-1833 

25-504 

1-4960 

78-106 

1-3681 

51-068 

1-1770 

24-707 

1-4940 

77-309 

1-3630 

50211 

1-1709 

23-910 

1-4910 

76-512 

1-3579 

49-414 

1  -1648 

23-113 

1.4880 

75-715 

1-3529 

48-617 

1-1587 

22-316 

1-4850 

74918 

1-3477 

47-820 

1  1526 

21-519 

1-4820 

74-121 

1  -3427 

47-023 

1-1465 

20722 

1-4790 

73-324 

1-3376 

46-226 

1-1403 

19-925 

1-4760 

72-527 

1-3323 

45-429 

1-1345 

19-128 

1-4730 

71-730 

1-3270 

44-632 

1-1286 

18-331 

1-4700 

70-933 

1-3216 

43-835, 

1-1227 

17-534 

1-4670 

70-136 

1-3163 

43-038 

1-1168 

16-737 

1-4640 

69-339 

1-3110 

42-241 

1-1109 

15940 

1-4600 

68-542 

1  -3056 

41  -444 

1-1051 

15-143 

1-4570 

67-745 

1-3001 

40-647 

1-0993 

14-346 

1-4530 

66-948 

1-2947 

39-850 

1-0935 

13-549 

1-4500 

66-155 

1-2887 

39-053 

1-0878 

12-752 

1-4460 

65-354 

1-2826 

38-256 

1-0821 

11-955 

1-4424 

64-557 

1-2765" 

37-459 

1  -0764 

11-158 

1-4385 

63-760 

1-2705 

36-662 

1-0708 

10-361 

1-4346 

62-963 

1-2644 

35-865 

1-0651 

9-564 

1-4306 

62-166 

1-2583 

35-068 

1-0595 

8-767 

1-4269 

61-369 

1-2523 

34-271 

1-0540 

7-970 

1-4228 

60-572 

1  -2462 

33474 

1  0485 

7-173 

1-4189 

59-775 

1-2402 

32-677 

1  -0430 

6-376 

1-4147 

58-978 

1-2341 

31-880 

1-0375 

5-579 

1-4107 

58-181 

1-2277 

31-083 

1-0320 

4-782 

1-4065 

57-384 

1-2212 

30-286 

1-0267 

3985 

1-4023 

56-587 

1-2148 

29-489 

1-0212 

3-188 

1-3978 

55-790 

1  -2084 

28-692 

1  0159 

2391 

1-3945 

54-993 

1-2019 

27-895 

1-0106 

1594 

1-3882 

54-196 

1-1958 

27-098 

1  -0053 

0-797 

1-3833 

53-399 

fiii 


TABLE  V. 

TABLE  of  Lowitz  showing  the  Quantity  of  Absolute  Alcohol  in  Spirits  of 
different  Specific  Gravities. 


100  Parts 

Sp.  Gravity. 

llOO  Parts 

Sp.  Gravity. 

100  Parts 

Sp.  Gravity. 

Ale. 

Wat 

At  680 

At  0()o. 

Ale. 

Wat. 

At  680 

At  600. 

Ale. 

Wat. 

A  t6go 

A  1600. 

00 

0 

0-791 

0796 

66 

34 

0877 

0-881 

32 

68 

0-952 

0955 

99 

1 

0794 

0-798 

65 

35 

0-880 

0883 

31 

69 

0-954 

0-957 

98 

2 

0-797 

0-801 

64 

36 

0882 

0-886 

30 

70 

0-956 

0-958 

97 

3 

0-800 

0-804 

63 

37 

0-885 

0-889 

29 

71 

0957 

0-960 

96 

4 

0-803 

0-807 

62 

38 

0-887 

0-891 

28 

72 

0  959 

0-962 

95 

5 

0-805 

0-809 

61 

39 

0-889 

0-893 

27 

73 

0-961 

0-963 

94 

6 

0-808 

0-812 

60 

40 

0-892 

0-896 

26 

74 

0-963 

0-965 

93 

7 

0-811 

0-815 

59 

41 

0-894 

0898 

25 

75 

0965 

0967 

92 

8 

0-813 

0-817 

58 

42 

0-896 

0-900 

24 

76, 

0-966 

0-968 

91 

9 

0-816 

0-820 

57 

43 

0-899 

0.902 

23 

77 

0968 

0-970 

90 

10 

0-818 

0-822 

56 

44 

0-901 

0-904 

22 

78 

0-970 

0-972 

89 

11 

0821 

0-825 

55 

45 

0-903 

0-906 

21 

79 

0971 

0-973 

88 

12 

0823 

0-827 

:  54 

46 

0-905 

0908 

20 

80 

0-973 

0974 

87 

13 

0-826 

0-830 

53 

47 

0-907 

0'910 

19 

81 

0-974 

0-975 

86 

14 

0-828 

0-832 

52 

48 

0-909 

0912 

18 

82 

0-976 

0977 

85 

15 

0-831 

0-835 

51 

49 

0-912 

0-915 

17 

83 

0-977 

0-978 

84 

16 

0-834 

0-838 

50 

50 

0914 

0917 

16 

84 

0-978 

0979 

83 

17 

0-836 

0-840 

49 

51 

0-917 

0-920 

15 

85 

0  980 

0981 

82 

18 

0-839 

0-843 

48 

52 

0-919 

0-922 

14 

86 

0-981 

0-982 

81 

19 

0-842 

0-846 

47 

53 

0-921 

0924 

13 

87 

0-983 

0984 

80 

20 

0-844 

0  848 

46 

54 

0-923 

0-926 

12 

88 

0-985 

>986 

79 

21 

0-847 

0-851 

45 

55 

0-925 

0-928 

11 

89 

0-986 

0-987 

78 

22 

0-849 

0-853 

44 

56 

0-927 

0930 

10 

90 

0-987  0-988 

77 

23 

0-851 

0-855 

43 

57 

0930 

0933 

9 

91 

0-988  0-989 

76 

24 

0-853 

0-857 

42 

58 

0-932 

0935 

8 

92 

0-989  0-990 

75 

25 

0856 

0-860 

41 

59 

0-934 

0-937 

7 

93 

0  991  0-991 

74 

26 

0-859 

0-863 

40 

60 

0-936 

0939 

6 

94 

0-992  0992 

73 

27 

0-861 

0-865 

39 

61 

0-938 

0-941 

5 

95 

0-994 

72 

28 

0-863 

0-867 

38 

62 

0-940 

0-943 

4 

96 

0-995 

71 

29 

0.866 

0-870 

37 

63 

0-942 

0-945 

3 

97 

0-997 

70 

30 

0-868 

0-872 

36 

64 

0-944 

0-947 

2 

98 

0-998 

69 

31 

0-870 

0-874 

35 

65 

3-946 

0-949 

1 

99 

0-999 

68 

32 

0-872 

0-875 

34 

66 

3-948 

0-951 

0 

100 

1-000 

67 

33 

0-875  1 

0-879 

33 

67 

3950 

0-953 

54* 


642 


TABLE  VI. 


TABLE  showing  the  Specific  Gravity  of  Liquids,  at  the   Temperature  of 
55°  Fahr.  corresponding  to  the  Degrees  of  Baume's  Hydrometer. 

For  Liquids  lighter  than  Water. 


Deg. 

Sp.  Gr.  Deg. 

Sp.  Gr. 

Deg. 

Sp.  Gr 

Deg. 

Sp.  Gr. 

Deg. 

Sp.  Gr. 

10  = 

1.000 

17 

=  -949 

23 

=  -909 

29 

=  -874 

35 

=  -842 

11 

•990 

18 

•942 

24 

•903 

30 

•867 

36 

•837 

12 

•985 

19 

•935 

25 

•897 

31 

•861 

37 

•832 

13 

•977 

20 

•928 

26 

•892 

32 

•856 

38 

•827 

14 

•970 

21 

•922 

27 

•886 

33 

•852 

39 

•822 

15 

•963 

22 

•915 

28 

•880 

34 

•847 

40 

•817 

16 

•955 

For  Liquids  heavier  than  Water. 


Deg. 

Sp.  Gr. 

Deg. 

Sp.  Gr.l  Deg. 

Sp.  Gr. 

Deg. 

Sp.  Gr. 

Deg 

Sp.  Gr. 

0  = 

1-000 

15  = 

1-114 

30  = 

1-261 

45  = 

1-455 

60 

=  1-717 

3 

1-020 

18 

1-140 

33 

1-295 

48 

1-500 

63 

1-779 

6 

1-040 

21 

1-170 

36 

1-333 

51 

1-547 

66 

1-848 

9 

1-064 

24 

1-200 

39 

1-373 

54 

1-594 

69 

1-920 

12 

1-089 

27 

1-230 

42 

1-414       57 

1-659 

72 

2-000 

Mercaptan. — Professor  Zeise  of  Copenhagen  has  made  some  interesting 
researches  on  a  liquid  of  an  ethereal  character,  which  he  terms  mercaptan, 
from  its  energetic  action  on  peroxide  of  mercury  (corpus  mercurium  cap. 
tans).  When  sulphovinate  of  baryta  is  distilled  with  a  strong  solution  of 
protosulphuret  of  barium,  a  volatile  liquid  along  with  water  passes  over,  and 
sulphate  of  baryta  remains  in  the  retort,  there  being  no  other  residue  when 
the  ingredients  are  in  atomic  proportion.  The  ethereal  product,  which  is 
formed  on  the  surface  of  water,  consists  of  two  compounds,  separable  by  care- 
ful distillation,  one  termed  thialic  ether  (Qttov  sulphur),  and  the  other  mereap- 
tan.  The  latter  is  generated  in  still  larger  quantity  by  the  action  of  a  sul- 
phovinate with  bisulphuret  of  barium,  or  with  hydrosulphuret  of  barium 
(page  460) ;  but  in  no  case  is  the  theory  of  its  formation  complete,  owing  to 
the  simultaneous  production  of  thialic  ether,  the  composition  of  which  is  not 
yet  known. 

Mercaptan,  to  judge  of  the  facts  yet  ascertained,  consists  of  hydrogen 
united  with  a  compound  irnflammable  substance,  not  hitherto  obtained  in  a 
separate  state,  which  Zeise  calls  mercaptum  (corpus  mercurio  aptum)  from 
its  strong  affinity  for  mercury.  Like  cyanogen,  or  bisulphuret  of  cyanogen, 
it  combines  with  metals,  hydrogen,  and  doubtless  other  elements  ;  and  these 
compounds  are  called  mercaptides  or  mercapturets.  Mercaptan  is  a  mercap- 
turet  of  hydrogen.  Mercaptum  consists  of 


Sulphur 
Carbon  . 
Hydrogen 


32  2      2  eq. 

24-48     4  eq. 
5         5  eq. 


2S 
4C 
5H 


61-68     1  eq.          C4H5Sa 


Mercaptan  consists  of  one  eq.  of  mercaptum  and  one  eq.  of  hydrogen,  its 
symbol  being  H-f-C4H5Sa,  When  acted  on  by  potassium,  hydrogen  gas  is 
evolved,  and  mercapturet  of  potassium  is  formed.  With  the  peroxide  of  mer- 


643 

cury  it  acts  violently,  yielding"  water  and  a  white  crystalline  solid,  bimer- 
capturet  of  mercury,  which  may  be  decomposed  by  hydrosulphuric  acid, 
and  then  yields  bisulphuret  of  mercury  and  mercaptan.  In  fact,  mercapturn 
and  mercaptan  are  related  to  each  other,  and  apparently  to  many  other 
bodies,  like  cyanogen  and  hydrocyanic  acid.  ^fSjgaf&P 

Pure  mercaptan  is  best  prepared  by  decomposing  bimercapturet  of  mer- 
cury with  hydrosulphuric  acid.  It  is  a  colourless  liquid,  of  a  highly  pene- 
trating odour,  analogous  to  assafetida  and  garlic,  and  of  an  ethereal  saccha- 
rine taste.  It  retains  its  liquid  form  at  — 8°,  boils  at  143^°,  and  has  a 
specific  gravity  at  59°  of  0-842.  It  is  neutral  to  test-paper,  dissolves  in  ether 
and  alcohol  almost  in  all  proportions,  but  is  sparingly  soluble  in  water  (An. 
de  Ch.  et  de  Ph.  Iv.  87). 

Mellon. — When  bisulphuret  of  cyanogen,  quite  dry,  is  heated,  a  quantity 
of  sulphur  and  bisulphuret  of  carbon  are  developed  and  expelled ;  while  a 
lemon-yellow  powder  remains,  composed  of  six  eq.  of  carbon  and  four  eq.  of 
nitrogen.  It  bears  a  red  heat  without  change,  but  at  higher  temperatures 
is  resolved  into  pure  cyanogen  and  nitrogen  gases.  It  unites  directly  with 
chlorine  and  potassium  when  heated  with  them,  and  in  its  chemical  rela- 
tions appears  to  belong  to  the  same  class  of  bodies  as  cyanogen.  It  is  inso- 
luble in  water  and  alcohol.  When  digested  in  nitric  acid,  it  is  dissolved  and 
decomposed,  being  resolved,  with  scarcely  any  escape  of  binoxide  of  nitro- 
gen, into  ammonia  and  a  new  acid  termed  cyanilic  acid,  which  crystallizes 
from  the  solution  on  cooling.  The  crystals  of  cyanilic  acid  contain  21  per 
cent,  of  water,  which  may  be  expelled  by  heat,  and  the  acid  itself  has  pre- 
cisely the  same  composition  as  cyanuric  acid,  but  its  equivalent  is  twice  as 
great. 

Liebig,  the  discoverer  of  these  compounds,  has  in  the  same  essay  with 
them  (An.  de  Ch.  et  de  Ph.  Iv.  5.)  described  the  four  following  substances. 

Melam.— This  substance  is  formed  by  distilling  dry  hydrosulphocyanate 
of  ammonia,  or  what  amounts  to  the  same,  a  mixture  of  sal  ammoniac  and 
sulphocyanuret  of  potassium.  The  products  are  ammonia,  bisulphuret  of 
carbon,  hydrosulphuric  acid,  and  melam,  which  remains  in  the  retort,  mixed 
with  chloride  of  potassium  and  the  excess  of  sal  ammoniac.  By  levigating 
and  washing  the  residue,  the  melam  is  obtained  pure  in  the  form  of  a  yel- 
low powder.  When  heated  cautiously,  it  is  resolved  into  mellon,  ammonia, 
and  some  other  volatile  product.  By  digestion  with  nitric  acid  it  yields 
cyanuric  acid,  and  cyanic  acid  is  generated  when  it  is  fused  with  potassa. 
It  consists  of  twelve  eq.  of  carbon,  nine  eq.  of  hydrogen,  and  eleven  eq.  of 
nitrogen. 

Melamine. — It  is  generated  when  melam  is  boiled  with  hydrochloric  acid 
or  with  a  solution  of  pure  potassa,  or  when  mellon  is  boiled  with  that  alkali, 
ammonia  being  always  generated  at  the  same  time.  The  melamine  being  of 
sparing  solubility  in  water,  separates  in  colourless  crystals,  the  form  of 
which  is  a  rhombic  octohedron  when  perfect.  They  are  insoluble  in  alcohol 
and  ether. 

Melamine  has  no  alkaline  reaction  with  test-paper,  but  it  unites  with  all 
the  acids,  forming  well-crystallized  salts  with  them,  and  displaces  ammonia 
and  several  metallic  oxides  from  acids.  Melamine  is  thus  a  remarkable  in- 
stance of  the  artificial  production  of  an  alkaline  base.  It  is  composed  of  six 
eq.  of  carbon,  six  eq.  of  nitrogen,  and  six  eq.  of  hydrogen,  the  sum  of  these 
quantities  being  the  combining  quantity  of  melamine. 

Ammeline. — This  substance  is  generated  and  held  in  solution  by  the  al- 
kali, when  melam  is  boiled  in  a  solution  of  potassa ;  and  it  is  thrown  down 
as  a  white  precipitate  when  the  liquid  is  neutralized  by  acetic  acid.  It  is  in- 
soluble in  water,  alcohol,  and  ether,  but  it  is  dissolved  by  the  fixed  caustic 
alkalies  and  most  of  the  acids.  It  acts  towards  the  latter  as  a  base,  though 
in  a  less  distinct  manner  than  melamine.  It  is  composed  of  six  eq.  of  car- 
bon, five  eq.  of  hydrogen,  five  eq.  of  nitrogen,  and  two  eq.  of  oxygen. 

Ammelide. — Melamine,  as  also  melam,  is  resolved  by  strong  sulphuric 


644  APPENDIX. 

acid  into  arnmelide  arid  ammonia,  and  on  mixing  alcohol  with  the  solution, 
the  arnmelide  is  thrown  down  as  a  white  powder.  It  is  also  formed  by  boil- 
ing melamine  in  strong  nitric  acid  until  the  solution  is  complete.  Ammelide 
consists  of  twelve  eq.  of  carbon,  nine  eq.  of  hydrogen,  nine  eq.  of  nitrogen, 
and  six  eq.  of  oxygen. 

Carburetted  Hydrogen  in  the  Atmosphere. — M.  Boussinghault  has  proved 
that  in  the  air  of  Paris  a  small  quantity  of  hydrogen,  rarely  amounting  to 
1  in  10,000  measures,  is  present,  either  free  or  in  combination.  The  fact 
was  proved  by  passing  a  large  quantity  of  air  previously  dried  by  chloride 
of  calcium  and  sulphuric  acid  with  scrupulous  care,  through  a  red-hot  tube 
filled  with  turnings  of  metallic  copper,  when  a  small  quantity  of  water  was 
always  generated,  This  experiment  he  purposes  repeating  on  the  Alps.  He 
suspects  the  hydrogen  to  be  combined  with  carbon;  because  Saussure  has 
observed  that  air  deprived  of  carbonic  acid  gas,  and  then  mixed  with  hydro. 

fen  gas  and  detonated,  always  contained  traces  of  carbonic  acid.  (L'Institut, 
3  August,  1834.) 

Benzin. — Mitscherlich  has  noticed  that  when  benzoic  acid  is  distilled  with 
an  excess,  such  as  3  times  its  weight,  of  slaked  lime,  the  ticid  is  entirely  re- 
solved into  carbonic  acid,  which  unites  with  lime,  and  Faraday's  bicarbu- 
ret  of  hydrogen,  to  which  Mitscherlich  has  given  the  name  of  benzin.  The 
change  is  such  that 

1  eq.  hydrous  benzoic  acid         2      2  eq.  benzin  2(3H-f-6C) 

14C-T-6H-I-4O  -^     and  2  eq.  carbonic  acid   2(C+2O). 

Peligot  has  obtained  a  similar  result  by  distilling  hydrated  berizoate  of 
lime;  but  when  the  anhydrous  salt  is  used,  the  change  is  necessarily  some- 
what different,  and  a  volatile  liquid  called  benzone  passes  over,  carbonate  of 
lime  remaining  in  the  retort.  In  this  case 

1  eq.  anhydrous  benzoic  acid       3      1  eq.  benzone  13C-f-5H-f  O 

14C4-5H+3O  -^     and  1  eq.  carbonic  acid        C-+-2O. 

By  heating  benzone  with  lime  it  may  be  deprived  of  all  its  oxygen,  with 
production  of  carbonic  acid  and  naphthaline.  (L'Institut,  19  July,  1834.) 
These  phenomena  are  obviously  due  to  a  play  of  affinities  leading  to  the  pro- 
duction of  carbonic  acid. 

Mitscherlich  has  described,  under  the  name  of  sulpho-benzide,  a  com- 
pound formed  by  the  action  of  strong  sulphuric  acid  on  benzin,  the  reaction 
being  such  that 

2  eq.  benzin  .  .  .  2(3H+6C)  3  1  eq.  sulpho-benzide  5H-j-12C-J-S-f-20 
and  1  eq.  sulphuric  acid  S-j-30  -^  and  1  eq.  water  .  .  .  H-J-O. 

Strong  nitric  acid  acts  on  benzin  in  a  similar  manner.  (Mitscherlich's 
Lehrbuch  der  Chernie.) 

Naphtha. — -Reichenbach,  of  Blansko,  is  of  opinion  that  native  naphtha  is 
essentially  the  same  fluid  as  oil  of  turpentine,  and  contends  that  the  former 
is  not  generated  during  the  slow  changes  by  which  wood  is  converted  into 
coal,  but  existed  originally  in  the  wood  itself; — -that,  in  fact,  naphtha  is  the 
oil  of  turpentine  of  antediluvian  pine  forests.  This  view  is  founded  on  the 
close  similarity  in  the  properties  of  naphtha  and  oil  of  turpentine.  He  ob- 
tained naphtha  from  coal  by  distillation  at  212°.  Naphtha  is  certainly  not 
generated  by  heat  applied  to  beds  of  coal  in  the  same  manner  as  bituminous 
matter  is  generated  during  the  formation  of  coal-gas;  for  native  naphtha  is 
free  from  the  products  which  characterize  the  latter,  and  is  quite  different 
from  coal-tar  naphtha,  with  which  it  has  been  thought  identical.  (L'Institut, 
7  June,  1834). 

Xanthic  and  Hydroxantliic  Acid — When  bisulphuret  of  carbon  is  agitated 


APPENDIX,  645 

with  a  solution  of  pure  potassa  in  strong-  alcohol,  the  alkalinity  of  the  liquid 
disappears ;  and  on  exposing1  the  solution  to  a  temperature  of  32°,  colourless 
acicular  crystals  are  deposited  which  acquire  a  yellow  tint  on  exposure  to 
the  air.  Zeise,  who  first  prepared  this  salt  in  1822  (Annals  of  Phil.  N.  S.  iv.), 
supposed  it  to  consist  of  potassa  united  with  an  hydracid,  the  radical  of  which 
he  believed  to  be  a  sulphuret  of  carbon.  To  the  radical  of  this  hydracid  he 
applied  the  term  xanthoge.n  (from  £*v6o?  yellow,  and  yew*®  I  generate),  ex- 
pressive of  its  tendency  to  form  yellow  compounds;  arid  to  the  acid  he  gave 
the  name  of  hydroxanthic  acid.  He  has  since  substituted  the  name  of  xan- 
thic  acid,  from  finding-  that  it  contains  oxygen  as  one  of  its  elements.  He 
supposes  it  to  contain  the  elements  of  one  eq.  of  alcohol,  and  two  eq.  of 
bisulphuret  of  carbon;  but  its  real  nature  has  not  yet  been  satisfactorily 
determined. 

Xanthic  acid  is  a  colourless  oily  fluid,  heavier  than  water,  of  a  strong  pe- 
culiar odour,  and  a  taste  at  first  acrid  and  acid,  but  followed  by  bitterness 
and  astring-ency.  It  reddens  litmus  paper,  but  afterwards  bleaches  it.  It  is 
insoluble  in  water,  and  is  prepared  by  the  action  of  dilute  sulphuric  or  hy- 
drochloric acid  on  xanthate  of  potassa.  It  possesses  little  permanency,  be- 
ing decomposed  by  the  action  of  the  atmosphere;  and  at  a  heat  short  of  212° 
it  is  resolved  into  bisulphuret  of  carbon  and  an  inflammable  gas. 

Transmission  of  Heat  through  Solids  and  Liquids. — Melloni  has  proved 
that  solids  and  liquids  differ  in  transmissibility  to  the  rays  of  heat,  just  as 
they  differ  in  their  action  on  light.  This  may  be  expressed  by  the  terms 
transcalent  and  intranscalent  (trans  through,  caleo  I  heat),  or  diathermanous 
and  adiathermanous  (fta,  through,  Qt£{ua.tva>  I  heat),  corresponding  to  the 
adjectives,  transparent  and  opaque,  as  applied  to  light.  The  principal  conclu- 
sions flowing  from  his  researches  are  the  following : — 

1.  Though  transcalent  bodies  are  also  in  general  more  or  less  transparent, 
the  only  known  exceptions  being  opaque  black   glass  and  black  mica,  yet 
the  transcalency  and  transparency  of  a  substance  are  not  in  the  same  pro- 
portion.    Rock-salt  is  far  more  transcalent  than   glass  of  far  greater  trans- 
parency.    Chloride  of  sulphur  of  a  reddish-brown  tint  is  more  transcalent 
than  nut  or  olive  oil  of  a  light  yellow  colour,  and  these  than  the  purest  ether, 
alcohol,  and  water ;  while  their  transparency  is  in  the  opposite  order. 

2.  Radiant  heat,  falling   perpendicularly  on  laminse  of  transcalent  bodies 
having  parallel  surfaces,  suffers  in  all   the  same  degree  of  reflection,  which 
amounts  to  39-1000ths  of  the  incident  rays  on  entering,  and  37-1000ths  on 
leaving-  the  lamina. 

3.  Transcalent  bodies  differ  in  the  degree  of  their  transcalency.     Rock- 
salt  is  the  only  known   substance  which  is  perfectly  diatherrnanous :  heat 
from  any  source  falling  on  a  lamina  of  pure  rock-salt  with  parallel  faces  is 
not  at  all  absorbed,  all  the  rays  which  are  not  reflected  being  directly  trans- 
mitted ;  and  this  is  true  whether  the  lamince  be  thick  or  thin.     The  result 
is  different  with  other  transcalent  bodies,  which  always  absorb  a  portion  of 
the  incident  rays.     Of  100  rays  of  heat  from  the  same  source  successively 
incident  on  laminae   of  equal  thickness   of  rock-salt,  alum,  flint-glass,  and 
crown-glass,  the  transmitted  rays  were  92,  12,  65,  and  49.     Of  100  rays 
similarly  incident  on  strata  of  water,  chloride  of  sulphur,  bisulphuret  of  car- 
bon, ether,  and  alcohol,  the  transmitted  rays  were  11,  63,63,  21,  and  15. 
The  rays  transmitted  through  similar  laminae  of  coloured  glass  were  53  per 
cent,  with  violet  glass,  47  with  red,  34  with  yellow,  33  with  blue,  and  26 
with  green  glass. 

4.  In  glass  and  liquids  those  are  most  transcalent  which  have  the  greatest 
refractive  power  in   regard  to  light.     This  is  shown  in  No.  3,  where  only 
11  per  cent,  of  the  incident  heat  passed  through  water,  and  63  through  a 
similar  stratum  of  bisulphuret  of  carbon.     But  the  law  is  not  applicable  to 
crystalline  bodies:  thus,  as  above,  92  per  cent,  of  the  incident  rays  find  their 
way  through  rock-salt,  and  12  per  cent,  through  a  similar  stratum  of  alum  ; 
while  their  refractive  powers  for  light  are  nearly  the  same. 

5.  The  quantity  of  radiant  heat  transmissible  through  glass  varies  with 


646  APPENDIX. 

the  temperature  of  the  source  from  which  the  rays  emanate.  Of  100  rays 
successively  incident  on  the  same  lamina  of  glass  from  the  four  sources,  an 
oil-lamp,  red-hot  platinum,  blackened  copper  heated  to  734°,  and  the  same 
copper  at  212°,  the  number  of  rays  transmitted  were  77,  57,  34,  and  12. 
Similar  results  were  formerly  obtained  by  De  la  Roche  (Biot's  Traite  de 
Physique,  iv.  638) ;  and  Melloni  has  proved  that  diathermanous  bodies  in 
general  act  in  the  same  manner  as  glass.  The  only  exception  is  rock-salt, 
which  is  equally  permeable  to  rays  from  sources  of  a  low  as  of  a  high  tern- 
perature.  It  further  appears  that  rays  from  the  same  source  pass  through 
some  media  more  readily  than  through  others.  It  seems  an  unavoidable  in- 
ference from  Melloni's  experiments,  that  radiant  heat  has  different  proper- 
ties according  to  its  source;  that  there  are  various  kinds  or  states  of  radiant 
heat,  just  as  there  are  various  kinds  or  states  of  light  as  manifested  by  its 
different  colours.  The  rays  of  light  which  have  passed  through  blue  glass 
will  pass  through  a  second  blue  glass  more  easily  than  through  glass  of  a 
different  colour,  though  otherwise  less  opaque  than  the  blue  glass.  So  do 
calorific  rays,  after  transmission  through  water,  pass  through  a  second  stra- 
tum of  water  more  readily  than  through  liquids  otherwise  more  diatherma- 
nous, such  as  alcohol  or  ether.  The  water  absorbs  many  rays  which  might 
have  had  the  power  to  pass  through  alcohol,  and  gives  passage  to  others 
which  can  penetrate  water,  but  not  alcohol.  Hence  it  should  follow,  as 
Melloni  has  proved,  that  comparatively  little  heat  is  absorbed  by  multiplying 
screens  of  the  same  material,  or  increasing  the  thickness  of  one  screen :  it 
is  the  first  screen,  or  the  side  of  one  screen,  next  the  radiating  substance,  by 
which  the  principal  absorption  of  heat  is  effected.  The  quantity  of  heat 
arrested  by  increasing  the  thickness  of  a  screen  decreases  in  a  very  rapid 
ratio.  These  facts  establish  between  heat  and  light  new  and  deeply  interest- 
ing relations,  which  will  be  referred  to  in  the  next  section. 

6.  Melloni  has  established  the  refrangibility  of  heat  by  diathermanous 
media.  Prior  observers  failed  of  obtaining  decisive  evidence  of  this  pro- 
perty, in  consequence  of  using  prisms  or  lenses  of  glass,  the  feeble  tran^ca- 
lency  of  which  unfits  it  for  such  an  inquiry;  but  with  a  prism  of  rock-salt 
Melloni  easily  demonstrated  the  general  principle,  and  proved  that  heat 
from  different  sources,  like  light  of  different  colours,  has  different  degrees 
of  refrangibility. 

Polarization  and  Double  Refraction  of  Heat.— These  properties  of  radiant 
heat,  which  Melloni  with  all  his  skill  vainly  attempted  to  demonstrate,  have 
lately  been  established  in  regard  to  heat,  both  from  luminous  and  non-lumU 
nous  sources,  by  Forbes,-r-a  discovery  of  great  interest,  as  drawing  still 
closer  the  relations  of  heat  and  light,  and  for  which  he  has  received  the 
well-merited  honour  of  the  Keith  medal,  awarded  by  the  Royal  Society  of 
Edinburgh.  Forbes  has  polarized  heat  by  all  the  methods  which  polarize 
light, — by  reflection,  refraction,  and  double  refraction.  He  also  depolarized 
heat;  and  as  this  occurs  only  as  a  consequence  of  double  refraction,  he 
thereby  proved  the  double  refraction  of  heat.  The  instrument  used  by 
Forbes  was  the  thermo-ir.ultiplier,  brought  to  such  extreme  delicacy  that  it 
is  supposed  sensible  to  l-1500ths  of  a  degree  of  Fahrenheit's  thermometer. 
(Phil.  Trans.  Ed.  1835.) 

Velocity  of  Electricity. — Some  elegant  and  most  ingenious  experiments 
have  been  made  by  Wheatstone  to  determine  the  velocity  of  electricity  (Phil. 
Trans.  1834).  His  principal  conclusions  are  the  following: — 

1.  The  velocity  of  electricity  along  a  copper  wire  exceeds  that  of  light 
through  the  planetary  space. 

2.  The  disturbance  of  the  electric  equilibrium  in  a  wire  communicating 
at  its  extremities  with  the  two  coatings  of  a  charged  jar,  travels  with  equal 
velocity  from  the  two  ends  of  the  wire,  and  occurs  latest  in  the  middle  of 
the  circuit. 

3.  The  light  of  electricity  of  high  tension  has  a  less  duration  in  passing  as 
a  spark  than  the  millionth  part  of  a  second. 


APPENDIX.  647 

DanielVs  Constant  Battery. — An  excellent  ar- 
rangement has  been  described  by  Daniell,  of 
which  the  figure  in  the  margin  represents  a  modi- 
fication more  simple  and  perhaps  equally  effective. 
It  consists  of  a  cylinder  of  copper,  a  b  c  d  e  f,  3 
inches  wide  from  a  to  6,  1£  inches  from  c  to  d, 
and  4  inches  from  e  to/,  the  corresponding  heights 
being  half  an  inch,  5  inches,  and  2  inches ;  Imno, 
is  a  collar  of  copper,  which,  by  the  arms  r  r,  s  s, 
rests  on  the  top  of  the  cylinder,  and  to  which  a 
membranous  tube  formed  of  the  gullet  of  an  ox  is 
tied,  the  membrane  being  longer  than  the  copper 
cylinder  so  as  to  be  baggy  below,  and  nearly  fill 
the  space  e/;  up  q,  is  a  rod  of  amalgamated  zinc 
resting  on  the  collar  I  m  n  0,  by  means  of  a  piece 
of  wood  r  s,  which  perforates  it;  M,  £,  are  cups  to 
hold  mercury  for  making  contact.  Between  the  membrane  and  copper  cy- 
linder is  poured  a  saturated  solution  of  blue  vitriol,  and  within  the  membrane 
dilute  sulphuric  acid  of  about  sp.  gr.  1-136,  which  is  made  with  1  measure  of 
strong  acid  and  8  of  water.  The  exciting  acid  is  thus  in  contact  with  the 
zinc,  but  not  with  the  copper.  When  this  circle  is  in  action,  the  electric 
current  passes  from  the  zinc  through  the  acid,  membrane,  and  solution  of 
blue  vitriol  to  the  copper.  The  arrangement  is  founded  on  two  important 
principles,  established  by  Daniell : — 

1.  However  active  a  circle,  as  made  heretofore,  may  be  when  first  excited, 
its  energy  is  known  rapidly  to  diminish,  and  in  a  few  minutes  to  fall  much 
below  its  original  power.    Daniell  has  traced  the  cause  to  reduction  of  oxide 
of  zinc  by  nascent  hydrogen  at  the  surface  of  the  copper  plate,  whereby  this 
metal  becomes  coated  with  zinc,  and  is  thus  more  or  less  converted  at  its 
surface  into  a  zinc  plate;  and  as  two  zinc  plates  under  like  conditions  do 
not  produce  a  current,  of  course  the  action  declines.     In  the  new  circle  this 
defect  is  avoided  by  the  membranous  septum  which  protects  the  copper  plate 
from  contact  with  the  solution  of  zinc :  the  nascent  hydrogen  reduces  oxide 
of  copper,  and  a  film  of  bright  copper  is  deposited  on  the  copper  plate,  thus 
constantly  presenting  a  clean  good  conducting  surface ;  while  the  hydrogen 
itself,  not  escaping  as  gas,  no  longer  opposes  an  obstacle,  as  it  does  when 
allowed  to  assume  the  gaseous  form,  to  the  passage  of  electricity  from  the 
solution  to  the  copper  plate.     To  supply  the  loss  of  oxide  of  copper,  a  copper 
disc,  a,  a,  x,  6,  studded  with  holes  like  a  cullender,  is  supplied,  on  which  rest 
crystals  of  blue  vitriol,  whereby  the  solution  is  kept  saturated  and  its  con- 
ducting power  preserved.   When  the  acid  within  the  membrane  is  exhausted, 
the  membrane  itself  is  removed,  and  fresh  acid  supplied ;  but  to  prevent  the 
necessity  of  frequent  renewal,  the  lower  part  of  the  membrane  is  made  to 
act  as  a  reservoir  of  acid. 

2.  The  zinc  of  a  pair  of  plates  may  be  much  reduced  in  size  without  any 
loss  of  power :  strong  chemical  action  on  a  small  surface  of  zinc,  a  good 
conducting  solution,  and  a  bright  large  surface  of  copper,  are  conditions  by 
which  a  powerful  action  is  ensured.     This  is  indicated  by  Davy's  protectors 
for  copper  sheathing  (page  89) ;  but  it  was  not  previously  known  that  the 
principle  was  applicable  to  the  construction  of  voltaic  apparatus.     The  great 
merit  of  this  circle  is  its  constancy :  by  keeping  up  the  supply  of  blue  vitriol 
and  acid,  its  energy  will  continue  invariable  for  hours,  or  for  an  indefinite 
period.    A  similar  apparatus  has  been  described  by  Mullins  (Phil.  Mag.  & 
An.  ix.  122). 

Nitrosulphuric  Acid. — When  a  mixture  of  binoxide  of  nitrogen  and  sul- 
phurous acid  is  brought  into  contact  with  a  solution  of  potassa  or  ammonia, 
both  gases  are  absorbed,  and  a  peculiar  acid  is  generated,  which  has  been 
called  by  Pelouze,  its  discoverer,  nitrosulphuric  acid.  It  is  composed  of 
one  eq.  of  nitrogen,  one  of  sulphur^  and  four  of  oxygen,  200  volumes  of 


648  APPENDIX. 

binoxide  of  nitrogen  combining  with  100  of  sulphurous  acid.  The  nitrosul- 
phates  are  very  prone  to  decomposition,  a  sulphate  being  formed  with  the 
evolution  of  protoxide  of  nitrogen :  this  ensues  by  the  mere  dontact  of  cer- 
tain substances,  which  do  not  themselves  undergo  any  change,  such  as 
spongy  platinum,  silver  and  its  oxide,  charcoal  powder,  peroxide  of  manga- 
nese, and  solutions  of  corrosive  sublimate,  lunar  caustic,  and  the  sulphates 
of  the  oxides  of  zinc,  copper,  and  iron.  The  same  effect  is  produced  by  an 
acid,  as  when  an  attempt  is  made  to  procure  nitrosulphuric  acid  in  a  separate 
state  ;  even  the  carbonic  acid  of  the  atmosphere  being  capable  of  causing  the 
decomposition.  The  crystals  of  the  nitrosulphates  of  potassa  and  ammonia 
may  be  preserved  in  well-stopped  bottles  at  ordinary  temperatures.  The 
solutions,  on  the  contrary,  are  not  stable  above  the  freezing  point;  but  the 
stability  is  much  increased  by  an  excess  of  alkali.  On  this  is  founded  the 
best  mode  of  preparing  the  nitrosulphates,  which  consists  in  transmitting 
binoxide  of  nitrogen  through  a  strong  solution  of  sulphite  of  ammonia  or 
potassa  with  an  excess  of  alkali,  when  the  corresponding  nitrosulphate  sepa- 
rates in  colourless  prismatic  or  acicular  crystals.  The  dry  crystals  decom- 
pose at  a  moderate  heat,  namely,  at  230°  for  the  ammoniacal  salt,  and  266° 
for  that  of  potassa  ;  the  former  giving  rise  to  a  slight  explosion  owing  to  the 
rapid  evolution  of  protoxide  of  nitrogen.  The  decomposition  of  the  nitrosul- 
phate of  potassa  by  heat  is  particularly  interesting,  from  its  forming  sulphite 
of  potassa  and  binoxide  of  nitrogen,  instead  of  sulphate  of  potassa  and  the 
protoxide,  as  occurs  in  every  other  instance.  (Liebig,  Ann.  xv.  240.) 

Liquid  and  Solid  Carbonic  Acid. — Carbonic  acid  is  condensable  into  a 
liquid  at  32°  by  a  pressure  of  36  atmospheres.  Thilorier  first  congealed  the 
liquid  acid,  by  taking  advantage  of  the  cold  produced  by  its  own  evaporation, 
estimated  at — 180°,  being  the  first  instance  of  the  solidification  of  a  gas. 
The  solidified  gas  is  a  snow-white  substance  under  the  ordinary  atmospheric 
pressure.  When  exposed  to  the  air  it  evaporates  slowly  and  quietly,  and  is 
gradually  converted  into  carbonic  acid  gas.  The  sp.  gr.  of  the  liquid  acid 
at  32°  is  0-83.  It  dilates  remarkably  by  heat,  its  expansion  being  upwards 
of  four  times  that  of  air ;  20  volumes  of  the  liquid  at  32°  occupying  29 
volumes  at  86°,  and  its  sp.  gr.  varying  from  0-9  to  0-6  as  the  temperature 
rises  from — 4°  to  4-86°.  When  heated  from  32°  to  86°,  its  elasticity  rises  from 
36  to  73  atmospheres,  being  0-68  atmospheres  for  each  degree.  It  is  insolu- 
ble in  water  and  fat  oils,  but  soluble  in  all  proportions  in  ether,  alcohol, 
naphtha,  oil  of  turpentine,  and  bisulphuret  of  carbon.  The  evaporation  of 
its  ethereal  solution  causes  an  intense  degree  of  cold,  by  which  large  quan- 
tities of  mercury  may  be  frozen.  (Thilorier,  in  Ann.  de  Ch.  et  de  Ph. 
Ix.  427.) 


GENERAL  INDEX. 


Absolute  alcohol,  533 
Acetates,  484 
Acetous  fermentation,  560 
Acids,  definition  of,  403 

nomenclature  of,  123 

animal,  574 

sulphur,  458 

vegetable,  478 
Acid,  acetic  and  acetous,  483 

allantoic,  577 

ambreic,  582 

amniotic,  577 

amylic,  518 

antimonic,  358 

antimonious,  357 

arsenic,  336 

arsenious,  332 

aspartic,  551 

auric,  386 

azulmic,  552 

benzoic,  493 

boletic,  501 

boracic,  205 

boro-hydrofluoric,  243 

bromic,  238 

butyric,   caproic,   and  capric, 
580 

caffeic,  552 

caincic,  502 

camphoric,  500 

carbazotic,  503 

carbonic,  187 

liquid  and  solid,  648 

caseic,  549 

eerie,  529 

chloric,  220 

chloriodic,  233 

chlorocarbonic,  224 

chlorous,  219 

chloroxalic,  501 

cholesteric,  581 

cbolic,  601  * 

chromic,  340 

citric,  489 

columbic,  354 


Acids,  crameric,  502 

croconic,  482 

crotonic,  580 

cyanilic,  643 

elaiodic,  580 

ellagic,  499 

erythric,  575 
•a,     etherp-phosphoric,  539 

ethero-sulphuric,  539 

fluoboric,  242 

fluoric,  241 

fluosilicic,  241,  244 

formic,  480,  576 

gallic,  497 

glacial  phosphoric,  203 

hippuric,  576 

hircic,  580 

hydriodic,  229 

hydrobromic,  237 

hydrochloric,  214 

hydrocyanic,  501 

hydrofluoric,  240 

hydropersulphuric,  255 

hydroselenic,  255 

hydrosulphuric,  252 

hydrotelluric,  368 

hydroxanthic,  644 

hypochlorous,  217 

hyponitrous,  178 

hypophosphorous,  200 

hyposulphuric,  197 

hyposulphurous,  196 

igasuric,  501 

indigo-sulphuric,  546 

indigotic,  502 

iodic,  231 

iodous,  231 

jatrophic,  580 

kinic,  487 

lactic,  486 

lactucic,  502 

lampic,  536 

lithic,  574 

nialic,  488 

manganic,  308 

margaric,  579 

margaritic,  580 


650 


Acid,  mechloic,  556 
meconic,  494 
mellitic,  482 
metagallic,  499 
metameconic,  495 
metaphosphoric,  203 
molybdic  and  molybdous,  350 
moric  or  moroxylic,  500 
mucic  499 
muriatic,  214 
nanceic,  486 
nitric,  181 
nitro-muriatic,  216 
nitrosulphuric,  647 
nitrous,  179 
oleic,  579 
osmic,  396 
oxalic,  479 
oxymuriatic,  211 
paraphosphoric,  201 
paratartaric,  493 
pectic,  501 
perchloric,  221 
periodic,  232 
permanganic,  309 
phocenic,  580 
phosphoric,  201 
phosphorous,  201 
prussic,  501 
purpuric,  575 
pyrocitric,  .490 
pyrogallic,  498 
pyrokinic,  488 
pyroligneous,  483 
pyromalic,  488 
pyromucic,  500 
pyrophosphoric,  203 
pyrotartaric,  490 
pyro-uric,  575 
racemic,  492 
rheumic,  501 
ricinic,  580 
rocellic,  500 
rosacic,  575 
saccholactic,  499 
sebacic,  580 
selenic,  209 
selenious,  209 
silicic,  207 
silicated  fluoric,  344 
silico-hydrofluoric,  244,  472 
sorbic,  501 
stearic,  580 
suberic,  501 
succinic,  499 
sulpho-vinic,  538 
sulphuric,  193 
sulphuric,  fuming,  194 
sulphurous,  192 


Acid,  tannic,  495 

tannic,  artificial,  497 

tartaric,  490 

telluric,  367 

tellurous,  367 

titanic,  365 

tungslic,  352 

ulmic,  552 

uric,  574 

valerianic,  500 

yellow,  569 

vanadic,  347 

of  the  Vcsges,  492 

xanthic,  644 

xumic,  501 
Adipocire,  581 
Aeriform  bodies,  20 
Affinity,  chemical,  124 

table  of,  125 

single  elective,  125 

double  elective,  127 

disposing,  162 

by  what   circumstances  modi- 
fied, 128 

quiescent  and  divellent,  127 

measure  of,  133 

changes  that  accompany,  127 
Agedoite,  550 
Air,  atmospheric,  167 

alkaline,  245 

fixed,  187 
Alabaster,  425 
Alembroth,  salt  of,  465 
Albumen,  569 

vegetable,  549 
'  incipient,  603 
Alcoates,  534 
Alcohol,  533 

of  sulphur,  261 
Algaroth,  powder  of,  356 
Alizarine,  548 
Alkali,  definition  of,  403 

volatile,  245 

silicated,  207 
Alkalies,  vegetable,  504 
Alkaline  air,  245 
bases,  403 
earths,  275 
Alkalimeter,  451 
Allanite,  362 
Alloys,  267,  400 
Almond  oil,  524 
Aloes,  bitter  of,  504 
Althea,  513 
Alum,  428 

stone,  428 
Alumen  ustum,  429 
Alumina,  or  aluminous  earth,  297 
sulphates  of*  426 


Alumina,  double  sulphates  of,  428 

acetate  of,  485 
Aluminite,  426 
Aluminium  and  its  compounds,  296 

oxy fluoride  of,  473 
Amalgams,  399 
Amalgam  for  looking-glasses,  399 

ammoniacal,  166 

for  electrical  machines,  399 
Amalgamation  of  silver  ores,  382 
Amber,  499,  528, 
Ambergris  and  ambreine,  582 
American  hiccory,  548 
Amidine,  517 
Ammelide,  643 
Ammeline,  643 
Ammonia,  liquid,  247 

character  of  the  salts  of,  246 

cobaltate  of,  328 

sulphate  of,  424 

double  sulphates  of,  430 

sulphite  of,  431 

nitrate  of,  433 

phosphates  of,  441 

arse  ni  ate  of,  445 

carbonates  of,  452 

hydro-salts  oi'9  455 

sulphur-salts  of,  458 

chlorides  with,  469 

oxalate  of,  481 

acetate  of,  485 

lactate  of,  487 

magnesian  phosphate  of,  442 

subcarbonate  of,  452 

bimalate  of,  488 

citrate  of,  489 

succinate  of,  499 
Ammoniacal  gas,  245 
Ammonium,  420 

oxide  of,  420 

Ammoniuret  of  copper,  427 
Amnios,  liquor  of,  606 
Amygdalin,  554 
Analysis  defined,  4 

proximate  and  ultimate,  of  or- 
ganic  substances,  476 

of  minerals,  620 

of  gases  618 

of  mineral  waters,  625 
Anhydrite,  425 
Animal  chemistry,  568 

proximate  substances,  568 

substances,  analysis  of,  475 

oils  and  fats,  577 

acids,  574 

jelly,  571 

heat,  596 

fluids  598 

solids,  614 


:x.  651 

Antimonialis,  pulvis,  358 
Antimoniates,  358 
Antimonites,  358 
Antimony  and  its  compounds,  355 

regulus  of,  355 

argentine  flowers  of,  355 

glass,  liver,  and  crocus  of,  359 

alloys  of,  400 

golden  sulphuret  of,  359 

oxy  chloride  of,  359,  469 

tartrate  of,  and  potassa,  491 

test  of,  356 

Antimonio-sulphurets,  464 
Anthracite,  533 
Apatite,  441 
Aposepedine,  605 
Apparatus,  Donovan's,  279 

Nooth's,  188 
Aqua  potassse,  278 

fortis,  181 

regia,  216 
Arbor  Dianae,  384 

Saturni,  375 
Archil,  547 
Aricina,  511 

Arrangement  of  the  work,  4 
Arrow-root,  518 
Arseniates,  336,  444 
Arsenites,  332,  446 
Arsenic  and  its  compounds,  331 

white  oxide  of,  332 

tests  of,  333 

Marsh's  test  for,  335 

alloys  of,  400 

fuming  liquor  of,  337 
Arsenio-sulphurets,  461 
Arsenical  solution,  446 
Arseniuretted  hydrogen,  337 
Arthanatin,  554 
Arterialization,  590 
Asparagin,  550 
Asphaltum,  530 
Atmospheric  air,  167    "  . 

chemical  properties  of,  170 

physical  properties  of,  168 

analysis  of,  170 

weight  of,  167 
Atom,  definition  of,  142 
Atomic  theory,  Dalton's  view  of,  142 

weights,  143 

Attraction,  chemical^  vide  affinity, 
124 

cohesive,  2 

terrestrial,  or  gravity,  2 

electric,  71 
Aurates,  386 
Auro-chlorides,  465 
Azote,  166 


652 


INDEX. 


B 

Baldwin's  phosphorus,  69 

Balloons,  159 

Balsams,  528 

Barilla,  451 

Baryto-calcite,  455 

Barium  and  its  compounds,  287 

Baryta  or  barytes,  287 

hydrate  of,  288 

tests  of,  288 

sulphate  of,  425 

nitrate  of,  433 

nitrite  of,  435 

chlorate  of,  436 

arseniates  of,  446 

carbonate  of,  453 

double  carbonates  of,  455 

metaphosphate  of,  444 
Barley,  malting-  of,  563 
Barometer,  correction   of,   for   the 

effects  of  heat,  13 
Basis  in  dyeing1  (mordant),  544 
Bassorin,  551 

Battery,  Daniell's  constant,  647 
Battley's  sedative  liquor,  507 
Baume's  hydrometer,  degrees  of,  re- 
duced to  the  common  stand- 
ard, 642 
Bell-metal,  401 
Benzin,  644 
Benzoates,  494 
Benzoin,  493 
Benzone,  644 
Benzule,  494,  524 
Benzamide,  526 
Benzoine,  526 
Berberin,  553 
Bile,  600 

Biliary  concretions,  601 
Bismuth  and  its  compounds,  363 

magistery  of,  364 

butter  of,  364 

alloys  of,  400 

Bitter  almonds,  oil  of,  524 
Bittern,  235 
Bituminous  substances,  530 

wood,  532 
Bitumen,  530 
Black  dyes,  548 

flux,  334,  491 

lead,  318 

oxide  of  iron,  312,  314 

oxide  of  copper,  370 

vomit,  590 
Bleaching,  213 

powder,  436 
Blende,  321 


Block  tin,  322 
Blood,  582 

in  disease,  588 

cruor  or  crassamentum  of,  583 

coagulation  of,  587 

serum  of,  585 

serosity  of,  585 

colouring  matter  of,  585 

fibrin  of;  587 

butfy  coat  of,  583 
Blood-root,  514 
Blowpipe  with  oxygen,  161 

with  oxygen  and  hydrogen,  160 
Blue  dyes,  545 

Saxon,  546 

Boa  constrictor,  urine  of,  574 
Bodies,  isomorphous,  416 

isomeric,  152 

plesiomorphous,  419 
Boiling  point  of  liquids,  42 
Bone-earth,  441 
Bones,  614 
Boracite,  449 
Borates,  448 
Borax,  449 

glass  of,  449 
Boro-fluorides,  472 
Boron,  204 

terchloride  of,  224 
Boyle,  fuming  liquor  of,  457 
Brain,  analysis  of,  616 
Brass,  401 
Brazil  wood,  547 
Brazing,  400 
Bromates,  438 
Bromides,  238,  269 

double,  471 
Bromine,  234 

compounds  of,  236 
Brown  coal,  532 
Bronze,  401 
Brucia,  512 
Brunswick  green,  469 
Bryonin,  553 
Butter,  603 

of  zinc,  321 

of  bismuth,  364 
Butyrine,  580, 


Cadmium  and  its  compounds,  321 

CaflTein,  551 

Calamine,  319 

Calcium  and  its  compounds,  291 

Calcination,  267 

Calculi,  urinary,  612 

biliary,  601 

salivary,  598 


653 


Calculus,  mulberry,  482,  613 

fibrinous,  614 

uric  acid,  612 

bone-earth,  612 

ammoniaco-magnesian  phos- 
phate, 612 

fusible,  613 

cystic  oxide,  613 

xanthic  oxide,  614 
Calomel,  379 
Caloric,  5 

Calorimeter  of  Lavoisier  and  La- 
place, 31 
Calorimotor,  92 
Calx,  267 
Camphor,  524 

artificial*  523 
Camphorates,  500 
Cannel  coal,  532 
Cannon  metal,  401 
Canton's  phosphorus,  293 
Caoutchouc,  528 

volatile  liquid  of,  529 

mineral,  530 
Capacity  for  heat,  29 
Carbon,  184  ft 

chlorides  of,  222 

compounds  of,  187 
with  oxygen,  187 
with  hydrogen,  247 
with  nitrogen,  259 
with  sulphur,  261 
Carbonates,  general  properties  of, 
449 

double,  454 
Carbonic  oxide,  189 
Carbo-sulphurets,  460 
Carburets,  metallic,  274 
Carburetted  hydrogen,  light,  248 
Carmine,  547 
Cartilage,  614 
Caseous  matter,  603 

oxide,  604 
Caseum,  604 

Cassius,  purple  of,  323,  388 
Cassava,  518 
Catechu,  495 
Cathartin,  552 
Celestine,  425 
Cerasin,  519 
Cerate,  529 
Cerin,  529 
Cerium  and  its  cmpounds,  362 

oxychloride  of,  469 
Cerulin,  546 
Ceruse,  454 
Cerussa  acetata,  485 
Cetine,  581 


Cetrarin,  553 
Chalk,  453 

Chameleon,  mineral,  308 
Charcoal,  185 

animal,  or  ivory  black,  185 
Cheese,  603 
Chemical  affinity  or  attraction,  124 

symbols,  150       .  \i 

equivalents,  141 

mode  of  ascertaining,  139 
scale  of,  141 

formulae,  150 
Chemistry,  definition  of,  3 

analytical,  618 

organic,  474 

inorganic,  121 

vegetable,  476 

animal,  568 

Classification  of  chemical  substan- 
ces, 4 

Cleavage,  415 
Chlorates,  220,  435 
Chloric  ether,  542 
Chlorides  or  chlorurets,  213 

metallic,  268 

double,  465 

with  ammonia,  469 

with  phosphuretted  hydrogen, 
470 

of  carbon,  222 

of  iodine,  233 

of  sulphur,  223 

of  phosphorus,  223 
Chloride  of  boron,  224 

of  bromine,  238 

of  nitrogen,  221 

of  lime,  436 
Chlorine,  211 

compounds  of,  213 

nature  of,  226 

bleaching  powers  of,  213 

disinfecting  powers  of,  213 

theories  of,  226 
Chlorites,  436 
Chlorophane,  69 
Chlorurets,  213 
Chlorophyle,  554 
Chloro-nitrous  gas,  225 
Choke-damp,  189 
Cholesterine,  581 
Chromates,  447 

of  chlorides,  448 

of  silver,  448 
Chromate  of  iron,  339 
Chromium  and  its  compounds,  339 

sulphate  of,  427 

double  sulphate  of,  429 

oxalate  of,  and  potassa,  482 


55* 


654 


IITDISX. 


Chromium,  oxychloride  of,  343 
Chrome  alums,  429 

yellow,  447 
Chyle,  602 
Chyme,  599 
Cinchona  bark,  active  principles 

of,  509 

Cinchonia,  509 
Cinnabar,  382 

factitious,  382 
Citrates,  489 
Coke,  533 
Cloves,  oil  of,  524 
Coal,  532 

mines,  fire-damp  of,  249 
Coagulation  of  the  blood,  587 
Cobalt  and  its  compounds,  326 

sulphate  of,  427 
Cobaltate  of  ammonia,  328 
Cocculus  Indicus,  principle  of,  513 
Cochineal,  547 
Codeia,  508 
Cohesive  attraction,  2 

influence  of,  over  chemical  ac 

tion,  128 

Cold,  artificial  methods  of  produc- 
ing-, 39 

Colocyntin,  553 
Colouring  matter  of  the  blood,  585 

matters,  544 
Colours,  adjective  and  substantive, 

545 

Columbin,  556 

Columbium  and  its  compounds,  353 
Combination  defined,  134 
utility  of  laws  of,  138 
laws  of,  134 
historical  facts  relating  to  laws 

of,  138 

Combinations,  metallic,  267 
Combining  proportions,  134 
proportions,  table  of,  141 
proportions,     exemplifications 

of,  137 

Combustion,  156 
theories  of,  156 
spontaneous,  v.  Phosphurettec 

hydrogen  and  Pyrophorus. 
Composition  of  bodies,  136 

how  determined,  139 
Condenser,  80 
Conductor,  prime,  75 
Conductors  of  heat,  7 
Conduction  of  heat,  6 
Cooling  of  bodies,  14 
velocity  of,  14 
law  of,  by  Newton,  14 
Copal,  527 
Copper  nickel,  329 


lopper  and  its  compounds,  369 

test  of,  371 

alloys  of,  401 

pyrites,  369 

glance,  372 

sulphates  of,  427 

nitrate  of,  433 

arsenite  of,  446 

carbonate  of,  454 

tinning  of,  401 

acetates  of,  485 

black,  370 

ammoniacal  sulphate  of,  333, 
427 

white  muriate  of,  371 

sheathing,  preservation  of,  89 

resin  of,  371 

white,  of  the  Chinese,  401 

ore,  blue,  454 
Cork,  552 
Corrosive  sublimate,  379 

sublimate,  tests  of,  380 
Corydalia,  513 
Corundum,  397 
Coumarin,  526 

Count  Rumford's  mocHe  of  ascertain- 
ing the  conducting  power  of 
articles  of  clothing,  7 
Cream  of  milk,  603 

of  lime,  292 

of  tartar,  491 
Creosote,  530 
Crocus  of  antimony,  359 
Cryolite,  473  v 

Cryophorus,  46 
Crystallization,  409 

systems  of,  411 

water  of,  406 
Crystallography,  409 
Crystals,  angles,  planes,  and  edges 
of,  409 

structure  of,  415 

cleavage  of,  415 
Curcuma  paper,  548 
Curd,  603 
Cuticle,  615 
Cyanogen,  259 
Cynopia,  513 

Cystic  oxide  calculus,  613 
Cytisin,  552 

D 

Daphnia,  514 
Decomposition,  simple,  125 

double,  126 
Decrepitation,  408 
Definite   proportions,   doctrine  of, 

135 
Deflagration,  267,  432 


655 


Dephlogistigated  air,  153 

marine  acid,  211 
Deliquescence,  406 
Delphia,  513 
Derosne,  salt  of,  507 
Derbyshire  spar,  293 
Destructive  distillation,  476 
Detonating  powders,  435 
Dew,  formation  of,  13 

point,  52 

Diabetic  urine,  610 
Diathermanous  substances,  68 
Diamond,  186 

Differential  thermometer,  23 
Diffusiveness,  173 
Diffusion  tube,  173 
Digesting  flask,  626 
Dippers  oil,  578 
Distillation  by  descent,  319 

destructive,  476 
Dobereiner's  lamp,  159 
Dragon's  blood,  527 
Dutch  gold,  401 
Dyes,  545 


Earths,  pure,  275 

alkaline,  275 
Earth,  aluminous,  297 

siliceous,  207 
Ebullition,  42 
Efflorescence,  407 

influence  of,  over  affinity,  130 
Eggs,  570,  605 
Egg-shells,  615 
Elaine,  522 
Elastic  gum,  528 

Elasticity,   its  effects  on   chemical 
affinity,  130 

of  vapours,  47 
Elaterium,  556 
Elatin,  556 
Elective  affinity,  125 
Electric  attraction,  71 

repulsion,  71 

excitement,  causes  of,  75 

intensity,  83 
Electrical  battery,  79 

accumulation,  laws  of,  83 

machine,  75  ,  .* 

unit  jar,  82 
Electricity,  71 

elementary  facts  of,  71 

conductors  and  non-conductors 
of,  71 

vitreous  or  positive,  72 

resinous  or  negative,  72 

theories  of,  73 


Electricity,  induction  of,  78 

atmospheric,  77 

identical  with  lightning,  87 

thermo-,  75 

historical  notice  relating  to,  86 

condenser  of,  80 

velocity  of,  646 
Electro-chemical  decomposition, 

theory  of,  106 

Electro-chemical  equivalents,  105 
Electro-dynamics,  116 
Electro-magnetism,  116 
Electro-negative  and  positive  ele- 
ments, 107 
Electrometer,  balance,  82 

gold  leaf,  80 

torsion,  81 

volta-,  106 
Electrophorus,  80 
Electroscopes  and  electrometers,  80 
Elements,  what  and  how  many,  4 
Elementary    substances,    chemical 

equivalents  of,  141 
Emetia,  512 
Emetic  tartar,  491% 
Empyreal  air,  153* 
Emulsion,  522 
Endosmose,  594 
Epsom  salt,  425 
Equivalents,  chemical,  141 

scale  of,  141 
Erythrogen,  602 
Erythronium,  343 
Essential  oils,  522 

salt  of  lemons,  481 
Ethal,  581 
Ether,  535 

theory  of  the  formation  of,  537 

acetic,  542 

oxalic,  541 

chloric,  542 

cyanuric,  542 

hydriodic,  541 

hydrochloric,  540 

nitrous,  541 

oxidized,  543 

hydrobromic,  541 

pyroacetic,  543 

sulphocyanic,  542 

sulphuric,  536 

thialic,  642 

Etherine,  sulphate  of,  540 
Ethule  or  ethyle,  537 
Ethiops  mineral,  382 

per  se,  377 
Euchlorine,  217 
Eudiometer,  origin  of  the,  171 

Hope's,  619 

Volta's,  618 


656 


Evaporation,  4£ 

circumstances  influencing,  45 

cause  of,  41,  47 

limit  to,  49 

Leslie's  method  of  freezing  by, 

46 

Exosmose,  594 
Expansion  of  solids,  16 

of  liquids,  18 

of  gases,  20 
Extractive  matter,  554 
Extractum  Saturni,  485 
Eye,  humours  of,  606 

action  of,  on  light,  62 


Fat  of  animals,  577 
Feathers,  615 
Fecula,  517 
Fermentation,  557 

acetous,  560 

panary,  560 

putrefactive,  561 

saccharine,  557 

vinous,  558 
Fibre,  woody,  520 
Fibrin,  568 

of  the  blood,  587 
Filter,  624 

Fire-damp  of  coal  mines,  249 
•  Fixed  air,  187 

oils,  521 
Flame,  vide  Combustion  and  Car- 

buretted  Hydrogen. 
Flesh,  615 
Flint,  207 
Flowers  of  sulphur,  191 

argentine,  of  antimony,  355 
Fluidity  caused  by  heat,  37 

heat  of,  37 

Fluob orates  of  ammonia,  457 
Fluosilicate  of  ammonia,  457 
Fluorides,  metallic,  269 

double,  471 
Fluorine,  240 

theories  relating  to,  241 
Fluor  spar,  293 
Flux,  white  and  black,  491 
Fly  powder,  331 
Food  of  plants,  566 
Form,  changes  of,  exciter  of  elec- 
tricity, 77 
Freezing  mixtures,  tables  of,  39 

in  vacuo,  Leslie's  method  of, 

46 
Frigorific  mixtures  with  snow,  table 

of,  39 
Friction,  heat  produced  by,  54 


Friction,  electricity  excited  by,  75 
Fulminatiog  gold,  387 

platinum,  392 

silver,  384 
Fuming  liquor  of  Libavius,  325 

liquor  of  Boyle,  457 

liquor  of  arsenic,  337 
Fungin,  552 
Funnel,  624 
Fusion,  36 

watery,  406 

point  of,  265 
Fusible  metal,  400 
Fustic,  548 

G 

Galena,  373,  376 
Gallates,  498 
Gall-nuts,  495 
Gall-stones,  602 
Galvanic  battery,  92 

arrangements,  88 
Galvanism,  87 

how  developed,  87 

effects  of,  99 

chemical  agency  of  101 

electrical  agency  of,  100 

connexion  of,  with  magnetism, 
109 

theories  of  the  production  of,  94 
Galvanometer,  110 
Gases,  53 

mode  of  finding  the  specific 
gravity  of,  122 

mode  of  drying,  53 

condensation  of,  53 

law  of  expansion  of,  21 

diffusion  of,  172 

formula  for  correcting  the  ef- 
fects of  heat  on,  49 

specific  heat  of,  31  . 

their  bulk  influenced  by  mois- 
ture, and  the  formula  for 
correcting  its  effects,  50 

analysis  of  mixed,  618 

absorption  of,  by  charcoal,  185 

absorption  of,  by  water,  163 
Gastric  juice,  599 
Gelatin,  571 
Gentianin,  553 
Germination,  562 
Gibbsite,  298 
Gilding,  400 
Glance,  silver,  385 

coal,  533 

copper,  372 
Glass,  various  kinds  of,  207 

expansion  of,  by  heat,  17 


657 


Glass  of  antimony,  359 

of  borax,  449 
Glauber's  salt,  424 
Gliadine,  550 
Glucina,  300 

test  of,  301 

Glucinium  and  its  sesquioxide,  300 
Glue,  571 
Gluten,  549 
Glycerine,  580 
Gold  and  its  componnds,  385 

fulminating*  compound  of,  387 

ethereal  solution  of,  387 

alloys  of,  402 

mosaic,  326 

haloid  salts  of,  465 
Golden  sulphuret  of  antimony,  359 
Gong1,  Indian,  401 
Goulard's  extract  of  lead,  485 
Gouty  concretions,  575 
Grain  tin,  322 
Graphite,  318 
Gravel,  urinary,  612 
Gravitation,  2 

Gravity,  effect  of,  on  chemical  ac- 
tion, 133 

modes  of  determining  specific, 

121 
Green,  S cheele's,  446 

mineral,  454 

Brunswick,  469 
Growth  of  plants,  564 
Gum,  518 

resins,  528 

elastic,  528 

British,  518 
Gums,  519 
Gunpowder,  433 
Gypsum,  425 

H 

Haarkies,  330 
Hair,  615 
Haloid  salts,  464 
Hartshorn,  spirit  of,  245 
Harrowgate  water,  630 
Heat,  5 

definition  of,  5 

nature  of,  5 

communication  of,  by  contact,  6 

conduction  of,  6 

conductors  of,  table  of,  7 

radiation  of,  8 

what  surfaces  best  suited  for 
the  radiation  of,  9 

latent,  30 

free,  30 

luminous,  67 


Heat,  non-luminous,  11 

effects  of,  15 

expansion  by,.  15 
in  solids,  16 
in  liquids,  18 
in  gases,  20 

exception  to  the  law  of  expan- 
sion by,  20 

how  conducted  by  liquids  and 
gases,  8 

specific,  29 

laws  of  distribution  by  radia- 
tion of,  9 

capacities  of  bodies  for,  29 

-of  fluidity,  37 

sensible  and  insensible,  30 

sources  of,  54 

animal,  596 

radiant,  9 

reflection  of,  10 

polarization  of,  646 

double  refraction  of,  646 

absorption  of,  10 

transmission  of,  11 

through  solids  &  liquids,  645 

theory    of,     by    Prevost    and 
Pictet,  12 

application  of  Prevost's  theory 
of,  to  the  formation  of  dew, 
by  Dr.  Wells,  13 
Heavy  spar,  425 
Hematin,  547 

Haematite,  brown  and  red,  314,  315 
Hematosine,  585 
Hepar  sulphuris,  282 
Hiccory,  wild  American,  548 
Hogslard,  578 
Hircine,  580 

Homberg's  pyrophorus,  429 
Honey,  516 
Honey-stone,  482 
Hoofs,  615 
Hordein,  564 
Horn,  615 

silver,  384 

quicksilver,  379 

lead,  375 

Humours  of  the  eye,  606 
Hydrargo-bichlorides,  465 
Hydrates,  nature  of,  163 
Hydro,  how  employed,  163 
Hydriodates,  230 
Hydro-carbon  of  the  blood,  593 
Hydro-fluorides,  471 
Hydrocarburet,  248 
Hydrochl orates,  455 
Hydrogurets,  or  hydurets,  274 
Hydrogen,  158 

properties  of,  159 


658 


Hydrogen,  oxidation  of,  159 

peroxide  of,  163 

arseniurettecl,  337 

light  carburetted,  248 

and  carbon,  compounds  of,  247 

and  carbon,  ne\v  compounds  of, 
248 

phosphuretted,  257 

phosphuretted,  chlorides  with, 
.       470 

and  nitrogen,  245 

and  potassium,  281 

seleniuretted,  255 

solid  phosphuretted,  256 

spontaneously  inflammable 
phosphuretted,  258 

sulphuretted,  252 

persulphuret  of,  254 

telluretted,  368 

with  metals,  274 

auro-chloride  of,  466 

platino-biniodide  of,  471 
Hydrometer,  Baume's,  degrees  of, 
reduced    to    the     common 
standard,  642 
Hydro-salts,  455 
Hydro-sulphurets,  459 
Hygrometers,  51 
Hyp eroxy muriates,  220 


Iceland  spar,  453 
Ice,  19 

Igasurates,  501 
Imponderables,  5 

influence  of,  over  chemical  ac- 
tion, 133 

Incandescence,  68 
Incipient  albumen,  603 
Indigo,  545 
Indigogen,  503,  547 
Induction,  electric,  78 

Volta-electric,  117 

magneto-electric,  117 
Ink,  496 

marking,  434 

sympathetic,  328 
Inflammable  air  of  marshes,  248 
Ingenhauz's  method   of   ascertain- 
ing the  conducting  power  of 
solids,  7 
Insolubility,  influence  of,  on  affinity, 

130 

Insulators,  electrical,  72 
Inulin,  552 
lodates,  232,  437 
Iodides,  or  iodurets,  229 

metallic,  269 


Iodides,  double,  470 

oxy,  471 
Iodine,  227 

test  for,  229 

compounds  of,  229 

oxide  of,  231 

chlorides  of,  233 
Ipecacuanha,  emetic  principle    of, 

512 

Iridium  and  its  compounds,  397 
Iridio-chlorides,  468 
Iron  and  its  .compounds,  311 

ores  of,  311 

cast,  3 11 

rusting  of,  312 

pyrites,  317 

pyrites,  magnetic,  317 

sulphates  of,  426 

alum,  429 

metoric,  components  of,  311 

chromate  of,  447 

carbonate  of,  454 
Isinglass,  571 
Isomeric  bodies,  152 
Isomorphism,  416 
Isomorphous  substances,   table  of, 

416 
Ivory,  615 

black,  185 


Jelly,  animal,  571 

vegetable,  519 
Jet,  532 

K 

Kali,  278 

Kermes  mineral,  359 
Kelp,  451 
Kinates,  488 
King's  yellow,  338 
Kupfernickel,  329 


Lac  sulphuris,  192 

Lakes,  544 

Lactates,  487 

Lamp  without  flame,  536 

safety,  249 
Lampblack,  527 
Lapis  causticus,  278 

infernalis,  434 

lazuli,  285 
Lard,  578 
Latent  heat,  30 
Lateritious  sediment,  575 


Law  of  multiples   of  combining 

weights,  137 

of  multiples  of  combining  vol- 
umes, 145 
Laws  of  combination,  134 

of  the  distribution  of  radiant 

heat,  9 

Lead  and  its  compounds,  372 
white,  374,  454 
horn,  375 
ceruse  of,  454 
nitrates  of,  434 
nitrites  of,  435 
phosphate  of,  442 
arseniates  of,  446 
carbonate  of,  454 
oxychlorides  of,  469 
oxyiodldes  of,  471 
oxy fluoride  of,  473 
acetates  of,  485 
malate  of,  489 
alloys  of,  400 
Lemons,  acid  of,  489 

essential  salt  of,  481 
Lenses,  59  et  seq. 
of  the  eye,  61 
Lepidolite,  286 
Leucine,  569 
Leyden  jar,  78 

Libavius,  fuming  liquor  of,  325 
Ligaments,  615 
Light,  theories  of,  54 
diffusion  of,  55 
ordinary  ray  of,  64 
extraordinary  ray  of,  64 
reflection  of,  55 
refraction  of^  58 
double  refraction  of>  64 
polarized,  64 
decomposition  of,  65 
calorific  rays  of,  66 
prismatic  colours  of,  65 
chemical  rays  of,  67 
magnetizing  rays  of,  67 
necessary  to  vegetation,  565 
terrestrial,  68 
sources  of,  68 
Lightning,  87 
Lignin,  520 
Lime,  or  quicklime,  291 

water,  milk,  and  hydrate  of, 

292 

slaked,  292 
sulphate  of,  425 
sulphite  of,  431 
nitrate  of,  443 
phosphates  of,  441 
arseniates  of,  446 
carbonate  o£  453 


EX.  659 

Lime,  double  carbonates  of,  454 
oxalate  of,  482 
acetate  of,  485 
stone,  453 

Liniment,  volatile,  522 
I  Liquefaction,  36 
Liquids,  expansion  of,  by  heat,  18 

conducting  power  of,  8 
Liquor  sanguinis,  583 

silicum,  207 

^iquorice,  sugar  of,  516 
Litharge,  374 
.ithia,  or  lithion,  286 
sulphate  of,  424 
tests  of,  286 
Lithates,  574 

jthium  and  its  compounds,  285 
hydro-sulphuret  of,  460 
carbo-sulphuret  of,  461 
arsenio-persulphurets  of,  463 
molybdo-sulphuret  of,  463    • 
hydrargo-bichloride  of,  465 
Litmus,  547 

paper,  625 
_/iver  of  antimony,  359 

of  sulphur,  271,  282 
,ogwoocl,  547 
Luna  cornea,  384 
Lunar  caustic,  383,  434 
Lupulin,  552 
~,ymph,  606 

M 

Madder,  548 
Magnesia,  294 

tests  of,  295 

sulphate  of,  425 

nitrate  of,  433 

phosphates  of,  442  » 

carbonate  of,  453 

oxalate  of,  482 
Magnesian  limestone,  455,  621 
Magnesite,  453 
Magnesium  and  its  compounds,  294 

hydro-sulphuret  of,  460 

arsenio-persulphuret  of,  463 
Magnetic  iron  pyrites,  317 
Magnetism,  electro-,  116 
Magneto-electric  induction,  117 
Malachite,  454 
Malates,  488 
Maltha,  530 
Malting,  563 

Manganesium,  or  manganium,  304 
Manganese  and  its  compounds,  304 

sulphate  of,  426 

alum,  429 
Manna  and  mannite,  51 6 


660 


INDEX. 


Marble,  453 
Marrow,  spinal,  616 
Massicot,  374 
Margarine,  522,  579 
Matter,  physical  properties  of,  1 
chemical  properties  of,  3 
influence  of  quantity  of,  over 

affinity,  132 
Meconates,  495 
Medullin,  552 
Melam,  643 
Melamine,  643 
Mellon,  260,  643 
Membranes,  615 

permeability  of,  to  gases,  594 
Mercaptan,  642 
Mercaptum,  642 

Mercury  and  its  compounds,  377 
with  metals,  399 
sulphates  of,  427 
nitrates  of,  434 
carbonate  of,  454 
oxychloride  of,  469 
acetate  of,  486 
Metallic  combinations,  398 
bases  of  the  alkalies,  276 
bases  of  the  alkaline  earths, 

287 

bases  of  the  earths,  296 
Metals,  263 

general  properties  of,  263 
alloys  of,  267,  398 
alkaline  or  alkaligenous,  275 
table  of  discovery  of,  263 
table  of  specific  gravity  of,  264 
malleability  of,  264 
ductility  of,  265 
crystallization  of,  265 
tenacity  of,  265 
hardness  of,  265 
structure  of,  265 
native  state  of,  266 
action  of  heat  on,  266 
action  of  galvanism  on,  267 
fusibility  of,  table  of,  266 
oxidation  of,  267 
reduction  of,  267 
classification  of,  274 
compounds  of,  with 
chlorine,  268 
iodine,  269 
bromine,  269 
fluorine,  269 
sulphur,  269 
selenium,  271 
cyanogen,  272 
phosphorus,  274 
carbon,  274 
hydrogen,  274 


Metaphosphates,  443 
Meteoric  stones,  311 
Milk,  603 

sugar  of,  573 
Hindererus,  spirit  of,  485 
Mineral  chameleon,  308 

green,  454 

yellow,  469 

tar,  530 

pitch,  530 

waters,  analysis  of,  625 
Minerals,  analysis  of,  620 
Minium,  375 
Molasses,  516 
Molybdates,  350 

Molybdenum  and  its  compounds,  . 
349 

oxychloride  of,  351 
Molybdo-sulphurets,  463 
Mordant,  544 
Morphia,  505 

salts  of,  507 
Mosaic  gold,  326 
Mother  of  pearl,  615 
Mucilage,  518 
Mucus,  606 

Mulberry  calculus,  482,  613 
Multiples,  law  of,  137,  145 
Muriates,  455 

Muriatic  acid,  table  of  specific  gra- 
vity of,  216 
Muscle,  615 

converted  into  fat,  581 
Mustard,  oil  of,  524 
Mushrooms,  peculiar  substance  of, 

552 

Myrica  cerifera,  529 
Myricin,  529 


N 

Nails  of  animals,  61$ 

Narcotina,  507 

Narceia,  509 

Natrium,  283 

Natron,  284 

Nerves,  616 

Neutral  salts,  characters  of,  402 

Neutralization,  136 

Nickel  and  its  compounds,  329 

alloys  of,  401 

sulphate  of,  427 
Nicotina,  514 
Nitrates,  431 
Nitrites,  435 
Nitre,  432 

Nitric  oxide  gas,  176 
Nitrogen  gas,  166 


6.61 


Nitrogen,  properties  of,  166 

oxides  of,  167 

bicarburet  of,  259 

protoxide  of,  174 

binoxide  of,  176 

phosphuret  of,  260 

quadrochloride  of,  221 

teriodide  of,  233 

sulphuret  of,  262 

compounds    of,    with    carbon, 

259 

Nooth's  apparatus,  188 
Nomenclature,  122 


O 

Oil,  Dippel's  animal,  578 

of  vitriol,  193 

of  wine,  540 
Oils,  animal,  577 

fixed,  521 

drying,  or  siccative,  521 

volatile,  or  essential,  522 

vegetable,  521 
Ointments,  527 
Olefiant  gas,  250 
Oleine,  522,  579 
Olive  oil,  521 
Olivile,  553 
Opium,  active  principle  of,  505 

tests  of,  507 
Organic  chemistry,  474 

substances,  character  of,  476 
Orpiment,  338 
Osmazome,  615 

Osmium  and  its  compounds,  396 
Osmio-chlorides,  468 
Oxalates,  480 

Oxalammide,  or  oxamide,  481 
Oxidation,  154 
Oxide,  cystic,  613 

carbonic,  189 

caseous,  604 

zanthic,  614 
Oxides,  what,  123,  267 

nomenclature  of,  123 
Oxidum      manganoso-manganicumj 
307 

ferroso-ferricum,  315 
Oxygen,  153 

preparation  of,  153 

properties  of,  154 

necessary  to  respiration,  155 
Oxyhydrogen  blowpipe,  160 
Oxiodine,  232 
Oxychlorides,  468 
Oxy fluorides,  473 
Oxyiodides,  471 


Palladium  and  its  compounds,  392 
Palladio-chlorides,  467 
Panary  fermentation,  560 
Pancreatic  juice,  599 
Paper,  test,  preparation  of,  625 
Papin's  digester,  43 
Paracyanogen,  260 
Particles,    integrant     and    compo- 
nent, 3 
Patent  yellow,  469 
Pearls,  615 
Pearlash,  450 
Pectin,  520 

Pericardium,  liquor  of  the,  606 
Perchlorates,  436 
Perspiration,  fluid  of,  .608 
Petroleum,  530 
Pewter,  400 
Phenecin,  546 
Phlogiston,  158 
Phocenine,  580 
Phosgene  gas,  224 
Phosphates,  432 
Phosphites,  201 
Phosphorescence,  69 
Phosphoric  ether,  53,6 
Phosphorus,  197 

compounds  of,  with 
oxygen,  200 
hydrogen,  256 

chlorides  of,  223,  224 

sulphuret  of,  262 

Canton's,  69,  293 

Baldwin's,  69 
Phosphurets,  metallic,  274 
Phosphuretted  hydrogen,  257 
-    salts  of,  458 

chlorides  with,  470 
Photometer,  70 
Picamar,  531 
Picromel,  600 
Picrotoxia,  513 
Pinchbeck,  401 
Piperin,  552 
Pitchblende,  360 
Pitch,  mineral,  53O 
Pit-coal,  532 
Pittacal,  532 
Plants,  growth  of,  564 

digestion  of,  565 

food  of,  566 

respiration  of,  565 
Plaster  of  Paris,  425 
Plasters,  527     " 
Platinum  and  its  compounds,  389 

spongy,  467 

fulr'     A* 


56 


fulminating  powder  of,  392 


662 


Platinum,  alloy  of,  with  arsenic,  400 

Platino-chlorides,  466 

Platino-biniodides,  470 

Plesiomorphism,  419 

Plumbagin,  554 

Plumbago,  318 

Pollenin,  552 

Polychroite,  548 

Populin,  555 

Potash  and  pearlash,  450 

Potassa,  278 

hydrates  of,  278 

aqua,  278 

fusa,  278 

tests  of,  279 

sulphates  of,  423,  424 

sulphite  of,  431 

nitrate  of,  432 

nitrite  of,  435 

chlorate,  oxy muriate,  or  hyper 

oxymuriate  of,  435 
iodates  of,  437,  438 
phosphates  of,  441 
arseniates  of,  445 
arsenite  of,  446 
chromates  of,  447 
carbonates  of,  450,  451 
oxalates  of,  481 
acetate  of,  484 
malate  of,  488 
citrate  of,  489 
tartrates  of,  490 
tartrate  of,  and  soda,  491 
Potrisium  and  its  compounds,  276 
protoxide  of,  278 
teroxide  of,  280 
sulphur-salts  of,  458 
haloid  salts  of,  465 
hydro-sulphuret  of,  459 
carbo-sulphuret  of,  460 
arsenio-persulphurets  of,  462 
molybdo-sulphuret  of,  463 
Potato,  starch  of,  517 
Precipitate,  red,  378 
Pressure,  influence  of,  on  the  bulk 

of  gases,  168 
Prism,  65 

Prismatic,  or  solar  spectrum,  65 
Proof-spirit,  534 
Proportion,  combining,  136 
Proportions,  definite,  134 
Proximate  analysis,  476 
principles,  476 

of  vegetables,  476 
of  animals,  468 
Prussiate  of  mercury,  259 
Pulvis  antimonialis,  358 
Purple  powder  of  Cassias,  323,  388 
Purpurates,  575 


Pus,  607 

Putrefaction,  616 
Putrefactive  fermentation,  561 
Pyrites,  iron,  317 

copper,  369 
Pyroacetic  ether,  543 
Pyroxylic  spirit,  543 
Pyrometer  of  Daniell,  26 

Wedgwood's,  27 
Pyrophorus  of  Homberg,  429 
Pyrophosphates,  442 

Q 

Quantity,  influence  of,  on  affinity,  132 
Quercitron  bark,  548 
Quicklime,  291 
Quicksilver,  377 

horn,  379 
Quills,  615 
Quinia  or  quinine,  510 

R 

Racemates,  493 
Radiation,  8 

Rays  of  heat,  angles  of  incidence 
and  reflection  of,  10 

luminous,  11 

non-luminous,  8 
Rays  of  light,  55 

angles  of  incidence  and  reflec- 
tion of,  55 

angles  of  refraction  of,  58 
Realgar,  338 
:led  lead,  375 

precipitate,  378 

dyes,  547 

oxide  of  manganese,  307 

oxide  of  copper,  370 
deduction  of  metals,  267 
Rennet,  603 
fcesin  of  copper,  371 
Resins,  527 
lespiration,  590 

of  plants,  565 
letinasphaltum,  530 
lhaponticin,  553 
Rhein,  553 

Ihodium  and  its  compounds,  393 
Ihodio-chlorides,  467 
Ihubarbarin,  553 
iochelle  salt,  491 
Rouge,  548 

S 

Saccharine  fermentation,  557 
Saccharum  Saturni,  485 


INDEX. 


663 


Safety-lamp,  Sir  H.  Davy's,  249 

improvement    of,    by    Messrs. 

Upton  and  Roberts,  250 
Safflower,  548 
Saffron,  548 
Sago  and  salep,  518 
Sal  ammoniac,  456 
Salicin,  555 
Salifiable  base,  268 
Saliva,  598 
Salivary  matter,  598 
Salt,  common,  284 

Seignette  or  Rochelle,  491 

of  sorrel,  481 

microcosmic,  441 

of  Derosne,  507 

Glauber's  424 

of  lemons,  481 

rock,  bay,  fishery,  and  stoved, 
284     ' 

petre,  432 

spirit  of,  214 
Salts,  general  remarks  on,  402 

nomenclature  of,  123,  405 

classification  of,  405 

affinity  of,  for  water,  406 

crystallization  of,  409 

double  and  triple,  420 

deliquescent,  406 

watery  fusion  of,  406 

efflorescence  of,  407 

water  of  crystallization  of,  406 

decrepitation  of,  408 

plesiomorphism  of,  419 

of  morphia,  507 

isomorphous,  416 

oxy-,  419 

sulphates,  421 
double,  428 

sulphites,  431 

nitrates,  431 

nitrites,  435 

chlorates,  435 

perchlorates,  436 

chlorites,  436 

iodates,  437 

bromates,  438 

phosphates  438 

pyrophosphates,  442 

metaphosphates,  443 

arseniates,  444 

arsenites,  446 

chromates,  447 

chromates  of  chlorides,  448 

b orates,  448 

carbonates,  449 
double,  454 

hydro-,  455 

of  phosphuretted  hydrogen,  458 


Salts,  sulphur-,  458 

hydro-sulphurets,  459 

carbo-sulphurets,  460 

arsenio-sulphurets,  461 

molybdo-sulphurets,  463 

antimonio-sulphurets,  464 

tungsto-sulphurets,  464 

haloid,  464 

double  chlorides,  465 

hydrargo-bichlorides,  465 

auro-chlorides,  465 

platino-chlorides,  466 

palladio-chlorides,  467 

rhodio-chlorides,  467 

iridio-chlorides,  468 

osmio-ohlorides,  468 

oxychlorides,  468 

chlorides  with  ammonia,  469 

chlorides    with   phosphuretted 
hydrogen,  470 

double  iodides,  470 

oxyiodides,  471 

double  bromides,  471 

double  fluorides,  471 

hydro- flu  or  ides,  471 

boro-fluorides,  472 

silico-fluorides,  472 

titano-fluorides,  473 

oxyfluorides,  473 

oxalates,  480 

acetates,  484 

lactates,  487 

kinates,  488 

malates,  488 

citrates,  489 

tartrates  490 

benzoates,  494 

meconates,  495 

racemates,  493 

tannates,  497 

gallates,  498 

succinates,  499 

camphorates,  500 

igasurates,  501 
Sanguinaria  Canadensis,  514 
Sap  on  in,  554 
Sarcocoll,  553 
Saxon  blue,  546 
Scale  of  equivalents,  141 
Scheele's  green,  333,  446 
Sea-water,  627 
Secreted  animal  fluids,  598 
Sealing-wax,  527 
Scillitin,  554 

Sediment  of  urine,  575,  611 
Seignelte,  salt  of,  491 
Selenite,  425 
Selenium,  208 

oxide  of,  209 


664  Iir] 

Selenium,  bisulphuret  of  252 

Seleniuretted  hydrogen,  255 

Seleniurets,  metallic,  271 

Seleniuret  of  phosphorus,  262 

Senegin,  554 

Serosity  and  serum,  585 

Serous  membranes,  fluid  of,  606 

Serum,  583,  585 

Shells,  615 

Silica  or  siliceous  earth,  207 

Silicates,  207 

Silicated  alkali,  207 

Silicon  and  its  compounds,  205 

terbrornide  of,  240 

terchloride  of,  225 
Silico-fluorides,  472 
Silicum,  liquor,  207 
Silk,  615 
Silver  and  its  compounds^  382 

fulminating  compound  of,  384 

glance,  385 

alloys  of,  401 

amalgamation  of,  382 

sulphate  of,  428 

nitrate  of,  434 

phosphate  of,  442 

dipyrophosphate  of,  443 

arseniate  of,  446 

granulated,  383 

horn,  384 
Sinapisin,  556 
Skin,  615 
Slacked  lime,  292 
Slag  formed  in  the  reduction  of  iron, 

311 

Smalt,  327 
Soap,  579 
Soda  or  natron,  284 

tests  of,  284 

sulphates  of,  424 

sulphite  of,  431 

nitrate  of,  433 

nitrite  of,  435 

perchlorate  of,  436 

phosphates  of,  440 

pyrophosphates  of,  443 

meta phosphate  of,  444 

arseniates  of,  445 

arsenite  of,  446 

biborale  of>  449 

carbonates  of,  451,  452 

oxalate  of,  481 

acetate  of,  484 

malate  of,  488 

citrate  of,  489 

tartrate  of,  and  potassa,  491 

tartrate  of,  491 

Sodium    or   natrium,   and   its    com- 
pounds, 283 
protoxide  of,  284 


Sodium",  sesquioxide  of,  284 

chloride  of,  284 

hydro-sulphuret  of,  460 

sulphurets  of,  285 
Solania,  513 
Solar  rays,  65 
Solders,  400 
Selids,  expansion  of,  by  heat,  15 

liquefaction  of,  36 

conducting  power  of,  6 

specific  heat  of,  29 
Solution,  124 
Sorrel,  salt  of,  481 
Spar,  Iceland,  453 

fluor,  293 

heavy,  425 
Specific  gravity,  121 

heat,  29 

relation    of*    to     the    atomic 

weights,  35 
of  gases,  31 
Speculum  metal,  401 
Spectrum,  solar,  65 

calorific  rays  of  the,  66 
Spelter,  31 9 
Spermaceti,  581 

oil,  578 
Spirit,  proof,  534 

of  wine,  533 

pyroxylic,  543 

pyroacetic,  543 

of  Mindererus,  585 

of  hartshorn,  245 
Stannates,  324 
Starch,  517 
Starkey's  soap,  523 
Steam,  temperature  of,  43 

elasticity  of,  44 

latent  heat  of,  45 
Steam-engine,  principle  of,  44 
Stearine,  522,  578 
Steel,  319 

Indian  (wootz,)  401 

alloys  of,  401 
Stream  tin,  323 
Stibium,  355 
Strontia,  or  strontites,  290 

tests  of,  290 

sulphate  of,  425 

nitrate  of,  433 

nitrite  of,  435 

carbonate  of,  453 

acetate  of,  485 
Strontianite,  453 
Strontium  and  its  compounds,  289 

hydro-sulphuret  of,  460 

carbo  sulphuret  of,  461 
Strychnia,  511 
Suberin,  552 
Succinates,  499 


665 


Suet,  578 
Sugar,  515 

cf  lead,  485 

of  starch,  518 

of  grapes,  516 

of  liquorice,  516 

ofrnilk,  573 

of  diabetes,  573 

candy,  515 

Sulpho-sinapisin,  556 
Sulphates,  421 

double,  428 
Sulphites,  431 
Sulpho-benzide,  644 
Sulphur,  191 

oxides  of,  192 

flowers  of,  191 

hydrate  of,  192 

chlorides  of,  223 

acids,  458 

bases,  458 

salts,  458 

balsam  of,  523 
Sulphurets,  metallic,  269 
Sulphuretted  hydrogen,  252 

sulphites,  196 
Sulphuric  ether,  535 
Sulphuris,  lac,  192 
Sun,  heat  produced  by  the,  66 
Supporters  of  combustion,  156 
Surturbrand,  532 
Sweat,  608 
Synthesis  defined,  4 


Tallow,  578 

Tannic  acid,  or  tannin,  495 

acid,  artificial,  formation  of,  497 
Tanno-gelatin,  496 
Tantalum,  353 
Tantalite,  353 
Tapioca,  518 
Tar,  inflammable  principles  of>  530 

mineral,  530 
Tartar,  491 

cream  of,  491 

soluble,  490 

emetic,  491 
Turtrates,  490 
Tears,  606 
Teeth,  615 

Telescope,  construction  of,  57 
Telluretted  hydrogen,  368 
Tellurium  and  its  compounds,  367 
Temperature,  what,  28 

equilibrium  of,  9 
Tenacity  of  metals,  265 
Tendons,  615 


Thermometer,  or  thermoscope,  23 

air,  23 

differential,  23 

formula  for  converting  the  ex- 
pression of  one  into  another, 
25 

graduation  of  the,  25 

register,  27 
Thorina»  302 

teats  of,  302 

Thorium  and  its  compounds,  301 
Tin  and  its  compounds,  322 

alloys  of,  400 

oxychlorides  of,  468 

permurisrte  of,  325 
Tincal,  449 

Titanium  and  its  compounds,  364 
Titano-fluorides*  473 
Tombac,  401 
Traubensaure,  492  . 
Transfer,  galvanic,  101 
Train  oil,  578 
Treacle,  516 
Trona,  452 
Trough,  galvanic,  92 
Tungsten  and  its  compounds,  351 

oxy chloride  of,  353 
Tungstates,  352 
Tungsto-sulphurets,  464 
Turpeth  mineral,  428 
Turmeric,  548 

paper,  625 
Turnsol,  547 
Turpentine,  oil  of,  523 
Turkey  red,  548 
Type,  metal  for,  400 

U 

Ulmin,  552 

Ultimate  analysis^  476 

Ultramarine,  285 

Uranium  and  its  compounds,  360 

Urates,  574 

Urea,  572 

Urine,  608 

of  the  boa  constrictor,  574 
Urinary  concretions  or  calculi,  612 


Vacuum,  boiling  in,  43 

evaporation  in,  46 
Vanadium  and  its  compounds,  343 
Vaporization,  41 

cause  of,  41 
Vapour,  dilatation  of*  42 

density  of,  41 

elasticity  or  tension  of,  47 


666 


INDEX. 


Vapour,  latent  beat  of,  45 
presence  of,  in  gases,  50 
table  of  the  elastic  force  of,  44, 

636 

Varvicite,  308 
Vegetable  acids,  478 

acids,  table  of,  478 
.   alkalies,  504 

table  of,  505 
preparation  of,  505 
extract,  554 
jelly,  519 

gluten  and  albumen,  549 
chemistry,  476 
substances,  475   * 

having  oxygen  and  hydro- 
gen in  the  same  ratio  as 
in  water,  514 
oleaginous,    resinous,   and 

bituminous,  520 
Vegetation,  564 
Veratria,  512 
Verdigris,  486 
Verditer,  454 
Vermilion,  382 
Vinegar,  561 
Vinous  fermentation,  558 
Vision,  62 
Vital  air,  153 
Vitriol,  oil  of,  193 
blue,  427 
green,  426 
white,  426 
Volatile  alkali,  245 

liniment,  522 
Volta-electric  induction,  117 

electrometer,  106 
Volta's  eudiometer,  618 
pile,  92 
theory,  94 
Voltaic  circles,  laws  of  the  action 

of,  96 

Volumes,  theory  of,  144 
combining,  145 
table  of,  146 

*     W 

Water,  composition  of,  161 
properties  of,  162 
expansion  of,  in  freezing,  19 
boiling  and  freezing  points  of, 

25 

of  crystallization,  406 
basic,  407 
constitutional,  407 


Water,  rain,  snow,  spring,  well,  and 
river,  625 

of  the  sea  and  the  Dead  Sea, 

627 
Waters,  mineral,  625 

tables  of  composition  of,  629 

acidulous,  625 

alkaline,  626 

chalybeate   and    sulphuretted, 
626 

siliceous,  628 

saline,  626 
Wax,  529 
Welding,  312 
Wheat-flour,  517 
Whey,  603 
White  lead,  454 

copper,  401 
Wine,  quantity  of  alcohol  in,  535 

oil  of,  540 

Wires,  tenacity  of,  table  of,  265 
Wismuth,  363 
Witherite,  453 
Wood,  bituminous,  532 
Woody  fibre,  520 
Wool,  615 
Wootz,  401 


Xanthic  oxide  calculus,  614 
Y 

Yeast,  550 

Yellow,  mineral  or  patent,  469 

King's,  338 

chrome,  447 

dyes,  548 
Yttria  and  its  base,  301 


Zanthopicrin,  553 

Zaflfre,  326 

Zymome,  550 

Zinc  and  its  compounds,  319 

blende,  321 

brown  and  blue  blaze  of*  319 

butter  of,  321 

alloys  of,  401 

amalgam  of,  399 

sulphate  of,  426 

acetate  of,  486 

Zinetum,  319 
Zirconium  and  its  compounds,  302 


CORRIGENDA. 

Page  141,  in  the  table  of  chemical  equivalents,  for  Glucinium  1'77,  read 

Glucinium  26*5. 

"    in  the  same  table,  for  Silicium  7'5,  read  Silicon  22*5. 
150,  in  the  table  of  symbols,  for  Silicium,  read  Silicon, 
446,  line  8  from  bottom,  for  arseniates,  read  arsenites. 


UNIVERSITY  OF  CALIFORNIA  LIBRARY 

This  book  is  DUE  on  the  last  date  stamped  below. 

Fine  schedule:  25  cents  on  first  day  overdue 

50  cents  on  fourth  day  overdue 
One  dollar  on  seventh  day  overdue. 


APR  22  1947 
JAN  1 7  1367  9 1 


rats 

SAP  13  lag/ so- 


W«v1^ 

RECEIVED 

1  '68  -11  AM 

LOAN  DEPT. 

MAR  0  9  199D 
AWO  DISC  MAR  16 


LD  21-100m-12,>46(A2012sl6)4120 


U.C.  BERKELEY  LIBRARIES 


I 


*  <** 


